ArticlePDF Available

Advances in Nanomaterial‐based Water Treatment Approaches for Photocatalytic Degradation of Water Pollutants

Wiley
ChemCatChem
Authors:

Abstract and Figures

Demand of pure drinking water is increasing day by day in line with both a growing population and global industrialization. Studies in the past few decades on the application of advanced oxidation processes (AOP) for the treatment of wastewater containing perilous organic pollutants, are promising when compared to conventional water treatment methods. In case of AOP, generation of powerful oxidant radicals (.OH, HOO.) is crucial for the purpose of degradation. Several processes for the in‐situ generation of such highly reactive oxidants have been discussed. This Review highlights the literature reports on the degradation of various organic pollutants (dyes, pharmaceuticals, pesticides, herbicides, insecticides) by means of photocatalysis. A number of scientific investigations have been performed, which elucidate suitable properties (band gap energy, carrier transport, crystallinity etc.) for the deliberate design of efficient photocatalysts. The oxidation rates and degradation efficiency of photocatalysts are governed by some basic parameters, like organic pollutant concentration, photocatalyst concentration, pH, reaction temperature, light intensity, irradiation time, inorganic ions, oxidants, and these are also discussed. Titania and titania based materials have many attractive properties (nontoxicity, less costly, advanced optical properties, high stability) towards photo degradation process. Several studies have been reported investigating the intermediates produced during degradation process as well as the final degraded product, which might be toxic and/or hazardous to the human as well as to the environment. This review assimilates elaborate study on the mechanism of photocatalytic degradation of various organic pollutants.
This content is subject to copyright. Terms and conditions apply.
A preview of the PDF is not available
... Based on these findings, discs with four layers of nanoparticles appear to provide optimal results. The ideal concentrations ensure efficient absorption of UV light by TiO 2 , producing reactive electron-hole pairs crucial for dye breakdown (Som et al., 2020). However, with more TiO 2 layers, challenges emerge. ...
... As evident from Figures 6D, E, increasing the number of layers from 4 to 5 increases the likelihood of agglomeration in the nanoparticles. Nanoparticle agglomeration might reduce the reactive surface area and alter UV light dynamics more scattering than absorption, dampening photocatalysis (Som et al., 2020;Masouleh et al., 2022). Moreover, in higher TiO 2 layers, nanoparticles could scavenge reactive species, leading to a decreased removal rate (Bouarioua and Zerdaoui, 2017). ...
Article
Full-text available
Introduction: This research introduces an innovative photocatalytic reactor designed to address challenges in wastewater treatment, with a focus on enhancing dye degradation and reducing Chemical Oxygen Demand (COD). Methods: The reactor is designed with counter-rotational movements of discs to enhance hydrodynamics and mass transfer, along with a 3D-printed, interchangeable component system to boost efficacy. TiO2 nanoparticles, composed of 80% anatase and 20% rutile, are thermally immobilized on glass discs. The effectiveness of various treatment variables was assessed through a Central Composite Design (CCD), guided by a Response Surface Methodology (RSM) model. Results: The RSM analysis reveals that the linear, quadratic, and interactive effects of the counter-rotational movements significantly influence the efficiency of dye and COD removal. The RSM model yields coefficients of determination (R²) values of 0.9758 and 0.9765 for the predictive models of dye and COD removal, respectively. Optimized parameters for dye removal include a pH of 6.05, disc rotation speed of 22.35 rpm, initial dye concentration of 3.15 × 10⁻⁵ M, residence time of 7.98 h, and the number of nanoparticle layers set at 3.99, resulting in 96.63% dye removal and 65.81% COD removal under optimal conditions. Discussion: Notably, the reactor demonstrates potential for efficient treatment within a near-neutral pH range, which could reduce costs and resource use by eliminating the need for pH adjustments. The implementation of discs rotating in opposite directions marks a significant advancement in the process of dye removal.
Article
Water pollution and the global freshwater crisis are the most alarming concerns of the 21st century, as they threaten the sustainability and ecological balance of the environment. The growth of global population, climate change, and expansion of industrial processes are the main causes of these issues. Therefore, effective remediation of polluted water by means of detoxification and purification is of paramount importance. To this end, nanoscience and nanotechnology have emerged as viable options that hold tremendous potential toward the advancement of wastewater treatment methods to enhance treatment efficiency along with augmenting water supply via utilization of unconventional water sources. Materials at the nano level have shown great promise toward water treatment applications owing to their unique physicochemical properties. In this focus article, we highlight the role of new fundamental properties at the nano scale and material properties that are drastically increased due to the nano dimension (e.g. volume-surface ratio) and highlight their impact and potential toward water treatment. We identify and discuss how nano-properties could improve the three main domains of water remediation: the identification of pollutants, their adsorption and catalytic degradation. After discussing all the beneficial aspects we further discuss the key challenges associated with nanomaterials for water treatment. Looking at the current state-of-the-art, the potential as well as the challenges of nanomaterials, we believe that in the future we will see a significant impact of these materials on many water remediation strategies.
