Degradation of phenol in photo-Fenton process by phosphoric acid modified kaolin supported ferric-oxalate catalyst: Optimization and kinetic modeling

Phenol was degraded with phosphoric acid modified kaolin clay supported ferric-oxalate catalyst (AMKC). The degradation was achieved without initial pH adjustments to avoid the interference of buffering on the degradation kinetics. The degradation process was optimized to minimize the superfluous scavenging effect of excess dosage of hydrogen peroxide (HP) and AMKC on the kinetics study. The presence of Fe was confirmed by X-ray diffraction, Fourier Transform Infrared Spectroscopy, XRF and EDX results. Brunauer-Emmet-Teller result showed an increment in the surface area from 19 to 45 m(2)/g after the acid modification which led to structural and morphological changes as revealed by the Scanning Electron Microscopy (SEM). The best optimization result of the degradation of phenol obtained from the desirability plot gave 18.2% excess HP, 2.23 g of AMKC as the best condition to achieve 99.15% degradation of 100 ppm initial concentration of phenol at 30 degrees C in 5 min reaction time. Strong correlation between the experimental and predicted responses was observed with R-2 and R-adj(2) values of 0.9921 and 0.9810, respectively. In the kinetic study, degradation rate 50 ppm is 1.38 times faster than 200 ppm while the selectivity of AMKC for direct oxidation of phenol is 3.4 times higher than through intermediates. Only about 4% drop in catalyst activity was observed during the reusability studies after five experiments. This makes AMKC reliable for treating phenol polluted water. (C) 2012 Elsevier B.V. All rights reserved.