A Bi2WO6/Ag2S/ZnS Z-scheme heterojunction photocatalyst with enhanced visible-light photoactivity towards the degradation of multiple dye pollutants

Facile construction of multifunctional xNiCo2O4/BiVO4 heterojunction with accelerated charge transfer for efficient photocatalytic treatment of Cr (VI), MB and TC under visible light

The release of industrial effluents, comprising of organic dyes, antibiotics, and heavy metals poses substantial environmental and ecological threats. Among the different approaches, the utilization of heterogeneous photocatalysis based on semiconducting metal oxides is of paramount important to removal of organic ( MB dye and TC antibiotic) and inorganic pollutants ( Cr (VI) ) in wastewater. In this work, a new approach for creating type-II heterojunction photocatalysts named xNiCo2O4/BiVO4 or BNC is suggested. The as-prepared samples were thoroughly examined by means of several sophisticated analytical tools to investigate their physicochemical properties. These composites were utilized in the decomposition of MB dye, TC drug and the reduction of Cr (VI) under visible light irradiation. According to the findings, the creation of type-II heterojunction at BiVO4-NiCo2O4 interface greatly improved charge transportation while successfully preventing electron-hole recombination. Among the various composites studied, BNC-2 demonstrated an enhanced photocatalytic activity towards degradation of MB and TC, which were found to be 91 % over a period of 150 min and 95 % within only 60 min, respectively. Moreover, the photocatalytic reduction of Cr (VI) was accomplished 96 % within just 25 min. Additionally, it is discovered that BNC-2 displayed promising photostability and recyclability with a retention of >90 % after five consecutive cycles. The enhanced photocatalytic activity of BNC-2 is evidently attributed to the expedited separation and transfer of charges, as proven by photocurrent measurement, photoluminescence and electrochemical impedance spectroscopy analyses. Hence, the current amalgamation of NiCo2O4 and BiVO4 heterojunction composite has paved novel paths towards photocatalytic removal of organic as well as inorganic contaminants.

Bismuth-Based Z-Scheme Heterojunction Photocatalysts for Remediation of Contaminated Water

Agricultural runoff, fuel spillages, urbanization, hospitalization, and industrialization are some of the serious problems currently facing the world. In particular, byproducts that are hazardous to the ecosystem have the potential to mix with water used for drinking. Over the last three decades, various techniques, including biodegradation, advanced oxidation processes (AOPs), (e.g., photocatalysis, photo-Fenton oxidation, Fenton-like oxidation, and electrochemical oxidation process adsorption), filtration, and adsorption techniques, have been developed to remove hazardous byproducts. Among those, AOPs, photocatalysis has received special attention from the scientific community because of its unusual properties at the nanoscale and its layered structure. Recently, bismuth based semiconductor (BBSc) photocatalysts have played an important role in solving global energy demand and environmental pollution problems. In particular, bismuth-based Z-scheme heterojunction (BBZSH) is considered the best alternative route to overhaul the limitations of single-component BBSc photocatalysts. This work aims to review recent studies on a new type of BBZSH photocatalysts for the treatment of contaminated water. The general overview of the synthesis methods, efficiency-enhancing strategies, classifications of BBSc and Z-scheme heterojunctions, the degradation mechanisms of Z- and S-schemes, and the application of BBZSH photocatalysts for the degradation of organic dyes, antibiotics, aromatics compounds, endocrine-disrupting compounds, and volatile organic compounds are reviewed. Finally, challenges and the future perspective of BBZSH photocatalysts are discussed.

Advances in boron nitride-based nanomaterials for environmental remediation and water splitting: a review

Boron nitride has gained wide-spread attention globally owing to its outstanding characteristics, such as a large surface area, high thermal resistivity, great mechanical strength, low density, and corrosion resistance. This review compiles state-of-the-art synthesis techniques, including mechanical exfoliation, chemical exfoliation, chemical vapour deposition (CVD), and green synthesis for the fabrication of hexagonal boron nitride and its composites, their structural and chemical properties, and their applications in hydrogen production and environmental remediation. Additionally, the adsorptive and photocatalytic properties of boron nitride-based nanocomposites for the removal of heavy metals, dyes, and pharmaceuticals from contaminated waters are discussed. Lastly, the scope of future research, including the facile synthesis and large-scale applicability of boron nitride-based nanomaterials for wastewater treatment, is presented. This review is expected to deliver preliminary knowledge of the present state and properties of boron nitride-based nanomaterials, encouraging the future study and development of these materials for their applications in various fields.