Article
Full-text available
In the present work, the potential application of a fabricated halloysite nanotubes-Ag-TiO2 (HNT-Ag-TiO2) composite loaded with a binary surfactant mixture made up of lecithin and Tween 80 (LT80) in remediating oil spillages was examined. The as-prepared Ag-TiO2 that was used in the fabrication of the HNT-Ag-TiO2-LT80 composite was characterized by X-ray diffraction, Raman spectroscopy, UV–vis and diffuse reflectance spectroscopy, CV analyses, and SEM-EDX. The synthesized composite was also characterized by thermogravimetric analysis, Fourier-transform infrared spectroscopy, and scanning electron microscopy-energy dispersive X-ray spectroscopy. The synthesized composite was active in both the UV and visible light regions of the electromagnetic spectrum. The oil-remediating potential of the as-prepared composite was examined on crude oil, and aromatics and asphaltene fractions of crude oil. The composite was able to reduce the surface tension, form stable emulsions and smaller oil droplet sizes, and achieve a high dispersion effectiveness of 91.5%. A mixture of each of the crude oil and its fractions and HNT-Ag-TiO2-LT80 was subjected to photodegradation under UV light irradiation. The results from the GC-MS and UV–vis analysis of the photodegraded crude oil revealed that the photocatal composite was able to photodegrade the crude oil, aromatics, and asphaltene fractions of crude oil with the formation of intermediate photodegradation products depicting that the HNT-Ag-TiO2-LT80 has a potential as an oil spill remediation material.
Article
Photocatalytic degradation is a key technique in wastewater treatment, particularly for toxic dye removal, yet challenges related to poor hydrodynamics and mass transfer limitations persist. This study addresses these challenges by innovatively employing an adjustable-angle baffle in a plug flow reactor (PFR) to enhance dye removal efficiency. A lab-scale PFR with an adjustable baffle was utilised to assess the impact of various factors, including baffle angle, catalyst concentration, hydraulic retention time (HRT), pH, and initial dye concentration, on the removal of direct red 23 dye. The experimental design employed a central composite design (CCD), with subsequent data analysis using response surface methodology (RSM) and artificial neural network (ANN) models. The findings demonstrate that the adjustable baffle significantly impacts dye removal, achieving maximum efficiency at an optimal angle of 77.5 degrees. The ANN model outperformed the RSM model, with a higher determination coefficient (R2) of 0.994 compared to 0.928. Furthermore, RSM and genetic algorithms yielded closely aligned optimal conditions, validating their accuracy. The optimised conditions achieved a dye removal efficiency of 89.47%. Significantly, the study also identified degradation as the dominant mechanism over adsorption and highlighted the impressive stability of nano-Fe3O4 during the recycling process. Mineralisation analysis revealed the presence of lightweight organic residual molecules post-treatment. These outcomes demonstrate the effectiveness of adjustable baffles in PFRs, marking a significant advancement in wastewater treatment technologies and underscoring the critical role of baffle orientation and catalyst concentration in optimising dye removal processes.
Article
Full-text available
Carbamazepine (CBZ) is a typical class of pharmaceuticals and personal care products (PPCPs), and is a serious threat to the environment and human health. Photocatalytic degradation is an efficient technology to remove CBZ. However, the present work focused mainly on the improvement of photocatalytic degradation performance. The information about the effects of inorganic ions on the photocatalytic degradation activity of environmental pollutants is still scarce. This study systematically investigated the effects of inorganic ions on the photocatalytic degradation of CBZ in view of the practical applications. The addition of inorganic anions showed a negative effect on photocatalytic degradation of CBZ with the order of inhibition effects of HCO3− > Cl− > NO3−. This was due to the quenching effects of hydroxyl radicals or holes, which decreased the photocatalytic degradation of CBZ. The presence of Al3+ could adsorb on the surface of a photocatalyst to shield the active site, resulting in the decreased CBZ degradation, while coexistence of Ca2+ significantly promoted the photocatalytic degradation of CBZ owing to the enhanced CBZ adsorption. Mg2+ showed concentration and time-dependent effects (suppression or promotion) on the photocatalytic degradation of CBZ.
