Direct Electron Transfer Mechanism Research Articles

Carbon dioxide radical anion mediated dehalogenation kinetics and mechanisms of halogenated alkanes

Carbon dioxide radical anion (CO2•−) recently becomes appreciated in halogenated contaminants elimination; nevertheless, its application has been restricted by insufficient mechanistic understanding. Herein, we provided a quantitative insight into the kinetics and mechanisms of CO2•− mediated dehalogenation of halogenated alkanes. A CO2•− dominated UV254/H2O2/HCOO− system has been successfully established and demonstrated for effective elimination of 7 kinds of halogenated alkanes (71.3 % to 100 % of removal). Using a laser flash photolysis technology, the second-order rate constants of CO2•− (kCO2•−″) reacting with CCl4, CHCl3 and CH2Cl2 were firstly reported, to be 2.5 × 108, 6.2 × 107 and 5.8 × 106 M−1s−1, respectively. kCO2•−″ presented a significant negative correlation with the lowest unoccupied molecular orbital energy (ELUMO) of chlorinated alkanes, proving that the enhanced dehalogenation of CO2•− was attributed by direct electron transfer mechanism. A fitting model was developed accordingly for kCO2•−″ prediction. This study also demonstrated that the CO2•− mediated ARP effectively removed halogenated alkanes regardless of pH condition (6.0∼9.0) and bicarbonate concentrations. These findings are significant in advancing the scientific understanding of CO2•− mediated ARP. This reductive process a promising control strategy for halogenated contaminants, such as polyfluoroalkyl substances (PFAS) and halogenated pharmaceuticals.

Residence Time Reduction in Anaerobic Reactors: Investigating the Economic Benefits of Magnetite-Induced Direct Interspecies Electron Transfer Mechanism

Existing research on direct interspecies electron transfer (DIET) has predominantly focused on the types and concentrations of conductive materials across diverse anaerobic digestion. However, insufficient understanding of the impact of residence time, a critical economic factor, prompted this investigation. Magnetite, a conductive material, was introduced into the anaerobic digestion of food wastewater, leading to a significant increase in ultimate methane production (Bu) with 25 mM-Fe3O4 (p < 0.05). Despite a subsequent decline in methane production efficiency from 388.9% to 7.1% over the 15- to 65-day anaerobic digestion period, the initial impact of increased methane production due to magnetite addition was evident. Control’s maximum methane production rate (Rm) was 27.5 mL/day, reaching its highest point at 37.4 mL/day with 15 mM-Fe3O4, accompanied by a noteworthy 56.6% reduction in the attainment day of Rm (Rm-day), shortened to 8.2 days. Even with 100 mM-Fe3O4, while Bu showed no significant difference, Rm-day exhibited a substantial reduction of 22.8. Despite the lower overall anaerobic digestion efficiency under some magnetite input conditions, this study confirmed a substantial shortening of Rm-day, suggesting that the DIET mechanism induced by conductive materials such as magnetite could reduce the residence time in continuous-type anaerobic reactors, contributing to improved economic feasibility.

Synthesis, characterization, optimization and application of Pisum sativum peels S and N-doping biochars in the production of biogas from Ulva lactuca

This study assessed the usefulness of Pea Pisum sativum peels S-modified biochar (PPB–S) and Triethylenetetramine (TETA)-modified biochar (PPB-T) as improvers for biogas generation from green algae Ulva lactuca either individually or co-digested with Pea peels (PPs). BET, FTIR, TGA, XRD, XPS, SEM coupled with EDX were used to characterize the PPB-S and PPB-T biochars. EDX, FTIR, and XPS analyses proved the formation of sulphur and nitrogen groups on the surface of PPB-S and PPB-T. The kinetic study confirmed that the modified Gompertz model fits the experimental data satisfactorily, with R2 ranging between 0.948 and 0.991. The results suggested that adding 50 mg/L of PPB-S significantly increased the biogas production yield compared to all other studied treatments, either individually or in co-digestion with PPs. The extreme biogas production (498 mL/g VS) was formed when 50 mg/L of PPB-S was added to U. lactuca. According to Response surface methodology (RSM), the maximum biogas production among all experiments is 460.91 (ml/g VS), achieved for U. lactuca and PPB-S treatment corresponds to 54 days contact time and 50 mg/L of PPB-S dose. The direct electron transfer mechanism has been investigated in detail, and it is confirmed that conductive PPB-S can support electron transfer and promote methane production, as proved by the XPS and FTIR analyses, which the creation of sulphur groups on the PPB-S surface may propose. In this study, the use of PPB-S in biogas production aligns with the principles of a circular economy.

