Dechlorination Process Research Articles

Nitrogen and sulfur metabolism in anaerobic hydrogen-producing microbiome as a challenge for 2,4-DCP dechlorination

This research aimed to assess the effectiveness of anaerobic hydrogen-producing microbiomes (HMb) in treating different concentrations of 2,4-dichlorophenol (2,4-DCP) under controlled conditions. The dechlorination experiments were conducted at 41°C in 120-mL vials using a rotary culture device to ensure thorough mixing. The study focused on dechlorination kinetics and efficiency, dynamic changes in the nitrogen-sulfur cycle, and the impact of organic carbon availability. Results indicated that at concentrations below 50 mg/L, HMb achieved a maximum dechlorination rate (Rm) of about 0.7 mg/L-day, which declined to 0.3 mg/L-day at 100 mg/L, suggesting inhibition at higher concentrations. Over 180 days, NH4+-N concentrations decreased, while NO3--N fluctuated, highlighting complex nitrogen transformations influenced by carbon supply and microbial activity. Sulfate concentrations significantly declined in the first 60 days due to sulfur-oxidizing bacteria, including nitrogen-reducing sulfur-oxidizing bacteria (NR-SOB), which promoted anaerobic hydrogen production. Firmicutes increased from 19.5 % to 69.2 %, while Actinobacteria decreased from 73.0 % to 26.8 %, showing response to environmental conditions. The study highlights HMb's potential in bioremediation, enhancing dechlorination processes for environmental and renewable energy benefits.

Boosted electrochemical reduction detoxification and oxidation of clofibric acid by polymerized ionic liquid functionalized cathode: Parameter optimization and degradation mechanisms

The application of electrocatalytic degradation technology in the treatment of pharmaceuticals and personal care products (PPCPs) has attracted widespread attention currently. Through structure and properties characterization of catalysts we found that more uniformly distributed metal particles and excellent thermal stability were obtained by modification with poly(1-vinyl-3-butylimidazole hexafluorophosphate) ([(PV)BIM]PF6) on graphene to anchor the metal CoNi nanoparticles (CoNi/PILs-rGO). For assessing its application potential, the CoNi/PILs-rGO cathode in combination with Ti/RuO2/IrO2 anode to set up an experimental reaction system for the electrocatalytic degradation of clofibric acid (CA) simulated wastewater. Reactor settings for experimentation are optimized, and intermediates, alterations in toxicity during degradation, and active species are detected. The results of the single-factor experiment showed that the average removal rate of CA by the cathodic compartment was 97.18 % when the conditions were optimal. Two possible pathways of degradation are deduced from the CA intermediates, one is the C-Cl bond breaking in electrochemical reduction, and the other is that the C-O bond is directly broken by anodic reactive oxygen. Toxicity tests have shown that the anode produces some by-products that are more hazardous than the original chemical, while the cathode produces a dechlorination process that is ultimately more detoxifying.

Gamma irradiation-induced degradation of hexachlorobenzene in methanol: Kinetics, mechanism and dehalogenation pathway

