Enhanced solar light–driven photocatalytic degradation of tetracycline and organic pollutants by novel one–dimensional ZnWO4 nanorod–decorated two–dimensional Bi2WO6 nanoflakes

Chemical-Vapor-Deposition-Synthesized Two-Dimensional Non-Stoichiometric Copper Selenide (β-Cu2-xSe) for Ultra-Fast Tetracycline Hydrochloride Degradation under Solar Light

The high concentration of antibiotics in aquatic environments is a serious environmental issue. In response, researchers have explored photocatalytic degradation as a potential solution. Through chemical vapor deposition (CVD), we synthesized copper selenide (β-Cu2-xSe) and found it an effective catalyst for degrading tetracycline hydrochloride (TC-HCl). The catalyst demonstrated an impressive degradation efficiency of approximately 98% and a reaction rate constant of 3.14 × 10-2 min-1. Its layered structure, which exposes reactive sites, contributes to excellent stability, interfacial charge transfer efficiency, and visible light absorption capacity. Our investigations confirmed that the principal active species produced by the catalyst comprises O2- radicals, which we verified through trapping experiments and electron paramagnetic resonance (EPR). We also verified the TC-HCl degradation mechanism using high-performance liquid chromatography-mass spectrometry (LC-MS). Our results provide valuable insights into developing the β-Cu2-xSe catalyst using CVD and its potential applications in environmental remediation.

ZnWO4 nanorod-colloidal SnO2 quantum dots core@shell heterostructures: Efficient solar-light-driven photocatalytic degradation of tetracycline

Zinc tungsten oxide (ZW) and colloidal SnO₂ quantum dots (CS) were synthesized individually by hydrothermal and wet chemical methods. ZW-CS core@shell nanorods were prepared using a sonochemical method for the enhanced photocatalytic activity of tetracycline (TC) degradation. ZW-CS core@shell nanorods were systematically characterized by structural, morphological mapping and optical techniques. All characterization techniques were synchronized to confirm the construction of core@shell nanorods. Optical absorption studies indicate an increased light-capturing efficiency along with a reduced bandgap from 3.56 to 3.23 eV, which is further supported by photoluminescence. Mapping analysis from SEM and HR-TEM evidence the presence of elements as well as a core@shell nanostructure. The optimized sample of ZW-CS 1.0 shows improved photocatalytic degradation of TC under stimulated solar light. The TC degradation efficiency by ZW-CS 1.0 core@shell nanorods was about 97% within 2 h. The formation of core@shell nanorod structure might be the reason for the better photocatalytic tetracycline degradation performance.

High-Crystallinity BiOCl Nanosheets as Efficient Photocatalysts for Norfloxacin Antibiotic Degradation

Semiconductor photocatalysts are essential materials in the field of environmental remediation. Various photocatalysts have been developed to solve the contamination problem of norfloxacin in water pollution. Among them, a crucial ternary photocatalyst, BiOCl, has attracted extensive attention due to its unique layered structure. In this work, high-crystallinity BiOCl nanosheets were prepared using a one-step hydrothermal method. The obtained BiOCl nanosheets showed good photocatalytic degradation performance, and the degradation rate of highly toxic norfloxacin using BiOCl reached 84% within 180 min. The internal structure and surface chemical state of BiOCl were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, Fourier transform infrared spectroscopy (FTIR), UV-visible diffuse reflectance (UV-vis), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectra (XPS), and photoelectric techniques. The higher crystallinity of BiOCl closely aligned molecules with each other, which improved the separation efficiency of photogenerated charges and showed high degradation efficiency for norfloxacin antibiotics. Furthermore, the obtained BiOCl nanosheets possess decent photocatalytic stability and recyclability.

In2S3 nanoflakes grounded in Bi2WO6 nanoplates: A novel hierarchical heterojunction catalyst anchored on W mesh for efficient elimination of toluene

Toxic toluene can be completely oxidized in CO₂ and H₂O with novel three-dimensional (3D) In₂S₃@Bi₂WO₆ hierarchical crystals under visible light. Dense and uniform In₂S₃ nanoflakes are rooted in Bi₂WO₆ nanoplates which intercross with each other and are anchored on a pliable tungsten mesh. This leads to the construction of a stable and porous interface for adsorbing and decomposing target gaseous toluene. The firm contact between In₂S₃ and Bi₂WO₆ initiates the formation of a built-in electric field that helps in channeling the photogenerated electrons in Bi₂WO₆ CB to quench the holes in₂S₃ VB. This results in highly capable electrons and holes, as well as notable increase in the yields of •O₂^- and •OH. 99.7% of toluene is removed and 93.4% is converted to CO₂ when it is degraded in simulated air. This validates its remarkable efficacy in detoxifying toluene.