Article
Full-text available
In this work, the photocatalytic degradation of wastewater containing an organic dye (Methylene Blue) was investigated in a slurry-type reactor enhanced by air sparging. Commercial TiO2 was used as the photocatalyst which was activated using ultraviolet irradiation. The effects of initial dye concentration, photocatalyst loading, solution pH and air’s superficial velocity on the degradation efficiency were evaluated. The degradation efficiency of the dye increased with increasing the pH of the solution and decreasing the initial dye concentration. Moreover, increasing the catalyst loading up to 1 g/l showed an improvement in the degradation efficiency. However, the efficiency deteriorated with a further increase in the catalyst loading. Introducing air into the reaction medium in the form of micro-bubbles significantly improved the degradation efficiency by providing oxygen molecules required for the oxidation reaction. Furthermore, these air bubbles created turbulence in the reaction medium, which resulted in the enhancement of the mass transfer rate of dye molecules from the solution bulk to the catalyst surface with a subsequent increase in the degradation efficiency. A complete decolorization of 10 ppm dye solution was achieved in the neutral solution (pH = 7) with a catalyst loading of 1 g/l and an air superficial velocity around 2 cm/s. The effect of the air superficial velocity on the degradation reaction kinetics was investigated and the reaction was found to follow the pseudo second order rate law.
Article
Full-text available
Abstract In this study, a series of photocatalysts were prepared, namely bare 3D-TiO2 (b-3D-T), magnetic 3D-TiO2: (m3D-T) and magnetic 3D-TiO2@Hierarchical Porous Graphene Aerogels (HPGA) nanocomposite: (m3D-T-HPGA NC) by solvothermal process. The prepared photocatalysts were analyzed by using X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), Vibrating sample magnetometer (VSM), Brunauer–Emmett–Teller (BET) and Diffuse Reflectance Measurement – Ultraviolet (DRS-UV) to know their physical and chemical properties. The photocatalytic degradations of two toxic aquatic pollutants viz., Cr(VI) and bisphenol A (BPA) were tested by using the prepared photocatalysts. Parameters such as initial pollutant concentration, solution pH, photocatalyst dosage, wavelength and light intensity were investigated to optimize the process. The photocatalytic properties of prepared catalyst were analyzed based on the degradation of Cr(VI) and BPA under UV irradiation. The modified photocatalysts showed better performance as compared to b-3D-T photocatalyst. This better performance is ascribed to efficient charge transfer between b-3D-T nanoparticles to the porous graphene sheets. The maximum photocatalytic degradation of Cr(VI) was found to be 100% with m3D-T-HPGA NC within 140 min, whereas a removal efficacy of 100% and 57% was noticed in case of m3D-T and b-3D-T within 200 and 240 min, respectively. In the case of BPA, the maximum degradation efficiency was found to be 90% with m3D-T-HPGA NC within 240 min.
Article
Full-text available
Titanium dioxide (TiO 2) is described as an established material to remove pollutants from water. However, TiO 2 is still not applied on a large scale due to issues concerning, for example, the form of use or low photocatalytic activity. We present an easily upscalable method to synthesize high active TiO 2 nanoparticles on a polyethersulfone microfiltration membrane to remove pollutants in a continuous way. For this purpose, titanium(IV) isopropoxide was mixed with water and hydrochloric acid and treated up to 210 • C. After cooling, the membrane was simply dip-coated into the TiO 2 nanoparticle dispersion. Standard characterization was undertaken (i.e., X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, water permeance, contact angle). Degradation of carbamazepine and methylene blue was executed. By increasing synthesis temperature crystallinity and photocatalytic activity elevates. Both ultrasound modification of nanoparticles and membrane pre-modification with carboxyl groups led to fine distribution of nanoparticles. The ultrasound-treated nanoparticles gave the highest photocatalytic activity in degrading carbamazepine and showed no decrease in degradation after nine times of repetition. The TiO 2 nanoparticles were strongly bound to the membrane. Photocatalytic TiO 2 nanoparticles with high activity were synthesized. The innovative method enables a fast and easy nanoparticle production, which could enable the use in large-scale water cleaning.
Article
In this work, the efficiency of organic pollutants degradation over Ag nanoparticles (NPs) loaded Ag2SO3 (AgSS) photocatalyst and the impact of reaction parameters on the degradation process are studied. Visible light active, AgSS plasmonic photocatalyst, was prepared by precipitation and chemical reduction method. The formation and well dispersion of cubic Ag NPs on the Ag2SO3 surface with enhanced visible light absorption was investigated by X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM), Energy Dispersive X-ray analysis (EDX) and UV–vis-NIR spectrophotometer. The photocatalytic activity of the prepared photocatalysts was evaluated by organic dye and phenol degradation reaction. The effects of different factors such as catalyst composition, light source, initial pollutant concentration and pH of the solutions were studied using organic dye Rhodamine B (RhB). It was found that the localized surface plasmon resonance (LSPR) absorption of Ag NPs is strongly dependent on the size, shape and amount of the NPs loaded. 1-AgSS showed the best photodegradation performance with 99% RhB removal in 2 h. The photoactivity of the 1-AgSS was better at both high and low pH environment. The 1-AgSS composition showed reusability for five successive experimental cycles and good structural stability. Moreover, the formation of intermediates in phenol degradation reaction was confirmed over the 1-AgSS sample by UV-spectra and HPLC analysis. We believe that the synthesized AgSS photocatalysts have promising potential for the photocatalytic elimination of organic pollutants from industrial effluents.