Hexachlorobenzene (HCB), a persistent organic pollutant (POP) and organochlorine compound (OCC), poses significant environmental and health risks due to its high stability and solubility in fats, oils, and organic solvents. This study investigates the degradation of HCB in methanol using gamma irradiation with a60Co source. A 2 × 10−4 M solution of HCB in methanol was prepared and irradiated at a dose rate of 1.74 Gy/s. The degradation process was monitored using Gas Chromatography-Mass Spectrometry (GC-MS), with optimized parameters for effective separation and analysis of byproducts.The results demonstrated a 100% degradation of HCB at an absorbed dose of approximately 51 kGy. The degradation pathway involved successive dechlorination, forming various chlorinated benzene (CB) byproducts such as pentachlorobenzene (PCB), tetrachlorobenzenes (TeCB), trichlorobenzenes (TCB), dichlorobenzenes (DCB), and ultimately benzene.Ion chromatography (IC) analysis revealed a dose-dependent increase in Cl⁻ concentrations, confirming the efficiency of dechlorination. A chlorine mass balance was performed to evaluate the distribution of chlorine during the degradation process, tracking Cl⁻ ions, CBs, and residual HCB. As the dose increases, the chlorine content in residual HCB decreases significantly, with none remaining at 50.2 kGy and beyond. At 169.5 kGy, nearly all chlorine (99.96%) is unaccounted for, suggesting that it has likely been released as gaseous byproducts, such as Cl₂ or other volatile chlorinated compounds.The formation of solvated electrons and hydrogen radicals initiated the dechlorination process, as evidenced by the identified reaction mechanisms. Kinetic analysis indicated that the degradation followed pseudo-first-order kinetics, with a rate constant of 5 × 10−4 s−1. The study also outlines a dose-dependent trend in radiation chemical yields (G values), initially increasing to a peak of 7.3 × 10−2 molecules per 100 eV at 12.6 kGy and subsequently decreasing to as low as 5.4 × 10−4 at 50.2 kGy.This study highlights the effectiveness of gamma irradiation for the complete degradation of HCB in methanol, offering a promising method for the remediation of POPs-contaminated environments. The proposed mechanism and kinetic properties provide a comprehensive understanding of the radiolytic degradation process, paving the way for further applications in environmental cleanup technologies.

Analyzing Dehalochip: A functional DNA microarray for reductive dichlorination in chloroethene-contaminated sites

Interpreting high-throughput transcriptomic and metagenomic data from non-model microorganisms presents a challenge due to the significant number of genes with unknown functions and sequences. In this study, we applied an innovative microarray, Dehalochip, for detecting the expression of genes in various microorganisms, particularly focusing on genes involved in chloroethene degradation. Our results demonstrated that this approach can effectively identify dechlorination genes, such as 16S rRNA, tceA, bvcA, and vcrA, in Dehalococcoides mccartyi from samples of groundwater contaminated with chloroethene. Noticeably, the sensitivity and specificity of our Dehalochip are comparable to that of quantitative PCR. However, it stands out as a more viable option for in-situ applications due to its greater capacity to infer potential dechlorination genes. Consequently, we believe our dechlorination microarray offers valuable insights into the role of known microorganisms and their associated functional genes in chloroethene-contaminated environments. This contributes to a deeper understanding of the in-situ reductive dechlorination process.

PVC Dechlorination for Facilitating Plastic Chemical Recycling: A Systematic Literature Review of Technical Advances, Modeling and Assessment

Polyvinyl chloride (PVC) resins are widely used in modern society due to their acid and alkali resistance, low cost, and strong insulation properties. However, the high chlorine (Cl) content in PVC poses significant challenges for its recycling. This study reviews the treatment processes, model construction, and economic and environmental assessments to construct a methodological framework for the sustainable development of emerging dechlorination technologies. In terms of treatment processes, this study summarizes three types of processes, pretreatment, simultaneous dechlorination during chemical recycling, product purification, and emphasizes the necessity of dechlorination treatment from a systematic perspective. Additionally, the construction of models for dechlorination processes is investigated from the laboratory to the industrial production system to macro-scale material, in order to evaluate the potential inventory data and material metabolism behaviors. This review also summarized the methodology framework of Techno-Economic Analysis (TEA) and Life Cycle Assessment (LCA), which can be applied for evaluation of the economic and environmental performance of the dechlorination processes. Overall, this review provides readers with a comprehensive perspective on the state-of-the-art for PVC dechlorination technologies, meanwhile offering sustainable guidance for future research and industrial applications of chemical recycling of PVC waste.

