Second-order Rate Constants For Reactions Research Articles

Construction of a screening system for lipid-derived radical inhibitors and validation of hit compounds to target retinal and cerebrovascular diseases

Recent studies have highlighted the indispensable role of oxidized lipids in inflammatory responses, cell death, and disease pathogenesis. Consequently, inhibitors targeting oxidized lipids, particularly lipid-derived radicals critical in lipid peroxidation, which are known as radical-trapping antioxidants (RTAs), have been actively pursued. We focused our investigation on nitroxide compounds that have rapid second-order reaction rate constants for reaction with lipid-derived radicals. A novel screening system was developed by employing competitive reactions between library compounds and a newly developed profluorescence nitroxide probe with lipid-derived radicals to identify RTA compounds. A PubMed search of the top hit compounds revealed their wide application as repositioned drugs. Notably, the inhibitory efficacy of methyldopa, selected from these compounds, against retinal damage and bilateral common carotid artery stenosis was confirmed in animal models. These findings underscore the efficacy of our screening system and suggest that it is an effective approach for the discovery of RTA compounds.

Mechanistic Aspects of Photodegradation of Deoxynucleosides Induced by Triplet State of Effluent Organic Matter.

Excited triplet states of wastewater effluent organic matter (3EfOM*) are known as important photo-oxidants in the degradation of extracellular antibiotic resistance genes (eArGs) in sunlit waters. In this work, we further found that 3EfOM* showed highly selective reactivity toward 2'-deoxyguanosine (dG) sites within eArGs in irradiated EfOM solutions at pH 7.0, while it showed no photosensitizing capacity toward 2'-deoxyadenosine, 2'-deoxythymidine, and 2'-deoxycytidine (the basic structures of eArGs). The 3EfOM* contributed to the photooxidation of dG primarily via one-electron transfer mechanism, with second-order reaction rate constants of (1.58-1.74) × 108 M-1 s-1, forming the oxidation intermediates of dG (dG(-H)•). The formed dG(-H)• could play a significant role in hole hopping and damage throughout eArGs. Using the four deoxynucleosides as probes, the upper limit for the reduction potential of 3EfOM* is estimated to be between 1.47 and 1.94 VNHE. Compared to EfOM, the role of the triplet state of terrestrially natural organic matter (3NOM*) in dG photooxidation was minor (∼15%) mainly due to the rapid reverse reactions of dG(-H)• by the antioxidant moieties of NOM. This study advances our understanding of the difference in the photosensitizing capacity and electron donating capacity between NOM and EfOM and the photodegradation mechanism of eArGs induced by 3EfOM*.

Understanding Nucleophilicity of Pyridine-N-oxides Towards 2,4,6-Trinitrophenylbenzoate Through Simple Absorption Spectroscopic Studies

Aims: Understanding nucleophilicity of poor nucleophiles like pyridine-N-oxides. Background: Nucleophilicity plays a vital role in substitution reactions. It helps to determine the possibility and extent of the substitution reactions. The study of the nucleophilicity of poor nucleophiles is challenging, and it has limited substrate scope. Understanding the strength of nucleophilicity of such poor nucleophiles in a quantitative way is important. Objective: Understanding the strength of nucleophilicity of such poor nucleophiles in a quantitative way. Selection of appropriate electrophile for the reactions with the poor nucleophiles-pyridine-N-oxides. Development of suitable methodology for kinetic studies of the reaction. Methods: UV-Vis spectroscopic methods for monitoring the reactions. Results: The kinetic studies revealed that the second-order rate constants of the nucleophilic reactions are 1.67× 102 L mol-1 min-1, 29.8 L mol-1 min-1, 29.51 L mol-1 min-1, where the nucleophiles are p-methylpyridine-N-oxide, pyridine-N-oxide, and p-nitropyridine-N-oxide, respectively. The UV-Vis spectroscopic analysis revealed the nucleophilicity of p-methylpyridine-N-oxide > pyri-dine-N-oxide > p-nitropyridine-N-oxide. Conclusion: This comparative study suggests that the strength of nucleophilicity of the p-methylpyridine-N-oxide is 5.6 times and 66.53 times more than that of pyridine-N-oxide and p-nitropyridine-N-oxide, respectively, whereas the strength of nucleophilicity of the pyridine-N-oxide is 11.87 times more than that of p-nitropyridine-N-oxide.

