Ultrathin Ag2WO4-coated P-doped g-C3N4 nanosheets with remarkable photocatalytic performance for indomethacin degradation

Polyimide/Ag2WO4 Z-Scheme Heterojunction for Efficient Photocatalytic Degradation of Tetracycline

It is of great significance to construct a Z-scheme heterojunction for improving solar light harvesting and achieving efficient separation of photogenerated carriers and then enhancement of the photocatalytic performance of semiconductor photocatalysts. Herein, the direct Z-scheme PI/Ag2WO4 heterojunction was designed and prepared according to the band edge potentials of the semiconductor. Due to the fact that the Z-scheme structure not only endowed the PI/Ag2WO4 composites with efficient separation of photogenerated electron-hole pairs but also reserved the redox ability of the valence band and conduction band of monophase catalysts, the 50% PI/Ag2WO4 heterojunction exhibited excellent photocatalytic activity, which were 2.9 and 1.5 times those of the PI and Ag2WO4 photocatalysts, respectively. The photocatalytic reaction mechanism of PI/Ag2WO4 composites was confirmed by the results of TEM, UV-vis, XPS, and EPR experiments. This work provides a feasible strategy to design high-performance photocatalysts in the field of practice purification of wastewater.

Promoting the suitability of graphitic carbon nitride and metal oxide nanoparticles: A review of sulfonamides photocatalytic degradation

The widespread consumption of pharmaceutical drugs and their incomplete breakdown in organisms has led to their extensive presence in aquatic environments. The indiscriminate use of antibiotics, such as sulfonamides, has contributed to the development of drug-resistant bacteria and the persistent pollution of water bodies, posing a threat to human health and the safety of the environment. Thus, it is paramount to explore remediation technologies aimed at decomposing and complete elimination of the toxic contaminants from pharmaceutical wastewater. The review aims to explore the utilization of metal-oxide nanoparticles (MONPs) and graphitic carbon nitrides (g-C3N4) in photocatalytic degradation of sulfonamides from wastewater. Recent advances in oxidation techniques such as photocatalytic degradation are being exploited in the elimination of the sulfonamides from wastewater. MONP and g-C3N4 are commonly evolved nano substances with intrinsic properties. They possessed nano-scale structure, considerable porosity semi-conducting properties, responsible for decomposing wide range of water pollutants. They are widely applied for photocatalytic degradation of organic and inorganic substances which continue to evolve due to the low-cost, efficiency, less toxicity, and more environmentally friendliness of the materials. The review focuses on the current advances in the application of these materials, their efficiencies, degradation mechanisms, and recyclability in the context of sulfonamides photocatalytic degradation.

Accelerating the environmental applications of black phosphorus: A review

Since its rediscovery in 2014, layered black phosphorus (BP) has received extensive attention as a new two-dimensional semiconductor. BP is a promising material with properties of a large surface-to-volume ratio, wide light absorption range, tunable band gap, and high charge carrier mobility. These unique characteristics of BP make it a promising contender for various applications, particularly in the realm of environmental applications. This literature review provides a comprehensive discussion and overview of the latest developments in utilizing BP for environmental purposes. The review starts with the applications of BP in photocatalysis including photodegradation of refractory pollutants, H2 evolution reaction (HER), and reduction of CO2 and N2. In the following section, Environmental electrocatalysis of HER and N2 reduction reaction (NRR) is discussed. In addition, BP-based environmental sensing (detection of heavy metal ions, antibiotics, mycotoxins, NOx) and eco-friendly halogen-free flame retardant are summarized as well. Finally, a thorough comprehension of the current state and potential future trends of BP-based nanomaterials for various environmental applications are presented.

