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1944-3994/1944-3986 © 2022 Desalination Publications. All rights reserved.
Desalination and Water Treatment
www.deswater.com
doi: 10.5004/dwt.2022.29029
280 (2022) 89–127
December
Eective methods for removing dierent types of dyes – modelling analysis,
statistical physics treatment and DFT calculations: a review
M.G. El-Desoukya,*, M.A.G. Khalilb, M.A.M. El-Afifya, A.A. El-Bindaryc,
M.A. El-Bindaryd
aEgyptian Propylene and Polypropylene Company, Port Said 42526, Egypt, email: ch.moh.gamal@gmail.com (M.G. El-Desouky)
ORCID ID: https://orcid.org/0000-0001-6060-463X
bChemistry Department, Faculty of Science, Port Said University, Port Said 42511, Egypt, emails: magomaa@hotmail.com (M.A.G. Khalil)
ORCID Id: https://orcid.org/0000-0003-0653-2289, maher.elafify@yahoo.com (M.A.M. El-Afify) ORCID Id: https://orcid.org/
0000-0002-8764-7303
cChemistry Department, Faculty of Science, Damietta University, Damietta 34517, Egypt, email: abindary@yahoo.com (A.A. El-Bindary)
ORCID Id: https://orcid.org/0000-0002-4494-3436
dBasic Science Department, Higher Institute of Engineering and Technology, New Damietta, Egypt,
email: m.a_bindary@yahoo.com (M.A. El-Bindary) ORCID Id: https://orcid.org/0000-0001-5977-1465
Received 23 July 2022; Accepted 11 October 2022
abstract
Organic dyes, a class of highly poisonous and carcinogenic chemicals that pose serious health risks
to humans and aquatic life, are the most prevalent organic pollutants found in wastewater from
sectors such as textiles, rubber, and cosmetics. Organic dyes, a class of highly poisonous and car-
cinogenic chemicals that pose serious health risks to humans and aquatic life, are the most preva-
lent organic pollutants found in wastewater from sectors such as textiles, rubber, and cosmetics.
This review compares and contrasts several dye removals processes. Adsorption has proved to be
a quick and efficient way to get colours out of wastewater. This research focuses on the most recent
developments in porous materials for organic dye adsorption. Dyes were used to color food and
other industrial items, textiles, plastics, cosmetics, and tannery. Non-ionic dyes, cationic dyes (basic
dyes), and acid dyes are the three types of dyes (dispersed dyes). The process of removing dyes
from sewage from industry has become increasingly essential from an environmental standpoint.
In an aqueous system, cationic dyes have a net positive charge due to their sulphonate groups,
while anionic dyes have a net negative charge. To avoid contamination of the aquatic environment,
these waste dyes must be handled first. This dye’s aromatic composition offers it increased dura-
bility and makes it tough to decompose. Color wastes were removed from waste water via oxida-
tion, electrochemistry, coagulation, solvent extraction, photocatalytic degradation, ozonation, and
adsorption, among other ways. However, the adsorption process is more advantageous than other
ways. As a result of its ease of use, high effectiveness, simple design, easy availability of adsorbents,
and most importantly, its low cost. Different porous materials’ properties, functionalization, and
modification are also discussed. Also discussed are the adsorption behaviors and mechanisms of
these adsorbents in the adsorption of organic dyes. Finally, future research challenges and oppor-
tunities in the development of innovative materials for very efficient dye removal are suggested.
Keywords: Dyes; Adsorbents; Photocatalytic degradation
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–12790
1. Introduction
Dye production is one of the businesses that con-
tributes the most chemicals to sewage. Textile factories
are producing more than 700,000 tons of dyes that are
among the top three contaminants. Most reactive col-
orants are toxic and have a risk of teratogenic and car-
cinogenic mutations [1]. The origin of the dyes was much
later, when the indigo blue dye was found in mummy
wrappers in Egyptian tombs 4,000 y ago, it revolutionized
the dye industry. An organic colourant was discovered for
the first time [2]. Around the world, there are more than
100,000 commercially available dyes, and 7,107 tons of
colourants are produced year [3–5].
Water is a crucial component of the Earth’s environ-
ment is a necessary element of life. As the population and
living standards rise, so does the need for water, which is
rising daily [6,7]. Our water resources’ quality is declining
daily as a result of the persistent introduction of harmful
substances into them. The residues of medicines and other
drugs (new emerging pollutants) in water are among the
most dangerous contaminants [8]. These contaminants
are extremely hazardous because they can interfere with
human enzymatic, hormonal, and genetic systems [9].
Therefore, it is necessary and important to get rid of these
chemical and pharmaceutical residues in water before to
provide the neighborhood with water. According to the
2004 French Plan of National Sant Environment (PNSE), it
is required to check these pollutants in water before sup-
plying it to the population. In a nutshell, a growing topic
of research is the elimination of these new developing con-
taminants and contemporary necessity in environmental
science. Therefore, academics, researchers, doctors, and
regulatory agencies are concerned with getting drugs and
pharmaceuticals out of water [10].
The technique that seems to be the most useful and
effective is adsorption. It allows for the almost complete
removal of hazardous contaminants at low concentrations
[11]. The kind of adsorption material employed affects
how well different contaminants are removed. One of the
categories for these materials suggests that they can be
divided into natural and synthetic ones [12]. The first cat-
egory consists of carbons of diverse natural origins, chalk
and clay rocks, ash, peat, slag, zeolites, vermiculites, and
sand [13]. The second- category of adsorbents consists of
silica gels made from variously treated mineral raw mate-
rials, synthetic zeolites, titanium and zirconium hydrox-
ides or phosphates, activated carbons, ion exchange res-
ins, and polymers with chelate groups. The current sit-
uation of anthropogenic aquatic media is problematic,
and the majority of the available adsorption materials are
unable to sufficiently remove dangerous pollutants from
wastewater. As a result, it is essential to use advanced
technologies that have much large specific surface areas
and that have also been modified with different chem-
ically active groups to improve adsorption activity and
selectivity. Research efforts at many scientific schools are
focused on creating materials whose adsorption capacity
is several times more than that of traditional adsorbents
such activated carbon, zeolites, clays, etc. as a result of the
rapid expansion of the nanotechnology industry [14].
The fashion factories today use mostly direct dyes,
for example, synthetic organic dyes, dyes for manufactur-
ing, reactive dyes, and so on. Wide range of colorants and
chemicals used to make common shades of fabrics more
appealing to competitive market render them very complex.
Environmental concerns associated with the production and
application of colorants have evolved dramatically over the
past decade and are undoubtedly among the main driving
forces affecting the textile dye industry today. The term “nat-
ural dyes” is used to describe any dye that comes from an
organic source, such as plants, animals, or minerals. Natural
colours are generally insufficiently pigmented and must be
added to textiles using mordents, they are often metal salts
that have a preference for the colouring agent as well as the
fiber. Numerous businesses, notably the garment industry,
frequently use synthetic dyes.
As early as 1856, Perkin was the pioneer in the devel-
opment of manmade organic dye, mauve. The first organic
synthetic dye was developed at 1871, as Woulfe treated the
natural dye, indigo with nitric acid, to prepare picric acid
[15,16]. The fashion industries account for nearly 70% of the
highest use of dyestuffs. Disperse dye are the largest mar-
ket with a share of about 21% followed by direct dyes and
reactive dyes of 16% and 11%, respectively. Textile dyes are
usually graded either according based on their chemically
makeup or their application.
Many adsorbents have been created and modified in
recent years to be used in the adsorption of organic dyes.
Despite several excellent evaluations that compile numer-
ous related papers, the category of adsorbents in each
review is highly different and contentious because there
is no universally accepted criterion for adsorbents for dye
removal. The purpose of this work is to present recent
developments, with a particular emphasis on innovative
porous materials for the adsorption of dyes from a wide
angle. The technologies used to remove dyes and their neg-
ative consequences are outlined in this review. This work
offers fresh perspectives on the creation of innovative
porous materials, in particular with regard to their prop-
erties and use in the adsorption of dyes. A straightforward
classification system was also suggested for the choice of
typical adsorbents. Additionally, this review identifies the
crucial elements affecting the adsorption mechanism [17].
This paper also emphasizes adsorption isotherm, adsorp-
tion kinetics, and adsorption mechanism. Although sev-
eral materials exhibit excellent adsorption abilities, many
of them have not yet been developed for use on an indus-
trial scale and have their own limits. Based on these facts,
a thorough examination of the problems, the knowledge
gap, and the outlook for the future is presented at the end.
In the future, we hope that this work will serve as motiva-
tion for the development and use of new adsorbents. Dyes
very in resistance to sunlight, suddenness washing, air,
alkalis, and other chemicals; in their sensitivity to specific
fibers; their solubility and application process, as well as
their reactivity to cleaning chemicals and methods [18].
2. Classification of dyes
Table 1 summarizes the classifications of dyes based
on their use, this is organized in accordance with the
91M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
classification of the applications. For every application
class, it displays the main substrates, application tech-
niques, and typical chemical kinds. However not depicted
in Table 1, dyes are also utilized in high-tech fields such
as medicine, electronics, and non-impact printing. For
instance, they are utilized in ink-jet printing, direct and
thermal transfer printing, photocopying (photocopying
and laser printing), and electrophotography (both toner
and organic photoconductor). As in customary uses, azo
dyes predominate; other colours utilized include phtha-
locyanine, anthraquinone, xanthene, and triphenylmeth-
ane. The volume of these applications is currently modest
(between tens of kilos and several hundred tons annually)
high added value, though (a few hundred to several thou-
sand dollars per kg), having rapid growth rates (up to 60%).
2.1. Acid dyes
Such colors, in pH range 3.0–7.0, can be applied to cot-
ton, wool or silk. Such dyes wet-fastness ranges from mod-
erate to excellent and their luminosity is usually 5.0–6.0 in
the blue-scale range. Acidified solutions (formic or acetic
acid) are commonly used to synthesize the dyes, with the
degree of acidity varying depending on the dye’s quali-
ties. Acid dyes are usually vivid and may be washed at
various speeds. The dye molecules differ widely in com-
position and contain complex metals.
The group’s distinguishing characteristic is the existence
of sulphonated unit, which give water-solubility. Bonding
to wool occurs partly on the wool fiber due to contact with
these groups of sulphonated and groups of ammonium
(Figs. S1 and S2). The Van der Waals forces have extra
bonding interactions (Tables S1 and S2). Anionic dyes are
chromophoric azo systems (the most important group),
anthraquinone, triphenylmethane or copper phthalocya-
nine, which are soluble in water by addition of one to four
classes of sulphonates Tables S3 and S4. The example of
these dyes is shown in Fig. 1.
2.2. Basic dyes
Most commonly used to colour acrylic fibers, basic dyes
are water soluble. The majority of the time, they are observed
with a mordant (Figs. S3 and S4). A reagent is a chemical
substance that helps to set colours on textiles by forming an
insoluble compound with the dye.
Basic colouring, aside from acrylic, is not particularly
good for any other fiber because it is difficult to light Tables
5 and 8, wash, or rapidly change colours (Fig. 2). They are
thus typically used to offer fabrics that have already been
colored with acid colored with acid colors after treatment
(Tables S5–S7).
2.3. Azo dyes
Dyes classified as chromophores the presence of an azo
group (–N=N–). Are used in numerous types of industrial
dye, make up about one-half of all synthesized dyes and
mostly used in the clothing, fruit, paper, printing, leather
SO
3
Na
HO
H
2
N
N
N
SO
2
N
C
2
H
5
Acid Red57
SO
3
H
OH
NN
OCH
3
O
2
S
H
2
C
H
2
COHO
3
S
Remazol Red
Fig. 1. Examples of acid dyes.
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–12792
and synthetic cosmetics. Azo colors are structurally diverse,
However, the existence of an azo linkage, that is, N=N, is
their most notable structural trait. Because this bond can
happen many times, monoazo dyes only possess one azo
relation, whereas diazo dyes have two and triazo dyes
have three. Sulphonated azo dyes are azo dyes that con-
tain substituent sulfonate groups [19,20]. Azo groups cre-
ate a complex structure that enables dyes to display a wide
spectrum of colours when paired with aromatic substituents
or enolizable groups (Fig. 3).
2.4. Reactive dyes
Reactive dyes create a chemical compound when they
interact with fiber molecules. These dyes are made from
alkaline solutions or neutral solutions that are then alkalized
in a different phase. Heat treatment is occasionally used to
get different hues. [21]. To avoid unfixed dye, the fabric is
cleaned thoroughly with soap after tinting. Originally, only
active dyes were employed on cellulose fibers, but they are
currently used in various (Fig. 4).
2.5. Vat dyes
Vat colouring is insoluble in water and cannot stain
textiles directly. We can be made soluble, however, by low-
ering the alkaline solution that allows textile fibers to be
attached. Dye is returned to its insoluble state by after
that, there is oxidation or sun exposure. Original vat dye is
indigo. Those colors, including cotton, linen and rayon are
the best colors [22,23]. They are used to dye other fabrics like
wool, nylon, polyesters, acrylics and modacrylics with mor-
dants. Fig. 5 describes the usual chemical structures of vat
dyes.
2.6. Sulphur dyes
Using caustic soda and sodium sulfide, sulfur colorant
are insoluble and can be designed to be soluble. Dyeing is
achieved with huge amounts of salt at high temperature, in
order for the colour to permeate the fabric [24]. Extra colo-
rants and additives completely washed away. These colors
Crystal Violet
N
+
CH
3
N
CH
3
CH
3
H
3
C
Cl
-
Malachite Green
N
CH
3
H
3
C
N
+
CH
3
CH
3
N
CH
3
H
3
C
Cl
-
Fig. 2. Example of basic dyes.
Fig. 4. Dye (C.I. Reactive Red 198).
Fig. 3. Example azo dye.
93M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
are easy to light, to wash and to suddenly use mostly for
cotton and linen (Fig. 6).
2.7. Disperse dyes
Insoluble in water characteristic for dispersed colorant.
Such colors are finely ground can be utilized in the form of
a paste or powder that dissolves in water. These substances
breakdown and colour the fibers [25,26]. Initially created
for cellulose acetate coloring, these dyes are already com-
monly used to color nylon, cellulose triacetate, and acrylic
fibers as well. A typical disperse dye structure is shown
in Fig. 7.
2.8. Direct dyes
Without using mordents, direct colors effectively stain
cellulose fibres. We’ve colored wool, silk, nylon, cotton,
rayon, and a variety of other materials [27,28]. As they’re very
simple to light, such colors are not extremely bright and have
a slow washing time. The basic dye is given as an example
in Fig. 8.
Table 1
Usage and classification of dyes
Class Principal substrates Description Method of application Chemical types
Acid Leather, paper, inks,
wool, silk, and nylon
Anionic chemicals that
are water-soluble
Usually from neutral to acidic
dyebaths
Azo (including pre-
metallized), anthraquinone,
triphenylmethane, azine,
xanthene, nitro and nitroso
Basic Paper,
polyacrylonitrile,
modified nylon,
polyester and inks
Water-soluble, applied in
weakly acidic dyebaths;
very bright dyes
Applied from acidic dyebaths Cyanine, hemicyanine,
diazahemicyanine,
diphenylmethane,
triarylmethane, azo, azine,
xanthene, acridine, oxazine,
and anthraquinone
Direct Cotton, rayon, paper,
leather and nylon
Water-soluble, anionic
compounds; can be
applied directly to
cellulosics without
mordants (or metals like
chromium and copper)
Applied from neutral or slightly
alkaline baths containing
additional electrolyte
Azo, phthalocyanine,
stilbene, and oxazine
Disperse Polyester, polyamide,
acetate, acrylic and
plastics
Not water-soluble Fine aqueous dispersions often
applied by high temperature/
pressure or lower temperature
carrier methods; dye may be
padded on cloth and baked on or
thermofield
Azo, anthraquinone, styryl,
nitro, and benzodifuranone
Reactive Cotton, wool, silk,
and nylon
Water-soluble, anionic
compounds; largest dye
class
Reactive site on dye reacts
with functional group on fiber
to bind dye covalently under
influence of heat and pH
(alkaline)
Azo, anthraquinone,
phthalocyanine, formazan,
oxazine, and basic
Sulfur Cotton and rayon Organic compounds
containing sulfur or
sodium sulfide
Aromatic substrate vatted with
sodium sulfide and reoxidized
to insoluble sulfur-containing
products on fiber
Indeterminate structures
Vat Cotton, rayon, and
wool
Oldest dyes; more
chemically complex;
water-insoluble
Water-insoluble dyes solubilized
by reducing with sodium
hydrogen sulfite, then exhausted
on fiber and reoxidized
Anthraquinone (including
polycyclic quinones) and
indigoids
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–12794
2.9. Classification of dyes by use or application method
3. Toxicology and toxicity assessments
Over 30 years ago, the Western European Industry
that produces colourants started looking into the toxico-
logical and ecological effects of dyes, long before chemi-
cal and environmental restrictions existed (and pigments).