Oxygen-Controlled Electrocatalysis for Selective Dechlorination of 2-Chloro-5-Trichloromethyl Pyridine on Activated Ag Electrode

Electrochemical selective dechlorination can be regarded as one of the most promising strategies for generating high-valued chemicals. In the electrochemical dechlorination process of 2-chloro-5-trichloromethylpyridine (TCMP), except the anticipated dechlorination products involving 2-chloro-5-dichloromethylpyridine (DCMP), 2-chloro-5-chloromethylpyridine (CCMP), and 2-chloro-5-methylpyridine (CMP), some unexpected oxygen-incorporated products (6-chloronicotinic acid (CNA) and 6-chloronicotinoyl methyl ester (MCN)) can be obtained. Consequently, understanding the electrochemical dechlorination behavior of TCMP is crucial. Our research revealed that the activated Ag electrodes in halide ion solution exhibit enhanced electrochemical activities for electrochemical dechlorination of TCMP, compared with the pure Ag owing to the increased active specific surface areas and charge transfer. Second, oxygen participation in the reaction is a necessary condition for the formation of oxygen-incorporated products. A 100% selectivity of oxygen-incorporated products can be obtained at the potential of −0.6 V vs Ag/AgCl. Conversely, insufficient oxygen may lead to the potential becoming the determining condition that affects the reaction pathways. A more negative potential (−1.2 V vs Ag/AgCl) is conducive to the formation of dechlorination products with 94.2% conversion and 100% selectivity. This study, for the first time, elucidates the electrocatalyst, atmosphere, and potential-dependent activity and selectivity for the two dechlorination pathways of TCMP.

Electron beam synergetic removal of microplastics and hexavalent chromium: Synergetic removal process and mechanism

Microplastics are ubiquitous in the environment and aged microplastics are highly susceptible to absorbing pollutants from the environment. In this study, electron beam was innovatively used to treat PVC composite Cr(VI) pollutants (Composite contaminant formed by polyvinyl chloride microplastics with the heavy metal hexavalent chromium). Experiments showed that electron beam was able to achieve synergistic removal of PVC composite Cr(VI) pollutants compared to degrading the pollutants alone. During the electron beam removal of PVC composite Cr(VI) pollutants, the reduction efficiency of Cr(VI) increased from 57% to 92%, Cl− concentration increased from 3.52 to 12.41 mg L−1, and TOC concentration increased from 16.72 to 26.60 mg L−1. The research confirmed that electron beam can effectively promote the aging degradation of PVC, alter the physicochemical properties of microplastics, and generate oxygen-containing functional groups on the surface of microplastics. Aged microplastics enhanced the adsorption capacity for Cr(VI) through electrostatic and chelation interactions, and the adsorption process followed second-order kinetics and the Freundlich model. Theoretical calculations and experiments demonstrated that PVC consumed oxidizing free radical through dechlorination and decarboxylation processes, generating inorganic ions and small organic molecules. These inorganic ions and small organic molecules further reacted with oxidizing free radical to produce reducing free radicals, facilitating the reduction of Cr(VI). Cr(VI) continuously consumed the educing free radicals to transform into Cr (Ⅲ), enhancing the system oxidative atmosphere and promoting the oxidation degradation of PVC. This study investigated the formation and synergistic removal processes of PVC composite pollutants, offering new insights for controlling microplastics composite pollution.

Highly efficient removal of 1,1,1-trichloroethane from simulated groundwater by polydopamine-modified iron/polylactic acid/biochar composite coupling with Shewanella oneidensis MR-1

