Carbonate Radical Research Articles

A review on percarbonate-based advanced oxidation processes for remediation of organic compounds in water

Sodium percarbonate (SPC) is considered a potential alternative to liquid hydrogen peroxide (H2O2) in organic compounds contaminated water/soil remediation due to its regularly, transportable, economical, and eco-friendly features. The solid state of SPC makes it more suitable to remediate actual soil and water with a milder H2O2 release rate. Apart from its good oxidative capacity, alkaline SPC can simultaneously remediate acidized solution and soil to the neutral condition. Conventionally, percarbonate-based advanced oxidation process (P-AOPs) system proceed through the catalysis under ultraviolet ray, transition metal ions (i.e., Fe2+, Fe3+, and V4+), and nanoscale zero-valent metals (iron, zinc, copper, and nickel). The hydroxyl radical (•OH), superoxide radical (•O2−), and carbonate radical anion (•CO3−) generated from sodium percarbonate could attack the organic pollutant structure. In this review, we present the advances of P-AOPs in heterogeneous and homogeneous catalytic processes through a wide range of activation methods. This review aims to give an overview of the catalysis and application of P-AOPs for emerging contaminants degradation and act as a guideline of the field advances. Various activation methods of percarbonate are summarized, and the influence factors in the solution matrix such as pH, anions, and cations are thoroughly discussed. Moreover, this review helps to clarify the advantages and shortcomings of P-AOPs in current scientific progress and guide the future practical direction of P-AOPs in sustainable carbon catalysis and green chemistry.

Connecting the quantum and classical mechanics simulation world: Applications of reactive step molecular dynamics simulations.

This article presents the application of the reactive step molecular dynamics simulation method [M. Biedermann, D. Diddens, and A. Heuer, J. Chem. Theory Comput. 17, 1074 (2021)] toward two different atomistic, chemically reactive systems. During reactive steps, transitions from reactant to product molecules are modeled according to physically correct transition probabilities based on quantum chemical information about the reactions such as molecular reaction rates via instant exchange of the employed force field and a subsequent, short relaxation of the structure. In the first application, we study the follow-up reactions of singly reduced ethylene carbonate (EC) radicals in EC solution, first, via extensive ab initio molecular dynamics simulations and, second, with the reactive step algorithm. A direct comparison of both simulation methods shows excellent agreement. Then, we employ the reactive step algorithm to simulate the enolate formation of 2-methylcyclopropanone with the base lithium diisopropylamine. Thereby, we can demonstrate that the reactive step algorithm is also capable of capturing effects from kinetic vs thermodynamic control of chemical reactions during simulation.

The role of carbonate radicals on the kinetics, radical chemistry, and energy requirement of UV/chlorine and UV/H2O2 processes

Quantitative insight into the HCO3−-dependent degradation kinetics is critical to improve understanding of the UV processes for the most-cost effective application. In this study, we developed a kinetic model to precisely predict the kinetics in UV/H2O2 and UV/chlorine processes. The second-order rate constants of HO, Cl, ClO, Cl2−, and CO3− with carbamazepine (CBZ) were fitted as 1.3 × 109, 1.9 × 109, 1.8 × 106, 1.1 × 105, and 4.5 × 106 M−1 s−1, respectively. Based on the model, we investigated the significant impact of bicarbonate (HCO3−) and subsequently generated carbonate radical (CO3−) on CBZ degradation, radical chemistry, and energy requirement of UV/H2O2 and UV/chlorine processes. The presence of HCO3− inhibited CBZ degradation in UV/H2O2 and UV/chlorine processes to different degree. Contributions of HO, Cl, ClO, Cl2−, and CO3− to CBZ degradation in UV/H2O2 and UV/chlorine processes in the absence/presence of HCO3− were investigated. HO and CO3− make comparable contributions to CBZ degradation in UV/H2O2 process in the presence of HCO3− (2 mM), while ClO is always the main contributor at various HCO3− concentration of 0–2 mM. Furthermore, the presence of HCO3− in both processes increased the corresponding EE/O, when CBZ was degraded by an order of magnitude. Overall, HCO3− and CO3− influence the reactions and mechanism of UV/H2O2 and UV/chlorine processes, and have higher impact on UV/H2O2 process.

