Electron Exchange Capacity Research Articles

Multitargeted molecular docking and dynamics simulation studies of 1,3,4-thiadiazoles synthesised from (R)-carvone against specific tumour protein markers: An In-silico study of two diastereoisomers

In the present work, we describe the synthesis of new 1,3,4-thiadiazole derivatives from natural (R)-carvone in three steps including, dichloro-cyclopropanation, a condensation with thiosemicarbazide and then a 1,3-dipolar cycloaddition reaction with various nitrilimines. the targeted compounds were structurally identified by 1H &13C NMR and HRMS analyses. The cytotoxic assay demonstrated that some synthesized novel compounds were potent on certain cancer cell lines. Molecular modeling studies were undertaken to rationalize the wet lab study results. Furthermore, molecular docking was performed to unveil the binding potential of the most active derivatives, 3a and 6c, to caspase-3 and COX-2. The stabilities of the protein-compound complexes obtained from the docking were evaluated using MD simulation. Furthermore, FMO and related parameters of the active compounds and their stereoisomers were examined through DFT studies. The docking study showed compound 6c had a higher binding potential than caspase-3. However, the binding strength of 6c was found to be less than that of the standard drug, doxorubicin, as it formed lower conventional hydrogen bonds. On the other hand, compound 3a had a higher binding potential to COX-2. However, the binding potential 3a was much lower than that of the standard COX-2 inhibitor, celecoxib. The MD simulation demonstrated that the caspase-3-6c complex was less stable than the caspase-3-doxorubicin complex. In contrast, the COX-2-3a complex was stable, and 3a was anticipated to remain inside the protein's binding pocket. The DFT study showed that 3a had higher chemical stability than 6c. The electron exchange capacity, chemical stability, and molecular orbital distributions of the stereoisomers of the active compounds were also found to be alike.

Efficient electrocatalytic nitrate reduction using 3D copper foam-supported Co hexagonal nanoparticles in a membrane electrode assembly

Electrocatalytic nitrate reduction reaction (NO3RR) provides a promising route for nitrate recycling and ammonia production. In this work, Co nanoparticle catalyst was developed on a copper foam substrate (CoNPs/CF) by electrodeposition. The CoNPs/CF catalysis exhibits a Faradaic efficiency (FE) of 92.0% at −0.2 V vs. RHE and an NH3 yield rate of 14328.65 μg h−1 cm−2 at −0.5 V vs. RHE. In-suit Raman spectroscopy and theoretical calculations demonstrated that the 3D copper foam structure of the substrate enhances the electron exchange capacity, which promotes the adsorption of nitrate on the cobalt (Co) surface. Moreover, Membrane Electrode Assembly (MEA) is employed with CoNPs/CF, contributing to 98.43 mg h−1 with FE over 80%. Coupled with an air stripping process, this configuration has enabled the successful production of high-purity gaseous NH3 products. This work suggests a practical and viable approach for the conversion of wastewater nitrate into valuable ammonia products.

Variations in redox properties of biochar and humic acid induced by interactive molecular exchange

Biochar and humic substances are prevalent redox pools in the environment, which is critical to electron transfer in geochemical cycles and pollution control processes. The dissolution of biochar and the sorption of humic substances on biochar have the potential to redistribute redox substances, consequently altering the redox properties of solid and liquid phases. However, studies have often focused on either sorption or dissolution separately, overlooking the mutual effects and not involving redox properties. Herein, molecular interactions between biochar and humic acid (HA) and variations in their redox properties were elucidated using UPLC Orbitrap MS and mediated electrochemical measurement. The dissolution of biochar was far greater than the sorption of HA constituents, and HA enhanced the dissolution of biochar through molecular exchange. But preferential sorption of oxygenated aromatics to pine char (pi500) mainly by hydrogen bonding and higher saturated molecules to starch char (st700) mainly by hydrophobic interactions caused the oxygenated functional groups on biochar to increase (1 ~ 1.5 times). Thus the Electron exchange capacities (EEC) of pi500 and st700 turned to 1 ~ 3 times, and the EEC of HA decreased ca. 50%. Absorption (partition) caused more sorption of HA constituents to pi500 than to st700, while larger surface area resulted in higher EEC of st700 with sorbed HA. The enrichment of redox constituents on biochar is promising for its long-term use in waste reclamation and pollution control. The findings can aid in the understanding of variations in redox properties under interactions between pyrolytic and natural organic matter.Graphical

