Photocatalytic reduction of CO₂ to formate is a sustainable way to control atmospheric CO₂ concentration and simultaneously produce valuable products using the renewable energy (light) source. The Fe₂SnO₄/gCN photocatalyst generates formate from CO₂ photoreduction at a high rate, based on the S-scheme charge transfer mechanism, which facilitates high charge separation and photocatalyst redox abilities.

A Ruddlesden–Popper phase-layered perovskite Fe₂SnO₄ is coupled with graphitic carbon nitride (gCN) in an S-scheme heterojunction. The Fe₂SnO₄/gCN heterojunction is synthesized using the sonication–calcination method. The layered structure of Fe₂SnO₄ enhances charge migration toward the junction interface and enables the internal electric field, increasing the charge separation in the overall composite. The optical characteristics of Fe₂SnO₄/gCN show an excellent visible light utilization ability, thus expanding its applicability in solar (visible light)-driven catalytic approaches. A significant formate generation rate (2.043 mM h⁻¹ gcat⁻¹) is measured over the photocatalyst using the aqueous bicarbonate as the CO₂ precursor. The isotope labeling test corroborates the generation of formate from bicarbonate. Fe₂SnO₄/gCN also displays a good stability over five reaction–regeneration cycles. The band structure of Fe₂SnO₄/gCN in conjunction with the radicals detected via spin trapping confirms the development of the S-scheme heterojunction in Fe₂SnO₄/gCN. Herein, the fabrication of the layered perovskite-based S-scheme heterojunction paves a path for pursuing the solar-driven environmental remediation strategies.