Development of clay-Zno composite photocatalyst for effective photodegradation of eosin yellow dye from aqueous solution

Abstract

Three different composite photocatalysts of clay and ZnO with the composition of 12:88, 25:75 and 50:50, respectively have been prepared. Clay was used as support and Zinc acetate was used as precursor of ZnO. ZnO was produced from zinc acetate on reacting with (NH4)2CO3 followed by heating. Different techniques such as SEM (Scanning electron microscopy), FTIR (Fourier transform infrared spectroscopy), EDX (Energy dispersive X-ray spectroscopy) and XRD (X-ray diffractometry) were used to characterize the prepared composite. The SEM micrographs in different magnifications show that composite particles show different morphology than commercial ZnO and clay. With the increase of clay, the particle size of prepared composite decreases and the shapes of the particles modified accordingly. It should be of interest for pholocalalytic purposes since it expectantly improves the surface area. From the findings of EDX, if appears that the composites with the ratio of clay and ZnO 12:88, 25:75 and 50:50, respectively contain clay and ZnO only. FTIR spectral results predict that all the clay particles are completely covered when the composition of clay: ZnO are equal to 12:88 and 25:75. The number of particles remaining uncovered by ZnO increase with an increase in the fraction of clay. From the XRD patterns it appears that prepared composite contain both the clay and ZnO component. But the shift in peak position indicates that the interaction has occurred in molecular level. Removal efficiency comprising adsorption and photodegradation of a typical dye, Eosin yellow (EY) by the composite has been studied elaborately. Among the composite photocatalysts studied, the composite with a composition of clay: ZnO = 25:75 shows the best capacity of removing EY by both adsorption and photodegradation. At this composition, about 44.48% of EY degradation occurs from 2105 M aqueous solution on 0.2 g material. However, the overall removal of dye comprising adsorption and photodegradation is about 68:32% after 60 minutes photodegradation under UV light. Maximum degradation, 1.52 mg/g was achieved when 1.0×10-5 M EY was irradiated for 1 hour in 3.5 g/L of composite. A further increase in the composite material causes a decrease in the photodegradation. The effects of initial concentrations of EY, different light sources, anions and cations have been investigated to find out the conditions for the maximum degradation of EY in presence of 254 nm UV light. The degradation of EY was decreased with increasing of EY concentration. About 82.21% degradation of EY was observed when l.0l05 M EY was irradiated for 1 hour in 3.5 g/L of composite suspension. The effect of anion and cation have been studied and the effect of HCO3, CO32, Cl, NO3 and SO42 was found to be detrimental to the photodegradation of EY. Under the same experimental condition cationic effect was investigated. Addition of Zn2+ enhanced the percent degradation of EY. The effect of UV and visible light sources was investigated. The highest percentage of degradation of EY about 82.2% was found by irradiating the dye in the UV light source, where as Visible light showed 63% of degradation. The effect of UV light intensity also was investigated. A higher intense UV light leads to complete degradation.