Gang Liu

Abstract “Graphitic” (g)‐C 3 N 4 with a layered structure has the potential of forming graphene‐like nanosheets with unusual physicochemical properties due to weak van der Waals forces between layers. Herein is shown that g‐C 3 N 4 nanosheets with a thickness of around 2 nm can be easily obtained by a simple top‐down strategy, namely, thermal oxidation etching of bulk g‐C 3 N 4 in air. Compared to the bulk g‐C 3 N 4 , the highly anisotropic 2D‐nanosheets possess a high specific surface area of 306 m 2 g −1 , a larger bandgap (by 0.2 eV), improved electron transport ability along the in‐plane direction, and increased lifetime of photoexcited charge carriers because of the quantum confinement effect. As a consequence, the photocatalytic activities of g‐C 3 N 4 nanosheets have been remarkably improved in terms of •OH radical generation and photocatalytic hydrogen evolution.

Electronic structure intrinsically controls the light absorbance, redox potential, charge-carrier mobility, and consequently, photoreactivity of semiconductor photocatalysts. The conventional approach of modifying the electronic structure of a semiconductor photocatalyst for a wider absorption range by anion doping operates at the cost of reduced redox potentials and/or charge-carrier mobility, so that its photoreactivity is usually limited and some important reactions may not occur at all. Here, we report sulfur-doped graphitic C(3)N(4) (C(3)N(4-x)S(x)) with a unique electronic structure that displays an increased valence bandwidth in combination with an elevated conduction band minimum and a slightly reduced absorbance. The C(3)N(4-x)S(x) shows a photoreactivity of H(2) evolution 7.2 and 8.0 times higher than C(3)N(4) under lambda > 300 and 420 nm, respectively. More strikingly, the complete oxidation process of phenol under lambda > 400 nm can occur for sulfur-doped C(3)N(4), which is impossible for C(3)N(4) even under lambda > 300 nm. The homogeneous substitution of sulfur for lattice nitrogen and a concomitant quantum confinement effect are identified as the cause of this unique electronic structure and, consequently, the excellent photoreactivity of C(3)N(4-x)S(x). The results acquired may shed light on general doping strategies for designing potentially efficient photocatalysts.

Owing to wide-ranging industrial applications and fundamental importance, tailored synthesis of well-faceted single crystals of anatase TiO(2) with high percentage of reactive facets has attracted much research interest. In this work, high-quality anatase TiO(2) single-crystal nanosheets mainly dominated by {001} facets have been prepared by using a water-2-propanol solvothermal synthetic route. The synergistic functions of 2-propanol and HF on the growth of anatase TiO(2) single-crystal nanosheets were studied by first-principle theoretical calculations, revealing that the addition of 2-propanol can strengthen the stabilization effect associated with fluorine adsorption over (001) surface and thus stimulate its preferred growth. By measuring the (*)OH species with terephthalic acid scavenger, the as-prepared anatase TiO(2) single-crystal nanosheets having 64% {001} facets show superior photoreactivity (more than 5 times), compared to P25 as a benchmarking material.

Contrary to conventional understanding, clean anatase {001} facets exhibit lower photoreactivity than {101} facets. Furthermore, the {010} facets showed the highest photocatalytic reactivity in generating OH radicals and hydrogen evolution. This behavior was revealed by studies on crystals grown hydrothermally to have a predominance of {001}, {101}, or {010} facets (left to right in picture (a) and (b)–(d), respectively).