Biochar (BC) loaded with nanoscale zero-valent iron (nZVI) has been extensively used to remove chlorinated hydrocarbons from groundwater through biotic/abiotic reductive dechlorination. However, the rapid deactivation due to surface passivation, hydrophobicity, and inadequacy of carbon sources severely limits its practical application. Herein, a novel polydopamine (PDA)-modified iron/polylactic acid (PLA)/biochar composite (PDA@OBC-nZVI) was successfully synthesized to address this issue. Its effect and mechanism for 1,1,1-trichloroethane (1,1,1-TCA) removal from simulated groundwater coupling with Shewanella oneidensis MR-1 (MR-1) were investigated. Results showed that nZVI and PLA particles were uniformly dispersed on the BC surface, being smoother after PDA coating. The composite coupling with MR-1 exhibited efficient and long-term performances for 1,1,1-TCA removal. Under the experimental conditions comprising 10 % PLA mass fraction in the composite, 10 g·L−1 composite dosage and 20 mL·L−1 MR-1 inoculum volume, 83.14 % of 100 mg·L−1 1,1,1-TCA was removed by PDA@OBC-nZVI + MR-1 within 360 h, compared to only 48.12 % by PDA@OBC-nZVI alone. The primary removal pathways included the rapid chemical reductive dechlorination and the long-term microbial dissimilatory iron reduction. The synergistic dechlorination mechanism was manifested in the composite providing sustained carbon sources, accelerating electron transfer, raising sorbed Fe(II) level, and promoting cytochrome c secretion by MR-1. The novelty of this study is enhancing the hydrophilicity and redox activity of carbon-iron composites by PDA modification for the first time in 1,1,1-TCA removal. Overall, the results suggest that PDA@OBC-nZVI + MR-1 can effectively promote the reductive dechlorination process, being great potential for the remediation of chlorinated hydrocarbon-contaminated groundwater.

Synergy of atomic hydrogen reduction and reactive oxygen species oxidation over confined Mn bifunctional site for electrocatalytic deep mineralization

Traditional reduction or oxidation processes generating one−component free radicals face challenges in deep dechlorination and mineralization of chlorophenols from wastewater. Herein, an efficient electrocatalytic process has been developed, which couples atomic H* reduction with reactive oxidation species (•OH and 1O2) oxidation on a bifunctional cathode for 4 −chlorophenol (4 −CP) removal. The N − doped carbon nanotubes encapsulated manganese nanoparticles was fabricated as cathode, which could generate atomic H* , initiating nucleophilic hydrodechlorination in presence of confined MnO sites. Subsequently, electrophilic oxidation by generating mainly 1O2 on confined Mn7C3 sites and •OH on confined MnO sites, facilitating the oxidative processes. Experimental results and theory calculations demonstrated that reductive dechlorination and oxidative mineralization processes could mutually promote each other, resulting in an enhancement factor of 2.90. At pH 7, this process achieved 100 % removal for 4 −CP, 84 % dechlorination, 76 % total organic carbon (TOC) removal and low energy consumption (0.76 kWh g−1TOC) within 120 min. Notably, TOC for chlorophenols containing Cl substituents at different positions and real lake water containing 4 −CP could be almost completely removed. This research establishes confined non−noble bifunctional active sites that synergistically enhance reductive dechlorination and oxidative degradation processes, holding significant treatment potential for application in deep mineralization of organochlorine from water/wastewater.

Polydopamine-modified biochar supported polylactic acid and zero-valent iron affects the functional microbial community structure for 1,1,1-trichloroethane removal in simulated groundwater

In-situ enhanced bioreduction by functional materials is a cost-effective technology to remove chlorinated hydrocarbons in groundwater. Herein, a novel polydopamine (PDA)-modified biochar (BC)-based composite containing nanoscale zero-valent iron (nZVI) and poly-l-lactic acid (PLLA) (PB-PDA-Fe) was synthesized to enhance the removal of 1,1,1-trichloroethane (1,1,1-TCA) in simulated groundwater with actual site sediments. Its impact on functional microbial community structure in system was also investigated. The typical characterizations revealed uniform dispersion of PLA and nZVI particles on the BC surface, being smoother after PDA coating. The composite exhibited a significantly higher performance on 1,1,1-TCA removal (82.38%, initial concentration 100 mg/L) than Fe-PDA and PB-PDA treatments. The diversity and richness of the microbial community in the composite treatment consistently decreased during incubation due to a synergistic effect between PLLA-BC and nZVI. Desulfitobaterium, Pedobacter, Sphaerochaeta, Shewanella, and Clostridium were identified as enriched genera by the composite through DNA-stable isotope probing (DNA-SIP), playing a crucial role in the bioreductive dechlorination process. All the above results demonstrate that this novel composite selectively enhances the activity of microorganisms with extracellular respiration functions to efficiently dechlorinate 1,1,1-TCA. These findings could contribute to understanding the responsive microbial community by carbon-iron composites and expedite the application of in-situ enhanced bioreduction for effective remediation of chlorinated hydrocarbon-contaminated groundwater.

