Highly Efficient Low-Temperature Plasma-Assisted Modification of TiO2 Nanosheets with Exposed {001} Facets for Enhanced Visible-Light Photocatalytic Activity

Anatase TiO2 nanosheets with exposed {001} facets have been controllably modified under non-thermal dielectric barrier discharge (DBD) plasma with various working gas, including Ar, H-2, and NH3. The obtained TiO2 nanosheets possess a unique crystalline core/amorphous shell structure (TiO2@TiO2-x), which exhibit the improved visible and near-infrared light absorption. The types of dopants (oxygen vacancy/surface Ti3+/substituted N) in oxygen-deficient TiO2 can be tuned by controlling the working gases during plasma discharge. Both surface Ti3+ and substituted N were doped into the lattice of TiO2 through NH3 plasma discharge, whereas the oxygen vacancy or Ti3+ (along with the oxygen vacancy) was obtained after Ar or H-2 plasma treatment. The TiO2@TiO2-x from NH3 plasma with a green color shows the highest photocatalytic activity under visible-light irradiation compared with the products from Ar plasma or H-2 plasma due to the synergistic effect of reduction and simultaneous nitridation in the NH3 plasma.