Electron Redistribution in Iridium-Iron Dual-Metal-Atom Active Sites Enables Synergistic Enhancement for H2O2 Decomposition.

Developing efficient heterogeneous H2O2 decomposition catalysts under neutral conditions is of great importance in many fields such as clinical therapy, sewage treatment, and semiconductor manufacturing but still suffers from low intrinsic activity and ambiguous mechanism understanding. Herein, we constructed activated carbon supported with an Ir-Fe dual-metal-atom active sites catalyst (IrFe-AC) by using a facile method based on a pulsed laser. The electron redistribution in Ir-Fe dual-metal-atom active sites leads to the formation of double reductive metal active sites, which can strengthen the metal-H2O2 interaction and boost the H2O2 decomposition performance of Ir-Fe dual-metal-atom active sites. Ir-Fe dual-metal-atom active sites show a high second-order reaction rate constant of 3.53 × 106 M-1·min-1, which is ∼106 times higher than that of Fe3O4. IrFe-AC is effective in removing excess intracellular reactive oxygen species, protecting DNA, and reducing inflammation under oxidative stress, indicating its therapeutic potential against oxidative stress-related diseases. This study could advance the mechanism understanding of H2O2 decomposition by heterogeneous catalysts and provide guidance for the rational design of high-performance catalysts for H2O2 decomposition.

O-Semiquinone Radical and o-Benzoquinone Selectively Degrade Aniline Contaminants in the Periodate-Mediated Advanced Oxidation Process.

Advanced oxidation processes (AOPs) often employ strong oxidizing inorganic radicals (e.g., hydroxyl and sulfate radicals) to oxidize contaminants in water treatment. However, the water matrix could scavenge the strong oxidizing radicals, significantly deteriorating the treatment efficiency. Here, we report a periodate/catechol process in which reactive quinone species (RQS) including the o-semiquinone radical (o-SQ•-) and o-benzoquinone (o-Q) were dominant to effectively degrade anilines within 60 s. The second-order reaction rate constants of o-SQ•- and o-Q with aniline were determined to be 1.0 × 108 and 4.0 × 103 M-1 s-1, respectively, at pH 7.0, which accounted for 21% and 79% of the degradation of aniline with a periodate-to-catechol molar ratio of 1:1. The major byproducts were generated via addition or polymerization. The RQS-based process exhibited excellent anti-interference performance in the degradation of aniline-containing contaminants in real water samples in the presence of diverse inorganic ions and organics. Subsequently, we extended the RQS-based process by employing tea extract and dissolved organic matter as catechol replacements as well as metal ions [e.g., Fe(III) or Cu(II)] as periodate replacements, which also exhibited good performance in aniline degradation. This study provides a novel strategy to develop RQS-based AOPs for the highly selective degradation of aniline-containing emerging contaminants.

Ozonation of dioxolanes in water: Kinetics, transformation mechanism, and toxicity

Dioxolanes, which are structural analogs to dioxane, are emerging persistent mobile organic contaminants. These compounds are frequently detected in water and wastewater, but their removal has been rarely addressed in the literature. This work systematically investigated the ozonation of two representative dioxolanes, i.e., 1,3-dioxolane (1,3-D) and 2-methyl-1,3-dioxolane (2-M-1,3-D). The degradation rates of two dioxolanes exhibited a positive correlation with both ozone dosage and solution pH increment. Specifically, direct ozone oxidation dominates the degradation of dioxolanes at slightly acidic pH, while hydroxyl radical (•OH) becomes the primary oxidant under weak alkaline condition. The second-order reaction rate constants of ozone with 1,3-D and 2-M-1,3-D were determined to be 5.48 and 8.00 M−1s−1, respectively. The reaction rate constants with •OH were 9 orders of magnitude higher, reaching (3.75-8.18) × 109 and (2.65-5.78) × 109 M−1s−1 for 1,3-D and 2-M-1,3-D, respectively. A kinetic model involving 112 reactions well simulated the degradation of 1,3-D and 2-M-1,3-D under various conditions accordingly. Eight transformation products were identified totally, and seven of them (i.e., formic acid, acetic acid, oxalic acid, formaldehyde, acetaldehyde, glyoxylic acid, and 1,2-ethanediol monoacetate) were quantified. The observed evolution of these identified degradation products concludes that the degradation of 1,3-D and 2-M-1,3-D during ozonation mainly involves H-abstraction, dimerization, ring opening, disproportionation, and hydrolysis. This work not only provides essential kinetic data of dioxolanes, but also sheds light on their potential transformation mechanisms and aquatic environment risks during ozonation process.

