A novel Pd nano-skeleton (Pd NSs) modified Bi 2 MoO 6 balls photocatalyst was prepared by a facile hydrothermal treatment. The characterization by multiple techniques demonstrated the excellent light absorption and effective photo-generated electron-hole pairs separation performance of the composite catalyst, which further proved its superior photocatalytic property. Compared to the pure Bi 2 MoO 6 nanosheets, carbon quantum dots (CQDs) modified Bi 2 MoO 6 balls and Pd nanoparticles (Pd NPs) modified Bi 2 MoO 6 balls catalysts, 1.3% Pd NSs@Bi 2 MoO 6 sample exhibited the optimal catalytic performance for removing methyl orange (MO), methylene blue (MB), K 2 Cr 2 O 7 , phenol and the simulated wastewater mixture formed by the first three above under the illumination of visible light. Above all, the degradation efficiency increased about 5 times that of the pure Bi 2 MoO 6 balls for the degradation of MO. This great improvement was mainly attributed to Pd NSs with many contact edges, which provided more active sites for the adsorption reaction of organic dye molecules, following its better near-infrared light absorption capacity in the catalytic system. The active species mainly involved in the reaction were verified by ESR technique and the trapping test, mainly involving O 2 − , holes, OH, etc., and a possible photocatalytic reaction mechanism and pollutant degradation pathway were also proposed.
The specific roles of tartaric acid (TA), as an eco-friendly ligand, in homogeneous and heterogeneous copper-catalyzed systems were systematically revealed and new mechanisms of TA enhancing the three Fenton-like processes were proposed to provide a theoretical significance in overcoming the deficiency of conventional Fenton processes. The results identified hydroxyl radical (•OH) as the main species responsible for the simultaneous decomposition of TA and metronidazole (MNZ) according to TOC removal. The ESR technique was used to detect superoxide radicals (•O 2 − ), carbon-centered radical (•R) and hydrogen radical (•H) in the Cu 2+ /TA/H 2 O 2 system, which contributed to the acceleration of the Cu 2+ /Cu + redox cycle. The enhancing effect of TA on the homogeneous process was ascribed to the formation of a soluble complex with Cu 2+ , which favored the pH range extension, Cu + oxidation , and radical generation. Moreover, the adsorption of TA on the catalysts surface promoted the consumption of H 2 O 2 , inducing •OH generation. The formed surface complex (≡Cu 2+ -TA) also accelerated the regeneration of ≡Cu + , which was confirmed by density functional theory (DFT) calculation and surface characterization analysis (SEM, XRD, and XPS). The possible degradation pathways of MNZ in TA-modified Fenton-like system were also clarified.
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