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The impact of alkaline earth oxides on Bi2O3 and their catalytic activities in
photodegradation of Bisphenol A
Ümran ÜNLÜ, Sevgi KEMEÇ, Gülin Selda POZAN SOYLU*
Chemical Engineering Department Engineering Faculty, İstanbul University-
Cerrahpaşa, İstanbul, TURKEY
*Corresponding author adres: gpozan@istanbul.edu.tr
ORCIDs:
Gülin Selda POZAN SOYLU: https://orcid.org/0000-0003-0142-2478
Umran UNLU: https://orcid.org/0000-0003-4700-5004
Sevgi KEMEC: https://orcid.org/0000-0002-3938-7316
Cite as: Ünlü Ü, Kemeç S, Pozan Soylu GS. The impact of alkaline earth oxides on
Bi2O3 and their catalytic activities in photodegradation of Bisphenol A. Turkish Journal
of Chemistry. doi: 10.3906/kim-2101-30
Abstract
The BPA into wastewater has posed a threat to environment and human health. Hence,
we aimed to eliminate BPA in a short time and with a rapid degradation rate from food
wastewater. Herein, the effects of different alkaline-earth oxide doped with Bi2O3
nanoparticles on the photocatalytic degradation of bisphenol A were investigated. SrO-
Bi2O3, CaO-Bi2O3 and MgO-Bi2O3 binary oxides were prepared by wet-impregnation
method. The structural and optical features of catalysts were clarified BET, XRD, DRS,
FT-IR, PL and SEM techniques. The photocatalytic activities of catalyts were compared
for different light sources. Considering that the characterization analysis and
experimental results, the highly improved photocatalytic activity was mainly attributed
to the effective structure of the SrO-Bi2O3 binary oxide and the strong alkali properties
in the nanocomposite. Obviously, 5wt% SrO-Bi2O3 photocatalyst showed more
excellent degradation performance and highest degradation reaction rate (0.21 mg l-1
min-1) within 30 min. It was observed that the photocatalytic activity improved by the
additive of alkaline oxide on Bi2O3.
Keywords: Photocatalysis; alkaline earth oxide; Bisphenol A; degradation; UV-B
irradiation
1. Introduction
Bisphenol-A or BPA which can be synthesized organic compound, has the formula
(CH3)2C(C6H4OH)2. Research shows that BPA is one of the chemicals with the highest
production capacity than other chemicals throughout the World [1,2]. As mentioned in
the world health organization, BPA is a chemical utilized chiefly as a monomer in the
production of polymers such as epoxy resins and polycarbonate plastic (PC). Additionally,
it has uses in polysulfone, polyacrylate resins, and polyester, and flame retardants.
Polycarbonate (PC) is thoroughly used in food contact materials like baby bottles,
tableware, food containers, drink bottles, processing materials and water pipes. Epoxy
resins are utilized as preservative linings for a diversity of canned foods and drinks and as
a coating on lids of glass jars and bottles. (WHO, INFOSAN 2009) [2,3]. According to the
researchers BPA can mimic the actions of oestrogen, binding to the same receptor in the
body. So, degradation of BPA is important status [4]. Bisphenol-A is known to be one of
the notable EDC (Endocrine Distrupting Compunds) and harmful to human health,
agriculture and environment. BPA has stable structure so, degradation of Bisphenol A is
difficult [5-7]. Compounds such as BPA at low concentrations have been found to be
highly toxic, poorly biodegradable and present carcinogenic properties.
Pollutants like BPA effecting the environment are serious problem in improving
countries. Furthermore, the rising population and increasing requisitions for water
resources cause that there is a constantly growing in this problem. BPA is a substance
that affects human health and there is a problem such as global warming in our world, so
the treatment of wastewater has become very important. Development of
environmentally friendly methods for removal of BPA is one of the most relevant issues
in the field of reaching the clean water. Therefore, various methods like chemical
oxidation [7,8,9], physical elimination development [10], biodegradation [11],
adsorption [12] and photodegradation have been developed for the degradation of BPA
[13].
