Enhanced freezing-induced carbamazepine degradation by bromate under solar irradiation via the formation of hypobromous acid and hydroxyl radical

Inorganic substrates in frozen solutions: Transformation mechanisms and interactions with organic compounds - A review

In cold environments, such as polar regions and high latitudes, the freezing of aqueous solutions plays a crucial role in releasing and transforming nutrients, organic compounds, and trace gases. Freezing processes typically affect biogeochemical cycles and environmental processes by reducing the rate of chemical reactions. However, substantial studies have found that some chemical reactions may accelerate unexpectedly under freezing conditions. These reactions include oxidation of nitrite, dissolution of metals/metal oxides, transformation of halogen species, etc. Although freezing process significantly affects the interaction between the inorganic substrate and coexisting organic compounds, there are few review articles on the behavior of the inorganic compound. Therefore, this review examines the transformation behavior of inorganic substrates and their interactions with organic compounds during freezing. The transformation behavior of inorganic substrates during freezing was comprehensively discussed, their underlying mechanisms were elucidated, and the interactions between inorganic substrates and coexisting organic compounds were highlighted. Meanwhile, key factors influencing the freeze-induced chemical processes were articulated. Furthermore, the potential application of freezing reactions in engineering processes is explored. This article aims to improve understanding of the important role of freezing processes in the recycling of substrates in the natural environment and supplement knowledge in the field of ice chemistry.

Visible Light Boosted the Reduction of Cr(VI) in the Absence of Conventional Reductants in Frozen Solutions: The Overlooked Role of Inorganic Anions

The conversion of Cr(VI) in frozen solutions is a mysterious process in the water environment. It has traditionally been believed that the reduction of Cr(VI) can only occur through interaction with traditional reducing agents like natural organic matters (NOMs) and Fe(II), with H2O merely acting as a solvent. However, this study reveals that visible light can induce the reduction of Cr(VI) by H2O even without conventional reducing agents. Specifically, within the narrow liquid-like layer between ice crystals, there is a significant increase in concentrations of protons, Cr(VI), and anions (Cl-, SO42-, and NO3-), which promotes the formation of various complexes between Cr(VI) and anions. DFT results reveal 11 types of stable Cr(VI)-anion complexes in solution, with six exhibiting visible light absorption properties. Quadrupole time-of-flight (QTOF) mass spectrometry confirms that the abundance of these six complexes (Cl-CrO2-Cl, Cr2O6-Cl, Cl-Cr2O5-Cl, Cr2O6-OSO3H, HO3SO-Cr2O5-OSO3H, and Cr2O6-ONO2) correlates with the extent to which visible light promotes Cr(VI) reduction, thus highlighting their crucial role as photoreactive intermediate complexes during this conversion process. These findings suggest that H2O in frozen solutions should no longer be regarded solely as a solvent but also as a reactant, thereby inspiring deeper insights into frozen solution chemistry.

Bromate-induced oxidation of carbamazepine and toxicity assessment of transformation products in the freezing-sunlight process: Effects of trivalent chromium

Bromate (BrO3-)-induced pharmaceutical and personal care products (PPCPs) oxidation is enhanced in freezing systems. Reduced forms of metals are widely present, often coexisting with various contaminants. However, their effects on the interaction of PPCPs with BrO3- in ice in cold regions may have been overlooked. Herein we investigated the effects of representative reducing metal Cr(III) on the interaction between the representative PPCP carbamazepine (CBZ) and BrO3- in the freezing system. Our findings demonstrated that the degradation rate constants of CBZ by BrO3- and Cr(III) were 29.4%-60.3% lower than those by BrO3- in ice, revealing the inhibition of Cr(III) on CBZ degradation by BrO3- in ice. In BrO3-/freezing/sunlight system, BrO3- contributed 62.8% to CBZ degradation. In BrO3-/Cr(III)/freezing/sunlight system, Cr(III) promoted the generation of hydroxyl radical (·OH), leading to 51.0% contribution of ·OH to CBZ degradation. Oxidants were consumed by Cr(III) to form Cr(VI) rather than reacting with CBZ, thereby decreasing CBZ degradation by BrO3- in ice. Due to sunlight-induced Cr(VI) reduction in ice, only 0.3% of Cr(III) was converted to Cr(VI) in BrO3-/Cr(III)/freezing/sunlight system. BrO3--induced CBZ degradation rate in ice decreased in order of Fe(II), Cr(III), and Mn(II), which was due to the different reducing capabilities. An effective reduction in comprehensive toxicity of systems followed the freezing-sunlight process, even in the presence of Cr(III). This work sheds new light on the environmental behaviors and fate of PPCPs, brominated disinfection by-products, and reducing metals during seasonal freezing.

