A Review on Photocatalysis Used For Wastewater Treatment: Dye Degradation

Efficient removal of crystal violet dye from water using zinc ferrite-polyaniline nanocomposites

Nanomaterials are widely employed in wastewater treatment, among which nanoferrites and their composites hold significant prominence. This study adopts a green approach to synthesize zinc ferrite nanoparticles, subsequently integrating them with polyaniline (PANI) to fabricate the ZnFe2O4-PANI nanocomposite. Characterization of the prepared ZnFe2O4-PANI nanocomposite was conducted using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopic (SEM) techniques. Using Scherrer's equation, the crystallite size of the synthesized zinc ferrite nanoparticles was found to be 17.67 nm. SEM micrographs of the ZnFe2O4-PANI nanocomposite revealed that in situ polymerization of ZnFe2O4 with polyaniline transforms the amorphous surface morphology of the polymer into a homogeneous nanoparticle structure. The adsorption of crystal violet (CV) dye onto the surface of the ZnFe2O4-PANI nanocomposite depends on pH, adsorbent dosage, temperature, concentration levels and duration. The Langmuir adsorption model fitted the data well, indicating adherence to a pseudo-second-order kinetic pattern. Thermodynamic values ΔG°, ΔH° and ΔS° indicated that the adsorption process occurred spontaneously. Advantages and disadvantages of the technique have also been highlighted. Mechanism of adsorption is discussed. From the obtained results, it is evident that the ZnFe2O4-PANI nanocomposite holds promise as a sorbent for the removal of dye from wastewater.

Green route to fabrication of Semal-ZnO nanoparticles for efficient solar-driven catalysis of noxious dyes in diverse aquatic environments

This work successfully demonstrates a sustainable and environmentally friendly approach for synthesizing Semal-ZnO nanoparticles (NPs) using the aqueous leaf extract of Bombax ceiba L. These NPs exhibit an absorption peak at approximately 390 nm in the UV-visible spectrum and an energy gap (Eg) of 3.11 eV. Detailed analyses of the morphology and particle size using various spectroscopic and microscopic techniques, XRD, FE-SEM with EDS, and HR-TEM reveal crystallographic peaks attributable to the hexagonal phase, with an average crystal size of 17 nm. The Semal-ZnO NPs also exhibit a notable photocatalytic efficiency for degrading methylene blue (MB) and methyl orange (MO) under sunlight in different water samples collected from diverse natural sources, indicating that they are promising photocatalysts for environmental remediation. The photocatalytic efficiency of the biofabricated Semal-ZnO NPs is impressive, exhibiting a photodegradation rate of up to 99% for MB and 79% for MO in different water samples under exposure to sunlight. The novel phytofabricated Semal-ZnO NPs are thus a beacon of hope for the environment, with their desirable photocatalytic efficiency, pseudo-first-order kinetics, and ability to break down noxious dye pollutants in various aquatic environments.

Photochemical modification of tea waste by tungsten oxide nanoparticle as a novel, low-cost and green photocatalyst for degradation of dye pollutant

So far, many adsorbents and nanocomposites have been synthesized by different methods and used to remove or degradation of dye pollutants. Nowadays, the use of natural adsorbents and their modification with simple methods based on metal oxides are of interest to many researchers. In this study, for the first time, we report the simple and low-cost modification of tea pomace waste (TPW) with tungsten oxide (WO3) based on the photochemical method as a green, cost-effective, and biodegradable photocatalyst for the degradation of Rh B dye pollutant. The results obtained from FE-SEM, EDAX, XRD, XPS, PL, BET and UV-Vis Diffusive Reflectance (DRS) analyses confirmed the successful modification of the TPW surface with WO3 (WO3/TPW). The parameters affecting the photocatalytic behavior of WO3/TPW, including the time of photochemical modification and the type of radiation on its photocatalytic activity, were carefully optimized. WO3/TPW showed excellent photocatalytic activity compared to TPW for the degradation of Rh B dye pollutant under UV light for 30 min (94 %). Finally, the effective parameters on the value of Rh B dye degradation by WO3/TPW photocatalyst including pH, adsorbent dosage, the concentration of dye pollutant, and the kinetics of the degradation process were studied. It is expected that this type of photochemical modification method and natural WO3/TPW photocatalyst will be a promising path for the synthesis, modification, and increase of the photocatalytic performance of natural adsorbents.

