Construction of a visible light responsive dual Z-scheme NH2-MIL-101(Fe)/CdS/g-C3N4 ternary heterojunction photocatalyst for efficient CO2 photoreduction to methanol

The photocatalytic CO2 reduction reaction using various semiconductors is exceedingly difficult due to the recombination of photo-exited electron-hole (e−, h+), inefficient irradiated light utilization, and lower adsorption capacity of CO2. An efficient design of the photocatalyst system is required to address this issue. The metal–organic frameworks (MOFs), particularly NH2-MIL-101(Fe) (NML-101(Fe)), have demonstrated exceptional efficiency in CO2 adsorption, and reduction because of its large surface area, efficient charge separation capacity, and ligand-to-metal charge transfer effect (LMCT). The synergistic effect of semiconductors CdS, g-C3N4 (GCN), and metal–organic framework on efficient photocatalytic CO2 conversion to CH3OH was investigated here. The successful synthesis and design of a dual Z-scheme NML-101(Fe)/CdS/GCN (NMCG(X)) ternary hetero-nanostructured system (THS) was demonstrated, in which CdS nanoparticles and NML-101(Fe) are deposited on the surface of GCN to form a dual Z-scheme mechanism with excellent photocatalytic performance. After 8 h of visible light irradiation, NMCG8 nanocomposites containing 37.5 % GCN, 25 % CdS, and 37.5 % NML-101(Fe) exhibit 1.53 times higher methanol production (53.89 µmolg−1) than pure NML-101(Fe) (35.11 µmolg−1). The efficient reduction of CO2 was largely attributed to the systematic transportation of photo-exited e− and h+ mediated by the dual Z-scheme mechanism, as demonstrated by PL spectra, electrochemical impedance spectra (EIS) studies, and Transient photocurrent response testing.