Photocatalytic Wastewater Treatment Research Articles

Developing fine-tuned metal–organic frameworks for photocatalytic treatment of wastewater: A review

The environmental pollution is still one of the most serious problems facing mankind today, it is of great significance to develop novel wastewater treatment processes. Photocatalysis is regarded as one of the most promising techniques for wastewater treatment. Lately, there is a strong increase in the number of reports on the synthesis and applications of MOF-based photocatalysts. In this review, the typical modification strategies of MOFs for improving photocatalytic activities are summarized, such as optimization of preparation method, surface modification, doping metal ions, loading quantum dots as well as constructing the heterojunction. The main purposes of these modification strategies are to broaden the light absorption range of MOFs and increase the separation efficiency of photogenerated electron-hole pairs. Advantages and disadvantages of each modification strategy are also analyzed. Meanwhile, the applications of MOFs-based photocatalyst in wastewater treatment are briefly discussed, including reduction of metal ions, degradation of organic pollutants and inactivation of bacteria. More importantly, the challenges and outlooks about MOFs-based photocatalyst are proposed. In short, it is hoped that this review can provide some meaningful references for designing MOFs-based photocatalyst in future research.

Photocatalytic oxidation of glyphosate and reduction of Cr(VI) in water over ACF-supported CoNiWO4-gCN composite under batch and flow conditions

Photocatalytic treatment of wastewater using nanomaterials is an efficient energy saving technology. Yet the practical application of the technology is limited because of difficulty in developing the stable, supported photocatalytic nanoparticles that can be used under continuous flow conditions. Here, we report an efficient removal of glyphosate (GLP) and Cr(VI) from water under batch as well as continuous flow conditions using the activated carbon fiber (ACF)-supported nanocomposite of CoNiWO4 (CNW) and g-C3N4 (gCN), as a photocatalyst. CNW-gCN/ACF is synthesized using a one-step strategy, and spectroscopic characterization techniques are used to corroborate the formation of the Z-scheme-based CNW-gCN heterojunction in the ACF substrate. Efficacy of the photocatalyst is assessed in visible light irradiation. The batch activity data of the individual pollutant show the complete oxidation of GLP at 30 ppm and reduction of Cr(VI) at 200 ppm concentration levels in 60 and 150 min, respectively at 1 g/L dose of CNW-gCN/ACF. Photocatalytic efficiency of CNW-gCN/ACF in the simultaneous removal of both pollutants from co-contaminated feed is found to be greater than that in single-feed system under identical experimental conditions. Tested under flow conditions, CNW-gCN/ACF shows approximately the same rates of oxidation and reduction as prevalent under batch conditions, indicating the efficient immobilization of the nanocatalyst particles in ACF, which not only prevents elution of the catalyst but also improves its reusability. The toxicity data indicate the treated water samples to be non-toxic. The current study provides an efficient method for developing supported nanomaterial photocatalysts for treating flowing co-contaminated wastewater.

Photocatalytic Treatment of Methyl Orange Dye Wastewater by Porous Floating Ceramsite Loaded with Cuprous Oxide

It is well known that water treatment of printing and dyeing wastewaters is problematic. In order to decompose dyes from dyestuff wastewater and convert them into almost harmless substances for the natural environment, an easily prepared, efficient, practical, and easy-to-regenerate composite material was produced from porous floating ceramsite loaded with cuprous oxide (PFCC). The PFCC samples were prepared and characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The material was applied for photocatalytic degradation of methyl orange (MO) in water. The results show that the maximal degradation rate of MO was 92.05% when the experimental conditions were as follows: cuprous oxide loading rate of 8%, PFCC dosage of 20 g/L, the reaction time of 2 h, pH value of 8, and solution initial concentration of 30 mg/L. The degradation processes of MO fits well with the Langmuir–Hinshelwood model in reaction kinetics, and the Freundlich model in reaction thermodynamics, respectively. The degradation mechanism of MO was considered from two perspectives—one was the synergetic effect of adsorption and photocatalytic oxidation, and the other was the strong oxidation of hydroxyl radicals produced by photocatalysts.