Currently, a slew of laws and regulations mandate that
manufacturers examine the hazard potential of each of
their products.
Toxicology research focuses on a multitude of topics, the
most important of which is with (1) acute toxicity, (2) irrita-
tion of skin and eyes, (3) toxicity after repeated application,
(4) sensitization, (5) mutagenicity, and (6) cancerogenicity.
3.1. Acute toxicity
The first step in evaluating whether dyes are harmful
is to properly evaluate or assess their acute toxicity, as
defined by the EU Directive 67/548/EEC (with numerous
amendments). A detailed analysis of such data, includ-
ing skin and eye irritation, was collected from safety data
sheets for a number of commercial dyes, demonstrated
that the risk of these acute toxic consequences (also known
as “harmful” or “toxic”) was extremely low. Although the
review is from a long time ago, the conclusions can be
assumed to be still true today [29].
3.2. Sensitization
Textile dyes are suspected to be the source of skin
responses, according to dermatologists. Some reactive dyes
can cause contact dermatitis, allergic conjunctivitis, rhinitis,
N
H
O
N
H
O
Br
Br
Br
Vat Blue 5
N
H
O
N
H
O
SO3Na
NaO3S
Acid Blue 74
Fig. 5. Chemical structure of vat dyes.
Leuco Sulfur Black 1 Sulfur black
Fig. 6. Two sulfur dyes were use.
Fig. 7. Chemical structure of C.I. Disperse Red 8.
Fig. 8. Direct red 2.
95M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
occupational asthma, and other allergic reactions in textile
workers. The propensity of reactive dyes to mix with human
serum albumin is thought to be the cause (HSA) to give a
dye–HSA conjugate which acts as an antigen. The antigen
then creates particular immunoglobulin E (IgE) antibodies,
which cause allergic reactions via the production of inter-
mediates such as histamine [30]. A study of 414 workers
who had dye powder exposure, in 1985, a survey of work-
ers in the dye industry, including those in mixers, weighers,
dyehouse operators, and laboratories. Twenty-one of them
were found to have allergic reactions to one or more reactive
colours, including occupational asthma. ETAD published a
list of reactive dyes that induced respiratory or cutaneous
sensitization in workers exposed to them on the job. These
colours should be labelled appropriately in the EU, as they
are all classified in the European Inventory of Existing
Chemical Substances (EINECS).
Utilizing liquid dyes will help you prevent exposure
to colour dust, to lessen the risk, use personal protective
equipment and colours with low-dusting formulations.
Reactive dyes have various toxicological properties since
the reactive group is no longer present after dyeing and fix-
ing, additionally, the wearer’s flesh won’t be exposed due to
the high fastness qualities. As a result, no allergic reactions
have been documented in people who have worn reactive
coloured textiles.
Textile contact is thought to be responsible for 1%–2%
of all allergy disorders treated in German hospitals, with
dyes accounting for the majority of them. Disperse dyes
were the most noticeable, especially when used for skin-
tight, close-fitting clothing composed of synthetic fabrics.
Sweat fastness qualities of dyes on various textiles play a
big role in whether or not an allergic reaction is triggered.
If coloured on polyamide or semi-acetate, where the low
swet fastness allows the dyes to move to the skin, sensi-
tizing disperse dyes may produce allergic skin reactions.
In the 1980s, several severe allergic reactions were linked
to polyamide stockings and pantyhose’s, and in the 1990s,
sportswear (leggings) made of semi-acetate.
There has been no legal prohibition in any country to
date, but some organizations, such as the International
Association for Research and Testing in the Field of Textile
Ecology (ko-Tex), which awards eco-labels to environmen-
tally and toxicologically proven textiles, refuse to award
eco-labels to certain dyes [31].
3.3. Mutagenicity
Some dyes are mutagenic in nature. The Ames test is a
common initial screening procedure for evaluating a chemi-
cal’s mutagenicity. It is a process for creating bacterial point
mutation tests that uses specific bacterial strains Salmo
nella typhimurium with histidine-dependent growth.
A point mutation is identified by a dose-dependent rever-
sion to histidine-independent growth. It was discovered that
the Prival test, an adaptation of the Ames test, was superior
for mutagenicity testing of azo dyes. This test imitates how
an animal’s reductive enzymatic cleavage of the azobond
breaks it down [31].
It is commonly accepted that the development of can-
cer is a multiphase process, with the initiating phase being
particularly susceptible to the effects of genotoxic agents.
The bacterial reverse mutation test is a very sensitive
assay for the development of point mutations in bacteria
rather than a test for the complex multiple step process
of carcinogenesis in mammals, hence a strong relationship
between Ames test results and mouse cancer bioassays
cannot be envisaged. Validation tests reveal a weak cor-
relation between the endpoints of mutagenicity in bacteria
and carcinogenicity in rats.
A chromosomal aberration assay should be performed
if these findings indicate a possibility for mutagenicity, a
potential next step would be a cytogenetic test in vitro.
After proving a genotoxic potential in vitro, equivalent in
vivo investigations must be carried out in order to deter-
mine a possibly mutagenic potential in animals. After
proving a genotoxic potential in vitro, equivalent in vivo
investigations must be carried out in order to determine
a possibly mutagenic potential in animals. The test results
may also enable the estimation of a substance’s carcino-
genic potential [32].
3.4. Carcinogenicity
Some dyes and intermediates have been known to
be harmful for quite some time. The effects of acute, or
short-term, exposure are well understood. They’re kept
in check by maintaining chemical concentrations in the
workplace under strict guidelines and preventing physi-
cal contact with the material. Chronic effects, on the other
hand, are often not noticeable for many years after expo-
sure. Higher rates of benign and malignant tumours, par-
ticularly in the bladders of employees exposed to various
intermediate and dye manufacturing procedures, accord-
ing to statistics, during the years 1930–1960, dye-producing
countries recorded an increase in production. The chem-
icals in question were 2-naphthylamine [91-59-8,4-ami-
nobiphenyl [92-67-1], benzidine (4,4-diaminobiphenyl)
[92-87-5], fuchsine (C.I. Basic Violet 14, 42510 [632-99-5]),
and auramine (C.I. Solvent Yellow 2, 11020 [60-11-7]).
There’s a lot of evidence that these substances’ metabolites
are the ones that cause cancer. In most industrialised coun-
tries, strict rules governing the handling of recognised car-
cinogens have been enacted Table 2. Almost all dye busi-
nesses have stopped using these chemicals as a result of the
rules. Some colours have been proved carcinogens in animal
experiments and are likely carcinogens in humans [33,34].
4. Methods of dye removal
Dye techniques of elimination involve just initial water
treatment techniques like equalization and sediment are
carried out. Since there was no dye discharge cap for effluent.
Following the establishment of appropriate coloring
effluent release requirements, highly effective decolorization
processes, including colouring filter beds and the activated
sludge process, were implemented. Thereafter a color sew-
age treatment plant shown in Fig. 9 was the first of its kind.
Technique, referred to as the conventional colorant elim-
ination processes, used by the manufacturing concerned a
while before discontinued because of the high price oper-
ating and preservation. Many works are currently under
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–12796
Table 2
Different chemicals used in textile chemicals processing
Type Example
Acid Acetic acid, formic acid
Alkali Sodium hydroxide, potassium hydroxide, sodium carbonate
Blach Hydrogen peroxide, sodium hypochlorite, sodium chlorite
Dyes Reactive, direct, disperse, pigment, vat
Salt Sodium chlorite
Size Starch, PVA
Stabilizer Sodium silicate, sodium nitrate, organic stabilizers
Surfactant Detergent
Auxilary finishes Fire retardant, softner
Fig. 9. Techniques for removing colour from textile effluent.
97M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
way to find the best form of extracting dye as a result of
which dye discharge can be captured and recycled [35–39].
4.1. Biological dye removal approaches
The standard biological approach for treating dye waste
water is the widely and extensively used color removal pro-
cesses in most countries. A mixture of aerobic and anaerobic
processes is commonly regarded as the traditional procedure,
prior to the discharge of colored effluents into the atmosphere
process has been colorants method of choice processes primar-
ily since it is relatively low-cost and straightforward to com-
plete. Furthermore, this procedure is inadequate to entirely
remove dangerous materials of textile wastewater, hence why
coloured water can still be found in the atmosphere.
While traditional approach reduce need for in waste
water, there is a chemical oxygen present. Certain traditional
methods for extracting biological dye biomass of microbe’s
adsorption, algal decomposition, enzyme decomposition,
fungus farms, microbiological cultures, and pure or mixed
plants are all examples of deterioration. Aforementioned
processes in Table 3 laterally their definition, benefits
and disadvantages. Methods for extracting biological dye
integrate some type of living organism into their operation.
This approach should be used with caution, and it should
be maintained in engineering ethics.
4.2. Chemical procedures for removing dye
Chemical dye extraction procedures are those that
employ chemical or its principles to remove the color.
Accelerated oxidation, electrochemical destruction, elimina-
tion of the Fenton reaction dye, oxidation, zonation, photo-
chemical, and ultraviolet irradiation are all traditional ways
for removing chemical dye. Numerous chemical removal
efficiency techniques are more costly than biological and
physical dye removal techniques, with the exception of elec-
trochemical degradation removal efficiency technologies.
Chemical colour removal methods are frequently unappeal-
ing to businesses, necessitate specialized equipment, and use
a lot of electricity [40].
The strength of apparatus or units that remove chemical
colors necessitates a lot of electricity. Furthermore, large-
scale chemical and reagent usage is a well-documented issue
among chemical decolorization technique users [40]. Other
undesirable aspect of these methods is the development of
harmful secondary contamination that occurs after chemical
dye removal, posing a new disposal difficulty.
4.3. Physical techniques of dye removal
Methods of physical sorption process is usually a simple
procedure. Generally employed by the processes of mass
transportation adsorption, coagulation or flocculation, ion
exchange, and other conventional procedures for removing
visible dye are used. Radiation, filtration of membranes,
nanofiltration, or ultrafiltration and reverse osmosis.
Such approaches commonly selected their easiness and
effectiveness. Biological and chemical decolorization tech-
niques pale in comparison, process needs by far the least
amounts of chemicals [41]. This approach is considered more
dependable than the other two dye extraction procedures
because it does not involve living creatures.
4.4. Electrochemical methods
In the mid 1990’s electrocoagulation techniques were
developed. Efficient means to extracting ink. This technique
utilizes make the relationship among metal electrodes in the
effluent, including aluminium and iron, to enable the metal
plates move to dissolve in waste water.
Fe(OH)3, dissolved dyes may be extracted by precipi-
tation or flotation. This approach demonstrates high pro-
ductivity with respect to color removal and recalcitrant
pollutants degradation [42–44].
5. Efficiency of dye elimination techniques
Various approaches of treating effluents from holding
dye. Despite the fact that there are several methods avail-
able. Only a few examples include coagulation, chemi-
cal oxidation, membrane filtration, electrochemistry, and
aerobic and anaerobic microbial decomposition Tables 3–5.
5.1. Sedimentation
Primary method of most municipal wastewater treat-
ment facilities use this technique plants [45]. Variety pro-
cesses alternatives to choose from for improving suspended
particle gravity settlement, chemical flocculants, sedimen-
tation basins, and clarifiers are only a few examples Fig. 10.
Table 3
Advantages and disadvantages of chemical treatments
Methods Advantages Disadvantages
Treatments with chemicals
Process of oxidation Technology that is easier to use (H2O) The agent must be
activated in some way
(Reagent of Fenton) Fenton’s reagent is an excellent chemical tool Generating sediment
Ozonation Ozone must be utilized in its gaseous condition because it does
not increase the volume of wastewater or sediment
Half-life short (20 min)
Photochemical There is no sediment formed, and bad odors are much decreased By-product’s creation
NaOCl Begins and increases azo-bond cleavage Unleashes of aromatic amines
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–12798
5.2. Filtration technology
An integral component application for Microfiltration,
ultrafiltration, nanofiltration, and reverse osmosis are used
to purify drinking water and remediate wastewater. This
was investigated for deleting the color [45]. For a specific
water treatment purpose, each membrane method has its
own set of advantages and disadvantages. Among them,
microfiltration is of little use in because of its wide pores, it
is suitable for wastewater treatment, and while ultrafiltra-
tion and nanofiltration are two types of filtrations techniques
successful in dye molecules clog membrane pores fre-
quently, making separation techniques for textile wastewater
treatment ineffective Fig. 10.
5.3. Chemical treatment
A coagulating/flocculating agent is used to treat dye
chemically from waste water is one of the effective ways
to extract pigment [46,47]. The cycle includes introducing
agents’ effluent, for example (Al3+), (Ca2+) or (Fe3+) ions, and
produces flocculation’s. In addition to these other agents
were also used for the operation combination of two can also
be applied often to enhance the process Fig. 11.
5.4. Oxidation
Oxidation is a system using oxidizing agents to waste
water. Two methods usually viz. For treating effluents, par-
ticularly those obtained from initial treatment, chemical oxi-
dation and UV assisted oxidation with chlorine, hydrogen
peroxide, Fenton’s reagent, ozone, or potassium perman-
ganate are utilized (sedimentation). Because they require
small amounts and quick reaction periods, they are among
the most extensively utilized procedures for discoloration
processes. They are used to break down dyes partially or
entirely. On the other hand, full oxidation of the dye the-
oretically breaks down complex molecules into carbon
dioxide and water. The importance of pH and catalysts in
the oxidation process should not be underestimated.
5.5. Electrochemical methodology
The removal of color is often used as a tertiary therapy.
Decoloration can be accomplished either via consumable ingre-
dients or electrocoagulation. Several types of anodes are avail-
able, such as titanium, conducting. The electro- degradation of
dyes has been effectively carried out using boron doped dia-
mond electrodes and other experimental conditions [48].
Table 5
Benefits and drawbacks of biological therapy
Methods Advantages Disadvantages
Biological treatments
White-rot fungus cause discoloration Colorants can be degraded by white-rot
fungi via enzymes
The generation of enzymes has also
shown to be unreliable
Microbes from other cultures (mixed bacterial) Decolored in 24–30 h Under aerobic conditions, azo hues
are not easily digested
Living/dead microbial biomass adsorption Some colorants have a strong affinity for
microbial organisms
All dyes were unsuccessful
Textile-dye bioremediation systems that are
anaerobic
Under water-soluble dyes, azo must be
decolored
Methane and hydrogen sulphide
are produced during anaerobic
decomposition
Table 4
Physical and electrochemical treatments have advantages and downsides
Methods Advantages Disadvantages
Treatments that are physical
Activated carbon adsorption Effective treatment different colorant Extremely costly
Filtration using membranes All types of dye are eliminated Generated heavy sediment
Exchange of ions There is no loss of adsorbent during regeneration Not all dyes were successful
Irradiation Efficient laboratory oxidation Need much O2 dissolved
Electro kinetic coagulation Economically workable Strong development of sludge
Electrochemical treatments
Destruction through electrochemistry There are no chemicals used, and there is no sludge
build-up
Flow rates that are unusually
high are a strong indicator
99M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
5.6. Advanced oxidation processes (AOPs)
System requiring using multiple oxidation processes
at the same time, because a single oxidation system is fre-
quently insufficient for full colour degradation. Advanced
oxidation processes (AOPs) are reactions that include the
rapid formation of the highly reactive hydroxyl free radi-
cal, such as Fenton’s reagent oxidation, UV photolysis, and
sonolysis. They can breakdown colours at room temperature
and pressure, and they may be a better option than biolog-
ical treatment for waste streams containing hazardous or
bio-inhibitory contaminants [49].
