Construction of self-cleaning g-C3N4/Bi2MoO6/PVDF membrane and coupling with photo-Fenton-like reaction for sustainable removal of antibiotics in wastewater

Constructing a photocatalytic membrane and photo-Fenton reaction coupling system is a novel strategy to enhance the photocatalytic activity of the membrane and eliminate the problem of membrane contamination. Herein, a g-C3N4/Bi2MoO6/PVDF photocatalytic membrane was prepared using a tannic acid-assisted in-situ deposition method. The membrane was characterized by three advantages of photocatalytic, self-cleaning, and antibacterial properties. Under the photo-Fenton-like conditions, the membrane had superior photodegradation efficiency of 90.7% for tetracycline, one of the main antibiotic contaminants in the China's aquatic system. Moreover, the membrane had excellent photo-Fenton self-cleaning ability, its flux recovery rate was up to 96%-98% after the self-cleaning process. Photoluminescence spectra, diffuse UV-visible spectrum, transient photocurrent responses, and electrochemical AC impedance spectrum results show that the heterojunction structure formed by g-C3N4 and Bi2MoO6 could improve the separation efficiency of photogenerated electrons-hole pairs. Electron spin resonance spectroscopy confirmed the photo-electrons facilitated the formation of hydroxyl radical (·OH) in the existence of H2O2, which enhanced tetracycline degradation. Moreover, the superior photo-Fenton self-cleaning performance, which mainly relied on the active free radicals produced by the photo-Fenton-like membrane to remove dirt on the membrane surface or in the membrane pore channel. Our results may shed new light on the development of promising photocatalytic membrane systems by coupling with photo-Fenton-like processes, and facilitate their applications for wastewater treatment.

Effect of Bi2MoO6 Morphology on Adsorption and Visible-Light-Driven Degradation of 2,4-Dichlorophenoxyacetic Acid

The development of highly efficient and stable visible-light-driven photocatalysts for the removal of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) from water is still a challenge. In this work, Bi2MoO6 (BMO) materials with different morphology were successfully prepared via a simple hydrothermal method by altering the solvent. The morphology of the BMO material is mainly influenced by the solvent used in the synthesis (H2O, ethanol, and ethylene glycol or their mixtures) and to a lesser extent by subsequent thermal annealing. BMO with aggregated spheres and nanoplate-like structures hydrothermally synthesized in ethylene glycol (EG) and subsequently calcined at 400 °C (BMO-400 (EG)) showed the highest adsorption capacity and photocatalytic activity compared to other synthesized morphologies. Complete degradation of 2,4-D on BMO upon irradiation with a blue light-emitting diode (LED, λmax = 467 nm) was reached within 150 min, resulting in 2,4-dichlorophenol (2,4-DCP) as the main degradation product. Holes (h+) and superoxide radicals (⋅O2-) are assumed to be the reactive species observed for the rapid conversion of 2,4-D to 2,4-DCP. The addition of H2O2 to the reaction mixture not only accelerates the degradation of 2,4-DCP but also significantly reduces the total organic carbon (TOC) content, indicating that hydroxyl radicals are crucial for the rapid mineralization of 2,4-D. Under optimal conditions, the TOC value was reduced by 84.5% within 180 min using BMO-400 (EG) and H2O2. The improved degradation performance of BMO-400 (EG) can be attributed to its particular morphology leading to lower charge transfer resistance, higher electron-hole separation, and larger specific surface area.

Graphitic carbon nitride (g-C3N4)-assisted materials for the detection and remediation of hazardous gases and VOCs

Graphitic carbon nitride (g-C3N4)-based materials are attracting attention for their unique properties, such as low-cost, chemical stability, facile synthesis, adjustable electronic structure, and optical properties. These facilitate the use of g-C3N4 to design better photocatalytic and sensing materials. Environmental pollution by hazardous gases and volatile organic compounds (VOCs) can be monitored and controlled using eco-friendly g-C3N4- photocatalysts. Firstly, this review introduces the structure, optical and electronic properties of C3N4 and C3N4 assisted materials, followed by various synthesis strategies. In continuation, binary and ternary nanocomposites of C3N4 with metal oxides, sulfides, noble metals, and graphene are elaborated. g-C3N4/metal oxide composites exhibited better charge separation that leads to enhancement in photocatalytic properties. g-C3N4/noble metal composites possess higher photocatalytic activities due to the surface plasmon effects of metals. Ternary composites by the presence of dual heterojunctions improve properties of g-C3N4 for enhanced photocatalytic application. In the later part, we have summarised the application of g-C3N4 and its assisted materials for sensing toxic gases and VOCs and decontaminating NOx and VOCs by photocatalysis. Composites of g-C3N4 with metal and metal oxide give comparatively better results. This review is expected to bring a new sketch for developing g-C3N4-based photocatalysts and sensors with practical applications.

Accelerated radical generation from visible light driven peroxymonosulfate activation by Bi2MoO6/doped gCN S-scheme heterojunction towards Amoxicillin mineralization: Elucidation of the degradation mechanism

A novel S-scheme photocatalyst Bi₂MoO₆ @doped gCN (BMO@CN) was prepared through a facile microwave (MW) assisted hydrothermal process and further employed to degrade Amoxicillin (AMOX), by peroxymonosulfate (PMS) activation with visible light (Vis) irradiation. The reduction in electronic work functions of the primary components and strong PMS dissociation generate abundant electron/hole (e^-/h⁺) pairs and SO₄^*-,*OH,O₂^*-reactive species, inducing remarkable degeneration capacity. Optimized doping of Bi₂MoO₆ on doped gCN (upto 10 wt%) generates excellent heterojunction interface with facile charge delocalization and e^-/h⁺ separation, as a combined effect of induced polarization, layered hierarchical structure oriented visible light harvesting and formation of S-scheme configuration. The synergistic action of 0.25 g/L BMO(10)@CN and 1.75 g/L PMS dosage can degrade 99.9% of AMOX in less than 30 min of Vis irradiation, with a rate constant (k_obs) of 0.176 min^-1. The mechanism of charge transfer, heterojunction formation and the AMOX degradation pathway was thoroughly demonstrated. The catalyst/PMS pair showed a remarkable capacity to remediate AMOX-contaminated real-water matrix. The catalyst removed 90.1% of AMOX after five regeneration cycles. Overall, the focus of this study is on the synthesis, illustration and applicability of n-n type S-scheme heterojunction photocatalyst to the photodegradation and mineralization of typical emerging pollutants in the water matrix.

Uracil-mediated supramolecular assembly for C-enriched porous carbon nitrides with enhanced photocatalytic hydrogen evolution

The porous structure and the introduction of C doping together improve the activity of photocatalytic hydrogen production.

Construction of the Sn-doped defect pyrochlore oxide KNbMoO6·H2O/g-C3N4 composite and its photocatalytic reduction of CO2

The Sn-doped defect pyrochlore oxide KNbMoO6·H2O/g-C3N4 composite can be used as a photocatalyst for conversion of CO2 in order to deal with energy and environmental issues.