Recent advancements in the fabrication and photocatalytic applications of graphitic carbon nitride-tungsten oxide nanocomposites

The present review focuses on the widely used graphitic carbon nitride (g-C3N4)-tungsten oxide (WO3) nanocomposite in photocatalytic applications. These catalysts are widely employed due to their easy preparation, high physicochemical stability, nontoxicity, electron-rich properties, electronic band structure, chemical stability, low cost, earth-abundance, high surface area, and strong absorption capacity in the visible range. These sustainable properties make them predominantly attractive and unique from other photocatalysts. In addition, graphitic carbon nitride (g-C3N4) is synthesized from nitrogen-rich precursors; therefore, it is stable in strong acid solutions and has good thermal stability up to 600 °C. This review covers the historical background, crystalline phases, density-functional theory (DFT) study, synthesis method, 0-D, 1-D, 2-D, and 3-D materials, oxides/transition/nontransition metal-doped, characterization, and photocatalytic applications of WO3/g-C3N4. Enhancing the catalytic performance strategies such as composite formation, element-doping, heterojunction construction, and nanostructure design are also summarized. Finally, the future perspectives and challenges for WO3/g-C3N4 composite materials are discussed to motivate young researchers and scientists interested in developing environment-friendly and efficient catalysts.

Novel synthesis of siligraphene/tungstates (g-SiC/AWO) with promoted transportation of photogenerated charge carriers via direct Z-scheme heterojunctions

We developed here the efficient photocatalysts for the removal of high concentrations of tetracycline under visible light by immobilizing the AWO (A = Ag, Bi, Na) nanocrystals on the surface of siligraphene (g-SiC) nanosheets. The g-SiC/AWO composites was synthesized by magnesiothermic synthesis of g-SiC and sonochemical immobilization of tungstates. These new heterojunctions of g-SiC/tungstates show superior photocatalytic activities in the degradation of high concentrations of tetracycline and 97, 98, and 94% of tetracycline were removed by using low amounts of g-SiC/Ag₂WO₄, g-SiC/Bi₂WO₆, and g-SiC/Na₂WO₄ catalysts, respectively. Based on band structures, the band gaps reduce and the photocatalytic activities were extremely enhanced due to the shortening of electron transfer distance through the Z-scheme mechanism. Also, the graphenic structure of g-SiC is another parameter that was effective in improving photocatalytic performance by increasing the electron transfer and decreasing the rate of electron-hole recombination. Furthermore, the π back-bonding of g-SiC with metal atoms increases the electron-hole separation to enhance the photocatalytic activity. Interestingly, g-SiC composites (g-SiC/AWO) showed much higher photocatalytic properties compared to graphene composites (gr/AWO) and can remove the tetracycline even at dark by producing the oxygenated radicals via adsorption of oxygen on the positive charge of Si atoms in siligraphene structure.

Facile synthesis of direct Z-scheme UiO-66-NH2/PhC2Cu heterojunction with ultrahigh redox potential for enhanced photocatalytic Cr(VI) reduction and NOR degradation

Z-scheme heterojunction-based photocatalysts typically have robust removal efficiencies for water contaminants. Herein, we employed p-type PhC₂Cu and n-type UiO-66-NH₂ to develop a direct Z-scheme UiO-66-NH₂/PhC₂Cu photocatalyst with an ultrahigh redox potential for Cr(VI) photoreduction and norfloxacin (NOR) photodegradation. Moreover, UV-vis diffuse reflectance, photoelectrochemical measurements, photoluminescence (PL) spectra and electron spin resonance (ESR) technique revealed that the UiO-66-NH₂/PhC₂Cu composite boosted light capturing capacities to promote photocatalytic efficiencies. Strikingly, the optimized UiO-66-NH₂/PhC₂Cu50 wt% rapidly reduced Cr(VI) (96.2%, 15 min) and degraded NOR (97.9%, 60 min) under low-power blue LED light. In addition, the UiO-66-NH₂/PhC₂Cu photocatalyst also exhibited favorable mineralization capacity (78.4%, 120 min). Benefitting from the enhanced interfacial electron transfer and ultrahigh redox potential of the Z-scheme heterojunction, the UiO-66-NH₂/PhC₂Cu photocatalyst greatly enhanced the separation efficacies of photogenerated carriers. This resulting abundance of active species (e.g., e^-, h⁺, O₂^•-, and •OH) were generated to photo-reduce Cr(VI) and photo-oxidize NOR. Base on the identified intermediates, four degradation pathways of NOR were proposed. Finally, the Z-scheme mechanism were systematically confirmed through X-ray photoelectron spectroscopy (XPS), ESR, cyclic voltammetry (CV) tests, and photodeposition techniques.

