High efficient catalytic degradation of PNP over Cu-bearing catalysts with microwave irradiation

The catalytic capabilities of copper doped attapulgite (Cu/ATP) and silicon carbide (Cu/SiC) nanocomposites for p-nitrophenol (PNP) were characterized under microwave (MW) irradiation. Higher catalytic performance of Cu/SiC was obtained than that of Cu/ATP due to higher production rate of reactive oxygen species (ROS) as well as higher MW absorptivity. The electron (e−) - hole (h+) pairs were related to the generation of ROS on Cu/SiC. The modification Cu with SiC had an enhancement on the band gap and large EVB absolute values, which promoted the catalytic activity of Cu/SiC. An ROS-producing copper-redox cycle between CuI and CuII of Cu/ATP was responsible for PNP degradation. The produced CuI via thermal dissociation of [Cu-O-Cu]n species in Cu/ATP activated molecular oxygen, followed by Fenton-like reactions to produce ROS. The reusability of the catalysts and negligible phase transformation of Cu species after five rounds of cycle verified the catalyst stability. Based on Density functional theory (DFT) calculation and catalytic experimental analyses, the denitro-hydroxylation of PNP was the initial oxidation reaction step followed by further oxidation to form short-chain carboxylic acids. OH oxidation was predominant whereas O2− was not involved in the OH addition on the meta-position due to lower oxidation energy than the corresponding activation energies. Other than reactive species attack, the “hot spots” on the surface of Cu/SiC was responsible for thermal stabilization of PNP/intermediates in soil. In this study, MW-assisted Cu/ATP and Cu/SiC catalytic degradation of PNP was proved to be an efficient technology for wastewater treatment and soil remediation.