Amount Of Oxygen-containing Functional Groups Research Articles

Exfoliation of Graphite into Graphene Oxide and Reduction by Plant Extract to Synthesize Graphene

Graphene oxide (GO) is a demand material in industrial field for many applications such as electronic devices, capacitor and sensor. This is due to its unique structures and excellent properties. The GO sheets were exfoliated from graphite rod in electrochemical exfoliation. To reduce GO, an electrochemical reduction of GO using green tea was carried out in this research. The conventional chemical reduction method consumed highly toxic and strongly hazardous chemicals such as hydrazine to reduce GO to reduced GO (RGO). Therefore, a green synthesis method was proposed by using green tea leaves extract as the reducing agent to synthesize RGO. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) results show that low amount of oxygen-containing functional groups was remained after green tea reduction due to weak reduction capability by green tea. In addition, EDX indicates that oxygen content of GO was decreased from 23.23 to 16.89 Mass% after green tea reduction.

Effect of pyrolytic temperatures on the 2,4-dichlorophenol adsorption performance of biochar derived from Populus nigra.

To investigate the correlation between the physicochemical properties of biochar and its adsorption performance for 2,4-dichlorophenol (2,4-DCP), Populus nigra was subjected to oxygen-limited pyrolysis at temperatures ranging from 300 to 600 ℃. The experimental results showed that as the pyrolysis temperature increased, the specific surface area and degree of graphitization of the resultant biochar increased, but the amount of oxygen-containing functional groups decreased. Populus nigra biochar produced at 450 ℃ exhibits the best adsorption performance for 2,4-DCP due to its excellent physicochemical properties and greater electron exchange capability. The removal of 2,4-DCP is a multi-step adsorption process dominated by chemisorption, which involved oxygen-containing functional groups-mediated hydrogen bonding, as well as π-π electron donor-acceptor (EDA) interaction between the aromatic rings and Cl atoms. The study highlights the potential of Populus nigra residues for producing biochar as an affordable and effective adsorbent for 2,4-DCP removal.

Ultrafine red phosphorus confined in reasonably designed pitch-based carbon matrix built of well-interconnected carbon nanosheets for high-performance lithium and potassium storage

Red phosphorus has been well-recognized as promising anode materials for lithium-ion batteries (LIBs) and potassium-ion batteries (PIBs) due to its extremely high theoretical capacity and low cost. However, the huge volume change and poor electric conductivity severely limit its further practical application. Herein, the nanoscale ultrafine red phosphorus has been successfully confined in a three-dimensional pitch-based porous carbon skeleton composed of well-interconnected carbon nanosheets through the vaporization-condensation method. Except for the traditional requirement of high electric conductivity and stable mechanical stability, the micropores and small mesopores in the porous carbon matrix centered at 1 to 3 nm and the abundant amount of oxygen-containing functional groups are also beneficial for the high loading and dispersion of red phosphorus. As anode for LIBs, the composite exhibits high reversible discharge capacities of 968 mAh g−1, excellent rate capabilities of 593 mAh g−1 at 2 A g−1, and long cycle performance of 557 mAh g−1 at 2 A g−1. More impressively, as the anode for PIBs, the composite presents a high reversible capacity of 661 mAh g−1 and a stable capacity of 312 mAh g−1 at 0.5 A g−1 for 500 cycles with a capacity retention up to 84.3%. This work not only sheds light on the structure design of carbon hosts with specific pore structure but also open an avenue for high value-added utilization of coal tar pitch.

Direct electron transfer kinetics of histamine dehydrogenase at air plasma-treated graphite nanofibers

As histamine is one of the important mediators for allergic reactions, its efficient detection methods and real-time monitoring systems are required for food analyses and drug discoveries to suppress allergic reactions. Although histamine dehydrogenase (HmDH) is a promising candidate for developing enzyme-based electrochemical biosensors, some electron mediators are frequently employed to observe electrocatalytic currents for histamine oxidation. Here, direct electrochemistry of HmDH was studied at the surface of graphite nanofibers (GNFs), which provide active reaction sites for redox species. Air plasma-treated GNFs were used for constructing a three-dimensional network that works both as an electrical nanowire and an enzyme support. Even though the amount of oxygen-containing functional groups didn’t significantly increase at the GNF surface with increase in the air plasma treatment time, direct electron transfer from reduced HmDH by histamine to the GNFs was improved probably due to capped and curvature of the graphite edge sites with oxygen-containing functional groups, which were generated by the air plasma treatment. The air plasma-treated GNFs also allowed enhancement of the complex-formation reaction rate of HmDH with histamine, as the air plasma treatment time increased.

