Photochemical reaction kinetics and mechanisms of diethyl phthalate with N (III) in the atmospheric aqueous environment

Optical Variation and Molecular Transformation of Brown Carbon During Oxidation by NO3• in the Aqueous Phase

The NO3•-driven nighttime aging of brown carbon (BrC) is known to greatly impact its atmospheric radiative forcing. However, the impact of oxidation by NO3• on the optical properties of BrC in atmospheric waters as well as the associated reaction mechanism remain unclear. In this work, we found that the optical variation of BrC proxies under environmentally relevant NO3• exposure depends strongly on their sources, with enhanced light absorptivity for biomass-burning BrC but bleaching for urban aerosols and humic substances. High-resolution mass spectrometry using FT-ICR MS shows that oxidation by NO3• leads to the formation of light-absorbing species (e.g., nitrated organics) for biomass-burning BrC while destroying electron donors (e.g., phenols) within charge transfer complexes in urban aerosols and humic substances, as evidenced by transient absorption spectroscopy and NaBH4 reduction experiments as well. Moreover, we found that the measured rate constants between NO3• with real BrCs (k = (1.8 ± 0.6) × 107 MC-1s-1, expressed as moles of carbon) are much higher than those of individual model organic carbon (OC), suggesting the reaction with OCs may be a previously ill-quantified important sink of NO3• in atmospheric waters. This work provides insights into the kinetics and molecular transformation of BrC during the oxidation by NO3•, facilitating further evaluation of BrC's climatic effects and atmospheric NO3• levels.

Review of air-water interface adsorption and reactions between trace gaseous organic and oxidant compounds

The surface chemistry of the atmospheric aerosol through homogeneous and heterogeneous catalytic reactions in the bulk water and the air-water surface is reviewed. Water plays a critical role as a substrate or an actual reactant in atmospheric reactions. The atmospheric aerosol differs in shape and surface area. Many gaseous reactive species and oxidants react at the air-water surface. Different thermodynamic methods to estimate partitioning coefficients are explored. The Gibbs free energy is reduced when reactant gaseous species react with oxidant at the air-water surface; this phenomenon is explained using examples. Langmuir-Hinshelwood reaction mechanism to quantify the heterogeneous reaction rate at the air-water interface is discussed. Critical comparisons of various sampling techniques used to analyze adsorption and reaction at the water surface are presented. The heterogeneous reaction rate at the air-water surface is significantly higher than in the bulk water phase due to a cage effect, higher rate of reactions, and lower Gibbs free energy of adsorption.

Oxidation of phthalate acid esters using hydrogen peroxide and polyoxometalate/graphene hybrids

Phthalate acid esters (PAEs) have been adsorbed and oxidatively degraded into small molecules including lactic acid (LA), formic acid (FA), H₂O and CO₂ using polyoxometalates (POMs)/graphene hybrids. We demonstrated that super-lower concentrations of PAEs could be oxidized, which was due to their unique structure. POM molecules have been embedded onto graphene to form H₅PMo₁₀V₂O₄₀@surfactant(n)/Graphene(L wt%) (abbreviated as HPMoV@Surf(n)/GO(L wt%)) using surfactants with the carbon chain length n = 2, 4, 6 and 8 for the loading of HPMoV. The coexistence of the graphene and surfactant layer (on HPMoV@Surf(n)/GO(20 wt%)) adsorbed PAE molecules and transported them rapidly to HPMoV active sites. And n values determined the electron transfer ability between graphene and POMs that promoted PAEs oxidation. The loading of POMs on the surface of graphene permitted HPMoV@Surf(n)/GO(L wt%) act as interfacial catalyst which degraded various PAEs (i.e., diethyl phthalate (DEP), diallyl phthalate (DAP) and di (2-ethylhexyl) phthalate (DEHP)) while removed more than 70% of TOC and COD. The degradation of DEP achieved 93.0% with HPMoV@Surf(n)/GO(20 wt%) and H₂O₂, which followed first-order kinetics and the reaction activation energy (Ea) of 23.1 kJ/mol. Further, HPMoV@Surf(n)/GO(20 wt%) showed potential for the removal of PAEs in Wastewater Treatment Plant (WWTP), and the degradation efficiency for PAE (DEP) in secondary effluent achieved 55.0%. In addition, the loading method for POMs on graphene eliminated the leaching of POMs from graphene, and the degradation efficiency could still reach 88.1% after ten recycles.

Photochemical reaction of superoxide radicals with 1-naphthol

The photochemical reactions between 1-naphthol (1-NP) and the superoxide anion radical (O2•–) were investigated in detail by using 365 nm UV irradiation. The results showed that the conversion rate of 1-NP decreased with the increase of the initial concentration of 1-NP, whereas by increasing the pH and riboflavin concentration, the photochemical reaction was accelerated. The second-order reaction rate constant was estimated to be (3.64 ± 0.17) × 108 L mol−1 s−1. The major photolysis products identified by using gas chromatography – mass spectrometry (GC–MS) were 1,4-naphquinone and 2,3-epoxyresin-2,3-dihydro-1,4-naphquinone, and their reaction pathways were also discussed. An atmospheric model showed that both the bulk water reaction and the heterogeneous surface reaction deserve attention in atmospheric aqueous chemistry.