Article
Rapid recombination of photogenerated carriers and narrow visible light absorption range are two main defects in graphitic carbon nitride (g-C3N4)-based photocatalysts. To address these problems, construction of Z-scheme 2D/2D BiOBr/CDs/g-C3N4 heterojunction photocatalysts with carbon dots as solid-state electron mediators has been investigated. The resultant BiOBr/CDs/g-C3N4 hybrids exhibits remarkable interfacial charge transfer abilities and a broadened solar light absorption range owing to the short charge transport distance and the up-converted photoluminescence character of CDs. Simultaneously, the enhanced specific surface area and nanosheet structure impart more active sites to BiOBr/CDs/g-C3N4 composites. As a result, BiOBr/CDs/g-C3N4 composites reveal significant enhancement in the activity of photodegradation of ciprofloxacin (CIP) and tetracycline (TC) under visible and near infrared (NIR) light irradiation. Moreover, the photodegradation efficiency of BiOBr/CDs/g-C3N4 hybrids was significantly enhanced over that of pristine BiOBr nanosheets and g-C3N4 ultrathin nanosheets. The photocatalytic mechanism is expounded according to free radical capture experiments and electron spin resonance spin-trapping tests and the photodegradation intermediates of CIP were detected by liquid chromatography–mass/mass spectrometry. Moreover, BiOBr/CDs/g-C3N4 composites show excellent photostability and reusability after four runs for CIP degradation.
Article
Chiral pharmaceuticals (CPs), including non-steroid anti-inflammatory drugs (NSAIDs), β-blockers and some herbicide and pesticides, are widely used in aquaculture, clinical treatment and many other fields. However, people are increasingly concerned about such ubiquitous pollutants, which can frequently be detected in contaminated soil and water. In large part, the significant sources of chiral pharmaceuticals stem from industrial processes, such as the direct discharge of untreated or incompletely treated wastewaters containing chiral pharmaceuticals, incorrect storage and use, animal wastes and biosolids. The main ways for human exposure to chiral pharmaceuticals are the disease treatment process and chiral pharmaceuticals contaminants. According to the results of a series of toxic studies, some diseases, even cancers, may be associated with exposure to certain chiral pharmaceuticals. Therefore, the treatment of chiral pharmaceuticals has become an important issue. The current advanced remediation techniques for chiral pharmaceuticals include the conventional method (sorption and sonolysis), biotransformation (an aerobic granular sludge-sequencing batch reactor and constructed wetland system) and advanced oxidation processes (ozonation and photocatalysis). Herein, in this review, we summarize the current status and sources of chiral pharmaceuticals, potential effects on human health, as well as the superiority, disadvantages and prospects of current advanced remediation technologies. Moreover, we also anticipate the prospect of the future research needed for chiral pharmaceuticals pollutant remediation.
Article
During the last 30 years, environmental issues about the chemical and biological contaminations of water have become a major concern for society, public authorities and the industry. Most domestic and industrial activities produce wastewaters containing undesirable toxic contaminants. In this context, a constant effort must be made to protect water resources. Current wastewater treatment methods involve a combination of physical, chemical and biological processes, and operations to remove insoluble particles and soluble contaminants from effluents. This article provides an overview of methods for wastewater treatment, and describes the advantages and disadvantages of available technologies.
Article
Halide perovskites have attracted great attention in the fields of photovoltaics, LEDs, lasers, and most recently photocatalysis due to their unique optoelectronic properties. Here, we present an all‐inorganic halide perovskites CsPbBr3/TiO2 composite material for the selective benzyl alcohol oxidation to benzaldehyde under visible light illumination. The catalyst, which is prepared via a facile wet‐impregnation method, shows very good selectivities towards benzaldehyde (90 % at 50 % conversion). Action spectra and electron spin resonance (ESR) studies reveal that photo‐excited electrons formed within the CsPbBr3 upon visible light illumination take part in the reaction via the reduction of oxygen to form superoxide radicals. The detailed post‐catalysis characterization via UV‐vis spectroscopy, XRD, XPS, and HAADF‐STEM studies further demonstrates the good stability of the CsPbBr3 in terms of morphology and crystal structure under reaction conditions. This study sheds light on promising new photocatalytic application of halide perovskites.