Solar energy for liquid wastewater treatment with novel TiO2 supported catalysts

Photocatalytic oxidation is promising technology for removal of recalcitrant pollutants from water. Solar energy can be an interesting radiation source since the operating costs can be lower. However, the use of powder photocatalyst is a major drawback of the technology since suitable separation technologies are required and catalysts recovery is difficult. This work aims to test the suitability of using polymeric supports to immobilize TiO 2 in the reactor and apply it for parabens removal from water by solar photocatalytic oxidation. Polyurethanes (PU) and polydimethylsiloxane (PDMS) membranes were prepared and modified with TiO 2. While PU materials are only able to adsorb (35% in 1 h) parabens whichever the modification applied, modified PDMS was able to promote parabens photocatalytic oxidation removing 20% in 1 h under solar energy. Plasma/UV modification was able to active PDMS membranes (16% of methyl paraben (MP) removal) and further entrapment of TiO 2 in the polymeric matrix did not improve the process (18% of MP removal). Thus, only the superficial TiO 2 was active. Results show that PDMS is suitable material to support TiO 2 aiming photocatalytic wastewater treatment process using the Sun as a clean and renewable energy source.

N-Doped Carbon Dot Hydrogels from Brewing Waste for Photocatalytic Wastewater Treatment.

The brewery industry annually produces huge amounts of byproducts that represent an underutilized, yet valuable, source of biobased compounds. In this contribution, the two major beer wastes, that is, spent grains and spent yeasts, have been transformed into carbon dots (CDs) by a simple, scalable, and ecofriendly hydrothermal approach. The prepared CDs have been characterized from the chemical, morphological, and optical points of view, highlighting a high level of N-doping, because of the chemical composition of the starting material rich in proteins, photoluminescence emission centered at 420 nm, and lifetime in the range of 5.5–7.5 ns. With the aim of producing a reusable catalytic system for wastewater treatment, CDs have been entrapped into a polyvinyl alcohol matrix and tested for their dye removal ability. The results demonstrate that methylene blue can be efficiently adsorbed from water solutions into the composite hydrogel and subsequently fully degraded by UV irradiation.

Decoration of X2C nanoparticles on CdS nanostructures for highly efficient photocatalytic wastewater treatment under visible light

It is necessary to design and fabricate effective and stable heterostructures to enhance the photocatalyst performance. In this research, we developed stable metal carbide (Mo2C and W2C) embedded cadmium sulfide (CdS) hybrid nanostructure photocatalysts to increase the light adsorption capacity and effectively enhance the photocatalytic activity.A simple hydrothermal technique was employed to effectively fabricate the CdS and CdS:X2C (X = Mo or W) hybrid photocatalyst. Microscopy studies demonstrated the surface modification of the hybrid structure due to the X2C incorporation with CdS. X-ray photoelectron spectroscopy, X-ray diffraction, and energy dispersive analysis measurements were performed to characterize the hybrid structure materialization. The photocatalytic properties of CdS and CdS:X2C hybrid structures were evaluated by degrading Rhodamine B (RhB) under visible light. The polygonal shaped CdS:X2Cexhibited excellent photocatalytic activities. The highly porous structure of CdS:X2C indicated that manyexposed active facets were available due to the embedding of petal-shaped X2C, which enabled the effective adsorption and transference of RhB organic molecules to the active edges. Moreover, the hierarchical structure of CdS:X2Ccorresponded to a high light-absorption efficiency due to the increased length of light trails and enhanced interfacial shifting of the valence state electrons, which reduced the optical band-gap.

Photocatalytic treatment of detergent-contaminated wastewater: A short review on current progress

Photocatalytic treatment of detergent-contaminated wastewater: A short review on current progress

Ag3PO4-based photocatalysts and their application in organic-polluted wastewater treatment.