Using sodium percarbonate to suppress vertically distributed filamentous cyanobacteria while maintaining the stability of microeukaryotic communities in drinking water reservoirs

The increasing frequency and intensity of blooms of toxin- and taste & odour-producing filamentous cyanobacteria in water sources is a growing global issue. Compared to the common spherical Microcystis genus, the removal of filamentous cyanobacteria is more difficult in drinking water treatment plants; hence, abatement and control of the occurrence and proliferation of harmful filamentous cyanobacteria within drinking water sources is important for water supply. In this study, the solid sodium percarbonate (SPC), Na2CO3·1.5H2O2, was used as an algaecide to eliminate the cyanobacteria distributed throughout the water column in the surface and bottom layer of a reservoir serving as a drinking water source. Results showed that although the oxidation capacity of SPC was higher in the surface water due to the higher light intensity than in the bottom water, 3.0 mg/L SPC can still suppress the harmful cyanobacteria in the bottom water after 36 h because the carbonate ion generated by SPC decomposition can act as an activator of H2O2 to generate many reactive oxygen species — including superoxide radicals, carbonate radical anions, and hydroxyl radicals — even in the light-limited environment. The obtained inactivation rates for the main cyanobacteria in this reservoir followed the order: Pseudanabaena limnetica > Raphidiopsis curvata > Cylindrospermopsis raciborskii. 3.0 mg/L SPC has a slight impact on microeukaryotic communities according to the 18S rRNA gene sequencing, while 6.0 mg/L SPC changed the composition of eukaryotic phytoplankton and zooplankton clearly. Eukaryotic co-occurrence networks showed that although the network of eukaryotic plankton in treated surface water was more compact and clustered, stability of microeukaryotes in the treated surface water was lower than for the treated bottom water, owing to the higher oxidation capacity of SPC in the surface water. The results above not only have important implications for full-scale control of harmful cyanobacteria in drinking water sources, especially filamentous cyanobacteria with vertical distributions, but also help to ensure the health and stability of the whole aquatic ecosystem.

Construction of TiO2-Eggshell for Efficient Degradation of Tetracycline Hydrochloride: Sunlight Induced In-Situ Formation of Carbonate Radical.

Photocatalytic degradation of an antibiotic by utilizing inexhaustible solar energy represents an ideal solution for tackling global environment issues. The target generation of active oxidative species is highly desirable for the photocatalytic pollutants degradation. Herein, aiming at the molecular structure of tetracycline hydrochloride (TC), we construct sunlight-activated high-efficient catalysts of TiO2-eggshell (TE). The composite ingeniously utilizes the photoactive function of TiO2 and the composition of eggshell, which can produce oxidative ·CO3− species that are especially active for the degradation of aromatic compounds containing phenol or aniline structures. Through the synergistic oxidation of the··CO3− with the traditional holes (h+), superoxide radicals (·O2−) and hydroxyl radicals (·OH) involved in the photocatalytic process, the optimal TE photocatalyst degrades 92.0% TC in 30 min under solar light, which is higher than TiO2 and eggshell. The photocatalytic degradation pathway of TC over TE has been proposed. The response surface methodology is processed by varying four independent parameters (TC concentration, pH, catalyst dosage and reaction time) on a Box–Behnken design (BBD) to optimize the experimental conditions. It is anticipated that the present work can facilitate the development of novel photocatalysts for selective oxidation based on ·CO3−.

Mechanism of bicarbonate enhancing the photodegradation of β-blockers in natural waters

The impact of HCO3− on the photodegradation of β-blockers was investigated under simulated sunlight irradiation. The results show that in the presence of HCO3−, the photodegradation rates increase significantly for sotalol (SOT), whereas no effects on the degradation of carvedilol and arotinolol are observed. Using quenching experiments, electron paramagnetic resonance spectra and degradation product determination, we demonstrate that carbonate radical (CO3•−) is formed by direct oxidation of HCO3− by triplet-excited SOT (3SOT*) and plays a significant role in SOT photodegradation. Competition kinetics experiments show that the three β-blockers all have high second-order rate constants (107–108 M−1 s−1) for the reaction with CO3•−. However, only 3SOT* has a higher reduction potential that can oxidize HCO3− to produce CO3•−. Thus, enhanced SOT removal rates in the presence of HCO3− were observed. In addition, the results show that seawater DOM could increase HCO3−-induced photodegradation of SOT, whereas SRNOM mainly behaves as a CO3•− quencher and decreases the removal rate of SOT. The results underscore the role of HCO3− in limiting the persistence of organic pollutants like SOT in sunlit natural waters, and especially in marine and coastal waters.