2D/2D Phosphorus-Doped g-C3N4/Bi2WO6 Direct Z-Scheme Heterojunction Photocatalytic System for Tetracycline Hydrochloride (TC-HCl) Degradation

Bi₂WO₆-based heterojunction photocatalyst for antibiotic degradation has been a research hotspot, but its photocatalytic performance needs to be further improved. Therefore, 2D/2D P-doped g-C₃N₄/Bi₂WO₆ direct Z-scheme heterojunction photocatalysts with different composition ratios were prepared through three strategies of phosphorus (P) element doping, morphology regulation, and heterojunction, and the efficiency of its degradation of tetracycline hydrochloride (TC-HCl) under visible light was studied. Their structural, optical, and electronic properties were evaluated, and their photocatalytic efficiency for TC-HCl degradation was explored with a detailed assessment of the active species, degradation pathways, and effects of humic acid, different anions and cations, and water sources. The 30% P-doped g-C₃N₄/Bi₂WO₆ had the best photocatalytic performance for TC-HCl degradation. Its photocatalytic rate was 4.5-, 2.2-, and 1.9-times greater than that of g-C₃N₄, P-doped g-C₃N₄, and Bi₂WO₆, respectively. The improved photocatalytic efficiency was attributed to the synergistic effect of P doping and 2D/2D direct Z-scheme heterojunction construction. The stability and reusability of the 30% P-doped C₃N₄/Bi₂WO₆ were confirmed by cyclic degradation experiments. Radical scavenging experiments and electron spin resonance spectroscopy showed that the main active species were •O₂^- and h⁺. This work provides a new strategy for the preparation of direct Z-scheme heterojunction catalysts with high catalytic performance.

Underlying mechanisms of promoted formation of haloacetic acids disinfection byproducts after indometacin degradation by non-thermal discharge plasma

Indometacin (IDM), as a kind of non-steroidal anti-inflammatory drugs, has ecological and health risks, which is the potential precursor of chlorination disinfection byproducts (DBPs). Non-thermal discharge plasma was attempted to eliminate IDM and control subsequent DBPs formation. Satisfactory removal performance for IDM was realized by the plasma oxidation; almost 100% of IDM was removed within 2 min. Relatively greater removal efficiency was gained at a higher plasma voltage and a lower pH level. Electron paramagnetic resonance spectrometer revealed that reactive species ·OH, O₂·^-, and ¹O₂ were responsible for IDM decomposition. Based on analyses of Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, three-dimensional fluorescence spectrum, and gas chromatography-mass spectrometer, attacks of reactive species resulted in sequence breakages in functional groups of IDM, leading to production of small molecular alcohols, acids, and amines. Possible decomposition pathways of IDM were proposed. The produced acetamide and 1H-indol-5-ol were important precursors of DBPs. Formation and toxicity of nitrogen-containing DBPs were dramatically inhibited after IDM degradation; however, those of haloacetic acids were strengthened. The relevant roadmaps among DBPs and degradation intermediates were figured out. This study revealed the underlying mechanisms of IDM degradation by discharge plasma and its potential risks in chlorination disinfection.

Flower-like Ag2WO4/CeO2 heterojunctions with oxygen vacancies and expedited charge carrier separation boost the photocatalytic degradation of dyes and drugs

Charge carrier separation is a very important factor in photocatalysis, and it may be achieved through a variety of paths including the construction of heterojunctions and the formation of surface defects. Herein, we demonstrate the construction of flower-like Ag₂WO₄/CeO₂ heterojunctions (namely ACs) by in situ deposition of Ag₂WO₄ on the surface of flower-like CeO₂ with oxygen defects. The ACs with 2.3%, 3.8%, and 5.3% Ag₂WO₄ are defined as AC-1, AC-2, and AC-3, respectively, and we compare their photocatalytic removal efficiencies. Under visible light, AC-2 exhibits the highest photocatalytic removal efficiency toward cationic dye RhB and tetracycline (TC). The K value of AC-2 toward RhB degradation is determined to be 0.059 min^-1, which is 7.56 and 8.94-fold higher than those of Ag₂WO₄ (0.0078 min^-1) and CeO₂ (0.0066 min^-1), respectively. Moreover, the K value of AC-2 toward TC degradation (0.021 min^-1) is 4.04 and 5.68-fold higher than those of Ag₂WO₄ (0.0052 min^-1) and CeO₂ (0.0037 min^-1), respectively. Our results clearly demonstrate that the introduction of Ag₂WO₄ particles stimulates the formation of surface defects of CeO₂, improves the visible light absorption, accelerates the charge carrier separation, and consequently boosts the photocatalytic degradation of dyes and drugs.