Improved Synthesis of Cu2O NPs and Ascorbic Acid-Modified Derivatives for Adsorption of Brilliant Cresyl Blue: Surface and Reusability Studies

This study addresses the critical need for efficient and recyclable photocatalysts for water treatment applications by presenting a novel approach for the synthesis and characterization of copper (I) oxide (Cu2O) nanoparticles modified with ascorbic acid (Cu2O/AA). The motivation for this research stems from the increasing concern about environmental pollution caused by organic pollutants, such as Brilliant Cresyl Blue (BCB), and the necessity for sustainable solutions to mitigate this issue. Through comprehensive characterization techniques including Ultraviolet-Visible spectroscopy (UV-Vis), Fourier Transform Infrared spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), zeta potential measurements, and Brunauer-Emmett-Teller (BET) analysis, we demonstrate a significant modification to the electronic structure, enhancing the photocatalytic activity of Cu2O/AA. BET analysis revealed a mesoporous structure with a specific surface area of 2.7247 m2/g for Cu2O/AA, further emphasizing its potential for enhanced catalytic performance. The photocatalytic degradation studies showcased remarkable efficiency improvements, with degradation coefficients of 30.8% and 73.12% for Cu2O NPs and Cu2O/AA NC, respectively, within a 120 min timeframe. Additionally, recyclability experiments indicated sustained efficiency over five consecutive cycles, with both catalysts retaining crystalline integrity. These findings underscore the promising potential of Cu2O/AA nanoparticles as highly efficient and recyclable photocatalysts for the degradation of organic pollutants, offering superior performance compared to pure Cu2O NPs and addressing the pressing need for sustainable water treatment solutions.

Robust CA-GO-TiO2/PTFE Photocatalytic Membranes for the Degradation of the Azithromycin Formulation from Wastewaters

We have developed an innovative thin-film nanocomposite membrane that contains cellulose acetate (CA) with small amounts of TiO2-decorated graphene oxide (GO) (ranging from 0.5 wt.% to 2 wt.%) sandwiched between two polytetrafluoroethylene (PTFE)-like thin films. The PTFE-like films succeeded in maintaining the bulk porosity of the support while increasing the thermal and chemical robustness of the membrane and boosting the catalytic activity of TiO2 nanoparticles. The membranes exhibited a specific chemical composition and bonding, with predominant carbon-oxygen bonds from CA and GO in the bulk, and carbon-fluorine bonds on their PTFE-like coated sides. We have also tested the membranes' photocatalytic activities on azithromycin-containing wastewaters, demonstrating excellent efficiency with more than 80% degradation for 2 wt.% TiO2-decorated GO in the CA-GO-TiO2/PTFE-like membranes. The degradation of the azithromycin formulation occurs in two steps, with reaction rates being correlated to the amount of GO-TiO2 in the membranes.

Enhanced photocatalytic efficiency of porous ZnO coral-like nanoplates for organic dye degradation

ZnO nanomaterials have been extensively used as photocatalysts for the removal of pollutants in aqueous environments. This study explores the enhanced photocatalytic performance of porous ZnO coral-like nanoplates synthesized via a one-pot wet-chemical method and subsequent annealing treatment. Characterization through scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, photoluminescence (PL) spectroscopy, and Brunauer-Emmett-Teller (BET) measurements confirmed the nanoplates' porous structure, single-crystal structure, 100 nm thickness, and 80 nm pore size. These unique structural characteristics of the ZnO coral-like nanoplates enabled effective photodegradation of the organic dye rhodamine B (RhB) under visible light irradiation. Under simulated sunlight, the ZnO photocatalyst exhibited exceptional performance, achieving a 97.3% removal rate of RhB after 210 minutes of irradiation. The prepared ZnO photocatalyst also showed remarkable photostability and regeneration capability for RhB photodegradation with a decreased efficiency of less than 15% after eight testing cycles. The potential mechanism of the ZnO photocatalyst toward RhB degradation was also studied and is discussed in detail.

CdIn2Se4@chitosan heterojunction nanocomposite with ultrahigh photocatalytic activity under sunlight driven photodegradation of organic pollutants