ИЗУЧЕНИЕ МЕТОДОМ ЭЛЕКТРОННОГО ПАРАМАГНИТНОГО РЕЗОНАНСА ВЛИЯНИЯ ФИЗИКО-ХИМИЧЕСКИХ И СТРУКТУРНЫХ ХАРАКТЕРИСТИК КОСТНОЙ ТКАНИ НА ПРОЦЕССЫ ОСТЕОИНТЕГРАЦИИ ДЕНТАЛЬНЫХ ИМПЛАНТАТОВ С РАЗЛИЧНОЙ МИКРОСТРУКТУРОЙ ПОВЕРХНОСТИ

Aim. Study by the method of electronic paramagnetic resonance (EPR) physical- chemical and structural features of bone tissue and their effect on the processes of osseointegration during dental implantation using implants with different macro-microstructure of the surface.
 Material and methods. The experimental study was conducted on 7 Vietnamese visobryu-pig mini-pigs. Under anesthesia, implants with different macro-microstructures of the surface (SLA, RBM, ) were installed under the methods of direct and delayed implantation. At different dates of the experiment, after the appropriate anesthesia, the gentle method was to remove implants with small fragments of periemplant bone tissue. Macro-drugs of bone tissue of the jaws after sawing on blocks and extraction of implants, as well as appropriate preparation, were investigated by the method of stationary electronic paramagnetic resonance.
 Results. As a result of the study it was revealed that the insertation of the implant into the jaw bone leads to structural changes in the surrounding bone implant. After prior exposure, the EPR spectrums, caused by different types of paramagnetic centers, were observed in the samples studied. Two types of centers, , have been identified. and F is the center. The spectrum of the second type reflects the presence in hydroxiapatites of lattice defects associated with isomorphism, and, . The findings suggest that one of the reasons for the higher content of free radicals (SR) in bone tissue derived from radiation, after dental implantation is the weakening of chemical bonds, greater mobility of fragments that make up its structure. It must be assumed that the high content of SR in the bone in the postoperative period is nothing but a result of the disruption of the mineralization process, which is accompanied by the replacement of phosphate groups with carbonate ions that are free-radicalized. It has also been revealed that the structural integrity of the bone depends to a large extent on the degree of orderliness of microcrystals of hydroxyapatite. According to EPR, the most favorable bone recovery (the process of osseointegration) occurs when using implants with a surface, .
 Conclusions. EPR research of native and carbonate radicals is a unique tool for studying the physical and chemical and structural features of bone tissue and their role in the process of osseointegration of implants. The speed of osseointegration for implants with different microstructures of the surface varies. EPR can be used as an additional method to control the integration of implants into bone tissue.

Degradation of Congo red by UV photolysis of nitrate: Kinetics and degradation mechanism

The efficiency of Congo red (CR) removal by low-pressure ultraviolet photolysis of nitrate (UV/NO3−) process was investigated in this study. Results showed that CR degradation through direct UV (254 nm) photolysis could be ignored, but CR was obviously removed in UV/NO3− process. Moreover, the contributions of UV, NO2 and OH to the degradation of CR were explored to be roughly 0.63%, 17.46% and 81.90%, respectively. In addition, the observed pseudo-first-order rate constants for the degradation of CR (kobs) were assessed by the effects of different water matrices and operation conditions, including NO3− dosage, CR concentration, solution pH, chloride ion (Cl−), natural organic matter (NOM) and carbonate/bicarbonate (CO32−/HCO3−). The kobs was increased by nearly 12.9 times with the addition of NO3− dosage from 1 mM to 200 mM due to the generation of more active components (e.g., OH and NO2). Higher doses of CR reduced the kobs, which could be attributed to the filter effects of CR on UV irradiation. Although the photolysis of NO3− could be expedited under acidic conditions, the kobs was decelerated because of the protonation of CR (pKa = 4.1, 25 °C). While in alkaline conditions, the kobs was also reduced as the decrease in redox potential of OH. The presence of Cl− (0–7 mM) exhibited no scavenging effect on the kobs, which suggested the secondary radicals (i.e., chlorine radicals (e.g., Cl, Cl2−)) could oxidize CR effectively. NOM restricted the degradation of CR significantly, resulting from the filter effects of NOM (ε = 0.11 LmgC−1cm−1) on UV and the effects of radical scavenging. The kobs was improved obviously with the participation of CO32−/HCO3− (0–7 mM), ascribing to the oxidation of carbonate radical (CO3−) and the increased steady state concentration of NO2. The degradation of CR in UV/NO3− process has the potential for practical applications in real water. Furthermore, eight intermediates were proposed by Liquid chromatography-tandem mass spectrometry (LC-MS/MS). Hydroxylation, nitrification and other aromatic products in the reaction of CR with OH and/or NO2 were readily produced by H-abstraction, addition reaction and electron transfer.