A novel simultaneous abatement of bromate and diphenyl phosphate using the freezing process

The purification of bromate (BrO3-)-contaminated water has become a challenge because of its persistence and adverse effects. Furthermore, there has been concern over the release of byproducts, such as diphenyl phosphate (DPHP), from flame retardants in wastewater treatment plant (WWTP). In this study, we designed the water treatment system for the oxidation of DPHP accompanied by bromate (BrO3-) reduction via freezing the solution. A sample containing 10 μM DPHP, 100 μM Br-, and 50 μM BrO3-, with a pH of 3 was frozen at -20oC, approximately 25 μM BrO3- was reduced, and DPHP was fully eliminated after a 0.5 h reaction time. Conversely, these reactions did not advance in water at 20oC. This increase in the rate of chemical reaction in ice is the consequence of the freeze concentration effect, which refers to the extraction of dissolved chemical species into the liquid-like regions of the polycrystalline ice micro-structure during the freezing of the solution. The redox reactions among DPHP, Br-, and BrO3- become thermodynamically favorable due to the distinctive environment in the liquid brine in ice. The efficiency of the DPHP oxidation significantly increased with an increase in BrO3- concentration, and vice versa. The Br-/BrO3--induced HOBr production is proposed as a primary oxidant for DPHP degradation. The proton activity (pH) has a significant influence on the reaction efficiency. The low freezing temperature accelerated the reaction kinetics of DPHP degradation and BrO3- reduction. The results of this study indicate the possibility of utilizing ice chemistry for the BrO3- reduction that concomitantly removes DPHP for water treatment. This environmentally friendly water treatment method can be considered to implement in regions with a cold climate.

Reactive Oxygen Species Generated in Situ During Carbamazepine Photodegradation at 222 nm Far-UVC: Unexpected Role of H2O Molecules

When 222 nm far-UVC is used to drive AOPs, photolysis emerges as a critical pathway for the degradation of numerous organic micropollutants (OMPs). However, the photodegradation mechanisms of the asymmetrically polarized OMPs at 222 nm remain unclear, potentially posing a knowledge barrier to the applications of far-UVC. This study selected carbamazepine (CBZ), a prevalent aquatic antiepileptic drug that degrades negligibly at 254 nm, to investigate its photodegradation mechanisms at 222 nm. Accelerated CBZ treatment by 222 nm far-UVC was mainly attributed to in situ ROS generation via self-sensitized photodegradation of CBZ. By quenching experiments and EPR tests, •OH radicals were identified as the major contributor to the CBZ photodegradation, whereas O2•- played a minor role. By deoxygenation and solvent exchange experiments, the H2O molecules were demonstrated to play a crucial role in deactivating the excited singlet state of CBZ (1CBZ*) at 222 nm: generating •OH radicals via electron transfer interactions with 1CBZ*. In addition, 1CBZ* could also undergo a photoionization process. The transformation products and pathways of CBZ at 222 nm were proposed, and the toxicities of CBZ's products were predicted. These findings provide valuable insights into OMPs' photolysis with 222 nm far-UVC, revealing more mechanistic details for far-UVC-driven systems.

Simultaneous Oxidation of Bromide and Dissolution of Manganese Oxide Induced by Freezing

This study demonstrates that the oxidation of bromide by birnessite (δ-MnO2) results in the concurrent production of soluble manganese (Mn(II)) and reactive bromine (RBr) species in frozen solutions, a process not observed in aqueous solutions. This enhanced oxidation in ice is attributed to the concentration of protons, birnessite, or bromide in the ice grain boundary region. Furthermore, different types of commercial manganese oxides can also oxidize bromide to RBr and release Mn(II) in ice. The presence of fulvic acid (FA) further increases the simultaneous production of RBr and Mn(II) in ice, accompanying the formation of organobromine compounds (OBCs). In frozen δ-MnO2/Br-/FA system, a significant increase in OBCs, mainly highly unsaturated and phenolic compounds, was detected using Fourier transform ion cyclotron resonance mass spectrometry. A marked contrast was observed in the number of OBCs formed in frozen solutions (853 and 415 OBCs at initial pH 3.0 and 5.8, respectively) compared to their aqueous counterparts (11 and 23 OBCs). These findings introduce a new pathway for the formation of RBr, Mn(II), and OBCs in ice, highlighting the need for further research on the environmental fate of bromide and manganese.