Insight into enhanced photogeneration mechanism of reactive intermediates from dissolved black carbon by co-pyrolysis of plastics and biomass

The dissolved black carbon (DBC) derived from co-pyrolysis of plastic and biomass be released into aquatic environment. DBC was an important photoactive constituent, however, the photochemical activity of DBC from the co-pyrolysis plastic and biomass remains unclear. Herein three popular plastic wastes (polystyrene, PS; polylactic acid, PLA; plastic mulch film, PMF) and pine needle biomass prepared co-pyrolysis biochar, and effects of co-pyrolysis plastics on DBC’s photogeneration ability of reactive intermediates, affecting pollutant photodegradation, were investigated. In comparison to individual DBC, the mixed DBC from co-pyrolysis biochar had a lower molecular weight and more oxygen-containing groups. Quantum yields of singlet oxygen (1O2) and triplet state DBC (3DBC*) from mixed DBC were higher, especially PMF-DBC since its lower aromaticity and molecular weight connected with its higher E2/E3 and lower SUVA254 values. Steady-state photochemical experiment demonstrated 3DBC* formation rates for mixed DBC were lower than individual DBC, while the second-order reaction rate constants of 3DBC* with 2,4,6-trimethylphenol for mixed DBC were higher than that of individual DBC. Quenching experiment by sorbic acid to distinguish high/low-energy triplets revealed that contributions of low-energy triplets to 3DBC* and 1O2 generation decreased relative to individual DBC, indicating the transformation of reductive groups to oxidative groups, which was supported by the phototransformation kinetics. Quantum yields of 3DBC* and 1O2 were positively linear correlations with E2/E3 using twenty DBC samples. These findings are helpful in understanding DBC’s photochemical activity from co-pyrolysis of plastics and biomass, especially in aquatic environments adjacent to soil amended by biochar.

Electrophilicity, mechanism and structure–reactivity relationships of cyclic secondary amines addition to 2-methoxy-3,5-dinitropyridine

The second-order rate constants (k) for the nucleophilic aromatic substitution reactions of 2‑methoxy-3,5-dinitropyridine 1 with secondary cyclic amines 2a-c in acetonitrile solution at 20 °C are reported. The logarithms of these rate constants are particularly significant as possible measures of the electrophilicity parameters E for 2‑methoxy-3,5-dinitropyridine 1 according to the linear free energy relationship log k (20 °C) = sN(N + E). Additional kinetic data for reactions of 2-methoxy-3,5-dinitropyridine 1 with a series of nitroalkyl anions in DMSO solution are also measured and found to agree with those calculated by Mayr's approach from the known two solvent-dependent parameters N and sN of nitroalkyl anions and the electrophilicity parameter E measured in this work. A Single Electron Transfer (SET) mechanism is proposed for the SNAr reactions, on the basis of the linear Brönsted plot with the βnuc value of 0.94. The validity of this mechanism is confirmed by the agreement between the rate constants, k, and the oxidation potentials E° of these series of secondary cyclic amines. Also, reactivity descriptors such as the electronic chemical potential (μ), and the chemical hardness (η) for a series of pyridine derivatives were calculated by Density Functional Theory (DFT), and it is shown that the global electrophilicity index (ω = μ2/2η) is significantly correlated with the electrophilicity parameters E.

