Synthesis of S-Doped porous g-C 3 N 4 by using ionic liquids and subsequently coupled with Au-TiO 2 for exceptional cocatalyst-free visible-light catalytic activities

Abstract The development of new technologies for carbon dioxide reduction, water splitting, and pollutant degradation has been a demanding challenge in the globe due to critical energy and environmental issues. Herein, we have successfully synthesized sulfur doped porous g-C 3 N 4 (S-PCN) using ionic liquid, and then coupled nanocrystalline anatase TiO 2 and Au-modified TiO 2 to obtain nanocomposites. The amount-optimized 1 Au-6 T/6S-PCN nanocomposite exhibits exceptional visible-light activities for CO 2 conversion to CH 4 , H 2 evolution, and 2,4-dichlorophenol degradation, respectively by ∼32-time (365 μmol g −1 h −1 ), ∼41-time (330 μmol g −1 h −1 ) and ∼24-time (95% 10 mg h −1 L −1 ) enhancement compared to the porous g-C 3 N 4 (PCN). The calculated quantum efficiencies for CH 4 production and H 2 evolution are ∼4.67% and ∼3.34% at 420 nm wavelength. Based on these results, it is suggested that the exceptional photoactivities are attributed to the large surface area (100.5 m 2 g −1 ), extended visible-light response and enhanced charge separation via dopant induced surface-states and subsequently coupled Au-TiO 2 . Furthermore, the CO 2 and H as active radicals would be dominant to respectively initiate CO 2 and H 2 O reduction, and the produced OH plays a vital role in 2,4-dichlorophenol degradation. This work demonstrates that the designed PCN-based nanocomposites show promising applications in CO 2 photo-reduction, water splitting, and pollutant degradation.