This research focused on synthesizing a CdIn2Se4@Ch nanocomposite by doping CdIn2Se4 into chitosan using a photolysis assisted ultrasonic process. The aim was to enhance the photodegradation efficiency of ofloxacin and 2,4-dichlorophenoxyacetic acid under sunlight. The synthesized CdIn2Se4@Ch nanocomposite was investigated via different techniques, including XRD, XPS, FTIR, TEM, DSC, TGA, UV-Vis and PL. The study also investigated the influence of various reaction parameters, including the effects of inorganic and organic ions. The synthesized nanocomposite demonstrated exceptional efficiency, achieving 86 % and 95 % removal rates, with corresponding rate constants of 0.025 and 0.047 min-1. This performance surpasses that of CdIn2Se4 by approximately 1.35 and 2.25 times, respectively. The values of COD were decreased to 78 and 86 % for ofloxacin and 2,4-dichlorophenoxyacetic, while the TOC values decreased to 71 and 84 %, respectively, from their premier values. The improvement in performance is associated with the introduction of CdIn2Se4 into chitosan, resulting in the self-integration of Cd into the catalyst. This creates a localized accumulation point for electrons, enhancing the efficiency of charge separation and further reducing the surface charge of chitosan. Experimental evidence suggests that superoxide and hydroxyl radicals play a significant role in the photodegradation of pollutants. Additionally, the nanocomposite exhibits excellent stability and can be reused up to five times, indicating remarkable stability and reusability of the developed photocatalyst.

Rational design of CdS-enwrapped polypyrrole nanoparticles for wastewater treatment: removal of hazardous pollutants in aqueous solutions

The modern world requires a chemical industry that can run at low production costs while producing high-quality products with minimal environmental impact. The development of environmentally friendly, cost-effective, and efficient wastewater treatment materials remains a major problem for the sustainable approach. We prepared nanoscale cadmium sulfide (CdS)-enwrapped polypyrrole (PPy) polymer composites for degradation of organic pollutants. The prepared CdS@PPy nanocomposites were characterized by powder X-ray diffraction, scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible (UV) absorption spectroscopy, indicating proper intercalation between CdS and PPy. Consequently, the catalytic efficiency of the synthesized hybrid nanocomposites was analyzed through the degradation of methylene blue (MB) and rhodamine B (Rh B) under visible light irradiation. The measured degradation efficiency of the dye solutions under the photolysis process is about 18% and 23% for MB and Rh B dye, respectively. Furthermore, the recycle test result concludes that the CdS@PPy composite exhibits 91% and 89% of MB and Rh B dye degradation efficiency even at the 4th cycle, respectively. The positive synergistic impact of CdS and PPy may be the result of effective photocatalytic degradation of MB and RhB.

Photocatalytic Activity of BaAl2O4 for Water Purification

Degradation of dyes under natural light sources is one of the most active research areas in basic science for greener technology. In this context, the photocatalytic activity of semiconductors has received massive attention in solving water treatment-related issues as these possess enormous potential for degrading organic impurities. Here, we report that barium aluminate (BaAl2O4, BAO), which has been extensively studied for photoluminescence applications, is found to be a highly potent candidate for photocatalytic activities. We have explored the degradation of dyes (meant for water purification) by using the photocatalytic properties of pure and Dy- and Yb-codoped BAO. Crystal structure, electron microscopy, and Raman analysis of the autocombustion-synthesized pure and codoped BAO samples revealed significant morphological changes such as increased particle size and stabilization of rod-like structures. UV-vis absorbance measurements confirm the presence of multiple bandgaps in the BAO samples, which is substantiated by X-ray absorption spectroscopy measurements. Photocatalytic degradation studies of methylene blue (MB) dye (with different catalyst concentrations, dopings, and MB dye concentrations) have been carried out by using BAO. The kinetics of the photocatalytic degradation measurements has been explained by the Boltzmann distribution function, and the fastest (in less than 40 min), with more than 99% degradation of MB impurity, is reported here for the first time in BAO compounds. Synthesized BAO samples show excellent cyclic stability, which is essential for their potential applications in environmental remediation. The trade-off between the enhancement of surface area and increased particle size is considered the key parameter for controlling the photocatalytic performance of the BAO catalyst after Dy and Yb codopings.

The Solvent Role for the Decomposition of Paracetamol in Distilled and Drinking Water by Pure and Ag-Modified TiO2 Sol-Gel Powders