Oxidation of 4-tert-butylphenol by potassium permanganate and reduced formation of disinfection byproducts from chlorination

4-tert-butylphenol (4-tBP), a typical endocrine disruptor, is widely used as pharmaceutical and agricultural additive and has been detected in the aqueous environment. In this work, we systematically investigated the oxidation process of 4-tBP by potassium permanganate (KMnO4). The degradation condition was optimized by adjusting pH and oxidant dose. The removal efficiency could reach > 93% in 45 min under pH = 6.0–9.0 and [4-tBP]0:[KMnO4]0 = 1:2, where the maximum second-order reaction rate constant (kapp) was (2.48 ± 0.23) × 10−2 M−1 min−1. Common anions (Cl-, SO42-, NO3- and HCO3-) and cations (K+, Ca2+, Mg2+, Fe3+ and Cu2+) did not show apparent influence, while humic acid played a positive role in the degradation. A total of 20 products were identified and two main pathways of the oxidation process were proposed, which included hydroxylation and coupling. Through the theoretical calculations, the mechanism of the 4-tBP hydroxylation was explained as mono-oxygen transfer at the ortho site of the hydroxyl group and coupling was from the extraction of hydrogen at the hydroxyl group. Meanwhile, the toxicity assessment showed lowered biotoxicity of products as compared to the substrate. In addition, chlorination of degradation products would yield lower concentrations of disinfection byproducts (dichloroacetic acid, 4.5 μg/L; trichloroacetic acid, 4.7 μg/L, in ultrapure water) than the initial 4-tBP solution. These findings confirmed that KMnO4 could be used as a safe and promising technology for 4-tBP degradation.

Experimental determination and QSAR analysis of the rate constants for [formula omitted] reactions with aromatic micropollutants in water

S(IV)-based systems used for advanced oxidation processes (AOPs) have been constructed for the degradation of organic contaminants via oxysulfur radicals, including SO3•−, SO4•−, and SO5•−. Although SO5•− is proposed as an active species in AOPs processes, research on the reactivity of SO5•− has remained unclear. In this work, 53 target aromatic micropollutants (AMPs), including 13 phenols, 27 amines, and 13 PPCPs were selected to determine the second-order reaction rate constants for SO5•− using the competitive kinetics method, in which the kSO5•− values, observed at pH 4 ranged from (2.44 ± 0.00) × 105 M−1 s−1 to (4.41 ± 0.28) × 107 M−1 s−1. Quantitative structure-activity relationship (QSAR) models for the oxidation of AMPs by SO5•− were developed based on 40 kSO5•− values of amines and phenols, and their molecular descriptors, using the stepwise multiple linear regression method. This comprehensive model exhibited the excellent goodness-of-fit (Radj2 = 0.802), robustness (QLOO2 = 0.749), and predictability (Qext2 = 0.656), and the one-electron oxidation potential (Eox), energy of the highest occupied molecular orbital energy (EHOMO), and most positive net atomic charge on the carbon atoms (qC+) were considered the most influential descriptors for the comprehensive model, indicating that SO5•− oxidizes pollutants via single electron transfer reaction and exhibits a strong oxidation capacity, especially for pollutants containing electron-donating groups. Moreover, the kSO5•− values of 13 PPCPs were predicted using this comprehensive model, which suggested the practical application significance of the QSAR model. This study emphasizes the direct oxidation capacity of SO5•−, which is important to evaluate and simulate AOPs based on S(IV).

Selective oxidation of histamine H2-Receptor antagonists by peracetic Acid: Kinetics and mechanism

Peracetic acid (PAA) is an emerging substitutive oxidant to chlorine disinfectants owing to the low generation of harmful by-products. Herein, we report PAA-induced oxidation of histamine H2-receptor antagonists (HRAs) via non-radical participation for the first time. Results showed that PAA can selectively oxidize HRAs with high reactivity to ranitidine (RNTD), nizatidine (NZTD), cimetidine (CMTD), and famotidine (FMTD), but low reactivity to roxatidine (RXTD). PAA-induced HRAs oxidation followed the second-order kinetic reaction, the apparent second-order reaction rate constants (k2, app) of RNTD, FMTD, CMTD and NZTD were 18.78 ± (2.4), 37.22 ± (6.1), 36.53 ± (7.8), 30.04 ± (2.4) M−1•s−1, respectively. The value of k2, app decreased as pH increased. Scavenging experiments indicated that PAA-induced HRAs oxidation proceeded via a non-radical process. The theoretical calculation and product analysis further reveal that the reaction involves the double-electron transfer from thioether sulfur in HRAs to peroxide bond. HRAs oxidation by PAA was not affected by water matrices (Cl-, HCO3–, HA), which has good applicability in surface water (SW) and wastewater (WW). Toxicity assessment indicated ecotoxicity of oxidation products was much lower than that of HRAs. This work provided a facile and emerging technology to eliminate the HRAs and their toxicity in the wastewater.

