Plant-Based Phytochemicals for Synthesis of Z-Scheme In₂O₃/CdS Heterostructures: DFT Analysis and Photocatalytic CO₂ Reduction to HCOOH and CO

Photocatalytic CO₂ reduction shows potential for mitigating industrial emissions. Z-scheme In₂O₃/CdS(bio) heterostructures (25 nm, 217.0 m² g^-1 surface area) with a more negative conduction band synthesized using phytochemicals present in Aegle marmelos with short microwave irradiation inhibit CdS(bio) photocorrosion forming SO₄^2-. In₂O₃/CdS(bio) increased the photocurrent density (0.82 μA cm^-2) and CO₂ adsorption (0.431 mmol g^-1) significantly compared to CdS(bio) and In₂O₃(bio) NPs. Heterostructures increased decay time and reduced PL intensity by 46.28 and 61.80% over those of CdS(bio) and In₂O₃(bio) NPs. Density functional theory (DFT)-optimized geometry, band structure analysis, and density of states (DOS) studies indicate that the DOS of CdS is modified with In₂O₃ incorporation, enhancing charge separation. Optimal 0.4In₂O₃/CdS(bio) heterostructures exhibit remarkable CO₂ conversion to HCOOH/CO production of 514.4/162 μmol g^-1 h^-1 (AQY 4.44/2.45%), surpassing CdS(bio) and In₂O₃(bio) by 9 and 6.5 times, and retain their morphological and structural stability. This study provides valuable insight for developing bio-based CdS heterostructures for photocatalytic CO₂ reduction.