High-performance formaldehyde sensing of room-temperature UV-activated Mn-TiO₂: Key effects of different crystal...

Gas sensing is closely related to the behavior of photogenerated carriers. TiO₂ has been widely used to monitor and control various harmful gases in the environment; thus, optimizing carrier behavior-via methods such as doping and adjusting the material's crystalline phase structure-can effectively improve its gas sensing performance. In this work we focused on anatase, rutile, and anatase-rutile mixed crystals, synthesizing TiO₂ of different crystal structures. We also synthesized Mn-doped TiO₂ using the wet impregnation method. The gas sensing performance of these materials was investigated after UV activation at room temperature. The gas sensing performance showed that the rutile-anatase mixed crystals exhibited a response of 21.12 to 20 ppm formaldehyde, while 0.4 wt% manganese-doped TiO₂ exhibited a response of 538.15 to 20 ppm formaldehyde, demonstrating exceptionally high formaldehyde response capability and selectivity, with a detection limit as low as 8.4 ppb. To clarify the underlying mechanism, we comprehensively studied the effects of carrier behavior and surface gas adsorption on photochemical gas sensing performance using techniques including surface photovoltage (SPV), transient photovoltage (TPV), and density functional theory (DFT) calculations.