Multiple charge-carrier transfer channels of Z-scheme bismuth tungstate-based photocatalyst for tetracycline degradation: Transformation pathways and mechanism

Construction of Z-scheme AgCl/BiOCl heterojunction with oxygen vacancies for improved pollutant degradation and bacterial inactivation

A facile Z-scheme AgCl/BiOCl heterojunction photocatalyst with oxygen vacancies was fabricated by a water-bath method. The structural, morphological, optical and electronic properties of as-synthesized samples were systematically characterized. The oxygen vacancies were confirmed by EPR, which could optimize the band-gap of the AgCl/BiOCl heterojunction and improve the photo-induced electron transfer. The optimized AgCl/BiOCl heterojunction showed excellent photocatalytic degradation efficiency (82%) for tetracycline (TC). Simultaneously, E. coli was completely inactivated within 60 min due to the AgCl/BiOCl heterojunction. The elevated catalytic activity of the optimal AgCl/BiOCl heterojunction was ascribed to the synergistic effect of the enhanced light absorption and effective photoinduced charge carrier separation and transfer. Moreover, the degradation efficiency of the AgCl/BiOCl heterojunction towards ofloxacin, norfloxacin and Lanasol Red 5B was 73%, 74% and 96%, respectively. The experimental factors for the degradation efficiency of TC were also studied. Furthermore, active species trapping experiments indicated that superoxide radicals (˙O2-) were the main reactive species, and the Z-scheme charge transfer mechanism helped to improve the photocatalytic activity.

Efficient Photocatalytic Degradation of Tetracycline under Visible Light by an All-Solid-State Z-Scheme Ag3PO4/MIL-101(Cr) Heterostructure with Metallic Ag as a Charge Transmission Bridge

The Z-type Ag/Ag₃PO₄/MIL-101(Cr) heterojunction photocatalyst (referred to as AAM-x) was successfully prepared by a simple in situ precipitation method. The photocatalytic activity of the AAM-x samples was evaluated using a common tetracycline (TC) antibiotic. All AAM-x materials are more effective in removing TC than Ag₃PO₄ and MIL-101(Cr). Among them, AAM-3 exhibited efficient photodegradation efficiency and excellent structural stability, and the removal rate of TC (20 mg L^-1) by AAM-3 (0.5 g L^-1) under 60 min of visible light was 97.9%. The effects of photocatalyst dosage, pH, and inorganic anions were also systematically investigated. According to the X-ray photoelectron spectroscopy analysis, metallic silver particles appeared on the surface of the Ag₃PO₄/MIL-101(Cr) mixture during the catalyst synthesis. The results of photoluminescence spectra, photocurrent response, EIS, and fluorescence lifetime showed that AAM-3 has a high photogenic charge separation efficiency. An all-solid-state Z-type heterojunction mechanism including Ag₃PO₄, metallic Ag, and MIL-101(Cr) is proposed to rationalize the excellent photocatalytic performance and photostability of AAM-x composites and to explain the effect of metallic Ag acting as a charge transfer bridge. The TC intermediates were identified using liquid chromatography-mass spectrometry and possible routes of TC degradation were also discussed. This work provides a viable idea for removing antibiotics by an Ag₃PO₄/MOF-based heterogeneous structured photocatalyst.

Enhanced visible-light-driven photocatalytic degradation of tetracycline by 16% Er3+-Bi2WO6 photocatalyst

The widespread use of antibiotics in drug therapy and agriculture has seriously polluted the aquatic environment. Bismuth tungstate (Bi₂WO₆) is a new and efficient visible-light catalyst that is simple to prepare, non-toxic, stable, and corrosion resistant. Nonetheless, its efficiency has remained limited, and erbium (Er) mixing has been tested to address this. Here, a new Er³⁺-mixed Bi₂WO₆ photocatalyst was successfully prepared through the one-step hydrothermal method; pigments were characterized via XRD, SEM, BET, XPS, Uv-vis, PL and EIS. The results showed that the 16% Er³⁺-Bi₂WO₆ photocatalyst is a 250 nm flower-like nanosheet with a specific surface area of 67.1 m²/g and bandgap (Eg) of 2.35 eV, which provides the basis for superior performance. When the concentration of the catalyst was 0.4 g/L, 94.58% of the tetracycline (TC) solution (initial concentration of 10 mg/L) degraded within 60 min under visible light irradiation (λ ≥ 420 nm). ESR and LC-MS were used to identify the free radicals and intermediates for the degradation of TC pollutants; a photocatalytic degradation system and pathway were proposed. This solar-driven system will ultimately reduce resource consumption, providing a sustainable and energy-saving environmental decontamination strategy.