Previous studies have shown that photodegradation gives good results. So,
heterogeneous photocatalytic oxidation has been seen as potential effective technique to
detoriate environmental pollutant. With this in mind, we prefer heterogeneous
photocatalytic degradation which is more advantageous than the other methods since it is
low cost, reusable, provides complete degradation and it is eco-friend method.
BPA can be co-existing with other contaminants, so more selective catalysts
should be used. During the study we used alkali metal oxides on bismuth oxide. The
alkaline earth metals used in this study are often white in color and soft and workable. In
addition to being less reactive (prone to reactions) than alkali metals, their melting and
boiling temperatures are also lower. Ionization energies are also higher than alkali metals.
SrO impregnated with different proportions on Bi2O3 showed great selectivity and was
successful in a short time. In addition to these different catalysts were used as the main
catalyst [14-16]. When the previous studies were examined, titanium oxide was used
many times as the main catalyst, as it has a extended band gap [15-18]. In particular,
Bi2O3 has been used since it is a non-toxic and non-carcinogenic compound and has high
photocatalytic activity with a bandwidth ranging from 2.0-2.8 eV [19-22].
The use of binary metal oxides as photocatalysts has been made widely for decades
because of the fact that the morphological properties of the individual oxides can be
changed due to the formation of new sites in the interface between the components, or by
the incorporation of one oxide into the lattice of the other. They also found that this
enhancement was attributed to gradually increasing shift of the conduction bands with
increasing metal oxide contents, so resulting in a stronger reduction power of
photogenerated electrons and promoting the improved photocatalytic activity.
In the current study, MxOy–Bi2O3 (M: Ca, Mg, Sr) photocatalysts with various
loading of the metal oxides were prepared by impregnation method. The catalytic
activities of synthesized metarials were investigated by using UV irradiation. The
complete degradation of pollutants such as BPA by photocatalytic methods is a promising
solution for environmental problems and human healths. In this study, the purpose is to
explain the impact of parameters such as the use of different types of metal oxides and the
percentage of metal oxides on the photooxidation of BPA. Another aim is to reduce the
concentration of BPA. This is due to the fact that BPA has pollutants for the environment
and harmful effects on human health. Moreover, the relationships between the catalyst
morphologies and the photocatalytic activities were also investigated by using varied
characterization methods such as Scanning Electron Microscope (SEM), Diffuse
Reflectans Spectroscopy (DRS), Brunauer, Fourier Transform Infrared (FTIR), Emmet
and Teller (BET) and X-Ray Diffraction (XRD).
2. Experimentals and Methods
2.1. Materials
In this experimental study, essential materials were supplied commercially and utilized
without additional purification process. These materials are bismuth (III) nitrate
pentahydrate (98%; Alfa Aesar Company), strontium carbonate (99%; Alfa Aesar
Company), calcium nitrate tetrahydrate (Merck Company), strontium nitrate (Merck
Company), magnesium nitrate hexahydrate (LACHEMA Company), ultra pure water and
bisphenol A (>= 99%, Sigma Aldrich). In addition to these, the others like nitric acid
(65%), ethanol (absolute), aceonitrile (99.9%) and sodium hydroxide were bought from
Merck Company.
2.2. Catalyst Synthesis Methods
Co-precipitation method was utilized to synthesis Bi2O3 catalyst. 1.94 g of Bi(NO3)2.5H2O
weighed by precision balance. In addition, 1.12 M 20 ml HNO3 (nitric acid-65%) solution
and 0.2 M NaOH solution were prepared and kept in an ultrasonic bath for 15 minutes to
ensure better dissolution. Finally, 20 ml of 1.12 molar HNO3 solution was added to 1.94
of bismuth, which was weighed and then kept in the ultrasonic bath for 15 minutes. The
solution of resulting were mixed by magnetic mixer at the room temperature.
Subsequently, 0.2 M NaOH solution by adding drop by drop into the bismuth (III) nitrate
solution was provided to reach pH value 11 and then mixed for 2 h at 75 ° C to make a
homogenous yellowish mixture. Then this mixture was filtered as well as washed with
distilled water and absolute ethanol several times. Obtained this matter was dried in a
oven at 80°C for 2 h, then calcined at 450°C for 2 h.