Semiconductor photocatalysis technology has shown great potential in the field of organic pollutant removal, as it can use clean and pollution-free solar energy as driving force. The discovery of silver phosphate (Ag3PO4) is a major breakthrough in the field of visible light responsive semiconductor photocatalysis due to its robust capacity to absorb visible light < 520nm. Furthermore, the holes produced in Ag3PO4 under light excitation possess a strong oxidation ability. However, the strong oxidation activity of Ag3PO4 is only achieved in the presence of electron sacrifice agents. Otherwise, photocorrosion would greatly reduce the reuse efficiency of Ag3PO4. This review thus focuses on the structural characteristics and preparation methods of Ag3PO4. Particularly, the recent advances in noble metal deposition, ion doping, and semiconductor coupling, as well as methods of magnetic composite modification for the improvement of catalytic activity and recycling efficiency of Ag3PO4-based catalysts, were also discussed, and all of these measures could enhance the catalytic performance of Ag3PO4 toward organic pollutants degradation. Additionally, some potential modification methods for Ag3PO4 were also proposed. This review thus provides insights into the advantages and disadvantages of the application of Ag3PO4 in the field of photocatalysis, clarifies the photocorrosion essence of Ag3PO4, and reveals the means to improve photocatalytic activity and stability of Ag3PO4. Furthermore, it provides a theoretical and methodological basis for studying Ag3PO4-based photocatalyst and also compiles valuable information regarding the photocatalytic treatment of organic polluted wastewater.

Comparative study on photocatalytic degradation of methylene blue using pristine ZnO and Ni/ZnO composite films

Industrial dye wastewater is rich in organic molecules that are harmful to all types of living organisms. The present work investigates the potential of the incorporation of Ni nanoparticles into ZnO films in order to enhance the photocatalytic degradation performance. Pristine ZnO has been widely used as a photocatalyst in a photocatalytic degradation treatment of wastewater, however can only be activated by UV light. Incorporation of Ni into ZnO can broaden the light spectrum by using both visible light and UV for the reaction, therefore enhancing the degradation efficiency. The experimental runs were performed to evaluate the effect of incorporation of Ni nanoparticles into ZnO films and morphology of Ni nanoparticles (rod-cubic-like and chain-like shapes) on the photocatalytic degradation efficiency. In this study, methylene blue was used as a model wastewater. The results revealed that addition of Ni enhanced the degradation efficiency to 44% (rod-cubic-like) and 40% (chain-like), compared to that of pristine ZnO of 33%.

Photocatalytic ozonation in an immersion rotary body reactor for the removal of micro-pollutants from the effluent of wastewater treatment plants

Abstract Carrier-bound titanium dioxide catalysts were used in a photocatalytic ozonation reactor for the degradation of micro-pollutants in real wastewater. A photocatalytic immersion rotary body reactor with a 36-cm disk diameter was used, and was irradiated using UV-A light-emitting diodes. The rotating disks were covered with catalysts based on stainless steel grids coated with titanium dioxide. The dosing of ozone was carried out through the liquid phase via an external enrichment and a supply system transverse to the flow direction. The influence of irradiation power and ozone dose on the degradation rate for photocatalytic ozonation was investigated. In addition, the performance of the individual processes photocatalysis and ozonation were studied. The degradation kinetics of the parent compounds were determined using liquid chromatography tandem mass spectrometry. First-order kinetics were determined for photocatalysis and photocatalytic ozonation. A maximum reaction rate of the reactor was determined, which could be achieved by both photocatalysis and photocatalytic ozonation. At a dosage of 0.4 mg /mg DOC, the maximum reaction rate could be achieved using 75% of the irradiation power used for sole photocatalysis, allowing increases in the energetic efficiency of photocatalytic wastewater treatment processes. The process of photocatalytic ozonation is suitable to remove a wide spectrum of micro-pollutants from wastewater.