In this study, pure TiO2 gels were synthesized by applying the sol-gel method, using Ti(IV) butoxide with the addition of two different solvents, namely ethylene glycol (EG) and isopropanol (isop), with only air moisture present. It was established using XRD that the gel prepared with the addition of EG was amorphous even at 400 °C, while the other gel was amorphous up to 300 °C. It was found that TiO2 (anatase) had a dominant crystalline phase during heating to 600 °C, while at 700 °C, TiO2 (rutile) appeared. The as-obtained powdered materials were annealed at 500 °C and subsequently underwent photocatalytic tests with paracetamol. Additionally, the TiO2 samples were modified with Ag+ co-catalysts (10-2 M), using photofixation by UV illumination. The photocatalytic activity of the Ag-modified powders was also tested in the photodegradation of a commonly used paracetamol in aqueous solution under UV light illumination. The obtained data exhibited that the annealed samples had better photocatalytic efficiency and decomposed paracetamol faster in comparison to the non-annealed sol-gel powders. The highest degradation efficiency was observed for the TBT/isop/Ag material, with degradation efficiencies average values of 65.59% and 75.61% paracetamol achieved after the third cycle of photocatalytic treatment. The co-catalytically modified powders had higher photocatalytic efficiency in comparison to the pure nanosized powders. Moreover, the sol-gel powders of TBT/EG, TBT/EG/Ag (10-2 M), TBT/isop, and TBT/isop/Ag (10-2 M) demonstrated the ability to retain their photocatalytic activity even after three cycles of use, suggesting that they could find practical use in the treatment of pharmaceutical wastewater. The observed photocatalytic efficiency and positive impact of silver make the prepared powders a desirable choice for pharmaceutical drug degradation, helping to promote environmentally friendly and effective wastewater treatment technology.

Vacancy induced enhanced photocatalytic activity of nitrogen doped CuO NPs synthesized by Co-precipitation method

The chemical co-precipitation method, an effective approach in the synthesis of nanomaterials, was used to synthesize CuO nanoparticles (NPs). Structural and morphological modification of undoped and nitrogen (N) doped CuO nanoparticles were studied thoroughly using X-ray diffraction (XRD), FT-IR and field emission scanning electron microscope (FE SEM). Doping effect on defects was investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL) spectroscopy. Thus, the effect of doping on crystallinity, crystallite size, strain induced in lattice, defects and electron-hole recombination rate were investigated. Optical band gap was calculated using Kubelka-Munk function from the diffuse reflectance spectra (DRS) obtained using ultraviolet visible (UV-Vis) spectroscopy. Finally, photocatalytic performance was studied from rhodamine B (Rh B) degradation and reaction kinetics were analyzed. Maximum degradation efficiency was obtained for 1.0 mol% N doped CuO NPs which also exhibited minimum band gap and lowest electron-hole recombination rate. For the optimum doping concentration, nitrogen was found to create oxygen vacancies while substituting oxygen in the lattice, and thus reduce electron-hole recombination rate and increase photocatalytic degradation rate effectively.

Industrial-scale feasibility for textile wastewater treatment via Photocatalysis-adsorption technology using black sand and UV lamp

Dye-contaminated wastewater is a major environmental problem that requires effective and affordable treatment methods. This study investigates an innovative approach using black sand filtration assisted by UV light to remove methylene blue (MB) dye from wastewater. The motivation is to develop a sustainable low-cost wastewater treatment technology. Black sand's composition of iron oxide and other metal oxides enables the adsorption and photocatalytic degradation of dyes. The effects of operating parameters, including pH, bed height, flow rate, and initial MB concentration, were examined using a fixed-bed column system. The maximum adsorption capacity was 562.43 mg g-1 at optimal pH 10, 15 cm bed height, 50 ppm MB, and 53.33 mL min-1 flow rate. Mathematical models effectively described the experimental breakthrough curves. For real textile wastewater, black sand with a UV lamp removed 50.40% COD, 73.68% TDS, 43.82% TSS, and 98.57% conductivity, significantly outperforming filtration without UV assistance. Characterization via XRD, XRF, FTIR, zeta potential, and SEM revealed black sand's photocatalytic properties and mechanism of MB adsorption. The findings demonstrate black sand filtration plus UV irradiation as a feasible, sustainable technology for removing dyes and organics from wastewater. This method has promise for the scale-up treatment of textiles and other industrial effluents.

Advancing sustainable water treatment strategies: harnessing magnetite-based photocatalysts and techno-economic analysis for enhanced wastewater management in the context of SDGs