5.6.1. Photocatalysis
It also one of several efficient contaminant breakdown
and oxidation methods [49,50]. A catalyst’s valence band
electron is excited into the conduction band by light energy
from a light source, resulting in the creation of hydroxyl
radicals through a series of reactions. Because hydroxyl
radicals have a strong oxidation proclivity, they can
attack and oxidize almost any organic structure.
Fig. 10. Traditional wastewater treatment system.
Fig. 11. Linearized plots of adsorption isotherm models of MB at ZIF-8.
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127100
5.6.2. Sonolysis
Application of ultrasonic waves was used to decol-
orized and degrade colorant. Proposed a generic process
for sonochemical reactions focused on the emergence of
transient species during strong cavitation episodes [51].
5.7. Biological treatment
This is the most successful and commonly used method
for treating dyeing waste water [51–53]. A large number of
organisms were used to decolorize and mineralize differ-
ent dyes. The technique provides many advantages, such as
being comparatively cheap, small operation charges and not
being harmful to the end products of full mine realization.
5.8. Aerobic treatment
The most investigated microorganisms for their ability
to remediate coloured wastewaters are bacteria and fun-
gus. When in an aerobic setting, the organic compounds
are broken down by enzymes secreted by bacteria found in
wastewater. The task at hand to classify and isolate micro-
organisms that are aerobic that can degrade numerous
colorants that ongoing for in excess of two decades [53].
5.9. Fungal strains
Fungal strains various have studied in depth the strains
of fungi that can decoloring azo and triple phenyl meth-
ane colorants. Phanerochaete chrysosporium, has thoroughly
It has being researched for its capacity to decolorize a
widespread variety of colors by numerous works over the
past two decades [54,55]. In addition to this microorgan-
isms such as Rhizopus oryzae, Cyathus bulleri, Coriolus versi-
color, Funalia trogii, Laetiporus sulphureus, Streptomyces sp.,
Trametes versicolor and other microorganisms have also been
checked for decolorization of colorants. Specific parame-
ters, as an example pollutants dose of pollutants, dyestuff
concentration, temperature and initial pH, influence the
procedure of decolorization.
5.10. Anaerobic treatment
Ability methods for anaerobic digestion for the decom-
position of a wide range of materials of synthetic dyes
has been well-proven and confirmed. While some recent
attempts to decolorate although dyes have performed well
in aerobic environments, the prevalent belief that almost
all azo dyes are non-biodegradable persists in the con-
ventional aerobic energy system [56].
5.11. Treatment that is both aerobic and anaerobic
A treatment that includes both aerobic and anaerobic
components is suggested to provide promising results
for the purpose of obtain improved cleaning of colored
complexes derived by textile industries. A benefit such a
method, mineralization in total that frequently completed
thanks to the mutually beneficial behavior a variety of
organisms. In addition, the azo bond has the capability of
reduction can accomplished below reduced environments
in anerobic bioreactors and resulting aromatic amines
that are colourless and odourless can. The combination
anaerobic-azo dye treatment method is appealing since it
mineralizes under aerobic circumstances [57–60].
5.12. Ion exchange
Ion exchange is a chemical process that can be reversed
in which an ion from a solution is exchanged for an ion
that is equally charged but bound to a stationary solid
particle [61]. Change of ions together with adsorption for
industrial and fixed-bed purposes, these techniques can be
classed together as “sorption processes” for unified treat-
ment of high- quality water. Ion exchange has also proved
successful in the elimination of colours.
5.13. Adsorption
Adsorption is a method that can be used to treat indus-
trial wastewater in addition to having a wide range of
applications. In addition to being commonly used for
removal of dyes. The term adsorption refers to phase where
a substance is extracted out of its liquid or gaseous environ-
ment absorbed at a solid surface. The adsorption method is
considered In addition to initial effectiveness, it outperforms
alternative reclaimed water technologies, design simple,
ease of use, and inconsideration to toxic substances [62].
Adsorption is considered a flexible technology for
water and waste water treatment since adsorbent can also
be used to achieve very high rates of contaminant removal
[63,64]. Adsorption was widely used in the separation and
purification of industrial products. The removal of colorful
and colorless organic species from industrial waste water
is seen as a significant application of adsorption processes.
Adsorption method is used for removal.
The basic characteristic of an adsorption processes
material collection on the surface. Differentiating between
two forms of adsorption is now a customary. If, in fact,
attractiveness exists between both the solid surface and the
attached particles, the adsorption is called direct adsorption
(physisorption) [65].
In most cases, Van der Waals forces present the attrac-
tive forces is physical adsorption between both the particles
that have been adsorbed and the solid surface, they are nat-
urally weak, allowing in reversible adsorption. Treatment
systems are referred to as chemisorption when the inter-
action energy is resistant to chemical bonding. Despite the
stronger bonding in chemisorption, removing adsorbed
species from a solid surface is difficult. Variables including
dye content, starting pH, and discharge temperature can all
affect the decolorization procedure. While this strategy is
cost-effective, and biological treatments are excellent for a
wide spectrum of colours, the main disadvantages of biolog-
ical treatments include the colours’ poor biodegradability.
In terms of style and operation, there will be less flexibil-
ity greater aquatic requirements and longer time needed for
the operation of color removal, rendering impossible to extract
effluent dyes in liquid fermentation on a continuous basis.
101M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
The use of adsorbents will also remove any colours that
are hard to break down biologically. An excellent adsor-
bent [66] must have a high porosity (resulted in a wide sur-
face area) as well as the time it takes to reach adsorption
equilibrium is as low as feasible so that it may be used to
remove color waste quickly. Adsorbent had the advantage
of being reusable, as it can be used more than three times.
6. Adsorbents mainly used for dye waste water treatment
6.1. Alumina
Alumina a porosity crystalline gel that is manufactured
and affordable in various size particles with a range of
surface areas 200–300 m2/g [67].
6.2. Silica gel
Coagulated with the creation of porosity and abrasive
surfaces is caused by colloidal silicic acid, non-crystalline
granules of varying thickness. This exhibits an compari-
son to alumina, it has a larger surface areas, ranging from
250 to 900 m2/g [67].
6.3. Zeolites
Zeolites are significant naturally occurring as well
as synthetically manufactured microporous adsorbents.
They also go by the name “selective adsorbents,” which
highlights the importance of ion exchange and molecular
adsorption [68–70].
6.4. Activated carbon
Activated carbon is the first adsorbent that has been
discovered, and it is typically made from coal, coconut
shells, lignite, wood, and other materials using one of two
methods: chemical vs. physical [71–73].
6.5. Glycidyl methacrylate magnetite
Polymers have some major advantages over other
adsorbent materials; for instance, polymers could easily
manufactured in a variety of situations physicochemical
properties (scale, scale distribution, porosity, hydrophobic-
ity, etc.) and can be changed by inserting different ligands
into the structure to create unique sorbents. Macroporous
crosslinked glycidyl methacrylate (GMA) copolymers,
developed by radical suspension copolymerization, in the
form of standards beads of required size and porosity, have
already been used successfully for heavy and precious
metal sorption as well as for dye adsorbents.
Epoxy groups have one special ability to react. They
undergo ring opening with specific compounds that have
groupings of hydroxyl, amine, or activated methylene. Of
this reason, in mild reaction conditions, polymers with epoxy
(oxirane) groups give various functionalizing possibilities.
Oxirane-functioning polymers are rare.
Examples of these polymer are epoxidized polybutadi-
ene and phenol-formaldehyde resins with glycidyl groups
[74]. Glycidyl methacrylate is the only vinyl monomer
currently available to hold group oxirane.
6.6. Nanosphere magnetic metal oxide
Specific metal oxide for example,Fe3O4, Fe2O3, MnO,
Al2O3, TiO2, MgO, ZnO and Ce2O3 nanoparticles have been
utilized as an adsorbent pollutant removal [75]. Among
them, iron-based material has been attracted by several
researchers because of long-term stability, biocompatibil-
ity, amphoteric surface efficiency, enhanced functional role,
and dispensability are all factors to consider (α-Fe2O3) is the
under the much more sustainable iron oxide atmospheric
environments that is broadly catalysts, pigments, sensors,
gas filtration, and water recycling are just a few of the
applications also porous magnetite nanoparticles (Fe3O4),
have received a great agreement of consideration due to
their appealing applications especially like a fascinating
family of crystal structures [76]. Nano-scaled magnetite
has been considerable interest concerning to the size and
shape- controlled synthesis recent magnetic separation now
is common among used in the fields of medicine, diagnos-
tics, molecular biology, bioinorganic chemistry and cataly-
sis. Magnetic separation can be one of the promising ways
for a novel technique of environmental purification due to
the potential to generate no pollutants such as flocculants
and to processes large amounts of wastewater in a short
time. However, this approach is specially adapted when the
separation problem is complex, that is, when contaminated
water includes solid residues that exclude their treatment
in column with regards to the risks of filling. Magnetic sys-
tems often used in environmental applications are indus-
trial carriers consisting of magnetite particles distributed in
a cross-linked polymer matrix [77]. The removal of clothing
effluent dyes is of great importance [78]. The release of col-
ors into the atmosphere reflects only a small proportion of
water contamination, but due to their brightness, coloring
is evident in limited amounts. At the other hand, their pres-
ence inside industrial effluents also influences the processes
of photosynthesis. Therefore, a low-cost method needs to
be identified that is efficient in extracting dyes from large
amounts of effluents (Table 6).
6.7. Metal–organic frameworks (MOFs)
Metal–organic frameworks (MOFs) are porous crystal-
line materials they’re very well their numerous applications
that are well known for their various application (Table 7).
MOF materials are of particular interest due to the simple
tuning of their pore size and their high surface area. MOFs
also commonly used in plant of gasses and adsorption,
isolation, and storing of vapors [90].
6.8. Nanomaterials made of polymers
The drawback of nanoparticle agglomeration or sin-
tered, that diminishes the surface area of these nanopar-
ticles and decreases their contact areas [99], along with
superior tensile characteristics, easy handling, high degree
of dispersion, and relatively inexpensive [100,101], Use of
polymers in waste water treatment has attracted a lot of
attention. Such nanoparticles were routinely synthesized in
polymers for consistent distribution of nanoparticles and
enhanced conductivity of the polymeric nanocomposite
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127102
while processing industrial effluents. Polyaniline, poly-
pyrrole, polyparaphenylene vinylene, polyparaphenylene,
polythiophene, polyacetylene, and others are components
of additional savings with higher tensile strength across all
sorts of photodegradation due to its exceptional reliability,
easy fabrication, and quality in transporting high range
that can be functionalized (by HCl, H2SO4 etc.). Şen et al.
[102] to investigate the impact of pH, temperature, and the
initial quantity of methylene blue on the reaction kinetics
of adsorption between both the composite and the color,
researchers utilised a composite film made of polyethylene
(GCP) and green clay (MB) [102]. According to the find-
ings, increasing the MB content boosts adsorption, boosting
the pH from 5.5 to 9. The kinetic energy of the molecules
increases, leading to a rise in temperature. In addition, the
pseudo-second-order model was the most accurate kinetic
and thermodynamic model of adsorption. (ΔG: 70.64 kJ/
mol, ΔS: 70.64 J/mol·K, Ea: 12.37 kJ/mol at 308°C) revealed
that adsorption was spontaneous, physical, and low-energy
[103]. Gouthaman et al. [103] polyaniline-polyvinylpyr-
rolidone (PAPV) and polyaniline-polyvinylpyrrolidone
neodymium/ZnO (PAPV-NZO) polymeric nanocompos-
ites were effectively synthesized and characterized by
oxidation polymerization and used as adsorbents in the
discharge of Acid red 52 colour with various parameters
including time and adsorbent dosage. Due to the combi-
nation of NZO, which increases the conductivity, stability,
and surface area of PAPV-NZO with the requisite dye con-
centration and adsorbent dose of PAPV-NZO, PAPV-NZO
has a larger dye removal rate than PAPV ppm and 50 mg,
respectively. Moreover, in good conditions (pH 14 2,0.05 g
of adsorbent dosage with 3% N NZO in 80 ppm dye), PAPV-
NZO was removed 99.6% using the Langmuir model, pseu-
do-second-order kinetics, with the qmax of PAPV-NZO esti-
mated to be 159.36 mg/g. Mohammadikish and Jahanshiri
[104]. Two metal-based interaction polymers were pro-
duced (Pb2-FSL, Zn2-FSL) to assist in the degradation of
dissolved colors (methylene blue (MB), methyl orange
Table 6
Absorption coefficient comparisons (qm) of porous magnetic nanosphere iron oxide and various adsorbents for both RB5 and CR dye
Adsorbents Maximum adsorption
capacity (mg/g)
References
CR RB5
Dolomite 72.4 229.2 [79]
Banana peel powder 49.2 164.6 [80]
MgO FA 48.8 –[81]
Use of Macrocystis pyrifera biomass and zero-valent iron nanoparticles 39.9 –[82]
Fe3O418.0 – [83]
MoO2/CaSO4 composites 853.3 [84]
Hierarchical C/NiO-ZnO composite –613 [85]
Hydroxyapatite nanoparticles loaded on Zn –416.7 [81]
Amine-modified Biomass of Funalia trogii –193.7 [86]
Pineapple plant steam – 12.0 [87]
PEI-CW 77.5 34.4 [88]
Porous magnetic nanosphere iron oxide 1,070 1,621.59 [89]
Table 7
Absorption coefficient comparing (qm) of zeolitic imidazolate framework-8 and various adsorbents for both Malachite green dye
Adsorbent qm (mg/g) References
Using coconut fiber, activated carbon was created from coconut coir 27.44 [91]
SWCNT-COOH 19.84 [92]
Iron humate 19.2 [93]
Nanowires of Cd(OH)2 placed on activated carbon 19 [94]
MWCNT-COOH 11.73 [95]
SWCNTs 4.928 [94]
SWCNT-NH26.134 [94]
Activated carbons commercial grade (ACC) 8.27 [92]
Bentonite clay 7.716 [96]
Activated charcoal 0.179 [97]
ZIF-8 60.27 [98]
103M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
(MO)) The elimination of cationic MB was excellent for
both coordination polymers when the dye adsorption per-
formance of the synthesised coordination polymers was
investigated (97.2% for Pb coordination polymer and 99.9%
for due to the larger negative surface charge of Zn2-FSL,
the elimination efficiency of anionic methyl orange in the
case of Pb coordination polymer is significantly greater
(97.2%) in comparison to the situation of Zn coordination
polymer (23.1%). Furthermore, the pseudo-second-or-
der kinetics model was used to fit the adsorption kinetics
of both MB and MO onto Pb2-FSL and Zn2-FSL [104,105].
6.9. Carbonaceous nanomaterials
Carbon nanotubes (CNTs) are hollow cylindrical graph-
ite micro-crystals with excellent mechanical qualities long-
term stability, unusual electrical characteristics, and large
specific surface areas are just a few of the benefits.
Such nanoparticles have large surface areas and amor-
phous microporous surfaces, and they’re used in industries to
remove adsorbent dose, particularly once one liquid element
in a combination has to be preferentially adsorbed [106].
Despite the fact that CNTs get a high dye absorp-
tion rate capability owing of its hollowed and multilayer
nanostructured nanostructures architectures, they possess
big particular regions and are expensive prevents them from
being used in industry.
