Visible Light-driven Photocatalyst Research Articles

Enhanced photocatalytic properties of visible light-responsive ZnS/FeWO4 composites for degradation of tetracycline and Escherichia coli inactivation

The development of highly efficient visible light-driven photocatalysts for the removal of diverse pollutants is crucial for wastewater treatment. In this study, a series of ZnS/FeWO4 composites were prepared via a facile hydrothermal method combined with in situ calcination. The photocatalytic properties of the resulting ZnS/FeWO4 composites were evaluated for the degradation of tetracycline (TC) and the inactivation of Escherichia coli (E. coli), considering the environmental persistence and potential carcinogenicity of these pollutants. The optimized ZnS/FeWO4-1:2 photocatalyst demonstrated outstanding activity in the degradation of TC, achieving a degradation efficiency of 91.7 % (k = 0.0230 min⁻¹), which is significantly higher than that of pristine FeWO4 (67.5 %) and ZnS (53.4 %). Kinetic studies confirmed that the degradation process followed a pseudo-first-order kinetic model. Furthermore, the as-prepared photocatalyst exhibited excellent stability after five cycles. Additionally, the ZnS/FeWO4-1:2 composites showed potent inactivation efficiency, achieving approximately 96 % inactivation of 7.0 × 106 CFU/mL E. coli. These superior photocatalytic capabilities are attributed to the effective integration of FeWO4 with ZnS and the formation of optimal heterojunction structures. This incorporation leads to a delay in electron-hole recombination within the nanocomposites. Moreover, the enhancement mechanisms of photocatalytic TC degradation over ZnS/FeWO4-1:2 composites were discussed. The findings of this study provide valuable insights into the multi-application potential of ZnS/FeWO4-1:2 composites and demonstrate an effective approach to designing photocatalysts for wastewater treatment.

Enhanced photocatalytic degradation activity of titanium dioxide by adsorbing aromatic amines through N-bonding

Narrowing the wide band gap of TiO2 (∼3.2 eV) to enhance its visible light efficiency is crucial for advancing photocatalytic degradation of organic pollutants in industrial wastewater. In this study, we achieved band gap reduction and slowed recombination rates by adsorbing some aromatic amines, like aniline and its electron-donating derivatives, onto TiO2. The predominantly present N-bonded amine species reduced the band gap and decelerated charge carriers’ recombination, enhancing photocatalytic degradation under visible light. In contrast, the amine with electron-withdrawing group is adsorbed as only H-bonded species, which showed no improvement in photocatalytic activity, performing similarly to pristine TiO2. This surface modification strategy offers potential for creating visible light-driven photocatalysts for effective degradation of organic pollutants in water.

Designing A Visible Light Driven TiO2-Based Photocatalyst by Doping and Co-Doping with Niobium (Nb) and Boron (B)

Water pollution has emerged as a significant worldwide issue, with organic pollutants being a key contributor. Titanium dioxide (TiO2) has demonstrated promising photocatalytic performance in removing organic pollutants under ultraviolet (UV) irradiation. However, the wide band gap (3.2 eV) of TiO2 results in low absorption capacity of visible light, hindering its overall efficiency in degrading organic pollutants. To address the limitation, this research aimed to synthesize visible light-driven TiO2 photocatalyst with different polymorphs (anatase and rutile) and investigate the effect of various doping combination (Nb, B and Nb,B) and concentrations (0.25, 0.50, 0.75 and 1.00 mol%) on the photodegradation efficiency towards methylene blue (MB) dye solution. Anatase phase was obtained when TiO2-based nanopowders were calcined at 400 °C, while the rutile phase was formed at 900 °C based on XRD analyses. Additionally, the morphology analyses revealed that the particle size of anatase is much smaller than that of rutile. The presence of dopants further reduced the particle size of both anatase and rutile phases. Based on UV-Vis absorbance spectra analyses, the anatase Nb,B-TiO2 with 0.50 mol% of dopant concentration exhibited the best photocatalytic performance towards MB. Moreover, the anatse phase of 0.50 mol% Nb,B-TiO2 showed the narrowest band gap of 2.74 eV compared to the TiO2 (3.4 eV), representing a reduction of 19.41 %, according to UV-Vis analyses. These outcomes suggest the potential application of anatase phase of 0.50 mol% Nb,B-TiO2 in treating organic pollutants in wastewater under visible light conditions in future. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Standalone Highly Efficient Graphene Oxide as an Emerging Visible Light-Driven Photocatalyst and Recyclable Adsorbent for the Sustainable Removal of Organic Pollutants.

