Insight into CO₂ Photothermal hydrogenation mechanism of Geopolymer/g-C3N4/Ni(OH)2

Photothermal synergistic catalysis provides an efficient implementation strategy for CO₂ conversion into renewable energy. Here, we synthesized a geopolymer/g-C₃N₄/Ni(OH)₂ (GCN) photothermal catalyst featuring nanoscale-interval exposed adsorption and photothermal catalytic active sites through concurrent geopolymerization and alkaline precipitation reactions. The rational modulation of Ni(NO₃)₂ proportion induced explosive nucleation of Ni(OH)₂, ultimately resulting in a nanostructure where geopolymer nanoclusters and Ni(OH)₂ nanocrystals were intergrowth on the g-C₃N₄ interface. The construction of this ternary system effectively enhanced the photogenerated electrons transfer efficiency, and synergized with the thermal effect to significantly improve CO₂ reduction efficiency. And the GCN demonstrated exceptional capture capabilities for both CO₂ and H₂. Under light irradiation, GCN exhibited non-thermal photochemical effect characteristics. Through the photo-assisted thermal catalysis synergistic action, the CO₂ conversion product rate reached 1057.89 mmol.g cat −1 .h −1 , which was 17,869.84 times and 1.16 times higher than those under pure photocatalysis and pure thermal catalysis, respectively. The corresponding CO selectivity can reach 96.05 %. And GCN exhibited stable photothermal cycling performance, the production rate in the 10th cycle still reached 970.28 mmol·g cat −1 ·h −1 . Moreover, the formation of chemical bonds at the geopolymer/Ni(OH)₂ interface effectively suppressed the excessive reduction of Ni(OH)₂ to metallic Ni 0 , thereby inhibiting deep hydrogenation of CO and ensuring high CO selectivity. This study provides both theoretical and technical foundations for the development of low-cost and high-efficiency CO₂ photothermal reduction catalysts.