Carbon dioxide radical anion mediated dehalogenation kinetics and mechanisms of halogenated alkanes

Carbon dioxide radical anion (CO2•-) recently becomes appreciated in halogenated contaminants elimination; nevertheless, its application has been restricted by insufficient mechanistic understanding. Herein, we provided a quantitative insight into the kinetics and mechanisms of CO2•- mediated dehalogenation of halogenated alkanes. A CO2•- dominated UV254/H2O2/HCOO- system has been successfully established and demonstrated for effective elimination of 7 kinds of halogenated alkanes (71.3 % to 100 % of removal). Using a laser flash photolysis technology, the second-order rate constants of CO2•- ( [Formula: see text] ) reacting with CCl4, CHCl3 and CH2Cl2 were firstly reported, to be 2.5 × 108, 6.2 × 107 and 5.8 × 106 M-1s-1, respectively. [Formula: see text] presented a significant negative correlation with the lowest unoccupied molecular orbital energy (ELUMO) of chlorinated alkanes, proving that the enhanced dehalogenation of CO2•- was attributed by direct electron transfer mechanism. A fitting model was developed accordingly for [Formula: see text] prediction. This study also demonstrated that the CO2•- mediated ARP effectively removed halogenated alkanes regardless of pH condition (6.0∼9.0) and bicarbonate concentrations. These findings are significant in advancing the scientific understanding of CO2•- mediated ARP. This reductive process a promising control strategy for halogenated contaminants, such as polyfluoroalkyl substances (PFAS) and halogenated pharmaceuticals.

Photochemistry of tris(2,3,5,6-tetrathiaaryl)methyl radicals in various solutions

A detailed mechanism of TAM photolysis was studied and includes photoionization of the TAM radical with the formation of carbocation and further conversion of the carbocation under aerobic conditions into quinone-methide and under anaerobic conditions supposedly into an aromatic carbene.

Dechlorination and decomposition of chloroform induced by glow discharge plasma in an aqueous solution

In this study, efficient dechlorination and decomposition of chloroform (CF) induced by glow discharge plasma (GDP) in contact with a sodium sulfate solution was investigated. Intermediate byproducts were determined by ionic chromatography and headspace gas chromatography, respectively. Results showed that CF can be effectively dechlorinated and decomposed under the action of GDP. Both removal and dechlorination of CF increased with increasing pH and with addition of hydroxyl radical scavengers to the solution. Addition of H2O2 to the solution slightly decreased the CF removal. Formic acid, oxalic acid and dichloromethane were determined as the major intermediate byproducts. Final products were carbon dioxide and hydrochloric acid. Hydrated electrons were the most likely active species responsible for initiation of the dechlorination, and hydroxyl radicals may be the ones for the oxidation of the organic intermediate byproducts. Hydrolyses of the chloromethyl radicals contributed much in the mineralization of the organic chlorine. Reaction mechanism was proposed based on the dechlorination kinetics and the distribution of intermediate byproducts.