Recent advances in degradation of pharmaceuticals using Bi2WO6 mediated photocatalysis - A comprehensive review

The pollution of water bodies by residual pharmaceuticals is a major problem globally. Bismuth tungstate mediated photocatalysis has been effective in the removal of these organics from water. Bismuth tungstate (Bi₂WO₆) has proven to be an excellent visible light active photocatalyst because of its non-toxicity, low band gap energy and ease of preparation. It has been widely applied for the removal of a wide array of organic pollutants, particularly dyes, from wastewater. However, recently, much attention has been channelled to its application for the degradation of pharmaceuticals. In this present review, the recent trends in the applications of Bi₂WO₆ based photocatalysts for the removal of pharmaceuticals in wastewater are comprehensively discussed. The fabrication of Bi₂WO₆ based photocatalysts with enhanced photocatalytic performances through morphology control, doping and formation of heterojunctions are highlighted. Much discussion centres on the mechanisms and possible degradation pathways of antibiotic pharmaceuticals in wastewater. Finally, areas needing more attention and investigation on the use of Bi₂WO₆ based photocatalysts for removal of pharmaceuticals from wastewater especially towards real-life applications are presented for future research directions.

Construction of novel Zn2TiO4/g-C3N4 Heterojunction with efficient photodegradation performance of tetracycline under visible light irradiation

This work presented facile fabrication of carbon nitride (CN)/zinc titanate (ZT) heterojunction by one-step ball milling process for visible light-induced photocatalytic degradation. The phase structures, morphologies, functional groups, and optical properties of the prepared materials were systematically characterized by XRD, FTIR, UV-Vis DRS, and SEM techniques. The ball milling for 10 min significantly improved visible light absorption properties; the as-synthesized ZT/CN catalyst (2.8 eV) showed lower band gap energy than bare ZT (3.2 eV). This result revealed a successful incorporation. The photocatalytic activities of the heterostructure catalysts (ZT/CN) evaluated by degrading tetracycline under visible light irradiation and highest TC removal rate were obtained as 0.0193 min^-1 for ZT/CN/5, which was 6.2 times higher than that of bare CN. The most efficient photocatalyst (ZT/CN/5) could be performed three times without any loss of phase. In addition, the heterostructure catalyst was found as promising candidate for efficient photocatalytic degradation of other antibiotics and dye components.

Enhanced photocatalytic degradation of gaseous toluene and liquidus tetracycline by anatase/rutile titanium dioxide with heterophase junction derived from materials of Institut Lavoisier-125(Ti): Degradation pathway and mechanism studies

Anatase/rutile titanium dioxide (TiO₂) with heterophase junction and large Brunauer-Emmett-Teller (BET) specific surface area (50.1 m² g^-1) is successfully synthesized by calcinating Materials of Institut Lavoisier-125(Ti) (MIL-125(Ti)) with 30% O₂/Ar at the temperature of 600 °C (M-O-600). Several techniques are used to examine the physicochemical, photoelectrochemical and optical properties of samples, and their photocatalytic performances are evaluated by photodegradation of gaseous toluene and liquidus tetracycline (TC) under visible light illumination. It is found that the calcination temperature has significant influence on the crystal structure and physicochemical parameters of TiO₂. The weight fractions of rutile and anatase TiO₂ of M-O-600 are approximately 0.7 and 0.3, which displays outstanding photocatalytic activity. Through the construction of heterophase junction, M-O-600 has better oxygen adsorption and higher density of localized states, which effectively promotes the generation of superoxide radical (·O₂^-) and hydroxyl radical (·OH) species. In-situ infrared spectra indicate that toluene is oxidized to benzyl alcohol, benzaldehyde and benzoic acid in turn and then oxidized to formic acid and acetic acid before eventually degraded into H₂O and CO₂. Gas chromatography-mass spectrometry (GC-MS) is also used to further investigate the degradation pathway of toluene. Degradation pathway and mechanism of TC are studied by liquid chromatography-tandem mass spectrometry (LC-MS). Moreover, three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) and total organic carbon (TOC) show that TC can be effectively mineralized through a series of reactions by M-O-600 during photocatalysis.

Supported Atomically-Precise Gold Nanoclusters for Enhanced Flow-through Electro-Fenton

Gold (Au) has been considered catalytically inert for decades, but recent reports have described the ability of Au nanoparticles to catalyze H₂O₂ decomposition in the Haber-Weiss cycle. Herein, the design and demonstration of a flow-through electro-Fenton system based on an electrochemical carbon nanotube (CNT) filter functionalized with atomically precise Au nanoclusters (AuNCs) is described. The functionality of the device was then tested for its ability to catalyze antibiotic tetracycline degradation. In the functional filters, the Au core of AuNCs served as a high-performance Fenton catalyst; while the AuNCs ligand shells enabled CNT dispersion in aqueous solution for easy processing. The hybrid filter enabled in situ H₂O₂ production and catalyzed the subsequent H₂O₂ decomposition to HO·. The catalytic function of AuNCs lies in their ability to undergo redox cycling of Au⁺/Au⁰ under an electric field. The atomically precise AuNCs catalysts demonstrated superior catalytic activity to larger nanoparticles; while the flow-through design provided convection-enhanced mass transport, which yielded a superior performance compared to a conventional batch reactor. The adsorption behavior and decomposition pathway of H₂O₂ on the filter surfaces were simulated by density functional theory calculations. The research outcomes provided atomic-level mechanistic insights into the Au-mediated Fenton reaction.