A novel Z-scheme porous g-C3N4 nanosheet/Ag3PO4 photocatalyst decorated with N-doped CDs for high efficiency removal of antibiotics

A novel Bi12O17Cl2/GO/Co3O4 Z-type heterojunction photocatalyst with ZIF-67 derivative modified for highly efficient degradation of antibiotics under visible light

Levofloxacin (LVX) is difficult to be naturally degraded by microorganisms in water, and its residues in water will pose significant risks to human health and ecological environment. In this study, Bi12O17Cl2 was used as the main body, Bi12O17Cl2/GO/Co3O4 composite photocatalyst was prepared by pyrolysis of zeolitic imidazolate framework-67 (ZIF-67) combined with in-situ precipitation method and used to degrade LVX. A sequence of characterizations shows that addition of Co3O4 and graphene oxide (GO) increases the visible light response range, improves the separation efficiency of photogenerated electrons and holes (e--h+) of photocatalyst, and thus improves the degradation efficiency of LVX. Under the optimal reaction conditions, the LVX degradation rate of Bi12O17Cl2/1.5GO/7.5Co3O4 can reach 91.2 % at 120 min, and its reaction rate constant is the largest (0.0151 min-1), which is 2.17, 13.14 and 1.53 times that of Bi12O17Cl2, Co3O4 and Bi12O17Cl2/7.5Co3O4, respectively, showing better photocatalytic performance. Simultaneously, the recycling stability of Bi12O17Cl2/1.5GO/7.5Co3O4 was also verified. The capture experiments and electron EPR test results showed that superoxide radicals (•O2-) and photogenerated holes (h+) were the primary active substances in the reaction process. Finally, combined with HPLC-MS results, the photocatalytic degradation pathway of LVX was derived. This work will provide a theoretical basis for the design of Metal Organic Frameworks (MOFs)-derivative modified Bi12O17Cl2-based photocatalysts.

High performance visible light response of a Z-type Bi2WO6/BiOBr/RGO heterojunction photocatalyst for the degradation of norfloxacin

A Bi₂WO₆/BiOBr/RGO (BWO/BOB/RGO) composite photocatalyst with a Z-type heterojunction was prepared by a simple one-pot hydrothermal method, and the micro-morphology and physicochemical properties of the prepared samples were characterized. After reacting under visible light for 120 min, the degradation rate of 20 mg L^-1 norfloxacin (NOR) by BWO/BOB/RGO was 95.12%, and the kinetic constant of the reaction was 6.42 times higher than that of pure BiOBr. Furthermore, BWO/BOB/RGO also shows good recycling stability and universality. The characterization results show that the improvement of the photocatalytic performance of the catalyst is mainly due to the heterojunction formed between Bi₂WO₆, RGO and BiOBr, which enhances the visible light absorption ability, accelerates the photogenerated electron migration and improves the electron-hole pair separation efficiency. The introduction of Bi₂WO₆ and RGO into the catalyst also increased its specific surface area and made it have more surface-active sites. The results of radical capture experiments showed that ˙O₂^- and h⁺ played an important role in the BWO/BOB/RGO reaction system, and the intermediate products and possible degradation pathways of the system were detected and analyzed. Furthermore, the electron transfer mechanism of the Z-type heterojunction using RGO as an electron transport medium and the mechanism of photocatalytic degradation of norfloxacin were proposed.

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.

A novel g-C3N4 nanosheet/Ag3PO4/α-Bi2O3 ternary dual Z-scheme heterojunction with increased light absorption and expanded specific surface area for efficient photocatalytic removal of TC

A novel ternary dual Z-scheme 2D g-C₃N₄ nanosheet/Ag₃PO₄/α-Bi₂O₃ (CNN/AP/BO) photocatalyst was successfully synthesized by an in situ deposition and hydrothermal-calcination method. The coupling of AP and BO remarkably enhanced the photocatalytic tetracycline (TC) degradation under visible light illumination, with an optimal removal efficiency of 91.6% (60 min), which can be attributed to the extended visible-light absorption and increased specific surface area owing to the interfacial intimate coupling with well-matched energy band positions between semiconductors. The improved photocatalytic activity resulted from the abundant free radicals by the order of ˙O₂^- > h⁺ > ˙OH based on the electron spin resonance (ESR) and quenching experiment results. In addition, the possible mechanism of TC degradation over the ternary dual Z-scheme heterojunction CNN/AP/BO was proposed.