Construction of Macromolecules of Depolymerized Lignite.

Preparing ash-less coal and further converting it into chemicals is an efficient and promising means for lignite utilization. This work performed depolymerization of lignite to prepare ash-less coal (SDP) and separated it into the hexane-soluble fraction (HS), toluene-soluble fraction (TS), and tetrahydrofuran-soluble fraction (THFS). The structure of SDP and those of subfractions were characterized by elemental analysis, gel permeation chromatography, Fourier transform infrared spectroscopy, and synchronous fluorescence spectroscopy. The results show that SDP is a mixture of aromatic derivatives containing alkyl substituents and oxygen-containing functional groups. The number of condensed aromatic rings, the amount of oxygen-containing functional groups, and the molecular weight gradually increase as HS < TS < THFS. SDP was further analyzed by 1H-NMR and 13C-NMR to calculate its structural parameters. The macromolecule of THFS contains 15.8 total ring systems with 9.2 aromatic rings and 6.6 naphthenic rings. On average, each THFS molecule contains 6.1 alcohol hydroxyl groups, 3.9 phenol hydroxyl groups, 1.4 carboxyl groups, and 1.0 inactive oxygen-containing functional groups. The dominant reactions occurred during depolymerization are the breakage of ether linkages. The average THFS molecule consists of 3.3 structural units with aromatic nuclei (2.8 rings on average) linked with methylene, naphthene, and so forth.

SORPTION PROPERTIES OF OXIDIZED AND NON-OXIDIZED ACTIVATED CARBON FOR COPPER(II) IONS

The problem of obtaining effective sorption materials is relevant in connection with the growing volumes of industrial wastewater and the development of individual technologies for their purification, including sorption methods. Activated carbon has established itself as a unique sorbent with a high sorption capacity for compounds of various nature. Modification of its surface, its oxidation leads to an increase in adsorption activity. The aim of this work is to compare the sorption properties of oxidized and non-oxidized activated carbon with respect to copper(II) ions. The concentration of Cu(II) ions in the solution was determined by atomic absorption analysis on an MGA-915 spectrometer. The degree of coal oxidation was characterized by the value of the static exchange capacity. Studies on the model synthetic nitrogen-containing carbon SKN showed the presence of different amounts of oxygen-containing surface functional groups: weakly acidic (lactonic) ‒COO‒; strongly acidic (carboxylic) ‒COOH; phenolic ‒OH. It is shown that without access to oxygen, the mechanisms of interaction of activated carbon of different oxidation states with Cu(II) ions are different: when weakly oxidized carbon is used, reductive sorption occurs, and if highly oxidized carbon serves as a sorbent, ion exchange occurs. It was found that for SKN coal with a low oxygen content, the boundary sorption of Cu(II) ions in a deaerated medium is about 40 mg/g; in the presence of oxygen, it decreases to 6 mg/g. An increase in the proportion of carboxyl and phenolic groups leads to an increase in the sorption of Cu(II) ions. Reductive sorption of copper(II) from aerated solutions is thermodynamically prohibited. It is recommended to use additional oxidation of coal to increase the content of PFG and the sorption capacity of the sorbent. For the extraction of copper(II) from aqueous technological solutions, carbon materials with a sufficient amount of oxygen-containing functional groups of various nature are most effective.

