Indirect Z-scheme heterojunction of NH2-MIL-125(Ti) MOF/g-C3N4 nanocomposite with RGO solid electron mediator for efficient photocatalytic CO2 reduction to CO and CH4

Well-designed Z-scheme photocatalyst of NH2-MIL-125(Ti) MOF coupled g-C3N4 with RGO mediator synthesized with a facile hydrothermal method has been investigated for stimulating photocatalytic CO2 reduction under visible light. The amino-functionalized Ti-based MOF boosted the photocatalytic efficiency due to its high surface area and porous structure. Moreover, the NH2-MIL-125(Ti) MOF has a great ability for CO2 gas adsorption. The novel RGO-linked g-C3N4/NH2-MIL-125(Ti) nanocomposite exhibited efficient photocatalytic CO2 conversion to CH4 and CO. The experimental results showed that CO was the predominant reaction product with a production of 383.79 μmol g−1 achieved after 4 h irradiation which is 5 and 2.5 times higher compared to pure g-C3N4 and zero-MOF g-C3N4-RGO composite, respectively. However, the composite also exhibited a CH4 evolution of 13.8 μmol g−1. The amino functionality provided the MOF with antenna-like reaction sites with high affinity to CO2 molecules which improved the photocatalytic reduction of CO2 towards high CO production selectivity. An effective spatial separation and transfer of photogenerated charge carriers was also obtained as a result of RGO incorporation which constructed an effective Z-scheme bridge for the transfer of charges and limiting the high recombination rate of g-C3N4. The stability analysis of the newly developed composite revealed a continuous production of CO and CH4 in multiple cycles without any obvious deactivation under visible light. This work provides a new approach for the construction of Z-scheme heterojunction composites that would be beneficial for further investigations in selective CO2 conversion to solar fuels.