CuO Promotes the Formation of Halogenated Disinfection Byproducts during Chlorination via an Enhanced Oxidation Pathway.

Previous studies showed that cupric oxide (CuO) can enhance the formation of trihalomethanes (THMs), haloacetic acids, and bromate during chlorination of bromide-containing waters. In this study, the impact of CuO on the formation kinetics and mechanisms of halogenated disinfection byproducts (DBPs) during chlorination was investigated. CuO does not enhance the formation of DBPs (i.e., 1,1,1-trichloropropanone, chloroform, and trichloroacetaldehyde (TCAL) /dichloroacetonitrile) during chlorination of acetone, 3-oxopentanedioic acid (3-OPA), and aspartic acid, respectively. This indicates that the halogen substitution pathway cannot be enhanced by CuO. Instead, CuO (0.1 g L-1) accelerates the second-order rate constants for reactions of chlorine (HOCl) with TCAL, citric acid, and oxalic acid at pH 8.0 and 21 °C from <0.1 to 29.4, 7.2, and 15.8 M-1 s-1, respectively. Oxidation pathway predominates based on the quantification of oxidation products (e.g., a trichloroacetic acid yield of ∼100% from TCAL) and kinetic modeling. CuO can enhance the formation of DBPs (e.g., THMs, haloacetaldehydes, and haloacetonitriles) during chlorination of model compounds and dissolved organic matter, of which both halogen substitution and oxidation pathways are required. Reaction rate constants of rate-limiting steps (e.g., citric acid to 3-OPA, aromatic ring cleavage) could be enhanced by CuO via an oxidation pathway since CuO-HOCl complex is more oxidative toward a range of substrates than HOCl in water. These findings provide novel insights into the DBP formation pathway in copper-containing distribution systems.

Reactivity of Acrylamides Causes Cytotoxicity and Activates Oxidative Stress Response.

Acrylamides are widely used industrial chemicals that cause adverse effects in humans or animals, such as carcinogenicity or neurotoxicity. The excess toxicity of these reactive electrophilic chemicals is especially interesting, as it is mostly triggered by covalent reactions with biological nucleophiles, such as DNA bases, proteins, or peptides. The cytotoxicity and activation of oxidative stress response of 10 (meth)acrylamides measured in three reporter gene cell lines occurred at similar concentrations. Most acrylamides exhibited high excess toxicity, while methacrylamides acted as baseline toxicants. The (meth)acrylamides showed no reactivity toward the hard biological nucleophile 2-deoxyguanosine (2DG) within 24 h, and only acrylamides reacted with the soft nucleophile glutathione (GSH). Second-order degradation rate constants (kGSH) were measured for all acrylamides with N,N'-methylenebis(acrylamide) (NMBA) showing the highest kGSH (134.800 M-1 h-1) and N,N-diethylacrylamide (NDA) the lowest kGSH (2.574 M-1 h-1). Liquid chromatography coupled to high-resolution mass spectrometry was used to confirm the GSH conjugates of the acrylamides with a double conjugate formed for NMBA. The differences in reactivity between acrylamides and methacrylamides could be explained by the charge density of the carbon atoms because the electron-donating inductive effect of the methyl group of the methacrylamides lowered their electrophilicity and thus their reactivity. The differences in reactivity within the group of acrylamides could be explained by the energy of the lowest unoccupied molecular orbital and steric hindrance. Cytotoxicity and activation of oxidative stress response were linearly correlated with the second-order reaction rate constants of the acrylamides with GSH. The reaction of the acrylamides with GSH is hence not only a detoxification mechanism but also leads to disturbances of the redox balance, making the cells more vulnerable to reactive oxygen species. The reactivity of acrylamides explained the oxidative stress response and cytotoxicity in the cells, and the lack of reactivity of the methacrylamides led to baseline toxicity.