Transformation of metoprolol in UV/PDS process: Role and mechanisms of degradation and polymerization

Advanced oxidation processes for the treatment of organic pollutants in wastewater suffer from difficulties in mineralization, potential risks of dissolved residues, and high oxidant consumption. In this study, radical-initiated polymerization is dominated in an UV/peroxydisulfate (PDS) process to eliminate organic pollutant of pharmaceutical metoprolol (MTP). Compared with an ideal degradation-based UV/PDS process, the present process can save four fifths of PDS consumption at the same dissolved organic carbon removal of 47.3%. Simultaneously, organic carbon can be recovered from aqueous solution by separating solid polymers at a ratio of 50% of the initial chemical oxygen demand. The chemical structure of products was analyzed to infer the transformation pathways of MTP. Unlike previous studies on simple organic pollutants that the polymerization can occur independently, the polymerization of MTP is dependent on the partial degradation of MTP, and the main monomer in polymerization is a dominant degradation product (4-(2-methoxyethyl)-phenol, denoted as DP151). The separated solid polymers are formed by repeated oxidation and coupling of DP151 or its derivatives through a series of intermediate oligomers. This proof-of-concept study demonstrates the advantage of polymerization-dominated mechanism on dealing with large organic molecules with complex structures, as well as the potential of UV/PDS process for simultaneous organic pollution reduction and organic carbon recovery from aqueous solution.

Degradation of carbamazepine in ice with bromate and nitrite: Role of reactive nitrogen species

Seasonal freezing of waters occurs during winter in cold regions. Bromate ( [Formula: see text] ) is a disinfection by-product generated during water treatment, its interaction with emerging contaminants may be affected by freezing. Nitrite ( [Formula: see text] ) is widely distributed in the environment, whereas its effect on the interaction of emerging contaminants and [Formula: see text] in ice may have been overlooked. Herein carbamazepine (CBZ) was selected as a model emerging contaminant to elucidate the role of reactive nitrogen species (RNS) in contaminant transformation during the reduction of [Formula: see text] by [Formula: see text] in ice. Results indicated that freezing significantly enhanced CBZ degradation by [Formula: see text] . The CBZ degradation by [Formula: see text] and [Formula: see text] in ice was 25.4 %-27.8 % higher than that by [Formula: see text] . Contributions of hydroxyl radical (•OH), bromine radical (•Br), and RNS to CBZ degradation in freezing/dark or sunlight systems were 8.1 % or 15.9 %, 25.4 % or 7.2 %, and 66.5 % or 76.9 %, respectively. Most CBZ was degraded by RNS generated during the reduction of [Formula: see text] by [Formula: see text] in ice, resulting in 16.4 % of transformation products being nitro-containing byproducts. Hybrid toxicity of CBZ/ [Formula: see text] / [Formula: see text] system was reduced effectively after the freezing-sunlight process. This study can provide new insights into the environmental fate of emerging contaminants, [Formula: see text] , and [Formula: see text] in cold regions.

Photodegradation for different dissociated species of norfloxacin and ofloxacin in water ice under solar irradiation

Ice is an important medium that regulates the transformation of organic contaminants. Nonetheless, photodegradation of emerging fluoroquinolone (FQ) antibiotics in the ice, particularly those with varying dissociated species, remains inadequately explored. In this study, the photodegradation of norfloxacin (NOR) and ofloxacin (OFL) in different dissociated species in water ice were investigated. Results indicated that the quantum yield of the zwitterion for NOR in the ice was 1.7-5.0 times higher than that of the cation, and 1.3 times higher than that of the anion. The quantum yield of the zwitterion for OFL in the ice was 2.5-3.4 times higher than that of the cation, and 1.4 times higher than that of the anion. The degradation pathways of NOR and OFL with different dissociated species depended on their molecular structure. Most products possessed lower developmental toxicity than parent NOR and OFL, respectively. OFL showed a higher inhibitory rate of Escherichia coli activity at the initial time of photodegradation, which was higher than that of NOR. This study offers novel insights into the impact of dissociated species on the photodegradation of FQs in ice and contributes to understanding the environmental behavior of fluorinated pharmaceuticals in the cryosphere.