Comparison of degradation of methylene blue dye by ZnO, N doped ZnO and iron ore rejects
Textile effluent containing unused dye when released in surroundings pollutes water bodies. It requires processing before disposal. Iron ore reject created during mining creates environmental pollution but contains minerals of technological importance. It has ~30-50% iron in the form of γ-Fe2O3, α-Fe2O3 andFe3O4 is wasted if thrown in fields, so can be used to degrade organic dyes. Mineralization of methylene blue, MB a model dye is carried out using photocatalyst either iron ore reject, synthesized ZnO or ZnO1-xNxand the results are compared. ZnO is synthesised from oxalate and Nitrogen doped ZnO from hydrazinated oxalate precursors. FTIR study of zinc complexes indicates formation of precursors and XRD of decomposed complexes reveal formation of zinc oxide with wurtzite structure. The presence of nitrogen in ZnO1-xNx is confirmed by chemical estimation and XPS studies. SEM reveals the particle size of ZnO1-xNx ~69 nm and ZnO ~0.5 - 1µm. ZnO1-xNx absorbs in the visible region and ZnO in UV region. Band gap energy calculated using Diffuse reflectance Spectrum is 2.48 eV for the former, 3.19eV for the later and 2.38 eV for ore reject. Mineralizing property of ore reject, ZnO and ZnO1-xNx are compared by; Electron Spray Ionisation Mass spectrometry study (ESI-MS) of degradation products, COD measurement and CO2, NO3- and SO4-2 estimation.
Reusability study, kinetic study of degradation of MB dye using photocatalysts and ESI-MS study of degraded products of MB reveal better efficacy of iron ore rejects amongst three.Thus efficiency of iron ore reject > ZnO1-xNx. > ZnO as photocatalyst.
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