Furthermore, because to their tiny size, strong aggre-
gation, and curing capabilities, CNTs hard to remove from
water-based solutions. Considering expense issue and CNT
extraction via water environments can be overcome [107] as
a sustainable matrix for CNTs, by building CNT composites
using polymers, carbon, metal oxide, and other materials.
CNTs have lately been exploited as a potential nano-filler
in CNT-based nanocomposite with excellent absorption,
electrical, mechanical, and thermal properties, making
CNT-based composites efficient adsorbents. It is not just
adds to the number of active places, but also expands the
area covered. Areas vs. their primary materials CNTseACF
composites, CNTseFe3O4 composites, CNTsedolomite com-
posites, CNTsecellulose composites, and CNTsegraphene
composites are examples of these composites. Also, by
reducing aggregate formation the adsorption capabilities of
CNTs can be improved by making them more hydrophilic
in character, that results in the highest selectivity for the
adsorption of ionic species from aqueous media due to the
presence of oxygen-containing groups at the surface [108].
Dawood et al. [109] purified CNTs manufactured by
catalytic chemical vapour deposition (CCVD) process and
utilised as an adsorbent to eliminate dyes (BO) and (MV).
Different effects of parameter were studied. The great-
est clearance of methyl violet and basic orange dyes was
achieved at pH 14 8.5 and CNT dosages of 0.25 and 0.3 g/L,
respectively [110].
The percentage of dye adsorption was shown to be per
the Kumar et al. [110], dyes are much are inversely propor-
tional, although contact time is directly related.
The equilibrium reactive black (RB) adsorption is
strongly aligned to the Langmuir and Temkin isotherms,
and the pseudo-second-order model better represented
adsorption kinetics. As per Dutta et al. [111], MWCNT and
ACNT had a better affinity for cationic MG, MB, and RhB
dyes, while NH2CNT had a binds to receptors for anionic
dye MO [111].
The Langmuir equilibrium isotherm model also fit-
ted MG adsorption by ACNT, HCNT, MWCNT, and MO
adsorption by NH2CNT, with adsorption capacities of
198.41 (MWCNT), 194.55 (ACNT), 167.78 (HCNT), and
194.55 (NH2CNT) mg/g, respectively. The usage of the sor-
bents was also assessed, and it was discovered that after
three consecutive runs, they retained their efficiency (96%).
6.10. Nanofibers
Nanofiber is a polymer fiber with a diameter ranging
from 1 to 1,000 nm. A nanofiber absorbent has It has a sur-
face areas and length-to-diameter ratio, indicating that it
has a lot of surface area and a lot of adsorption active sites.
Separation requires only a minimal number of nanofibers,
resulting in a considerable decrease in desorption solvent
volume [112]. CNFs have evolved as an important choice
considering the low cost and ease of manufacture of tiny
tunable pore sizes in comparison to other adsorbents owing
to the increase expense of utilizing adsorbents like CNTs
and graphene in industrial topics. Techniques for produc-
ing nanofibers include spinning of melt, solution, emulsion,
and electro, with electro spinning being most common.
In principle, vapor-grown CNFs (VGCNFs) and electro
spun CNFs (ECNFs) are the two types of CNFs based on their
production, with the ECNFs being used in water purification
[113].
When compared to VGCNFs, electro spun nanofibers
have higher pore densities, they are much more effective as
water and air filtration because they have a greater surface
area per unit volume, lower and upper secondary pollutants,
higher permeability, a lower base weight, and a smaller fiber
diameter. When compared to cast polymer membranes, elec-
tro spun nanofibers have the drawback of being mechanically
unstable. Unless a nanofiber will have all the listed functions,
it helps to consider a function. This is usually achieved by
placing other materials or arranging special surface struc-
tures, which helps improve the capabilities of embedded
composites or structured nanofibers with a large surface area
and is one of the reasons why nanofibers have become pop-
ular in recent years. Ibupoto et al. [114] found that activated
carbon nanofibers had a remarkable adsorption efficiency,
completely decolorizing the dye solution within 60 min of
contact time, with adsorption data following the Langmuir
isotherm model with a qmax of 72.46 mg/g and best suited to
the pseudo-second-order kinetic model [114].
In Cheng et al. [115], DA@PDA nanofibers were used to
remove MB out of an aqueous phase inquiries. After 30 h of
interaction, the DA@PDA nanofiber was shown to have an
adsorption strength of approximately to 88.2 mg/g at a tem-
perature of 25°C and a pH of 6.5 [116].
Because of the electrostatic attraction between the sur-
face functional groups of the O-EC, it was found that porous
carbon nanofibers had a remarkable absorption capacity,
completely conditions or disables the dye solution within
60 min of contact hours, of adsorption data going to follow
the Langmuir isotherm model with a qmax of 72.46 mg/g and
best suited to the pseudo-second-order kinetic model, with
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127104
adsorption data following the Langmuir isotherm mode
[117]. At 25°C, electrospinning carbon nanofibers (ECNFs)
functionalized with MB dye had a greater affinity (170 mg/g)
than virgin ECNFs (32.5 mg/g). Thermodynamic research
(ΔG: 11.089 kJ/mol at 298 K; ΔH: 89.975 kJ/mol) revealed that
MB adsorption onto O-ECNFs was endothermic and sponta-
neous [117].
6.11. Xerogels and aerogels
Xerogels and aerogels are desirable possibilities as
adsorbents and catalyst support materials for a variety of
applications due to their huge surface areas, low cost, high
porosity, internal pore volume, and low density [117].
To make xerogels and aerogels with an appropriate
porous structure, excellent mechanical characteristics, and
distinct granule microstructures, the sol–gel process is being
used. These highly adsorbent particles are also chemically
and thermally stable, have a high sorption capacity even
after regeneration, and have a significant reactivity toward
a variety of substances, includes pollution gases and metal
ions. According to Wu et al. [118], xerogels have a number
of advantages, having the ability to make them in specified
shapes or thin films, easy extraction from sample solution,
and control over physical properties including hydropho-
bicity, porosity, and optical properties. Xerogels come in
three different forms: crystalline, amorphous, and g-forms
(silica gel) (alumina). Aerogels have more surface area, poros-
ity, and pore volume than xerogels, as evidenced by alumina
aerogels, that have a high surface area of 1,000 m2/g and a
pore volume of 17.3 cm3/g while retaining all other xerogel
characteristics. However, there is a scarcity of information
about their adsorption properties. Wu et al. wanted to know
how factors like solution pH, textural properties, hydropho-
bicity, and hydrogen bonding affect adsorption efficiency
[118]. The adsorption of four organic dyes (methyl orange,
alizarin red S, brilliant blue FCF, and phenol red) on porous
xerogels made to use a two-step sol–gel technique was exam-
ined. With increasing solution pH, electrostatic repulsion
between the dyes and the xerogel surface reduced adsorp-
tion, whereas the combined effects of increased hydrophobic-
ity or pore size/volume of the xerogels enhanced adsorption
capacity [119].
Kaya et al. [120] employed volcanic tuff to make silica
xerogel, which they then used as an adsorbent to remove
methylene blue (MB). Temperature had the greatest effect,
accounting for 54.50% of the variance in beginning MB con-
centrations, contact time, silica xerogel dose, temperature,
and pH are all variables that can be controlled. MB per-
centage removal of 96.18% and optimum adsorption ability
of 51.967 mg/g were reached under optimum conditions of
60 min contact time, initial MB concentration of 20 ppm, silica
xerogel dose of 0.0016 g/L, temperature of 40°C, and pH 5.
The maximum desorption accuracy was 88%, with the silica
xerogel retaining around 70% of adsorption efficiency after
five cycles [120].
Han et al. [121] two types of silica aerogels as adsorbents
to remove distinct dyes: one hydrophilic (hydroxyl-group)
and one hydrophobic (surface modified) (MSA) (HSA). The
goal was to see how these colours adsorb to different aero-
gel characteristics. After four regeneration cycles, the MSA
aerogel including a high surface area of 880.47 m2/g used
to have an adsorption capability of 65.74 mg/g for MB and
134.25 mg/g for RhB, as well as an adsorption effectiveness of
around 90%. The HSA aerogel with a specific surface area of
628.52 m2/g had a qmax of 47.21 mg/g for MB and 185.61 mg/g
for RhB after the third reuse cycle, as well as an adsorption
accuracy of over 80% [121].
7. Biosorption
7.1. Biosorption fundamental
Biosorption (biotechnological method) is an applied
part of environmental sustainability) [122]. It is regarded
as an environmentally benign, cost-effective, and efficient
water treatment method. It keeps the concentrations of var-
ious contaminants in the water within the permitted limits
set by various federal rules [123]. This green approach is
in line with green chemistry concepts. The principles of
the biosorption process, as well as its various constituents,
must be understood. In a nutshell, it is a procedure that is
not dependent on metabolism (passive uptake) according
to the use of biological effluent as well as removal vari-
ous pollutants in the water. In general, the recycling of
these biomasses results in a slew of advantages. Use they
have natural forms that have been altered contributes
straight to trash reduction [124].
This the ability to solve a wide range of ecological and
environmental issues. It also has notable characteristics
such as minimal operating and manufacturing costs, as well
as great efficiency.
7.2. Biosorption strategy
Biosorption has been evolving in recent years as a
multidimensionally successful method. When compared
to other traditional wastewater treatment methods, it is
regarded as an excellent alternative. Sorption is a phys-
icochemical process when sorbate molecules connect to
another substance’s surface (sorbent). Effluents that have
been purified of excellent quality are produced as a result
of this. Despite the use of the “bio” prefix to indicate a bio-
logical entity’s involvement, the term “biosorption” has a
simple definition. In terms of the sorption mechanism, both
bio-absorption and biosorption dimensions play a role. The
transfer of a material from one state to another is known as
absorption. It comprises gas absorption by aqueous solution
or liquid absorption by a solid). Adsorption is a chemical
bond, but it’s also a physical one between a sorbent and a
sorbate that results in a sorbent-sorbate interface, adsorp-
tion is a chemical bond [125]. In a nutshell, biosorption is
a passive, physiologically unaffected process that encom-
passes all aspects of sorbate-biomatrix interaction (biosor-
bent). It is important in a variety of processes that occur
spontaneously in several scientific fields [126].
7.3. Biosorbents selectivity
Appropriate biosorbent choice is thought to become the
most important factor to consider when choosing one. The
price of biomass and where it comes from are important
factors to consider when choosing a biosorbent. To be used
105M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
for the manufacture of various biosorbents, dead biomass
takes precedence over live biomass [127]. There are numer-
ous benefits to using dead biomass. It can be summarized
as follows: (1) No need to include growing demands (such
as media and minerals) in the bulk solution; (2) There are
no toxicity restrictions; (3) Reuse and recoveries of saturat-
ing biosorption and adsorb contaminants are both conceiv-
able; and (4) Modeling of contaminant absorption that is
more mathematically and statistically simple. Furthermore,
the biosorbent chosen must meet a number of criteria,
including environmental friendliness, Biocompatibility,
availability, and feasibility are all factors that must be
considered. This ensures its ability to detoxify a variety
of contaminants found in water. Biosorbent must also
possess a variety of other appealing characteristics. This
is demonstrated by its strong high sorption effectiveness
vs. contaminants, exceptional durability, and renewability.
Recyclability and adaptation of the biosorbent to varied
designs (e.g., batch, fixed bed systems) should be taken into
account [128]. Based on the concept of trash as wealth, the
available wastes should be given priority. Because of their
environmental friendliness, they can be used for a variety
of purposes. It’s cost- effective because it solves disposal
issues while also generating cash for a variety of sectors. The
abundant organic materials, in truth, are structurally quite
different [129].
Amongst ligands that make it up these molecules are
alcohol, amino, aldehydes, carboxylic, hydroxyl, phosphate,
thiol, ketones, phenolic, and ether groups. They can interact
with target pollutants through a variety of processes since
they are present in variable degrees.
Biosorption is a promising approach that can be used
instead of traditional methods. It is contingent on with use
of bio-waste to remove many types of contaminants from
water. Its premise is based on the idea of getting two uses
out of bio-waste. This is accomplished by recycling material
in order to directly contribute to waste reduction while also
maximising the advantages obtained [130].
As a result, it is possible to meet the emission reduction
targets set by international or national rules, as well as the
World Health Organization (WHO) [131]. It stands out for its
reduced operational and product attribute, as well as flexibil-
ity, ease of use, and effectiveness, are all advantages chitosan
(ii) biochar [132]; (iii) activated carbon [133]; (iv) bio-nano-
composites; (v) bio-hydrogels [134]; (vi) Alternative and
effective sorbents based on marine algae are being studied for
wastewater treatment. It takes into account globally distrib-
uted renewable resources. Color and colloid content are used
to classify it. Chlorophyta, Phaeophyta, and Rhodophyta algae are
the three basic kinds of algae found in oceans. Recent research
has established the usage of microalgae as a viable option.
For instance, Afshariani and Roosta [135] investigated
methylene blue sorption in aqueous solutions using batch
and continuous methods. The greatest sorption was 87.69
3.22 mg/g at a pH of 9 and a temperature of 30°C. As an
additional leather coloring absorbent, puree microalgae bio-
mass (microalgae biofuel effluent) was explored. Aqueous
dye solutions of Acid blue 161 were used to conduct bio-
sorption tests (AB-161). At 25°C and 40°C, respectively,
75.78 and 83.2 mg/g of dye were adsorbed, respectively.
Biomass reduced dye amount by 76.65% in effluents from
a real tannery, according to the data. Alginate, carrageenan,
and polycolloid make comprise the cell wall of algae, is
primarily made up of polysaccharides. These elements are
capable of the removal of a wide range of pollutants from
water [136]. Both macro and microalgae have been used as
ideal options to produce various organic dyes, in addition to
the removal of toxic metals from aquatic systems [137].
A green macroalga (Enteromorpha flexuosa) was tested
for its ability both crystal violet (CV) and methylene blue
(MB) were extracted from aqueous solutions. Under optimal
settings of parameters for CV and MB, percentage elimina-
tion of 90.3% and 93.4%, respectively, were obtained [138].
Green algae are mostly made up of cellulose, which is
mixed with polysaccharides to make glycoproteins. There
are numerous functional groups (as amino, hydroxyl, and
carboxyl) describe these molecules. They are extremely
important in the sorption process [139,140].
Fucoidans, mannitol, laminarins, fucoxanthin, halo-
genated compounds, polyphenols, and terpenoids are all
examples of alginates are some of the metabolites that dis-
tinguish brown algae [141]. Salts of calcium, phosphate,
and sodium used to make alginates. The brown seaweed
cell wall is primarily composed of sodium salts. Its weight
has increased by about 30%–40%. Polysaccharides that are
anionic, linear, and water soluble. Brown seaweed alginate
was obtained using a variety of pre-extraction preparation
procedures [141]. These natural biopolymers are widely
used in a variety of applications in the environment.
It is frequently employed as a possible sorbent for
removing different pollutants from water [142]. It refers to
possessing diverse functional groups.
Several researchers examined biochar generated heavy
metals elimination from aqueous solution using microalgae
pyrolysis as another type of sorbent. A batch system has
been used to test biochar for Co(II) elimination efficiency
Freundlich, Temkin, and D–R isotherms all well-fitting by
equilibrium data. 1.117 mg/g was the Langmuir biosorp-
tion capability [143]. Water dracaenas are used to make
biochar (Eichhornia crassipes) has been shown a good sor-
bent material for removing heavy metals and a way to
control this invasive plant. Using water hyacinth biomass
as a biochar feedstock has a number of advantages. The
added benefit of decreasing the species’ impact on deli-
cate aquatic ecosystems as an invasive species. The max-
imal sorption capacities of biochar-alginate capsules for
the value of extracting cadmium from an aqueous solution
varied from 24.2 to 45.8 mg/g [144]. At 55°C, the greatest
biosorption ability for ytterbium was 0.642 mmol/g, accord-
ing to the equilibrium research. Calcium carbonate was
utilized to manufacture sodium alginate-based beads with
various concentrations of pore-forming agent to improve
the sorption capabilities of alginate gel beads [145]. Cu(II)
adsorption capacity raised by at minimum a factor of two
(from 13.69 to 33.88 mg/g) according to the experimental
results [145]. Other experimental technique for alginate
was to phosphorylate alginate-PEI beads and use them for
the sorption of Nd(III) and Mo(VI) [146]. Phosphorylation
increases the sorption of Nd(III) significantly, but phos-
phorus groups have a more restricted effect on Mo(VI).