Caffeic acid accelerated the Fe(II) reinvention in Fe(III)/PMS system for bisphenol A degradation: Oxidation intermediates and inherent mechanism

Fe(II)-catalyzed PMS process was widely used in the degradation of refractory pollutants in wastewater, while its performance was restricted by the slow regeneration efficiency of Fe(II). Herein, caffeic acid (CFA), a representative of hydroxycinnamic acids, was introduced into Fe(III)/PMS system to accelerate the transformation of Fe(III) to Fe(II) and promote the removal of bisphenol A (BPA). Under optimum condition of 0.1 mM CFA, 0.05 mM Fe(III), and 0.5 mM PMS, almost complete removal of BPA can be achieved within 20 min, which was roughly 6.2 times higher than that in Fe(III)/PMS system. As the addition of CFA into Fe(III)/PMS system, pH application range was widened from acidic to alkaline conditions. The reduction and chelation of CFA expedited the Fe(III)/Fe(II) cycle by forming CFA-Fe chelate, thereby facilitating the PMS activation. Based on LC-MS analysis and DFT calculation, the intermediate products of CFA were found to play a decisive role in boosting the regeneration of Fe(II), and the toxicity of these intermediates towards organisms was evaluated by ECOSAR. The alcohol-scavenging and chemical probe tests certified that hydroxyl radical (•OH), sulfate radical (SO4•-), and Fe(IV) coexisted in Fe(III)/CFA/PMS system, and the second-order reaction rate constants of •OH and SO4•- reacted with CFA were calculated to be 3.16✕109 and 2.30✕1010 M−1 s−1, respectively. Two major degradation pathways of BPA, •OH addition and SO4•- induced hydroxylation reaction, were proposed. This work presented a novel green phenolic compound that expedited the Fe(II)-catalyzed PMS activation process for the treatment of organic contaminants.

Kinetics of carbon dioxide absorption in aqueous blend of 1-(2-aminoethyl) piperazine using a stirred cell reactor.

Carbon capture utilization and storage (CCUS), the technology for decarbonizing carbon dioxide (CO2) from greenhouse gas emitters such as steel, cement, oil, gas, petrochemicals, chemicals, and fertilizers, has a critical role to play in the world to achieve industrial net zero targets by 2050. CO2 can be separated from industrial exhaust gases/flue gases using amine-based solvents utilizing the post-combustion CO2 Capture process. One most crucial solvent characterization for this application is the kinetics of CO2 absorption. This work identifies aqueous 1-(2-aminoethyl) piperazine (AEPZ) as a potential candidate for CO2 capture solvent. The kinetics of absorption of CO2 in aqueous AEPZ is studied using stirred cell reactor. The experiments are performed at temperatures ranging from 303 to 333K with weight fractions of AEPZ in an aqueous solution ranging from 0.1 to 0.4. One of the critical parameters of the kinetic study is Henry's constant which is determined experimentally using another stirred cell reactor at a similar temperature and pressure range. The experimental data shows that the overall rate constant is Kov = 2.52987 × 10-4mol/m2s-kPa for 0.1 wt fr. of AEPZ at 313K with an initial CO2 partial pressure of 10kPa. The temperature dependency relation of the second-order reaction rate constant, [Formula: see text] is found to be [Formula: see text] using the Arrhenius equation. The activation energy of 0.3 wt fr. AEPZ is found to be 42.42kJ/mol. In addition, the density and viscosity of the aqueous solvent are determined at a wide range of temperatures. The diffusivity of CO2 and physical solubility used in the model development has also been determined. The kinetic parameters obtained from this study are helpful in the process design of CO2 capture in a regenerative process with a blended solvent with AEPZ.

