Photoluminescence and enhanced photocatalytic activity of mechanically activated graphite-zinc oxide composites

In this work, we show evidence of enhanced photocatalytic activity in mechanically activated graphite-zinc oxide (ZnO) composites using time-resolved photoluminescence (TRPL) and time-integrated photoluminescence (TIPL) spectroscopy. The graphite-ZnO composites were synthesized through facile mixing and grinding of graphite and ZnO precursors without any heat treatment. The precursors were ground at room temperature with varying graphite to ZnO mass ratios of 3:1, 2:2, and 1:3 for 0, 2, and 4 h. Raman spectroscopy and x-ray diffractometry confirm the presence of both graphite and ZnO and corroborate the graphite-to-ZnO ratio. XRD results also show a hexagonal wurtzite ZnO crystal structure. To determine the photocatalytic activity of the composites, the degradation of methylene blue (MB) under UV light was measured with a UV-vis spectrophotometer. Nearly full degradation was achieved within a half hour for all composite samples. The kinetic rates of 0.10 min(-1) were also estimated for mixed and unground samples and samples ground for 2 h. Time-resolved photoluminescence (TRPL) and time-integrated photoluminescence (TIPL) spectroscopy reveal longer lifetimes and more intense UV emissions, respectively, for composite samples compared to pure ZnO. We propose that the even agglomeration of zinc oxide particles on graphite due to grinding enhances the photocatalytic degradation by the zinc oxide. TRPL and TIPL spectroscopy implies the excellent binding between ZnO and graphite, which greatly contributes to the decreased charge recombination resulting in the superior photocatalytic activity observed with our samples.