Chlorination By-products Research Articles

The Role of Hygiene in a Sustainable Approach to Managing Pool Water Quality

To achieve sustainable swimming pool water management, it is necessary to minimize the consumption of energy, water, and chemical agents to maintain the appropriate water quality. Some of the pollutants are introduced by swimmers and can be relatively easily removed if swimmers take a shower before entering a pool. Thus, this research questions how much of an impact this simple act could have on the water quality and generally on sustainable water management in swimming pools. To address this question, experiments were conducted at the AGH Swimming Pool in Kraków, in a real facility—a hot tub—with the participation of volunteers who took a shower in Variant 1 and did not in Variant 2. The assessment was made on the basis of selected microbiological and physicochemical parameters of swimming pool water, including disinfection by-products. The research results proved that taking a shower can significantly reduce the load of pollutants users introduce into swimming pool water and can contribute to more efficient and ecological treatment of swimming pool water and minimize the negative impact on the health of swimming pool users (microbiological contaminants and precursors of harmful chlorination by-products).

Meta-analysis and Mendelian randomization study on the association between exposure to chlorinated disinfection byproducts and preterm birth risk.

This study aims to investigate the correlation between exposure to disinfection byproducts of chlorination and preterm birth (PTB) through evidence-based medicine Meta-analysis and Mendelian randomization (MR) analysis. Meta-analysis was conducted on 17 studies involving 1,251,426 neonates, revealing a higher risk of PTB with exposure to total trihalomethanes (TTHMs) and chloroform. Mendelian randomization (MR) analysis confirmed a causal relationship between chlorides and PTB. TTHMs and chloroform were associated with increased PTB risk, while haloacetic acids showed no significant association. TTHMs were linked to small gestational age. Ethnicity and study design influenced heterogeneity. Exposure to chlorination byproducts, particularly TTHMs and chloroform, poses a significant risk for PTB. MR analysis supports a causal relationship between chlorides and PTB, highlighting the importance of water disinfection byproduct control in preventing PTB.

Water-Soluble Iron Porphyrins as Catalysts for Suppressing Chlorinated Disinfection Byproducts in Hypochlorite-Dependent Water Remediation.

We are facing a world-wide shortage of clean drinking water which will only be further exacerbated by climate change. The development of reliable and affordable methods for water remediation is thus of utmost importance. Chlorine (which forms active hypochlorites in solution) is the most commonly used disinfectant due to its reliability and low cost. One drawback is that it reacts with organic pollutants to generate toxic chlorinated byproducts. To mitigate chlorination in water remediation, we have investigated the use of catalytic amounts of charged water-soluble iron porphyrins. These are known to activate hypochlorite to generate high valent oxoiron species. We studied the depletion of the model micropollutant phenol and the accumulation of chlorinated disinfection byproducts under water remediation conditions, using iron porphyrins [(TMPyP)FeCl]Cl4 and (NH4)4[(TPPS)FeCl] as catalysts, by membrane inlet mass spectrometry. Despite bearing opposite charges on the meso-substituent, both iron porphyrins suppress the formation of chlorinated disinfection by-products equally well. To gain further insight, spectroscopic studies were performed. These showed the transient formation of Compound II, followed by either regeneration of the iron(III) porphyrin at low NaOCl concentrations, or total decomposition of the porphyrin complex at high NaOCl concentrations. Potential future directions for modifications of porphyrin-based catalysts are discussed.

Multistage Generation Mechanisms of Reactive Oxygen Species and Reactive Chlorine Species in a Synergistic System of Anodic Oxidation Coupled with in Situ Free Chlorine and H2O2 Production.

