Investigation of metal oxides toward organic dyes decolourisation and environmental remediation

Abstract

Enormous interest has been focused on metal oxides in its photocatalytic capabilities toward oxidizing organic dyes and environmental remediation. Zinc oxide (ZnO), titanium dioxide (TiO2) and iron oxide (Fe3O4) have been used as the heterogeneous photocatalysts to photodegrade three organic dyes, which are methylene blue (MB), phenol red (PR) and methyl orange (MO). Series of 3.0 ml dyes samples in aqueous solutions were placed into a UV chamber under UV-C (254 nm) light irradiation. The oxides powder was characterised by XRD, FESEM and TEM analysis, where ZnO nanoparticles was in hexagonal wurtzite crystal structure (SG: P63mc) with average crystalline size of (91 ± 12) nm and TiO2 nanoparticles was pure anatase of tetragonal crystal structure (SG: I4/amd) with average crystalline size of (117 ± 16) nm. Fe3O4 nanoparticles was in cubic spinel crystal structure with average crystalline size of (62.1 ± 5.7) nm. The photocatalyst loading (0.5 – 3.5wt%), initial dye concentration (MB: 2 – 12 ppm, PR: 8 – 48 ppm, MO: 12 – 32 ppm) and irradiation duration on the decolourisation of dye samples were examined. Based on time requirement, the photocatalytic decolourisation rate increased with increasing metal oxide loading and decreased with the increasing of the initial dye concentration. The superior photocatalyst was ZnO with a loading of 2.5 wt% followed by TiO2 (3.0 wt%) and least photocatalytic capability was Fe3O4 (3.0 wt%). On the other hand, the most photostable dye is MO followed by PR and MB.