Peroxymonosulfate assisted pesticide breakdown: Unveiling the potential of a novel S-scheme ZnO@CoFe2O4 photo-catalyst, anchored on activated carbon

A ternary hetero-junction was prepared by anchoring ZnO@CoFe2O4 (ZCF) on activated carbon (AC) and employed as a UV-assisted peroxymonosulfate (PMS) activator to boost the degradation of diazinon (DZN) pesticide. The structure, morphology, and optical properties of the ZCFAC hetero-junction were characterized through a series of techniques. The highest degradation efficiency of DZN (100% in 90 min) was achieved by the PMS-mediated ZCFAC/UV system, superior to other single or binary catalytic systems due to the strong synergistic effect between ZCFAC, PMS, and UV. The operating reaction conditions, synergistic effects, and the possible pathways of DZN degradation were investigated and discussed. Optical analysis showed that the band-gap energy of the ZCFAC hetero-junction not only enhanced the absorption of UV light but also reduced the recombination of photo-induced electron/hole pairs. Both radical and non-radical species (HO•, SO4•-, O2•-, 1O2, and h+) took part in the photo-degradation of DZN, assessed by scavenging tests. It was found that AC as a carrier not only improved the catalytic activity of CF and ZnO nanoparticles and conferred high stability for the catalyst but also played a crucial role in accelerating the catalytic PMS activation mechanism. Moreover, the PMS-mediated ZCFAC/UV system showed good reusability, universality, and practical applicability potential. Overall, this work explored an efficient strategy for the best use of hetero-structure photo-catalysts towards PMS activation to achieve high performance in decontaminating organic compounds.

Simultaneous adsorption of ciprofloxacin drug and methyl violet dye on boron nitride nanosheets: experimental and theoretical insights

In this study, hexagonal boron nitride (BN) with a sheet-like morphology is successfully synthesized by reacting borax (Na2B4O7·10H2O) and urea (CO(NH2)2) powders in air via a facile microwave-assisted method within a short reaction time (15 min). The as-prepared product is structurally characterized via Fourier transformation infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersion X-ray analyzer (EDX), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) surface area measurements. The adsorption process of methyl violet (MV) as a model of organic dyes and ciprofloxacin (CIP) as a model of antibiotics onto the boron nitride nanosheets has been experimentally and theoretically studied. The BN nanosheets exhibit the maximum adsorption capacity of 320.94 mg g-1 for MV dye and 266.29 mg g-1 for CIP antibiotic. The Freundlich isotherm model was suitable to describe the adsorption equilibrium isotherm data and the pseudo second-order model reflected the adsorption kinetics well. The calculated thermodynamic parameters show that the adsorption process is spontaneous under the measured conditions. The adsorption of CIP, MV and CIP + MV molecules on the surface of BN has been investigated through DFT calculations. The charge transfer and high adsorption capacity demonstrate the potential of BN nanosheets as an adsorbent for the simultaneous removal of MV dye and CIP drug from contaminated water.

Outlook on bismuth-based photocatalysts for environmental applications: A specific emphasis on Z-scheme mechanisms

Semiconductor photocatalysis is thought to be a viable solution for addressing the growing problem of environmental pollution. Bismuth (Bi) metal oxides can function as a direct plasmonic photocatalyst or cocatalyst to accelerate the photogenerated charge separation and thus improve their photocatalytic activity. Hence, Bi-based photocatalysts have received a lot of attention due to their extensive environmental applications, including pollutant remediation and energy concepts. Massive efforts have been undertaken in the recent decade to find superior Bi-metal oxides (Bi₂XO_6, X = MO, W, or Cr) and to uncover the corresponding photocatalytic reaction mechanism for the degradation of organic contaminants in water. Herein, the unique crystalline and electronic properties and main synthesis methods, as well as the major Bi-Based direct Z-scheme photocatalysts, are timely discussed and summarized in their usage in water treatment. Besides, the impact of Bi₂XO₆ in energy storage devices and solar energy conversion is reviewed as an energy application. Finally, the future development and challenges of Z-scheme-based Bi₂XO₆ photocatalysts are briefly explored, summarized, and forecasted.