One-Step construction of Polyimide/NH2-UiO-66 heterojunction for enhanced photocatalytic degradation of sulfonamides

Photocatalysis treatment is a promising technology to eliminate water pollutants. Herein, we constructed polyimide/NH₂-UiO-66 composites (PUs) through a facile one-step solvothermal method for the photocatalytic degradation of sulfonamides. The optimized photocatalyst PU1.5 was superior to the photocatalysts prepared through multi-step methods due to the more exposed (001) facets of polyimide and the better distribution of small NH₂-UiO-66 particles. PU1.5 showed the highest photocatalytic activity, which was 9.5 and 92.0 times higher than that of polyimide and NH₂-UiO-66. Such improvement was attributed to the improved carrier separation efficiency resulted from direct Z-scheme heterojunction. The probable degradation pathway of sulfathiazole was proposed by the LC-MS/MS and Density Functional Theory (DFT) calculation. Furthermore, the reduced toxicity and the little antibacterial activity of intermediates was investigated by the Quantitative Structure-Activity Relationship (QSAR) analysis and the residual antibiotic activity experiment. The study might provide a new strategy for designing composite photocatalyst to achieve efficient removal of pollutants.

Preparation of metal-free BP/CN photocatalyst with enhanced ability for photocatalytic tetracycline degradation

The successful application of photocatalysis in practical water treatment opreations relies greatly on the development of highly efficient, stable and low-cost photocatalysts. The low-cost metal-free photocatalyst made up of black phosphorus (BP) and graphitic carbon nitride (CN) was successfully constructed and firstly used for the photocatalytic treatment of antibiotic contaminants in this work. Compared with bare CN, the BP/CN photocatalyst exhibited the enhanced photocatalytic performance for tetracycline hydrochloride (HTC) degradation, that 99% of HTC was removed by 6BP/CN (doping amount of BP was 6%) within 30 min under the simulated visible-light irradiation. The efficiency was even comparable to those of some high-efficiency photocatalysts recently-reported such as Fe⁰@POCN, CuInS₂/Bi₂MoO₆ and Cu₂O@HKUST-1. Under natural sunlight illumination, the determined apparent rate constant for degradation of HTC by BP/CN was 2.7 times as that by P25 TiO₂. The experimental results indicated that loading BP on CN could enhance the separation of charge carriers and promote the ability of light absorption for visible-light, thus leading to a greater catalytic activity. Meanwhile, the influences of different operating variables (pH, water, ion and HTC concentration) on HTC degradation were studied in detail. Furthermore, the degradation pathway of HTC was also proposed. In addition, the photocatalytic activity of the BP/CN for production of hydrogen peroxide (H₂O₂) was also studied, which could reach up to 501.04 μmol g^-1h^-1. It is anticipated that BP/CN photocatalyst could be used for practical water treatment.

Construction of double-functionalized g-C3N4 heterojunction structure via optimized charge transfer for the synergistically enhanced photocatalytic degradation of sulfonamides and H2O2 production