Porous pie-like nitrogen-doped biochar as a metal-free peroxymonosulfate activator for sulfamethoxazole degradation: Performance, DFT calculation and mechanism

Design and development of low-cost, high-efficient, metal-free persulfate heterogeneous catalysts was a hot research topic. Herein, porous pie-like nitrogen-doped biochar (NBC) was prepared by one step high temperature pyrolysis of rape straw, urea and ZnCl2 mixture, and applied for peroxymonosulfate (PMS) activation toward sulfamethoxazole (SMX) degradation. Among these as-prepared catalysts, the NBC2.0 sample presented the best catalytic activity, with the 99.8 % SMX degradation efficiency in 5 mins and the 81.7 % total organic carbon (TOC) removal rate in 30 mins. Additionally, it could realize an excellent SMX degradation in the wide pH range of 3.0 to 9.0, and possessed the high degradation efficiency in presence of various organic pollutants or in real water environments, indicating its good pH adaptability, universality and practicality. Mechanistic investigations disclosed that the NBC2.0/PMS/SMX system involved both radical and non-radical degradation pathways, with singlet oxygen (1O2) and the direct electron transfer mechanism being the main contributors. The main active reaction sites of NBC were graphitic N, pyridinic N and C = O group, as corroborated by density functional theory (DFT) calculation and X-ray photoelectron spectroscopy (XPS) measurement. The possible SMX breakdown routes were determined by intermediate identification. This work provides a promising metal-free persulfate catalyst for environment remediation.

Promotion of Direct Electron Transfer to Cytochrome c by Functionalized Thiophene‐based Conducting Polymers

AbstractControlling direct electron transfer (DET) to redox proteins is of great interest for fundamental studies on biochemical processes and the development of biotechnological devices, such as biosensors or enzymatic fuel cells. Cytochrome c is a classical model protein for studying DET reactions that plays a key role in the onset of cellular apoptosis and the mitochondrial respiratory chain. In this contribution, we explored DET between cyt c and conducting polymers bearing the chemical structure of thiophene, specifically PEDOT, and its OH‐containing derivative, PHMeEDOT. The combination of electrochemistry and in situ FTIR spectroscopy allowed us to gain more insight into the inner mechanism of DET at physiological pH. Hydrophilic interactions favour the correct orientation of the heme crevice of cytochrome c towards the polymer surface. When a positive charge is injected into the conducting polymer, the increasing electrostatic repulsion between protein and surface induces the desorption of lysine residues near the heme group and stimulates protein flipping. This effect was more pronounced at PEDOT‐ than PHMeEDOT‐modified electrodes since the latter shows stronger interactions with lysine residues, partially hindering protein rotation at moderate potential. The potential‐induced reorientation process was similar on both polymer surfaces, only at high positive potentials.

Promoted degradation of tetracycline by FeNi alloys embedding in biochar activating peroxydisulfate: Performance and mechanism

Bimetallic FeNi alloys embedding into biochar (FeNi-BC) catalysts with different Fe/Ni molar ratio were fabricated using rose petal as biomaterials. The as-fabricated FeNi-BC was employed to activate peroxydisulfate (PDS) toward tetracycline (TC) degradation. The effects of Fe/Ni atomic ratio on the structure feature of FeNi-BC and PDS activation efficiency were explored in detail. Results show that the optimum Fe0.8Ni0.2-BC prepared with Fe/Ni molar being 8:2 exhibited the best PDS activation efficiency toward TC degradation, with 97.01% of TC being removed in 15 min. Combining with the electron paramagnetic resonance (EPR), reactive oxygen species quenching, and electrochemical tests, the direct electron transfer (DET) and singlet oxygen accounted for TC degradation in the Fe0.8Ni0.2-BC activating PDS system. Because of that, the Fe0.8Ni0.2-BC had satisfactory resistance to inorganic anions and natural organic matters (NOMs). Based on the structure-activity relationship, it was found that more Fe0 and pyrrolic N formation in FeNi alloys than single Fe or Ni embedding in BC facilitated in more PDS adsorption, thus more PDS* complex formation on the surface of catalysts to boost the TC degradation through DET mechanism. Moreover, Fe0.8Ni0.2-BC possessed trace Fe and Ni leaching, satisfactory stability, and easy recycling via magnetic separation. This study not only offers new insights for discriminating the catalytic active sites of biochar embedded bimetallic alloys catalysts activating PDS but also developed cost-effective and environment friendly catalysts for high-efficiently remove antibiotics via PS-AOPs.

