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

摘要

This paper describes the effect of temperature and initial concentration of H_2O_2, Fe(II), PhNO_2 and dissolved oxygen on the degradation rate of PhNO_2 in homogeneous aqueous solution by 'Fenton-like' reagent ([H_2O_2]_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 PhNO_2 when conversion of the latter was less than 25%. This fact suggests that hydroxylation of PhNO_2 was promoted by HO~· radicals. The reaction was investigated in a completely mixed-batch reactor under a wide range of experimental conditions: pH ～3.0; 278-318 K; 1.5<[H_2O_2]_o<26.5 mM; 0.04<[Fe(II)]_o<1.1 mM; 0.3<[PhNO_2]_o<2.5 mM; and 0<[O_2]_o<1.4 mM. The activation energy for the degradation of PhNO_2 was determined to be 59.7 kJ mol~(-1). The degradation rate of PhNO_2 follows pseudo-first-order kinetics. The results of this study demonstrate that the degradation rate of PhNO_2 in the 'Fenton-like' system could be predicted with sufficient precision by the equation R_D = 1.05 * 10~(11) exp(-59.7/RT)[H_2O_2]_o~(0.68)[Fe(II)_o~(1.67)[PhNO_2]_o~(-0.32). The second-order rate constant for the overall rate of H_2O_2 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 ～10~(-13) M, as estimated by two independent methods.