Dechlorination of 2,4-dichlorophenol by nickel nanoparticles under the acidic conditions

Metal nanoparticles are effective for remediation of contamination with a range of compounds including chlorinated organics. However, the sorption process of the passivation oxide layers on the metal nanoparticle surfaces may result in incomplete degradation of contaminants. This phenomenon can be prevented by an acidic washing procedure or reaction in an acidic medium. In this paper, nickel nanoparticles manufactured via the carbonyl powder process were analyzed using scanning electron microscopy, transmission electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy. The sorption and degradation of 2,4-dichlorophenol (2,4-DCP) by nickel nanoparticles under acidic conditions was then investigated. Transmission electron microscopy and XRD results showed that the nickel nanoparticles range in size from 10 to 20 nm, and a thin passivation layer of NiO is present on the surface. This oxide layer can be removed by pretreatment washing with acidic solutions. It was indicated that dechlorination was the key reaction pathway for degradation of 2,4-DCP by nickel nanoparticles under acidic conditions. The main degradation products were 4-Chlorophenol, 2-Chlorophenol, and Phenol, and among these, Phenol was dominant. The acidic medium promoted degradation by providing an appropriate pH, and H⁺ may be involved in the reaction. Dechlorination of 2,4-DCP by nickel nanoparticles under the acidic condition follows the second order kinetic model, and the rate constants at 298, 306, 316 K are 0.02, 0.2 and 0.3 (g L h)⁻¹, respectively.