In order that preparing of binary catalyst, impregnation method was used. This
method is based on impregnation of metal oxide solutions onto pure bismuth oxide
catalyst. When preparing solutions, attention was paid to the weight percentages of metal
oxides present in the binary catalyst. Firstly, nitrous forms of metal oxides
(Ca(NO3)2.4H2O, Mg(NO3)2.6H2O, Sr(NO3)2) and 0.2 M solution of 5% by weight in
binary catalyst were prepared. These solutions were added dropwise to the powdered pure
bismuth oxide catalyst to give a wet mixture and then dried at 105 ° C. This process was
continued until the solutions were finished. It was then dried in oven at 105 ° C for 16
hours and then was calcined at 500 °C during 3 hours.
2.3. Catalyst Characterization
Total catalyst surface area of the catalyts was measred by nitrogen adsorption/desorption
using a Quantachrome Instrument. All catalysts were degassed under vacuum at 200 °C
for 4 h.
Crystallographic structure of catalyts were determined by x-ray powder diffraction
using CuKα radiation (λ= 1.54056 Å) with a Rigaku D/Max-2200 powderx-ray
diffractometer. Before the analysis was run, the samples were gently granulated in an
agate mortar to reduce the required orientation. Patterns were recorded at scan speed 2
degree of two-theta in the range of 10- 90° 2θ.The average crystallite size (Davg) was
computed using the Debye-Scherrer equation.
The powders were examined with a high resolution scanning electron microscope
(SEM) (JEOL/JSM-a6335F) for possible differences in morphologies and size
distributions of the powders.
FT-IR spectra were examined by FT-IR spectroscopy (Perkin Elmer Precisely Spectrum
One). KBr powder was used to prepare KBr pellets for samples. The samples were
acquired as 100 scans with 4 cm−1 resoluton
Optical energy gap of nanopowders were carried out by a double –beam UV-
Shimadzu 3600 UV-Vis-NIR spectrophotometer equipped a diffuse reflectance (DR)
accessory.
The energy of band gap for the catalyst was evaluated by using the Kubelka-Munk
formula with Tauc’s relation (Eq. (1)), which derived from DRS measurement.
(1)
In this expression, hν is the energy of a single proton, α is the optical absorption co-
efficiency, Eg is the optical band gap energy, A is constant for direct band gap transitions,
the value of exponent parameter n denotes the nature of sample transition (n= ½ is used
for the catalyts). R is the absolute reflectance value; F(R) is proportional to the absorption
coefficient (α).
Morover, photoluminescence (PL) spectra were obtained on a Cary Eclipse
fluorescence spectrophotometer (Agilent Technologies). The catalyst was excited by a
xenon lamp light source by 450 nm at the room temperature.
2.4. Studies on photocatalytic activity
The experiment of BPA degradation was carried out over MxOy–Bi2O3 (M: Ca, Mg, Sr)
binary oxide in a cylindrical quartz micro-photoreactor. 50 mL of a 25 mg/L aqueous BPA
solution was prepared and then 100 mg of catalyst was added in this mixture to initiate the
reaction. Before exposure illumination, the solution was stirred in the dark for 1 hour to
establish an the adsorption- desorption equilibrium between the catalyst and the liquid.
All reactions were conducted at ambient temperature under constant magnetic stirring and
natural pH conditions. The photocatalytic activity of catalyst were compared using
different light sources (UV-B, sunlight and visible light irradiation). Durring the
irradiation, sample was taken at regular intervals from the solution and filtered through a
PTFE filter (pore size 0.45 mm for use total organic content (TOC) measurement (TOC-
V, Shimadzu) and HPLC analysis. The analysis of BPA was performed by a HPLC
(Thermo Scentific) using C18 column. The mobile phase consists of a mixture of water
and acetonitrile (40:60, v/v).