Levofloxacin degradation under visible-LED photo-catalyzing by a novel ternary Fe-ZnO/WO3 nanocomposite

As semiconductor photocatalysts showing their efficient redox ability upon illumination, new development of materials to enhance the pollution degradation is gaining popularity, especially on their oxidation ability. In this study, a highly stable ternary Fe-ZnO/WO₃ nanocomposite photocatalyst has been synthesized in order to improve charge transfer of photocatalytic oxidation under 30W LED light (425-470 nm) to efficiency degrade the Levofloxacin (LVF) in the solution. This catalyst was characterized and analyzed by XRD, FE-SEM, HR-TEM, X-ray XPS, UPS, PL, TRPL, LSV, EIS, and Photocurrent. Various important factors for the photodegradation were investigated, including Fe content, initial LVF concentration, catalyst dosage, and solution pH. The optimal conditions were Fe 1.0 wt%, LVF 10 mg L^-1, Fe-ZnO/WO₃ dosage 0.5 g L^-1, and pH 7 for LVF photodegradation up to 96% with a kinetic rate constant of 0.0342 min^-1 and were stable in photodegradation efficiency (90%) after five test cycles. In the visible LED light, the activation bandgap was estimated to be 2.75 eV with high electron-hole pair separation and charge transfer from Fe-ZnO to WO₃ that could enhance the generation of active species of ^•OH. Moreover, the more effective charge separation of Fe-ZnO/WO₃ were confirmed by lower PL intensity and longer charge carrier lifetime. Fe-ZnO/WO₃ also demonstrated the excellent electrochemical properties with high photocurrent and small resistance. For the LVF degradation, 3 possible pathways were proposed with 12 intermediate products. This study demonstrated that the synthesized Fe-ZnO/WO₃ could serve as a reliable visible-light responsive photocatalysts with the potential for degrading antibiotics in solution.

Transformation of CuS/ZnS nanomaterials to an efficient visible light photocatalyst by 'photosensitizer' graphene and the potential antimicrobial activities of the nanocomposites

We report the growth of CuS/ZnS (CZS) nanoparticles (NPs) on the graphene sheet by a facile green synthesis process. The CuS/ZnS-graphene (CZSG) nanocomposites exhibit enhanced visible light photocatalytic activity towards organic dye (methylene blue) degradation than that of CZS nanoparticles. To find the reason for the enhanced photo-activity, we propose a new photocatalytic mechanism where graphene in the CZSG nanocomposites acts as a 'photosensitizer' for CZS nanoparticles. This distinctive photocatalytic mechanism is noticeably different from all other previous research works on semiconductor-graphene hybrid photocatalysts where graphene behaves as an electron reservoir to capture the electrons from photo-excited semiconductor. This novel idea of the photocatalytic mechanism in semiconductor-graphene photocatalysts could draw a new track in thinking for designing of graphene-based photocatalysts for solving environmental pollution problems and they also show remarkable antimicrobial activities.

Recent progress in g-C3N4, TiO2 and ZnO based photocatalysts for dye degradation: Strategies to improve photocatalytic activity

Water contamination by dyes is a matter of concern for human health and the environment. Various methods (membrane separation, coagulation and adsorption) have been explored to remove/degrade dyes. However, now the exploitation of semiconductor assisted materials using renewable solar energy has emerged as a potential candidate to resolve the issue. Although, single component photocatalysts (ZnO, TiO₂, ZrO₂) were experimented, due to their low efficiency and stability due to the high recombination rate electron-hole pair and inefficient visible light absorption, composites of semiconductor materials are being used. Semiconductor heterojunction systems are developed by coupling two or more semiconductor components. The synergistic effect of their properties, such as adsorption and improved charge carrier migration, is observed to increase overall stability. This review covers recent progress in advanced nanocomposite materials based on g-C₃N₄, TiO₂ and ZnO used as photocatalysts with details of enhancing the photocatalytic properties by heterojunctions, crystallinity and doping. The conclusion at the end displays a summary, research gaps and future outlook. A holistic analysis of recent progress to demonstrate the efficient heterojunctions for photodegradation with optimal conditions, this review will be helpful for the development of efficient heterostructured systems for photodegradation. This review covers references from the year 2017-2020.

