Visible light assisted decolorization of azo dyes: Direct Red 16 and Direct Blue 71 in aqueous solution on the p-CuFeO2/n-ZnO system

• Visible light degradation of DR16 and DB71 in single and binary system is tested.
• A mechanism for electronic transition between CuFeO2 and ZnO is proposed.
• CuFeO2/ZnO exhibits excellent azo dyes degradation under the visible light.

The photodegradation of Direct Blue 71 (BD71) and Direct Red (DR16) dyes in both single and binary systems on the p-CuFeO2/n-ZnO system is studied under visible light. The effects of operating parameters like irradiation time, pH and initial dye concentration are investigated. The first-order derivative spectrophotometric method is used to analyze simultaneously DB71 and DR16 in binary solutions. The model of the Langmuir–Hinshelwood is applied for the photodegradation kinetic in single solutions. The apparent rate constant of DR71 is slightly higher than that of DR16. The mineralization of the dyes is confirmed by the Total Organic Carbon (TOC) at natural pH. In single system, the mineralization yields of DB71 and DR16 (50 mg L−1) are respectively 56 and 52% after 60 of illumination min and increase up to 87 and 84% after 210 min. On the contrary, the mineralization in binary system (50 mg L−1 DB71 + 50 mg L−1 DR16) is found to be 40% after 60 min and reaches 82% after 210 min. A photocatalytic degradation mechanism is proposed to explain the high activity under visible light.

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