Enhanced degradation of aqueous tetracycline hydrochloride by integrating eggshell-derived CaCO3/CuS nanocomposite with advanced oxidation process

Persulfate (PS)-based advanced oxidation process (AOP) has attracted wide attention in recent years, in which it is crucial to develop a cost-effective and environmentally friendly catalyst. Herein, a waste eggshell derived eggshell/CuS (ES-CuS) composite catalyst was successfully prepared in a simple way, and used in combination with PS to degrade tetracycline hydrochloride (TCH). Our results showed that the coated CuS had a sheet-like structure and was evenly distributed on the surface of the eggshell, which could effectively prevent agglomeration and enhance catalytic performance. Electron spin resonance (ESR) and free radical capturing experiments confirmed that a series of active species such as sulfate radicals (SO4−), hydroxyl radicals (OH), as well as carbonate radicals (CO3-) were produced during the catalysis process, which is the main reason for enhanced catalytic effect compared with that of the pure CuS. A possible degradation pathway was proposed. It can be expected that discarded eggshells can be used as a low-cost carrier for the synthesis of various composites to achieve its valorization, which have very broad development prospects in the field of environmental remediation or catalysis.

Roles of hydroxyl and carbonate radicals in bisphenol a degradation via a nanoscale zero-valent iron/percarbonate system: influencing factors and mechanisms.

In this work, nanoscale-zero-valent iron (nZVI) was applied to activate sodium percarbonate (SPC) to eliminate bisphenol A (BPA), which poses a risk to ecological and human health as a typical endocrine disruptor. The influence of nZVI loading, SPC dosing, initial pH, and the presence of inorganic anions (including Cl−, HPO42−, NO3− and NO2−) and humic acid on BPA removal by the nZVI/SPC system were investigated. Based on the scavenger test results, ˙OH and CO3˙− participated in the degradation of BPA, and ˙OH was illustrated to be the dominant radical. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis suggested that surface iron oxide generation, electron transfer and Fe2+ release were the main processes of the SPC activation by nZVI. Moreover, BPA transformation products were detected by LC-MS allowing the proposal of a possible degradation pathway of BPA. Along with the degradation of the parent compound BPA, the total organic carbon (TOC) gradually decreased, while the bio-toxicity increased at the initial stage of the reaction (0–3 min) and then decreased to a lower level rapidly at 20 min. Overall, this study evidenced the feasibility of the nZVI/SPC system to efficiently degrade BPA, broadening the applications of nZVI in wastewater treatment.

Characteristics of Carbonate Formation from Concentrated Seawater Using CO2 Chemical Absorption Methodology.

Carbon capture and storage is a popular CO2-reduction technology, and carbon capture and utilization (CCU) technology has been reported frequently over the years. However, CCU has certain disadvantages, including the requirement of high energy consumption processes such as mineral carbonation. In addition, stable metal sources are required to fix CO2. This study used concentrated seawater to supply metal ions. In addition, the selected 5 wt % amine solution changed CO2 into aqueous CO2 to reduce the additional energy required to form the metal carbonate under moderate conditions. As a result, precipitates were formed because of the reaction of carbonate radicals with metal ions in the seawater. These precipitates were analyzed by X-ray diffraction and field-emission scanning electron microscopy, and they were found to mostly consist of CaCO3 and NaCl. Furthermore, it was verified that the conversion solution maintained its CO2-loading capacity even after the solids and liquid were filtered twice. Therefore, the proposed method permits a substantial reuse of CO2 and waste seawater when sufficient metal ions are supplied. Therefore, methods to improve their purity will be developed in future studies.