Tribocatalytic degradation of dyes by tungsten bronze ferroelectric Ba2.5Sr2.5Nb8Ta2O30 submicron particles

Searching for a new approach in environmental remediation in terms of dye degradation is important in industrialized society. In this work, ferroelectric Ba2.5Sr2.5Nb8Ta2O30 (BSNT) submicron powders prepared by the high-temperature solid-phase method are used for dye degradation under magnetic stirring. The dye in solution can be quickly degraded by magnetically stirring BSNT submicron particles in the dark in ambient temperature conditions. More importantly, the degradation efficiency can be greatly improved through simple modification of the stirring materials from glass to polypropylene, with a degradation efficiency of rhodamine B as high as 99% in 1.5 h at a gentle stirring speed of 300 rpm. Control experiments reveal that the degradation of the dye is mainly contributed by the friction between BSNT submicron particles and PTFE stirring rods. It is proposed that the friction between ferroelectric polar BSNT particles and PTFE causes charge transfer and induces a non-zero internal electric field to drive the separation of electron-hole pairs in BSNT particles, resulting in a novel tribocatalytic degradation of the dye, which is proven by the detection of ˙OH and ˙O2 - intermediate products during stirring. This work demonstrates that the friction energy of ferroelectric materials with strong polarization is an alternative approach for highly efficient dye degradation.

Photocatalytic-persulfate- oxidation for diclofenac removal from aqueous solutions: Modeling, optimization and biotoxicity test assessment

In this paper, the influence of several aquatic factors (the nature of catalyst, the initial pH and the initial concentration of the pollutant) on the photocatalytic degradation of diclofenac (DFC), one of the most widely prescribed anti-inflammatory non-steroidal drug, was studied. Also, in order to examine the intensification process, the variation of the photocatalytic DFC degradation in the presence of sodium persulfate (PPS) was analyzed. It was found that, compared to titanium dioxide (TiO₂), the zinc oxide (ZnO) photocatalyst performed exceptionally well, with a 96.13% DFC degradation efficiency after 150 min. The photodegradation of DFC by ZnO catalyst fitted well the Langmuir-Hinshelwood kinetic model. The maximum efficiency is 97.27% for simulated solar-UVA/ZnO/PPS and 77% for simulated solar-UVA/ZnO. In order to determine the optimal conditions leading to the maximization of DFC removal, an artificial neural network (ANN) modeling approach combined with genetic algorithm (GA) was applied. The best ANN determined had a correlation of 0.999 and it was further used in the process optimization where a 99.7% degradation efficiency was identified as the optimum under the following conditions: DFC initial concentration 37,9 mg L^-1, pH 5,88 and PPS initial concentration 500 mg L^-1. The effectiveness of the process and the toxicity of the pharmaceutical pollutants and their by-products were also evaluated and confirmed by the biological tests using liver and kidney of Mus musculus mice.

Photocatalytic degradation of organic dye and tetracycline by ternary Ag2O/AgBr-CeO2 photocatalyst under visible-light irradiation

In this work, CeO2 nanosheets decorated with Ag2O and AgBr are successfully fabricated via a simple sediment-precipitation method. The as-prepared ternary Ag2O/AgBr-CeO2 composite with double Z-scheme construction was analyzed by various analytical techniques. Ag nanoparticles (NPs) used as the electron medium could reduce the recombination of photoelectrons and holes, thus leading to the improvement of photocatalytic performance of these catalysts. Due to the unique structure and composite advantages, the optimal Ag2O/AgBr-CeO2 photocatalysts exhibit the superior tetracycline (TC) degradation efficiency of 93.23% and favorable stability with near-initial capacity under visible light irradiation. This ternary Z-scheme structure materials will be the well-promising photocatalysts or the purification of antibiotic wastewater.