Novel Control Strategy for Membrane Biofouling by Surface Loading of Aerobically and Anaerobically Applicable Photocatalytic Optical Fibers Based on a Z-Scheme Heterostructure Zr-MOFs/rGO/Ag3PO4 Photocatalyst

The high replacement cost of modified membranes in antibiofouling application is inevitable. Here, surface-loaded photocatalytic optical fibers (POFs) were developed as antibiofouling strategies to replace membrane modification. To prepare aerobically and anaerobically applicable POFs, novel visible light-driven zirconium-based metal-organic framework/reduced graphene oxide/Ag₃PO₄ (Zr-MOFs/rGO/Ag₃PO₄) Z-scheme heterojunctions were constructed and coated on optical fibers. After loading the POFs on the membrane surface, the antibiofouling capability of the POFs was demonstrated during membrane filtration of bacteria and foulants under visible light irradiation. The disinfection efficiencies of the POFs against Escherichia coli and Staphylococcus aureus reached 95.7 and 92.4%, respectively, by aerobic treatment and 90.3 and 85.5%, respectively, by anaerobic treatment. For the inactivated bacteria, cell membrane and membrane-associated functions were destroyed, accompanied by antioxidant enzyme decomposition, loss of cell respiration and adenosine triphosphate (ATP) synthesis capacity, and leakage and oxidation of protein, lipid, potassium, DNA, and RNA. During membrane filtration of model foulants and membrane bioreactor sludge, the POFs significantly alleviated the membrane flux decline by foulant disintegration. By qualitative and quantitative detection and quenching tests of reactive species, aerobically generated ^•O₂^- and ^•OH and anaerobically generated ^•OH from POFs played dominant roles in the antibiofouling process. This work provides unique insights into membrane fouling control based on environmentally friendly and efficient photocatalytic technology.

Enhancement of redox capacity derived from O-doping of g-C3N4/WO3 nanosheets for the photocatalytic degradation of tetracycline under different dissolved oxygen concentration

Element doping is an essential method for adjusting band structure, light absorbance and charge transfer, and separation of semiconductors. Besides this, whether the photocatalyst can function in an oxygen-deficient environment is also important. Herein, a novel Z-scheme heterojunction photocatalyst O-doped g-C₃N₄/WO₃ (OCN/W) was fabricated and used for the photocatalytic degradation of tetracycline (TC) at different dissolved oxygen concentrations. The introduction of O atoms into g-C₃N₄via hydrothermal treatment manipulates the band structure of the material by increasing the conduction band potential, thus producing more ˙O₂^-. The TC removal rate of OCN/W-2.0 is 89.8% within 60 min under visible light irradiation, which is 1.77 times higher than that of porous g-C₃N₄ nanosheets (PCN). Furthermore, the photocatalytic performance of OCN/W-2.0 also reaches 75% even under oxygen-deficient conditions. The effects of different anions and humic acid in the reaction system can be neglected. The enhanced performance can be attributed to the improved charge separation and the outstanding optical properties of the Z-scheme heterojunction. A possible mechanism was postulated, in which ˙O₂^- and h⁺ are the main reactive species in TC degradation. The OCN/W-2.0 shows a stable structure and outstanding reusability. This work provides insight into antibiotics removal under different dissolved oxygen conditions and the design of photocatalysts for practical applications.

Pollutant degradation with mediator Z-scheme heterojunction photocatalyst in water: A review

The Z-scheme heterojunction is a photocatalyst with narrow band gap and sufficiently high oxidization and reduction powers for degradation of pollutants in waters. This review firstly summarizes the fundamentals of photocatalysis, and explains the need to develop Z-scheme heterojunctions to harvest energy from sunlight effectively. Secondly, contemporary reports of degradation wastewater pollutants, including organic dyes, antibiotics, and other chemicals are reviewed and discussed. A challenge in the selection of an appropriate Z-scheme for removing a specific pollutant is the lack of available energy levels that are offered by the catalyst and the lack of redox energy levels that are required to break down essential chemical bonds of the pollutants. With reference to the redox energy levels offered by the active photocatalytic species, the redox energy levels of specific pollutants studied in literature are estimated. Challenges and prospects concerning the use of the Z-scheme to degrade recalcitrant pollutants under irradiation by sunlight are outlined at the end of this review.