Nd(III) maximal capacity to absorb increased from 0.61 to
1.46 mmol/g after phosphorylation of alginate-PEI beads.
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127106
Because molybdate species have a high affinity for amine
groups [146], the increase in Mo(VI) absorption substantially
decreased pronounced (from 1.46 to 2.09 mmol/g) [147].
Chitosan is a type of chitin that has been modified. It’s
mostly fashioned from either crab or shrimp shells [128].
The sorption qualities of six distinct crosslinking agents
used to crosslink chitosan sorbents were compared three
ionic agents: sodium citrate, sodium tripolyphosphate, and
sulfosuccinic acid, as well as three covalent agents: glutar-
aldehyde, epichlorohydrin, trimethylo propane, and tri-
glycidyl ether) [148]. The chitosan hydrogel’s reactivity to
the Reactive Black 5 dye was dramatically influenced by
ionic crosslinking [148]. After 24 h of sorption, chitosan
cross-linked with sodium citrate and sulfosuccinate had a
sorption potential of 46.7% and 37.2%, respectively, as com-
pared to non-crosslinked chitosan [148]. Chitosan had been
bonded with glutaraldehyde and trimethylolpropane trigly-
cidyl ether after 24 h of sorption. 35.3% and 26.6% lower
sorption potentials than unmodified chitosan, respectively.
The unmodified chitosan had the highest sorption capac-
ity (2,307 mg/g), the absorbent capabilities of the ionically
crosslinked hydrogels ranged from 2,005 to 2,164 mg/g. The
adsorption capabilities of the covalently chemically bonded
hydrogels were 2,083–2,183 mg/g [148]. To eliminate (CV)
and (MO) from wastewater, a polypyrrole-decorated chi-
tosan-based mag-sorbent was created. At the ideal con-
ditions, CV and MO removal performance was 88.11 and
92.89%, respectively.
The dynamics of pseudo-second-order accurately
approximated CV removal, whereas the PSO closely
matched MO’s. The Langmuir adsorption isotherm for CV
and MO was quite near to the estimates of adsorption equi-
librium, with maximal potentials of sorption in monolay-
ers of 62.89 and 89.29 mg/g, respectively. Immobilization
of chitosan on another polymer is another means of mod-
ifying it. Chitosan, for illustration, was finally converted
using 4-methyl-2-(naphthalen-2-yl)-N-propylpentanamide
functionalized ethoxy-silica and then tested for MB and
AB 25 [149]. Adsorption produce of MB was 3 times higher
with composite beads compared with chitosan beads, and
1.4 times higher with AB 25. Other chitosan hybrid com-
posite with a saturated adsorption capacity of 627 mg/g was
created by doping a small amount of chitosan and Y(III)
ions onto acid-modified fly ash (named MFA) [150]. The
researchers worked hard to improve chitosan’s selectivity
for certain metal ions. Chitosan microparticles grafted with
2-mercaptobenzimidazole, for example, extremely sorbents
that are selective to be developed. Magnetite particles are
also a key component in making chitosan microparticles
easier to use and recover. The sorbent was shown to have
a high selectivity for precious metals as compared to base
metals. Elwakeel et al. [151] found that combining chitosan
with 2-MBI results in a highly efficient sorbent for recover-
ing valuable metals from acidic leachates. Batch experiments
were used to evaluate heavy metal ions (Mn, Fe, Co, Ni, Cu
and Zn) have different adsorption capacities on chitosan
than their comparable anions, SO4, Cl–, and No3. Using col-
umn tests, the selectivity of a number of heavy metal ions
was evaluated. Both the sulphate ions and the heavy metal
cations in the sulphate salts, adsorb to a far greater amount
than the comparable Cl–, and No3 salts. [152].
Luo et al. [153] developed a luminous to effectively
eliminate Cr, researchers used a chitosan-based hydrogel
that includes titanate and cellulose nanofibers enhanced
with carbon dots (VI). The sorbent’s Cr(VI) sorption ability
was increased by porous designs, additional titanate, and
cellulose nanofibers modified with carbon dots (maximum
adsorption capacity, 228.2 mg/g) [153]. A variety of magne-
tized enhanced chitosan sorbents with core-brush topology
were generated by grafting co-polymerization on the surface
of chitosan/Fe3O4 composite particles and utilized to extract
two drugs (diclofenac sodium and tetracycline hydrochlo-
ride) from water [154]. Method for designing adsorbents
based on topological and chemical architectures. Because
of the larger surface areas and functionalization, all of
improved chitosan sorbents were more efficient at removing
contaminants.
Solution casting process was used to create a range of
new chitosan/nanodiamond (chitosan/ND) composites with
varying surface carboxyl groups and concentrations of NDs.
As adsorbent for a model anionic dye, powdery chitosan/
ND composites were used (methyl orange, MO). The high-
est adsorption capability of pure CTS was increased from 167
to 454 mg/g by adding NDs with a high carboxylic content
(ND-H) to chitosan, according to experimental data. The
extraordinary dye adsorption the oxygen-containing groups
on the outer surface of NDs, which would be beneficial for
hydrogen bonding and electrostatic interactions with the
dye molecules, were connected to the ability on chitosan/ND
composites [155].
CaCO3 was among the most adaptable materials ever
devised by man. It’s all over the place. accounting for more
over 4% of the planet’s entire crust. Chalk, marble, and lime-
stone are examples of prevalent CaCO3 forms. Bivalves, cor-
als, and snails, among other aquatic biota, have shells are
the primary sources of bio-calcium. Aragonite, calcite, and
vaterite are the three primary types of carbonates. Though
chemically identical, the whiteness, homogeneity, thickness,
and purity of various forms differ. CaCO3 is widely utilized
in the cement industry because of its distinctive white hue.
It’s also used in applications as a spacer and/or coating pig-
ment, plastics, paints, and paper. In addition, because of its
antacid qualities, CaCO3 is employed acidic conditions in
soil and water in industrial environments. CaCO3 helps the
environment by treating contaminated water. In tissue bio-
engineering, it is commonly employed. CaCO3 is abundant
in two types of sepia and bivalve shells are two types of
marine trash. Shells from the aforementioned aquatic biota
function as external and interior bones, protecting the soft
parts of bivalve’s bodies. SS stands for sepia shells and is a
by-product of the fishing industry. Provide predators with
mechanical defence. Despite their high calcium content,
they are often discarded without being valued commer-
cially. This could result in some local environmental prob-
lems, particularly in Egypt’s Port Said. Exploiting this waste
product for color removal would provide a win-win situa-
tion. According to a literature review, color removal with
cuttlefish bones has received very little attention [156].
Anadara uropigimelana bivalve shells were originally
used as a biosorbent for MB recovery from an aqueous solu-
tion. Under ideal conditions, 93.6% of the MB was removed
(starting pH of 10.4, sorbent dosage of 1 g/L, initial MB
107M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
concentration of 20 mg/L, and temperature of 25°C). But at
the other hand, bivalve shells, are 95% CaCO3 with 5% pro-
tein and carbohydrate content. It’s employed as an adsor-
bent material for the environment because of its structural
and surface qualities.
Pollutants are removed from the environment through
a variety of methods. Calcium carbonate compounds are
a type of calcium carbonate that can be made in a variety
of ways generated immediately by reacting CaCO3 with a
hydrochloric solution is calcium chloride (CaCl2). Using
wasted eggshells to manufacture vaterite calcium carbon-
ate microparticles, the removal effects and underlying pro-
cess for a variety of heavy metal ions were studied. Pb(II)
(99.9%), Cr(III) (99.5%), Fe(III) (99.3%), and Cu(II) (57.1%)
were all removed differently by CaCO3. Sepia shells (cuttle-
fish bones) were used to make a sorbent that was tested for
cationic dye (crystal violet, CV) and anionic dye sorption
(Congo red, CR). To modify the sorbent, sepia shell pow-
der was mixed with urea in the presence of formaldehyde
(SSBC). CV and CR have maximal sorption capacities of
0.536 and 0.359 mmol/g, respectively, at pH 10.6 and 2.4
[157]. SSBC is a software that allows you to connect to the
internet. At pH 10.5 and 2.3, maximum sorption capaci-
ties for MB and RB5 are 0.794 mmol/g (254.05 mg/g) and
0.271 mmol/g (269.18 mg/g). Biosorbents based on chitosan
and alginate had the greatest metal ion elimination sorp-
tion capacities when compared to the other biosorbents
studied. For cationic dye elimination, one of most power-
ful sorbents were chitosan-based, whereas, alginate-based
sorbents were the most effective. The chemical stability
of alginate has been proven. Chitosan composites with
cross-linking agents added, on the other hand, could be
able to overcome this drawback.
The recycling of these biomasses will, in general, yield
several benefits. Its use will contribute to the reduction of
waste. Furthermore, pollutant concentrations in various
water resources will be reduced. Many environmental issues
can be solved this way. Other notable advantages, such as
cheap operating and manufacturing costs as well as great
efficiency, may be realized. The PSO accurately approxi-
mated CV adsorption, whereas the PFO closely matched
MO’s. The Langmuir adsorption isotherm for CV and MO
was closely adsorption equilibrium values were matched.
Adsorption efficiency of MB was three times higher with
composite beads compared with chitosan beads, and
1.4 times higher with AB 25 [150]. The researchers worked
hard to improve chitosan’s selectivity for certain metal ions.
Grafting 2-mercaptobenzimidazole onto chitosan micro-
particles, for example, lets extremely selective sorbents to
be developed. Magnetite particles are also a key compo-
nent in making chitosan microparticles easier to use and
recover. The sorbent was shown to have a high selectivity
for precious metals as compared to base metals (Table 8).
Pollutants are removed from the environment through
a variety of methods [158]. Calcium chloride is one of the
calcium carbonate compounds that can be made quickly
by combining CaCO3 with a hydrochloric solution (CaCl2).
Utilizing wasted oyster shells to manufacture vaterite cal-
cium carbonate microparticles, the elimination effects
and underlying process for a variety of heavy metal ions
were studied. CaCO3 eliminated 99.9% of Pb(II), 99.5%
of Cr(III), 99.3% of Fe(III), and 57.1% of Cu(II) (Lin et al.,
2020). Sepia shells (cuttlefish bones) were used to create
a sorbent that was tested for cationic dye (crystal violet,
CV) and anionic dye sorption (Congo red, CR). To mod-
ify the sorbent, sepia shell powder was mixed with urea
and formaldehyde (SSBC). Maximum sorption capacities
for CV and CR at pH 10.6 and 2.4, respectively, are 0.536
and 0.359 mmol/g [157]. SSBC is a software that allows
you to connect to the internet. At pH 10.5 and 2.3, maxi-
mum sorption capacities for MB and RB5 are 0.794 mmol/g
(254.05 mg/g) and 0.271 mmol/g (269.18 mg/g). With such a
maximal absorption rate of 441 mg/g, an environmentally
friendly sorbent based on marine brown algae and bivalve
shells was recently investigated for subsequent uptake of
Congo red dye and copper(II) ions [157]. Biosorbents based
on chitosan and alginate had metal ions elimination with
the highest sorption capabilities when compared to the
other biosorbents studied. For cationic dye elimination, a
most powerful substances were chitosan-based sorbents,
whereas alginate-based sorbents were the most effec-
tive. The chemical stability of alginate has been proven.
Cross-linking agents added to chitosan composites, on the
other hand, could be able to overcome this drawback.
The recycling of these biomasses will, in general, yield
several benefits. Its use will contribute to the reduction of
waste. Furthermore, pollutant concentrations in various
water resources will be reduced. Many environmental issues
can be solved this way. Other notable advantages, such as
cheap operating and manufacturing costs as well as great
efficiency, may be realized.
8. Equilibrium and kinetic modelling
In adsorption research, equilibrium isotherms and
kinetic models are critical because they allow for optimal
dye adsorption experimental design. There are additional
regression analyses displayed. Because linear modelling con-
tradicts the premise that the least squares method is correct,
nonlinear modelling is more accurate [166].
The PSO the most appropriate model for dye adsorp-
tion kinetics, as shown in Eqs. (1) and (2) show the different
types of kinetic pseudo-first-order and pseudo-second-order
models, respectively, where qe and qt (mg/g) are the quanti-
ties of colors extracted by the adsorbent at equilibrium and
at any time t, respectively, and K2 is the pseudo- second-
order adsorption model’s rate constant (mg/min)(min).
lo
glog .
qq qKt
et e
1
2 303 (1)
t
qKq
t
q
tee
1
2
2 (2)
Many researchers are interested in pollutant adsorp-
tion on adsorbent surfaces, as well as determining which
adsorption capability and isotherm models best fit exper-
imental data. Isotherms depict the relationship between
the pollutant concentration in solution and the amount
of contamination absorbed by the solid phase when both
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127108
phases are in equilibrium and understood in terms of how
contaminants are adsorbed. Adsorption isotherms can be
used to evaluate the adsorption capacity and the best cir-
cumstances for good adsorption. Experimental data are
analyzed using the correlation coefficient (R2) to see if
they follow isotherm theories. The equilibrium adsorption
isotherm investigates the distribution of in between solid
adsorbent and the liquid solution adsorbate molecules or
ions. Fitting isotherm data to a variety of isotherm models
is a useful step that may be used to design the adsorption
process and determine the best isotherm model.
The Langmuir and Freundlich isotherm models are given
in linear form and are based on the ideal assumptions of
monolayer adsorption of adsorbate on the adsorbent sur-
face, where Eq. (3) (linear) and Eq. (4) (non-linear) show
the various forms of the isotherm model [167].
C
qqK
C
q
e
emL
e
m
1 (3)
The monolayer adsorption that occurs at certain homog-
enous spots on the adsorbent is represented by the Langmuir
isotherm. There is no more adsorption on a site after
it has been occupied by a contaminant.
The mechanism of adsorption for the equilibrium isother-
mal adsorption system, as demonstrated by the adsorption
isotherm and kinetic of methylene blue on ZIF-8, is one of
the most important pieces of knowledge. Therefore, the most
pertinent correlation for the curves of equilibrium needs to
be determined. Four adsorption isotherm models, Langmuir,
[168] Freundlich, [169] Dubinin-Radushkevich [170] and
Temkin, [171] were helpful in evaluating the experimental
effects of adsorption in this study [172].
In order to conduct isothermal adsorption studies at
room temperature, 0.02 g of ZIF-8 was added to 25 mL of
MB aqueous solution at various concentrations as a starting
point in the range 2.7 × 10–3 mol/L to 2.2 × 10–3 mol/L Fig. 11
and Table 8. The equilibrium was then achieved after shaking
the solution for 90 min at 110 rpm.
With the proposed chemisorption procedure, the mean
energy value of sorption for MB is 15.9 kJ/mol (Fig. 11).
The physical separation energy limit (below 8 kJ/mol)
and chemical sorption (up to 8 kJ/mol) sorption is usu-
ally acknowledged to be 8 kJ/mol. It’s assumed (Table 9).
Based on their R2 values, the models are sorted in the fol-
lowing order: For MB, Langmuir > Temkin > Dubinin-
Radushkevich > Freundlich > Langmuir > Temkin >
Dubinin-Radushkevich > Freundlich.
Further research into the MB adsorption at the adsorbent was
conducted in order to understand more about the adsorption
properties, which were crucial for the validation of the method’s
output [175]. The pseudo-first-order and pseudo-second-order
kinetic, Weber and Morris, and Elovich equations utilized to
analyzed the adsorption findings (Fig. 12). The calculated data
is summarized in Table 10 [176,177]. The correlation coeffi-
cients demonstrate that the pseudo-second-order kinetic equa-
tion was utilized to better understand the adsorption process,
demonstrating that chemical adsorption was a rate-controlled
process.