Transformation and degradation of tebuconazole and its metabolites in constructed wetlands with arbuscular mycorrhizal fungi colonization

Arbuscular mycorrhizal fungi (AMF) colonization has been used in constructed wetlands (CWs) to enhance treatment performance. However, its role in azole (fungicide) degradation and microbial community changes is not well understood. This study aims to explore the impact of AMF on the degradation of tebuconazole and its metabolites in CWs. Total organic carbon levels were consistently higher with the colonization of AMF (AMF+; 9.63- 16.37 mg/L) compared to without the colonization of AMF (AMF-; 8.79–14.48 mg/L) in CWs. Notably, tebuconazole removal was swift, occurring within one day in both treatments (p = 0.885), with removal efficiencies ranging from 94.10 % to 97.83 %. That's primarily due to rapid substrate absorption at the beginning, while degradation follows with a longer time. Four metabolites were reported in CWs first time: tebuconazole hydroxy, tebuconazole lactone, tebuconazole carboxy acid, and tebuconazole dechloro. AMF decreased the abundance of tebuconazole dechloro in the liquid phase, suggesting an inhibitory effect of AMF on dechlorination processes. Furthermore, tebuconazole carboxy acid and hydroxy were predominantly found in plant roots, with a higher abundance observed in AMF+ treatments. Metagenomic analysis highlighted an increasing abundance in bacterial community structure in favor of beneficial microorganisms (xanthomonadales, xanthomonadaceae, and lysobacter), along with a notable presence of functional genes like codA, NAD, and deaD in AMF+ treatments. These findings highlight the positive influence of AMF on tebuconazole stress resilience, microbial community modification, and the enhancement of bioremediation capabilities in CWs.

Adsorption of tetracycline by hydrochar derived from co-hydrothermal carbonization of polyvinyl chloride and garden waste: Adsorption characteristics and enhancement mechanism

The environmental risk posed by tetracycline (TC) in aquatic environments cannot be overlooked, and hydrochar has shown promising potential for adsorbing and removing TC. This study utilized polyvinyl chloride (PVC) and garden waste (GW) as feedstock, preparing hydrochar through co-hydrothermal carbonization (co-HTC), aiming to investigate its adsorption performance for TC. The results demonstrated that the equilibrium adsorption amount of hydrochar produced via co-HTC (HPG) for TC was increased by 28.11% and 406.03% compared to hydrochar derived from PVC and GW, respectively. The HTC temperature and reaction time were positively correlated with the TC adsorption amount of HPG, but the increase was limited beyond 220 °C and 4 h, while the PVC blending ratio had a minor effect on TC adsorption. Subsequently, the adsorption characteristics of HPG for TC were systematically investigated to clarify the effects of adsorption conditions, environmental factors, and regeneration cycles on the adsorption performance of HPG; and further through the properties characterization of HPG and hydrochar prepared from the individual feedstock, the potential mechanism enhancing TC adsorption in co-HTC was explored. HPG adsorbed TC through the interaction between surface carbonyl groups and TC's π-electrons, while PVC produced carbonyl compounds through dechlorination and intramolecular dehydration during co-HTC. GW facilitated the dechlorination process of PVC and provided a substrate for the linkage of carbonyl compounds. This study revealed the adsorption performance and mechanism of hydrochar derived from co-HTC of PVC/GW for TC, offering insights for utilizing hydrochar from organic waste for antibiotic pollution control.

New insights and reaction mechanisms on ZrO2 (110) surface enhanced catalytic hydrolysis of CFC-12: a density functional theory study.

