Band structure engineering for a graphitic carbon nitride-based hybrid with improved photocatalytic CO2 reduction performance

Graphitic carbon nitride has emerged as a sustainable photocatalyst for CO₂ reduction, yet its efficiency is constrained by narrow light absorption and inefficient charge separation. To overcome these limitations, this work introduces a dual-engineering strategy combining doping and thermodynamic band structure regulation. Boron (B) doping of graphitic carbon nitride nanosheets (CNNs) at different temperatures (BCN_x) induces a maximum 0.12 eV bandgap narrowing and upward conduction band shift, extending light absorption to 457 nm. By coupling BCN_x with sodium 2,5,8-tri(40-pyridyl)-1,3,4,6,7,9-hexaazaphenalenate (TPHAP), we achieve adjustable band alignment, where B-CN₄₀₀/TPHAP exhibited the optimal offset of the conduction band (ΔE_CB = 0.43 eV), creating a strong interfacial driving force for charge separation. This optimized alignment drives efficient charge separation and transfer, yielding a record CO production rate of 60.5 μmol g⁻¹ with 97.1% CO selectivity. Furthermore, through systematic characterization studies, we investigated the optimal band alignment matching to determine its impact on the formation of band offset. This study establishes a universal paradigm for photocatalytic material design, demonstrating that synergistic band structure modulation and interfacial engineering can unlock the full potential of hybrids for solar fuel production.