Twin S-Scheme g-C<sub>3</sub>N<sub>4</sub>/CuFe<sub>2</sub>O<sub>4</sub>/ZnIn<sub>2</sub>S<sub>4</sub> Heterojunction with a Self-Supporting Three-Phase System for Photocatalytic CO<sub>2</sub> Reduction: Mechanism Insight and DFT Calculations
Dongdong Liu, Lipeng Jiang, Dengqian Chen, Zhengkai Hao, Bowen Deng, Yunyun Sun, Xin Liu, Boyin Jia, Limei Chen, Huitao Liu
Abstract
The use of photocatalytic solar energy to drive CO 2 reduction is beneficial for addressing fossil fuel shortages and environmental pollution issues. We synthesized a twin S-scheme g-C 3 N 4 /CuFe 2 O 4 /ZnIn 2 S 4 heterojunction, which was used to construct a self-supporting three-phase system for photocatalytic CO 2 reduction. Two built-in electric fields in this heterojunction induced effective migration of photogenerated carriers, resulting in a wide light response range and strong oxidation ability. This twin S-scheme photocatalytic system without a sacrificial agent had high CH 4 selectivity (96.8%) and surprise production rate of CH 4 (267.4 μmol g –1 h –1 ), and still maintained an excellent cycle rate (249–267.4 μmol g –1 h –1 ) during five cycles. In addition, g-C 3 N 4 /CuFe 2 O 4 /ZnIn 2 S 4 heterojunction possessed both hydrophilicity and hydrophobicity, which achieved an efficient transformation of CO 2 into CH 4 by controlling interface wettability. g-C 3 N 4 as a hydrophobic layer promoted CO 2 mass transfer to achieve the enrichment of CO 2 on the heterojunction surface; ZnIn 2 S 4 as a hydrophilic layer could well adsorb H 2 O, which was further oxidized by the photogenerated holes into many protons (H + ). Finally, DFT calculations found that Fe–N bonds located between g-C 3 N 4 and CuFe 2 O 4 played a crucial role during the photocatalytic CO 2 reduction. They served as a bridge for electron transfer to induce the bending adsorption of CO 2, which enhanced the adsorption of *CO and stabilization of *H.