Energy band reconstruction mechanism of Cl-doped Cu2O and photocatalytic degradation pathway for levofloxacin

Abstract

Cl-doped Cu 2 O microparticles were prepared by hydrothermal synthesis . XRD, BET, SEM, TEM, UV–Vis and RSM were used to reveal the microstructure, optical properties and degradation regularity of the Cl-doped Cu 2 O microparticles. The band gap structures and state densities of Cl-doped Cu 2 O microparticles were computed based on density functional theory . The major intermediate degradation products and potential photocatalytic degradation pathways of levofloxacin were identified by HPLC–MS/MS. The photocatalytic active sites of levofloxacin and its intermediate products were calculated based on the frontier electron densities. The results showed that the prepared Cl-doped Cu 2 O microparticles increased the specific surface area and absorption efficiency of visible light compared with undoped pure Cu 2 O. The doping of Cl introduced hybrid orbitals and oxygen vacancy defects in the Cu 2 O crystal cell and decreased the forbidden bandwidth of Cu 2 O crystal microparticles, leading to a redshift of the absorption edge . Cl doping could form a shallow donor impurity energy level composed of Cl 3 p orbital in the energy gap of Cu 2 O and make the energy band denser and move to a lower energy, which could promote the electron leap to the conduction band through the impurity level . The doping of Cl can make the density of states curve of the Cu 2 O crystal shift to low-energy and the Cl-doped Cu 2 O rendered to half-metallic behavior and characteristic behavior of an n type semiconductor. The photocatalytic degradation of levofloxacin was attributed to attack of photogenerated holes and hydroxyl radicals , and the ring opening of the piperazine ring by oxidation and decarboxylation reactions from the quinolone ring might be two photocatalytic degradation pathways. This study revealed the mechanism of oxygen vacancy formation and the change rules of the band structure by doping of the nonmetal chlorine into Cu 2 O crystallites . • Migration laws of band structure and state density of Cl-doped Cu 2 O were revealed. • Doping of Cl introduced hybrid orbitals and oxygen vacancies in the Cu 2 O crystal. • Doping of Cl decreased band gap of Cu 2 O and led to red shift of absorption edge. • Holes and hydroxyl radicals are the main photocatalytic active species. • Degradation paths of levofloxacin were piperazine ring opening and decarboxylation.