Electro-oxidation (EO) is an efficient approach to removing refractory organics in wastewater. However, the interference from chlorine ions (Cl-) can generate reactive chlorine species (RCS), potentially leading to the production of undesirable chlorinated byproducts. A novel approach involving the cathodic oxygen reduction reaction (ORR) for in situ H2O2 production has emerged as a promising strategy to counteract this issue. This study systematically investigated the dynamics and transformation of RCS and reactive oxygen species (ROS) in an ORR/chloride-containing EO (EO-Cl) system, elucidating their respective roles in organic removal and chlorinated byproduct minimization. Distinct generation rates and patterns were observed for free chlorine and H2O2 in the ORR/EO-Cl system. The rapid generation of free chlorine at the anode quickly reached a dynamic equilibrium, which contrasted with the moderate, continuous cathodic production of H2O2, resulting in considerable H2O2 accumulation over time. This difference established kinetics-driven ROS and RCS formation and distribution, influencing the subsequent organic degradation process. Three distinct stages were identified in the degradation process. In stage I, free chlorine was the primary species, along with reactive species including Cl2•-, 1O2, ClO•, HO•, and Cl•. In stage II, the gradual accumulation of H2O2 consumed free chlorine, favoring the formation of 1O2 and HO•. In stage III, excessive H2O2 quenched the free radicals. Insights into these multistage mechanisms reveal that the rapid degradation of chlorinated byproducts by 1O2 and HO• occurs in stage II of the ORR/EO-Cl system.

Elimination of mutagenic contaminants from water using cellulose bearing ferrous-phthalocyanine

BackgroundWe previously investigated methods for separating mutagenic contaminants from aqueous solutions using cellulose-bearing covalently bound trisulfo-Cu-phthalocyanine (blue cotton and blue rayon). Mutagenic contaminants with three or more fused aromatic rings in their structures were adsorbed onto blue cotton and rayon. Since Cu-phthalocyanine is considered an unsuitable absorption ligand for byproducts of water chlorination, such as 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (Mutagen X or MX), we investigated the development of a new material for the elimination of MX from aqueous solvents.ResultsWe selected green cellulose powder bearing ferrous phthalocyanine (FePh), hereafter referred to as green cellulose or GP, as the candidate material. GP is composed of cationized cellulose (white cellulose, WP) and FePh tetracarboxylic acid. The mutagenicity of MX dissolved in buffer or dimethyl sulfoxide (DMSO) solution significantly decreased after treatment with GP. The effects of GP on the elimination of MX from the solvent were very close to being expired after 70 cycles of repeated adsorption of the same GP, and the capacity of GP for MX removal was estimated to be exhausted after 120 cycles of repeated adsorption based on the extrapolation of the obtained result; thus, the interacting ligands on GP may be saturated after complete MX adsorption. The mutagenicity of MX dissolved in aqueous buffer significantly decreased after treatment at pH7.4 but not at pH 4.0. Since MX is dissociated to be the anionic form at pH 6 or higher, the negative charge of MX in the buffer at pH 7.4 may interact with the positive charge of ferrous ions in GP to create a linkage between MX and GP. After GP adsorbed MX, mutagenicity was extracted with water or acetonitrile and recovered in the eluent. Thus, the reversible interaction between MX and FePh may have caused adsorption of MX onto GP.ConclusionGP could be used as a new eliminator and recovery agent for MX in chlorinated drinking water. Developing new materials for the removal and recovery of agents for the detection of mutagenic contaminant-related chlorination in water is beneficial for environmental health.

Inhibition of inorganic chlorinated byproducts formation during electrooxidation treatment of saline phenolic wastewater via synergistic cathodic generation of H2O2