Oxidation of tetracycline hydrochloride by peroxomonosulfate and peroxodisulfate on a ZnNi@NC carbonaceous catalyst: Role of non-radical species and mediated or direct electron transfer mechanisms

This study investigated the activation pathways of peroxomonosulfate (PMS) and peroxodisulfate (PDS) on a metal-based carbon catalyst (ZnNi@NC) for the degradation of tetracycline hydrochloride (TC). ZnNi@NC was synthesized via pyrolysis of metal-organic frameworks (MOFs), which yielded Ni species encapsulated in a Ni3ZnC0.7 layer and N,O-doped graphitic carbon nanotubes. The catalytic performance of ZnNi@NC in PMS and PDS activation for TC degradation was found to be excellent. The ZnNi@C/PMS and ZnNi@C/PDS systems successfully degraded 13 mg of TC within 100 min. We complemented these results with quenching experiments and utilized characterization techniques, such as electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopy (FTIR), to verify the activation of PMS and PDS, leading to the production of singlet oxygen and the formation of a surface-active complex. Additionally, our research demonstrated that ZnNi@NC facilitated electron transfer between surface-active PDS and adsorbed TC, as confirmed through electrochemical analytical characterization. Further insights from scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) revealed that active sites, including graphitic N and pyrrolidinic N species, played a pivotal role in singlet oxygen generation. Specifically, PMS activated through a direct electron transfer pathway, while PDS employed an indirect electron transfer pathway. Furthermore, the study emphasized that the N,O-doped graphitic carbon framework played a key role in the formation of surface-activated PMS/PDS. In conclusion, this work provides novel insights into the distinct functionalities of Ni-based carbon catalysts in persulfate activation.

Genomic Insights into Syntrophic Lifestyle of 'Candidatus Contubernalis alkaliaceticus' Based on the Reversed Wood-Ljungdahl Pathway and Mechanism of Direct Electron Transfer.

The anaerobic oxidation of fatty acids and alcohols occurs near the thermodynamic limit of life. This process is driven by syntrophic bacteria that oxidize fatty acids and/or alcohols, their syntrophic partners that consume the products of this oxidation, and the pathways for interspecies electron exchange via these products or direct interspecies electron transfer (DIET). Due to the interdependence of syntrophic microorganisms on each other's metabolic activity, their isolation in pure cultures is almost impossible. Thus, little is known about their physiology, and the only available way to fill in the knowledge gap on these organisms is genomic and metabolic analysis of syntrophic cultures. Here we report the results of genome sequencing and analysis of an obligately syntrophic alkaliphilic bacterium 'Candidatus Contubernalis alkaliaceticus'. The genomic data suggest that acetate oxidation is carried out by the Wood-Ljungdahl pathway, while a bimodular respiratory system involving an Rnf complex and a Na+-dependent ATP synthase is used for energy conservation. The predicted genomic ability of 'Ca. C. alkaliaceticus' to outperform interspecies electron transfer both indirectly, via H2 or formate, and directly, via pili-like appendages of its syntrophic partner or conductive mineral particles, was experimentally demonstrated. This is the first indication of DIET in the class Dethiobacteria.

