Rate equation for the degradation of nitrobenzene by 'Fenton-like' reagent

This paper describes the effect of temperature and initial concentration of H2O2, Fe(II), PhNO2 and dissolved oxygen on the degradation rate of PhNO2 in homogeneous aqueous solution by 'Fenton-like' reagent ([H2O2](o) >> [Fe(II)](o)). The oxidation products o-, m- and p-nitrophenol were found as intermediates in the ratio 1:1.3-2.8:1.4-2.7 as compared with PhNO2 when conversion of the latter was less than 25%. This fact suggests that hydroxylation of PhNO2 was promoted by HO. radicals. The reaction was investigated in a completely mixed-batch reactor under a wide range of experimental conditions: pH similar to3.0; 278-318 K; 1.5 < [H2O2](o) < 26.5 mM; 0.04 < [Fe(II)](o) < 1.1 mM; 0.3 < [PhNO2](o) < 2.5 mM; and 0 < [O-2](o) < 1.4 mM. The activation energy for the degradation of PhNO2 was determined to be 59.7 kJ mol(-1). The degradation rate of PhNO2 follows pseudo-first-order kinetics. The results of this study demonstrate that the degradation rate of PhNO2 in the 'Fenton-like' system could be predicted with sufficient precision by the equation R-D=1.05x10(11)exp(-59.7/RT)[H2O2](o)(0.68)[Fe(II)](o)(1.67)[PhNO2](o)(-0.32). The second-order rate constant for the overall rate of H2O2 decomposition by Fe(III) was found to be 0.83 M-1 s(-1) at 298 K. The value of the steady-state HO. radical concentration in the 'Fenton-like' reaction was found to be similar to10(-13) M, as estimated by two independent methods. (C) 2002 Elsevier Science Ltd. All rights reserved.