Facile Synthesis of BiVO4@ZIF-8 Composite with Heterojunction Structure for Photocatalytic Wastewater Treatment.

Water pollution has always been a serious problem across the world; therefore, facile pollutant degradation via light irradiation has been an attractive issue in the field of environmental protection. In this study, a type of Zn-based metal–organic framework (ZIF−8)-wrapped BiVO4 nanorod (BiVO4@ZIF−8) with high efficiency for photocatalytic wastewater treatment was synthesized through a two-step hydrothermal method. The heterojunction structure of BiVO4@ZIF−8 was confirmed by morphology characterization. Due to the introduction of mesoporous ZIF−8, the specific surface area reached up to 304.5 m2/g, which was hundreds of times larger than that of pure BiVO4 nanorods. Furthermore, the band gap of BiVO4@ZIF−8 was narrowed down to 2.35 eV, which enabled its more efficient utilization of visible light. After irradiation under visible light for about 40 min, about 80% of rhodamine B (RhB) was degraded, which was much faster than using pure BiVO4 or other BiVO4-based photocatalysts. The synergistic photocatalysis mechanism of BiVO4@ZIF−8 is also discussed. This study might offer new pathways for effective degradation of wastewater through facile design of novel photocatalysts.

Construction of an efficient and durable hierarchical porous CuO/SiO2 monolith for synergistically boosting the visible-light-driven degradation of organic pollutants

• Hierarchical porous CuO/SiO 2 monoliths in centimeter scale were prepared. • Synthesis via facile wet impregnation of precursor salt into SiO 2 monoliths. • Effective photocatalytic abatement of dye and insecticide in visible light. • Easily recoverable nature of solid-rock-like monolith renders it highly reusable. Monolithic materials have emerged as promising catalysts for photocatalytic wastewater treatment. Herein, hierarchical porous CuO/SiO 2 monoliths were constructed via the wet-impregnation method. The crystalline nature of the prepared material was confirmed through XRD while XPS analysis was carried out to find out the chemical bonding states of the elements. EDS and elemental-mapping confirmed the successful formation of the material and a homogeneous dispersion of elements. SEM images exhibited the interconnected porous network morphology of the monoliths while the surface area analysis affirmed that the monoliths were hierarchical porous along with a substantial surface-area of ∼286 m 2 /g. Optical properties demonstrated that the material was visible-light-driven having a small band-gap of ∼1.33 eV as well as a slow e − /h + recombination-rate. The assessment of the photoactivity of the monolith was done by conducting the detoxification of model contaminants; rhodamine-B dye (Rh-B) and a colorless insecticide, thiamethoxam (TM). The impact of diverse parameters namely catalyst-concentration, contaminant-pH, and illumination-area on the degradation efficacies was also examined. The maximum removal efficiency of 90.5% with a rate constant of 0.01255 min −1 was realized for Rh-B at optimal conditions, whereas for TM, ∼55% degradation occurred with a rate constant of 0.00443 min −1 . The highly reusable feature of the monolith (∼12%-reduction in efficacy post 5 cycles) was justified by the XRD, surface area and SEM analyses after the photocatalytic experiment. Around 60% Rh-B and 20.05% TM was mineralized after the photocatalytic reaction as estimated through TOC analyses. The scavenger experiments revealed that holes were chiefly involved in the reactions. The present investigation emphasizes the superiority of the monolithic photocatalysts over powdered catalysts to combat water pollution.

