Photocatalytic peroxydisulfate activation for dissolved organic matter degradation in eutrophic lake water using S-scheme BiVO4/g-C3N4 3D/2D heterojunction under visible light

Large amounts of carbon are stored primarily in dissolved organic matter (DOM), which plays an important indicator of lake eutrophication. However, removing DOM from eutrophic lakes remains a major challenge. Herein, a novel S-scheme flower-like microsphere BiVO4/nanosheet g-C3N4 3D/2D heterojunction was successfully constructed using a two-step method for DOM degradation of real eutrophic lake water in the presence of peroxydisulfate (PDS). 1.0-BiVO4/g-C3N4/PDS exhibited highly efficient photocatalytic performance with an 87.8% removal rate of DOM for 60 min, which was 5.3 and 8.9 times higher than BiVO4/PDS and g-C3N4/PDS, respectively. Sulfate radical (·SO4−), hydroxyl radical (·OH) and singlet oxygen (1O2) were mainly responsible for DOM degradation in the 1.0-BiVO4/g-C3N4/PDS system, and the transformation pathway of 1O2 was emphatically analyzed. In addition, the changes of fluorescence components in DOM were detected using synchronous fluorescence spectra, second derivative spectra, and two-dimensional correlated spectroscopy analysis. Humic-like fluorescence, fulvic-like fluorescence, and protein-like substances were removed higher than 85.30%, 73.02%, and 67.23% by the 1.0-BiVO4/g-C3N4 catalyst activating the PDS under visible light (VL), respectively. When the toxicity of catalytically treated eutrophic lake water was estimated by growth inhibition of Escherichia coli, the biotoxicity of DOM decreased continuously in the BiVO4/g-C3N4/PDS/VL coupling process. Theoretical calculations and photoelectrochemical tests suggested that the BiVO4/g-C3N4/PDS catalytic activity enhancement was attributed to the S-scheme mechanism and hybrid advanced oxidation process. It is expected that this work can provide new insight into DOM degradation in eutrophic lake water by the heterogeneous photocatalysis combined with the PDS activation system.