Herein, we explore the holistic integration of magnetite-based photocatalysts and techno-economic analysis (TEA) as a sustainable approach in wastewater treatment aligned with the Sustainable Development Goals (SDGs). While considerable attention has been devoted to photocatalytic dye degradation, the nexus between these processes and techno-economic considerations remains relatively unexplored. The review comprehensively examines the fundamental characteristics of magnetite-based photocatalysts, encompassing synthesis methods, composition, and unique properties. It investigates their efficacy in photocatalytic degradation, addressing homogeneous and heterogeneous aspects while discussing strategies to optimize photodegradation efficiency, including curbing electron-hole recombination and mitigating scavenging effects and interference by ions and humic acid. Moreover, the management aspects of magnetite-based photocatalysts are examined, focusing on their reusability and regeneration post-dye removal, along with the potential for reusing treated wastewater in relevant industrial applications. From a techno-economic perspective, the study evaluates the financial feasibility of deploying magnetite-based photocatalysts in wastewater treatment, correlating reduced pollution and the marketing of treated water with social, economic, and environmental objectives. By advocating the integration of magnetite-based photocatalysts and TEA, this paper contributes insights into scalable and profitable sustainable wastewater treatment practices. It underscores the alignment of these practices with SDGs, emphasizing a comprehensive and holistic approach to managing wastewater in ways that meet environmental, economic, and societal objectives.

Green synthesis of CuO/Fe2O3/ZnO ternary composite photocatalyst using grape extract for enhanced photodegradation of environmental organic pollutant

This research delves into fabricating a CuO/Fe2O3/ZnO (CFZ) ternary composite photocatalyst, employing grape extract for its eco-conscious synthesis. The method intricately integrates copper acetate, ferric nitrate, and zinc acetate as precursor compounds, harmonizing them with grape extract serving as a green reducing agent. Meticulous microwave treatment and controlled calcination orchestrate the nuanced formation of the desired composite material. The extensive characterization, involving X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDXS), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), and photoluminescence (PL) spectroscopy, unveils an array of favorable physical, chemical, and optical attributes conducive to proficient photocatalysis. Notably, CFZ-10mc showcases a narrower bandgap of 1.91 eV, which is pivotal for bolstering electron-hole separation, thereby enhancing its photocatalytic efficacy. Assessment of CFZ's performance in degrading Rhodamine B (RhB) under UV irradiation highlights an impressive 88.8% degradation efficiency within 120 min, accompanied by a kinetic rate constant of 1.81 × 10-2 min-1. Deliberation upon crucial parameters, including photocatalyst dosage, initial RhB pH, and reactor energy consumption, introduces the electrical energy per order (EEO) as a notable efficiency metric. CFZ manifests a substantial reduction in operational costs, estimated to be 18.10 times lower than conventional photolysis, signifying an EEO value of 509.17 kWh m-3 order-1. Optimal operational conditions propose a photocatalyst content of 1.5 g L-1 and an initial RhB pH of 7, fostering the prevalence of the primary active species, •OH. These findings illuminate CFZ's potential in mitigating organic pollutants, underlining its pivotal role in sustainable water remediation. Additionally, practical implementation guidelines for leveraging CFZ's capabilities in real-world applications are presented with care and consideration.

Advanced oxidation and biological integrated processes for pharmaceutical wastewater treatment: A review

The stress of pharmaceutical and personal care products (PPCPs) discharging to water bodies and the environment due to increased industrialization has reduced the availability of clean water. This poses a potential health hazard to animals and human life because water contamination is a great issue to the climate, plants, humans, and aquatic habitats. Pharmaceutical compounds are quantified in concentrations ranging from ng/Lto μg/L in aquatic environments worldwide. According to (Alsubih et al., 2022), the concentrations of carbamazepine, sulfamethoxazole, Lutvastatin, ciprofloxacin, and lorazepam were 616-906 ng/L, 16,532-21635 ng/L, 694-2068 ng/L, 734-1178 ng/L, and 2742-3775 ng/L respectively. Protecting and preserving our environment must be well-driven by all sectors to sustain development. Various methods have been utilized to eliminate the emerging pollutants, such as adsorption and biological and advanced oxidation processes. These methods have their benefits and drawbacks in the removal of pharmaceuticals. Successful wastewater treatment can save the water bodies; integrating green initiatives into the main purposes of actor firms, combined with continually periodic awareness of the current and potential implications of environmental/water pollution, will play a major role in water conservation. This article reviews key publications on the adsorption, biological, and advanced oxidation processes used to remove pharmaceutical products from the aquatic environment. It also sheds light on the pharmaceutical adsorption capability of adsorption, biological and advanced oxidation methods, and their efficacy in pharmaceutical concentration removal. A research gap has been identified for researchers to explore in order to eliminate the problem associated with pharmaceutical wastes. Therefore, future study should focus on combining advanced oxidation and adsorption processes for an excellent way to eliminate pharmaceutical products, even at low concentrations. Biological processes should focus on ideal circumstances and microbial processes that enable the simultaneous removal of pharmaceutical compounds and the effects of diverse environments on removal efficiency.

