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Size-Dependent Photocatalytic Activity of Cubic Boron Phosphide Nanocrystals in the Quantum Confinement Regime

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journal contribution
posted on 04.09.2019, 17:41 by Hiroshi Sugimoto, Bálint Somogyi, Toshiyuki Nakamura, Hao Zhou, Yuichi Ichihashi, Satoru Nishiyama, Adam Gali, Minoru Fujii
Cubic boron phosphide (BP) is an indirect band gap semiconductor with a band gap of 2.0 eV and promising for a highly stable photocatalyst to produce hydrogen from water under visible light irradiation. Here, we performed a comprehensive study on the energy-level structure and photocatalytic activity of BP nanocrystals (NCs) in the quantum confinement regime (<5 nm in diameter). First, we calculated the electronic structure of cubic BP NCs up to 2.8 nm in diameter, hexagonal BP nanoflakes, and cubic/hexagonal BP nanostructures by density functional theory and time-dependent density functional theory. We then synthesized BP NCs with 2–13 nm in diameters and performed detailed structural analyses and optical measurements. The photocatalytic bleaching experiments for dye molecules under visible light irradiation revealed that the bleaching rate depends strongly on the size of BP NCs; the increase in the band gap of BP NCs by the quantum size effects (QSE) enhanced the photocatalytic activity. The band gap increase by the QSE also enhanced the rate of photocatalytic hydrogen evolution in water.