Synthesis of S-Doped porous g-C3N4 by using ionic liquids and subsequently coupled with Au-TiO2 for exceptional cocatalyst-free visible-light catalytic activities

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-C3N4 (S-PCN) using ionic liquid, and then coupled nanocrystalline anatase TiO2 and Au-modified TiO2 to obtain nanocomposites. The amount-optimized 1 Au-6 T/6S-PCN nanocomposite exhibits exceptional visible-light activities for CO2 conversion to CH4, H2 evolution, and 2,4-dichlorophenol degradation, respectively by ∼32-time (365 μmol g−1h−1), ∼41-time (330 μmol g−1h−1) and ∼24-time (95% 10 mg h−1L−1) enhancement compared to the porous g-C3N4 (PCN). The calculated quantum efficiencies for CH4 production and H2 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 m2g−1), extended visible-light response and enhanced charge separation via dopant induced surface-states and subsequently coupled Au-TiO2. Furthermore, the CO2 and H as active radicals would be dominant to respectively initiate CO2 and H2O 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 CO2 photo-reduction, water splitting, and pollutant degradation.