Effect of pH on the photocatalytic performance of ZnO particle in removal of rhodamine B
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Date
2019-07
Authors
Nurul Syuhada Binti Samsuddin
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Abstract
ZnO based advanced oxidation process is an emerging technique for wastewater treatment. Many photocatalytic studies of ZnO particles were performed under pH 6 – pH 8. Nevertheless, the effluent discharged from industries such as printing and textile factories may contain pollutants that could change the pH of effluents. The presence of –H groups (acidic condition) and –OH groups (basic condition) could alter the surface of ZnO particles and thus affect its photocatalytic performance. In this work, photocatalytic performances of ZnO particles in degrading RhB solution at various pH levels, i.e. pH 3, pH 5, pH 7, pH 9 and pH 11, were studied. In general, the photodegradation efficiency of ZnO particles was slightly better in alkaline solutions than that in acidic solutions. This was attributed to photocorrosion effect of ZnO particles that took place in acidic solutions. In alkaline solution, the negatively charged surface of ZnO particles allowed more adsorption of cation RhB dyes on the catalyst surface, leading to more effective photodegradation efficiency. Also, the generation of more reactive species such as eand •O2- free radicals in alkaline solutions, as proven by the scavenger tests, improved ZnO particles photocatalytic performance. The effect of different type of acid was also studied by using HCl and H2SO4. The photodegradation efficiency of ZnO particles was better in H2SO4 (99.82 %) than in HCl (94.48 %). Lastly, the photocorrosion effect on ZnO particles was higher under UV light and in acidic condition. This is because, at extreme pH values such as pH 3, the ZnO particles were readily dissolved. Thus, the weight loss of ZnO particles increased.