Jiabin Chen

Decolorization of azo dye by peroxymonosulfate activated by carbon nanotube: Radical versus non-radical mechanism

Carbon nanotube (CNT) has been shown to effectively activate peroxymonosulfate (PMS) to remove contaminants, whereas controversial activation mechanisms (radical vs non-radical mechanism) were previously proposed. Here we report that radical-induced decolorization of acid orange 7 (AO7) dominated in the CNT activated PMS system, but non-radical mechanism was also involved at high Cl- concentration. CNT exhibited high activity in activating PMS to decolorize AO7. The decolorization rate of AO7 increased with increasing PMS dosages and CNT loadings, rising temperature and higher pH. Radical quenching and photoluminescence techniques confirmed the decolorization of AO7 in the CNT/PMS system was caused by the radical oxidation, which dominantly took place on the surface of CNT, rather than the bulk solution. The presence of Cl- exhibited a dual effect on AO7 decolorization. Low concentration of Cl- slightly inhibited AO7 decolorization, but further raising the concentration to above 0.1M significantly accelerated its decolorizaition. Cl- was confirmed to react with PMS to generate HClO, which effectively bleached AO7 through non-radical process rather than radical process. The decolorization of AO7 induced from the non-radical process exhibited different degradation products and less mineralization in comparison to that derived from radical process.

Fe(III)-promoted transformation of β-lactam antibiotics: Hydrolysis vs oxidation

The widely used β-lactam antibiotics are susceptible to oxidative and/or hydrolytic degradation promoted by some metal ions (e.g., Cu(II)). Ferric ions (Fe(III)) are among the most common metal ions, but their role in the environmental transformation and fate of β-lactam antibiotics is still unknown. This study elucidates that Fe(III) can promote degradation of β-lactam antibiotics under environmental aquatic conditions. Degradation rate constants of ampicillin (AMP) linearly increased with increasing Fe(III) concentration, but were independent of AMP concentration when AMP was higher than Fe(III) concentration. Neutral pH was most favorable for Fe(III)-promoted degradation of AMP, and the promoted degradation was also significant in real surface water and wastewater matrix. Among the various β-lactam antibiotics, Fe(III)-promoted degradation of penicillins was faster than that of cephalosporins. Product analysis indicated that only two isomers of hydrolysis products were observed without detection of oxidation products. The Fe(III)-promoted degradation likely occurred via complexation of β-lactam antibiotics with carboxyl group and tertiary nitrogen, and then enhancing the hydrolytic cleavage of β-lactam ring. This study is among the first to identify the role of Fe(III) in the degradation of β-lactam antibiotics and elucidate the mechanism. The new findings indicate iron species are among the factors affecting the environmental fate of β-lactam antibiotics.

Oxidation of cefalexin by thermally activated persulfate: Kinetics, products, and antibacterial activity change

While the widely used β-lactam antibiotics, such as cephalosporins, are known to be susceptible to oxidation by sulfate radical (SO4-), comprehensive study about SO4--induced oxidation of cephalosporins is still limited, such as the impact of water matrices, and the structure and antibacterial activity of transformation products. Herein, the oxidation of cefalexin (CFX), a most frequently detected cephalosporin, was systematically investigated by thermally activated persulfate (PS). CFX oxidation followed pseudo-first-order kinetics, and SO4- dominantly contributed to the overall oxidation of CFX. The impact of water matrices, such as Cl-, HCO3- and natural organic matter, on CFX degradation was predicted using a pseudo-steady-state kinetic model. The secondary reactive species, such as chlorine and carbonate radicals, were found to contribute to CFX degradation. Product analysis indicated oxidation of CFX to six products (molecular weight of 363), with two stereoisomeric sulfoxides as the primary oxidation products. It was thus suggested that the primary amine on the side chain, and the thioether sulfur and double bond on the six-membered ring were the reactive sites of CFX towards SO4- oxidation. Antibacterial activity assessment showed that the biological activity of CFX solution was significantly diminished after treatment by the thermally activated PS.

Oxidation of Cefalexin by Permanganate: Reaction Kinetics, Mechanism, and Residual Antibacterial Activity

The oxidation of cefalexin (CFX), a commonly used cephalosporin antibiotic, was investigated by permanganate (PM) in water. Apparent second-order rate constant of the reaction between CFX and PM was determined to be 12.71 ± (1.62) M−1·s−1 at neutral pH. Lower pH was favorable for the oxidation of CFX by PM. The presence of Cl− and HCO3− could enhance PM-induced oxidation of CFX, whereas HA had negligible effect on CFX oxidation by PM. PM-induced oxidation of CFX was also significant in the real wastewater matrix. After addition of bisulfite (BS), PM-induced oxidation was significantly accelerated owing to the generation of Mn(III) reactive species. Product analysis indicated oxidation of CFX to three products, with two stereoisomeric sulfoxide products and one di-ketone product. The thioether sulfur and double bond on the six-membered ring were the reactive sites towards PM oxidation. Antibacterial activity assessment indicated that the activity of CFX solution was significantly reduced after PM oxidation.

Correction to: Ultrasound enhanced activation of peroxydisulfate by activated carbon fiber for decolorization of azo dye

The correct name of the 5th Author is Jiabin Chen.