Photochemical reaction kinetics and mechanism of bisphenol A with K2S2O8 in aqueous solution: a laser flash photolysis study

The photochemical reaction kinetics and mechanism of bisphenol A (BPA) with potassium persulfate (K2S2O8) were investigated by using 266 nm laser flash photolysis and gas chromatography mass spectrum (GC-MS) technique. Sulfate radical (SO4•−), generated upon K2S2O8 photolysis, reacted with BPA with the overall rate constant of (1.61 ± 0.15) × 109 L mol−1 s−1, and two main reaction mechanisms were involved. One was addition channel to generate BPA–SO4•− adduct with a specific second-order rate constant of (1.09 ± 0.15) × 109 L mol−1 s−1. Molecular oxygen was involved in the decay of the BPA–SO4•− adduct with a rate constant of (1.28 ± 0.14) × 108 L mol−1 s−1. Another channel was the formation of BPA’s phenoxyl radical, likely derived from a deprotonation of the cation radical (BPA•+) generated from single electron transfer reactions. The specific rate constant of BPA’s phenoxyl radical formation was determined to be (6.16 ± 0.08) × 108 L mol−1 s−1. The overall rate constant was in line with the sum of aforementioned two specific rate constants for two main reaction channels. By comparing these rate constants, it was indicated that SO4•− addition channel accounted for ∼65% (1.09/1.61) to the overall reaction, and phenoxyl radical formation accounted for only ∼35% (0.62/1.61). The transformation products of BPA were identified by using GC-MS including 4-isopropylphenol, 4-isopropenylphenol, and 2,4-di-tert-butylphenol, and the reaction mechanism was proposed. These results may provide microscopic kinetics and mechanism information on BPA degradation using SO4•−-based advanced oxidation processes.

Phthalate esters (PAEs) in atmospheric particles around a large shallow natural lake (Lake Chaohu, China)

The pollution of phthalate esters (PAEs) remains an important issue in the world. Current studies mainly focused on atmospheric PAEs in urban area with strong anthropogenic activities, but there were no studies on PAEs in the ambient air around large natural lake. This paper focused on two sites around Lake Chaohu to investigate the monthly occurrence, composition and source of PAEs in the atmospheric particles around large shallow natural lake. New insights into atmospheric PAEs in large shallow natural lake and the overall fate of PAEs in lake ecosystem were given. The concentrations of the Σ₁₃PAEs in atmospheric particles were at a significantly low level ranging from 2740 to 11,890 pg·m^-3 and 2622 to 15,331 pg·m^-3 in ZM (the lakeshore site) and HB (the downtown site), respectively. There were no statistically significant differences of PAEs between ZM and HB. The highest atmospheric PAE concentrations in August were likely related to the long-range transport from Guangdong Province. Di(2-ethylhexyl) phthalate (DEHP), diisobutyl phthalate (DIBP) and dibutyl phthalate (DBP) were the main PAE congeners. Temporally, DIBP and DBP had the highest fractions in winter and the lowest fractions in summer. It might be justified by the condensation of DIBP and DBP from gas phase to particulate phase at low temperature. Multimedia comparison of PAE profiles in Lake Choahu revealed that low molecular weight (LMW) congeners were transported mainly through water while high molecular weight (HMW) congeners were transported mainly through atmosphere.

Rate Constants and Mechanisms of the Reactions of Cl• and Cl2•- with Trace Organic Contaminants

Cl^• and Cl₂^•- radicals contribute to the degradation of trace organic contaminants (TrOCs) such as pharmaceutical and personal care products and endocrine-disrupting chemicals. However, little is known about their reaction rate constants and mechanisms. In this study, the reaction rate constants of Cl^• and Cl₂^•- with 88 target compounds were determined using laser flash photolysis. Decay kinetics, product buildup kinetics, and competition kinetics were applied to track the changes in their transient spectra. Cl^• exhibited quite high reactivity toward TrOCs with reaction rate constants ranging from 3.10 × 10⁹ to 4.08 × 10¹⁰ M^-1 s^-1. Cl₂^•- was less reactive but more selective, with reaction rate constants varying from <1 × 10⁶ to 2.78 × 10⁹ M^-1 s^-1. Three QSAR models were developed, which were capable of predicting the reaction rate constants of Cl₂^•- with TrOCs bearing phenol, alkoxy benzene, and aniline groups. The detection of Cl^•-adducts of many TrOCs suggested that Cl^• addition was an important reaction mechanism. Single electron transfer (SET) predominated in reactions of Cl^• with TrOCs bearing electron-rich moieties (e.g., sulfonamides), and their cation radicals were observed. Cl^• might also abstract hydrogen atoms from phenolic compounds to generate phenoxyl radicals. Moreover, Cl^• could react with TrOCs through multiple pathways since more than one transient intermediate was detected simultaneously. SET was the major reaction mechanism of Cl₂^•- reactions with TrOCs bearing phenols, alkoxy benzenes, and anilines groups. Cl₂^•- was found to play an important role in TrOC degradation, though it has been often neglected in previous studies. The results improve the understanding of halogen radical-involved chemistry in TrOC degradation.