The correlation between electron exchange capacity of Fenton-like heterogeneous catalyst and catalytic activity

Electron transfer played key role in peroxymonosulfate (PMS) activation for heterogeneous Fenton-like catalysts (HFCs). However, the relationship between electron exchange capacity (EEC) and catalytic activity of HFCs has not been elucidated. Herein, thirteen HFCs reported in our previous studies were selected to measure their EEC via electrochemical methods and to investigate the correlation between EEC and catalytic activity for PMS. The results show that nitrogen-doped graphene oxide had much higher EEC (5.299 mM(e) g−1), followed by reduced graphene oxide (3.23 mM(e) g−1), nitrogen-doped biochar-700 (2.032 mM(e) g−1), graphene oxdie (1.789 mM(e) g−1), nitrogen-doped biochar-300 (1.15 mM(e) g−1), g-C3N4 (0.752 mM(e) g−1) and biochar (0.351 mM(e) g−1). For carbon materials, their catalytic activity was not determined by electron donor capacity (EDC), electron acceptor capacity (EAC) and EEC (EDC + EAC), but was linear correlation with |EDC-EAC| that can characterize the extent of HFCs reacting with PMS. The higher the |EDC-EAC| is, the higher the catalytic activity of HFCs is. For carbonaceous materials, their catalytic activity was not proportional to EAC, but had good linear correlation with EDC and |EDC-EAC|. The discrepancy between carbon materials and carbonaceous materials could be due to the different activation mechanisms. Further analysis found that there was no correlation between EEC and the reactive species derived from PMS, indicating that the produced reactive species was not only controlled by EEC. This study firstly elucidated the correlation between EEC and catalytic activity of HFCs, and |EDC-EAC| could be used as an index for evaluating the catalytic activity of HFCs.

Harnessing the potential of ginkgo biloba extract: Boosting denitrification performance through accelerated electron transfer

Ginkgo biloba extract (GBE) had several effects on the human body as one of the widely used phytopharmaceuticals, but it had no application in microbial enhancement in the environmental field. The study focused on the impact of GBE on denitrification specifically under neutral conditions. At the identified optimal addition ratio of 2% (v/v), the system exhibited a noteworthy increase in nitrate reduction rate (NRR) by 56.34%, elevating from 0.71 to 1.11 mg-N/(L·h). Moreover, the extraction of microbial extracellular polymeric substance (EPS) at this ratio revealed changes in the composition of EPS, the electron exchange capacity (EEC) was enhanced from 87.16 to 140.4 μmol/(g C), and the transfer impedance was reduced within the EPS. The flavin, fulvic acid (FA), and humic acid (HA) provided a π-electron conjugated structure for the denitrification system, enhancing extracellular electron transfer (EET) by stimulating carbon source metabolism. GBE also improved electron transfer system activity (ETSA) from 0.025 to 0.071 μL O2/(g·min·prot) and the content of NADH enhanced by 22.90% while significantly reducing the activation energy (Ea) by 85.6% in the denitrification process. The synergy of improving both intracellular and extracellular electron transfer, along with the reduction of Ea, notably amplified the initiation and reduction rates of the denitrification process. Additionally, GBE demonstrated suitability for denitrification across various pH levels, enhancing microbial resilience in alkaline conditions and promoting survival and proliferation. Overall, these findings open the door to potential applications of GBE as a natural additive in the environmental field to improve the efficiency of denitrification processes, which are essential for nitrogen removal in various environmental contexts.

