Adjustment and Matching of Energy Band of TiO₂‑Based Photocatalysts by Metal Ions (Pd, Cu, Mn) for Photoreduction of CO₂ into CH₄

A series of the metal ions (Pd, Cu, and Mn) modified TiO₂ photocatalysts are synthesized via simple sol–gel method. Characterized by X-ray diffraction, Raman, UV–vis absorption spectra, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, time-resolved photoluminescence (PL) decay curves, and PL, it was revealed these introduced metal ions existed as O–Me–O species (Me: Pd, Cu, and Mn) on the surface of TiO₂. The corresponding theory calculation is used to investigate the electronic density of states and band structure of the metal ions (Pd, Cu, and Mn) modified TiO₂. The modified TiO₂ photocatalysts exhibit an improved photocatalytic performance on reduction of CO₂ and H₂O into methane (CH₄), attributed to the contribution of surface species by enhancing the visible absorption efficiently, separating charge carriers, and matching of the redox potential on the photoreduction of CO₂ into CH₄. This article could provide a wider understanding about the adjustment and matching of the energy level for the synthesis and design of functional materials with excellent photocatalytic performance