The electrochemical treatment of saline wastewater is prone to the formation of inorganic chlorinated byproducts, being a significant challenge for this technology. In this study, we introduce an electrooxidation system utilizing a self-supporting nitrogen-doped carbon-based cathode embedded in carbon cloth (N@C-CC), designed to generate H₂O₂. This system aims to rapidly neutralize free chlorine produced at the anode, a precursor to inorganic chlorinated byproducts, thereby reducing their formation. Our results demonstrate that using the N@C-CC cathode in saline wastewater treatment yielded considerably lower concentrations of ClO₃⁻ and ClO₄⁻ (0.08 mM and 0.024 mM, respectively), which were only 20.5% and 22.7% of the levels produced using a Pt cathode without H₂O₂ generation. Moreover, the presence of cathodically generated H₂O₂ that quenches free chlorine did not significantly impact the degradation performance of phenol. Electron paramagnetic resonance tests and quenching experiments indicated that 1O₂ was primarily responsible for phenol removal. Validation with real wastewater demonstrated reductions of 68.6% and 56.3% in ClO3− and ClO4− concentrations, respectively, while effectively removing other pollutants. This study thus offers a compelling method for mitigating the formation of inorganic chlorinated byproducts during the electrooxidation of saline wastewater.

Aged Microplastics and Antibiotic Resistance Genes: A Review of Aging Effects on Their Interactions.

Background: Microplastic aging affects the dynamics of antibiotic resistance genes (ARGs) on microplastics, yet no review presents the effects of microplastic aging on the associated ARGs. Objectives: This review, therefore, aims to discuss the effects of different types of microplastic aging, as well as the other pollutants on or around microplastics and the chemicals leached from microplastics, on the associated ARGs. Results: It highlights that microplastic photoaging generally results in higher sorption of antibiotics and ARGs due to increased microplastic surface area and functional group changes. Photoaging produces reactive oxygen species, facilitating ARG transfer by increasing bacterial cell membrane permeability. Reactive oxygen species can interact with biofilms, suggesting combined effects of microplastic aging on ARGs. The effects of mechanical aging were deduced from studies showing larger microplastics anchoring more ARGs due to rough surfaces. Smaller microplastics from aging penetrate deeper and smaller places and transport ARGs to these places. High temperatures are likely to reduce biofilm mass and ARGs, but the variation of ARGs on microplastics subjected to thermal aging remains unknown due to limited studies. Biotic aging results in biofilm formation on microplastics, and biofilms, often with unique microbial structures, invariably enrich ARGs. Higher oxidative stress promotes ARG transfer in the biofilms due to higher cell membrane permeability. Other environmental pollutants, particularly heavy metals, antibacterial, chlorination by-products, and other functional genes, could increase microplastic-associated ARGs, as do microplastic additives like phthalates and bisphenols. Conclusions: This review provides insights into the environmental fate of co-existing microplastics and ARGs under the influences of aging. Further studies could examine the effects of mechanical and thermal MP aging on their interactions with ARGs.

Performance assessment of food safety systems (FSMSs and FSC) in water bottling factories in view of their contextual characteristics

Foodborne illnesses affect 30% of people in developed nations and lead to financial difficulties in less wealthy countries. Insufficient understanding of pathogens and inadequate food safety practices in water bottling facilities impede progress. To prevent illnesses, ensuring clean water, proper sanitation, and good hand hygiene are essential in order to decrease the 829,000 annual deaths related to diarrhea. This study aimed to evaluate the performance of food safety systems in water bottling factories in view of their contextual characteristics. A study was conducted in northwestern Ethiopia at water bottling factories from January 2023 to August 2023. This study used a mixed method approach to collect and analyze data through laboratory testing, observations, interviews, questionnaires, and document analysis. The Kruskal‒Wallis H test was used to compare mean scores of context riskiness and food safety output across four clusters, while the Mann‒Whitney U test was used to compare means between certified and noncertified factories. In our study, 43% of the samples showed positive total plate count. The result also indicated the presence of potentially dangerous by-products of chlorine, trihalomethanes was found in bottled water. On average, the manufacturers operated in a moderate risk context. Inadequate food safety outcomes resulted from lower food safety management systems scores. Factories with insufficient Food Safety Management Systems often face challenges marked by safety protocol discrepancies, leading to higher risks of contamination and non-compliance with regulations. This assessment underscores the need for tailored interventions focusing on specific contextual barriers to improve food safety outcomes in the bottled water industry.

