Y. Doekhi-Bennani
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de Waterinnovatieprijs 2021, categorie Gezond Water en Gezonde Bodem. ...
de Waterinnovatieprijs 2021, categorie Gezond Water en Gezonde Bodem.
Graphdiyne as a novel nonactive anode for wastewater treatment
A theoretical study
Removal of bromate (BrO3−) has gained increasing attention in drinking water treatment process. Photocatalysis technology is an effective strategy for bromate removal. During the photocatalytic reduction of bromate process, the photo-generated electrons are reductive species toward bromate reduction and photo-generated holes responsible for water oxidation. In this study, the monoclinic bismuth vanadate (BiVO4) single crystal was developed as a visible photocatalyst for the effective removal of bromate. The as-synthesized BiVO4 photocatalyst with optimized {010} and {110} facets ratio could achieve almost 100% removal efficiency of BrO3− driven by visible light with a first-order kinetic constant of 0.0368 min−1. As demonstrated by the electron scavenger experiment and density functional theory (DFT) calculations, the exposed facets of BiVO4 should account for the high photocatalytic reduction efficiency. Under visible light illumination, the photo-generated electron and holes were spatially transferred to {010} facets and {110} facets, respectively. The BiVO4 single crystal photocatalyst may serve as an attractive photocatalyst by virtue of its response to the visible light, spatially charge transfer and separation as well as high photocatalytic activity, which will make the removal of BrO3− in water much easier, more economical and more sustainable.
Currently available (photo-)electrochemical technologies for water treatment establish a trade-off between low-pollutant concentration and costs. This paper aims at decoupling these two variables by designing a photo-oxidation device using earth abundant materials and an electronic-free approach. The proposed device combines a graphite/graphite electrochemical system with a silicon-based solar cell that provides the necessary electrical power. First, the optimum operational voltage for the graphite/graphite electrochemical system was found to be around 1.6 V. That corresponded closely to the voltage produced by an a-Si:H/a-Si:H tandem solar cell of approximately 1.35 V. This configuration was shown to provide the best pollutant degradation in relation to the device area, removing 70% of the initial concentration of phenol and 90% of the methylene blue after 4 h of treatment. The chemical oxygen demand (COD) removal of these two contaminants after 4 h of treatment was also promising, 55 and 30%, respectively. Moreover, connecting several solar cells in series led to higher pollutant degradation but lower COD removal, suggesting that the degradation of the intermediate components is a limiting factor. This is expected to be due to the higher currents achieved by the series-connected configuration, which would favor other reactions such as polymerization over the degradation of intermediate species.
The removal of organics by photoelectrocatalytic oxidation offers a viable option to remove the contaminants at low concentrations. In this paper, we propose a BiVO4 thin films synthesized via spray pyrolysis for photoelectrocatalyic oxidation of phenol with solar light. We compare the properties of BiVO4 with those of the commonly used photocatalyst TiO2. In addition, BiVO4 films with W gradient doping were fabricated and tested for improving the photocatalytic performance of BiVO4. X-ray diffraction, atomic force microscopy, incident photon to current efficiency and spectrophotometry have been conducted for BiVO4 films of different thicknesses, as well as for TiO2. The electrochemical impedance spectroscopy and dark conductivity measurements were conducted. Phenol removal has been measured for both the TiO2 and BiVO4 samples. The best performance was found to be for a 300 nm undoped BiVO4 film, being able to reduce the phenol concentration up to 30.0% of the initial concentration in four hours.