Development of a novel solar energy controllable Linear fresnel photoreactor (LFP) for high-efficiency photocatalytic wastewater treatment under actual weather

Solar-energy-enabled photocatalysis is promising for wastewater treatment. However, due to the changes in the solar position and variable weather conditions, providing optimized light and temperature for photocatalysis under actual weather remains to be a technical difficulty. In this study, a novel Linear fresnel photoreactor (LFP) was firstly developed for wastewater treatment. LFP could achieve effective adjustment of sunlight by flexibly controlling 6 mirrors according to solar position and weather conditions. On sunny condition, LFP could maintain the optimal light irradiance and temperature, while on overcast condition it could provide the highest possible light irradiance and temperature. In the comparative experiments between LFP and Inclined Plate Collector (IPC) (as control reactor) which passively receive sunlight, the Rhodamine B degradation efficiencies in LFP were 2.19 folds, 1.5 folds and 2.28 folds higher than control under the temporarily overcast, totally to slightly overcast and sunny conditions, respectively. In addition, the efficiencies of Amoxicillin degradation and Escherichia coli disinfection in LFP were also 2 folds and 1.37 folds higher than control in sunny conditions, respectively. Furthermore, whole-year estimation indicated that LFP is effective to optimize light irradiance and temperature in typical densely populated areas of the world to achieve high-efficiency wastewater treatment. These results proved that LFP, as an effective solar energy controllable reactor, has great potential in promoting the development of green wastewater treatment infrastructure to improve global public health and achieve eco-friendly society.

Anchoring bismuth oxybromo-iodide solid solutions on flexible electrospun polyacrylonitrile nanofiber mats for floating photocatalysis

Constructing floating photocatalysts with highly efficient visible-light utilization is a promising approach for practical photocatalytic wastewater treatment. In this study, we anchored bismuth oxybromo-iodide (BiOBrxI1-x (0 ≤ x ≤ 1)) on flexible electrospun polyacrylonitrile (PAN) nanofiber mats to create BiOBrxI1-x@PAN nanofibers with tunable light absorption properties as floating photocatalysts at room temperature. As x increased, the photocatalytic activity of the BiOBrxI1-x@PAN nanofibers with similar loading content initially increased, and then decreased, for the degradation of bisphenol A (BPA) and methyl orange (MO) under visible-light irradiation (λ > 420 nm) conditions. The BiOBrxI1-x@PAN (0 < x < 1) nanofibers exhibited better photocatalytic performance compared to the BiOBr@PAN and BiOI@PAN nanofibers. Under visible-light irradiation, the BPA degradation rate of the BiOBr0.5I0.5@PAN nanofibers was 1.9 times higher than that of the BiOI@PAN nanofibers, while the BiOBr@PAN nanofibers had no noticeable degradation performance. The MO degradation rate of the BiOBr0.5I0.5@PAN nanofibers was 2.5 and 3.2 times higher than that of the BiOBr@PAN and BiOI@PAN nanofibers, respectively. The enhanced performance possibly originated from a balance between the light absorption and redox capabilities, along with efficient separation of electron-hole pairs in the BiOBr0.5I0.5@PAN nanofibers, as determined by ultraviolet-visible diffuse reflectance spectroscopy, X-ray photoelectron spectra analysis of the valence bands, and photocurrent response characterization. Compared to the powder structures, the BiOBrxI1-x@PAN nanofibers showed enhanced performance due to the excellent dispersion and immobilization of the BiOBrxI1-x solid solution, which provided more active sites during photocatalytic degradation. In addition, their flexible self-supporting structures allowed for floating photocatalysis near the water surface. They could be reused directly without separation and maximized the absorption of visible light during the photocatalytic reaction. Therefore, these solid-solution-based floatable nanofiber photocatalysts are good potential candidates for wastewater treatment applications.

MoSe2 Nanoflowers for Highly Efficient Industrial Wastewater Treatment with Zero Discharge.

