Facile synthesis of ternary dual Z-scheme g-C3N4/Bi2MoO6/CeO2 photocatalyst with enhanced 4-chlorophenol removal: Degradation pathways and mechanism

CeO2 nanospheres incorporated with Bi2MoO6/g-C3N4 enhanced photocatalysis towards environmental pollutant Rhodamine B removal

We have adopted a novel CeO2/Bi2MoO6/g-C3N4-based ternary nanocomposite that was synthesized via hydrothermal technique. The physiochemical characterization of as-prepared samples was examined through various analytical techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy TEM, photoluminescent spectra (PL), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), and ultraviolet diffuse reflectance spectroscopy (UV-DRS) technique. In addition, the photocatalytic performance was carried out by degradation of Rhodamine B dye under visible light irradiation using this nanocatalyst. The ternary nanocomposite achieved 94% of the degradation efficiency within 100 min which is higher than the pristine and binary composites under the predetermined condition pH = 7, Rhodamine B dye = 5 mg/L, and catalyst concentration = 150 mg/L. The experimental synergetic effect of CeO2/Bi2MoO6/g-C3N4 ternary nanocomposite has been ascribed to the interfacial charge carrier migration between CeO2, Bi2MoO6, and g-C3N4. The optical absorption range of CeO2/Bi2MoO6/g-C3N4 ternary nanocomposite was enhanced, and the band gap was reduced up to 2.2 eV. In addition, scavenger trapping experiment proves that the super oxide anions (O2-.) and photogenerated holes are the major active species. The reusability and stability experiment proved the CeO2/Bi2MoO6/g-C3N4 ternary nanocomposite keeps good durability during the photocatalytic degradation process after the five successive cycles. Furthermore, based on the results, the charge carrier transfer photocatalytic mechanism was also discussed. This CeO2/Bi2MoO6/g-C3N4 ternary nanocomposite may offer the cheapest material and extend the great opportunity for clean and environmental remediation approach under the visible light irradiation.

Enhanced removal of pesticide micropollutant and bacteria using solar light-assisted Ag-doped TiO2: prospects for environmental and health impacts

Pesticide micropollutants like 4-chlorophenol (4CP) and E. coli bacteria represent a substantial hazard, impacting both the environment and human health. This study delves into the effectiveness of Ag-doped TiO2 (Ag@TiO2) in removing both 4CP and E. coli. Ag@TiO2 has demonstrated remarkable effectiveness in removing 4CP under both solar and visible light conditions, earning degradation efficiencies of 91.3% and 72.8%, respectively. Additionally, it demonstrates outstanding photodegradation efficiency for 4CP (98.8%) at an initial concentration of 1 mg L-1. Moreover, Ag@TiO2 exhibited substantially higher removal performance for 4CP (81.6%) compared to TiO2 (27.6%) in wastewater. Analysis of the radicals present during the photodegradation process revealed that ·O2- primarily drives the decomposition of 4CP, with h+ and ·OH also playing significant roles in the oxidation reactions of the pollutant. Interestingly, even under dark conditions, Ag@TiO2 exhibited the capability to eliminate approximately 20% of E. coli, a percentage that increased to over 96% under solar light. In addition, the prospects for environmental and health impacts of utilizing Ag@TiO2 for pesticide micropollutant removal and bacteria were discussed.

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.

Construction of Bi/BiOI/BiOCl Z-scheme photocatalyst with enhanced tetracycline removal under visible light

Bi/BiOI/BiOCl composite photocatalyst was constructed by one-step stirring approach at ambient environment to remove of tetracycline (TC) antibiotics via photodegradation in aqueous medium. A systematic discussion of the architecture, composition, formation, photochemical performance and photocatalytic activity of Bi/BiOI/BiOCl was carried out. By adjusting the experimental conditions, it was found that the Bi/BiOI/BiOCl photocatalyst obtained by using 0.7 mmol NaBH4, I/Cl = 5% and reacting for 6 h had the greatest removal performance. Under visible light irradiation, the photocatalytic degradation efficiency of TC reached 90.3% within 60 min, surpassing that of single BiOCl and BiOI. Through the active species removal experiment, it was determined that •O2- made a primary contribution to the photocatalytic degradation process. Moreover, the formation of Z-scheme heterojunction in Bi/BiOI/BiOCl was discussed, analyzing the photocatalytic mechanism and TC degradation pathway. The ecological toxicity of TC solution before and after degradation to rice seedlings was preliminarily tested. This study provides an idea for one-step synthesis of bismuth-based composite photocatalysts, with potential applications in the photocatalytic degradation of antibiotics.