Combined effects of various conductive materials and substrates on enhancing methane production performance

The addition of conductive materials (CMs) to anaerobic digestion (AD) has recently been receiving considerable attention as it could improve the rate of methane production through the direct interspecies electron transfer (DIET) mechanism. Although several DIETs via CMs have been studied, research directly comparing the effects of different CM additions under the same experimental conditions remains limited and no studies till date that consider the combined effects of substrate together with CM additions. In this study used three different CMs; granular activated carbon (GAC), multi-walled carbon nanotubes (MWCNT), and polyaniline (PANI) to evaluate their effect on methane production in two sets of studies, one using sodium propionate and the other using ethanol as substrates. The results showed that when sodium propionate was used, there were no changes observed in the methane production rate, despite the addition of CM. Contrastingly, when ethanol was used, methane production was enhanced, where GAC, MWCNT, and PANI were 2.3, 1.9. and 1.2 times faster than the control, respectively. Furthermore, microbial analysis indicated that when ethanol substrate was used, there was an increase in Geobacteraceae, which contributes to the DIET. The order of Geobacteraceae abundance (GAC > MWCNT > PANI > Control) corresponded with a higher rate of methane production, implicating that abundance of Geobacteraceae could directly improve the AD performance. These results show that the combined effect of substrate and CM is very important for DIET to improve AD performance, and that ethanol as substrate with GAC as CM are the most effective combination.

Carbon nitride with a tailored electronic structure toward peroxymonosulfate activation: A direct electron transfer mechanism for organic pollutant degradation

The persulfate-based nonradical reaction process has gained increasing attention in removing organic contaminants, and the process dramatically needs affordable, robust, high-performance heterogeneous catalysts. Herein, dimethyl formamide (DMF) incorporated graphitic carbon nitride (DCN) was synthesized. The molecular engineering of the heptazine unit in DCN improves the electron mobility, strengthens the built-in electric field, and provides abundant active sites, thus enabling DCN to efficiently activate PMS for organic degradation, with 100 % removal of BPA within 12 min. The investigation of the reactive species and electrochemical properties confirmed the direct electron transfer in the PMS activation for organic degradation over DCN. More importantly, DCN can be used as a membrane catalyst in a flowing catalytic unit, enabling continuous water purification and catalyst regeneration. This work provides novel guidance for metal-free catalyst design and profound insights into the persulfate-based heterogeneous catalytic oxidation process for water decontamination technology.

Recycling waste iron-rich algal flocs as cost-effective biochar activator for heterogeneous Fenton-like reaction towards tetracycline degradation: Important role of iron species and moderately defective structures

Harvesting aquatic harmful algal blooms (HABs) and reusing them is a promising way for antibiotic degradation. Herein, a novel iron-rich biochar (Fe-ABC), derived from algal biomass harvested by magnetic coagulation, was successfully designed and fabricated as activator for heterogeneous Fenton-like reaction. The modification methods and pyrolysis temperatures (400–800 °C) were optimized to enhance the formation of rich iron species and moderately defective structure, yielding Fe-ABC-600 with enhanced electron transfer and H2O2 activation capability. Thus, Fe-ABC-600 exhibited superior removal efficiency (95.33%) on tetracycline (TC), where the presence of multiple iron species (Fe3+, Fe2+ and Fe4+) and moderately defective structure accelerating the Fenton-like oxidation. The concentration of leaching Fe after each reaction was all below 0.74 mg/L in five cycles, ensuring the sustained degradation. And •OH was proved to be the major radical contributing to the degradation of TC, as well as the direct electron transfer mechanism together, in which the CO acted as electron regulator and electron donor. Fe-ABC as a cost-effective catalyst has notable application potentials in TC removal from wastewater owing to its remarkable advantages of high resource utilization, enhanced catalytic property, high ecological safe, notable TC degradation efficiency, low cost and environmental-friendliness.

Enhanced ferrate(VI) oxidation of organic pollutants through direct electron transfer