Freon, a greenhouse gas that contributes to the depletion of the ozone layer, has been the subject of investigation in this study. The catalytic hydrolysis enhancement of CFC-12 by ZrO2 was examined using a density functional theory approach. A detailed reaction mechanism and a new reaction pathway were proposed. The study found that CFC-12 is more likely to be adsorbed on the ZrO2 surface in the CFC-12-TO(F) configuration, while H2O is more likely to be adsorbed on the ZrO2 surface in the H2O-TO(H) configuration. Additionally, H2O replaces CFC-12 on the surface of ZrO2. The hydrolysis of CFC-12 is primarily determined by the first dechlorination process, while the defluorination process is comparatively easier. ZrO2 has a catalytic effect on both dechlorination and defluorination processes, with a more pronounced effect on the former. The production of C-OH bonds is inhibited, which facilitates the dechlorination and defluoridation processes. This work was carried out in the Dmol3 program in the Material Studio 2017, including the geometric structure optimization and energy calculations. The GGA/PBE method was used in this work, along with the DNP basis, spin-polarized set, and DFT-D correction. The possible TSs were guessed based on the linear synchronous transit/quadratic synchronous transit/conjugate gradient (LST/QST/CG) method, and they were further confirmed and reoptimized to ensure that the only one imaginary frequency exists in the TSs.

In situ redox growth of Pd/CuOx for enhanced electrocatalytic degradation of organic chlorides via indirect atomic H* reduction

Efficient utilization of atomic hydrogen (H*) is crucial for electrocatalytic dechlorination. We synthesized a Pd/CuOx cathode by atomic reconstruction to boost H* utilization, creating additional active sites within a biphasic interface. This enhanced H* generation degraded 2,4-dichlorophenoxyacetic acid (2,4-D) with a 96 % removal efficiency at 4 mA cm2 and 1.96 kWh m3 energy consumption. Cyclic voltammetry (CV) showed a 0.009 μmol cm2 increase H* on the Pd/CuOx cathode compared to the pristine Cu cathode. The contribution of H* to the electrocatalytic dechlorination process was further corroborated by scavenging experiments and electron spin resonance investigation. We then evaluated the toxicity of products during the degradation process. Density functional theory calculations revealed that the coordination structure between CuOx and Pd optimized the dissociation of H2O and the free adsorption energy of hydrogen. This research introduces an effective alternative to enhance the H* production for the removal of organochlorine compounds from wastewater.

Characteristics and degradation mechanisms of polychlorinated naphthalenes in surface soil in Yangtze River Delta, China

Both thermal and environmental processes are significant factors influencing the existing characteristics, e.g., congener distributions, and existing levels, of polychlorinated naphthalenes (PCNs) in the environment. Soil plays an important role in the life cycle of PCNs, but degradation of PCNs in soils has never been reported. In this study, we collected surface soil samples from 13 cities in the Yangtze River Delta, which is one of the most crowded areas of China and analyzed the samples for 75 PCNs. The long-range transportation from polluted areas was the major source for PCNs in remote areas, but the PCN profiles in remote areas reported in our previous studies were different from those in human settlement in this study, indicating there is a transformation of PCNs after emissions from anthropogenic activities. Two experiments were then designed to reveal the degradation mechanisms, including influencing factors, products, and pathways, of PCNs in surface soils. Based on the experiments, we found that the major factor driving the losses of PCNs in surface soils was volatilization, followed by photo irradiation and microbial metabolism. Under photo-irradiation, the PCN structures would be destroyed through a process of dechlorination followed by oxidation. In addition, the dechlorination pathways of PCNs have been established and found to be significantly influenced by the structure-related parameters.