3. Results and Discussion
3.1. Structural, morphological and optical properties
The composition of the catalyst was determined using Thermo Elemental X Series ICP-
MS. The actual weight percentages of the catalysts in the binary oxide catalysts were
evaluated by ICP- MS analysis. The calculated wt% of the catalysts and the ICP-MS
values were almost similar. Furthermore, ICP-MS values of the two representative
catalysts clearly suggest that there may not be any noticable differences between the
calculated values and ICP values for the other weight percentages of metal oxides.
The diffraction patterns of powder samples were examined to indentify the phase
structures. XRD patterns representing this are show in Figure 1. Monoclinic α-Bi2O3
nanorods from corresponding to JCPDS files (No. 41-1449) was observed as the main
crystalline phase. In addition, tetragonal MgO (JCPDS 45-0946), cubic CaO (JCPDS 82-
1691), and tetragonal SrO (JCPDS 48-1477) were detected in the XRD analysis. The
crystallite sizes of the catalyts are presented in Table.
After the impregnation of metal nitrate on Bi2O3, the lattice structure of Bi2O3 did
not change. However, the average crystallite size of Bi2O3 changed with addition of metal
oxide on Bi2O3. The crystallite size decreased with only the adding of metal oxide. After
the XRD analysis, the crystallite sizes of samples were calculated as 41, 19, 17 and 15 nm
for Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3, respectively. It has expressed that
small crystallite size causes higher photocatalytic activity for the increased reactive sites
and the promoted electron-hole seperation efficiency [23].
Accordingly, the 5SrO-Bi2O3 binary oxide is expected to show higher
photocatalytic activity due to its low crystallite size.
The morphology and particle size of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3 and 5SrO-
Bi2O3 were observed by SEM in Figure 2a, Figure 2b Figure 3c and Figure 3d,
respectively. Figure 2a exhibits the SEM photograph of samples. The morphology of
pure Bi2O3 is purely a nanorod. The metal oxide particles were observed on the surface of
nano Bi2O3.
5SrO/Bi2O3 catalyst has uniform morphology whereas; 5CaO/Bi2O3 and
5Mg/Bi2O3 are in irregular sizes and shapes. It was observed that SrO was distributed over
the surface of nano Bi2O3 compared to CaO and MgO. The homogeneous distribution of
the SrO structure on the nano Bi2O3 surface has played a role in improving the high
photocatalytic activity.
The change in the band gap energy of Bi2O3 with alkaline earth oxide loading was
investigated using UV–Vis diffuse reflectance spectroscopy. Figure 4 corresponds to UV-
Vis DRS spectra of the catalysts. The band gap energies of the samples were calculated
from graphical extrapolation by using Tauc Plot ((hνα)1/n = A(hν-Eg)) adapted for
Kubelka-Munk function [24]. The calculated band gap values are given in Table.
According to the results, the band gap of pure Bi2O3 is 2.99 eV, whereas the band gap is
decreased to 2.82 eV by the loading of 5 wt % SrO. The band gap of 5CaO/Bi2O3 and
5Mg/Bi2O3 are about 2.89, 2.92 eV, respectively. According these results, the loading of
alkaline-metal oxide on Bi2O3 powder could significantly shift the optical band gap width
Eg. It can be caused that the optical properties of the samples were affected by the
quantum size, which is a consequence of the extent of the electron delocalization. As seen
SEM image, MgO structure covered to Bi2O3 external surface. Therefore, the diffuse
reflactance spectrum of 5MgO/Bi2O3 is more different than others. Because of band gap
value of Bi2O3, we studied the photocatalytic degradation of Bisphenol-A under UV
irradiation. Figure 5 shows the FTIR spectra from 4000 to 400 cm-1 for pure Bi2O3 and
alkaline earth oxide additive Bi2O3 catalysts. Infrared spectroscopy technology is used to
detect the presence of functional groups such as hydroxyl radical (•OH) adsorbed on the
surface of synthesized nanoparticles. In the photocatalytic degradation experiments, the
surface OH groups can not only embrace the photogenerated holes to form hydroxyl
radical (•OH) but also serve as active sites for the adsorption of reactants [25]. The
intensive signal at around 1430-1445 cm-1 for all alkaline-doped catalyst was attributed to
the absorption of non-bridging O-H groups [26]. The concentration of the hydroxyl group
was affected by the addition of alkaline oxide to Bi2O3. OH bending appears in the spectra
for 5SrO/TiO2 and 5CaO/Bi2O3 catalyst at about 1439 cm-1. However, this peak was not
observed after MgO loading. These results are in line with the activity results.