Fast degradation of phthalate acid esters by polyoxometalate nanocatalysts through adsorption, esterolysis and oxidation

A novel route was created to facilitate the degradation of diethyl phthalate (DEP) upon micellar polyoxometalate (POM) catalysts and H₂O₂. The best catalytic activity was obtained using [C₁₆H₃₃N(CH₃)₃]H₄PMo₁₀V₂O₄₀ (N-hexadecyl-N,N,N-trimethylammonium tetrahydrogen decamolybdo-divanadophosphate, abbreviated as (CTA)H₄PMoV) with 90.2% degradation efficiency within 30 min, while the chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiency were about 77.7% and 74.3% within 40 min. The highest efficiency was attributed to the concentration of DEP by amphiphilic POM catalyst, coupling with its strong Brønsted acidity and higher redox potential to catalyze esterolysis and oxidation of DEP. This allowed the phthalate acid esters (PAEs) with long carbon chains in super low concentration of 0.03 μM to be efficiently decomposed. The above synergistic effects explored DEP being degraded into ethanol, lactic acid and CO₂, which were non-toxic to the water surroundings. And the reaction activation energy (Ea) of 12.49 kJ/mol was obtained upon the degradation of DEP with (CTA)H₄PMoV followed first-order kinetics. Meanwhile, (CTA)H₄PMoV acted as a heterogeneous catalyst, which showed long duration and higher stability with only 3.7% loss amount during ten recycles.

Degradation of diethyl phthalate (DEP) by vacuum ultraviolet process: influencing factors, oxidation products, and toxicity assessment

The vacuum ultraviolet (VUV) process, which can directly produce hydroxyl radical from water, is considered to be a promising oxidation process in degrading contaminants of emerging concern, because of no need for extra reagents. In this study, the influencing factors and mechanism for degradation of diethyl phthalate (DEP) by the VUV process were investigated. The effects of irradiation intensity, inorganic anions, natural organic matter (NOM), and H₂O₂ dosage on the performance of VUV process were evaluated. The results showed that DEP could be more efficiently degraded by the VUV process compared with ultraviolet (UV)-254-nm irradiation. The presence of HCO₃^-, NO₃^- and NOM in the aqueous solutions inhibited the degradation of DEP to a different degree, mainly by competing hydroxyl radicals (HO^•) with DEP. Degradation rate and removal efficiency of DEP by VUV process significantly enhanced with the addition of H₂O₂, while excess H₂O₂ dosage could inhibit the DEP degradation. Moreover, based on the identified seven oxidation byproducts and their time-dependent evolution profiles, a possible pathway for DEP degradation during the VUV process was proposed. Finally, the ecotoxicity of DEP and its oxidation byproducts reduced overall according to the calculated results from Ecological Structure Activity Relationships (ECOSAR) program. The electrical energy per order (EE/O) was also assessed to analysis the energy cost of the DEP degradation in the VUV process. Our work showed the VUV process could be an alternative and environmental friendly technology for removing contaminants in water.

Photochemical oxidation of di-n-butyl phthalate in atmospheric hydrometeors by hydroxyl radicals from nitrous acid

The photochemical oxidation of di-n-butyl phthalate (DBP) by ^•OH radicals from nitrous acid (HONO) in atmospheric hydrometeors was explored by two techniques, steady-state irradiation, and laser flash photolysis (LFP). The effects of atmospheric liquid parameters on DBP transformation were systematically evaluated, showing that DBP does not react with HONO directly and ^•OH-initiated reactions are crucial steps for consumption and transformation of DBP. Two reaction channels are operative: ^•OH addition and hydrogen atom abstraction. The overall rate constant for the reaction of DBP with ^•OH is 5.7 × 10⁹ M^-1 s^-1, and its specific rate constant for addition is 3.7 × 10⁹ M^-1 s^-1 determined by using laser flash photolysis technique. Comparing the individual reaction rate constant for aromatic ring addition with the total rate constant, the majority of the ^•OH radicals (about 65%) attack the aromatic ring. The major transformation products were identified by GC-MS, and the trends of their yields derived from both ring addition and H-abstraction with time are discussed. These results provide important insights into the photochemical transformation of DBP in atmospheric hydrometeors and contribute to atmospheric aerosol chemistry.