A review on the applications of zinc tungstate (ZnWO4) photocatalyst for wastewater treatment

The monoclinic wolframite-phase structure of ZnWO₄ materials has been frequently synthesised, characterised, and applied in optical fibres, environmental decontamination, electrochemistry, photonics, catalysis, and not limited to magnetic applications. However, the problems of crystal growth conditions and mechanisms, growth, the crystal quality, stability, and the role of synthesis parameters of ZnWO₄ nanoparticles remain a challenge limiting its commercial applications. This review presents recent advances of ZnWO₄ as an advanced multi-functional material for Industrial wastewater treatment. The review also examines the influence of the synthesis parameters on the properties of ZnWO₄ and provides insight into new perspectives on ZnWO₄-based photocatalyst. Many researches have shown significant improvement in the efficiency of ZnWO₄ by mixing with polymers and doping with metals, nonmetals, and other nanoparticles. The review also provides information on the mechanism of doping ZnWO₄ with metals, non-metals, metalloids, metals oxides, and polymers based on different synthesis methods for bandgap reduction and extension of its photocatalytic activity to the visible region. The doped ZnWO₄ photocatalyst was a more effective and environmentally friendly material for removing organic and inorganic contaminants in industrial wastewater than ordinary ZnWO₄ nanocrystalline under suitable growth conditions.

One-pot synthesis of bismuth yttrium tungstate nanosheet decorated 3D-BiOBr nanoflower heterostructure with enhanced visible light photocatalytic activity

A visible light driven BiOBr/Bi_xY_1-xWO₆ nanocomposite photocatalyst of various compositions are prepared by the addition of different amounts of KBr (0.5, 1.0, 1.5, 2.0 mmol) in Bi_xY_1-xWO₆ by a one-pot hydrothermal method. Furthermore, the photocatalytic properties of the as-prepared materials are analyzed by the decomposition of methylene blue under visible light illumination. In particular, the BiOBr/Bi_xY_1-xWO₆ nanocomposite prepared by taking 1.5 mmol of KBr present a superior photocatalytic ability (78.3%) with the rate constant value 0.016 min^-1, a low bandgap (E_g = 2.51 eV) as well as photoluminescence emission intensity than other photocatalysts prepared in this study. The radical scavenging studies revealed that OH and h⁺ performed an imperative role in the decomposition of methylene blue. Furthermore, the optimized photocatalyst is stable even after four cycles, which exposes the excellent photostability and reusability properties of the photocatalyst. In addition, a plausible mechanism of decomposition of methylene blue under visible light irradiation is also proposed.

An effective CuO/Bi2WO6 heterostructured photocatalyst: Analyzing a charge-transfer mechanism for the enhanced visible-light-driven photocatalytic degradation of tetracycline and organic pollutants

Over the past few years, industrial pollution has had a negative impact on aquatic life by releasing significant amounts of hazardous chemicals into the ecosystem. Therefore, it is imperative to develop photocatalytic materials with good photocatalytic activity and easy separation. Photocatalytic degradation has been employed for the removal of such contaminants using binary hybrid nanocomposites as photocatalysts. In the present study, binary CuO/Bi₂WO₆ (CuBW) nanocomposites with different loadings of Bi₂WO₆ (~5, 10, and 15 mg) were successfully constructed using a simple hydrothermal method and used as a potential photocatalyst for the degradation of tetracycline (TC) and methylene blue (MB) under visible-light irradiation. The structure, surface morphology, and optical properties were studied to investigate the formation of the heterostructure. Among the prepared samples, the CuBW nanocomposite containing the optimum content of Bi₂WO₆ (~10 mg) exhibited superior activity toward the photocatalytic degradation of TC (97.72%) in 75 min and MB (99.43%) in 45 min under visible-light illumination. Radical trapping experiments suggested that holes and •OH radicals were the dominant reactive species during the photocatalytic process. The photoelectrochemical results also confirmed the improved separation and transfer of electron-hole pairs at the interface of Bi₂WO₆ and CuO. Our results demonstrate that the binary CuO/Bi₂WO₆ nanocomposite has significant potential applications in the field of photocatalysis due to its enhanced separation of the photoexcited charge carriers and strong synergistic interactions.

