Photocatalytic hydrogen generation from water-methanol mixtures using nanocrystalline ZnFe ₂O ₄ under visible light irradiation

A spinel crystal structure of ferrite containing zinc (ZnFe ₂₄) was synthesized by using the polymer complex method. A pure phase ZnFe ₂O ₄ was obtained at a relatively lower temperature of 900 °C. The as-synthesized nanoparticles are agglomerates of crystals with an average size of ∼50 nm, as estimated from the X-ray diffraction analysis. The band gap of the n-type semiconducting metal oxide, as determined by using an ultraviolet-visible diffuse reflectance spectrometer was found to be 1.90 eV (653 nm). The photocatalytic activity of ZnFe ₂O ₄ was investigated by using the photoreduction of water under visible light (≥420 nm), which was found to be much higher than that of the well-known TiO _2-xN _x photocatalyst. This superior performance is attributed to the larger surface area, the uniform and well-dispersed deposition of the Pt co-catalyst over the surface, and the small band gap of the chemically-prepared ferrite photocatalyst.