In addition, the infrared spectrum of Bi2O3 was not observed any hydroxyl group.
This result shows that the removing most of the adsorbed water from the surface of Bi2O3
with calcination process. In the spectrum, the band arises at 1300 cm-1 from the weak
band of Bi–O –(NBO) bond in BO3 units for 5CaO/Bi2O3 and 5SrO /Bi2O3. This peak was
not observed for 5MgO/ Bi2O3. The low absorption band at around 830 cm-1 seemed in
FTIR spectra of samples is the stretching vibration of Bi─O bonds in BiO6 octahedral
units [27]. The Bi─O bending vibration was observed at about 497, 537 and 830 cm−1 for
Bi2O3. FTIR spectra of 5CaO/Bi2O3 revealed the existence of peak at 874 cm-1 which are
the characteristic bands of Ca-O [28]. In addition, the peak of the Sr-O band was
observed at 857 cm−1 in the spectrum [29].
As a result of the FT-IR study, it was understood that Sr2+ and Ca2+, except Mg2+,
entered into the lattice of nano Bi2O3.
The ionic radiuses of Sr2+ (1.21 Å) and Ca2+ (1.08) are larger than Bi3+ (1.03 Å) but
less than O2- (1.31 Å). These ions can homogenously substituted or introduced into the
nano Bi2O3 matrix to produce oxygen vacancies that accelerate the transition and
nanocrystalline growth of Bi2O3 [30].
The occurrence of Bi−O−Sr prevents the transition of Bi2O3 phase and prevents the
agglomeration of nano Bi2O3 particles. There is no evidence for an isomorphic settlement
of Mg2+ to the Bi2O3 structure observed due to the ionic radius of Mg2+(0.86 Å) are lower
than Bi3+ by adding Mg2+ to the nano Bi2O3 structure [31].
Photoluminescence spectroscopy is a widely used technique for characterization of
optical and electronic properties of semiconductors and molecules. Photoluminescence
can measure the purity and crystal quality of semiconductors and give some information
oxygen vacancies, photo-induced charge carrier separation and recombination processes
surface states in nano-sized semiconductor materials. At low Pl density, the
recombination rate of the electron hole is also low [32].
PL spectra of the catalysts are shown in Figure 6. It was understood that the PL
emission spectra of the catalysts were at the same peak maximum but different densities.
A strong emission peak at about 393 nm was obtained in the PL spectrum of the catalysts.
It was determined that the density of the 5SrO-Bi2O3 catalyst in the emission spectrum
was the lowest and this decrease showed the low recombination rate of the holes. As a
result, it can be said that the 5SrO-Bi2O3 catalyst helps inhibit the recombination of
electrons and holes and improve photocatalytic activity.
3.2. Photocatalytic activity results
The photocatalytic activity of alkaline earth oxides loaded Bi2O3 was examined for
Bisphenol A degradation. We based on Langmuir-Hinshelwood (L-H) kinetic model [33]
in our experiments. It can be expressed by Equation 2 below:
ln(Co/C) = kobst (2)
Assuming that C=Co at t=0 with low initial BPA concentration, where t is the
given irradiation time and kobs is the rate constant of the observed pseudo-first order
reaction. After experiments, we calculated the photocatalytic degradation efficiencies and
reaction rates for the different photocatalysts and the numerical values of gain are
presented in Table.
