Commercial TiO2 (anatase) was successfully modified with Ag nanoparticles at different nominal loadings (1%–4%) using a liquid impregnation method. The prepared materials retained the anatase structure and contained a mixture of Ag0 and AgI species. Samples exhibited extended light absorption to the visible region. The effect of Ag loading on TiO2 is studied for the photocatalytic reduction of CO2 to CH4 in a gas–solid process under high-purity conditions. It is remarkable that the reference TiO2 used in this work is entirely inactive in this reaction, but it allows for studying the effect of Ag on the photocatalytic process in more detail. Only in the case of 2% Ag/TiO2 was the formation of CH4 from CO2 observed. Using different light sources, an influence of the localized surface plasmon resonance (LSPR) effect of Ag is verified. A sample in which all Ag has been reduced to the metallic state was less active than the respective sample containing both Ag0 and Ag+, indicating that a mixed oxidation state is beneficial for photocatalytic performance. These results contribute to a better understanding of the effect of metal modification of TiO2 in photocatalytic CO2 reduction.
Microsphere Sn3O4 flower-like structure has been successfully synthesized using a novel microwave-assisted hydrothermal method and comprehensively characterized by X-ray diffraction (XRD), field emission gun scanning electron microscope (FEG-SEM) and UV Vis spectrophotometer equipped with diffuse reflectance spectroscopy (UV-Vis DRS). In order to examine its photocatalytic performance, two synthetic azo-based dyes, acid yellow 17 (AY17) and direct blue 71 (DB71), have been used as organic pollutant models degraded under visible-light illumination. The results show that the negative charges of Sn3O4 produce higher efficiency photocatalytic activity on DB71 degradation compared to that on AY17 degradation. Further investigation has confirmed that the adsorption capacities played the main role in determining photocatalytic performance and differentiated the quantum yield of dye degradation. Moreover, the different adsorption capacities are generated by the formation of electrostatic interaction and repulsion between surface charge of Sn3O4 and dyes functional groups.
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