Fe(VI) is a versatile agent for water purification, and various strategies have been developed to improve its pollutant removal efficiency. Herein, it was found that in addition to intermediate iron species [Fe(IV)/Fe(V)], direct electron transfer (DET) played a significant role in the abatement of organic pollutants in Fe(VI)/carbon quantum dots (CQDs) system. Around 86, 83, 73, 64, 52, 45 and 17% of BPA, DCF, SMX, 4-CP, phenol, p-HBA, and IBP (6 μM) could be oxidized by 30 μM of Fe(VI), whereas with the addition of CQDs (4 mg/L), the oxidation ratio of these pollutants increased to 98, 99, 80, 88, 87, 66 and 57%, respectively. The negative impact induced by solution pH and background constituents on Fe(VI) abatement of pollutants could be alleviated by CQDs, and CQDs acted as catalysts for mediating DET from organic pollutants to Fe(VI). Theoretical calculation revealed that iron species [Fe(VI)/Fe(V)/Fe(IV)] was responsible for the oxidation of 36% of phenol, while DET contributed to the oxidation of 64% of phenol in the Fe(VI)/CQDs system. Compared with iron species oxidation, the CQDs mediated DET from pollutants to Fe(VI) was more efficient for utilizing the oxidation capacity of Fe(VI). The DET mechanism presented in the study provides a prospective strategy for improving the pollution control potential of Fe(VI).

Modulating the redox couples of graphene-like NBC-TiO2@FeMn through forming photo-Fenton system for boosting persulfate activation to accelerate the contaminant degradation

The sluggish cycling of redox couples hampers the practical application of catalysts in contaminant degradation. Herein, a novel strategy was introduced by constructing a photo-Fenton system onto the graphene-like NBC to realize the ultrafast modulating of redox couples during the contaminant degradation. The constructed NBC-TiO2@FeMn (NBTF) exhibits a higher proportion of reductive redox couples (Fe (II)/Mn (II)) after the degradation, which is attributable to the photo-Fenton system and the graphene-like NBC with high electron transfer efficiency. Density functional theory (DFT) calculations also confirm that constructing the photo-Fenton system on graphene-like NBC greatly enhances electron transfer, enabling the modulation of redox couples during the degradation process. During activation, various reactive oxygen species (including •OH, SO4•-, high-valent metal oxides, and non-radical pathways) are generated, effectively degrading pulp wastewater Tetrachloroguaiacol (TeCG) with a degradation efficiency of 98.8 % within 14 min. Quenching experiments and EPR spectroscopic analysis indicate that the degradation of TeCG is mainly mediated by hydroxyl radicals (•OH) and sulfate radicals (SO4•-) as predominant pathways, while high-valent metal oxides, 1O2 and direct electron transfer mechanisms act in a cooperative manner. Substitution reaction on active sites reveal that both FeMn LDH and graphene-like NBC are identified as the main active sites, with Mn exhibiting superior PMS activation compared to Fe. A possible degradation pathway of TeCG is proposed, and a decrease in the toxicity of intermediates is observed. This study provides a new perspective on the modulation of redox couples in SR-AOPs to realize sustainable pollutants degradation.

Spatial self-confinement of heterogeneous metallic CoX (X = Cu, Ni, Fe) within laminated porous carbon assemblies to efficiently activate peroxymonosulfate for tetracycline destruction

Sustainable and universal fabrication of carbon-loaded non-precious bimetallic nanocatalysts with tuned catalytic surface sites is crucially important but challengeable toward peroxymonosulfate(PMS)-motivated antibiotic degradation. We propose herein a universal, easily removable and sustainable salt template-mediated spatial self-confinement strategy to fabricate bimetallic nanoparticles deposited onto lamellar porous carbon assemblies for PMS-assisted tetracycline hydrochloride (TCH) destruction. Among CoX@C-600 (X = Cu, Ni, Fe) samples, CoCu@C-600 has the highest catalytic performance with a degradation efficiency of 98.6% and a rate constant of 0.3174 min−1 for TCH degradation via PMS motivation. The synergy between the heterogeneous metallic Co and Cu nanoparticles, unique tertiary pore structure and copious surface-exposed active sites are responsible for the high performance of CoCu@C-600. The magnetically recoverable CoCu@C-600 shows a good separation property and can be reused for five consecutive runs. Experimental and characterization results affirm the radical/non-radical (major active species of SO4•− and 1O2) and direct electron transfer mechanism. The degradation pathways and toxicity evaluation with the CoCu@C-600/PMS system are unveiled. The rational architecture design and catalytic site regulation are inspirable for universal syntheses of efficient catalysts for antibiotic degradation.

