The reaction pathway and mechanism of 2,4-dichlorophenol removal by modified fly ash-loaded nZVI/Ni particles

Nanoscale zero-valent iron (nZVI) is more valuable in environmental restoration than other materials. Chemical treatment of fly ash (CFA) was employed as a support material to disperse iron nickel bimetal nanoparticles (CFA-nZVI/Ni) to remove 2,4-dichlorophenol (2,4-DCP). Batch experiments showed that 2,4-DCP was completely removed by CFA-nZVI/Ni, and an optimal loading ratio was 8:1. The degradation of 2,4-DCP by CFA-nZVI/Ni was a chemical control reaction with an activation energy of 95.6 kJ mol^-1 and followed pseudo-first-order kinetics. The addition of Cl^- increased the removal rate of 2,4-DCP by 4%, while the addition of CO₃^2- and SO₄^2- decreased the removal rate of 2,4-DCP by 32% and 72.3%, respectively. The removal process of 2,4-DCP by CFA-nZVI/Ni included adsorption and reduction. The 2-CP (7.1 mg/L) and 4-CP (11.6 mg/L) could be converted to phenol using the CFA-nZVI/Ni system. Cl on the para-position of 2,4-DCP was simpler to remove than on the ortho-position. The following steps were taken in the electrophilic substitution reaction between substituted phenols and hydrogen radicals: 2,4-DCP > 2-CP > 4-CP > phenol. This research provides a novel concept to effectively remove 2,4-DCP and mechanism analysis.