Water pollution is one of the leading causes of death and disease worldwide, yet mitigating it remains a challenge. This paper presents an efficient new strategy for the processing of wastewater utilizing an accessible redox reaction with MoSe2 nanoflowers, which shows a strong oxidizing ability and permits the decomposition of dye molecules in dark environments without the need for an external power source. This reaction can treat wastewater at a decomposition rate above 0.077 min−1, even when interacting with organic pollutants at concentrations up to 1500 ppm. Theoretical calculations by Dmol3 simulation elucidates that the reactions proceed spontaneously, and the kinetic constant (k obs) for this redox reaction with 10 ppm RhB dye is 0.53 min−1, which is 65 times faster than the titanium dioxide photocatalytic wastewater treatment. More importantly, the residual waste solution can be further utilized as a precursor to reconstruct the MoSe2 nanoflowers. To demonstrate the effectiveness and reusability, the treated effluent is directly used as the sole source of irrigated water for plants with no adverse effect. This method offers an eco‐friendly and more accessible way to treat industrial wastewater with zero‐discharge.

Enhanced performance of photocatalytic treatment of Congo red wastewater by CNTs-Ag-modified TiO2 under visible light.

In order to improve the treatment efficiency of printing and dyeing wastewater, the carbon nanotubes-silver-modified-titanium dioxide (CNTs-Ag-TiO2, CAT) ternary composite was prepared by a mechanical mixing method. It was found that the morphology of the prepared CAT sample was uniformly coated with strips of CNTs, speckled Ag, and lumpy TiO2. The (002) crystal plane of CNTs, the (101) crystal plane of TiO2, and the (111) crystal plane of Ag were observed, which possessed functional groups such as Ti-OH and Ti-O-C, indicating that the prepared CAT sample had photocatalytic reaction sites. The visible light utilization of titanium dioxide can be improved. The treatment effect of different proportions of CNTs-Ag-TiO2 on Congo red wastewater was tested, and the results showed that the optimum degradation effect of Congo red wastewater was CNTs: Ag = 10:1, and the doped amount of CNTs/Ag was 15%, and the removal rate of Congo red wastewater could reach 100% within 140 min. The excellent removal effect of CAT ternary composite on Congo red wastewater provided a new idea and way for the modification of TiO2 and its composites for the potential of organic dyes degradation.

Bi2O3 immobilized 3D structured clay filters for solar photocatalytic treatment of wastewater from batch to scaleup reactors

3D structured clay filters were synthesized using the 3D printed molds. The Bi2O3 photocatalyst was immobilized on the surface of the clay filter using sol-gel dip, soak and calcination at 450 °C. The X-Ray Diffraction analysis of the immobilized filter showed the growth of tetragonal β-Bi2O3 on the clay. The diffused reflectance UV–Vis spectroscopy confirmed the presence of β-Bi2O3 on the clay with a broad optical absorption in the visible range and an estimated bandgap of 2.38 eV. The morphology of the Bi2O3 filter showed uniform layered films on the irregular grains of calcined clay with a crackly appearance. The photocatalytic properties of the Bi2O3 filter were evaluated for the degradation of the anionic indigo carmine (IC) dye and Bisphenol-A (BPA) under visible light and natural sunlight. Bi2O3 coated filter was more effective under natural sunlight because of the high intensity of solar irradiation. Total organic carbon analysis revealed up to 30% and 70% mineralization of the IC and BPA moieties, respectively. A recirculating semi-batch reactor with the upscaled configuration of the Bi2O3 filter was designed to degrade a large volume of both individual and mixed IC and BPA solutions. The overall results revealed a high potential of the Bi2O3 clay filter for the treatment of organic pollutants.

3D-printed photoreactor with robust g-C3N4 homojunction based thermoset coating as a new and sustainable approach for photocatalytic wastewater treatment