Regulating localized state electron and ordered electron transfer in Cu2Se using Indium element for efficient heterogeneous Fenton-like process

Local electron density at the reaction center atoms is closely related to the H2O2 activation performance of a heterogeneous Fenton-like catalyst. However, the random electron transfer often restricts the oriented electron delivery to the active center. In this study, we proposed that only efficient electrons and their ordered transfer were desirable to boost Cu(II)/Cu(I) cycle for H2O2 activation based on regulation of local electron density and electron transfer efficiency of Cu atoms in Cu2Se. Experimental results and density function theory (DFT) calculation proved that Indium atom can drive electrons to accumulate on Cu active center and provide an efficient electron transfer pathway in CuInSe2 (from Se → Cu to In → Se → Cu). Hence, compared with Cu2Se, more reductive electrons can participate in the H2O2 activation process for CuInSe2, which resulted in much more efficient ofloxacin (OFX) degradation with a TOC removal rate up to 71.5 %. The electron exchange capacity of CuInSe2 was further regulated by changing the atomic ratios of Cu and In elements including CuInSe2, Cu1.5In0.5Se2 and Cu1.75In0.25Se2. CuInSe2 had the lowest electron exchange capacity and exhibited the highest reaction activity with a radical transformation efficiency from H2O2 of 9.83 × 10-4, in contrast, the value for Cu1.75In0.25Se2 was 2.78 × 10-4. We provided a new insight for improving the heterogeneous Fenton catalytic performance.

Rape Straw Biochar Application Enhances Cadmium Immobilization by Promoting Formation of Sulfide and Poorly Crystallized Fe Oxide in Paddy Soils

The mechanisms of rape straw biochar that affect the fixation of cadmium (Cd) in paddy soil by influencing redox of iron and sulfur are unclear. Several anaerobic incubation experiments were carried out using Cd-contaminated paddy soils (LY and ZZ). Rape straw biochar at pyrolysis temperatures of 450 °C (LRSB) and 800 °C (HRSB) was selected as the soil remediation agent. The electron exchange capacity and electrical conductivity were higher in HRSB than those in LRSB. The lower pe + pH in HRSB enhanced Fe oxide reduction, with a maximum increase in Fe2+ of 46.0% in ZZ. Compared to treatment without biochar (CK), the poorly crystallized Fe oxide (Feo) in HRSB increased by 16.8% in ZZ. This induced Cd bound to Fe, and Mn oxides fraction (Fe-Mn Cd) increased by 42.5%. The SO42−-S content in LRSB was 4.6 times that of HRSB. LRSB addition increased acid-volatile sulfide by 46.4% and 48.9% in LY and ZZ soils, respectively, compared to CK. This resulted in an increase in sulfide’s contribution to Cd fixation, with values rising from 24.2% to 37.8% in LY and 19.1% to 29.8% in ZZ. Overall, LRSB reduced Cd mobility by forming more sulfide, while HRSB increased Fe-Mn Cd by increasing Feo.

Influence of biochar derived from sugarcane bagasse at different carbonization temperatures on anammox granular formation

Biochar derived from sugarcane bagasse, carbonized at temperatures of 300, 550, and 800 °C, exhibit different characteristics, such as pH, functional groups, specific surface area, and released nutrients. These three types of biochar were separately added into the enriched anammox cultures, influencing granular formation and nitrogen removal. The addition of biochar300 proved to be the most effective in stimulating anammox granular formation. On day 141 of operation, granular size >1.40 mm could be observed in all 3 biochar-amended reactors. The volatile suspended solids of these granules increased 3.2-fold, 1.2-fold, and 1.8-fold respectively compared to the reactor control without biochar addition. Furthermore, both short-term and long-term investigations of biochar addition demonstrated that biochar300 consistently promoted anammox activity surpassing additions of biochar550 and biochar800, especially during the start-up period. Based on various biochar300 dosing experiment, the higher doses may indicate higher electron exchange capacity. However, doses at levels ≥20 g L−1 negatively impacted the performance of the anammox system. The addition of biochar550 and 800 led to crystal accumulation and precipitation within granules. The crystals were identified as calcite, carbonate hydroxyapatite, and hydroxyapatite by using the XRD technique. Moreover, microbial community after the long-term biochar addition was analyzed by using next-generation sequencing technique.

