A nonradical oxidation process initiated by Ti-peroxo complex showed high specificity toward the degradation of tetracycline antibiotics

Nonradical oxidation has received wide attention in advanced oxidation processes for environmental remediation.Understanding the relationship between material characteristics and their ability to initiate nonradical oxidation processes is the key to better material design and performance.Herein,a novel titanium-based metal-organic framework MIL-125-Ti/H_(2)O_(2) system was established to show a highly selective degradation efficacy toward tetracycline antibiotics.MIL-125-Ti with the abundance of TiO6 octahedra units was found to effectively activate H_(2)O_(2) under dark conditions by forming an oxidative Ti-peroxo complex.The presence of the Ti-peroxo complex,confirmed by UV-visible spectrophotometer,fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopy characterizations,showed superior degradation(>95%removal rate)of oxytetracycline hydrochloride(OTC),doxycycline hydrochloride,chlortetracycline hydrochloride,and tetracycline.Density functional theory calculations were performed to assist the elucidation on the mechanism of H_(2)O_(2) activation and antibiotics degradation.The MIL-125-Ti/H_(2)O_(2) system was highly resistant to halogens and background organics,and could well maintain its original catalytic activity in actual water matrices.It retained the ability to degrade 75%of OTC within ten test cycles.This study provides new insight into the nonradical oxidation process initiated by the unique Ti-peroxo complex of Ti-based MOF.

Topological defects strengthened nonradical oxidation performance of biochar catalyzed peroxydisulfate system

Nonradical oxidation based on peroxydisulfate(PDS)activation has attracted increasing attention for selective degradation of organic pollutants.Herein,topological defects were introduced into biochar(BC)via removing N atoms in N-doped BC(NBC)in an attempt to improve the nonradical catalytic performance.Compared to the pristine BC and NBC,the introduction of topological defects could achieve up to 36.6-and 8.7-times catalytic activity enhancement,respectively.More importantly,it was found that the catalytic activity was dominated by topological defects,which was verified by the significant positive correlation between the pseudo-first-order rate constants and the content of topological defects.Theoretical calculations suggested that topological defects enhanced the electrondonating ability of BC by reducing the energy gap,which made the electrons transfer to PDS molecules more easily.As a result,holes were generated after the carbon defects lost electrons,and induced a nonradical oxidation process.Benefiting from the merits of nonradical oxidation,the developed BC/PDS system showed superior performance in removing electron-rich contaminants in the presence of inorganic anions and in the actual environments.This study not only provides a potential avenue for designing efficient biochar-based catalysts,but also advances the mechanism understanding of nonradical oxidation process induced by carbon defects.

Degradation of neonicotinoids with different molecular structures in heterogeneous peroxymonosulfate activation system through different oxidation pathways

The elimination of neonicotinoids(NEOs)from water has been a research priority due to their threats to human health and ecosystems.In this study,we established the heterogeneous peroxymonosulfate(PMS)activation system using manganese catalyst(Mn NC)and cobalt catalyst(Co NC)to trigger the nonradical oxidation and synergistic oxidation pathway,respectively to remove NEOs.The results showed that the nonradical oxidation system exhibited superior NEOs degradation capability.The composition of organic pollutants in wastewater significantly impacted subsequent degradation processes.The charge distribution and reaction sites of various NEOs were analyzed using density functional theory(DFT)calculations,and it demonstrated the electron distribution and activity of NEOs were significantly influenced by the type and number of substituents.Nitro group(–NO_(2))and cyanide group(–C≡N)were identified as strong electron-withdrawing groups and prone to be attacked by negatively charged radicals.The transformation of NEOs was analyzed,and result showed that the C and N sites adjacent to the nitro group and cyanide group were more susceptible to oxidation attacks.S and N atoms,which possess strong electronegativity and high electron cloud density,were identified as key active sites in the degradation pathway.The outcomes of this study provide valuable guidance for the oriented regulation of oxidation pathways towards efficient removal of NEOs in water.