Decomposition of microplastics using copper oxide/bismuth vanadate-based photocatalysts: Insight mechanisms and environmental impacts

To mitigate marine pollution, we improved the photo-Fenton reaction of modified nanoscale CuO/BiVO4 photocatalysts to resolve the challenge of efficient microplastic degradation in wastewater treatment. Material property analysis and computational results revealed that deposition of CuO onto BiVO4 nanocomposites improved photocatalytic activity by promoting an excess of electrons in CuO and surface charge transfer, resulting in an increased production of e--h+ for ROS generation via H2O2 activation. 1O2 was dominated and identified through quenching experiments, XPS analysis, and EPR. ROS generation increased via H2O2 activation, causing major surface abrasion and increased carbonyl and vinyl indices in microplastics. Treated water had minimal impact on Lycopersicon esculentum Mill. seedling growth but caused considerable mortality in cell lines and Moina macrocopa mortality at greater dosages due to their sensitivity to ions and H2O2 residuals. Overall, this treatment can effectively degrade microplastics, but the dilution of treated water is still needed before being discharged.

Nanoscale Heterogeneities and Composition-Reactivity Relationships in Copper Vanadate Photoanodes

The photoelectrochemical performance of thin film photoelectrodes can be impacted by deviations from the stoichiometric composition, both at the macroscale and at the nanoscale. This issue is especially pronounced for the class of ternary compounds that are currently investigated for simultaneously achieving the optoelectronic characteristics and chemical stability required for solar fuel generation. Here, we combine macroscopic photoelectrochemical testing with atomic force microscopy (AFM) and scanning transmission X-ray microscopy (STXM) to reveal relationships between photoelectrochemical activity, nanoscale morphology, and local chemical composition in copper vanadate (CVO) thin films as a model system. For films with varying Cu/(Cu + V) ratios around the ideal stoichiometry of stoiberite Cu₅V₂O₁₀, AFM resolves submicrometer morphology variations, which correlate with variations of the Cu content resolved by STXM. Both stoichiometric and Cu-deficient films exhibit a clear photoresponse, which indicates electronic tolerance to reduced Cu content. While both films exhibit homogeneous O and V content, they are also characterized by local regions of Cu enrichment and depletion that extend beyond individual grains. By contrast, Cu-rich photoelectrodes exhibit a tendency toward CuO secondary phase formation and a significantly reduced photoelectrochemical activity, indicating a significantly poor electronic tolerance to Cu-enrichment. These findings highlight that the average film composition at the macroscale is insufficient for defining structure-function relationships in complex ternary compounds. Rather, correlating microscopic variations in chemical composition to macroscopic photoelectrochemical performance provides insights into photocatalytic activity and stability that are otherwise not apparent from pure macroscopic characterization.

Improved Performance of BiVO4 via Surface-Deposited Magnetic CuFe2O4 for Phenol Oxidation and O2 Reduction and Evolution under Visible Light

Monoclinic BiVO₄ (BiV) is a good photoanode for water oxidation but a poor photocatalyst for organic oxidation because of slow O₂ reduction. In this work, a well-crystallized BiV microdecahedron (1-2 μm) has been deposited with a poorly crystallized cubic CuFe₂O₄ (CF) nanosphere (100 nm). For phenol oxidation and O₂ reduction to H₂O₂ in aqueous suspension under visible light, 1 wt % CF/BiV was more active than BiV by approximately factors of 14 and 7, respectively, while CF was almost not active. A (photo)electrochemical measurement showed that CF/BiV was more active than BiV not only for phenol and water oxidation under visible light but also for O₂ reduction and water oxidation in the dark. Moreover, as compared to BiV, CF/BiV was more efficient in the charge transfer to a solution species but less efficient either in the light-on electron generation or in the light-off electron disappearance. Based on the solid band edge potentials measured by ultraviolet photoelectron spectroscopy, a possible Z scheme mechanism is proposed involving charge recombination at the CF/BiV interfaces followed by the increased O₂ reduction on CF and the increased phenol oxidation on BiV.