Recent progress in transition metal oxide/sulfide quantum dots-based nanocomposites for the removal of toxic organic pollutants

Water is an essential solvent that is extremely necessary for the survival of life. Water pollution due to the increased utilization of water for various processes, including domestic and industrial activities, poses a special threat that contaminates both surface and ground water. In recent years, advanced oxidation processes (AOPs) have been applied to deal with wastewater problems, which is a green method used to oxidize organic contaminants with strong oxidative radical species. Among the AOPs, photocatalytic technology is one of the most promising strategies for wastewater cleaning, which fulfills the aims of environmentally friendly and sustainable development. Owing to their unique electronic, optical, and structural properties, nanoscale semiconductors have received substantial interest as materials for AOPs, particularly inspired by their superb quantum confinement effects and large surface-area-to-volume ratio, which are essential for catalytic reaction kinetics. Recent advancements have revealed that semiconductor nanocrystals, known as quantum dots (QDs), are newly emerging zero-dimensional (0-D) nanomaterials, which have garnered much attention owing to their special physiochemical characteristics such as high conductivity, thermo-chemical and opto-mechanical stability, high adsorption coefficients, and, most importantly, their admirable recyclability. In this review, we provide a clear understanding of the importance of semiconductor QD-based nanocomposites in the degradation of organic pollutants, in addition to the mechanism involved in the reaction process. Following this, the enhancement of different materials, such as metal oxides and metal sulfide QD-based nanocomposites, is discussed in the context of combating environmental pollution.

Enhanced solar-light-driven photocatalytic and photoelectrochemical properties of zinc tungsten oxide nanorods anchored on bismuth tungsten oxide nanoflakes

At present, sustainable water supply and energy generation are the most important challenges faced by humankind globally. Thus, it is crucial to progress ecological techniques for sustainable removal of organic pollutants from wastewater and generation of hydrogen as an alternative to fossil fuels. In this study, zinc tungsten oxide (ZnWO₄) nanorods, bismuth tungsten oxide (Bi₂WO₆) nanoflakes, and Bi₂WO₆/ZnWO₄ (BO-ZO) nanocomposites were prepared via a simple hydrothermal approach. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, diffuse reflectance spectroscopy, and electrochemical analyses were conducted to confirm the formation of the BO-ZO heterostructure. The structural and morphological analyses revealed that the ZnWO₄ nanorods were moderately dispersed on the Bi₂WO₆ nanoflakes. The bandgap tuning of BO-ZO nanocomposite confirmed the establishment of the heterostructure with band bending properties. The BO-ZO nanocomposite could degrade 99.52% of methylene blue (MB) within 60 min upon solar-light illumination. The photoelectrochemical (PEC) measurement results showed that the BO-ZO nanocomposite showed low charge-transfer resistance and high photocurrent response with good stability. The BO-ZO photoanode showed a low charge-transfer resistance of 35.33 Ω and high photocurrent density of 0.1779 mA/cm² in comparison with Ag/AgCl in a 0.1 M Na₂SO₃ electrolyte under solar-light illumination. The MB photocatalytic degradation and PEC water oxidation mechanisms of the nanocomposite were investigated.

Enhanced solar-light-driven photocatalytic properties of novel Z-scheme binary BiPO4 nanorods anchored onto NiFe2O4 nanoplates: Efficient removal of toxic organic pollutants

Global environmental problems have been increasing with the growth of the world economy and have become a crucial issue. To replace fossil fuels, sustainable and eco-friendly catalysts are required for the removal of organic pollutants. In this study, nickel ferrite (NiFe₂O₄) was prepared using a simple wet-chemical synthesis, followed by calcination; bismuth phosphate (BiPO₄) was also prepared using a hydrothermal method. Further, NiFe₂O₄/BiPO₄ nanocomposites were prepared using a hydrothermal technique. Numerous characterization studies, such as structural, morphology, surface area, optical, photoluminescence, and photoelectrochemical investigations, were used to analyze NiFe₂O₄/BiPO₄ nanocomposites. The morphology analysis indicated a successful decoration of BiPO₄ nanorods on the surface of NiFe₂O₄ nanoplate. Further, the bandgap of the NiFe₂O₄/BiPO₄ nanocomposites was modified owing to the formation of a heterostructure. The as-prepared NiFe₂O₄/BiPO₄ nanocomposite exhibited promising properties to be used as a novel heterostructure for tetracycline (TC) and Rhodamine B (RhB) removal. The NiFe₂O₄/BiPO₄ nanocomposite degrades TC (98%) and RhB (99%) pollutants upon solar-light irradiation within 100 and 60 min, respectively. Moreover, the trapping experiments confirmed the Z-scheme approach of the prepared nanocomposites. The efficient separation and transfer of photogenerated electron-hole pairs rendered by the heterostructure were confirmed by utilizing electrochemical impedance spectroscopy, photocurrent experiments, and photoluminescence. Mott-Schottky measurements were used determine the positions of the conduction and valence bands of the samples, and the detailed mechanism of photocatalytic degradation of toxic pollutants was projected and discussed.