Selective separation of Bi3+ from La3+/Ac3+ by sorption on sulfonated carbon materials for use in an inverse 225Ac/213Bi radionuclide generator: Batch and column tests

213Bi-labeled radiopharmaceuticals for cancer treatment are receiving considerable interest. 213Bi must be separated from the parent radionuclide 225Ac in a radionuclide generator, but the choice of a suitable sorbent material with high chemical and radiolytic stability is challenging. Present work reports on the synthesis of sulfonated carbon materials (SCMs) prepared by carbonization of methyl cellulose at temperatures between 300 and 800 °C, followed by a sulfonation process. These SCMs were evaluated as sorbents in inverse 225Ac/213Bi generators. The sulfonated carbon material prepared at 500 °C (SCM-500) was selected as the most promising candidate sorbent based on its unique aromatic carbon structure, sufficient amount of oxygen-containing functional groups, and selective sorption performance towards La3+/Bi3+. In addition, various variables, including the acidity of the solutions, salt concentrations, and sorption time have been evaluated for separating Bi3+ from La3+ (as a surrogate of Ac3+) by performing batch sorption experiments. SCM-500 was found to exhibit a high sorption Bi3+ selectivity over La3+ at low pH or in the presence of a high concentration of NaNO3. The optimized conditions in a column tests with this sorbent demonstrated a high chemical 213Bi yield (94 ± 3%) with less than 0.04% 225Ac relative to the eluted 213Bi activity. These results indicate that SCM-500 is a promising material for use in an inverse 225Ac/213Bi radionuclide generator. Furthermore, a conceptual design of an inverse 225Ac/213Bi radionuclide for medical applications is suggested based on the separation properties of SCM-500 and AG MP-50.

Investigation the adsorption mechanism of a non-ionic surfactant on graphene oxide and its derivatives (kinetic, isotherm curves, thermodynamic, and effect of salts studies)

In this work, the adsorption of Triton X-100 (TX-100), a non-ionic surfactant, on graphene oxide (GO)-based adsorbents was considered, and the adsorption mechanism, bonding between TX-100 molecules and GO derivatives, kinetic, isotherm, and thermodynamic studies were investigated. The adsorbents were GO, reduced GO (rGO), GO-humic acid (GO-HA), and GO-saponin (GO-SA) and their surface area of them were 261.8, 304.1, 348.1, and 458.6 m2/g, respectively. The results showed that the optimum pH and contact time for TX-100 adsorption were 3 and 60 min, respectively. The most significant factor in the adsorption process was the surface chemistry of the adsorbent, which affect the bonds between the adsorbate and the adsorbent. In other words, the amount of H-bonding, which was related to the amount of oxygen-containing functional groups, played an important role in TX-100 adsorption. With the reduction of oxygen-containing functional groups, the possibility of π – π and π-cationic bonds increased, and the adsorption capacity was related to the amount of π-bonding. Also, it was concluded that the pore-filling occurred and increased the adsorption capacity in mesoporous adsorbents. The surface area of the adsorbent and the electrostatic charge of its surface did not affect the adsorption capacity.

Influence of Water on the Methane Adsorption Capacity of Organic-Rich Shales and Its Controlling Factors: A Review

A typical feature of shale gas reservoirs is that they contain a significant amount of adsorbed gas. The evaluation and prediction of adsorbed gas play important roles in shale gas exploration and development. However, the presence of water in shale reservoirs makes this work more difficult. In recent years, research related to the occurrence and distribution of water in shales and its effect on methane adsorption have become a prominent issue. In this paper, the factors controlling water in shale nanopores and its influence on methane adsorption were systematically reviewed. It is revealed that the connate water content in shales and their water absorption capacity vary widely, and both are mainly related to the organic matter contents and properties and mineral compositions. The water absorption capacity of organic matter in shales is mainly affected by its nanopore content, structure and surface chemical properties (such as the type and amount of oxygen-containing functional groups), which are jointly constrained by its kerogen type and maturity. Even under moist conditions, the organic matter in shales still shows a strong methane adsorption capacity, although the water decreases the adsorption capacity to some extent. The hydrophilicity of different minerals in shales varies greatly, but the type and amount of clay minerals are the main factors affecting the adsorbed water content or water adsorption capacity of shales. The nanopore structure and characteristics of shales, such as the pore type, specific surface area, pore size distribution and heterogeneity, directly impact the occurrence and distribution of water. The competition for adsorption between water and methane at some adsorption sites is the main mechanism for the reduction in the methane adsorption capacity of moist shales. In addition, external environmental factors, such as pressure and temperature, can change the distribution and occurrence of water in shales and, thus, the influence of water on the methane adsorption capacity to a certain extent. This paper also discusses some current issues regarding the effect of water on methane adsorption capacity and highlights future research directions in this field.

