Structure engineering of TiO2-based photocatalysts: From charge regulation to energy and environmental applications

TiO 2 photocatalysis is shaped by the coupled effects of crystal structure, surface chemistry and reaction environment. This review examines five routes for engineering TiO 2 : phase, facet and morphology control; defect regulation; elemental doping; cocatalyst and atomic-site design; and semiconductor heterojunction construction, with particular attention to the evidence needed to support S-scheme charge transfer. Each route is discussed in relation to carrier behavior, surface reactions and the conditions that limit performance. Applications are considered across hydrogen production, carbon conversion, selective chemical synthesis, environmental purification and resource recovery. Reported activity is interpreted alongside relevant illumination and reaction conditions, while the discussion also addresses operando characterization, defect populations, reactor transport, immobilization, stability and cost. The comparison shows that no single structural descriptor predicts performance across different reactions. More reliable design starts by identifying the rate-limiting step under the intended operating conditions and verifying that the proposed active structure persists during use.