Synthesis of Cu2O/ZnO/kaolinite composite for the degradation of methylene blue under visible light

Abstract

Different chemicals used during the industrial processing such as textiles, leathers, papers, and cosmetics are released to the environment and cause severe problems. These released chemicals contain tremendous amounts of toxic organic pollutants, inorganic pollutants and heavy metals. Due to their effects on the environment, they should be controlled effectively and economically to survive human life and the environment through photodegradation process by using photocatalyst materials. Herein, we design to synthesize a novel Cu2O/ZnO/kaolinite composite by co precipitation method. The synthesized composite catalysts are termed as 5CZK, 10CZK, 15CZK, and 20CZK which represents 5 %, 10 %, 15 % and 20 % of Cu2O, respectively, on ZnO/kaolinite composite. The X-ray Diffraction (XRD), Differential Thermal Analysis (DTA), Thermogravimetric Analysi (TGA), Atomic Absorption Spectroscopy (AAS), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and UV Visible Diffuse Reflectance Spectroscopy (UV-visible DRS ) were used to characterize the as-synthesized catalysts. Moreover, the photocatalytic degradation of methylene blue dye was selected as a target organic pollutants and evaluated under visible light irradiation. The highest performance for the degradation of 125 mL (10 ppm) methylene blue dye was achieved by 25 mg of 10CZK catalyst within 105 min. The enhanced degradation of 10CZK composite may be due to the synergetic effects and light-responsive under visible light by Coupling p-type Cu2O with n-type ZnO which in turn reduce the electron-hole pair recombination through the formation of heterojunction. Hence, in our study, the optimum ternary catalyst was achieved by loading 10 % of Cu2O on the ZnO/kaolinite composite with appropriate conditions. On the other hand, the preferable conditions for MB dye degradation in acidic, neutral and basic media were also checked. The complete degradation of MB dye was achieved in basic media within 30 min and almost suppressed with decreased pH to acidic media. This shows that the cationic MB dye prefer basic sites for adsorption and strong attraction force between the negatively charged kaolinite and cationic dye in basic media. Besides, the stability and reusability of the catalyst were also checked. The catalyst shows good stability and reusability until 5th cyle. This reveals that the synthesized composite catalyst also could be applicable for environmental remediation and industrial applications with low cost.