The degradation efficiency (R%) of BPA was calculated by Equation (3):
R% =
100×
−
o
o
CCC
(3)
Firstly, we tested UV-B light and visible light as the different light source for
degradation of BPA by using pure Bi2O3 and the degradation efficiencies of pure Bi2O3
were 76% and 47% for 30 min, respectively. The activity results show that although Bi2O3
can be activated under different irradiation, it is not sufficient for complete of BPA.
Moreover, we studied with SrO-Bi2O3 binary oxide prepared varying SrO loadings.
The degradation efficiency for the SrO-Bi2O3 binary oxide rised with the rise in the
amount of SrO charges to Bi2O3. It showed the highest percentage of BPA degradation
(100%) in 30 minutes with a loading of 5% by weight SrO. However, there was no
significant change in activity after this weight percentage and the value remained the same
as the higher loading of SrO. The numerical values of gain showed that the structural and
optical characterization of the samples and SrO dispersion on the surface affected with the
loading of SrO in the binary oxide.
In addition, the performance of 5SrO-Bi2O3 catalyst was studied with UV-B light
and visible light for BPA degradation. According the experimental results, binary metal
oxide nanoparticles are more photoactivated under UV light than visible light irradiation.
The degradation of BPA under visible light and UV-B light (64 W) showed 35% and
100% for 30 min, respectively.
In addition, the reusability of the 5SrO-Bi2O3 catalyst was studied on fresh dye
samples (5 trials). 5SrO-Bi2O3, when used for the first time, could degrade 98.52% BPA,
with a small change (to 94.29%) in the efficiency when used for five times. This decrease
in the efficiency for 5SrO-Bi2O3 catalyst resulted probably from the photocorrosion effect.
In this study, the photodegradation of BPA includes three steps. In the first stage,
the transmission of electrons excited by photons emitted from the UV-B source from the
valence band to the conduction band takes place. In the second stage, the holes formed
due to the excitation process act as decomposing agent or combine with the surface
hydroxyl species on the binary oxide to form the hydroxyl radical. In the last stage, the
contaminant is attacted by the holes or hydroxyl radicals by the photons from the UV-B
source.
Figure 7a shows the photocatalytic degradation of BPA in the pure Bi2O3 and
alkaline earth oxide additive Bi2O3 catalysts under UV-B illumination at different
irradiation time. When the degradation results are evaluated, the photocatalytic
degradation rates of the BPA in 30 min with the binary metal oxides are sorted in
descending order: 5SrO─Bi2O3 (ca. 100%), 5CaO─Bi2O3 (ca. 88%), 5MgO─Bi2O3 (ca.
84%) and Bi2O3 (ca. 76%). Obviously, 5SrO─Bi2O3 catalyst improved the degradation of
BPA in a short time and with high efficiency compared to other catalysts and pure Bi2O3.
The results show that •OH radical adsorbed on the catalyst was play an extreme role in the
photodegradation of BPA. A small difference in the efficiency during the photocatalytic
degradation of BPA can be elucidated by the free •OH radicals involved to a small extent
in the photodegradation process [34].
The measured TOC removal results for the photodegradation of BPA with
5SrO─Bi2O3, 5CaO─Bi2O3 and 5MgO─Bi2O3 are shown in the Figure 7b. 25 ppm BPA
completely decomposed in 30 min with 5SrO─Bi2O3 binary oxide and 94% TOC removal
was obtained in 30 min. It is clear that the total mineralization is completed in the
presence of 5SrO─Bi2O3 catalyst.
The acid-base properties of the oxide catalyst can also affect the photocatalytic
activity as well as its structural and optical properties.
As known, alkalinity of alkaline earth oxide increases from MgO to SrO. It seems
that the activity changes in parallel with the alkalinity. As a result, the addition of strong
basic alkaline oxide caused an increase in both the photocatalytic activity and the final
conversion in oxidative degradation of BPA over catalysts. In addition to this result, the
tendency of MgO to form larger particles on Bi2O3 surface also caused a decrease in BPA
conversion.
In the study, it was understood that the changes in surface area, band gap energy
and crystallite size were not as much as the changes in catalytic activity. These differences
in activity are thought to be due to the active species on the surface of the oxide mixtures.