Carbon-based nanostructures are promising eco-friendly multifunctional nanomaterials because of their tunable surface and optoelectronic properties for a variety of energy and environmental applications. The present study focuses on the synthesis of graphene oxide (GO) with particular emphasis on engineering its surface and optical properties for making it an excellent adsorbent as well as a visible light-active photocatalyst. It was achieved by modifying the improved Hummers method through optimizing the synthesis parameters involved in the oxidation process. This controlled synthesis allows for systematic tailoring of structural, optical, and surface functionality, leading to improved adsorption and photocatalytic properties for the sustainable removal of organic pollutants in water treatment. Several spectroscopic and microscopic characterization techniques, such as XRD, SEM, Raman, UV-visible, FTIR, TEM, XPS, BET, etc. were employed to analyze the degree of oxidation, surface chemistry/functionalization, morphological, optical, and structural properties of the synthesized GO nanostructures. The analyses showed excellent surface functionality with surface active sites for better adsorptive removal and a tunable band gap from 2.51 to 2.76 eV exhibiting excellent natural sunlight activity (>99%) for photocatalytic removal of the organic pollutant. Various adsorption isotherms have been studied with excellent adsorption capability (Qmax = 454.54 mg/g) as compared to the literature. The study introduces GO both as a proficient stand-alone (sole) nanoadsorbent as well as a nanophotocatalyst for the efficient removal of organic dye pollutants in water treatment. Additionally, the article highlights the sustainable solar light-induced green chemistry aspects of GO as an excellent recyclable adsorbent as a result of its self-cleaning ability under natural sunlight, demonstrating its potential in real eco-friendly environmental and practical applications.

Visible light- and dark-driven degradation of palm oil mill effluent (POME) over g-C3N4 and photo-rechargeable WO3.

The investigations of real industrial wastewater, such as palm oil mill effluent (POME), as a recalcitrant pollutant remain a subject of global water pollution concern. Thus, this work introduced the preparation and modification of g-C3N4 and WO3 at optimum calcination temperature, where they were used as potent visible light-driven photocatalysts in the degradation of POME under visible light irradiation. Herein, g-C3N4-derived melamine and WO3 photocatalyst were obtained at different calcination temperatures in order to tune their light absorption ability and optoelectronics properties. Both photocatalysts were proven to have their distinct phases, crystallinity levels, and elements with increasing temperature, as demonstrated by the ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) results. Significantly, g-C3N4 (580°C) and WO3 (450°C) unitary photocatalysts exhibited the highest removal efficiency of POME without dilution due to good crystallinity, extended light absorption, high separation, and less recombination efficiency of electron-hole pairs. Furthermore, surprisingly, the superior energy storage photocatalytic performance with outstanding stability by WO3 achieved an approximately 10% increment during darkness, compared with g-C3N4 under visible light irradiation. Moreover, it has been proven that the WO3 and g-C3N4 photocatalysts are desirable photocatalysts for various pollutant degradations, with excellent visible-light utilization and favorable energy storage application.

Visible Light-Driven SnIn4S8 Photocatalyst Decorated on Polyurethane-Impregnated Microfiber Non-Woven Fabric for Pollutant Degradation.

