Solar photocatalytic degradation of organic pollutants in textile industry wastewater by ZnO/pumice composite photocatalyst

ZnO-pumice composite photocatalyst was synthesized and characterized using Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and X-ray fluorescence (XRF). The photocatalyst was then used for the photocatalytic degradation of textile effluent under sunlight irradiation. The process variables affecting the photocatalytic degradation were optimized using central composite design, and the kinetic data obtained at different solution pH (4, 7 and 10) were evaluated using pseudo-first-order approximation of the Langmuir-Hinshelwood model. The optimization results showed that the predicted values of degradation efficiency matched the observed values reasonably well with R-2 = 0.9677 and Adj-R-2 = 0.9387. At the optimum values of 3.0 g/L catalyst dosage, 4.01 solution pH and 45.04 min irradiation time, the predicted and experimental degradation efficiencies were 93.04 and 90.17%, respectively. The kinetic study revealed that the degradation of dye molecules in the effluent obeyed a pseudo-first-order rate law with reaction rate constants of 0.0597, 0.0558 and 0.0535 min(-1) at pH of 4, 7 and 10, respectively.