Adsorptive Elimination of a Cationic Dye and a Hg (II)-Containing Antiseptic from Simulated Wastewater Using a Metal Organic Framework

Several types of pollutants have acute adverse effects on living bodies, and the effective removal of these pollutants remains a challenge. Safranin O (a biological dye) and merbromin (a topical mercury-containing antiseptic) are considered organic pollutants, and there are only a few reports on their removal. Synthesized and well-characterized (through PXRD, FTIR, FESEM, and EDS analysis) MOF-5 was used for the first time in the removal of safranin O and merbromin from simulated wastewater and real wastewater. In both cases, MOF-5 effectively removed contaminants. We found that in simulated wastewater, the highest efficiency of removal of safranin O was 53.27% (for 15 mg/L) at pH 10, and for merbromin, it was 41.49% (for 25 mg/L) at pH 6. In the case of real wastewater containing natural ions (Na+, K+, F-, Cl-, SO42-, PO43-, Mg2+, and Ca2+) and other molecules, the removal efficiencies of these two dyes decreased (34.00% and 26.28% for safranin O and merbromin, respectively) because of the presence of other ions and molecules. A plausible mechanism for the removal of these pollutants using MOF-5 was proposed.

Development of stable S-scheme 2D-2D g-C3N4/CdS nanoheterojunction arrays for enhanced visible light photomineralisation of nitrophenol priority water pollutants

The investigation focused on creating and studying a new 2D-2D S-scheme CdS/g-C3N4 heterojunction photocatalyst. Various techniques examined its structure, composition, and optical properties. This included XRD, XPS, EDS, SEM, TEM, HRTEM, DRS, and PL. The heterojunction showed a reduced charge recombination rate and more excellent stability, helping to lessen photocorrosion. This was due to photogenerated holes moving more quickly out of the CdS valence band. The interface between g-C3N4 and CdS favored a synergistic charge transfer. A suitable flat band potential measurement supported enhanced reactive oxygen species (ROS) generation in degrading 4-nitrophenol and 2-nitrophenol. This resulted in remarkable degradation efficiency of up to 99% and mineralization of up to 79%. The findings highlighted the practical design of the new 2D-2D S-scheme CdS/g-C3N4 heterojunction photocatalyst and its potential application in various energy and environmental settings, such as pollutant removal, hydrogen production, and CO2 conversion.

Recent advances in visible light-activated photocatalysts for degradation of dyes: A comprehensive review

The rapid development in industrialization and urbanization coupled with an ever-increasing world population has caused a tremendous increase in contamination of water resources globally. Synthetic dyes have emerged as a major contributor to environmental pollution due to their release in large quantities into the environment, especially owing to their high demand in textile, cosmetics, clothing, food, paper, rubber, printing, and plastic industries. Photocatalytic treatment technology has gained immense research attention for dye contaminated wastewater treatment due to its environment-friendliness, ability to completely degrade dye molecules using light irradiation, high efficiency, and no generation of secondary waste. Photocatalytic technology is evolving rapidly, and the foremost goal is to synthesize highly efficient photocatalysts with solar energy harvesting abilities. The current review provides a comprehensive overview of the most recent advances in highly efficient visible light-activated photocatalysts for dye degradation, including methods of synthesis, strategies for improving photocatalytic activity, regeneration and their performance in real industrial effluent. The influence of various operational parameters on photocatalytic activity are critically evaluated in this article. Finally, this review briefly discusses the current challenges and prospects of visible-light driven photocatalysts. This review serves as a convenient and comprehensive resource for comparing and studying the fundamentals and recent advancements in visible light photocatalysts and will facilitate further research in this direction.

High-performance photocatalytic reduction of Cr(VI) using a retrievable Fe-doped WO3/SiO2 heterostructure