In recent years, polyurethane has drawn great attention because of its many advantages in physical and chemical performance. In this work, firstly, polyurethane was impregnated in a non-woven fabric (NWF). Then, polyurethane-impregnated NWF was coagulated utilizing a wet phase inversion. Finally, after alkali treatment, microfiber non-woven fabrics with a porous polyurethane matrix (PNWF) were fabricated and used as substrates. SnIn4S8 (SIS) prepared by a microwave-assisted method was used as a photocatalyst and a novel SIS/PNWF substrate with multiple uses and highly efficient catalytic degradation ability under visible light was successfully fabricated. The surface morphology, chemical and crystal structures, optical performance, and wettability of SIS/PNWF substrates were observed. Subsequently, the photocatalytic performance of SIS/PNWF substrates was investigated by the decomposition of rhodamine B (RhB) under visible light irradiation. Compared with SIS/PNWF-2% (2%, the weight ratio of SIS and PNWF, same below), SIS/PNWF-5% as well as SIS/PNWF-15%, SIS/PNWF-10% substrates exhibited superior photocatalytic efficiency of 97% in 2 h. This may be due to the superior photocatalytic performance of SIS and the inherent hierarchical porous structure of PNWF substrates. Additionally, the hydrophobicity of SIS/PNWF substrates can enable them to float on the solution and further be applied on an open-water surface. Furthermore, tensile strength and recycle experiments demonstrated that SIS/PNWF substrates possessed superior mechanical strength and excellent recycle stability. This work provides a facile and efficient pathway to prepare SIS/PNWF substrates for the degradation of organic pollutants with enhanced catalytic efficiency.

Rational design of 2D Janus P3m1 M2N3 (M = Cu, Zr, and Hf) and their surface-functionalized derivatives: ferromagnetic, piezoelectric, and photocatalytic properties.

In this study, first-principles calculations were employed to rationally design two-dimensional (2D) Janus transition metal nitrides of P3m1 M2N3 phases, where M is a d-block element (Sc-Zn, Y-Cd, Hf-Hg). Among the 29 examined 2D M2N3, three 2D phases, namely P3m1 Cu2N3, Zr2N3, and Hf2N3, exhibit excellent thermodynamic, dynamic, mechanical, and thermal stabilities. These novel Janus 2D materials exhibit ferromagnetic metallic and half-metallic behavior. The related 2D Janus surface-functionalized derivatives, Cu2N3H, Cu2N3F, Cu2N3Cl, Zr2N3H, Hf2N3H, and Hf2N3F, are all dynamically stable. The 2D Janus P3m1 phases of Zr2N3H, Hf2N3H, and Hf2N3F, all with M in the +IV oxidation state, act as semiconductors in the visible region, with energy band gaps of 2.26-2.70 eV at the HSE06 level of theory. On the other hand, the 2D Janus P3m1 Cu2N3X phases (where X = H, F, and Cl) are ferromagnetic half-metals. Additionally, it has been unveiled that there are high hole mobilities (∼6 × 103 cm2 V-1 s-1) derived from the moderate deformation potential and effective mass in the 2D Janus P3m1 Zr2N3H, Hf2N3H, and Hf2N3F phases. Uniaxial strain engineering has demonstrated the outstanding in-plane piezoelectric properties of 2D Janus P3m1 Zr2N3H, Hf2N3H, and Hf2N3F with high d11 values (∼99.91 pm V-1). Furthermore, the desirable band-edge alignments and high anisotropic carrier mobilities of 2D Janus P3m1 Zr2N3H, Hf2N3H, and Hf2N3F phases indicate their potential as visible light-driven photocatalysts for water splitting reactions on different facets. These properties render 2D Janus P3m1 Zr2N3H, Hf2N3H, and Hf2N3F phases promising for use in optoelectronics, piezoelectric sensing, and photocatalysis applications.

Light-driven photocatalysis as an effective tool for degradation of antibiotics.

