Mechanism of p-Type Heteroatom Doping of Lithium Stannate for the Photodegradation of 2,4-Dichlorophenol: Enhanced Hole Oxidative Capability and Concentrations

A systematic evaluation of enhancing photocatalysis via aliovalent cation doping is conducted. Cation In³⁺, being p-type-doped, was chosen to substitute the Sn site (Sn⁴⁺) in Li₂SnO₃, and the photodegradation of 2,4-dichlorophenol was applied as a model reaction. Specifically, Li₂Sn_0.90In_0.10O₃ exhibited superior catalytic performance; the photodegradation efficiency reached about 100% within only 12 min. This efficiency is far greater than that of pure Li₂SnO₃ under identical conditions. Density functional theory calculations reveal that introducing In³⁺ increased the electron mobility, yet decreased the hole mobility, leading to photogenerated carrier separation. However, photoluminescence and time-resolved photoluminescence suggest that In³⁺ induced nonradiative coupling in the matrix, reducing the photogenerated carrier separation ratio compared with that of Li₂SnO₃. The optical band gap of Li₂Sn_0.90In_0.10O₃ was almost unchanged compared with that of Li₂SnO₃ via ultraviolet-visible absorption. The increased photocatalytic efficiency was ascribed to the lower valence band position and enhanced hole concentrations by valence band X-ray photoelectron spectroscopy and electrochemical measurements. Finally, a 2,4-dichlorophenol degradation pathway, an intermediate toxicity assessment, and a photocatalytic mechanism were proposed. This work offers insights into designing and optimizing semiconductor photocatalysts with high performance.