In-situ formation of the heterovalent 2D Ti3C2Tx@MOF-CuII/CuI for their continuous and high efficiency photothermal and photocatalytic reduction of CO2.

The direct photocatalytic reduction of CO2 into valuable chemicals and fuels using non-precious metal catalysts offers a promising strategy to address the energy crisis and mitigate carbon emissions. However, designing highly efficient photocatalysts remains a significant challenge. In this work, we fabricate two-dimensional (2D) Ti3C2Tx@MOF-CuII/CuI heterojunctions that exhibit a CO evolution rate of 141.6 μmol·g-1·h-1, which is approximately 21.8 and 13.0 times that of pristine 2D Ti3C2Tx and 2D MOFCu, respectively. Furthermore, the synergistic combination of the photothermal effect of Ti3C2Tx and the nanoscale pseudo-greenhouse effect of the MOF-Cu layers further enhances the photocatalytic activity of the heterojunction, surpassing that of previously reported MXene-based materials. Characterization and computational studies reveal that the high intrinsic reducibility of Ti3C2Tx drives the reduction of about 53% of Cu2+ to Cu+ in the resulting 2D Ti3C2Tx@MOF-CuII/CuI heterojunctions. The abundant Cu2+/Cu+ sites are uniformly distributed throughout the heterostructure, leading to a reduced energy barrier for key reaction intermediates. In addition, the proper ratio of Cu2+/Cu+ endow the 2D Ti3C2Tx@MOF-CuII/CuI heterojunctions with good cyclic catalysis, thus realizing the continuous photocatalytic reduction. This study provides deep insights into the construction of heterovalent Cu2+/Cu+ heterojunctions based on MOFs and MXene, enabling the highly efficient collaborative photothermal and photocatalytic CO2 reduction.