Table 8
Different biosorbents’ sorption capability and elimination (percentage) are compared
Biosorbent Contaminant Biosorption
capacity (mg/g)
Mechanism of biosorption References
Green microalgae Chlorella pyrenoidosa RB 63.14 Electrostatic interaction [79]
Sepia shell based composites Methylene blue 254.05 Electrostatic interaction [138]
Sepia shell based composites RB5 269.18 Electrostatic interaction [138]
Magnetic chitosan glutaraldehyde composite Crystal violet 105.47 Electrostatic interaction [159]
ILAC Reactive blue
dye
364.4 Electrostatic interaction [160]
Ethylenediamine modified fiber obtained
from natural Populus tremula
AB 25 67 Van der waals forces π–π stack-
ing and hydrogen bond
[161]
Carica papaya wood Malachite green 52.63 Electrostatic interaction [102]
Grape pomace KROM KGT
dye
180.2 Electrostatic interaction [162]
Chemically modified masau stones Orange (II) dye 136.8 Hydrogen bonding and electro-
static interaction
[163]
Millimetre-sized chitosan/carboxymethyl
cellulose hollow capsule
Methylene blue 64.6 Electrostatic interaction, com-
plexation, hydrogen bonding
and Van der waals forces
[164]
Millimetre-sized chitosan/carboxymethyl
cellulose hollow capsule
Acid blue 113
dyes
526.8 Electrostatic interaction, com-
plexation, hydrogen bonding
and Van der waals forces
[164]
Date seeds activated carbon (DSAC) Acid yellow 99 563.07 Chemisorption [165]
Date seeds activated carbon (DSAC) Malachite green 91.22 Chemisorption [165]
109M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
Table 9
Adsorption of MB by ZIF-8 isotherms and their linear forms [173,174]
Isotherm Equation Value of parameters
Langmuir
C
qqK
C
q
e
emL
e
m
1
qm,exp (mmol/g) 1.681
qm (mmol/g) 1.686
KL (dm3/mg) 40,067.56
R20.9995
Freundlich ln ln lnqK
nC
eF e
1
n4.308
KF (dm3/mg) 10.078
R20.7738
Dubinin–Radushkevich ln lnqQK
e
DR DR
2
QDR 1.243
KDR –1.97E-09
Ea15.9
R20.897
Temkin
qKC
eT TT e
ln ln
βT10,866.54
KT (dm3/mg) 14.83
R20.948
Fig. 12. Linearized plots of adsorption kinetic models of MB at ZIF-8.
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127110
9. Thermodynamic modelling
The describes the overall is significantly influenced by
thermodynamic modeling, which includes characteristics
such as ΔG, ΔH and ΔS determining It is an adsorption pro-
cess in and of itself, regardless about whether the adsorp-
tion reaction is endothermic or exothermic. The change
in Gibb’s free energy (ΔG) is shown in Eq. (4) [178].
ΔGo = ΔHo − TΔSo (4)
used a graph to obtain thermodynamic parameters and
their values. Because adsorption method exothermic, ΔH°
value was negative. Negative Gibb’s free energy (ΔG) val-
ues The spontaneous nature of RhB adsorption on MgO-
FCM-NPs, whereas the positive enthalpy (H) values of RhB
adsorption onto MgO-FCM-NPs illustrates the endothermic
character of the process [179]. RBB adsorption on P-g-Fe2O3
was other study discovered it to be non-spontaneous and
endothermic.
10. Dye adsorption simulation and molecular modelling
For better dye adsorption understanding processes,
computational tool would provide additional or alternate
data. Removal of colorant from environmental waste, numer-
ous computer chemical technologies used. Density functional
theory (DFT) and binitio approaches are the most commonly
utilized in dye adsorption molecular simulation research
[180]. However, certain experiments the experiments were
carried out using numerical simulations and QM/MM
(quantum mechanics and molecular mechanics).
The majority of dye adsorption DFT investigations are
conducted to obtain additional data in additional to the
results of the experiments [180]. DFT-based characteristics
like chemical roughness, chemical potential, dipole moment,
electrophilicity and nucleophilicity indices, Fukui indices,
HOMO and LUMO, or UV-Vis spectra are calculated to
analyse the interactions of dyes and adsorbents [180]. The
adsorption of three coumarin-based dyes was investigated.
On various collections of TiO2 using a combined DFT and
TD-DFT investigation used both DFT and experimental
approaches to the adsorption of two cationic dyes (meth-
ylene blue with Basic Yellow). The B3LYP exchange and
correlation functionals were used in the DFT investigation,
in addition to the 6-31G (d,p) basis set Electrophilicity and
nucleophilicity indices of the dyes [181].
Used Bombaxbuonopozense as an adsorbent to study
the B3LYP/6-31G was used to bind two cationic dyes (Basic
Blue 41 and Basic Yellow 28) (d,p). The chemical hardness
index, as well as the electrophilicity and nucleophilicity
indices, were used to calculate various DFT descriptors.
Estimated solvation free energies, Fukui indices, chemical
hardness, and dipole moments at the CAM-B3LYP/6e31G
(d,p) theoretical level to investigate the azo dyes dissoci-
ation (named blue acid 113, 114, 118, and 120) by oxida-
tion. Demonstrated that the experimental data and the
theoretically calculated oxidation mechanism were in good
accord. Liu et al. [182] used DFT/LDA-CAPZ and experi-
mental approaches to look into the adsorption properties
of Sm2CuO4 for MG. The adsorption energy computed
using DFT in this study matched the actual results [182].
DFT simulations were used by Luo et al. [183] to investi-
gate Cucurbit uril adsorption of acidic blue 25. To compare
the UV-Vis spectrum with experimental data, the scientists
employed the theoretical level of B3LYP/6-31 G (d) and the
PCM solvation model.
DFT, in addition to providing complimentary informa-
tion, it provides alternative information to experimental
data the adsorption energy is calculated. The adsorption
energy is the binding energy between both the absorbent
and the dye. Since it accounts for the interaction between
the adsorbent and the dye, it could be used as an indication
of sorption strength Haouti et al. [184]. The absorption of
crystal violet and toluidine blue onto Na-montmorillonite
nano-clay was investigated using molecular dynamics and
DFT-based molecular descriptors.
The adsorption energies reveal that crystal violet
and toluidine blue can be effectively removed by the
Na-montmorillonite nano-clay. Dastgerdi [184] also used
Table 10
For the adsorption of MB by ZIF-8, kinetic parameters and their correlation coefficients [173,174]
Model Equation Value of parameters
Pseudo-first-order kinetic loglog .
qq qKt
et e
1
2 303
K1 (min–1)–0.0144
qe (mmol/g) 0.107
R20.88588
Pseudo-second-order kinetic t
qKq
t
q
tee
1
2
2
K2 (min–1)0.526
qe (mmol/g) 1.645
R20.9998
Intraparticle diffusion qK
tX
ti
1
2
Ki (mg/g·min1/2)0.00723
X (mg/g) 0.58
R20.92685
Elovich
qt
t
11
ln ln
β (g/mg) –3.86
α (mg/g·min) 2.85
R20.349
Experimental data qe,exp (mmol/g) 1.635
111M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
DFT to explore the use of bifunctional carbon nanotubes to
remove indigo carmine colour. The PerdeweBurkeeErnzerh
exchange and correlation functional was utilised in com-
bination with the double numeric plus polarization basis
set. Functionalization boosts carbon nanotube adsorption
capacity, according to the adsorption energies.
Molecular simulations have been used to investigate
dye adsorption, numerous computational methodologies
have been explored. The majority of the investigations used
additional information based on dye DFT descriptors can
be obtained using DFT and ab-initio methods. Researchers
can use features to predict and explain how the dye will
interact with the adsorbent. Despite the fact that these
descriptions are useful as used in conjunction with exper-
imental results, they cannot be used alone to describe dye
adsorption on adsorbents.
Static DFT studies (or genuine DFT research used for
adsorption process) are unable to adequately describe the
interaction between dyes (or adsorbates in general) and
adsorbents. This is because DFT investigations focused solely
on dye interaction with adsorbents, rather than dye connec-
tions with the solvent or other molecules in the environment.
In rare cases where the interaction between dyes and their
surroundings is stronger than the interaction between dyes
and the adsorbent, the current DFT results will be null.
Only a few MD simulations are capable of accurately
describing dye adsorption. Only certain adsorbents with
well-known molecular structures can be used with this
method. The structure of the adsorbent is unknown in gen-
eral (Table 11).
Even though these descriptions are beneficial when used
in conjunction with experimental results, they are not suffi-
cient on their own they cannot be used alone to describe dye
adsorption on adsorbents.
Static DFT analyses (or genuine DFT research used for
dye adsorption) are unable to adequately describe the inter-
action between dyes (or adsorbates in general) and adsor-
bents. This is because DFT investigations focused solely on
dye interactions with adsorbents, rather than dye interac-
tions with the solvent or other molecules in the environment.
10.1. Active sites
The method of analysing the responsive groups evalu-
ated adsorbate/adsorbents organization and determining
the electrophilic/nucleophilic attack area as well as the
electrostatic potential zero areas called as molecular elec-
trostatic potential (MEP) (Fig. 13). MEP were cast-off to
map entire MB’s electron density surface in this investiga-
tion. Different shades were used to indicate the MEP’s vari-
ables in these maps (red, yellow, green, light blue and blue)
(Fig. 14). Similarly, red and yellow colours were used to
indicate negative MEP levels, that are connected with elec-
trophilic assault; blue colours were used to indicate positive
MEP values, whose are linked with nucleophilic attack; and
green was used to indicate the MEP zero area (Fig. 15). As
shown in MEP map, the MEP of adsorbate indicates that
the adsorbate is more or less susceptible to nucleophilic
attack. Furthermore, the MEP map demonstrates that the
MEP for the MB adsorbate accepts that the MB is typically
prone to nucleophilic attacks (Table 11) [185,186] (Fig. 16).
11. Statistical physical modeling
11.1. Adsorption isotherm modeling
Use of The use of theoretical values to correspond
equilibrium data is a crucial part of the original design
and operation of an adsorption process. Statistical physics
methods were used to explain the experimental adsorption
data: the monolayer adsorption models coupled with ideal
gas (MMIG) (Eq. 5) and the monolayer adsorption model
coupled with real gas (MMRG) (Eq. 6). Fitting approach
was indeed using nonlinear optimisation depending on the
Generalized Reduced Gradient method Microsoft Excel’s
solver add-in (Microsoft Corporation, 2007). As a result,
it was widely believed that the most appropriate model
was determined by the magnitude of the correlation coef-
ficient, R2 as adsorbate molecules can interact with nearby
molecules in either an attractive or repellent manner. Based
on the surface properties of the adsorption process, these
adsorbate interactions may coexist and cause adsorption
competition that influences the final findings [187,188].
MMIG: Q
nN
W
c
a
m
1
(5)
MMRG: QnN
WbC
Cee bC
bC
a
m
C
n
11
1
2
(6)
Electron density Molecular electrostatic potential (MEP)
Fig. 13. The whole electron density surfaces is mapped using the electron density molecular electrostatic potential (MEP) for MB.
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127112
Table 11
Quantum chemical parameters computed for the investigated dyes
Comp. EHOMO (eV) ELUMO (eV) ΔE (eV) X (eV) η (eV) Pi (eV) σ (eV–1)S (eV–1)Ω (eV) ΔNmax
MB –5.196 –4.51 0.683 4.85 –1.915 –4.9 –0.5 –0.95 –22.56 2.53
AR57 –0.17 –0.13 0.04 0.15 –0.045 –0.15 –22.2 –0.0225 –0.001 3.333
RR –0.109 –0.249 –0.14 0.179 –0.1945 –0.179 –5.14 –0.0973 –0.003 0.920
Electron density Molecular electrostatic potential (MEP)
Fig. 14. Total electron density surface mapped with electron density molecular electrostatic potential (MEP) for MG.
Fig. 15. Molecular orbital density pattern of optimum MB structures at the frontier.
Fig. 16. Optimized structures of frontier molecular orbital density distribution of (a) AR57 and (b) RR.
113M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
11.2. Statistical physics characterization
The method to mathematical modelling basis of statis-
tical physics in the gaseous or liquid phase of equilibrium
adsorption is a potent technique for characterization during
absorption, there are interface effects. The parameter esti-
mates that may be retrieved do have a physical meaning that
helps to explain the observable adsorption characteristics.
As a consequence, all of the MMRG model’s fitting parame-
ters were presented in this paragraph and then investigated
to describe and explain the studied adsorption [188].
12. Conclusion
This scope the elimination of colours from wastewaters
utilizing various adsorbents such as metal oxide, MOF’s,
alumina, and zeolite are efficient for dyes and wastewater
removal. To increase the number of accessible sorption sites
and binding functional groups on the produced adsorbent
surfaces, a variety of physical and chemical treatments
can be used to change biomass porosity and surface areas.
The much more commonly reported adsorption meth-
ods for the removal of both inorganic and organic dyes
include electrostatic contact, ion exchange, and complex-
ation. Despite the great progress in the creation of various
biosorbents, there are still several issues connected with
these materials, such as pH stability, sorption capacity, and
durability, that must be addressed in future applications.
Dyes residues in water are causing widespread concern
because of the potentially dangerous effects they have
on the environment. New generation water contaminants
have been discovered to be the cause of the contamination
of several water supplies. These developing contaminants
have been removed using a variety of new generation
nano-adsorbents. Even at low concentrations, that is, μg/L,
these new generation nano-adsorbents may remove new
generation contaminants across a range of pH and tem-
perature conditions. These adsorbents only require a little
dose, which makes their use cost-effective. Additionally, it
is noted that the removal duration, which ranges from 1.0
to 15.0 min, is relatively quick. New generation nano-ad-
sorbents are only occasionally used to remove new gen-
eration contaminants. In order to remove new emerging
pollutants, even at the trace level, there is a tremendous
need to develop more novel and secure new generation
nano-adsorbents with higher affinity, capacity, selectivity,
and ability to perform under diverse experimental settings.
Funding
This research received no external funding.
Declaration of interest
The authors declare that they have no known compet-
ing financial interests or personal relationships that could
have influenced the work reported in this paper.
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Fig. S1. Acid red 57.
