Rational design of {0 0 1}-faceted TiO2 nanosheet arrays/graphene foam with superior charge transfer interfaces for efficient photocatalytic degradation of toxic pollutants

Abstract

Exposing high-energy active facets for nanocrystals has received increasing attentions due to its intrinsic surface-dependent properties in extensiveapplications. Unfortunately, most anatase TiO2 crystals were dominated by the thermodynamically stable {101} facets instead of the much more catalytically active {001} facets. Meanwhile, the photo-generated electrons and holes in TiO2 might experience a rapid recombination, which significantly diminishes the efficiency of the photocatalytic reaction. Herein, we integrated {001} facets TiO2 nanosheet arrays into a free-standing graphene foam through a facile vacuum filtration process combined with a solvothermal method. Uniformly distributed TiO2 nanosheet arrays were in situ intercalated into interlayers of flexible graphene foam and were simultaneously anchored on its surface to form 3D hierarchical porous architecture, which was highly appreciated for its easy separation and recycling after photocatalytic process. The multifunctional TiO2/graphene foam exhibited superior photocatalytic activity, and the rate constants (k) of the TiO2/graphene foam towards degradation of methyl orange (MO) and phenol were 4, 8.7 times higher than commercial P25, respectively. Inspiringly, the TiO2/graphene foam also achievedhigh efficiency in Cr(VI) photoreduction with 92% removal yield. The remarkably photocatalytic capability of the TiO2/graphene foam was attributed to the synergistic effects arising from intrinsic single crystalline TiO2 with high percentage exposure of {001} facets, as well as a good linkage between TiO2 and graphene, which could facilitate the surface catalytic reaction by providing abundant reactive sites for an effective molecular oxygen activation and strengthening the interfacial charge transfer both in-plane and vertical transportation. The recycling experiments presented these flexible foam catalysts were stable and could be reused with high efficiency after 12 runs. This work would provide a feasible strategies to design outstanding TiO2-based photocatalysts with highly reactive {001} facet, and also offer more extensive possibilities in a broad application range.