Construction of Bi12O17Cl2/ZnO-CN Z-scheme photocatalyst with ZIF-8 as precursor to remove antibiotics and Cr(VI) under visible light: Optimization, mechanism and degradation path

In this work, Bi12O17Cl2 and ZIF-8 were synthesized via a facile in-situ precipitation method, while ZnO-CN was obtained through the pyrolysis of ZIF-8. Then, a novel Bi12O17Cl2/ZnO-CN composite catalyst with Z-scheme heterojunction was prepared by mechanical mixing-low temperature activation method. When the ZnO-CN is pyrolyzed at 550 ℃ and accounts for 10 wt% in the Bi12O17Cl2/ZnO-CN composite, the composite exhibited a significantly higher degradation rate for levofloxacin hydrochloride (LVX) (94.50%) compared to Bi12O17Cl2 (67.30%) and ZnO-CN (36.80%), while also achieving a high removal rate of Cr(VI) under acidic conditions (92.00%). And the toxicity of LVX to wheat decreased significantly after photocatalytic degradation. Meanwhile, the Bi12O17Cl2/ZnO-CN has good universality, salt resistance and reuse stability. The experimental results of sample characterization show that the improved photocatalytic performance of Bi12O17Cl2/ZnO-CN composite can be attributed to the high-efficiency separation of electron-hole pairs (e--h+), enhanced light absorption in the visible region, increased specific surface area and active sites. Both the free radical capture experiment and electron paramagnetic resonance (EPR) test indicate that •O2- and h+ are the primary active species in the process of degrading LVX by Bi12O17Cl2/ZnO-CN. Combined with mechanism exploration experiment and iquid chromatography-mass spectrometry (LC-MS) analysis, a possible direct Z-scheme heterojunction electron transfer mechanism and photocatalytic degradation pathways for LVX was proposed. This work enhances the photocatalytic performance of Bi12O17Cl2 and provides an idea for antibiotic or Cr(VI) wastewater treatment.

Intensifying anaerobic digestion of 5-hydroxymethylfurfural via granular activated carbon supplementation

5-hydroxymethylfurfural (5-HMF) is typically found in hydrolysate produced by thermal pretreatment and wastewater streams, and its presence can significantly inhibit anaerobic digestion (AD) performance. This study comprehensively investigates the impact of adding 1–5 g/L granular activated carbon (GAC) on the AD of 0.5–4 g/L 5-HMF. The innovation of this study is to clarify the mechanism of direct interspecies electron transfer (DIET) in the AD system with 5-HMF as the sole source. Compared to the control group, adding 5 g/L GAC shows the most significant promotion effect, which increases the electron transfer activity of the sludge by 27.0%–75.0% and enhances the methane production peak rate by 27.5%–68.1%. GAC supplementation can rapidly reduce the concentration of 5-HMF by adsorption and alleviate its inhibition of microorganisms. SEM and microbial community analyses show that GAC enriches electroactive microbes and can promote AD by establishing the DIET pathway.

Permanganate activation with Mn oxides at different oxidation states: Insight into the surface-promoted electron transfer mechanism

The development of new strategies to improve the removal of organic pollutants with permanganate (KMnO4) is a hot topic in water treatment. While Mn oxides have been extensively used in Advanced Oxidation Processes through an electron transfer mechanism, the field of KMnO4 activation remains relatively unexplored. Interestingly, this study has discovered that Mn oxides with high oxidation states including γ-MnOOH, α-Mn2O3 and α-MnO2, exhibited excellent performance to degrade phenols and antibiotics in the presence of KMnO4. The MnO4- species initially formed stable complexes with the surface Mn(III/IV) species and showed an increased oxidation potential and electron transfer reactivity, caused by the electron-withdrawing capacity of the Mn species acting as Lewis acids. Conversely, for MnO and γ-Mn3O4 with Mn(II) species, they reacted with KMnO4 to produce cMnO2 with very low activity for phenol degradation. The direct electron transfer mechanism in α-MnO2/KMnO4 system was further confirmed through the inhibiting effect of acetonitrile and the galvanic oxidation process. Moreover, the adaptability and reusability of α-MnO2 in complicated waters indicated its potential for application in water treatment. Overall, the findings shed light on the development of Mn-based catalysts for organic pollutants degradation via KMnO4 activation and understanding of the surface-promoted mechanism.