Graphitic carbon nitride: a sustainable photocatalyst for organic pollutant degradation and antibacterial applications

Recently, graphitic carbon nitride (GCN) has been found to be of great interest in various sustainable applications. In this study, a simple preparation method using urea was utilized to synthesize GCN. In order to understand various morphological, structural, and optical aspects of the as-prepared sample, GCN was characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Brunauere-Emmette-Teller (BET), scanning electron microscopy (SEM), and diffused reflectance spectra (DRS) analysis. The visible-light-driven photocatalytic activity of prepared GCN was analyzed for various cationic dyes (Crystal violet, rose bengal, rhodamine B, auramine O, methylene blue) and anionic dyes (phenol red, xylenol orange, cresol red, methyl orange). The calculated efficiencies of degradation and values of apparent rate constant for all dye samples suggested that cationic dyes are more actively degraded using GCN than anionic dyes. In addition, GCN was further analyzed for its splendid antibacterial activity against pathogenic bacteria (Klebsiella pneumonia and Escherichia coli). The synthesized photocatalyst holds a bright scope for the efficient remediation of organic pollutants and bacterial disinfection in wastewater. Graphical abstract.

Fabrication of a Novel AgBr/Ag2MoO4@InVO4 Composite with Excellent Visible Light Photocatalytic Property for Antibacterial Use

A novel AgBr/Ag2MoO4@InVO4 composite photocatalyst with different heterojunction structures was successfully constructed by compounding InVO4 with Ag2MoO4 and AgBr. According to the degradation, antibacterial and free radical trapping data, the photocatalytic antibacterial and antifouling activities of AgBr/Ag2MoO4@InVO4 composite were evaluated, and the corresponding photocatalytic reaction mechanism was proposed. Adding AgBr/Ag2MoO4@InVO4 composite, the degradation rate of ciprofloxacin (CIP) achieved 95.5% within 120 min. At the same time, the antibacterial rates of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) achieved 99.99%. The AgBr/Ag2MoO4@InVO4 composite photocatalyst showed promising usage in photocatalytic antibacterial and purification areas.

A dual surface inorganic molecularly imprinted Bi2WO6-CuO/Ag2O heterostructure with enhanced activity-selectivity towards the photocatalytic degradation of target contaminants

The proposed mechanism reveals that under visible light, MG and AO dyes can be selectively degraded by produced radicals at the surface of the inorganic molecularly imprinted Ag₂O-CuO-Bi₂WO₆ heterojunction.

Interaction-determined sensitization photodegradation of dye complexes by boron nitride under visible light irradiation: experimental and theoretical studies

In this paper, the sensitization photodegradation of single and mixed dyes by wide band gap boron nitride (BN, 3.94 eV) under visible light irradiation has been investigated for the first time.

The effective photocatalysis and antibacterial properties of AgBr/AgVO3 composites under visible-light

With the discharge of large amount of organic pollutants and antibiotics into the water environment, the water cycle has been seriously polluted, and at the same time, various drug-resistant bacteria have emerged in succession, which poses a serious threat to human health. In recent years, photocatalytic nanomaterials have become a research hotspot in the antimicrobial area. In this study, AgBr/AgVO3 photocatalysts were prepared by a hydrothermal process and an in situ growth method. The composites were tightly connected by the (501) plane of AgVO3 and the (200) lattice plane of AgBr. The photocatalytic activity was tested by degrading Rhodamine B (RhB) solution under visible-light, and the result indicated that the photodegradation rate for RhB solution was 92.3% by the photocatalysis with 0.5AgBr/AgVO3 and the photocatalytic performance of 0.5AgBr/AgVO3 was improved compared to pure AgVO3 and AgBr. In addition, more than 99.997% of E. coli, S. aureus, and P. aeruginosa cells were killed by the photocatalysis with 0.5AgBr/AgVO3 within 30 min. These results demonstrated that the 0.5AgBr/AgVO3 heterojunction photocatalyst could be widely used in the treatment of environmental pollution and in the antibacterial field.