Tong Xu

Bio: Tong Xu is an academic researcher from Dalian University of Technology. The author has contributed to research in topics: Phthalate & Kinetics. The author has an hindex of 3, co-authored 8 publications receiving 77 citations.

Effects of Atmospheric Water on ·OH-initiated Oxidation of Organophosphate Flame Retardants: A DFT Investigation on TCPP

Abstract: Tris(2-chloroisopropyl) phosphate (TCPP), a widely used organophosphate flame retardant, has been recognized as an important atmospheric pollutant. It is notable that TCPP has potential for long-range atmospheric transport. However, its atmospheric fate is unknown, restricting its environmental risk assessment. Herein we performed quantum chemical calculations to investigate the atmospheric transformation mechanisms and kinetics of TCPP initiated by ·OH in the presence of O2/NO/NO2, and the effects of ubiquitous water on these reactions. Results show the H-abstraction pathways are the most favorable for the titled reaction. The calculated gaseous rate constant and lifetime at 298 K are 1.7 × 10–10 cm3molecule–1 s–1 and 1.7 h, respectively. However, when considering atmospheric water, the corresponding lifetime is about 0.5–20.2 days. This study reveals for the first time that water has a negative role in the ·OH-initiated degradation of TCPP by modifying the stabilities of prereactive complexes and transi...

Development of Prediction Models on Base-Catalyzed Hydrolysis Kinetics of Phthalate Esters with Density Functional Theory Calculation.

Abstract: Many phthalate esters (PAEs) are chemicals of high production volume and of toxicological concern. The second-order rate constant for base-catalyzed hydrolysis (kB) is a key parameter for assessing environmental persistence of PAEs. However, the kB values for most PAEs are lacking, and the experimental determination of kB encounters various difficulties. Herein, density functional theory (DFT) methods were selected by comparing empirical kB values of five PAEs and five carboxylic acid esters with the DFT-calculated ones. Results indicate that PAEs with cyclic side chains are more vulnerable to base-catalyzed hydrolysis than PAEs with linear alkyl side chains, followed by PAEs with branched alkyl side chains. By combining experimental and DFT-calculated second-order rate constants for base-catalyzed hydrolysis of one side chain in PAEs (kB_side chain), quantitative structure–activity relationship models were developed. The models can differentiate PAEs with the departure of the leaving group (or the nucleo...

Prediction Models on pKa and Base-Catalyzed Hydrolysis Kinetics of Parabens: Experimental and Quantum Chemical Studies.

Abstract: Parabens for which the molecules contain hydrolytic and ionizable groups, are emerging pollutants due to their ubiquity in the environment However, lack of pKa and second-order base-catalyzed hydrolysis kinetics (kB) values limits their environmental persistence assessment Herein, six parabens were selected as reference compounds for which the pKa and kB values were measured experimentally A semiempirical quantum chemical (QC) method was selected to calculate pKa of the parabens, and density functional theory (DFT) methods were selected to calculate kB for neutral and anionic forms of the parabens, by comparing the QC-calculated and determined values Combining the QC-calculated and experimental pKa and kB values, quantitative structure-activity relationships with determination coefficients (R2) being 0947 and 0842 for the pKa and kB models, respectively, were developed, which were validated and could be employed to efficiently fill the kB and pKa data gaps of parabens within applicability domains The base-catalyzed hydrolysis half-lives were estimated to range from 6 h to 152 × 106 years (pH 7-9, 25 °C), further necessitating the in silico models due to the tedious and onerous experimental determination, and the huge number of hydrolyzable and ionizable chemicals that may be released into the environment

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

New Insights into the Degradation Mechanism of Perfluorooctanoic Acid by Persulfate from Density Functional Theory and Experimental Data

Abstract: Thermally activated persulfate is a promising oxidant for in situ remediation of perfluorooctanoic acid (PFOA), yet a comprehensive understanding of the degradation mechanism is still lacking. In this study, we used density functional theory (DFT) calculations and experimental data to map entire reaction pathways for the degradation of PFOA by persulfate, with specific considerations on the influence of pH. The DFT results showed that the rate-limiting step was the first electron abstraction from PFOA, yet the generation of SO4•- from the decomposition of persulfate contributed a large part of the free energy of activation (ΔG‡) for the overall reaction. The subsequent steps did not contribute to the ΔG‡. For the electron abstraction from PFOA, we investigated reactions using protonated and deprotonated species of PFOA and SO4•- and showed that the reaction of anionic PFOA with HSO4• was most favorable with a ΔG‡ of 7.2 kJ/mol. This explains why low pH (<3.5) is a sine qua non condition for the degradation of PFOA by persulfate. The overall ΔG‡ derived theoretically based on the pathway involved HSO4• was consistent with the ΔG‡ determined experimentally. This study provides valuable insight into remediation strategies that include persulfate as an oxidizing agent for perfluoroalkyl carboxylic acids.

Decomposition Mechanism of C5F10O: An Environmentally Friendly Insulation Medium.

Abstract: SF6, the most widely used electrical-equipment-insulation gas, has serious greenhouse effects. C5F10O has attracted much attention as an alternative gas in recent two years, but the environmental impact of its decomposition products is unclear. In this work, the decomposition characteristics of C5F10O were studied based on gas chromatography–mass spectrometry and density functional theory. We found that the amount of decomposition products of C5F10O, namely, CF4, C2F6, C3F6, C3F8, C4F10, and C6F14, increased with increased number of discharges. Under a high-energy electric field, the C–C bond of C5F10O between carbonyl carbon and α-carbon atoms was most likely to break and generate CF3CO•, C3F7• or C3F7CO•, CF3• free radicals. CF3•, and C3F7• free radicals produced by the breakage more easily recombined to form small molecular products. By analyzing the ionization parameters, toxicity, and environmental effects of C5F10O and its decomposition products, we found that C5F10O gas mixtures exhibit great decom...

Organophosphate Ester Transport, Fate, and Emissions in Toronto, Canada, Estimated Using an Updated Multimedia Urban Model.

Abstract: Organophosphate esters (OPEs), used as flame retardants and plasticizers, occur at relatively high concentrations in urban air and surface waters. We tested the hypothesis that some OPEs could be considered persistent and mobile organic compounds (PMOCs), using the poly parameter linear free energy relationship-modified Multimedia Urban Model (ppLFER-MUM) in Toronto, Canada, as a case study. Modeled air emissions of ∑6OPEs of 3300 (190–190 000) kg yr–1 were 10–100 times higher than emissions of polychlorinated biphenyls (∑5PCBs) and polybrominated diphenyl ethers (∑5PBDEs). Model results suggested that measured ∑6OPE stream concentrations of ∼2000 ng L–1 originate from emissions to urban air transferred to water mostly via precipitation. Water transport removed 7–28% of total air inputs compared to 0.1–10% for PCBs and 2–10% for PBDEs. Chlorinated OPEs were efficiently transported via surface water due to their persistence and high solubility. Loadings of ∑6OPEs to Lake Ontario from wastewater treatment p...