Antibiotic contamination has become a severe issue and a dangerous concern to the environment because of large release of antibiotic effluent into terrestrial and aquatic ecosystems. To try and solve these issues, a plethora of research on antibiotic withdrawal has been carried out. Recently photocatalysis has received tremendous attention due to its ability to remove antibiotics from aqueous solutions in a cost-effective and environmentally friendly manner with few drawbacks compared to traditional photocatalysts. Considerable attention has been focused on developing advanced visible light-driven photocatalysts in order to address these problems. This review provides an overview of recent developments in the field of photocatalytic degradation of antibiotics, including the doping of metals and non-metals into ultraviolet light-driven photocatalysts, the formation of new semiconductor photocatalysts, the advancement of heterojunction photocatalysts, and the building of surface plasmon resonance-enhanced photocatalytic systems.

SnS2 based SnS2/rGO/g-C3N4 Z-scheme ternary nanocomposites for efficient visible light-driven photocatalytic activity

Novel ternary composite photocatalyst SnS2/rGO/g-C3N4 in a Z-scheme configuration was synthesized using hydrothermal method for the degradation of dye pollutants from the industrial wastes. To enhance photocatalytic effectiveness, we employed Z-scheme architecture by utilizing SnS2 as a semiconductor with the unique electronic properties of rGO and g-C3N4 for promoting efficient charge separation. The synthesized ternary composite materials were characterized by various spectroscopic and microscopic techniques. The photocatalytic activities of these samples were evaluated through the degradation of Methylene Blue (MB) dye under visible light. Notably, the catalysts SnS2, SnS2/rGO, SnS2/g-C3N4, and SnS2/rGO/g-C3N4 exhibited degradation efficiencies of 55%, 57%, 64%, and 86%, respectively, after 70 min. Among these, the ternary composite catalyst of SnS2/rGO/g-C3N4 exhibited enhanced degradation performance. Furthermore, when exposed to visible light, the unique crisscross morphology and Z scheme architecture effectively promote light utilization efficiency, providing ample reactive sites and leading to a higher degradation percentage. Further optimization of experiments for this composite material involved in varying catalyst loadings, dye concentrations, and pH levels. The SnS2/rGO/g-C3N4 composite exhibited optimal degradation performance with 5 mg catalyst in a 25 ppm MB solution within 100 ml. This composite was identified for the first time as an excellent visible light-driven photocatalyst for MB, displaying high degradation efficiencies. These findings emphasize the promising potential of the SnS2/rGO/g-C3N4 ternary nanocomposite for applications in visible light-driven photocatalysis.

Visible light-driven photocatalyst δ‑Bi7VO13 nanoparticles synthesized by thermal plasma

Visible light-driven photocatalyst δ‑Bi7VO13 nanoparticles synthesized by thermal plasma

Constructing In2S3/CdS/N-rGO Hybrid Nanosheets via One-Pot Pyrolysis for Boosting and Stabilizing Visible Light-Driven Hydrogen Evolution

The construction of hybrid junctions remains challenging for the rational design of visible light-driven photocatalysts. Herein, In2S3/CdS/N-rGO hybrid nanosheets were successfully prepared via a one-step pyrolysis method using deep eutectic solvents as precursors. Benefiting from the surfactant-free pyrolysis method, the obtained ultrathin hybrid nanosheets assemble into stable three-dimensional self-standing superstructures. The tremella-like structure of hybrid In2S3/N-rGO exhibits excellent photocatalytic hydrogen production performance. The hydrogen evolution rate is 10.9 mmol·g−1·h−1, which is greatly superior to CdS/N-rGO (3.7 mmol·g−1·h−1) and In2S3/N-rGO (2.6 mmol·g−1·h−1). This work provides more opportunities for the rational design and fabrication of hybrid ultrathin nanosheets for broad catalytic applications in sustainable energy and the environment.

