p-Nitrophenol degradation by a heterogeneous Fenton-like reaction on nano-magnetite: Process optimization, kinetics, and degradation pathways

TLDR: In this paper, a four factor central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables for the degradation of p-Nitrophenol (p-NP).

Abstract: Heterogeneous Fenton-like reactions on nano-magnetite (Fe 3 O 4 ) were investigated for the degradation of p-Nitrophenol (p-NP). A four factor central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables. A significant quadratic model ( P -value  R 2  = 0.9442) was derived using analysis of variance (ANOVA), which was adequate to perform the process variables optimization. Optimum conditions were determined to be 1.5 g L −1 Fe 3 O 4 , 620 mM H 2 O 2 , pH 7.0 and 25–45 mg L −1 p-NP. More than 90% of p-NP was experimentally degraded after 10 h of reaction time under the optimum conditions, which agreed well with the model predictions. The results demonstrated that the degradation of p-NP was due to the attack of hydroxyl radicals ( OH) generated by the surface-catalyzed decomposition of hydrogen peroxide on the nano-Fe 3 O 4 , i.e. heterogeneous Fenton-like reactions. Possible mechanisms of p-NP degradation in this system were proposed, based on intermediates identified by LC–MS and GC–MS and included benzoquinone, hydroquinone, 1,2,4-trihydroxybenzene and p-nitrocatechol. The kinetic analysis implied that the generation rate of OH ( V OH ) was increased along with the degradation of p-NP. This was attributed to the formation of acidic products, which decreased the solution pH and enhanced the decomposition of absorbed hydrogen peroxide via a radical producing pathway on the nano-Fe 3 O 4 surface.