Clarification of the Effects of Oxygen Containing Functional Groups on the Pore Filling Behavior of Discharge Deposits in Lithium–Air Battery Cathodes Using Surface-Modified Carbon Gels

In lithium–air batteries (LABs), controlling the characteristics of the Li2O2 deposited during discharging can lead to the reduction of the large overpotential required for charging. The large overpotential is one of the most significant problems that needs to be solved to improve the cycle performance of LABs. Here, we focused on the effects of functional groups in the cathode carbon on the characteristics of the Li2O2 deposited during discharging and the cathode performance of LABs. In this study, 4 types of carbon gels (CGs) were prepared using different treatment methods to modify their surface properties. The types and amounts of oxygen-containing functional groups (OCFGs) existing within the CGs were clarified along with the number of edge H’s by a high-sensitivity temperature-programmed desorption (TPD) technique. The results of N2 adsorption analysis of discharged CGs suggested that, by increasing the number of OCFGs from 0.40 to 1.80 mmol g–1 through acid treatment, the ratio of Li2O2 deposited within the mesopores of the porous carbon particles can be increased from 1% to 60%. This significant change in the manner of Li2O2 deposition led to the reduction of the charging overpotential. Side reactions that are thought to deteriorate cycle performance tended to proceed in CGs having a large number of OCFGs. This negative effect could be reduced by removing carboxyl groups in the CGs through simple heat treatment at 300 °C in an inert atmosphere. Our study clarified the critical roles of OCFGs in the cathode during the discharging and charging of LABs. The obtained knowledge can be utilized for the development of a high-performance cathode for LABs.

Agricultural Wastes for Full-Cell Sodium-Ion Batteries: Engineering Biomass Components to Maximize the Performance and Economic Prospects

Lignin is one of the most abundant biopolymers in nature. Although lignin-derived hard carbon (L-HC) has potential to be used as a sodium-ion battery (SIB) anode but is limited by its poor electrochemical performance. In nature, lignin normally coexists with cellulose and hemicellulose in agricultural biomass, and studies have applied different agricultural biomasses to make SIB anodes; however, the underlying mechanism, especially the functionality of each component, is still unclear. In this study, we aim to combine lignin with cellulose and/or hemicellulose to produce hard carbons with outstanding electrochemical performance and low cost, and more importantly, unveil the underlying mechanisms. We found that the poor electrochemical performance of L-HC was mainly due to its large surface area with high amount of oxygen-containing functional groups and its unique physical structure that inhibit effective Na diffusion. Combining lignin with either cellulose or hemicellulose led to significantly improved electrochemical performance of the resulting hard carbon, with cellulose mainly contributing to the increase of capacity and hemicellulose mainly contributing to the stability of capacity during cycling and at high current density. Based on the comprehensive consideration of both electrochemical performance (half and full cells) and economic perspectives, lignin combined with cellulose showed great potential. Our study shed light on the contributions of each major biomass component on physical and electrochemical properties of resulting hard carbon and designed a unique way to improve L-HC.

A carbon felt cathode modified by acidic oxidised carbon nanotubes for the high H2O2 generation and its application in electro-Fenton

ABSTRACT Herein, a carbon felt (CF) cathode modified by the acidic oxidised carbon nanotubes (OCNTs) exhibited a high yield of the H2O2 generation in electro-Fenton. Rotating disk electrode (RDE) measurements showed that the selective generation of H2O2 occurred on the CF cathode coated by OCNTs (OCNTs/CF), which was attributed to the high amount of oxygen-containing functional groups in OCNTs. Moreover, the pollutant degradation efficiency could almost reach 100% within 60 min in electro-Fenton with OCNTs/CF as the cathode. Furthermore, the pollutant removal efficiency was kept constant after five consecutive cycles, indicating the high stability of OCNTs/CF cathode. Besides, the hydrophilicity of OCNTs/CF cathode was significantly enhanced owing to the abundant oxygen-contained functional groups on the surface of the OCNTs/CF cathode, which facilitated the mass transfer between the OCNTs/CF cathode and the reactants in the bulk solution. To reveal the possible mechanism in electro-Fenton equipped with the OCNTs/CF cathode, quenching experiments and electron paramagnetic resonance (EPR) investigations were further conducted. This work provided valuable insights into the fabrication of the non-metallic cathode with a high ability towards H2O2 generation in electro-Fenton for efficient pollutant removal.