2-Amino-2-hydroxymethyl-1,3-propanediol for CO2 capture: study on equilibrium, absorption kinetics, catalytic desorption, and amine regeneration

The CO2-capturing performance of a sterically hindered amine, 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD), was systematically studied in this work. First, absorption kinetics was investigated using the stirred-cell technique. At T = 308 K, CO2 reacted with AHPD according to a second-order reaction (rate constant = 264 m3/kmol-s), whose activation energy was 33 kJ/mol. Second, the solubility of CO2 in AHPD at 308 K was measured up to 100 kPa CO2 partial pressure. For instance, it was shown that the loading capacity of AHPD (2.5 M) was 0.56 mol/mol, while the equilibrium CO2 partial pressure was 79 kPa. Third, a closed-loop absorber-desorber setup was used to test solvent performance for capturing CO2 from CO2/air mixture (12:88 v/v). The two columns were continuously operated at 313 (absorber) and 383 K (desorber) at 0.1 MPa pressure. Around 75% CO2 was absorbed using 12 wt. % AHPD (or 0.9 M). The value of QReg (regeneration energy) was 6.28 MJ/kg CO2. It was thus evident that AHPD is a credible hindered amine-based solvent. A comparison of its equilibrium, kinetic and regeneration features with 2-amino-2-methyl-1-propanol (AMP) was provided. Finally, three rate promoters–hexamethylene diamine (HMDA), monoethanolamine (MEA) and AMP–were added to AHPD. The performance of HMDA was most promising. In a batch desorption setup, it was shown that alumina catalyst improved desorption of CO2 from loaded AHPD/HMDA mixtures. This work will stimulate further interest in the use of AHPD solutions for CO2 removal.

Effect of adsorption on ferrihydrite on the photoreactivity of dissolved black carbon for photodegradation of sulfadiazine

The selective adsorption of dissolved black carbon (DBC) on inorganic minerals is a widespread geochemical process in the natural environment, which could change the chemical and optical properties of DBC. However, it remains unclear how selective adsorption affects the photoreactivity of DBC for photodegradation of organic pollutants. This paper was the first to investigate the effect of DBC adsorption on ferrihydrite at different Fe/C molar ratios (Fe/C molar ratios of 0, 7.50 and 11.25, and marked as DBC0, DBC7.50 and DBC11.25) on the photoproduction of reactive intermediates generated from DBC and their interaction with sulfadiazine (SD). Results showed that UV absorbance, aromaticity, molecular weight and contents of phenolic antioxidants of DBC were significantly decreased after adsorption on ferrihydrite, and higher decrease was observed at higher Fe/C ratio. Photodegradation kinetics experiments showed that observed photodegradation rate constant of SD (kobs) increased from 3.99 × 10−5 s−1 in DBC0 to 5.69 × 10−5 s−1 in DBC7.50 while decreased to 3.44 × 10−5 s−1 in DBC11.25, in which 3DBC* played an important role and 1O2 played a minor role, while ·OH was not involved in the reaction. Meanwhile, the second-order reaction rate constant between 3DBC* and SD (kSD, 3DBC*) increased from 0.84 × 108 M−1 s−1 for DBC0 to 2.53 × 108 M−1 s−1 for DBC7.50 while decreased to 0.90 × 108 M−1 s−1 for DBC11.25. The above results might be mainly attributed to the fact that the decrease of phenolic antioxidants in DBC weakened the back-reduction of 3DBC* and reactive intermediates of SD as the Fe/C ratio increased, while the decrease of quinones and ketones reduced the photoproduction of 3DBC*. The research revealed adsorption on ferrihydrite affected the photodegradation of SD by changing the reactivity of 3DBC*, which was helpful to understand the dynamic roles of DBC in the photodegradation of organic pollutants.

Oxidation of 1,3-diphenylguanidine (DPG) by goethite activated persulfate: Mechanisms, products identification and reaction sites prediction

