Ferrate(VI) oxidation of substituted nitrobenzene compounds: Kinetics, degradation, and oxidized products

Abstract

Nitrobenzene pollutants are discharged in large quantities into water bodies, posing a serious threat to the ecological environment. However, the effects of the nitrobenzene compounds with different structures on the Fe(VI) degradation process remain unclear. This research selects four different substituted nitrobenzene compounds (1,2-dinitrobenzene (1,2-DB), 4-nitrochlorobenzene (4-NCB), pentachloronitrobenzene (PCT), and 3,4-dinitrochlorobenzene (3,4-DTB)) and explores the oxidative degradation effect of ferrate(VI) based on experimental results and theoretical calculations. The reaction of Fe(VI) (800 μM) with each of the four nitrobenzene compounds (40 μM) reflected second-order reaction kinetics at pH 8: 4-NCB (127.08 M−1s−1) > PCT (113.13 M−1s−1) > 1,2-DB (100.1 M−1s−1) > 3,4-DTB (96.459 M−1s−1). Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) analysis detected the main intermediates, which consisted of hydroxylation, ring-opening, coupling, and amine-based products. Free radicals in the reaction system were identified and analyzed, and hydroxyl radicals and carbon dioxide radicals were found. In addition, density functional theory (DFT) was used to explore the degradation mechanisms in the reaction between each of the four substances and hydroxyl radicals, with the active sites of the nitrobenzenes during the Fe(VI) degradation process determined through the calculation of molecular descriptors. Toxicity analysis with ECOSAR software indicated Fe(VI) reduced the toxicity of the nitrobenzenes. This study provides experimental and theoretical support for the reaction mechanism between nitrobenzenes and Fe(VI), as well as further understanding of the degradation mechanism of nitrobenzene compounds.