Supporting information
119M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
Table S1
Bond length at Acid red 57
Atom Actual (Å) Optimum (Å)
O(35)-Lp(72) 0.600 0.600
O(35)-Lp(71) 0.600 0.600
O(34)-Lp(70) 0.600 0.600
O(34)-Lp(69) 0.600 0.600
O(31)-Lp(68) 0.600 0.600
O(31)-Lp(67) 0.600 0.600
O(30)-Lp(66) 0.600 0.600
O(30)-Lp(65) 0.600 0.600
O(29)-Lp(64) 0.600 0.600
O(29)-Lp(63) 0.600 0.600
N(14)-Lp(62) 0.600 0.600
N(13)-Lp(61) 0.600 0.600
O(11)-Lp(60) 0.600 0.600
O(11)-Lp(59) 0.600 0.600
C(37)-H(58) 1.113 1.113
C(37)-H(57) 1.113 1.113
C(36)-H(56) 1.113 1.113
C(36)-H(55) 1.113 1.113
C(36)-H(54) 1.113 1.113
C(27)-H(53) 1.100 1.100
C(26)-H(52) 1.100 1.100
C(25)-H(51) 1.100 1.100
C(24)-H(50) 1.100 1.100
C(23)-H(49) 1.100 1.100
C(19)-H(48) 1.100 1.100
C(18)-H(47) 1.100 1.100
C(17)-H(46) 1.100 1.100
C(16)-H(45) 1.100 1.100
N(12)-H(44) 1.050 1.050
N(12)-H(43) 1.050 1.050
O(11)-H(42) 0.972 0.972
C(10)-H(41) 1.100 1.100
C(9)-H(40) 1.100 1.100
C(5)-H(39) 1.100 1.100
C(1)-H(38) 1.100 1.100
C(22)-C(27) 1.395 1.420
C(26)-C(27) 1.395 1.420
Atom Actual (Å) Optimum (Å)
C(25)-C(26) 1.395 1.420
C(24)-C(25) 1.395 1.420
C(23)-C(24) 1.395 1.420
C(22)-C(23) 1.395 1.420
C(15)-C(20) 1.395 1.420
C(19)-C(20) 1.395 1.420
C(18)-C(19) 1.395 1.420
C(17)-C(18) 1.395 1.420
C(16)-C(17) 1.395 1.420
C(15)-C(16) 1.395 1.420
C(6)-C(5) 1.396 1.420
C(4)-C(5) 1.404 1.420
C(3)-C(4) 1.414 1.420
C(10)-C(4) 1.404 1.420
C(9)-C(10) 1.396 1.420
C(8)-C(9) 1.392 1.420
C(7)-C(8) 1.396 1.420
C(3)-C(7) 1.404 1.420
C(2)-C(3) 1.404 1.420
C(1)-C(2) 1.396 1.420
C(6)-C(1) 1.392 1.420
N(21)-C(22) 1.266 1.462
N(21)-C(37) 1.470 1.470
S(33)-N(21) 1.696
C(20)-S(33) 1.790
N(14)-C(15) 1.260 1.456
N(13)-N(14) 1.248 1.248
C(7)-N(13) 1.260 1.456
C(8)-N(12) 1.266 1.462
C(2)-O(11) 1.355 1.355
C(6)-S(28) 1.790
C(36)-C(37) 1.523 1.523
S(33)-O(35) 1.450 1.450
S(33)-O(34) 1.450 1.450
S(28)-O(31) 1.660
S(28)-O(30) 1.450 1.450
S(28)-O(29) 1.450 1.450
O(31)-Na(32) 2.180
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127120
Table S2
Bond angle of Acid red 57
Atom Actual (Å) Optimum (Å)
H(58)-C(37)-H(57) 109.520 109.400
H(58)-C(37)-N(21) 109.462
H(58)-C(37)-C(36) 109.462 109.410
H(57)-C(37)-N(21) 109.442
H(57)-C(37)-C(36) 109.442 109.410
N(21)-C(37)-C(36) 109.500
H(56)-C(36)-H(55) 109.520 109.000
H(56)-C(36)-H(54) 109.462 109.000
H(56)-C(36)-C(37) 109.462 110.000
H(55)-C(36)-H(54) 109.442 109.000
H(55)-C(36)-C(37) 109.442 110.000
H(54)-C(36)-C(37) 109.500 110.000
Lp(72)-O(35)-Lp(71) 120.000 131.000
Lp(72)-O(35)-S(33) 120.000
Lp(71)-O(35)-S(33) 120.000
Lp(70)-O(34)-Lp(69) 120.000 131.000
Lp(70)-O(34)-S(33) 120.000
Lp(69)-O(34)-S(33) 120.000
N(21)-S(33)-C(20) 109.462
N(21)-S(33)-O(35) 109.520
N(21)-S(33)-O(34) 109.462
C(20)-S(33)-O(35) 109.442
C(20)-S(33)-O(34) 109.500
O(35)-S(33)-O(34) 109.442 116.600
Lp(68)-O(31)-Lp(67) 117.390 131.000
Lp(68)-O(31)-S(28) 103.298
Lp(68)-O(31)-Na(32) 103.298
Lp(67)-O(31)-S(28) 106.760
Lp(67)-O(31)-Na(32) 106.760
S(28)-O(31)-Na(32) 120.000
Lp(66)-O(30)-Lp(65) 120.000 131.000
Lp(66)-O(30)-S(28) 120.000
Lp(65)-O(30)-S(28) 120.000
Lp(64)-O(29)-Lp(63) 120.000 131.000
Lp(64)-O(29)-S(28) 120.000
Lp(63)-O(29)-S(28) 120.000
C(6)-S(28)-O(31) 109.462
C(6)-S(28)-O(30) 109.442
C(6)-S(28)-O(29) 109.500
O(31)-S(28)-O(30) 109.520
O(31)-S(28)-O(29) 109.462
O(30)-S(28)-O(29) 109.442 116.600
H(53)-C(27)-C(22) 120.000 120.000
H(53)-C(27)-C(26) 120.000 120.000
C(22)-C(27)-C(26) 120.000
H(52)-C(26)-C(27) 120.001 120.000
H(52)-C(26)-C(25) 120.001 120.000
C(27)-C(26)-C(25) 119.997
H(51)-C(25)-C(26) 119.998 120.000
H(51)-C(25)-C(24) 119.998 120.000
Atom Actual (Å) Optimum (Å)
C(26)-C(25)-C(24) 120.003
H(50)-C(24)-C(25) 120.000 120.000
H(50)-C(24)-C(23) 120.000 120.000
C(25)-C(24)-C(23) 120.000
H(49)-C(23)-C(24) 120.002 120.000
H(49)-C(23)-C(22) 120.002 120.000
C(24)-C(23)-C(22) 119.997
C(27)-C(22)-C(23) 120.003 120.000
C(27)-C(22)-N(21) 119.999 120.000
C(23)-C(22)-N(21) 119.999 120.000
C(22)-N(21)-C(37) 120.000 108.000
C(22)-N(21)-S(33) 120.000
C(37)-N(21)-S(33) 120.000
C(15)-C(20)-C(19) 120.000 120.000
C(15)-C(20)-S(33) 120.000
C(19)-C(20)-S(33) 120.000
H(48)-C(19)-C(20) 120.001 120.000
H(48)-C(19)-C(18) 120.001 120.000
C(20)-C(19)-C(18) 119.997
H(47)-C(18)-C(19) 119.998 120.000
H(47)-C(18)-C(17) 119.998 120.000
C(19)-C(18)-C(17) 120.003
H(46)-C(17)-C(18) 120.000 120.000
H(46)-C(17)-C(16) 120.000 120.000
C(18)-C(17)-C(16) 120.000
H(45)-C(16)-C(17) 120.002 120.000
H(45)-C(16)-C(15) 120.002 120.000
C(17)-C(16)-C(15) 119.997
C(20)-C(15)-C(16) 120.003 120.000
C(20)-C(15)-N(14) 119.999 120.000
C(16)-C(15)-N(14) 119.999 120.000
Lp(62)-N(14)-C(15) 109.939 122.500
Lp(62)-N(14)-N(13) 109.939 120.000
C(15)-N(14)-N(13) 107.500 107.500
Lp(61)-N(13)-N(14) 109.939 120.000
Lp(61)-N(13)-C(7) 109.939 122.500
N(14)-N(13)-C(7) 107.500 107.500
H(44)-N(12)-H(43) 120.000 118.800
H(44)-N(12)-C(8) 120.000
H(43)-N(12)-C(8) 120.000
Lp(60)-O(11)-Lp(59) 108.537
Lp(60)-O(11)-H(42) 110.335 101.100
Lp(60)-O(11)-C(2) 110.335
Lp(59)-O(11)-H(42) 109.815 101.100
Lp(59)-O(11)-C(2) 109.815
H(42)-O(11)-C(2) 108.000 108.000
H(41)-C(10)-C(4) 119.626 120.000
H(41)-C(10)-C(9) 119.626 120.000
C(4)-C(10)-C(9) 120.747
H(40)-C(9)-C(10) 120.007 120.000
H(40)-C(9)-C(8) 120.007 120.000
C(10)-C(9)-C(8) 119.987
121M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
Atom Actual (Å) Optimum (Å)
C(9)-C(8)-C(7) 119.994 120.000
C(9)-C(8)-N(12) 120.003 120.000
C(7)-C(8)-N(12) 120.003 120.000
C(8)-C(7)-C(3) 120.738 120.000
C(8)-C(7)-N(13) 119.631 120.000
C(3)-C(7)-N(13) 119.631 120.000
C(5)-C(6)-C(1) 119.986 120.000
C(5)-C(6)-S(28) 120.007
C(1)-C(6)-S(28) 120.007
H(39)-C(5)-C(6) 119.627 120.000
H(39)-C(5)-C(4) 119.627 120.000
C(6)-C(5)-C(4) 120.746
Atom Actual (Å) Optimum (Å)
C(5)-C(4)-C(3) 119.266 120.000
C(5)-C(4)-C(10) 121.470 120.000
C(3)-C(4)-C(10) 119.264 120.000
C(4)-C(3)-C(7) 119.270 120.000
C(4)-C(3)-C(2) 119.266 120.000
C(7)-C(3)-C(2) 121.464 120.000
C(3)-C(2)-C(1) 120.741 120.000
C(3)-C(2)-O(11) 119.630 124.300
C(1)-C(2)-O(11) 119.630 124.300
H(38)-C(1)-C(2) 120.002 120.000
H(38)-C(1)-C(6) 120.002 120.000
C(2)-C(1)-C(6) 119.996
Fig. S2. Remazol red.
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127122
Table S3
Bond length of Remazol red
Atom Actual (Å) Optimum (Å)
O(35)-H(53) 0.942 0.942
C(28)-H(52) 1.113 1.111
C(28)-H(51) 1.113 1.111
C(28)-H(50) 1.113 1.111
O(26)-H(49) 0.942 0.942
C(21)-H(48) 1.113 1.111
C(21)-H(47) 1.113 1.111
C(20)-H(46) 1.113 1.111
C(20)-H(45) 1.113 1.111
C(19)-H(44) 1.100 1.100
C(17)-H(43) 1.100 1.100
C(16)-H(42) 1.100 1.100
O(11)-H(41) 0.972 0.972
C(10)-H(40) 1.100 1.100
C(9)-H(39) 1.100 1.100
C(6)-H(38) 1.100 1.100
C(5)-H(37) 1.100 1.100
C(4)-H(36) 1.100 1.100
C(14)-C(19) 1.395 1.420
C(18)-C(19) 1.395 1.420
C(17)-C(18) 1.395 1.420
C(16)-C(17) 1.395 1.420
C(15)-C(16) 1.395 1.420
C(14)-C(15) 1.395 1.420
C(5)-C(6) 1.396 1.420
C(1)-C(6) 1.404 1.420
C(2)-C(1) 1.414 1.420
C(7)-C(1) 1.404 1.420
C(8)-C(7) 1.396 1.420
C(9)-C(8) 1.392 1.420
C(10)-C(9) 1.396 1.420
C(2)-C(10) 1.404 1.420
C(3)-C(2) 1.404 1.420
C(4)-C(3) 1.396 1.420
C(5)-C(4) 1.392 1.420
C(21)-C(20) 1.523 1.505
O(22)-S(32) 1.660
C(21)-O(22) 1.402 1.389
O(29)-C(20) 1.402 1.398
C(18)-S(31) 1.815 1.815
C(15)-O(27) 1.355 1.355
N(13)-C(14) 1.260 1.456
N(12)-N(13) 1.248 1.248
C(8)-N(12) 1.260 1.456
C(7)-O(11) 1.355 1.355
C(3)-S(23) 1.790
S(32)-O(35) 1.660
S(32)-O(34) 1.450 1.450
S(32)-O(33) 1.450 1.450
O(29)-O(30) 1.428 1.437
Atom Actual (Å) Optimum (Å)
O(30)-S(31) 1.660
O(27)-C(28) 1.402 1.396
S(23)-O(26) 1.660
S(23)-O(25) 1.450 1.450
S(23)-O(24) 1.450 1.450
Table S4
Bond angel of Remazol red
Atom Actual (Å) Optimum (Å)
H(53)-O(35)-S(32) 120.000
O(22)-S(32)-O(35) 109.462
O(22)-S(32)-O(34) 109.442
O(22)-S(32)-O(33) 109.500
O(35)-S(32)-O(34) 109.520
O(35)-S(32)-O(33) 109.462
O(34)-S(32)-O(33) 109.442 116.600
C(18)-S(31)-O(30) 120.000
O(29)-O(30)-S(31) 120.000
C(20)-O(29)-O(30) 98.700 98.700
H(52)-C(28)-H(51) 109.520 109.000
H(52)-C(28)-H(50) 109.462 109.000
H(52)-C(28)-O(27) 109.462 106.700
H(51)-C(28)-H(50) 109.442 109.000
H(51)-C(28)-O(27) 109.442 106.700
H(50)-C(28)-O(27) 109.500 106.700
C(15)-O(27)-C(28) 110.800 110.800
H(49)-O(26)-S(23) 120.000
C(3)-S(23)-O(26) 109.462
C(3)-S(23)-O(25) 109.442
C(3)-S(23)-O(24) 109.500
O(26)-S(23)-O(25) 109.520
O(26)-S(23)-O(24) 109.462
O(25)-S(23)-O(24) 109.442 116.600
S(32)-O(22)-C(21) 120.000
H(48)-C(21)-H(47) 109.520 109.400
H(48)-C(21)-C(20) 109.462 109.410
H(48)-C(21)-O(22) 109.462 106.700
H(47)-C(21)-C(20) 109.442 109.410
H(47)-C(21)-O(22) 109.442 106.700
C(20)-C(21)-O(22) 109.500 107.400
H(46)-C(20)-H(45) 109.520 109.400
H(46)-C(20)-C(21) 109.462 109.410
H(46)-C(20)-O(29) 109.462 106.700
H(45)-C(20)-C(21) 109.442 109.410
H(45)-C(20)-O(29) 109.442 106.700
C(21)-C(20)-O(29) 109.500 107.400
H(44)-C(19)-C(14) 120.000 120.000
H(44)-C(19)-C(18) 120.000 120.000
C(14)-C(19)-C(18) 120.000
C(19)-C(18)-C(17) 119.997 120.000
C(19)-C(18)-S(31) 120.001 118.000
123M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
Atom Actual (Å) Optimum (Å)
C(17)-C(18)-S(31) 120.001 118.000
H(43)-C(17)-C(18) 119.998 120.000
H(43)-C(17)-C(16) 119.998 120.000
C(18)-C(17)-C(16) 120.003
H(42)-C(16)-C(17) 120.000 120.000
H(42)-C(16)-C(15) 120.000 120.000
C(17)-C(16)-C(15) 120.000
C(16)-C(15)-C(14) 119.997 120.000
C(16)-C(15)-O(27) 120.002 124.300
C(14)-C(15)-O(27) 120.002 124.300
C(19)-C(14)-C(15) 120.003 120.000
C(19)-C(14)-N(13) 119.999 120.000
C(15)-C(14)-N(13) 119.999 120.000
C(14)-N(13)-N(12) 107.500 107.500
N(13)-N(12)-C(8) 107.500 107.500
H(41)-O(11)-C(7) 108.000 108.000
H(40)-C(10)-C(9) 119.631 120.000
H(40)-C(10)-C(2) 119.631 120.000
C(9)-C(10)-C(2) 120.738
H(39)-C(9)-C(8) 120.003 120.000
H(39)-C(9)-C(10) 120.003 120.000
C(8)-C(9)-C(10) 119.994
C(7)-C(8)-C(9) 119.987 120.000
Atom Actual (Å) Optimum (Å)
C(7)-C(8)-N(12) 120.007 120.000
C(9)-C(8)-N(12) 120.007 120.000
C(1)-C(7)-C(8) 120.747 120.000
C(1)-C(7)-O(11) 119.626 124.300
C(8)-C(7)-O(11) 119.626 124.300
H(38)-C(6)-C(5) 119.627 120.000
H(38)-C(6)-C(1) 119.627 120.000
C(5)-C(6)-C(1) 120.746
H(37)-C(5)-C(6) 120.007 120.000
H(37)-C(5)-C(4) 120.007 120.000
C(6)-C(5)-C(4) 119.986
H(36)-C(4)-C(3) 120.002 120.000
H(36)-C(4)-C(5) 120.002 120.000
C(3)-C(4)-C(5) 119.996
C(2)-C(3)-C(4) 120.741 120.000
C(2)-C(3)-S(23) 119.630
C(4)-C(3)-S(23) 119.630
C(1)-C(2)-C(10) 119.270 120.000
C(1)-C(2)-C(3) 119.266 120.000
C(10)-C(2)-C(3) 121.464 120.000
C(6)-C(1)-C(2) 119.266 120.000
C(6)-C(1)-C(7) 121.470 120.000
C(2)-C(1)-C(7) 119.264 120.000
Fig. S3. Crystal violet.