In situ synthesis of highly dispersed Fe/C catalysts with pomelo peel as carbon source in CO2 hydrogenation to light olefins

Although considerable progress has been made in the hydrogenation of CO2 to light olefins through the modified Fischer-Tropsch synthesis route (CO2-FTS), the design of catalysts with high selectivity and stability is still a challenge. Herein, a simple, highly dispersed and scalable Fe/C-400 catalyst was prepared by in-situ pyrolysis using pomelo peel (PP) as carbon source, and was first used in CO2 hydrogenation to light olefins. This catalyst exhibited a high space time yield of light olefins (48.3 μmolCO2·gFe−1·s−1), and the light olefins selectivity and O/P were 63.0% and 9.0, respectively. More surprisingly, no obvious deactivation was observed within 200 h. A series of characterization techniques such as TEM, TG-MS, FTIR, XPS, H2-TPR and 57Fe Mössbauer spectrum showed that the naturally abundant oxygen-containing functional groups in PP support could impart metal-support interactions that enhance the dispersion of iron species. The modulation of the catalyst phase composition was achieved by simply varying the residual amount of oxygen-containing functional groups to impart different metal-support interactions. The catalysts prepared at lower pyrolysis temperatures retained more oxygen-containing functional groups and therefore had stronger metal-support interactions, which facilitated the formation of more active phases. Overall, this newly developed catalyst realized the high activity and high stability production of CO2 hydrogenation to light olefins, providing a cost-effective and sustainable way for its industrial application.

Fabrication and Characterization of Clinacanthus nutans Mediated Reduced Graphene Oxide Using a Green Approach

The reduction of graphene oxide (rGO) utilizing green methods such as plants has attracted much attention due to its productivity, eco—friendly features, and cost effectiveness. In the present study, the reflux method was employed to synthesize Clinacanthus nutans (C. nutans) leaf extract mediated rGO using a simple approach. The synthesized rGO was characterized using various spectroscopic and microscopic techniques. The UV-Vis spectrum demonstrated the absorption peak of rGO (270 nm) at distinct locations, while the FTIR analysis demonstrated that the amount of oxygen group in rGO was reduced. The Raman analysis confirms the reduction of GO by a slight increase in the D—band to G—band intensity ratio. The XRD spectra demonstrated that rGO was successfully produced based on the illustrated 2Ɵ angles at a peak of 22.12° with d-spacing of 0.40 nm. FESEM clearly reveals the morphology of rGO that shows crumpled thin sheets, a rougher surface, and a wave—shaped corrugated structure. The reduction of GO was analyzed in the removal of the hydroxyl group and amorphotization of sp2 carbon structures. The C/O ratio in rGO was higher than GO which indicates the small amount of oxygen-containing functional groups were still presented in the reduced graphene oxide. Furthermore, the cyclic voltammetry behavior of a modified screen—printed carbon electrode (SPCE) was measured. The redox reactivity of rGO—SPCE has been affirmed and compared with GO—SPCE and bare—SPCE. The toxicity using A. salina cysts demonstrated that rGO is less toxic compared to GO. The analysis adequately supports the synthesis of rGO and the effective removal of oxygen-containing functional groups from GO. The findings herein illustrate that C. nutans mediates the synthesis of rGO and is a promising eco-friendly substitute to conventional carbon-based fabrication.

Effect of the pore structure of coal-based activated carbon and hydrogen addition on methane decomposition for the preparation of carbon nanotubes