Voltage-confined flow-through anodic oxidation enables efficient pollutant removal and no chlorinated byproducts formation

The formation of chlorinated by-products in the treatment of chloride-laden water/wastewater by advanced oxidation processes (AOPs) has become a severe challenge to their environmentally benign application. Herein, we propose an efficient and safe alternative, i.e., flow-through anodic oxidation (FTAO) system based on the nonradical direct electron transfer (DET) process at low voltage. By controlling the anode potential below the threshold for chlorine evolution at the anode, this system achieved zero formation of inorganic and organic chlorinated byproducts whilst significantly eliminated the biotoxicity of the parent micropollutant. Meanwhile, due to the nonradical direct oxidation mechanism, the voltage-confined FTAO system attained high efficiency and selectivity for the micropollutant removal from a complex matrix containing naturally co-existing anions and organic matter. The feasibility of FTAO applications was further evaluated by removing various pollutants (including antibiotics and phenols) from actual municipal effluent and surface water. More than 96% percentage removal was achieved at extremely low energy consumption (0.003–0.017 kWh m−3). In summary, our results provide insight into the development of novel electrochemical technologies free from secondary pollution towards environmental remediation applications and beyond.

Critical review on toxic contaminants in surface water ecosystem: sources, monitoring, and its impact on human health.

Surface water pollution is a critical and urgent global issue that demands immediate attention. Surface water plays a crucial role in supporting and sustaining life on the earth, but unfortunately, till now, we have less understanding of its spatial and temporal dynamics of discharge and storage variations at a global level. The contamination of surface water arises from various sources, classified into point and non-point sources. Point sources are specific, identifiable origins of pollution that release pollutants directly into water bodies through pipes or channels, allowing for easier identification and management, e.g., industrial discharges, sewage treatment plants, and landfills. However, non-point sources originate from widespread activities across expansive areas and present challenges due to its diffuse nature and multiple pathways of contamination, e.g., agricultural runoff, urban storm water runoff, and atmospheric deposition. Excessive accumulation of heavy metals, persistent organic pollutants, pesticides, chlorination by-products, pharmaceutical products in surface water through different pathways threatens food quality and safety. As a result, there is an urgent need for developing and designing new tools for identifying and quantifying various environmental contaminants. In this context, chemical and biological sensors emerge as fascinating devices well-suited for various environmental applications. Numerous chemical and biological sensors, encompassing electrochemical, magnetic, microfluidic, and biosensors, have recently been invented by hydrological scientists for the detection of water pollutants. Furthermore, surface water contaminants are monitored through different sensors, proving their harmful effects on human health.

Health Risk Assessment of Employees Exposed to Chlorination By-products of Recreational Water in Large Amusement Parks in Shanghai

Objective Chlorination is often used to disinfect recreational water in large amusement parks; however, the health hazards of chlorination disinfection by-products (DBPs) to occupational populations are unknown. This study aimed to assess the exposure status of chlorinated DBPs in recreational water and the health risks to employees of large amusement parks.Methods Exposure parameters of employees of three large amusement parks in Shanghai were investigated using a questionnaire. Seven typical chlorinated DBPs in recreational water and spray samples were quantified by gas chromatography, and the health risks to amusement park employees exposed to chlorinated DBPs were evaluated according to the WHO's risk assessment framework.Results Trichloroacetic acid, dibromochloromethane, bromodichloromethane, and dichloroacetic acid were detected predominantly in recreational water. The carcinogenic and non-carcinogenic risks of the five DBPs did not exceed the risk thresholds. In addition, the carcinogenic and non-carcinogenic risks of mixed exposure to DBPs were within the acceptable risk limits.Conclusion Typical DBPs were widely detected in recreational water collected from three large amusement parks in Shanghai; however, the health risks of DBPs and their mixtures were within acceptable limits.

