Enhanced CO₂ Reduction with Cs₂AgBiBr₆-gC₃N₄ Heterojunction Photocatalysts Prepared by Green Synthesis

Halide perovskites are increasingly explored for CO 2 photoreduction to carbonaceous products and fuels. However, multistep solution-based perovskite synthesis not only poses significant safety concerns but also introduces trap states in the perovskite, negatively impacting its properties/activities. In this work, we develop Cs 2 AgBiBr 6 - x GCN heterojunction (GCN, graphitic carbon nitride) by an environmentally nonhazardous hand-grinding method. The photocatalytic CO 2 reduction activity of these hybrid catalysts is investigated in isopropyl alcohol using a 250 W mercury vapor lamp as an irradiation source. A high average CO and CH 4 yield of 12.14 and 8.85 μmol/g/h is achieved for Cs 2 AgBiBr 6 -1GCN. These results exhibit 3- and 9.8-fold improvement in CO and CH 4 production compared to pristine Cs 2 AgBiBr 6 . Space charge limited current and XPS measurements prove that GCN incorporation reduces the trap density, increases the carrier mobility, and induces strain in the perovskite. The interfacial defect passivation at the heterojunction ensures a faster and smoother charge transport, as confirmed by EIS Nyquist plots, suggesting enhanced CO 2 photoconversion activity. These results extend the use of lead-free halide double perovskites in the photocatalysis field for solar fuels, leveraging a solvent-free dry synthesis route to diversify the utilization of perovskite heterostructure photocatalysts.