A g-C3N4/rGO/Cs3Bi2Br9 mediated Z-scheme heterojunction for enhanced photocatalytic CO2 reduction

Abstract

Photocatalytic CO₂ reduction plays a crucial role in advancing solar fuels, and enhancing the efficiency of the chosen photocatalysts is essential for sustainable energy production. This study demonstrates advancements in the performance of g-C₃N₄ as a photocatalyst achieved through surface modifications such as exfoliation to increase surface area and surface oxidation for improved charge separation. We also introduce reduced graphene oxide (rGO) in various ratios to both bulk and exfoliated g-C₃N₄, which effectively mitigates charge recombination and establishes an optimal ratio for enhanced efficiency. g-C₃N₄/rGO serves to fabricate a hybrid organic/inorganic heterojunction with Cs₃Bi₂Br₉, resulting in a g-C₃N₄/rGO/Cs₃Bi₂Br₉ composite. This leads to a remarkable increase in photocatalytic conversion of CO₂ and H₂O to CO, H₂ and CH₄ at rates of 54.3 (±2.0) μmol_e⁻ g⁻¹ h⁻¹, surpassing that of pure Cs₃Bi₂Br₉ (11.2 ± 0.4 μmol_e⁻ g⁻¹ h⁻¹) and bulk g-C₃N₄ (5.5 ± 0.5 μmol_e⁻ g⁻¹ h⁻¹). The experimentally determined energy diagram indicates that rGO acts as a solid redox mediator between g-C₃N₄ and Cs₃Bi₂Br₉ in a Z-scheme heterojunction configuration, ensuring that the semiconductor (Cs₃Bi₂Br₉) with the shallowest conduction band drives the reduction and the one with the deepest valence band (g-C₃N₄) drives the oxidation. The successful formation of this high-performance heterojunction underscores the potential of the developed composite as a photocatalyst for CO₂ reduction, offering promising prospects for advancing the field of solar fuels and achieving sustainable energy goals.