TiO₂ derived from TiC reaction in HNO₃: Investigating the origin of textural change and enhanced visible-light absorption and applications in catalysis

This paper presents the decomposition of TiC in nitric acid aqueous solution at 70°C to form porous TiO₂ (anatase) containing both N and C atoms (N,C-TiO₂), with visible-light sensitive catalytic activities (λ > 400 nm). TiC is gradually dissolved in the solution and transformed into spherically shaped TiO₂ nanoparticles in the initial reaction stage. As these spherical particles grow to a certain size (> ∼150 nm), aggregation occurs to form porous, irregular particles. The X-ray photoelectron study indicates that the anatase contains N and C atoms with multiple bonding states. The presence of these impurities induces significantly enhanced visible light absorption, as compared to the N- or C-doped case. This porous, N and C-containing anatase shows versatile photoactivities. Under visible light irradiation, the N,C-modified TiO₂ can catalyze OH radical formation demonstrated by hydroxylation of terephthalic acid. Photocatalytic degradation of methylene blue (MB) on the N,C-modified TiO ₂, an air-solid model system for self-surface cleaning, at wavelengths of 314, 366, 436 and 520 nm is investigated, and exhibits a relative efficiency ratio of 1.00:0.85:0.71:0.32 after 30 min photoirradiation. The quantum yields for visible-light wavelengths of 436 and 520 nm are roughly estimated to be 4.0 × 10^-5 and 1.8 × 10^-5 MB molecule per photon, respectively. H₂ production from water reduction over the N,C-modified TiO₂ loaded with PtO_x is also demonstrated.