Activated carbon with a hierarchical micro/mesoporous carbon structure was synthesized using Shenmu coal as the raw material, which was impregnated with KOH (K) in different K/C ratios before carbonization at various temperatures. The obtained material was loaded with nickel and then employed as catalyst for the catalytic methane decomposition (CMD) to prepare carbon nanotubes. Using a constant nickel loading, the effects of the pore structure of the different activated carbon materials and hydrogen addition on the preparation of carbon nanotubes were investigated. The results show that the coal-based activated carbon with a micropore content of 0.8, synthesized at a carbonization temperature of 850 °C and a K/C ratio of 2, is the most suitable carrier for the methane cracking catalyst to produce carbon nanotubes. The diameter of the prepared carbon nanotubes is in the range of 50–120 nm with a length of 5–15 μm. The addition of hydrogen can prevent the high-temperature decomposition of oxygen-containing functional groups, and the activity of the catalyst can be maintained by inhibiting carbon deposition. Furthermore, the hydrogen present in the CMD process can promote the formation of carbon nanotubes with larger diameters (50–350 nm) and shapes. The nanotubes are more curved, and their length is reduced to 5–11 μm. Finally, the formation mechanism of carbon nanomaterials is discussed according to the morphological changes of the products after hydrogen addition and the existing theories. In conclusion, appropriate amounts of oxygen-containing functional groups and larger micropore volumes facilitate the pyrolysis of coal-based activated carbon catalysts in the preparation of carbon nanotubes.

Mechanism of Improved Lithium-Sulfur Battery Performance by Oxidation Treatment to Microporous Carbon as Sulfur Matrix

1. IntroductionLithium-sulfur (Li-S) batteries are rechargeable devices assembled with a sulfur cathode and a lithium metal anode. Li-S batteries have twice the volumetric energy density and 5 times the gravimetric energy density of lithium-ion batteries (LIB). Hence, Li-S batteries are expected to be applied to stationary power sources and EV vehicles [1]. However, Li-S batteries have the following issues:・Sulfur and the final discharge product (Li2S) are insulators.・In the discharge process, sulfur expands up to 1.8 times, so the structure of batteries is unstable.・Intermediate products (Li2Sx (x = 4 – 8)) dissolve in an electrolyte; Li2Sx (x = 4 – 8) diffused to an anode to provide an insulating layer at the anode surface.・In the charge process, Li2Sx (x = 4 – 8) causes redox shuttling.As a result, Li-S batteries cannot charge and discharge stably. In order to deal with this problem, Nazar et al. reported the method that sulfur is confined in porous carbon [2]. This approach provides a cathode realizing good electronic conductivity, restriction of sulfur expansion, and suppression of Li2Sx (x = 4 – 8) dissolution. Although these improved characteristics allow Li-S batteries to operate, The discharge capacity of Li-S batteries is still not high enough and this needs to be addressed.In our previous study, we reported that oxidation treatment to microporous carbon (MC) with HNO3 improves Li-S batteries' discharge capacity [3]. Moreover, we clarified that the discharge capacity of Li-S batteries has an approximate proportional relation with the amount of oxygen-containing functional groups on the MC surface [4].This work attempts to elucidate the mechanism of improved Li-S battery performance by oxidation treatment to MC. Our report would lead to the proposal of a novel strategy to improve the performance of Li-S batteries.2. Method2.1 Preparation of Oxidized MC-Sulfur composite (Ox MC-S)MC was added into 69 wt.% HNO3 and refluxed at 120ºC for 2 h. By vacuum filtration and washing with deionized water, Ox MC was obtained. Ox MC dried in vacuum at 80ºC overnight was mixed with sulfur at a weight ratio of Ox MC: S = 48: 52. The mixture was thermally annealed at 155ºC for 5 h (Ox MC-S). Untreated MC was also composited with sulfur by the same method (MC-S).2.2 Assembling of CellsEach MC-S cathode was prepared by mixing the MC-S, acetylene black, carboxymethyl cellulose, and styrene butadiene rubber at a respective weight ratio of 89: 5: 3: 3 and coating the resulting aqueous slurry on an Al foil current collector. The cells with the MC-S electrode and Li metal foil as an anode were assembled in a glove box filled with Ar. Lithium bis(trifluorosulfonyl)imide (LiTFSI): tetraglyme (G4): hydrofluoroether (HFE) = 10: 8: 40 (by mol) was used as the electrolyte.2.3 Electrochemical Impedance Spectroscopy (EIS)To elucidate the effect of oxidation treatment on the internal resistance of Li-S batteries, EIS was carried out at various potentials (Discharge 2.0 – 1.0 V and Charge 1.0 – 3.0 V). The obtained Nyquist plots were used for the evaluation of solid electrolyte interphase (SEI) resistance (Rsei), charge-transfer resistance (Rct), and Warburg impedance (Rw). Rw was investigated with the calculation of Warburg coefficient (σ).3. Major results and conclusionSince oxidation treatment to MC significantly increased the discharge capacity of Li-S batteries [3][4], it was expected that oxidation treatment would lower the internal resistance of Li-S batteries. EIS of MC-S and Ox MC-S at various potentials showed that oxidation treatment reduced Rsei by an average of 12.2 Ω. This indicates that the SEI thickness was reduced, or the SEI was composed of highly ion-conductive components by the oxidation treatment. Rct decreased only at lower potentials, and the Warburg coefficient decreased except at the end of charge and discharge potential. These results suggest that the oxidation treatment decreases overall resistance, but especially SEI resistance and Warburg impedance, which may improve the discharge capacity of Li-S batteries.We will also report the activation energy of Rsei and Rct and mechanism analysis of decreasing Rsei by oxidation to MC. This work was supported by “Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA-SPRING [JPMJAL1301])” from JST.[1] Y. Guo et al., Angew. Chem. Int. Ed., 52 (2013) 13186.[2] X. Ji et al., Nat. Mater., 8 (2009) 500.[3] S. Okabe et al., Electrochemistry, 85 (2017) 671.[4] L. Yoshida et al., ECS 238th PRiME Meeting s (2020).