Recently, the rapid technological advancement in photocatalysis has gained popularity as a means of addressing climate change and environmental degradation issues. The rapid surge in interest for 3D-printing process has delivered solutions for a broad spectrum of needs primarily due to its flexibility, cost effectiveness and environmental friendliness. In addition, the development in synergizing photocatalysis and 3D-printing technology has provided an optimistic outlook for sustainable wastewater treatment. In present study, a 3D-printed photocatalytic reactor was successfully designed and constructed via digital light processing technique. Besides that, a visible-light sensitive photocatalyst, graphitic carbon nitride homojunction was synthesized via a facile hydrothermal approach. The as-developed photocatalyst was then prepared in a form of thermoset coating and subsequently applied onto the base of 3D-printed photoreactor. A series of characterization tests were conducted to gain an in-depth understanding of the surface morphology and topology, chemical structure, thermal stability, elemental compositions, and surface wettability of the photocatalyst system. The photocatalytic performance of the graphitic carbon nitride homojunction-based thermoset coating was evaluated via Rhodamine B (RhB) dye degradation under the irradiation of a 50 W LED light. A removal efficiency of 95.62% was achieved within 24 h with a corresponding kinetic rate constant of 2.1 × 10−3 min−1. The recyclability of the photocatalytic system was verified by assessing its photoactivity for five consecutive cycles and retained 98.5% of its initial photoactivity. Overall, this research work may intrigue more exploration between interdisciplinary researchers in the field of photocatalysis and additive manufacturing, especially for sustainable environmental remediation.

A review of graphene‐TiO2 and graphene‐ZnO nanocomposite photocatalysts for wastewater treatment

AbstractTechnologies for wastewater remediation have been growing ever since the environmental and health concern is realized. Development of nanomaterials has enabled mankind to have different methods to treat the various kinds of inorganic and organic pollutants present in wastewater from many resources. Among the many materials, semiconductor materials have found many environmental applications due to their outstanding photocatalytic activities. TiO2 and ZnO are more effectively used as photocatalyst or adsorbents in the withdrawal of inorganic as well as organic wastes from the wastewater. On the other hand, graphene is tremendously being investigated for applications in environmental remediation in view of the superior physical, optical, thermal, and electronic properties of graphene nanocomposites. In this work, graphene‐TiO2 and graphene‐ZnO nanocomposites have been reviewed for photocatalytic wastewater treatment. The various preparation techniques of these nanocomposites have been discussed. Also, different design strategies for graphene‐based photocatalyst have been revealed. These nanocomposites exhibit promising applications in most of the water purification processes which are reviewed in this work. Along with this, the development of these nanocomposites using biomass‐derived graphene has also been introduced.Practitioner Points Graphene‐TiO2 and graphene‐ZnO nanocomposites are effective for wastewater treatment through photocatalysis. These nanocomposite photocatalysts have been used in the form of membrane as well as antibacterial agents. Synthetic strategies and design considerations of graphene‐based photocatalyst play a major role. Biomass‐derived graphene‐TiO2 and graphene‐ZnO nanocomposites have also found application in wastewater treatment.

Photocatalysis: an effective tool for photodegradation of dyes-a review.

The disposal of dye-contaminated wastewater is a major concern around the world for which a variety of techniques are used for its treatment. The photocatalytic treatment of dye-contaminated wastewater is one of the treatment methods. Semiconductor-assisted photocatalytic treatment of dye-contaminated wastewater has gained pronounced attention recently. This review outlines the recent advancements in the photocatalytic treatment of dye-contaminated wastewater. The photocatalytic degradation of dyes follows three types of mechanisms: (1) dye sensitization through charge injection, (2) indirect dye degradation through oxidation/reduction, and (3) direct photolysis of dye. Several experimental parameters like initial concentration of dyes, pH, and catalyst dosage significantly affect the photocatalytic degradation of dyes. The photocatalytic materials can be categorized into three generations. The single-component (e.g., ZnO, TiO2) and multiple component semiconductor metal oxides (e.g., ZnO-TiO2, Bi2O3-ZnO) are categorized as first-generation and second-generation photocatalysts, respectively. The photocatalysts dispersed on an inert solid substrate (e.g., Ag-Al2O3, ZnO-C) are classified as third-generation photocatalysts. Finally, we reviewed the challenges that affect the photocatalytic degradation of dyes.