The enhancement of the photocatalytic performance of pristine WO3 was systematically adjusted due to its fast recombination rate and low reduction potential. A designed heterostructure photocatalyst was necessarily synthesised by Fe3+ metal ions doping into WO3 structure with and composition modification. In this study, we synthesised a retrievable Fe-doped WO3/SiO2 heterostructure using a surfactant-assisted hydrothermal method. This heterostructure was then employed as an effective photocatalyst for the removal of Cr(VI) under visible light irradiation. Enlarged photocatalytic reduction was observed over a synergetic 7.5 mol% Fe-doped WO3/SiO2-20 nanocomposite, resulting in dramatically increased activity compared with undoped WO3 and SiO2 nanomaterials under visible light illumination within 90 min. The presence of 7.5 mol% Fe3+ ion dopant in WO3 optimised electron-hole recombination, consequently reducing WO3 photocorrosion. After adding SiO2 nanoparticles, the binary WO3-SiO2 nanocomposite played roles as both adsorbent and photocatalyst to increase specific surface area. Thus, the 7.5 mol% Fe-doped WO3/SiO2-20 nanocomposite catalyst had more active sites on the surface of catalyst, and enhanced photocatalytic reduction was significantly achieved. The results showed 91.1% photocatalytic reduction over the optimum photocatalyst, with a photoreduction kinetic rate of 21.1 × 10-3 min-1, which was approximately four times faster than pristine WO3. Therefore, the superior optimal photocatalyst demonstrated reusability, with activities decreasing by only 9.8% after five cycles. The high photocatalytic performance and excellent stability of our photocatalyst indicate great potential for water pollution treatments.

Photocatalytic Activity and Self-Cleaning Effect of Coating Mortars with TiO2 Added: Practical Cases in Warm Sub-Humid Climates

In this study, the photocatalytic activity of coating mortars with synthetized and commercial TiO2 nanoparticles added has been evaluated at 2, 3 and 5% by weight of cement by calculating the degradation efficiency of methyl orange and red wine dyes exposed to both visible-light and UV radiation; also, the self-cleaning effect of coatings exposed to weather conditions (warm sub-humid climate) was assessed. TiO2 nanoparticles were synthesized via the sol-gel method to a low synthesis temperature and characterized via X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results show synthesized TiO2 particles in anatase phase with a crystallite size of 14.69 nm, and hemispherical particles with sizes of submicron order. The addition percentage with the best performance in the coating mortars was 3%, with both commercial and synthesized TiO2; however, coating mortars with synthesized TiO2 exhibited the highest degradation efficiency for both dyes when they were exposed to visible light, while mortars with commercial TiO2 exhibited the highest degradation efficiency when exposed to UV radiation. In addition, in coating mortars with synthesized TiO2, the self-cleaning effect was evident from the beginning of exposure to weather, reaching the largest dye-free surface at the end of exposure. The compressive strength increased significantly in mortars with TiO2 addition.

Green Synthesis of TiO2 Using Impatiens rothii Hook.f. Leaf Extract for Efficient Removal of Methylene Blue Dye

In this work, TiO2 nanoparticles (NPs) were effectively synthesized by a green method using the Impatiens rothii Hook.f. leaf (IL) extract as a capping and reducing agent. The as-synthesized TiO2 NPs were characterized by different characterization methods such as the Brunauer-Emmett-Teller (BET) analysis, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), diffused reflectance spectroscopy (DRS), and X-ray diffraction (XRD) and Raman spectroscopy. The specific surface area from BET analysis was found to be 65 m2/g. The average crystallite size from XRD analysis and average particle size from SEM analysis were found to be ∼11 and ∼25 nm, respectively. The Raman spectroscopy and XRD results showed that the biosynthesized (IL-TiO2) nanoparticles were purely anatase phase. XPS analysis illustrated the formation of Titania with an oxidation state of +4. The DRS study showcased that a blue-shifted intense absorption peak of IL-TiO2 (3.39 eV) compared to the bulk material reported in the literature (3.2 eV). HRTEM micrograph showed the presence of grain boundary with d spacings of 0.352, 0.245, and 0.190, which correspond to the lattice planes of (101), (004), and (200), respectively. From the EDX analysis, the weight percents of titanium and oxygen were found to be 54.33 and 45.67%, respectively. The photoinduced degradation of methylene blue (MB) dye was investigated in the presence of biosynthesized IL-TiO2 NPs photocatalyst. The effect of parameters like catalyst dosage (30 mg/L), initial concentration of MB (15 ppm), pH (10.5), and contact time (100 min) on the removal efficiency was optimized. The maximum photodegradation efficiency under the optimized conditions was found to be 98%.