Broad-bandgap porous graphitic carbon nitride with nitrogen vacancies and oxygen doping for efficient visible-light photocatalytic degradation of antibiotics

Effective degradation methods are required to address the issue of antibiotics as organic pollutants in water resources. Herein, a two-stage thermal treatment method was used to prepare porous graphitic carbon nitride (g-C3N4) modified with nitrogen vacancies and oxygen doping at the N-(C)3 position and deep in the g-C3N4 framework. Compared with bulk g-C3N4 (BCN) (7 ± 1 m2/g), the modified sample (RCN-2h) possesses a larger specific surface area (224 ± 1 m2/g), a larger bandgap (by 0.19 eV), and a mid-gap state. In addition, RCN-2h shows 15.4, 11.2, and 9.5 times higher photodegradation rates than BCN for the degradation of 100% ofloxacin (OFX) (within 15 min), tetracycline (within 15 min), and sulfadiazine (within 35 min), respectively. The RCN-2h catalyst also exhibits superior stability and reusability. Systematic characterization and density functional theory calculations demonstrate that the synergistic effect of the porous structure, nitrogen vacancies, and oxygen doping in RCN-2h provides additional reaction sites, improved charge separation efficiency, and shorter diffusion paths for reactants and photogenerated charge carriers. Trapping experiments reveal that •O2- is the main active species in OFX photodegradation, and a possible photodegradation pathway is identified using liquid chromatography-mass spectrometry. Benefiting from the simplicity of synthesis methods and the superiority of elemental doping, carbon nitride materials with functional synergy have great potential for environmental applications.

One-pot solvothermal synthesis of Bi/Bi2S3/Bi2WO6 S-scheme heterojunction with enhanced photoactivity towards antibiotic oxytetracycline degradation under visible light

A novel noble-metal-free ternary Bi/Bi₂S₃/Bi₂WO₆ S-scheme heterojunction and Schottky junction was successfully synthesized by one-pot solvothermal method. UV-Vis spectroscopy showed improved light absorption in the ternary composite structure. Electrochemical impedance spectroscopy and photoluminescence spectroscopy confirmed the reduced interfacial resistivity and photogenerated charge recombination rate of the composites. Using oxytetracycline (OTC) as model pollutant, Bi/Bi₂S₃/Bi₂WO₆ presented high photocatalytic activity towards OTC degradation, where the removal rate of Bi/Bi₂S₃/Bi₂WO₆ was 1.3 and 4.1 times higher than that of Bi₂WO₆ and Bi₂S₃ under visible light irradiation in 15 min, respectively. The excellent visible photocatalysis activity was attributed to the SPR effect of metal Bi and the direct S-scheme heterojunction of Bi₂S₃ and Bi₂WO₆ with the matched energy band structure, which led to the increased electron transfer rate and high separation efficiency of the photogenerated election-hole pairs. After seven cycles, the degradation efficiency for 30 ppm OTC with Bi/Bi₂S₃/Bi₂WO₆ only decreased 20.4%. In the degradation solution, the composite photocatalyst leached only 16 ng/L Bi and 26 ng/L W of metal with high photocatalytic stability. Moreover, free radical quenching experiment and electron spin-resonance spectroscopy experiment revealed that ·O₂^-, ¹O₂, h⁺ and ·OH played crucial roles in the photocatalytic degradation of OTC. Based on the analysis of high performance liquid chromatography-mass spectrometry for the intermediates in the degradation process, the degradation pathway was provided. Finally, combined with ecotoxicological effect analysis, the decreased toxicity of OTC after degradation towards rice seedlings was confirmed.