Boosting peroxymonosulfate activation over partial Zn-substituted Co3O4 for florfenicol degradation: Insights into catalytic performance, degradation mechanism and routes

Florfenicol (FLO) is a broad-spectrum halogenated antibiotic (containing F and Cl atoms), and the discharged FLO in wastewater exhibits potential biotoxicity. Peroxymonosulfate (PMS) activation can generate reactive oxygen species (ROSs) to realize efficient degradation of organic pollutants. Herein, Zn-substituted Co3O4 (ZnxCo) catalysts were prepared and applied in PMS activation for FLO degradation. The physicochemical properties were systematically studied by combining experiments and density functional theory (DFT) calculation. The Zn partial substitution induced electron rearrangement and promoted oxygen vacancy (OV) formation in Co3O4. Zn0.03Co catalyst exhibited superior FLO removal, achieving a higher reaction rate of 0.112 min−1 than Co3O4 (0.053 min−1). The FLO degradation was highly dependent on the factors of PMS/Zn0.03Co/FLO dosage, temperature, initial pH, and coexisting inorganic anions. The Zn0.03Co also displayed outstanding performance in PMS activation for degradation of various typical organic pollutants. Electron paramagnetic resonance (EPR) spectra and quenching experiments indicated that both radical species (·OH, SO4·-, and ·O2-) and nonradical species (1O2) contribute to FLO removal. The redox cycle of Co3+/Co2+ and OVs played an essential role in PMS activation. The electron structure of FLO and parameters of PMS adsorbed on ZnxCo were calculated. The longer length of CoO and OO bonds for the adsorbed PMS could enhance its activation to generate ROSs. The intermediates were detected, and five degradation pathways were proposed. The acute and chronic toxicities of intermediates suggested that the dechlorination process is important for the toxicity attenuation of FLO. This study clarified the performance enhancement mechanism of Zn substitution on FLO degradation by PMS activation using Co3O4 based catalyst, which favors the development of PMS-based advanced oxidation processes for wastewater treatment.

Unveiling Low Temperature Assembly of Dense Fe-N4 Active Sites via Hydrogenation in Advanced Oxygen Reduction Catalysts.

The single-atom Fe-N-C is a prominent material with exceptional reactivity in areas of sustainable energy and catalysis research. It is challenging to obtain the dense Fe-N4 site without the Fe nanoparticles (NPs) sintering during the Fe-N-C synthesis via high-temperature pyrolysis. Thus, a novel approach is devised for the Fe-N-C synthesis at low temperatures. Taking FeCl2 as Fe source, a hydrogen environment can facilitate oxygen removal and dichlorination processes in the synthesis, efficiently favouring Fe-N4 site formation without Fe NPs clustering at as low as 360 °C. We shed light on the reaction mechanism about hydrogen promoting Fe-N4 formation in the synthesis. By adjusting the temperature and duration, the Fe-N4 structural evolution and site density can be precisely tuned to directly influence the catalytic behaviour of the Fe-N-C material. The FeNC-H2-360 catalyst demonstrates a remarkable Fe dispersion (8.3 wt %) and superior acid ORR activity with a half-wave potential of 0.85 V and a peak power density of 1.21 W cm-2 in fuel cell. This method also generally facilitates the synthesis of various high-performance M-N-C materials (M=Fe, Co, Mn, Ni, Zn, Ru) with elevated single-atom loadings.

Dechlorination of a real plastic waste pyrolysis oil by adsorption with zeolites

The adsorptive dechlorination of a pyrolysis oil coming from real plastic waste was investigated using different Na-zeolites (4A, 13X, and Y) as adsorbents. The dechlorination experiments were performed in a fixed bed trap under inert atmosphere operating at moderate temperatures (< 180 °C). The dechlorination efficiency of the adsorbents was significantly improved by performing a dehydration pre-treatment due to the removal of water molecules physisorbed on the zeolite surface. Among the zeolitic materials tested, 13X zeolite showed the best dechlorination efficiency, which was related to its high content of Lewis acid sites (attributed to the presence of Na+ cations ionically interacting with the zeolite framework), acting as chemisorption sites, as well as the high accessibility of the FAU-zeolitic topology to the Cl-containing compounds. For that sample, a detailed study of the adsorption temperature (from 30 to 180 °C) and time on stream (1–6 h) was further carried out. The maximum chlorine removal efficiency was achieved, reducing the chlorine content of the pyrolysis oil from 421 to 45 ppm, at temperatures of about 150 – 180 °C. Interestingly, under these conditions, thermal or catalytic cracking effects of the zeolite on the feedstock were not observed. However, the study of the time on stream showed that, after 3 h, the chlorine removal efficiency of the zeolite started to decrease. Thus, different regeneration treatments were evaluated proving that, after a combustion at 600 °C, the zeolite recovered its initial dechlorination efficiency. This research reveals the potential of the adsorptive dechlorination process with Na-zeolites to reduce the chlorine content in plastic pyrolysis oils under mild operating conditions.