Biochar establishing syntrophic partnership between exoelectrogens to facilitate extracellular electron transfer

Biochar was regarded as a promising accelerator for extracellular electron transfer (EET), while the mechanism of biochar facilitating electricity harvest in bioelectrochemical system (BES) was in debates. In this study, sawdust-based biochar with low conductivity but strong redox-based electron exchange capacity was added into BES with two forms, including a suspended form (S-BC) added in anode chamber and a fixed form closely wrapping up the anode (F-BC). Compared with the control group, S-BC and F-BC addition dramatically increased accumulated electricity output by 2.0 and 5.1 times. However, electrochemical analysis characterized the lowest electrochemical property on anode surface in F-BC modified group. A 2nd period conducted by separating F-BC modified group with “aged F-BC + new anode” group and “single aged anode” group demonstrated that F-BC contributed >95 % to the current generation of F-BC modified group, while the anode almost acted as a conductor to transfer the generated electrons to cathode. Microbial community analysis revealed that both heterotrophic and autotrophic exoelectrogens contributed to current generation. The presence of biochar upregulated functional genes encoding cytochrome-c and type IV pilus, thereby boosting electricity harvest efficiency. Interestingly, the heterotrophic exoelectrogens of Geobacter/Desulfovibrio tended to attach on fixed surfaces of both biochar and anode, and the autotrophic exelectrogen of Hydrogenophaga was selectively enriched on biochar surfaces whatever fixed or suspended form. Consequently, a syntrophic partnership between Geobacter/Desulfovibrio and Hydrogenophaga was potentially establishment on F-BC surface for highly-efficient electricity harvest. In this syntrophic EET model, biochar potentially acted as the redox-active mediator, which temporarily accepted electron released by Geobacter/Desulfovibrio via acetate oxidation, and then donated them to Hydrogenophaga attached on biochar surfaces for autotrophic EET. This was distinct from a regular EET conducted by heterotrophic exoelectrogens. These findings provided new insights to understand the mechanisms of biochar facilitating EET by syntrophic metabolism pathway.

The degradation of p-nitrophenol by biochar is dominated by its electron donating capacity

The typical aromatic and phenolic pollutant, p-nitrophenol (PNP), is extensively used in the industry and can seriously threaten the environmental health. Biochar, as a solid carbon-rich material, can directly degrade PNP. It has been reported that the PNP degradation by biochar is closely related to the electron exchange capacity of biochar (the sum of electron donating and accepting capacities). However, the roles of electron donating and accepting capacity of biochar in PNP degradation have not been distinguished before. In this study, the biochar samples were chemically modified to manipulate the electron donating and accepting capacities of biochar samples. Compared with pristine biochar (3.67 %), modified biochar had higher degradation efficiencies of PNP (>7.81 %). The strictly positive correlation between the electron donating capacities and the PNP degradation rates of biochar samples (r = 0.98, p < 0.05) indicated that the PNP degradation process by biochar is dominated by the reduction process. Although both the oxidation and reduction degradation products were found in the degradation system, the quenching experiment of OH, a key radical in the process of oxidation degradation, further proved that the oxidation process just played a minor role (<10 %) in the PNP degradation by biochar. This study shed light on the degradation mechanism of PNP by biochar and could promote the application of biochar in the pollution remediation.

Pyrogenic carbon accelerates iron cycling and hydroxyl radical production during redox fluctuations of paddy soils

Carbon materials (e.g., pyrogenic carbon (PyC)) are widely used in agricultural soils and can participate in various biogeochemical processes, including iron (Fe) cycling. In soils, Fe(II) species have been proposed as the main active contributor to produce reactive oxygen species (ROS), which are involved in various biogeochemical processes. However, the effects of PyC on the transformation of different Fe species in soils and the associated production of ROS are rarely investigated. This study examined the influence of PyC (pyrolyzed at 300–700 °C) on Fe(II)/Fe(III) cycling and hydroxyl radical (·OH) production during redox fluctuations of paddy soils. Results showed that the reduction of Fe(III) in soils was facilitated by PyC during anoxic incubation, which was ascribed to the increased abundance of dissimilatory Fe(III)-reducing microorganisms (biotic reduction) and the electron exchange capacity of PyC (abiotic reduction). During oxygenation, PyC and higher soil pH promoted the oxidation of active Fe(II) species (e.g., exchangeable and low-crystalline Fe(II)), which consequently induced higher yield of ·OH and further led to degradation of imidacloprid and inactivation of soil microorganisms. Our results demonstrated that PyC accelerated Fe(II)/Fe(III) cycling and ·OH production during redox fluctuations of paddy soils (especially those with low content of soil organic carbon), providing a new insight for remediation strategies in agricultural fields contaminated with organic pollutants.Graphical