As emerging pollutants continue to be discovered, studies on the degradation behavior of emerging pollutants have proliferated, but few studies have focused on the reactivity of the new pollutants themselves. The work investigated the oxidation of a representative roadway runoff-derived organic contaminant, 1,3-diphenylguanidine (DPG) by goethite activated persulfate (PS). DPG exhibited the highest degradation rate (kd = 0.42 h−1) with present of PS and goethite at pH 5.0, then started to decrease with increasing pH. Chloride ion inhibited DPG degradation by scavenging HO·. Both HO· and SO4−· were generated in goethite activated PS system. Competitive kinetic experiments and flash photolysis experiments were conducted to investigate free radical reaction rate. The second-order reaction rate constants for DPG reacting with HO· and SO4−· were quantified (kDPG + HO·,kDPG + SO4-·), which both reached above 109 M−1 s−1. Chemical structures of five products were identified, four of them were previously detected in DPG photodegradation, bromination and chlorination processes. By density functional theory (DFT) calculations, ortho- and para- C were more easily attacked by both HO· and SO4−·. Abstraction of H on N by HO· and SO4−· were the favorable pathways, and the product TP-210 might be generated by cyclization of DPG radical from abstraction of H on N (3). The results of this study help us to better understand the reactivity of DPG with SO4−· and HO·.

Performance evaluation of the UV activated chlorite process on trimethoprim: Degradation efficiency, energy consumption and disinfection by-products formation

As the primary inorganic by-product species of ClO2, chlorite is believed to have negative toxicological effects on human health and therefrom greatly limits the wide application of ClO2 in water treatment. The synergistic trimethoprim (TMP) removal concerning degradation efficiency, energy consumption and disinfection by-products (DBPs) formation in the UV activated chlorite process accompanied by the simultaneously elimination of chlorite was comprehensively evaluated. UV/chlorite integrated process removed TMP far more rapidly than UV (1.52%) or chlorite (3.20%) alone due to the endogenous radicals (Cl•, ClO• and •OH), the contributing proportions of which were 31.96%, 19.20% and 44.12%. The second-order rate constants of TMP reaction with Cl•, ClO• and •OH were determined to be 1.75 × 1010, 1.30 × 109 and 8.66 × 109 M−1 s−1. The effects of main water parameters including chlorite dosage, UV intensity, pH as well as water matrixes (nature organic matter, Cl− and HCO3−) were examined. kobs obeyed the order as UV/Cl2>UV/H2O2≈UV/chlorite>UV, and the cost ranking via electrical energy per order (EE/O, kWh m−3 order−1) parameter was UV/chlorite (3.7034) > UV/H2O2 (1.1625) >UV/Cl2 (0.1631). The operational scenarios can be optimized to achieve the maximum removal efficiencies and the minimum energy costs. The destruction mechanisms of TMP were proposed by LC-ESI-MS analysis. The overall weighted toxicity in subsequent disinfection was assessed as UV/Cl2>UV/chlorite > UV, the values of which in post-chlorination were 6.2947, 2.5806 and 1.6267, respectively. Owing to the vital roles of reactive chlorine species (RCS), UV/chlorite displayed far higher TMP degradation efficiency than UV, and concurrently presented much less toxicity than UV/Cl2. In an effort to determine the viability of the promising combination technology, this study was devoted to reduce and reuse chlorite and synchronously realize the contaminants degradation efficiently.

Novel activation of sulfite by perovskite CaCu3Ti4O12 for As(III) oxidation: Kinetics and mechanism

A new activation technology for sulfite (S(IV)) using a perovskite CaCu3Ti4O12 (CCTO) catalyst has been proposed to remediate the As(III) polluted water. When 0.05 g·L−1 CCTO and 0.4 mmol·L−1 S(IV) were mixed, 90.6% of As(III) could be removed in 30 min at an initial pH of 8.0. Dissolved oxygen played an indispensable role in the reaction. CCTO can interact with S(IV) via a heterogeneous catalytic route on its surface. Electrochemical characterization indicated that the electron transfer process between the surface Cu/ Ti atoms and S(IV) ions evoked the activation of S(IV), leading to the generation of SO4•−, which played a dominant role in the oxidation of As(III). Density functional theory (DFT) calculations have disclosed the spontaneous adsorption of sulfite on CCTO surface. A kinetics study determined the steady-state concentration of SO4•− to be 4.29 × 10−14mol·L−1, which reacts with As(III) with a second-order reaction rate constant of 3.83 × 1010L·mol−1·s−1. Furthermore, the CCTO catalyst was highly reusable, the structure of which did not significantly alter during the reaction. Therefore, the CCTO/S(IV) system is a promising and efficient advanced oxidation technique for the purification of As(III) in water.