Ultra-small zinc oxide nanosheets anchored onto sodium bismuth sulfide nanoribbons as solar-driven photocatalysts for removal of toxic pollutants and phtotoelectrocatalytic water oxidation

Heterostructured nanohybrids were prepared from sodium bismuth sulfide (NaBiS₂) and zinc oxide (ZnO) through hydrothermal process. The nanocomposite was used for tetracycline (TC) degradation as well as photoelectrochemical (PEC) water oxidation. Morphology and structural analyses were performed to confirm the dispersion of ultra-small ZnO nanosheets into the NaBiS₂ nanoribbons. By tuning the band gap, it was possible to degrade tetracycline toxic pollutant within 90 min under the simulated solar light irradiation, while PEC suggested a lower charge-transfer resistance, high photocurrent response, and exceptionally good stability. The highest photocurrent density of 0.751 mAcm^-2 vs. Ag/AgCl in 0.1 M Na₂SO₃ solution was observed under solar-light illumination. Detailed photocatalytic mechanisms for the degradation of TC and PEC water oxidation are discussed.

Highly efficient activation of peroxymonosulfate by Co3O4/Bi2WO6 p-n heterojunction composites for the degradation of ciprofloxacin under visible light irradiation

Photocatalytic technology assisted via peroxymonosulfate (PMS) has good potential in water treatment. In this study, the Co₃O₄/Bi₂WO₆ composite was constructed via an in-situ calcination process and used to activate PMS for the degradation of ciprofloxacin (CIP) under visible light irradiation. The obtained 5 wt% Co₃O₄/Bi₂WO₆(CBWO-2) can highly effectively remove 86.2% CIP within 5 min visible light irradiation in presence of PMS. The excellent degradation performance of Co₃O₄/Bi₂WO₆/PMS system can be attributed to the synergistic effect between p-n heterojunction and PMS activation. The conduction band and valence band deviation between Co₃O₄ and Bi₂WO₆ were calculated by XPS techniques. Besides, DFT calculations were performed to further confirm the internal structure between Co₃O₄ and Bi₂WO₆. This work not only provides an approach to fabricate heterostructures but also indicated that Co₃O₄/Bi₂WO₆/PMS/Vis system is a potential environment remediation alternative for the efficient removal of recalcitrant organic compounds from wastewaters.

Spherical Bi2WO6/Bi2S3/MoS2 n-p Heterojunction with Excellent Visible-Light Photocatalytic Reduction Cr(VI) Activity

Exploiting excellent photocatalytic activity and stable heterostructure composites are of critical importance for environmental sustainability. The spherical Bi₂WO₆/Bi₂S₃/MoS₂ n-p heterojunction is first prepared via an in situ hydrothermal method using Bi₂WO₆, Na₂MoO₄·2H₂O, and CH₄N₂S, in which the intermediate phase Bi₂S₃ is formed due to chemical coupling interaction of Bi₂WO₆ and CH₄N₂S. Scanning electron microscopy indicates that the compactness of the sample can be easily adjusted by changing the contents of S and Mo sources in the solution. The results of ultraviolet–visible (UV–vis) diffuse reflectance spectra, photoluminescence, transient photocurrent response, and electrochemical impedance spectra indicate that the formation of heterojunctions contributes to enhancing visible-light utilization and promoting photogenerated carrier separation and transfer. The composite material is used as a catalyst for the visible light photocatalytic reduction of Cr(VI). Remarkably, the optimal Bi₂WO₆/Bi₂S₃/MoS₂ n-p heterojunction achieves the greatest Cr(VI) reduction rate of 100% within 75 min (λ > 420 nm, pH = 2); this rate is considerably better than the Cr(VI) reduction rate of pure Bi₂WO₆. The recycling experiment also reveals that the photocatalytic performance of the n-p heterojunction toward Cr(VI) is still maintained at 80% after three cycles, indicating that the n-p heterojunction has excellent structural stability. The capture experiment proves that the main active species in the system are electrons. The reasonable mechanism of Bi₂WO₆/Bi₂S₃/MoS₂ photocatalytic reduction Cr(VI) is proposed. Our work provides new research ideas for the design of ternary heterojunction composites and new strategies for the development of photocatalysts for wastewater treatment.