Straw Biochar-Facilitated Methanogenesis from Acetic Acid and Ethanol: Correlation with Electron Exchange Capacity

Straw biochar prepared by three methods (i.e., pyrochar, HNO3-modified pyrochar, and hydrochar) was added to the anaerobic digestion system with acetic acid and ethanol as substrates to explore the effects of biochar on methane production, substrate degradation, and microbial community structure. The biogas yields of the biochar-supplemented groups all increased, and the maximum methane yield was found in the hydrochar group, which was 45.4% higher than the control. In the ethanol-fed reactor, the maximum partial pressure of hydrogen in the headspace of the hydrochar reactor was reduced from 3.5% (blank reactor) to 1.9%. Overall, methane production is directly proportional to the electron exchange capacity (EEC) value of biochar. Furthermore, the bio-aging process increased the EEC of each kind of biochar to 5.5–8.1%, which was favorable for the sustainable promotion of methanogenesis. The increased methane yield from the bio-aged biochar could either be attributable to the changes in surface oxygen-containing functional groups or the selectively enriched microbial community on the biochar, such as Geobacter, which could participate in direct interspecies electron transfer.

Alkalization-induced disintegration increased redox activity of solid humic acids and its soil biogeochemical implications

Solid humic acids (HAsolid) plays a significant role in maintaining soil ecosystem services, especially in alkaline soil. The unique chemical structures and electrochemical properties are the cores that HAsolid works. In this study, the alkalization-induced variations of particle morphology, functional groups and redox activity of HAsolid were investigated and its soil biogeochemical implications were discussed. Atomic force microscopy (AFM) deflection images and zeta potential results showed that alkalization induced disintegration of HAsolid, with particle size reducing to 200 nm when pH value reached 10.0. This result suggested that HAsolid could exist in alkaline soil. AFM-IR along with fluorescence intensity of HAsolid at different pH further proved that the supramolecular aggregation of HAsolid became loose and dispersive with more redox-active functional groups exposure after alkalization, which could lead to HAsolid susceptible to degradation in alkaline soil. Conductivity of HAsolid decreased 42.86 % when pH increased from 5.0 to 10.0, while electron exchange capacity (EEC) of HAsolid increased 45.30 %, indicating the increase of redox activity of HAsolid. Increase of redox activity of HAsolid by alkalization-induced disintegration not only can accelerate organic pollutant degradation via enhancing microbial co-metabolism, but also speed up the organic carbon loss. This study contributes to a better understanding of the role of HAsolid in organic carbon stocks and fluxes of alkaline soils and has great implications for soil biogeochemical process.

Ball-milled PET plastic char as an electron shuttle accelerated anaerobic degradation of 2,4,6-trichlorophenol in water environment

11The number behind BMPC denotes the pyrolysis temperature.The combination of carbonaceous materials and microbial degradation is an attractive measure in improving the removal efficiency of organic pollutants in water environment. In this study, the anaerobic dechlorination in a coupled system of ball-milled plastic chars (BMPCs) and the microbial consortium were investigated. The anaerobic microorganism cultured from raw sludge (CAM) contributed to the dechlorination of the 2,4,6-trichlorophenol (2,4,6-TCP) into 4-chlorophenol (4-CP) as the final product via ortho-dechlorination in all testing groups. The dechlorination rate was accelerated in different BMBC plus CAM groups than that in only CAM group (0.048 d−1), of which, it was greater in BMPC-500 plus CAM group (0.375 d−1) than that in BMPC-700 plus CAM group (0.171 d−1). The electron exchange capacity (EEC) of BMPCs decreased with the increase of pyrolysis temperature (0.053 mmol e−/g for BMPC-500 and 0.037 mmol e−/g for BMPC-700), which directly affected anaerobic dechlorination. Direct interspecies electron transfer (DIET) of BMPCs also boosted the biogas yield by 1.5 times compared to that without BMPCs. Microbial community analysis illustrated that BMPCs helped to enrich the putative dechlorinating bacteria. The abundance of Clostridium_aenus_stricto_12, as a dominant dechlorinator, significantly increased from 0.02 % to 11.3 % (without BMPCs), 39.76 % (BMPC-500) and 9.3 % (BMPC-700), and followed by， Prevotella and Megaspheara, which was reported to take part in anaerobic dechlorination and digestion as H2 producers, also increased in the presence of BMPC. This study contributes to the realization of 2,4,6-TCP in-situ reduction technology and provides a scientific reference for anaerobic dechlorination by cultured anaerobes combined with BMPCs.