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127124
Table S5
Bond length of crystal violet
Atom Actual (Å) Optimum (Å)
C(28)-H(59) 1.113 1.113
C(28)-H(58) 1.113 1.113
C(28)-H(57) 1.113 1.113
C(27)-H(56) 1.113 1.113
C(27)-H(55) 1.113 1.113
C(27)-H(54) 1.113 1.113
C(25)-H(53) 1.100 1.100
C(24)-H(52) 1.100 1.100
C(22)-H(51) 1.100 1.100
C(21)-H(50) 1.100 1.100
C(20)-H(49) 1.113 1.113
C(20)-H(48) 1.113 1.113
C(20)-H(47) 1.113 1.113
C(19)-H(46) 1.113 1.113
C(19)-H(45) 1.113 1.113
C(19)-H(44) 1.113 1.113
C(17)-H(43) 1.100 1.100
C(16)-H(42) 1.100 1.100
C(14)-H(41) 1.100 1.100
C(13)-H(40) 1.100 1.100
C(9)-H(39) 1.113 1.113
C(9)-H(38) 1.113 1.113
C(9)-H(37) 1.113 1.113
C(8)-H(36) 1.113 1.113
C(8)-H(35) 1.113 1.113
C(8)-H(34) 1.113 1.113
C(5)-H(33) 1.100 1.100
C(4)-H(32) 1.100 1.100
C(2)-H(31) 1.100 1.100
C(1)-H(30) 1.100 1.100
C(11)-C(25) 1.395 1.420
C(24)-C(25) 1.395 1.420
C(23)-C(24) 1.395 1.420
C(22)-C(23) 1.395 1.420
C(21)-C(22) 1.395 1.420
C(11)-C(21) 1.395 1.420
C(13)-C(12) 1.504 1.503
C(17)-C(12) 1.504 1.503
C(16)-C(17) 1.343 1.337
C(15)-C(16) 1.504 1.503
C(14)-C(15) 1.504 1.503
C(13)-C(14) 1.343 1.337
C(1)-C(6) 1.395 1.420
C(5)-C(6) 1.395 1.420
C(4)-C(5) 1.395 1.420
C(3)-C(4) 1.395 1.420
C(2)-C(3) 1.395 1.420
C(1)-C(2) 1.395 1.420
N(26)-C(28) 1.470 1.470
N(26)-C(27) 1.470 1.470
Atom Actual (Å) Optimum (Å)
C(23)-N(26) 1.266 1.462
N(18)-C(20) 1.500 1.500
N(18)-C(19) 1.500 1.500
C(15)-N(18) 1.300 1.300
C(10)-C(12) 1.337 1.337
C(10)-C(11) 1.337 1.503
C(3)-C(10) 1.337 1.503
N(7)-C(9) 1.470 1.470
N(7)-C(8) 1.470 1.470
C(6)-N(7) 1.266 1.462
Table S6
Bond angle of crystal violet
Atom Actual (Å) Optimum (Å)
H(59)-C(28)-H(58) 109.520 109.000
H(59)-C(28)-H(57) 109.462 109.000
H(59)-C(28)-N(26) 109.462
H(58)-C(28)-H(57) 109.442 109.000
H(58)-C(28)-N(26) 109.442
H(57)-C(28)-N(26) 109.500
H(56)-C(27)-H(55) 109.520 109.000
H(56)-C(27)-H(54) 109.462 109.000
H(56)-C(27)-N(26) 109.462
H(55)-C(27)-H(54) 109.442 109.000
H(55)-C(27)-N(26) 109.442
H(54)-C(27)-N(26) 109.500
C(28)-N(26)-C(27) 120.000
C(28)-N(26)-C(23) 120.000 108.000
C(27)-N(26)-C(23) 120.000 108.000
H(53)-C(25)-C(11) 120.000 120.000
H(53)-C(25)-C(24) 120.000 120.000
C(11)-C(25)-C(24) 120.000
H(52)-C(24)-C(25) 120.001 120.000
H(52)-C(24)-C(23) 120.001 120.000
C(25)-C(24)-C(23) 119.997
C(24)-C(23)-C(22) 120.003 120.000
C(24)-C(23)-N(26) 119.998 120.000
C(22)-C(23)-N(26) 119.998 120.000
H(51)-C(22)-C(23) 120.000 120.000
H(51)-C(22)-C(21) 120.000 120.000
C(23)-C(22)-C(21) 120.000
H(50)-C(21)-C(22) 120.002 120.000
H(50)-C(21)-C(11) 120.002 120.000
C(22)-C(21)-C(11) 119.997
H(49)-C(20)-H(48) 109.520 109.000
H(49)-C(20)-H(47) 109.462 109.000
H(49)-C(20)-N(18) 109.462
H(48)-C(20)-H(47) 109.442 109.000
H(48)-C(20)-N(18) 109.442
H(47)-C(20)-N(18) 109.500
H(46)-C(19)-H(45) 109.520 109.000
125M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
Atom Actual (Å) Optimum (Å)
H(46)-C(19)-H(44) 109.462 109.000
H(46)-C(19)-N(18) 109.462
H(45)-C(19)-H(44) 109.442 109.000
H(45)-C(19)-N(18) 109.442
H(44)-C(19)-N(18) 109.500
C(20)-N(18)-C(19) 120.000 117.200
C(20)-N(18)-C(15) 120.000 121.400
C(19)-N(18)-C(15) 120.000 121.400
H(43)-C(17)-C(12) 118.376 120.000
H(43)-C(17)-C(16) 118.376 120.000
C(12)-C(17)-C(16) 123.248
H(42)-C(16)-C(17) 118.380 120.000
H(42)-C(16)-C(15) 118.380 120.000
C(17)-C(16)-C(15) 123.240
C(16)-C(15)-C(14) 113.511 120.000
C(16)-C(15)-N(18) 123.244 120.000
C(14)-C(15)-N(18) 123.244 120.000
H(41)-C(14)-C(15) 118.377 120.000
H(41)-C(14)-C(13) 118.377 120.000
C(15)-C(14)-C(13) 123.245
H(40)-C(13)-C(12) 118.377 120.000
H(40)-C(13)-C(14) 118.377 120.000
C(12)-C(13)-C(14) 123.246
C(13)-C(12)-C(17) 113.508 120.000
C(13)-C(12)-C(10) 123.246 120.000
C(17)-C(12)-C(10) 123.246 120.000
C(25)-C(11)-C(21) 120.003 120.000
C(25)-C(11)-C(10) 120.000 120.000
C(21)-C(11)-C(10) 119.997 120.000
C(12)-C(10)-C(11) 120.000 120.000
C(12)-C(10)-C(3) 120.000 120.000
C(11)-C(10)-C(3) 120.000 120.000
H(39)-C(9)-H(38) 109.520 109.000
Atom Actual (Å) Optimum (Å)
H(39)-C(9)-H(37) 109.462 109.000
H(39)-C(9)-N(7) 109.462
H(38)-C(9)-H(37) 109.442 109.000
H(38)-C(9)-N(7) 109.442
H(37)-C(9)-N(7) 109.500
H(36)-C(8)-H(35) 109.520 109.000
H(36)-C(8)-H(34) 109.462 109.000
H(36)-C(8)-N(7) 109.462
H(35)-C(8)-H(34) 109.442 109.000
H(35)-C(8)-N(7) 109.442
H(34)-C(8)-N(7) 109.500
C(9)-N(7)-C(8) 120.000
C(9)-N(7)-C(6) 120.000 108.000
C(8)-N(7)-C(6) 120.000 108.000
C(1)-C(6)-C(5) 120.000 120.000
C(1)-C(6)-N(7) 120.000 120.000
C(5)-C(6)-N(7) 120.000 120.000
H(33)-C(5)-C(6) 120.001 120.000
H(33)-C(5)-C(4) 120.001 120.000
C(6)-C(5)-C(4) 119.997
H(32)-C(4)-C(5) 119.998 120.000
H(32)-C(4)-C(3) 119.998 120.000
C(5)-C(4)-C(3) 120.003
C(4)-C(3)-C(2) 120.000 120.000
C(4)-C(3)-C(10) 120.000 120.000
C(2)-C(3)-C(10) 120.000 120.000
H(31)-C(2)-C(3) 120.002 120.000
H(31)-C(2)-C(1) 120.002 120.000
C(3)-C(2)-C(1) 119.997
H(30)-C(1)-C(6) 119.999 120.000
H(30)-C(1)-C(2) 119.999 120.000
C(6)-C(1)-C(2) 120.003
Fig. S4. Malachite green.
M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127126
Table S7
Bond length of crystal violet
Atom Actual (Å) Optimum (Å)
C(25)-H(51) 1.113 1.113
C(25)-H(50) 1.113 1.113
C(25)-H(49) 1.113 1.113
C(24)-H(48) 1.113 1.113
C(24)-H(47) 1.113 1.113
C(24)-H(46) 1.113 1.113
C(23)-H(45) 1.113 1.113
C(23)-H(44) 1.113 1.113
C(23)-H(43) 1.113 1.113
C(21)-H(42) 1.113 1.113
C(21)-H(41) 1.113 1.113
C(21)-H(40) 1.113 1.113
C(19)-H(39) 1.100 1.100
C(18)-H(38) 1.100 1.100
C(16)-H(37) 1.100 1.100
C(15)-H(36) 1.100 1.100
C(14)-H(35) 1.100 1.100
C(13)-H(34) 1.100 1.100
C(11)-H(33) 1.100 1.100
C(10)-H(32) 1.100 1.100
C(5)-H(31) 1.100 1.100
C(4)-H(30) 1.100 1.100
C(3)-H(29) 1.100 1.100
C(2)-H(28) 1.100 1.100
C(1)-H(27) 1.100 1.100
C(15)-C(8) 1.504 1.503
C(19)-C(8) 1.504 1.503
C(18)-C(19) 1.343 1.337
C(17)-C(18) 1.504 1.503
C(16)-C(17) 1.504 1.503
C(15)-C(16) 1.343 1.337
C(9)-C(14) 1.395 1.420
C(13)-C(14) 1.395 1.420
C(12)-C(13) 1.395 1.420
C(11)-C(12) 1.395 1.420
C(10)-C(11) 1.395 1.420
C(9)-C(10) 1.395 1.420
C(1)-C(6) 1.395 1.420
C(5)-C(6) 1.395 1.420
C(4)-C(5) 1.395 1.420
C(3)-C(4) 1.395 1.420
C(2)-C(3) 1.395 1.420
C(1)-C(2) 1.395 1.420
N(20)-C(25) 1.500 1.500
N(22)-C(24) 1.470 1.470
N(22)-C(23) 1.470 1.470
C(12)-N(22) 1.266 1.462
N(20)-C(21) 1.500 1.500
C(17)-N(20) 1.300 1.300
C(7)-C(9) 1.337 1.503
C(7)-C(8) 1.337 1.337
C(6)-C(7) 1.337 1.503
Table S8
Bond angle of crystal violet
Atom Actual (Å) Optimum (Å)
H(51)-C(25)-H(50) 109.520 109.000
H(51)-C(25)-H(49) 109.462 109.000
H(51)-C(25)-N(20) 109.462
H(50)-C(25)-H(49) 109.442 109.000
H(50)-C(25)-N(20) 109.442
H(49)-C(25)-N(20) 109.500
H(48)-C(24)-H(47) 109.520 109.000
H(48)-C(24)-H(46) 109.462 109.000
H(48)-C(24)-N(22) 109.462
H(47)-C(24)-H(46) 109.442 109.000
H(47)-C(24)-N(22) 109.442
H(46)-C(24)-N(22) 109.500
H(45)-C(23)-H(44) 109.520 109.000
H(45)-C(23)-H(43) 109.462 109.000
H(45)-C(23)-N(22) 109.462
H(44)-C(23)-H(43) 109.442 109.000
H(44)-C(23)-N(22) 109.442
H(43)-C(23)-N(22) 109.500
C(24)-N(22)-C(23) 120.000
C(24)-N(22)-C(12) 120.000 108.000
C(23)-N(22)-C(12) 120.000 108.000
H(42)-C(21)-H(41) 109.520 109.000
H(42)-C(21)-H(40) 109.462 109.000
H(42)-C(21)-N(20) 109.462
H(41)-C(21)-H(40) 109.442 109.000
H(41)-C(21)-N(20) 109.442
H(40)-C(21)-N(20) 109.500
C(25)-N(20)-C(21) 120.000 117.200
C(25)-N(20)-C(17) 120.000 121.400
C(21)-N(20)-C(17) 120.000 121.400
H(39)-C(19)-C(8) 118.376 120.000
H(39)-C(19)-C(18) 118.376 120.000
C(8)-C(19)-C(18) 123.248
H(38)-C(18)-C(19) 118.380 120.000
H(38)-C(18)-C(17) 118.380 120.000
C(19)-C(18)-C(17) 123.240
C(18)-C(17)-C(16) 113.511 120.000
C(18)-C(17)-N(20) 123.244 120.000
C(16)-C(17)-N(20) 123.244 120.000
H(37)-C(16)-C(17) 118.377 120.000
H(37)-C(16)-C(15) 118.377 120.000
C(17)-C(16)-C(15) 123.245
H(36)-C(15)-C(8) 118.377 120.000
H(36)-C(15)-C(16) 118.377 120.000
C(8)-C(15)-C(16) 123.246
H(35)-C(14)-C(9) 120.000 120.000
H(35)-C(14)-C(13) 120.000 120.000
C(9)-C(14)-C(13) 120.000
H(34)-C(13)-C(14) 120.001 120.000
H(34)-C(13)-C(12) 120.001 120.000
127M.G. El-Desouky et al. / Desalination and Water Treatment 280 (2022) 89–127
Atom Actual (Å) Optimum (Å)
C(14)-C(13)-C(12) 119.997
C(13)-C(12)-C(11) 120.003 120.000
C(13)-C(12)-N(22) 119.998 120.000
C(11)-C(12)-N(22) 119.998 120.000
H(33)-C(11)-C(12) 120.000 120.000
H(33)-C(11)-C(10) 120.000 120.000
C(12)-C(11)-C(10) 120.000
H(32)-C(10)-C(11) 120.002 120.000
H(32)-C(10)-C(9) 120.002 120.000
C(11)-C(10)-C(9) 119.997
C(14)-C(9)-C(10) 120.003 120.000
C(14)-C(9)-C(7) 119.999 120.000
C(10)-C(9)-C(7) 119.999 120.000
C(15)-C(8)-C(19) 113.508 120.000
C(15)-C(8)-C(7) 123.246 120.000
C(19)-C(8)-C(7) 123.246 120.000
C(9)-C(7)-C(8) 120.000 120.000
C(9)-C(7)-C(6) 120.000 120.000
C(8)-C(7)-C(6) 120.000 120.000
C(1)-C(6)-C(5) 120.000 120.000
C(1)-C(6)-C(7) 120.000 120.000
C(5)-C(6)-C(7) 120.000 120.000
H(31)-C(5)-C(6) 120.001 120.000
H(31)-C(5)-C(4) 120.001 120.000
C(6)-C(5)-C(4) 119.997
H(30)-C(4)-C(5) 119.998 120.000
H(30)-C(4)-C(3) 119.998 120.000
C(5)-C(4)-C(3) 120.003
H(29)-C(3)-C(4) 120.000 120.000
H(29)-C(3)-C(2) 120.000 120.000
C(4)-C(3)-C(2) 120.000
H(28)-C(2)-C(3) 120.002 120.000
H(28)-C(2)-C(1) 120.002 120.000
C(3)-C(2)-C(1) 119.997
H(27)-C(1)-C(6) 119.999 120.000
H(27)-C(1)-C(2) 119.999 120.000
C(6)-C(1)-C(2) 120.003
