Tunable CO₂-to-syngas conversion via strong electronic coupling in S-scheme ZnGa₂O₄/g-C₃N₄ photocatalysts

The conversion of CO₂ into syngas, a mixture of CO and H₂, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa₂O₄ nanodots (∼7 nm) rooted g-C₃N₄ nanosheets (denoted as ZnGa₂O₄/C₃N₄) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO₂-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C₃N₄ and highly distributed ZnGa₂O₄ nanodots synergistically contribute to a strong interaction between metal oxide and C₃N₄ support. Furthermore, the desirable S-scheme heterojunction in ZnGa₂O₄/C₃N₄ efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa₂O₄/C₃N₄ exhibited remarkable activity and selectivity in photochemical conversion of CO₂ into syngas, with a syngas production rate of up to 103.3 μ mol g⁻¹ h⁻¹, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H₂ ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO₂-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.