Effective Reinforcement of Visible Light Photocatalytic and Gas Sensing Characteristics of Nanocrystalline TiO2: Gd-Based Nb and Mo Dopants

Efficient compositions for the selective detection of ethanol gas and the removal of organic contaminants were realized by codoping of (Gd, Nb) and (Gd, Mo) ions into TiO2. TiO2, Ti0.96Gd0.01Nb0.03O2, and Ti0.96Gd0.01Mo0.03O2 samples were prepared by a coprecipitation method. For all compositions, a crystalline anatase phase of TiO2 was detected. Compared to pure TiO2, the absorption edges of Ti0.96Gd0.01Nb0.03O2 and Ti0.96Gd0.01Mo0.03O2 samples were red-shifted, further broadening towards visible light. The morphological studies demonstrate that the grains of TiO2 were more refined after (Gd, Nb) and (Gd, Mo) codoping. The photocatalytic efficiency of the Ti0.96Gd0.01Mo0.03O2 catalyst for degrading 20 mg/L reactive yellow 145, brilliant green, and amoxicillin was 98, 95, and 93% in 90 min, respectively. The reusability experiments indicate that the Ti0.96Gd0.01Mo0.03O2 catalyst had high stability during reuse. The high photocatalytic activity of the Ti0.96Gd0.01Mo0.03O2 catalyst was correlated to the broad visible-light absorption and effective separation of electron-hole pairs by Gd3+ and Mo6+ cations. The gas sensing characteristic is reflected by the high sensitivity of the Ti0.96Gd0.01Nb0.03O2 sensor to ethanol gas in the presence of different gases at 275 °C. The obtained results indicated that the (Gd, Mo) mixture could more effectively induce the photocatalytic properties of TiO2 while (Gd, Nb) dopants were the best for reinforcing its sensing characteristics.

Bi/BiOI/carbon quantum dots nano-sheets with superior photocatalysis

A new photocatalyst of Bi/BiOI/Carbon quantum dots (CQDs) was synthesized via a simple method. Photocatalytic performance of Bi/BiOI/CQDs was evaluated by photodegradation of RhB. Experiment indicated that the introduction of CQDs could improve the photocatalysis activity of BiOI obviously. Moreover, there is a optimum percentage of CQDs. In this photocatalytic system, the enhanced photoactivity was mainly attributed to the heterojunction interface between CQDs and BiOI, as well as the enhanced light harvesting for the appropriate CQDs introduction. The radicals trapping experiments revealed that O2˙-, ˙OH and h+ were the main active species during the photocatalysis process.

O, Asma K.A.A A, Eida Mohammad A, Ali Khan MW. Optimization of Pseudomonas aeruginosa isolated for bioremediation from Ha'il region of Saudi Arabia

Majority of dyes are toxic to all the living organisms and inherently resistant to microbial degradation. Hence, decolorization and degradation of textile dye methyl red were evaluated using isolated bacterial strain Pseudomonas aeruginosa (P. aeruginosa). Methyl red dye decolorization by P. aeruginosa with respect to various parameters was optimized. Data shows that maximum possible decolorization was seen at 50 ppm dye concentration, 1400 mg/l glucose concentration, 700 mg/l sodium chloride (NaCl) concentration, pH 9, temperature 38°C, 1000 mg/l urea concentration P. aeruginosa AM-1 strain. The highest percent (91.1%) of bioremediation was achieved at 40 ppm dye concentration in Allium cepa test. These findings suggest P. aeruginosa strain (AM-1) has the potential to be used in the biological treatment of highly toxic dye which is main constituent of dyeing mill effluents due to its high decolorization activity with simple conditions. Strain AW-1 strain also has potential to bioremediate other wastewater containing methyl red dye.

Harnessing Bio-Immobilized ZnO/CNT/Chitosan Ternary Composite Fabric for Enhanced Photodegradation of a Commercial Reactive Dye

Growing demand for sustainable wastewater treatment drives interest in advanced photocatalytic materials. Immobilized photocatalysts hold potential for addressing industrial wastewater organic pollutants, offering substantial surface area, agglomeration prevention, and easy removal. In this study, we successfully immobilized ZnO and carbon nanotubes onto a textile substrate through bilateral esterification and explored their effectiveness as a potent photocatalyst for degrading of commercial textile colorant reactive blue 4 (RB-4) colorant. Findings demonstrated significant improvements in photocatalytic performance upon integrating ZnO and CNTs into the fabric, coupled with chitosan immobilization. The immobilization process of ZnO and CNTs onto the substrate was elucidated through a proposed reaction mechanism, while the appearance of carbonyl peaks at 1719.2 cm-1 in the composite fabric further confirmed bilateral esterification. The as-developed immobilized nano-catalyst exhibited remarkable photocatalytic efficiency with an impressive 93.54% color degradation of RB-4. This innovative approach underscores the immense potential of the ternary immobilized (ZnO/fCNT/chitosan) composite fabric for efficient photocatalytic degradation in textile coloration processes. Exploring the early-stage development of immobilized photocatalysts contributes to safer and more eco-friendly practices, addressing pressing environmental challenges effectively.