Slow photon photocatalytic enhancement of H2 production in TaON inverse opal photonic crystals

In this study, tantalum oxynitride inverse opal (TaON IO) photonic crystals with different macropore diameters (D) were synthesized in a two-step process involving colloidal crystal templating and thermal nitridation, then applied as visible light-driven photocatalysts for hydrogen production. The TaON inverse opals showed photonic band gaps (PBGs) at visible wavelengths, with the PBG position redshifting as the diameter of the macropores increased in accordance with a modified Bragg's law expression. By aligning the electronic absorption edge of TaON (Eg ∼ 2.4 eV) with the blue edge (short-wavelength side) or red edge (long-wavelength side) of the PBGs, slow photon enhancement of photocatalytic H2 generation was realized. H2 production tests conducted in 10 vol% methanol containing H₂PtCl6 under Xe lamp irradiation (150 W) showed that the hydrogen production rate was enhanced by ∼1.3–1.4 times when the TaON absorption edge (∼510 nm) aligned with blue edge of the PBG (0.3421 mmol g−1 h−1) or the red edge of the PBG (0.3254 mmol g−1 h−1) in the inverse opals. The red edge enhancement was due to increased light absorption and charge carrier generation in TaON, whereas the blue edge effect was likely due to suppression of electron-hole pair recombination. Results demonstrate that photonic crystal engineering to exploit slow photon effects is a viable approach for boosting photocatalytic hydrogen production rates.

Ce-doped TiO2-zeolite fibers: visible light-driven photocatalysts for indigo dye degradation.

Indigo dye is a poisonous dye that threatens human health by polluting the environment. Therefore, we prepared a visible light-sensitive photocatalyst to eliminate indigo dye especially from water sources. In this study, sol-gel and electrospinning methods have been performed to synthesize Ce-doped TiO2-zeolite fibers for indigo degradation. The structural and optical properties of the synthesized fibers were investigated by XRD, SEM, EDX, and UV-Vis spectrophotometer techniques. It has been shown that 3% Ce-doped TiO2/zeolite fibers have the highest photocatalytic activity with 100% degradation after 150h, showing that the light absorption of TiO2 expands into the visible light area by Ce doping and absorption into the zeolite. The recyclability analyses of the spent photocatalyst exhibited 87.0% degradation of indigo after four cycles, demonstrating the stability of the fiber. An effective photocatalyst has been obtained by improving the photocatalytic and electrochemical properties thanks to the fibers' high surface area and the zeolite's porous structure. Based on these findings, the study reveals the significant potential of Ce-doped TiO2/zeolite fibers for the purification of wastewater under visible light.

Anti-fouling and self-cleaning ability of BiVO4/rGO and BiVO4/g-C3N4 visible light-driven photocatalysts modified ceramic membrane in high performance ultrafiltration of oily wastewater

Oily wastewater is one of the most harmful and resistant types of wastewater that cannot be treated with the usual and traditional methods. In this study, the visible light-driven photocatalysts BiVO4/rGO and BiVO4/g-C3N4 were made using the hydrothermal method. After that, a simple sol-gel method was used to make a photocatalytic ultrafiltration membrane with good self-cleaning and anti-fouling properties that can effectively separate oily wastewater. Photocatalyst properties were identified by using XRD, FTIR, DRS, N2 absorption-desorption, and zeta potential analysis. The performance of photocatalytic membranes was then investigated in oily wastewater treatment. Antifouling parameters, underwater oil contact angle, surface roughness, and electrochemical properties were measured to look into the membrane's antifouling properties. The use of a BiVO4/rGO composition with 20 wt% of rGO produced an underwater oil contact angle of 158°. Also, after 3 h of 3000 ppm oily wastewater filtration, the permeate flux was double that of the UF membrane without a photocatalytic coating, and the TOC removal efficiency was more than 99%. Measurement of antifouling parameters revealed that flux recovery was 89% compared to 51% for the UF membrane, and the total fouling ratio was reduced from 57% to 21%.

