Abstract
Efficient charge transfer and effective separation of photo-generated charge carriers are pivotal to the photocatalytic process. In this study, a novel CoAl(2)O(4)@nitrogen-doped graphitic carbon (CoAl(2)O(4)@NGC) composite photocatalyst was fabricated via a stepwise hydrothermal method coupled with high-temperature calcination, and its photocatalytic performance for CO(2) reduction was systematically investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photoelectrochemical measurements were employed to characterize the phase structure, microstructure, surface chemical state and photoelectrochemical properties of the catalyst. Spinel-structured CoAl(2)O(4) nanoparticles were uniformly anchored on the NGC substrate, forming a well-integrated composite interface. XPS analysis confirmed the coexistence of Co(2+)/Co(3+) mixed valence states in CoAl(2)O(4) which provides abundant redox sites for CO(2) activation. Photocatalytic tests showed that CoAl(2)O(4)@NGC exhibits excellent catalytic activity and cycling stability, with CO and CH(4) yields of 27.88 μmol·g(-1)·h(-1) and 23.90 μmol·g(-1)·h(-1), respectively. The narrow bandgap (1.54 eV) enhances visible light absorption, while efficient electron-hole separation and reduced charge transfer resistance improve photocatalytic efficiency. Theoretical calculations further reveal that CoAl(2)O(4)@NGC lowers the adsorption free energy of CO(2) and the energy barrier for COOH formation, thus facilitating the photocatalytic CO(2) reduction. This work provides insights for the design of efficient and stable photocatalysts for CO(2) reduction and deepens the understanding of the synergistic catalytic mechanism in the spinel/nitrogen-doped carbon composite system.