Study of the enhanced visible-light-sensitive photocatalytic activity of Cr2O3-loaded titanate nanosheets for Cr(vi) degradation and H2 generation

Abstract

Visible-light-sensitive titanate nanosheets (TNSs) were synthesized with Cr₂O₃ successfully loaded and well dispersed on Cr(III)-TNSs by a one-step hydrothermal method for enhanced photocatalytic activity. As in our previous reports, the as-prepared samples clearly exhibited a porous flake-like structure with a large specific surface area (300–400 m² g⁻¹). Accompanied with the hydrothermal growth of the TNSs, the loaded Cr₂O₃ not only influenced the layered structure of the TNSs, but also brought about a remarkable enhancement of the visible-light response and the separation of photogenerated carriers. The XPS fitting results indicated that the Cr ions mainly existed in the trivalent form and caused a change in the binding states towards Ti and O. Based on the evaluation of the photocatalytic activity, it was found that the Cr(III)-TNSs obtained a significant improvement for RhB and K₂Cr₂O₇ (Cr(VI)) degradation under visible-light irradiation, which was attributed to retarding the charge recombination and the effective electron transfer from Cr₂O₃ to TNSs. The better photocatalytic activity was obtained with an optimal content (0.5 at%) of Cr³⁺, and the degradation rate (K_app) was 2.9-fold and 4.1-fold, respectively, as compared to TNSs. The samples were also evaluated in photocatalytic H₂ generation with the photodeposition of Pt nanoparticles as cocatalysts. The results showed that the visible-light H₂ production rate of Pt_0.25/Cr(III)-TNSs (0.25 wt% of Pt) was observably enhanced under the efficient sacrificial agent/water system, giving a relatively high H₂ generation rate of 473 μmol h⁻¹ g⁻¹ at 0.5 at% of Cr³⁺ content. The cyclic tests demonstrated the good stability and recycling performance of the samples. Alternative mechanisms for the visible-light-sensitive photocatalytic activity were also proposed.