Synergistic effect of pH solution and photocorrosion of ZnO particles on the photocatalytic degradation of Rhodamine B

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This research aims to study the synergistic effect of pH solution and photocorrosion of ZnO particles on the photodegradation of Rhodamine B (RhB) dye. The stability of ZnO particles was investigated by zeta potential measurement. The structure, morphology and photocatalytic activity of ZnO were analysed by X-ray diffraction, scanning electron microscope and ultraviolet–visible spectrophotometer, respectively. The ZnO particles were highly crystalline with a bandgap energy of 3.23 eV. The surface charges of particles were found to be pH-sensitive, where they were more negative under alkaline condition, i.e., −11.1, −5.3 and −38.2 mV at pH 3, 7 and 11, respectively. ZnO particles that dissolved in pH 3 solution produce Zn2+ ions, while precipitation of Zn(OH) 4 2− was observed in pH 11 solution, resulting in morphology change of ZnO from rod shape to lamellar shape . The synergistic effect of photocorrosion and dissolution of ZnO particles in acidic solution reduced RhB dye removal efficiency from ~90% at pH 7 to ~70% at pH 3. In alkaline solution, ZnO particles displayed remarkable reusability as it still recorded a 94.8% degradation efficiency after five successive cycles.