Presented paper

IMWA2019 Students work

Enhanced Chromium(VI) Removal From Effluents Using Zinc Stannate-Tin Oxide Nanomaterial

Onwudiwe, Damian (1); Oyewo, Opeyemi (2)
1: North West University, Mmabatho 2735, South Africa; 2: Tshwane University of Technology, Pretoria, 0001, South Africa

Enhanced Chromium(VI) Removal From Effluents Using Zinc Stannate-Tin Oxide Nanomaterial

1Damian C. Onwudiwe, 2Opeyemi A. Oyewo

1Department of Chemistry, Faculty of Natural and Agricultural Sciences, North-West University,Mafikeng Campus, Private Bag X2046, Mmabatho 2735, South Africa. Email-

2Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, 0001, South Africa

The water from chromite mines are invariably contaminated with hexavalent chromium, Cr(VI), which are responsible for significant concentration (10 to 4000 mg/kg (ppm)) of total chromium in air, water and soil environment. As a very strong oxidizing agent with cytotoxic, mutagenic and carcinogenic properties, exposure to Cr(VI) above the permissible limit results in a wide range of clinical/health hazards such as damage to liver, kidney, and lung carcinoma. Consequently, Cr(VI) has been placed on the priority list of toxic pollutants by the US Environment Protection Agency (USEPA) and a maximum acceptable concentration of 50 μg L−1 in potable water has been mandated by both USEPA and World Health Organisation (WHO). The chromium based hazards could be averted by adopting control measures which allows the treatment of discharge from of any chromium based industries before the water is released into the environment. Therefore, it is of great importance to explore the efficient ways for the treatment of Cr(VI)-rich wastewater.

In the present study, a good pair of heterostructure photocatalyst of Zn2SnO4–SnO2, as novel nanomaterials for the removal of Cr(VI) from effluents under visible light was prepared. The ternary complex oxide was characterized by using XRD, SEM and TEM techniques. The significance of this material is the synergy obtained by the combination of the two photocatalysts (Zn2SnO4 and SnO2), and their susceptibility towards tuning of their properties by altering their compositions.

The obtained data were exploited for kinetic evaluations. The optimal removal of Cr(VI) was found to be favorable at pH 4.5. The removal efficiency was found to increase with increase in the concentration of Sn4+ ion, and indicated that the photocatalytic activity of the synthesized composites also depended on their compositions. The kinetics of the photocatalysis process was evaluated and was found to follow pseudo second-order model, and the possible photocatalytic removal mechanism of Cr(VI) were also proposed.

The results showed that the use multication oxides nanomaterial with enhanced absorption of the visible light, in addition to the effective transfer and separation of the photogenerated charge carriers, could efficiently remove Cr(VI) contaminants from aqueous solutions.