Enhanced treatment of high chloride organic wastewater under lower peroxymonosulfate consumption: A pathway for the formation of Fe(IV)=O excited by chloride ions

The inhibition of oxidation efficiency and the formation of toxic chlorinated organic byproducts owing to Cl- still represent a significant threat to the treatment of high chloride organic wastewater using advanced oxidation processes. This study explores new pathways for utilizing Cl- to promote the formation of Fe(Ⅳ)=O by single atom Fe-CNs catalysts under peroxymonosulfate (PMS) system, which significantly increases sulfamethoxazole (SMX) degradation rate constant by 2.97 times, enhances PMS utilization efficiency (reducing by 92 % PMS consumption) and simultaneously avoids the formation of chlorinated organic byproducts. Experiments and theoretical calculation revealed that the in-situ generated HClO (generated via the reaction of PMS and Cl-) more easily reacts with Fe–pyridinic N active sites of Fe-CNs catalysts to generate Fe(Ⅳ)=O through a lower-energy-barrier pathway, rather than directly oxidates pollutants. This study provides an approach to utilize omnipresent Cl- achieving high efficiency, high selectivity, low PMS consumption and harmless treatment for chloride-containing organic wastewaters.

Complexation with Metal Ions Affects Chlorination Reactivity of Dissolved Organic Matter: Structural Reactomics of Emerging Disinfection Byproducts.

Metal ions are liable to form metal-dissolved organic matter [dissolved organic matter (DOM)] complexes, changing the chemistry and chlorine reactivity of DOM. Herein, the impacts of iron and zinc ions (Fe3+ and Zn2+) on the formation of unknown chlorinated disinfection byproducts (Cl-DBPs) were investigated in a chlorination system. Fe3+ preferentially complexed with hydroxyl and carboxyl functional groups, while Zn2+ favored the amine functional groups in DOM. As a consequence, electron-rich reaction centers were created by the C-O-metal bonding bridge, which facilitated the electrophilic attack of α-C in metal-DOM complexes. Size-reactivity continuum networks were constructed in the chlorination system, revealing that highly aromatic small molecules were generated during the oxidation and decarbonization of metal-DOM complexes. Molecular transformation related to C-R (R represents complex sites) loss was promoted via metal complexation, including decarboxylation and deamination. Consequently, complexation with Fe3+ and Zn2+ promoted hydroxylation by the C-O-metal bonding bridge, thereby increasing the abundances of unknown polychlorinated Cl-DBPs by 9.6 and 14.2%, respectively. The study provides new insights into the regulation of DOM chemistry and chlorine reactivity by metal ions in chlorination systems, emphasizing that metals increase the potential health risks of drinking water and more scientific control standards for metals are needed.

Effective inhibition of chloride ion interference in photocatalytic process by negatively charged molecularly imprinted photocatalyst: Behavior and mechanism

The ubiquitous chloride ions (Cl−) in water seriously interfere with pollutant oxidation and inevitably generate undesirable chlorinated byproducts. In this study, we report for the first time that a negatively charged molecularly imprinted photocatalyst (MIP) can effectively inhibit Cl− interference and suppress the production of chlorination byproducts (the yield of chloroacetic acid was only 16 % of the bare photocatalyst system) while ensuring efficient degradation of target pollutants, thereby greatly improving the safety of the pollutant degradation process. Taking antibiotics as target pollutant, we investigated the mechanism of action of MIP by comparing the antibiotic degradation pathways, fate of photogenerated active species and production of reactive chlorine species (RCS) in the MIP and bare photocatalyst system. The mechanism by which MIP inhibits Cl− interference was mainly based on a synergy between electrostatic repulsion and steric hindrance induced by the specific capture of antibiotics in imprinted cavity, which effectively suppressed the production of RCS and hindered the participation of RCS in antibiotics degradation. In addition, MIP showed good compatibility with common cations, anions and organic matter, and performed well within a broad pH range in various water environments. Thus, the negatively charged MIP provides a feasible approach for the safe and efficient removal of pollutants in Cl− containing water.

Degradation of organic pollutants by the Cl-/PMS process.

