Study of adsorption-oxidative degradation of PAHs over organic–inorganic hybrid layered double hydroxides†

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are well-known hazardous pollutants. As a result, numerous methods have been designed and developed for their effective treatment. In this study, an adsorption-oxidation degradation process was explored for PAH degradation using CuZnFeAl layered double hydroxide (LDH), which was synthesized using a co-precipitation method. LDH was then subjected to high-temperature roasting to obtain CuZnFeAl layered double oxide (LDO), which was subsequently modified with a sodium dodecyl sulfate solution (SDS) to obtain SDS/LDO. Characterization studies substantiated that SDS/LDO was successfully modified. Naphthalene (Nap) and phenanthrene (PA) were used as PAH model pollutants and the degradation effects of different oxidants were evaluated. The results of adsorption-oxidation coupling degradation showed that the conversion rates of Nap and PA using ozone as an oxidant over SDS/LDO reached 98.5% and 99.9%, respectively. The kinetic study of the degradation of Nap and PA by adsorption-oxidation showed that the degradation of Nap and PA followed pseudo-first-order reaction kinetics. A mechanism study verified the existence of several free radicals, such as ˙OH, ¹O₂ and ˙O²⁻, which can continuously degrade PAHs. The degradation of Nap and PA gradually resulted in small organic molecular compounds, such as phenolic compounds, esters and alcohols, and were finally oxidized into H₂O and CO₂.