Fabrication of mesoporous sulfated ZnO-modified g-C3N4 and TiO2 photocatalysts for CO2 reduction in gas phase

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Sulfated ZnO (S@ZnO) was synthesized using liquid self-assembly process through a sol-gel approach in the presence of F127 triblock copolymer. The obtained mesoporous ZnS was oxidized to ZnO and the rest part of ZnS formed surface sulfate species (SO42⁻) over the ZnO (S@ZnO) during the calcination at 450 °C. FT-IR spectrum of S@ZnO nanocomposite verified the existence of the surface ZnO sulfated, and the XPS spectrum confirmed the occurrence of S6⁺ ions to prove the surface sulfate species (SO42⁻) over the sulfated ZnO. The obtained S@ZnO was incorporated with g-C3N4 and TiO2 to yield S@ZnO/g-C3N4 and S@ZnO/TiO2 nanocomposites. Photocatalytic CO2 reduction at gaseous utilizing illumination and H2O as an electron donor was conducted to produce CH4 over the photocatalysts. The obtained S@ZnO/g-C3N4 and Pt/S@ZnO/g-C3N4 nanocomposites revealed that 3.17 and 6.36 ppm CH4 were formed within 6 h of illumination, respectively. The CH4 yields on the different photocatalysts were determined in the following trend of Pt/S@ZnO/g-C3N4 (6.36 ppm) > S@ZnO g-C3N4 (3.17 ppm) >g-C3N4, and S@ZnO (not detected). The yields of CH4 trends were 10 % S@ZnO/TiO2 (16.67 μmol g−1 h−1) > 20 % S@ZnO/TiO2 (15.16 μmol g−1 h−1) > 5 % S@ZnO/TiO2 (8.45 ppm) > S@ZnO (not detected) after 6 h of illumination. The maximum CH4 formation rate of 10 % S@ZnO/TiO2 nanocomposites was determined about of 16.67 μmol g−1 h−1. The present work is anticipated to be of great significance for highly active visible-light-induced ternary S@ZnO/TiO2 and S@ZnO/g-C3N4 photocatalysts for photoreduction of CO2.