Qualitative and quantitative contributions of intermolecular interactions, quantum chemical calculation, biological activity and visible-light driven photo catalysts studies of nickel complex of 4-amino-N-(5-methyl-1,3,4-thiadiazol-2-yl)benzenesulfonamide

This study reports the successful synthesis and characterization of a nickel complex of the sulfamethizole (smtz) ligand. The complex was characterized using 1H NMR and FT-IR spectroscopic analyses. The synthesized complex exhibited promising properties as a biological and visible light-driven photocatalyst. Under visible light radiation, it displayed remarkable photo-degradation capabilities, achieving a degradation efficiency of 91.2% within 80 min against a solution of methylene blue (MB) with a concentration of 10 PPM in 100 mL. To understand the complex's biological response, viscosity measurements were conducted to investigate its mode of binding with CT-DNA. The results demonstrated that the nickel complex exhibited stronger inhibitory activity and lower cytotoxicity compared to the smtz ligand, as evidenced by cytotoxic analysis and minimum inhibitory concentration (MIC) data against a range of gram-positive and gram-negative pathogens. Furthermore, the crystal structure of the complex was determined through single-crystal X-ray diffraction analysis, revealing its crystallization in the triclinic space group P-1. The asymmetric part of the unit cell consisted of a Ni0.5 metal atom, one -Picoline solvent molecule, one smtz ligand, and one coordinated water molecule. To gain further insights into the complex's properties, Hirshfeld surfaces (HS) and a 3D energy framework approach were utilized to visualize its active and inactive surfaces. The analysis indicated that the dispersion energy contribution in molecular packing was significantly greater than that of electrostatic energy. Additionally, calculations of the HOMO-LUMO energy and other quantum chemical parameters were performed to understand the molecule's stability. Overall, the synthesized nickel complex of the sulfamethizole ligand exhibited remarkable photocatalytic properties, strong inhibitory activity against pathogens, and a stable crystal structure. These findings contribute to the understanding of the complex's potential applications in photocatalysis and biomedical research.

Visible light-driven photocatalysts, quantum chemical calculations, ADMET-SAR parameters, and DNA binding studies of nickel complex of sulfadiazine

A 3D-supramolecular nickel integrated Ni-SDZ complex was synthesized using sodium salt of sulfadiazine as the ligand and nickel(II) acetate as the metal salt using a condensation process and slow evaporation approach to growing the single crystal. The metal complex was characterized for its composition, functional groups, surface morphology as well as complex 3D structure, by resorting to various analytical techniques. The interacting surface and stability as well as reactivity of the complex were carried out using the DFT platform. From ADMET parameters, human Intestinal Absorbance data revealed that the compound has the potential to be well absorbed, and also Ni-SDZ complex cannot cross the blood–brain barrier (BBB). Additionally, the complex's DNA binding affinity and in-vivo and in-vitro cytotoxic studies were explored utilizing UV–Vis absorbance titration, viscosity measurements, and S. pombe cells and brine shrimp lethality tests. In visible light radiation, the Ni-SDZ complex displayed exceptional photo-degradation characteristics of approximately 70.19% within 70 min against methylene blue (MB).

La1.33-xNa3xTi2O6/Na3La2(BO3)3 heterostructure transformed from La2Ti2O7 plates for enhanced photocatalytic H2 evolution

Perovskite-type oxide semiconductors, as promising photocatalysts, possess flexible structures with corner-shared BO6 octahedrons and A cations, but are limited by the broad band gaps and severe photo-induced carrier recombination. Herein, a series of La1.33-xNa3xTi2O6/Na3La2(BO3)3 composites were synthesized by annealing the layered La2Ti2O7 with NaBH4. The doping of Na+ ions in perovskite's A-site promotes the transformation of La2Ti2O7 into La1.33-xNa3xTi2O6 phase, meanwhile, substituted La species turn into Na3La2(BO3)3 phase. The crystalline degree of perovskite structure evolves with the ratio of Na+ ions in the A site, and La2Ti2O7 undergoes amorphization, recrystallization, and further decomposition as the Na species increases. In well-crystallized La1.17Na0.48Ti2O6/Na3La2(BO3)3, intimate interfacial contacts induce extended optical absorption and optimized charge transfer. Under visible light irradiation, the sample exhibits significantly enhanced photocatalytic H2 evolution activity, with hydrogen production rate reaching 660 μmol∙g−1·h−1, whereas La2Ti2O7 has almost no catalytic activity. This work presents a novel strategy to transform the perovskite oxides at a relatively low temperature by exchanging cations with reductive NaBH4. It demonstrates applications in the development of visible light-driven perovskite-based heterogeneous photocatalysts.

