Construction of anatase@rutile core@shell TiO2 nanosheets with controllable shell layer thicknesses for enhanced ethanol sensing

Anatase@rutile core@shell TiO2 (A@R-TiO2) nanosheets with varied thicknesses of rutile shell layers have been constructed via two-step hydrothermal processes. Rutile shell layers with controllable thicknesses (1.9-6.8 nm) are generated on the surfaces of anatase TiO2 (A-TiO2) nanosheets by regulating HCl concentrations and hydrothermal reaction times. This new type of A@R-TiO2 nanosheets exhibits an evident enhancement in ethanol sensing response and a reduction in optimum operation temperature in comparison with A-TiO2 nanosheets. A rutile shell layer thickness-dependent ethanol sensing response is revealed. The A@R-TiO2 nanosheets with a shell layer of approximately 5.0 nm show the highest response of 43.9-500 ppm ethanol at 270 degrees C, which is 4.35 times higher than that of A-TiO2 nanosheets. The formation of TiO2 polymorphism junctions leads to the electron transferring from inner anatase cores to outer rutile shells and the enrichment of active O species on the surfaces of rutile shells, contributing greatly to the improved ethanol sensing properties of A@R-TiO2 nanosheets. The unique core@shell structure with enhanced surface area is also responsible for the further resistance modulation and increased ethanol sensing performances of A@R-TiO2 nanosheets.