Enhanced photocatalytic activity of 1 0 1-oriented bipyramidal TiO2 agglomerates through interparticle charge transfer

By Eui-Hyun Kong and Jonghun Lim and June Ho Lee and Wonyong Choi and Hyun Myung Jang
Published in Applied Catalysis B: Environmental NULL 2015

Abstract

Uniformly packed dense TiO2 bipyramid agglomerates (BPA) with the dominantly exposed 1 0 1 facets were designed and synthesized by using a simple solvothermal process. From scanning electron microscopy (SEM) image, \BPA\ consists of uniformly and densely packed nanoparticles forming secondary mesopores. \BPA\ structure was intentionally crushed by ball-milling to obtain c-BPA, the photoactivity of which was compared with BPA. The photocatalytic activities of as-prepared \BPA\ and c-BPA were investigated for hydrogen production and 4-chlorophenol degradation and compared with \P25\ as a reference TiO2. The \BPA\ showed much higher photocatalytic activities than those of c-BPA and \P25\ (randomly aggregated commercial TiO2 nanoparticles). The marked efficiency improvement in \BPA\ can be ascribed to the noble nanostructural features: (i) the agglomerated bipyramid (BP) units suppressing the electron-hole recombination through efficient interparticle charge transfer, (ii) the well-developed mesopores allowing the efficient diffusion of reactants and products, (iii) the highly 1 0 1-oriented \BP\ units that help efficient charge separation, and (iv) a good crystallinity of the \BP\ units. These superior properties of \BPA\ were also confirmed in their photoelectrochemical behaviors: the electrode of \BPA\ exhibited the highest photocurrent under \UV\ light, the slowest decay of open-circuit potential after turning off the light, and the lowest charge transfer resistance from the electrochemical impedance spectroscopic (EIS) measurement, which implies the retarded recombination of charge pairs and efficient interparticle charge transfer on BPA. The controlled agglomerated structure of the nano-sized TiO2 can enhance the photocatalytic and photoelectrochemical properties through efficient interparticle charge transfer.

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