PREPARATION AND APPLICATION OF ZnFe2O3/α- Al2O3 COMPOSITE PHOTOCATALYSTS FOR TEXTILE EFFLUENT TREATMENT

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Department of Engineering

ABSTRACT
Photocatalysis has continued to attract increasing attention due to its numerous applications in the energy and environmental fields. Present work was aimed at the development of ZnFe2O4 and α-Al2O3 supported ZnFe2O4 visible – light responsive photocatalysts for the treatment of textile effluent. ZnFe2O4 and α-Al2O3 supported ZnFe2O4 were synthesized using co–precipitation route followed by calcination at 500 0C. The synthesized photocatalysts were characterized using x–ray diffraction (XRD), Specific surface area analysis, Scanning electron microscopy (SEM) and pH at point of zero charge analysis (pHpzc), respectively. XRD analysis revealed low crystallinity of the synthesized ZnFe2O4. The specific surface areas of the photocatalysts decrease with increase in the ZnFe2O4 loadingon the surface of the support. SEM analysis showed that the size of ZnFe2O4 particles is much smaller than that of the α-Al2O3support, and that ZnFe2O4 are uniformly dispersed on the supports. The pHpzc was found to increase with increase in the ZnFe2O4. The photocatalytic activity of the synthesized photocatalysts was evaluated by studying the decolourization kinetics of methylene blue (MB).The ZnFe2O4 is characterized by low crystallinity. The size of ZnFe2O4 particles is smaller than that of the α-Al2O3 support. The percentage degradation of MB increased with increase in the ZnFe2O4 loading from 10 wt% to 30 wt% and decreased when the loading was raised to 40 wt%. The photocatalytic activity of 30 wt % ZnFe2O4/α-Al2O3 is higher than those of ZnFe2O4 and other α-Al2O3 supported photocatalysts containing 10 wt%, 20 wt% and 40 wt% of ZnFe2O4. α-Al2O3 support improves the photocatalytic activity of ZnFe2O4 under visible light irradiation, and the optimum loading of ZnFe2O4 on α-Al2O3 is 30 wt %. Analysis of the kinetic data for the photocatalytic degradation of MB using the Langmuir–Hinshelwood kinetic model yielded 0.005 mgL−1min−1 for the intrinsic photocatalytic reaction rate constant and 0.111 Lmg−1 for the adsorption equilibrium constant. Photocatalytic treatment of real textile effluent resulted in more effective (when compared to photolytic treatment) in the reduction of effluent’s colour, COD, pH, conductivity and TDS. 30 wt% ZnFe2O4/Al2O3 was found to be more effective than bare ZnFe2O4 for the reduction of effluent’s colour, COD, pH, conductivity and TDS