The viewpoints on whether high concentrations of chloride ion (Cl-) promote or inhibit the oxidation activity of activated persulfates are still inconclusive. Furthermore, the degradation of organic pollutants by the persulfates in the presence of high Cl- concentrations without any activation medium has not yet been studied. In this work, the efficiency and mechanism of degradation of organic pollutants such as carbamazepine (CBZ), sulfadiazine (SDZ), and phenol (PN) by Cl--activated PMS (denoted as Cl-/PMS) were investigated. Results showed that Cl- could effectively activate PMS for the complete removal of CBZ, SDZ, and PN with reaction kinetic constants of 0.4516min-1, 0.01753min-1, and 0.06805min-1, respectively. Parameters such as PMS dose, Cl- concentration, solution pH, and initial concentrations of organic pollutants that affect the degradation efficiencies of the Cl-/PMS process were optimized. Unlike conventional activated persulfates, it was confirmed that the free chlorine was the main active species in the Cl-/PMS process. Finally, the degradation by-products of CBZ and SDZ as well as their toxicity were detected, and a possible degradation pathway for CBZ and SDZ was proposed. Though higher toxic chlorinated by-products were generated, the Cl-/PMS process was still an efficient oxidation method for the removal of organic pollutants in aqueous solutions which contain high concentrations of Cl-.

Inhibition of chlorinated byproducts formation by boron-doped rGO electrodes during electrooxidation of trace organic contaminants

To minimize toxic inorganic chlorinated byproducts formation by anodic oxidation of chloride containing water, an electrode was fabricated by coating boron-doped reduced graphene oxide (BDrGO) on carbon paper. The BDrGO electrode only converted 0.03 to 0.4 % of the initial chloride (5–25 mM) to byproducts across a wide pH range (3−10), which is approximately two orders of magnitude lower than other commonly used anodes. The mechanism for inhibiting chlorinated byproducts was attributed to the higher overpotential for the chlorine evolution reaction on the BDrGO electrode and the slower reaction rates (< 2 × 10−11 M s–1) of pathways responsible for chlorinated byproducts formation. The BDrGO electrode was capable of oxidizing contaminants, with oxidation pathways predominated by chlorine radicals (e.g., ClO•, Cl•, Cl2•–) (> 50 %). During electrolysis of authentic surface water, the BDrGO electrode transformed trace organic contaminants (> 90 %) without producing unacceptable levels of chlorinated byproducts.

Energy-efficient treatment of refractory industrial effluent using flow-through electrochemical processes: Oxidation mechanisms and reduction of chlorinated byproducts

While flow-through anodic oxidation (FTAO) technique has demonstrated high efficiency to treat various refractory waste streams, there is an increasing concern on the secondary hazard generation thereby. In this study, we developed an integrated system that couples FTAO and cathodic reduction processes (termed FTAO-CR) for sustainable treatment of chlorine-laden industrial wastewater. Among four common electrode materials (i.e., Ti4O7, β-PbO2, RuO2, and SnO2-Sb), RuO2 flow-through anode exhibited the best pollutant removal performance and relatively low ClO3 and ClO4 yields. Because of the significant scavenging effect of Cl− in real wastewater treatment, the direct electron transfer process played a dominant role in contaminant degradation for both active and nonactive anodes though active species (i.e., active chlorine) were involved in the subsequent transformation of the organic matter. A continuous FTAO-CR system was then constructed for simultaneous COD removal and organic and inorganic chlorinated byproduct control. The quality of the treated effluent could meet the national discharge permit limit at low energy cost (∼4.52 kWh m3 or ∼0.035 kWh g1-COD). Results from our study pave the way for developing novel electrochemical platforms for the purification of refractory waste streams whilst minimizing the secondary pollution.