Synergistic algal/bacterial interaction in membrane bioreactor for detoxification of 1,2-dichloroethane-rich petroleum wastewater

The study addressed the challenge of treating petroleum industry wastewater with high concentrations of 1,2-dichloroethane (1,2-DCA) ranging from 384 to 1654 mg/L, which poses a challenge for bacterial biodegradation and algal photodegradation. To overcome this, a collaborative approach using membrane bioreactors (MBRs) that combine algae and bacteria was employed. This synergistic method effectively mitigated the toxicity of 1,2-DCA and curbed MBR fouling. Two types of MBRs were tested: one (B-MBR) used bacterial cultures and the other (AB-MBR) incorporated a mix of algal and bacterial cultures. The AB-MBR significantly contributed to 1,2-DCA removal, with algae accounting for over 20% and bacteria for approximately 49.5% of the dechlorination process. 1,2-DCA metabolites, including 2-chloroethanol, 2-chloro-acetaldehyde, 2-chloroacetic acid, and acetic acid, were partially consumed as carbon sources by algae. Operational efficiency peaked at a 12-hour hydraulic retention time (HRT) in AB-MBR, enhancing enzyme activities crucial for 1,2-DCA degradation such as dehydrogenase (DH), alcohol dehydrogenase (ADH), and acetaldehyde dehydrogenase (ALDH). The microbial diversity in AB-MBR surpassed that in B-MBR, with a notable increase in Proteobacteria, Bacteroidota, Planctomycetota, and Verrucomicrobiota. Furthermore, AB-MBR showed a significant rise in the dominance of 1,2-DCA-degrading genus such as Pseudomonas and Acinetobacter. Additionally, algal-degrading phyla (e.g., Nematoda, Rotifera, and Streptophyta) were more prevalent in AB-MBR, substantially reducing the issue of membrane fouling.

Carboxymethyl cellulose stabilization induced changes in particle characteristics and dechlorination efficiency of sulfidated nanoscale zero-valent iron

Polymer stabilization, exemplified by carboxymethyl cellulose (CMC), has demonstrated effectiveness in enhancing the transport of nanoscale zero-valent iron (nZVI). And, sulfidation is recognized for enhancing the reactivity and selectivity of nZVI in dechlorination processes. The influence of polymer stabilization on sulfidated nZVI (S-nZVI) with various sulfur precursors remains unclear. In this study, CMC-stabilized S-nZVI (CMC-S-nZVI) was synthesized using three distinct sulfur precursors (S2−, S2O42−, and S2O32−) through one-step approach. The antioxidant properties of CMC significantly elevated the concentration of reduced sulfur species (S2−) on CMC-S-nZVIs, marking a 3.1–7.0-fold increase compared to S-nZVIs. The rate of trichloroethylene degradation (km) by CMC-S-nZVIs was observed to be 2.2–9.0 times higher than that achieved by their non-stabilized counterparts. Among the three CMC-S-nZVIs, CMC-S-nZVINa2S exhibited the highest km. Interesting, while the electron efficiency of CMC-S-nZVIs surged by 7.9–12 times relative to nZVI, it experienced a reduction of 7.0–34% when compared with S-nZVIs. This phenomenon is attributed to the increased hydrophilicity of S-nZVI particles due to CMC stabilization, which inadvertently promotes the hydrogen evolution reaction (HER). In conclusion, the findings of this study underscores the impact of CMC stabilization on the properties and dechlorination performance of S-nZVI sulfidated using different sulfur precursors, offering guidance for engineering CMC-S-nZVIs with desirable properties for contaminated groundwater remediation.