Cerium-Based Metal–Organic Framework Nanorods Nucleated on CeO2 Nanosheets for Photocatalytic N2 Fixation and Water Oxidation

The photofixation of N2 to NH3 is the most promising and environmental benign technique compared to the conventional Haber–Bosch process. However, faster excitons recombination, slow charge diffusion rate, strong N≡N, and low selectivity are the associated shortcomings that reduce the catalytic efficiency of single framed photocatalytic systems. Herein, we report a rod-sheet p–n heterojunction-based binary photocatalytic system where a rod-shaped Ce-metal–organic framework (MOF) was nucleated over CeO2 nanosheets (NSs) via a hydrothermal method. The designed oxygen vacancies rich binary heterojunction ((1:1) CeO2/UNH (Ce)) shows excellent N2 reduction and O2 evolution rates, i.e., 47.55 μmol L–1·h–1 and 370.18 μmol·h–1 with apparent conversion efficiencies (ACEs) of 0.33% and 8.5%, respectively. Further, the observed high catalytic activity is attributed to the effective photoexcited charge separation and transfer ability of the binary system in addition to an oxygen vacancy presence, which successfully actives the adsorbed N2 molecule via back-donation mechanism and promotes the reduction process. The occurrence of a binary composite is well-justified via X-ray diffraction (XRD), UV–vis diffuse reflection spectroscopy (DRS), Fourier transform infrared (FTIR), Raman, and transmission electron microscopy (TEM) analysis, whereas the origin of p–n heterojunction at the interfacial region is confirmed by Mott–Schottky (MS) measurement. Additionally, the efficient electron–hole pair anti-recombination and oxygen vacancy presence is well-demonstrated through photoluminescence (PL), Bode phase, transient current, Raman, and X-ray photoelectron spectroscopy (XPS) analysis, respectively. Further, the binary hybrid contains both crystalline and amorphous regions (confirmed by high-resolution TEM (HRTEM)), which facilitate a faster charge carrier diffusion and N2 adsorption–activation process.