Overlooked formation of chlorinated coupling byproducts during phenol degradation with ferrate(VI) oxidation technology

Currently, ferrate(VI) oxidation technology (FOT) has been regarded as one of the most promising options for the degradation of emerging organic pollutants. However, the role and transformation of chloride ions (Cl−) in FOT have not been well explored. The current study aims to investigate the formation of chlorinated phenolic byproducts upon ferrate(VI) oxidation processes. The obtained results indicate that chlorides suffering ferrate(VI) attack will be transformed to active chlorine species (ACS), which will subsequently lead to the formation of highly toxic aromatic chlorinated byproducts. The identified byproducts include common chlorinated phenolic derivatives, as well as complex chlorinated oligomer byproducts with ether structures (mainly dimers and trimers). While the formation of common chlorophenols can be ascribed to the electrophilic substitution reactions mediated by ACS, the oligomer byproducts are generated via coupling reactions between chlorinated phenoxy radicals. ECOSAR software predicts that the generated chlorinated oligomer byproducts exhibit high ecotoxicological effects. As a whole, the above findings shed light on the potential risk of FOT in real practice.

Bone char switch on reductive dehalogenation of trichloroethene by series of Fe(II)-bearing minerals: The balance between kinetics and electron efficiency

Fe(II)-bearing minerals might be able to drive the attenuation of chlorinated ethene in soil and groundwater, however, with relatively slow kinetics. In this study, bone char(BC) was selected as an efficient and benign catalyst to prepare composites with three different Fe(II)-bearing minerals (Green rust (GR), Fe(OH)2 and FeS), respectively, for enhanced trichloroethylene (TCE) dehalogenation. The kinetics experiment demonstrated that the presence of BC could effectively switch on the TCE dehalogenation by these solids, while these Fe(II)-bearing minerals alone can barely reduce any TCE. Surprisingly, the Fe(OH)2-BC showed fastest TCE reduction rate, followed by GR-BC and FeS-BC in sequence. Acetylene was confirmed as the major dehalogenation products while other chlorinated byproducts were hardly detected. The electron efficiency (ηe) for TCE reduction was further calculated and compared among these BC amended systems, the results show that the highest ηe value was recorded in GR-BC system as 33.14% with high loading of TCE. Solid phase characterization confirmed that the high loading of amorphous Fe(II) on the BC surface might effectively improve the TCE dehalogenation kinetics, while the well crystallized Fe(II)-bearing minerals would increase the electron efficiency. According to this mechanism, it might be possible to achieve balance between kinetics and electron efficiency. Stress resistance test in real groundwater matrix and life cycle analysis (LCA) was conducted to further verify the application potential of these composites.

Construction of ZIF-derived CoCrOx/HZSM5 catalysts for deep catalytic oxidation of dichloromethane: Synergistic of B acid, L acid, and redox sites

The acidic and oxidizing properties of the catalyst are critical for the removal of chlorinated volatile organic compounds (CVOCs). An excellent catalyst often requires outstanding chlorine resistance and byproduct inhibition. In this study, CoOx, which is widely used for the removal of volatile organic compounds (VOCs) because of its outstanding activity was chosen to provide oxidizing properties. To address the potential for chlorination byproducts and the lack of activity, we loaded CoOx on the acidic carrier HZSM-5 by ZIF-derived method, then doped CrOx using impregnation method to enhance both oxidation and acidity. It was found that ZIF-derived method disperse CoOx nicely thus providing more oxidation sites. Besides, CrOx effectively increases the superficial lattice oxygen of the catalyst to compensate for the loss of sites due to the occupation of oxygen vacancies by DCM during the oxidation process. This contributes to the superior oxidizability of the modified catalysts, which explains the high CO2 selectivity. Invigoratingly, CrOx can increase the ratio of Lewis acid to Brønsted acid to completely break the C–Cl bond, hence eliminating the possibility of chlorine-containing byproducts and accomplishing a deeper degradation of CVOCs. The bimetallic catalysts we prepared have high activity and can achieve very low or even zero byproduct generation. In addition, the catalyst shows outstanding stability and water resistance, which is quite meaningful in the field of catalytic oxidation of CVOCs.