Engineering Z-scheme TiO2-OV-BiOCl via oxygen vacancy for enhanced photocatalytic degradation of imidacloprid

The development and application of photocatalysts with strong redox ability to degrade refractory pesticides is the key to eliminating pesticide contamination. In this work, we develop a facile, time-saving, and surfactant-assisted method to fabricate a new Z-scheme heterojunction based on TiO2/BiOCl. This photocatalyst is rich in oxygen vacancy defects (TiO2-OV-BiOCl), and displays an excellent photocatalytic degradation performance for imidacloprid (IMD), and a possible degradation pathway of IMD is provided. The surfactant F127 plays an essential role in regulating the oxygen vacancy defects (OVDs) of TiO2-OV-BiOCl, where the OVD mainly exists in 5 layer BiOCl ultrathin nanosheets. Free radical trapping experiments demonstrate that the introduction of an OVD in BiOCl as a 'charge mediator' changes the charge-transfer mode from a type-II mechanism to a Z-scheme mechanism. The formation of a Z-scheme heterojunction leads to an excellent light utilization and higher separation efficiency of photogenerated charge carriers with a prolonged lifetime compared to those of BiOCl and TiO2/BiOCl. This work highlights the critical role of an OVD in the construction of a Z-scheme heterojunction of TiO2/BiOCl, and it can be applied to construct efficient photocatalytic systems for pesticide degradation.

Metal–organic complex-derived 3D porous carbon-supported g-C3N4/TiO2 as photocatalysts for the efficient degradation of antibiotic

g-C₃N₄/TiO₂/CNOT heterojunction photocatalysts exhibit efficient synergistic adsorption–photocatalysis performance for the removal of chlortetracycline hydrochloride (CTC-HCl).

Construction of cerium oxide nanoparticles immobilized on the surface of zinc vanadate nanoflowers for accelerated photocatalytic degradation of tetracycline under visible light irradiation

Construction of Z-scheme heterojunction has been deemed to be an effective and promising approach to boost the photocatalytic activity on account of accelerating the separation efficiency of the photogenerated carriers and maintaining the strong redox ability. Herein, an attractive CeO₂/Zn₃V₂O₈ Z-scheme heterojunction photocatalyst was rationally constructed by zero-dimensional (0D) CeO₂ nanoparticles immobilized on the surface of three-dimensional (3D) Zn₃V₂O₈ nanoflowers using a simple mixing method, and applied to the photocatalytic degradation of tetracycline (TC) under visible light irradiation. As expected, it was observed that the prepared CeO₂/Zn₃V₂O₈ hybrid illustrated significantly boosted the photocatalytic activity for the elimination of TC compared to pure Zn₃V₂O₈. More importantly, the optimized CeO₂(40 wt%)/Zn₃V₂O₈ hybrid owned the largest elimination rate of TC with 1.13 × 10^-2 min^-1, which was around 8.1 and 3.8 times as high as single CeO₂ (0.14 × 10^-2 min^-1) and Zn₃V₂O₈ (0.30 × 10^-2 min^-1), respectively. The appreciable performance improvement was mainly ascribed to the formation of Z-scheme heterojunction between CeO₂ and Zn₃V₂O₈, facilitating the transfer rate of photogenerated carriers and remaining the high reducibility of photoexcited electrons in CeO₂ and strong oxidizability of photoinduced holes in Zn₃V₂O₈. Active species capture experiments and electron spin resonance spectra showed that superoxide radicals and holes were the main active species for TC degradation. Besides, the possible degradation pathways of TC were speculated by identifying degradation intermediates, and the reasonable degradation mechanism including migration and transport behaviors of charge carriers and generation processes of reactive species were revealed in depth. This investigation enriches Zn₃V₂O₈-based Z-scheme heterojunction photocatalytic system and offers a new inspiration for the construction and fabrication of high-efficiency Z-scheme heterojunction photocatalysts to remove the antibiotics from wastewater.