The molecular dynamics study of atomic compound and functional groups effects on the atomic/thermal behavior of polyethylene glycol/graphite-based matrixes

In this study, Molecular Dynamics (MD) simulations were conducted for a thermophysical analysis of polyethylene glycol (PEG)/graphite (G), PEG/expanded graphite (EG), PEG/graphite oxide nanoparticle (GONP), and PEG/reduced GONP (rGONP) nanocomposites as shape stabilized phase change materials (SSPCMs). Specifically, thorough information regarding the PEG penetration in diverse graphite atomic structures and thermal conductivity (TC) under varied temperatures was investigated. The results of equilibrium MD simulations showed that PEG atoms penetration was increased at first and then remained constant with step time. Further, non-equilibrium MD simulations revealed that the thermal conduction could be improved by introducing graphite whit nanostructure and a low amount of oxygen-containing functional groups (relative to rGONP). So that the TC measured for PEG/rGONP is about 18% higher than that of PEG/GONP. We expect MD outcomes of this research could benefit the future development of SSPCMs with high TC.

Continuous cycling of carbon-based capacitive deionization systems: An evaluation of the electrode performance and stability

• Electrode pore size distribution and apparent morphology are immune to oxidation. • Electrode oxidation will increase oxygen-containing functional groups on the surface. • Slight oxidation helps to improve the desalination performance of the electrode. • The degree of oxidation of the carbon electrode corresponds to the number of cycles. • Electrode oxidation evaluation system is of great significance to CDI technology. Activated carbon is widely used as the electrode in capacitive deionization technology (CDI), because of its simple manufacturing and low price. However, the evaluation system of carbon electrode oxidation degree and running time is lacking in existing studies, and the reasons for the changes caused by carbon electrode oxidation are not in-depth enough and limits its application. In this study, polyvinylidene fluoride/activated carbon (PVDF/ACP) composite electrode was prepared through coating. Electrode characterization and electrochemical testing were used to characterize PVDF/ACP anode after long-term circulation in NaCl solution. It was found that the pore size distribution and apparent morphology of the electrode were immune to the influence of carbon electrode oxidation, but the acidic functional groups on the electrode surface increased significantly and the electrochemical properties changed. Combined with the CDI desalination experiment, the relationship between oxidation degree and cycle number was revealed. The results show that the electrode with 0 ∼ 20 cycles is relatively stable and its performance is slightly improved. A small amount of oxygen-containing functional groups contributes to the electrode performance. The performance of the electrode with 20 ∼ 40 cycles to deteriorate suddenly, and a large number of oxygen-containings functional groups will affect the equilibrium potential and ion transports of electrode. The electrode performance degrades slowly after 40 ∼ 80 cycles. After 80 cycles, the electrode performance remained unchanged and the carbon electrode reached the oxidation threshold.