Designing Solid Electrolyte Interface for Stabilized Silicon Anode for Lithium-Ion Battery

The exploration for the next generation of anode materials in the lithium-ion batteries is a vital subject in energy storage field. Silicon (Si) stands out among all the candidate materials due to its high theoretical specific capacity (4200 mAh/g for Li4.4Si), high safety and low cost. However, one of the biggest issues causing rapid capacity fade of Si anode is the continuous breakage and reformation of SEI due to unstable electrode/electrolyte interphase. One effective way to address it is to use electrolyte additives as represented by vinylene carbonate (VC) and fluoroethylene carbonate (FEC). It is believed that the decomposition of FEC generates electrochemical stable LiF and elastomeric polymerizable vinylene carbonate radical. These decomposition products form a passive layer on Si surface, leading to improved electrochemical performance. However, it is hard to control the composition and structure of the SEI.We take a different approach attempting to solve the above issue. Organic functional groups are introduced on the surface of Si nanoparticles (SiNPs) via Pt-catalyzed hydrosilylation reaction. The surface group helps form more robust SEI thus boosts the electrochemical performance of silicon anode evidenced in both half- and full-cells. This method provides an efficient approach confronting the issues associated with SEI. Figure 1

Kinetic Selectivity of Lithium Alkyl Carbonate Formation from Combination Reactions of Ethylene Carbonate Radical Anions

The mechanism responsible for predominant alkyl carbonate formation over butylene dicarbonate from the reductive decomposition of ethylene carbonate has been elucidated using ab initio molecular dy...

Reevaluation of the contributions of reactive intermediates to the photochemical transformation of 17β-estradiol in sewage effluent

Photodegradation of the natural steroid 17β-estradiol (E2), an endocrine-disrupting hormone that has been widely detected in aquatic environments, was investigated in wastewater effluents at various pH ranges under simulated solar irradiation. The rate of E2 degradation in the sewage effluents was stable at pH 6.0-7.0 but suddenly increased from pH 8.0-10.0. The second-order reaction rate constants of E2 with 3EfOM* and CO3•− were measured to increase 11.0-fold and 18.0-fold from pH 6.0 to 10.0, respectively. Two main reasons are proposed for this sharp increase. First, the change in the ionization state of E2 made it susceptible to oxidation by triplet-state effluent organic matter (3EfOM*) and carbonate radicals (CO3•−). Second, the steady-state concentration of CO3•− increased with increasing pH. Indirect photolysis was suggested to be the main degradation pathway in the sewage effluents, and 3EfOM* was proposed to play a major role at pH 8.0-9.0, while CO3•− played a significant role at pH 10.0. In this study, EfOM was shown for the first time to inhibit the oxidation of E2 initiated by 3EfOM* and CO3•−. Thus, we suggest that EfOM plays a dual role in the photodegradation of E2: EfOM can not only be activated as 3EfOM* to degrade E2 but also can inhibit the degradation of E2 by reducing the E2 oxidation intermediate back to E2. The estrogenic activity of the photodegradation products was also studied. The in vitro estrogenic activity of E2 solutions decreased approximately as fast as the E2 photodegradation occurred in the effluent water at various pH values, suggesting that solar photodegradation in sewage effluents reduces the risk of endocrine disruption in waters impacted by E2 and subject to continuing inputs. The results of this study are important for predicting the environmental fate of endocrine-disrupting chemicals and developing methods for their removal from aquatic environments.

Fenton-like treatment for reduction of simulated carbon-14 spent resin

Spent resins with 14C are enlisted among the most problematic radioactive wastes. In current study, we successfully prepared the simulated 14C-loaded spent resins using HCO3−, and for the first time the Fenton-like treatment of simulated 14C-loaded spent resins were compared with fresh Amberlite IRN-150 resin (without simulated 14C loading) by optimizing the influential reaction parameters. The experimental results revealed that 91.26 % weight loss and 85.47 % in TOC removal were achieved for fresh Amberlite IRN-150 resin (without simulated 14C loading) using 0.35 M Cu(II) catalyst, 30 % H2O2 as oxidant at pH 2, and 90 ± 3 °C temperature for 4 h reaction time. However, the simulated 14C-loaded spent resin using HCO3− exhibited 87.34 % weight loss under the similar reaction conditions. The reduction in weight loss (%) of simulated 14C-loaded spent resin was attributed to the presence of HCO3− on the resins, which could produce the carbonate radical (CO3-∙) of lower oxidation capability as compared to hydroxyl radical and in turn affect the efficacy of Fenton-like treatment for simulated 14C-loaded spent resin. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FT-IR) analyses were used to characterize and the results also supported the resin’s degradation.