4. Conclusions
The effects of different alkaline-earth oxide doped with Bi2O3 nanoparticles on the
photocatalytic degradation of bisphenol A were investigated. SrO-Bi2O3, CaO-Bi2O3 and
MgO-Bi2O3 binary oxides were prepared by wet-impregnation method. The
photocatalytic activities of catalyts were compared for different light sources.
Considering that the characterization analysis and improved photocatalytic activity results
are mainly varied in relation to the effective structure of SrO-Bi2O3 binary oxide and the
strong basic properties in the nanocomposite. Obviously, 5wt% SrO-Bi2O3 photocatalyst
showed more excellent degradation performance and highest degradation reaction rate
(0.21 mg l-1 min-1) within 30 min. It was observed that the photocatalytic activity
improved by the addition of alkaline-earth oxide on Bi2O3.
In this study, Sr2+ played an important role in reducing the crystallite size of nano
Bi2O3. The small particle size of 5SrO-Bi2O3 and uniformly distribution of SrO on the
pure nano Bi2O3 surface were very effective in the short time and complete degradation of
BPA.
The findings of this study elucidated an approach for the removal of BPA in the
water through photocatalytic of degradation by alkaline-earth oxide doped with Bi2O3.
Acknowledgements
This work was supported by the Scientific Research Projects Coordination Unit of
Istanbul University-Cerrahpasa.
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List of Tables
Table. Crystallite size, specific surface area, band gap and morphology of materials and
BPA degradation efficiencies over 30 min (%).
List of Figures
Figure 1 XRD patterns of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3 catalysts.
Figure 2 SEM images of (a) Bi2O3, (b) 5MgO-Bi2O3 catalysts.
Figure 3 SEM images of (c) 5CaO-Bi2O3, (d) 5SrO-Bi2O3 catalysts.
Figure 4 DRS spectra of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3 catalysts.
Figure 5 FTIR spectra of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3 catalysts.
Figure 6 Photoluminescence spectrum of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3
catalysts.
Figure 7 (a) Degradation activities of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3
catalysts. (b) Inset shows the impact of surfactant on TOC removal in the BPA
degradation.
Table. The crystallite size, specific surface area, band gap, morphology of materials, reaction rate constant and Bisphenol-A (BPA)
degradation efficiency over 30 min (%).
Catalys
Crystallite Size
(nm)
S
BET
(m2g-1)
Band gap
(eV)
BPA degradation
efficiencies (%)
k
r
(mgL-1min-1)
Bi
2
O
3
41
15
2.99
76
0.037
5%MgO-Bi
2
O
3
5%CaO- Bi2O3
5%SrO- Bi2O3
17
19
15
7
10
10
2.92
2.88
2.84
84
88
100
0.036
0.069
0.21
Figure 1 XRD patterns of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3 catalysts.
Figure 2 SEM images of (a) Bi2O3, (b) 5MgO-Bi2O3 catalysts.
Figure 3 SEM images of (c) 5CaO-Bi2O3, (d) 5SrO-Bi2O3 catalysts.
Figure 4 DRS spectra of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3 catalysts.
4000 3500 3000 2500 2000 1500 1000 500
420
499
536
590
666
839
1068
13771292
Bi2O3
4000 3500 3000 2500 2000 1500 1000 500
497 418
857
824
1331
1439
5SrO/Bi
2
O
3
5MgO/Bi
2
O
3
4000 3500 3000 2500 2000 1500 1000 500
537 420
874
824
1330
1439
2159
5CaO/Bi
2
O
3
Wavenumbers [1/cm]
Transmittance (%)
4000 3500 3000 2500 2000 1500 1000 500
420
573
826
1423
Figure 5 FTIR spectra of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3 catalysts.
Figure 6 Photoluminescence spectrum of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3
catalysts.
Figure 7 (a) Degradation activities of Bi2O3, 5MgO-Bi2O3, 5CaO-Bi2O3, 5SrO-Bi2O3
catalysts. (b) Inset shows the impact of surfactant on TOC removal in the BPA
degradation.
