The Preliminary Studies on the Tremendous Degradation Rate of Methylene Blue with Cu-doped α-MnO₂ Photocatalyst Under UV Light Irradation

Abstract

Dye contaminations have severe impacts to environment (air, soils, plants, water) due to their adverse effects. Most dyes are toxic, carcinogenic, mutagenic and resistant to bio-degradation. Photocatalysis-based advanced oxidation process (AOP) has been considered as the most effective and efficient way to treat this recalcitrant compounds. Manganese oxides are ubiquitous and environmentally friendly in natural environments and can act as semiconducting materials. Tunnel structure of manganese oxide such as α-MnO2 (cryptomelane) has been widely studied for broad applications as Fenton-based AOP. Catalytic efficiency of α-MnO2 could be further increased by doping α-MnO2 with a metal ion like the Cu ion. Although the synthesis and catalytic activity of Cu-α-MnO2 have been reported by previous studies, its photocatalytic performance using this one-pot-sol-gel approach for MB degradation has never been reported previously. Herein, Cu-doped α-MnO2 was synthesized by one-pot sol-gel method and characterized by X-ray diffraction (XRD), BET surface area and atomic absorption spectroscopy (AAS). The AAS results suggested the presence of Cu ions in α-MnO2 since the increase in doping Cu resulted in the corresponding increase in Cu content in the α-MnO2. The BET surface area indicated that the doping 10% Cu in α-MnO2 led to about two fold increase in suface area compared to undoped α-MnO2. The photo catalytic performance of Cu-α-MnO2 via UV light irradiation for the degradation of methylene blue (MB) was significantly higher that that of undoped α-MnO2 and was associated with the increased in surface area of Cu-α-MnO2 over undoped α-MnO2. The maximum degradation of MB was 97.9, 98.3, 98.7 and 99.5% achieved using α-MnO2, 1% Cu-α-MnO2, 5% Cu-α-MnO2, and 10% Cu-α MnO2 and 10% Cu-α-MnO2.