Charging-discharging cycles of geobattery activated carbon enhance iron reduction and vivianite recovery from wastewater

Vivianite as a significant secondary mineral of dissimilatory iron reduction (DIR) exhibits marvelous potential to solve eutrophication as well as phosphorus shortage. Geobattery represents by natural organic matters (NOM) with rich functional groups influences bioreduction of natural iron mineral. Activated carbon (AC) which contains abundant functional groups is expected to serve as geobattery, but there remains insufficient understanding on its geobattery mechanism and how it benefits the vivianite formation. In this study, the charging and discharging cycle of “geobattery” AC enhanced extracellular electron transfer (EET) and vivianite recovery was demonstrated. Feeding with ferric citrate, AC addition increased vivianite formation efficiency by 141 %. The enhancement was attributed to the electron shuttle capacity of storage battery AC, which was contributed by the redox cycle between CO and O–H. Feeding with iron oxides, huge gap of redox potential between AC and Fe(III) minerals broke through the reduction energy barrier. Therefore the iron reduction efficiency of four Fe(III) minerals was accelerated to the same high level around 80 %, and the vivianite formation efficiency were increased by 104 %–256 % in pure culture batches. Except acting as storage battery, AC as a dry cell contributed 80 % to the whole enhancement towards iron reduction, in which O–H groups were the dominant driver. Due to the rechargeable nature and considerable electron exchange capacity, AC served as geobattery playing the role of both storage battery and dry cell on electron storaging and transferring to influence biogeochemical Fe cycle and vivianite recovery.

Enhanced microbial reduction of Cr(VI) in soil with biochar acting as an electron shuttle: Crucial role of redox-active moieties

Biochar has been proven to participate in the biotic reduction of hexavalent chromium (Cr(VI)) in environment since its involvement may accelerate the extracellular electron transfer (EET). However, roles of the redox-active moieties and the conjugated carbon structure of biochar in this EET process remain unclear. In this study, 350 °C and 700 °C were selected to produce biochar with more O-containing moieties (BC350) or more developed conjugated structures (BC700), and their performances in the microbial reduction of soil Cr(VI) were investigated. Our results showed that BC350 presented a 241% increase of Cr(VI) microbial reduction after 7-day incubation, much higher than that of BC700 (39%), suggesting that O-containing moieties might play more important roles in accelerating the EET process. Biochar, especially BC350 could serve as an electron donor for microbial anaerobic respiration, but its contribution (73.2%) as an electron shuttle for EET was dominant to the enhanced Cr(VI) reduction. The positive correlation between electron exchange capacities (EECs) of pristine and modified biochars and the corresponding maximum reduction rates of Cr(VI) evidenced the crucial role of redox-active moieties in electron shuttling. Moreover, EPR analysis suggested the nonnegligible contribution of semiquinone radicals in biochars to the accelerated EET process. This study demonstrates the crucial role of redox-active moieties, i.e., O-containing moieties in mediating the EET process during the microbial reduction of Cr(VI) in soil. Findings obtained will advance the current understanding of biochar as an electron shuttle participating in the biogeochemical processes of Cr(VI).