Herein, supporting g-C₃N₄ embedded with benzene-ring (BCN) on P-modified g-C₃N₄ (PCN) successfully synthesized the homogeneous photocatalyst BCN/PCN (PBCN) via a simple thermal polymerization reaction. Under blue-light (LED) irradiation, the optimized PBCN (0.448 min^-1) demonstrated excellent photocatalytic performance, attaining over 74 times the degradation rate for sulfisoxazole (SSZ) in contrast to non-functionalized g-C₃N₄ (CN, 0.006 min^-1). Theoretical calculations revealed that the substitution of heterocyclic rings in the g-C₃N₄ triazine networks with benzene-rings enabled them to serve as electron donors, while promoting photoinduced spatial charge dissociation. Further, the carrier PCN tended to serve as electron acceptors to form electron-rich corner-phosphorous sites. Reactive species experiments demonstrate that the O₂˙^- and h⁺ constituted the primary photocatalytic mechanism of SSZ degradation. The potential SSZ degradation routes were predicted based on the transformation products via mass spectrometry. Finally, the composite materials also exhibited excellent photocatalytic activity in the conversion of solar energy to chemical energy (H₂O₂). This study guides the rational modification of g-C₃N₄-based semiconductors to achieve green energy production and beneficial ecological applications.

Investigation of Fe-Doped Graphitic Carbon Nitride-Silver Tungstate as a Ternary Visible Light Active Photocatalyst

The rapid population growth and economic development have largely contributed to environmental pollution. Various advanced oxidation processes have been used as the most viable solution for the reduction of recalcitrant pollutants and wastewater treatment. Heterogeneous photocatalysis is one of the broadly used technologies for wastewater treatment among all advanced oxidation processes. Graphitic carbon nitride alone or in combination with various other semiconductor metal oxide materials acts as a competent visible light active photocatalyst for the removal of recalcitrant organic pollutants from wastewater. Rational designing of an environment-friendly photocatalyst through a facile synthetic approach encounters various challenges in photocatalytic technologies dealing with semiconductor metal oxides. Doping in g-C3N4 and subsequent coupling with metal oxides have shown remarkable enhancement in the photodegradation activity of g-C3N4-based nanocomposites owing to the modulation in g-C3N4 bandgap structuring and surface area. In the current study, a novel ternary Fe-doped g-C3N4/Ag2WO4 visible light active photocatalyst was fabricated through an ultrasonic-assisted facile hydrothermal method. Characterization analysis included SEM analysis, FTIR, XRD, XPS, and UV-Visible techniques to elucidate the morphology and chemical structuring of the as-prepared heterostructure. The bandgap energies were assessed using the Tauc plot. The ternary nanocomposite (Fe-CN-AW) showed increased photodegradation efficiency (97%) within 120 minutes, at optimal conditions of pH = 8, catalyst dose = 50 mg/100 ml, an initial RhB concentration of 10 ppm, and oxidant dose 5 mM under sunlight irradiation. The enhanced photodegradation of rhodamine B dye by ternary Fe-CN-AW was credited to multielectron transfer pathways due to insertion of a Fe dopant in graphitic carbon nitride and subsequent coupling with silver tungstate. The data were statistically assessed by the response surface methodology.

Surface modification of BiOBr/TiO2 by reduced AgBr for solar-driven PAHs degradation: Mechanism insight and application assessment

A novel solar active AgBr/BiOBr/TiO₂ catalyst was synthesized by a facile coprecipitation method for solar-driven water remediation. The synthesized material composed of flower-like TiO₂ nanoparticles loaded on BiOBr nanosheets and with homogeneous surface distributed Ag/AgBr nanoparticles. The internal electric field between BiOBr/TiO₂ heterojunction greatly facilitated the charge carrier migration; the introduction of narrow band gap semiconductors (AgBr and BiOBr) promoted the visible light adsorption; and the Ag/AgBr nanoparticles acted as photosensitizer to further improve the light utilization. The new material showed 7.6- and 4.0-times activity of pure TiO₂ and BiOBr under solar light, and the contribution of reactive species on anthracene degradation followed the order of h⁺ >O₂^•-> •OH. The degradation mechanism and pathway were proposed based on intermediates analysis and DFT calculation. The QSAR analysis revealed that the environmental risks of contaminants were greatly reduced during the photocatalysis process but some intermediates were still toxic. The high photocatalytic activity, stability and adaptability all indicated that this new material owns great application potential for cost-effective photocatalytic remediation of persistent organic contaminants under solar light.

