Degradation mechanisms, kinetics and eco-toxicity assessment of 2,4-Dinitrophenol by oxygen-containing free radicals in aqueous solution

Abstract

2,4-Dinitrophenol (DNP) as a widely used chemical is harmful to human health. Highly active free radicals-based advanced oxidation technology (AOT) has been successfully applied to degrade DNP in wastewater. This work aims to systematically and comprehensively analyse the oxidative degradation of DNP caused by eleven different oxygen-containing free radicals (HO·, SO4 −· , H2PO4 ·, NO3 ·, , , BrO·, ClO·, HO2 ·, , and ) involved in wastewater treatment. The quantum chemical methods are used to clarify thermodynamic feasibility, favourable site, and characteristics of reactions between different oxygen-containing free radicals and DNP based on three reaction mechanisms of free radical addition, hydrogen atom abstraction, and single electron transfer. The DNP degradation initiated by H2PO4 ·/NO3 ·/HO· is relatively easy to proceed. The kinetic data of the above reactions assist the thermodynamic analysis results. Particularly, the reaction pathways of complete degradation process of HO· and DNP are proposed. The production paths of main intermediates/products detected in the experiments are determined. The total rate constant of HO· and DNP is calculated to be 1.23×108 M-1s-1. The ecotoxicity evaluation suggests most intermediates/products is decreased during degradation, and a small part of by-products are still toxic. In addition, some insights into the AOT treatment of wastewater containing DNP are provided. GRAPHICAL ABSTRACT