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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.209

The role of zinc metal salts on size, morphology and photocatalytic activity of ZnO S.S. Nkabinde, X. Mathebula, Z. Tetana, N. Moloto* Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, Wits, 2050, Republic of South Africa

Corresponding author email address: [email protected]

Abstract

Herein, we report on the syntheses of ZnO nanoparticles using different precursors Zn(NO3)2•6H2O, Zn(CH3COO)2•2H2O, ZnCl2, and ZnSO4.H2O by a microwave assisted method. The different precursors resulted in different structural, optical and photocatalytic degradation of Rhodamine B dye. The nanoparticles resulted in rod-like and pseudo-spherical morphologies when the ZnO2•6H2O, (Zn(CH3COO)2•2H2O and ZnCl2 precursors were used, with the proportion of the spherical morphology in each photocatalyst varying in the order Zn(NO3)2•6H2O > Zn(CH3COO)2•2H2O > ZnCl2. The ZnSO4.H2O precursor yielded trapezium shaped particles that were agglomerated through oriented attachment. For photocatalytic degradation studies, the fastest degradation was achieved using the S NO3photocatalyst, which degraded the dye in a period of 120 min, followed by S CH3COO- at 150 min, SCl- at 180 min and SSO42- managing to degrade only 15 % of the dye after 240 min. The difference in the activity was attributed to surface area differences, which followed the order SNO3- > SCH3COO- >SCl- > SSO42-, with the photocatalyst that had the highest surface area showing high degradation rates. The high degradation rate observed for the S NO3photocatalyst was also attributed to the presence of a large number of spherical particles thereby having a larger proportion of the high energy [0001] and [000-1] faces known to be highly active.

INTRODUCTION A lot of interest has risen towards ZnO due to the wide range of properties that it possesses such as semiconducting, piezoelectricity, conductivity, photoactivity and ferromagnetism [1–3]. Recently, ZnO has shown superior properties as a photocatalyst used in the photocatalytic degradation of organic dyes (e.g. methyl orange, Rhodamine B, crystal violet) in aqueous solution [4-7]. The environmental friendliness and cheapness associated with photocatalytic degradation of organic dyes has changed the scientific focus when it comes to solving problems such as water pollution in rivers. One way that has been used to ensure that water pollution caused by organic dyes in rivers is effectively removed is to synthesize nanomaterials that are effective as photocatalysts.

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Effective photocatalysts have been previously obtained by using nanoparticles with certain morphologies and sizes, and this can be achieved by varying the way in which the nanoparticles are synthesized [8,