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

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 S^6⁺ 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.