Hierarchical porous carbon derived from coal-based carbon foam for high-performance supercapacitors

Hierarchical porous carbon (HPC) from bituminous coal was designed and synthesized through pyrolysis foaming and KOH activation. The obtained HPC (NCF-KOH) were characterized by a high specific surface area (SBET) of 3472.41 m2/g, appropriate mesopores with Vmes/Vtotal of 57%, and a proper amount of surface oxygen content (10.03%). This NCF-KOH exhibited a high specific capacitance of 487 F/g at 1.0 A/g and a rate capability of 400 F/g at 50 A/g based on the three-electrode configuration. As an electrode for a symmetric capacitor, a specific capacitance of 299 F/g at 0.5 A/g was exhibited, and the specific capacitance retained 96% of the initial capacity at 5 A/g after 10,000 cycles. Furthermore, under the power density of 249.6 W/kg in 6 mol/L KOH, a high energy density of 10.34 Wh/kg was obtained. The excellent charge storage capability benefited from its interconnected hierarchical pore structure with high accessible surface area and the suitable amount of oxygen-containing functional groups. Thus, an effective strategy to synthesize HPC for high-performance supercapacitors serves as a promising way of converting coal into advanced carbon materials.

Molecular-mass distribution of humus acids of taiga soils

Purpose of the study: to reveal the influence of hydromorphism and agricultural use on the molecular-mass distribution (MMD) of humic (HAs) and fulvic acids (FAs) isolated from the soils of the European northeast of Russia. To assess the influence of the acidity of the medium on the MWD of FAs. Place and time of the event. The studies were carried out on the territory of the middle taiga (Maksimovsky station of the Institute of Biology of the Federal Research Center of the KSC UB RAS, located 8 km west of the city of Syktyvkar and the field of the Syktyvkar state farm, 5 km south-west of Syktyvkar, on the watershed of the Sysola and Vazhel-yu rivers) and northern taiga (3 km west of the Troitsko-Pechorsk station). The objects of the study were humic substances isolated from typical podzolic (Eutric Albic Retisol (Loamic)), gleypodzolic (Eutric Albic Stagnic Retisol (Loamic)), peaty-podzolic surface-gleyed (Eutric Albic Stagnic Histic) Retisol (Loamic Eutric Albic Retisol (Loamic)) soils. The soil sampling period is from 1 to 30 August 2014. Methodology. Quantitative analysis of the MMD of HA and FA preparations was performed using liquid size exclusion chromatography (gel chromatography) on Sephadex G-25 and G-100 gels with continuous automatic registration of the optical density of the eluate (λ = 280 nm) in a quartz flow cell, K 9 × 60 cm column (Pharmacia, Sweden). Distilled water, 0.05 M NaOH solution, and Tris-HCl buffer with pH = 8.2 were used as the eluent. Main results. Studies of the MMD of humic substances have been carried out. It was found that HAs contain three fractions with different molecular weights: ≥ 150 kDa, 73–80 kDa, and 13–23 kDa; FAs – two fractions: ≥ 5 kDa, 1–2 kDa. The low molecular weight of FAs, together with a large amount of oxygen-containing functional groups, contributes to their better solubility and migration ability in soils. The HAs of automorphic soils are characterized by a high content of low molecular weight fractions, and the proportion of the high molecular weight fraction in the HAs of the litter is 1.5–2.0 times higher than in the HAs of the podzolic horizon, which may be due to the migration of the low molecular weight fraction down the profile. The high proportion of the acidic low molecular weight fraction in the podzolic horizon promotes the decomposition of soil minerals and their leaching into the illuvial horizon. The influence of agricultural use of soils on the fractional composition of humic compounds is estimated. A sharp increase in the share of the high molecular weight fraction in the preparations of HAs of arable podzolic soil by 2–4 times compared with the HAs of virgin podzolic soils was noted, which is due to the cultivation of the arable horizon, the nature of the incoming plant residues and the increased microbiological activity of the developed soils. The effect of acidity of the medium on the character of chromatograms of FA preparations isolated from the main types of soils of the Komi Republic was studied. It has been shown that in the region of high pH values of the eluent 9–13, the absence of fractionation is associated with the association of FAs, a change in their conformation, and the effect of “over-exclusion”. Elution with distilled water (pH = 6.5) allows the separation of FAs into two fractions with molecular weights ≥ 5 kDa and 1–2 kDa.