Peroxymonosulfate and peroxydisulfate activation by fish scales biochar for antibiotics removal: Synergism of N, P-codoped biochar

Social development is accompanied by technological progress, which commonly leads to the expansion of pollution As an essential resource of modern medical treatment, antibiotics have become a hot topic in the aspect of environmental pollution. In this study, we first used fish scales to synthesize N, P-codoped biochar catalyst (FS-BC) as peroxymonosulfate (PMS) and peroxydisulfate (PDS) activator to degrade tetracycline hydrochloride (TC). At the same time, peanut shell biochar (PS-BC) and coffee ground biochar (CG-BC) were prepared as reference materials. Among them, FS-BC exhibited the best catalytic performance due to the excellent defect structure (ID/IG = 1.225) and the synergism of N, P heteroatoms. PS-BC, FS-BC and CG-BC achieved degradation efficiencies of 86.26%, 99.71% and 84.41% for TC during PMS activation and 56.79%, 93.99% and 49.12% during PDS, respectively. In both FS-BC/PMS and FS-BC/PDS systems, non-free radical pathways involved singlet oxygen (1O2), surface-bound radicals mechanism and direct electron transfer mechanism. Structural defects, graphitic N and pyridinic N, P–C groups and positively charged sp2 hybridized C adjacent to graphitic N were all critical active sites. FS-BC has the potential for practical applications and development because of its robust adaptation to pH and anions and stable re-usability. This study not only provides a reference for biochar selection, but also suggests a superior strategy for TC degradation in the environment.

Carbon, iron, and polymer-based conductive materials for improving methane production in anaerobic wastewater treatment systems: A review on their direct interspecific electron transfer mechanism

Organic compounds in wastewater have a high potential to be converted to (bio)methane (CH4) via anaerobic processes for energy recovery. Facilitating direct interspecies electron transfer (DIET) between microorganisms with the addition of conductive materials, as opposed to the conventional anaerobic biological process, has been viewed as an efficient strategy for boosting the efficiency of CH4 production. In recent years, extensive research has been conducted on the performance, mechanisms, and technical uses of conductive materials, such as carbon, iron and polymer-based materials in anaerobic wastewater treatment systems. In this review, the properties of conductive materials have been comprehensively reviewed and summarized, along with their application strategies to enhance CH4 production. In addition, the paper focuses on the methane production mechanism in anaerobic bioreactors, in the presence of carbon, iron, and polymer-based materials. The DIET theory employed for methane synthesis and the involvement of various organic wastes including ethanol, butyrate, propionate, and complex organic compounds are also elaborated upon. The prospective future research directions were also identified and stated in this review.

Reductive dechlorination of chlorinated ethenes by ball milled and mechanochemically sulfidated microscale zero valent iron: A comparative study

Ball milling is an effective technique to not only activate and reduce the size of commercial microscale zero valent iron (mZVI) but also to mechanochemically sulfidate mZVI. Yet, little is known about the difference between how chlorinated ethenes (CEs) interact with ball milled mZVI (mZVIbm) and mechanochemically sulfidated mZVI (S-mZVIbm). We show that simple ball milling exposed the active Fe0 sites, while mechanochemical sulfidation diminished Fe0 sites and meanwhile increased S2- sites. Mechanochemical sulfidation with [S/Fe]dosed increased from 0 to 0.20 promoted the particle reactivity most for TCE dechlorination (∼14-fold), followed by PCE and 1,1-DCE while it diminished the reactivity for trans-DCE (∼0.4-fold), cis-DCE (∼0.02-fold) and VC (∼0.002-fold) compared to simple ball milling. Sulfidation also improved the electron efficiency of CE dechlorination, except for cis-DCE and VC. The kSA of cis-DCE, VC and trans-DCE dechlorination positively correlated with surface Fe0 content, suggesting their dechlorination was mainly mediated by Fe0 site or reactive atomic hydrogen. The kSA of TCE dechlorination positively correlated with surface S2- content and the dechlorination mainly occurred on S2- sites via direct electron transfer. Increased sulfidation favored direct electron transfer mechanism. The kSA of PCE and 1,1-DCE was not dependent on either parameter and their dechlorination was equally achieved through either mechanism.