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

Heterogeneous Fenton-like reactions on nano-magnetite (Fe3O4) 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 < 0.0001, R2 = 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 Fe3O4, 620 mM H2O2, 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-Fe3O4, 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 (VOH) 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-Fe3O4 surface.

Graphical abstractHeterogeneous Fenton-like reactions on nano-magnetite (Fe3O4) were investigated for the degradation of p-Nitrophenol (p-NP).Figure optionsDownload full-size imageDownload high-quality image (124 K)Download as PowerPoint slideHighlights► Degradation of p-NP in water by heterogeneous Fenton on nano-Fe3O4 at neutral pH. ► Parameter optimization by central composite design and response surface methodology. ► Primary reactive species, intermediate products and kinetics of p-NP degradation. ► An environmentally benign technology for remediation of p-NP and other contaminants.