Photocatalytic phenol oxidation over ball milled hexagonal boron nitride

Abstract

Due to their high toxicity, even a small amount of phenols entering the surrounding aquatic environment poses a serious danger to all living beings. To address this important problem, commercial micron-sized h-BN powder was ball milled at 450, 600 and 750 rpm, surface-functionalized with hydroxyl and amino groups by sonication, and characterized as a promising photocatalyst. The samples were studied by X-Ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, 11B nuclear magnetic resonance, scanning and transmission electron microscopy, diffuse reflectance ultraviolet–visible spectroscopy and photoluminescence spectroscopy. At all rates of mechanical processing without the use of auxiliary reagents, exfoliation of h-BN flakes was achieved. An increase in the ball milling rate led to a decrease in crystallinity and structure refinement, which was accompanied by the formation of a large number of dislocations and nanocrystallites 2–5 nm in size. Upon subsequent sonication, the BN powder underwent partial oxidation and functionalization with O(H) groups. The observed increase in the photocatalytic activity of ball-milled h-BN particles in the phenol oxidation reaction is explained by an increase in the 254 nm UV-light absorption, a decrease in the rate of electron-hole recombination, and an increase in the formation rate of OH radicals. Our results clearly show the promise of ball milled commercial micron-sized h-BN powder as a photocatalyst in the phenol oxidation reaction.