Quantification of seasonal photo-induced formation of reactive intermediates in a municipal sewage lagoon upon sunlight exposure

Photochemically produced reactive oxygen species in wastewater lagoons upon sunlight exposure are important in the attenuation of emerging contaminants (ECs). The production of reactive radicals in wastewater lagoons depends on both environmental factors and the composition of effluent organic matter (EfOM) in the wastewater. Knowing the steady state concentrations of these reactive species produced in a particular lagoon wastewater is critical to the prediction of the persistence and attenuation of ECs in that sunlit wastewater treatment lagoon. This study quantified the formation of four photochemically produced reactive intermediates (PPRIs): hydroxyl radical, carbonate radical, singlet oxygen, and triplet excited state EfOM in 11 samples collected from a municipal wastewater lagoon over a full year. The temporal distribution of these key PPRIs in the lagoon under investigation was determined in relation to sunlight irradiance, wastewater composition and temperature. Greater sunlight intensity led to greater PPRI production over the year. Increasing wastewater temperature from 12 to 25 °C led to greater production of singlet oxygen, a moderate decrease in hydroxyl radical and increase in triplet excited state EfOM, and minimal impact on carbonate radical production. The optical properties of the lagoon wastewater of Napierian absorption coefficient (A300) and E2:E3 ratio could be used as indicators of the formation of singlet oxygen (Pearson's r = 0.79) and triplet excited EfOM (Pearson's r = 0.76) produced upon solar irradiation. The concentration of carbonate radical formed was strongly correlated to the nitrate level in the wastewater (Pearson's r = 0.85). The findings could be used for modelling the seasonal sunlight-induced photolysis process of ECs during lagoon-based wastewater treatment, with a view to optimising the treatment process, predicting the efficacy of EC removal, and risk assessment of the treated water.

Theoretical investigation on the contribution of HO[rad], SO4[rad]- and CO3[rad]- radicals to the degradation of phenacetin in water: Mechanisms, kinetics, and toxicity evaluation

Indirect oxidation induced by reactive free radicals, such as hydroxyl radical (HO), sulfate radical (SO4-) and carbonate radical (CO3-), plays an important or even crucial role in the degradation of micropollutants. Thus, the coadjutant degradation of phenacetin (PNT) by HO, SO4- and CO3-, as well as the synergistic effect of O2 on HO and HO2 were studied through mechanism, kinetics and toxicity evaluation. The results showed that the degradation of PNT was mainly caused by radical adduct formation (RAF) reaction (69% for Г, the same as below) and H atom transfer (HAT) reaction (31%) of HO. For the two inorganic anionic radicals, SO4- initiated PNT degradation by sequential radical addition-elimination (SRAE; 55%), HAT (28%) and single electron transfer (SET; 17%) reactions, while only by HAT reaction for CO3-. The total initial reaction rate constants of PNT by three radicals were in the order: SO4- > HO > CO3-. The kinetics of PNT degradation simulated by Kintecus program showed that UV/persulfate could degrade target compound more effectively than UV/H2O2 in ultrapure water. In the subsequent reaction of PNT with O2, HO and HO2, the formation of mono/di/tri-hydroxyl substitutions and unsaturated aldehydes/ketones/alcohols were confirmed. The results of toxicity assessment showed that the acute and chronic toxicity of most products to fish increased and to daphnia decreased, and acute toxicity to green algae decreased while chronic toxicity increased.