Study on the Photocatalysis Mechanism of the Z-Scheme Cobalt Oxide Nanocubes/Carbon Nitride Nanosheets Heterojunction Photocatalyst with High Photocatalytic Performances

An efficient Z-scheme Co₃O₄/g-C₃N₄ heterojunction photocatalyst was developed via in-situ forming Co₃O₄ nanocubes on the g-C₃N₄ nanosheet in the hydrothermal process. The obtained photocatalyst exhibited high photocatalytic activity for the visible-light-driven catalytic reduction of Cr(VI) and catalytic oxidation of tetracycline (TC). Among the as-synthesized catalysts, Co₃O₄/g-C₃N₄-0.04 (the mass ratio of g-C₃N₄ to Co₃O₄ is 0.04) sample exhibits the most efficient catalytic activities. The photocatalytic reduction and photocatalytic oxidation efficiencies of Co₃O₄/g-C₃N₄-0.04 can obtain 81.3 and 92.6 %, respectively. Moreover, the TC is mineralized in the course of photocatalytic degradation, 72.2% of TOC is removed from the reaction system. In addition, the apparent quantum efficiency for the removal of Cr(VI) was also obtained and the the Co₃O₄/g-C₃N₄-0.04 could achieve the highest apparent quantum efficiency among the samples. The enhancing photocatalytic activities originated from the efficient interfacial charge migration and separation obtained in Co₃O₄/g-C₃N₄-0.04, which is preliminarily confirmed by the photoluminescence spectra, time-resolved photoluminescence spectra and the photoelectrochemical characterizations. Finally, we speculate that the Co₃O₄/g-C₃N₄ heterostructures follow a more reasonable Z-scheme charge transfer in this study, which is confirmed by analyzing the results of electron paramagnetic resonance, radical scavenging experiments, and theoretical calculations.

Insights into the photocatalysis mechanism of the novel 2D/3D Z-Scheme g-C3N4/SnS2 heterojunction photocatalysts with excellent photocatalytic performances

A novel 2D/3D Z-scheme g-C₃N₄/SnS₂ photocatalyst was successfully fabricated via self-assembly forming 3D flower-like SnS₂ microspheres on the surface of the 2D g-C₃N₄ nanosheets. The photocatalytic performances of the samples were systematically explored through catalytic reduction of Cr⁶⁺ and oxidation of Bisphenol S (BPS) under the illumination of visible light, and the photocatalytic degradation pathway of BPS was also proposed based on the degradation products confirmed by GCMS. Among the as-prepared samples, 0.4-g-C₃N₄/SnS₂ exhibited the most efficient photocatalytic performances, and the apparent quantum efficiency (QE) for the removal of Cr⁶⁺ could achieve 30.3 %, which is 2.8 times higher than that of the SnS₂. The enhancing photocatalytic activities originated from the efficient interfacial charge migration and separation obtained in g-C₃N₄/SnS₂, which was firstly verified via the photoluminescence spectra, time-resolved photoluminescence spectra and photoelectrochemical characterizations. Importantly, the DFT calculated shows that the band distribution of the g-C₃N₄/SnS₂ sample is staggered near the forbidden, which can facilitate the efficient interfacial charge migration and separation as well as result in the improvement of the catalytic activity. Finally, we put forward a more reasonable Z-scheme charge transfer mechanism, it was verified by analysing the results of free radical scavenging tests, EPR experiments and theoretical calculations.

Doping of Graphitic Carbon Nitride with Non-Metal Elements and Its Applications in Photocatalysis

This review outlines the latest research into the design of graphitic carbon nitride (g-C3N4) with non-metal elements. The emphasis is put on modulation of composition and morphology of g-C3N4 doped with oxygen, sulfur, phosphor, nitrogen, carbon as well as nitrogen and carbon vacancies. Typically, the various methods of non-metal elements introducing in g-C3N4 have been explored to simultaneously tune the textural and electronic properties of g-C3N4 for improving its response to the entire visible light range, facilitating a charge separation, and prolonging a charge carrier lifetime. The application fields of such doped graphitic carbon nitride are summarized into three categories: CO2 reduction, H2-evolution, and organic contaminants degradation. This review shows some main directions and affords to design the g-C3N4 doping with non-metal elements for real photocatalytic applications.