Solar hydrogen generation from spinel ZnFe2O4photocatalyst: effect of synthesis methods

This paper investigates solar radiation-induced photocatalytic hydrogen generation using spinel ZnFe2O4 (ZFO) photocatalysts fabricated using different routes, viz., solid state reaction (SSR), polymer complex (PC), microwave sintering (μW) and self-propagating combustion (SPC) method. The physicochemical properties of the photocatalysts like crystallinity, surface area, band gap and band energetics is studied as it influences their photochemical behavior. The study reveals a high crystallinity of the ZFO photocatalysts, those are synthesized using SSR, PC and μW methods, where SSR method yields the larger dimension crystallites of ~53 nm. The nanoparticles obtained from SPC methodology exhibit a relatively large surface area and a smaller crystallite size of around ~18 nm. Monodispersed particles with comparatively large surface area are obtained in the case of PC method. ZFO obtained from μW synthesis exhibits enhanced optical properties, thus favoring high absorption of solar photons. A relatively more negative flat band potential is displayed by the μW samples (−0.543 vs normal hydrogen electrode) as estimated from the electrochemical measurements. Consequently, these samples yield a higher quantum yield (0.19%) for hydrogen evolution even without co-catalyst loading. On the contrary, the photocatalysts obtained by SSR and PC methods did display an enhancement in the quantum yield as compared to the μW samples but only after Pt co-catalyst loading. Copyright © 2015 John Wiley & Sons, Ltd.