Kinetics and pathways of the degradation of PPCPs by carbonate radicals in advanced oxidation processes

The carbonate radical (CO3•−) is a typical secondary radical observed in engineering and natural aquatic systems. This study investigated the degradation kinetics of 20 pharmaceuticals and personal care products (PPCPs) by CO3•− and the transformation pathways of a typical PPCP (naproxen) that is susceptible to CO3•−. CO3•− is highly selective for compounds containing aniline and phenolic hydroxyl groups as well as naphthalene rings, such as sulfamethoxazole, sulfamethazine, salbutamol, propranolol, naproxen, and macrolide antibiotics such as azithromycin, for which the second-order rate constants range from 5.6 × 107 M−1s−1 to 2.96 × 108 M−1s−1. A good linear relationship is observed between the natural logarithms of kCO3•− and the negative values of the Hammett Σσp+ constant for aromatic PPCPs, indicating that electron-donating groups promote the attack of benzene derivatives by CO3•−. The contribution of CO3•− to naproxen degradation is significant in different processes such as UV/H2O2, UV/persulfate, UV/chlorine, and UV/monochloramine, in the presence of HCO3−, which compensates for the decreased contributions of primary radicals. In particular, the formation of CO3•− increases the first-order rate constant of naproxen by 127% in UV/monochloramine in the presence of 50 mM HCO3− compared to that without HCO3−. Natural organic matter (NOM) exerts a slight scavenging effect on CO3•−, decreasing the inhibition effect of NOM on the degradation of naproxen by UV/H2O2 in the presence of HCO3−. The pathways involved in the transformation of naproxen by CO3•− include decarboxylation, hydroxylation, ketonization, demethylation and aldolization. In addition, the alteration of the genotoxicity during naproxen degradation by CO3•− was negligible.

Carbonate Radical Oxidation of Cylindrospermopsin (Cyanotoxin): Kinetic Studies and Mechanistic Consideration.

Cylindrospermopsin (CYN) is one of the most important cyanobacterial toxins frequently found in surface waters. We reported the detailed kinetics and pathways for the reaction of CYN with carbonate radicals (CO3•-). The rate constants of neutral and deprotonated CYN with CO3•- were found to be (1.2 ± 0.7) × 107 M-1 s-1 and (3.0 ± 0.4) × 108 M-1 s-1, respectively. The transformation products for the oxidation of CYN by CO3•- were identified by high-resolution mass spectrometry, illustrating that the guanidine and bridged hydroxyl portions were the primary moieties attacked by CO3•-. Thus, three transformation pathways, including cleavage of the hydroxymethyluracil moiety, hydroxylation, and oxidation of the bridged hydroxyl group, are proposed for the CO3•- oxidation of CYN. Moreover, this study reported that dissolved organic matter (DOM) reduced the transformation rate of CYN by inhibiting the transformation of oxidation intermediates. Finally, the role of CO3•- in CYN degradation was estimated in both sunlit surface waters and advanced oxidation processes (AOPs), demonstrating that CO3•- played an important role in CYN attenuation under nonacidic environmentally relevant conditions. The kinetic parameters and product information obtained in this study will be of considerable interest for the application of AOPs and predicting the environmental fate of CYN.

Possible Effect of Climate Change on Surface-Water Photochemistry: A Model Assessment of the Impact of Browning on the Photodegradation of Pollutants in Lakes during Summer Stratification. Epilimnion vs. Whole-Lake Phototransformation.

Water browning in lakes (progressive increase of the content of chromophoric dissolved organic matter, CDOM) has the potential to deeply alter the photodegradation kinetics of pollutants during summer stratification. Browning, which takes place as a consequence of climate change in several Nordic environments, causes the thermocline to be shallower, because higher CDOM decreases the penetration of sunlight inside the water column. Using a model approach, it is shown in this paper that pollutants occurring in the epilimnion would be affected differently depending on their main photodegradation pathway(s): almost no change for the direct photolysis, slight decrease in the degradation kinetics by the hydroxyl radicals (•OH, but the resulting degradation would be too slow for the process to be effective during summer stratification), considerable decrease for the carbonate radicals (CO3•−), increase for the excited triplet states of CDOM (3CDOM*) and singlet oxygen (1O2). Because it is difficult to find compounds that are highly reactive with CO3•− and poorly reactive with 3CDOM*, the degradation rate constant of many phenols and anilines would show a minimum with increasing dissolved organic carbon (DOC), because of the combination of decreasing CO3•− and increasing 3CDOM* photodegradation. In contrast, overall photodegradation would always be inhibited by browning when the whole water column (epilimnion + hypolimnion) is considered, either because of slower degradation kinetics in the whole water volume, or even at unchanged overall kinetics, because of unbalanced distribution of photoreactivity within the water column.