Dual utilization of aloe peel: Aloe peel-derived carbon quantum dots enhanced anaerobic co-digestion of aloe peel

Carbon materials have been widely used in anaerobic digestion (AD), but the role of zero-dimensional carbon quantum dots (CQDs) in anaerobic co-digestion (AcoD) has not yet been reported. In this work, the effect of aloe peel-derived CQDs (AP-CQDs) on the AcoD system of aloe peel and dairy manure was investigated. The addition of AP-CQDs accelerants increased the cumulative CH4 yield from 201.14 to 266.92–339.64 mL/g VS and increased total chemical oxygen demand removal efficiency from 34.72 % to 48.77–57.87 %. The use of a digestate with 0.36 wt.% of AP-CQDs resulted in a thermogravimetric mass loss of 47.15 % and a promising total nutrient content of 46.65 g/kg. The excellent electron exchange capacity of AP-CQDs may facilitate direct interspecies electron transfer during the AD process. Moreover, the use of AP-CQDs can enrich methanogenic microorganisms (Methanosarcina and Methanobacterium). These findings provide a viable strategy for improving methane production and create awareness regarding the dual use of biomass waste.

The mechanism of p-nitrophenol degradation by dissolved organic matter derived from biochar

Recently, p-nitrophenol (PNP), a common organic environmental pollutant, has been reported to be degraded by biochar. Although the degradation mechanism of PNP by biochar has been explored, the role of biochar-derived dissolved organic matter (BDOM) in PNP degradation remains unclear. Two BDOM samples were prepared in this study, and their PNP degradation performance was analyzed. BDOM5 (prepared at 500 °C) exhibited higher PNP degradation ratio than BDOM7 (prepared at 700 °C). The extent of PNP degradation per unit of BDOM5 and BDOM7 reached 9.54 and 4.19 mg/mg, respectively. Gas chromatography–mass spectrometry (GC–MS) analysis showed that both oxidative and reductive processes contributed to the PNP degradation by BDOM. Compared with BDOM7, the higher PNP removal of BDOM5 was due to the higher electron exchange capacity. Furthermore, hydroxyl radicals (OH) played a critical role in the oxidative degradation process of PNP by BDOM. This study sheds light on the phenomenon of PNP degradation by BDOM and these results may be useful for accurately assessing the environmental impact of biochar application.

Electron exchange capacity of pyrogenic dissolved organic matter (pyDOM): complementarity of square-wave voltammetry in DMSO and mediated chronoamperometry in water.

Pyrogenic dissolved organic matter (pyDOM) is derived from black carbon, which is important in the global carbon cycle and other biogeochemical redox processes. The electron-exchange capacity (EEC) of pyDOM has been characterized in water using mediated chronoamperometry (MCA), which gives precise results under specific operational conditions, but the broader significance of these EECs is less clear. In this study, we described a novel but complementary electrochemical approach to quantify EECs of pyDOM without mediation using square-wave voltammetry (SWV) in dimethyl sulfoxide (DMSO). Using both the SWV and MCA methods, we determined EECs for 10 pyDOMs, 6 natural organic matter (NOM) samples, and 2 model quinones. The two methods gave similar EECs for model quinones, but SWV gave larger EECs than MCA for NOM and pyDOM (by several-fold and 1-2 orders of magnitude, respectively). The differences in the EECs obtained by SWV and MCA likely are due to multiple factors, including the potential range of electrons sampled, kinetics of electron transfer from (macro)molecular structures, and coupling of electron and proton transfer steps. Comparison of the results obtained by these two methods should provide new insights into important environmental processes such as carbon-cycling, wildfire recovery, and contaminant mitigation using carbon-based amendments.

Novel nitrogen-doped biochar supported magnetite promotes anaerobic digestion: Material characterization and metagenomic analysis

Although different conductive materials have been applied to anaerobic digestion, there has not been a material that can really combine their merits and make up their shortcoming from each other. In this study, a novel nitrogen-doped biochar supported magnetite (Fe3O4@N-BC) was synthesized. Various material characterizations confirmed that nitrogen atoms were successful doped into the biochar and magnetite precipitated on its surface. 5 g/L Fe3O4@N-BC achieved the highest promotion of cumulative CH4 production by 1.75 times compared with the blank group. Further metagenomic analysis revealed that Fe3O4@N-BC could increase the gene abundances of pilA, MmcA, Fpo, Rnf and HdrEd in bacteria Clotridium, Pseudomonas and Syntrophomonas and archaea Methanosarcina. Redundancy analysis showed that it was electrical conductivity and electron exchange capacity that were the key physicochemical characteristics for Fe3O4@N-BC to facilitating direct interspecies electron transfer. This study provides a reference for future conductive material synthesis and its application for anaerobic digestion.