Novel magnetically separable Fe₃O₄@ZnO core–shell nanocomposite for UV and visible light photocatalysis

Photocatalysis is an unconventional, yet promising method that can combat industrial water pollution by decomposing toxic organic effluents into harmless moieties under suitable irradiation sources. Synthesis of magnetically separable Fe₃O₄@ZnO core–shell nanoparticles at low temperature for the visible light photodegradation of aqueous azo-dye pollutant, methyl orange is reported. Fe₃O₄ nanoparticles were synthesised by co-precipitation method following which ZnO was grown by reflux reaction with a Fe₃O₄: ZnO molar ratio of 1: 10. The formation of Fe₃O₄@ZnO nanoparticles were confirmed by X-ray diffraction and Fourier Transform Infrared Spectroscopy. The bandgap was measured using diffuse reflectance spectroscopy and the photodegradation efficiency of Fe₃O₄@ZnO nanoparticles on the decolouration of methyl orange was measured under both 365 nm UV and visible light excitations. The magnetic separability, surface area of 36 m²/g and visible light absorption make Fe₃O₄@ZnO nanoparticles favourable for solar photocatalysis. The point of zero charge (pzc) of the Fe₃O₄@ZnO nanoparticles determined by the pH drift method was found to be 6.4, which makes the operating pH of the solution (pH= 6) suitable for adsorption/photodegradation. The decolouration of the dye under visible light irradiation closely competed with the decolouration observed under UV irradiation. This is an extremely useful technique in water treatment, especially to treat toxic effluents from several colouring industries.