Cobalt Hydrogen-Bonded Organic Framework as a Visible Light-Driven Photocatalyst for CO2 Cycloaddition Reaction.

A novel cobalt hydrogen-bonded organic framework (Co-HOF, C24H14CoN4O8) was synthesized from a mixed linker, that is, 2,5-pyridinedicarboxylic acid (PDC) and 2,2'-bipyridyl (BPY) linkers and cobalt ion through a simple, one-pot, low-cost, and scalable solvothermal method. The Co-HOF was fully characterized using several analytical and spectroscopic techniques including single-crystal X-ray diffraction, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray, and X-ray photoelectron spectroscopy. The Co-HOF exhibits high thermal and chemical stabilities compared to previously reported HOF materials. Moreover, Co-HOF shows excellent photocatalytic activity under visible light irradiation due to its narrow band gap of 2.05 eV. The cycloaddition reaction of CO2 to variable epoxides was investigated to evaluate the photocatalytic performance of Co-HOF under visible light radiation and was found to produce the corresponding cyclic carbonates in yields up to 99.9%.

Band-gap engineering of zirconia by nitrogen doping in reactive HiPIMS: a step forward in developing innovative technologies for photocatalysts synthesis.

In the global context of climate change and carbon neutrality, this work proposes a strategy to improve the light absorption of photocatalytic water-splitting materials into the visible spectrum by anion doping. In this framework, reactive high power impulse magnetron sputtering (HiPIMS) of a pure Zr target in Ar/N2/O2 gas mixture was used for the deposition of crystalline zirconium oxynitride (ZrO2-xNx) thin films with variable nitrogen doping concentration and energy band-gap. The nitrogen content into these films was controlled by the discharge pulsing frequency, which controls the target surface poisoning and peak discharge current. The role of the nitrogen doping on the optical, structural, and photocatalytic properties of ZrO2-xNx films was investigated. UV-Vis-NIR spectroscopy was employed to investigate the optical properties and to assess the energy band-gap. Surface chemical analysis was performed using X-ray photoelectron spectroscopy, while structural analysis was carried out by X-ray diffraction. The increase in the pulse repetition frequency determined a build-up in the nitrogen content of the deposited ZrO2-xNx thin films from ∼10 to ∼25at.%. This leads to a narrowing of the optical band-gap energy from 3.43 to 2.20eV and endorses efficient absorption of visible light. Owing to its narrow bandgap, ZrO2-xNx thin films obtained by reactive HiPIMS can be used as visible light-driven photocatalyst. For the selected processing conditions (pulsing configuration and gas composition), it was found that reactive HiPIMS can suppress the hysteresis effect for a wide range of frequencies, leading to a stable deposition process with a smooth transition from compound to metal-sputtering mode.

Natural marmatite photocatalyst for treatment of mineral processing wastewater to help zero wastewater discharge

Mineral processing wastewater (MPW) with large discharge and high toxicity affects environmental safety, and the realizing zero discharge of MPW is of great significance for reducing environmental pollution, saving water resources, and promoting the sustainable development of the mining industry. In this study, we reported natural marmatite (NM) as a low-cost and efficient photocatalyst for the treatment of MPW to help zero wastewater discharge. The photocatalytic activity of NM was evaluated by the removal of total organic carbon (TOC) from MPW under visible-light illumination, and the optimal degradation conditions were discussed. Results showed that superoxide free radicals (·O2−) were the dominant active species responsible for organic pollutants degradation, and 74.25% TOC removal was obtained after 120 min reaction under the optimum treatment conditions. Meanwhile, the wastewater treated by NM photocatalysis can be reused in the flotation system without adverse impact on the product index. Based on these findings, a model of zero wastewater discharge for flotation with the help of photocatalytic treatment was established, it indicated that the water of the whole system can be balanced without affecting the ore dressing index, which showed that visible light-driven photocatalyst has a promising application prospect in the treatment and recycling of industrial wastewater.