Black Carbons Research Articles

Effect of dissolution for black carbon on the adsorption capacity for methylene blue: Equilibrium, kinetics and thermodynamics

Black carbon was widely researched due to its significant role on the global carbon cycle and contaminant transport, and most people were concerned about the property of the dissolved black carbon from black carbon. In this work, we focused on the research of the residual those of black carbon. Two kinds of black carbon originated from peanut shell and bamboo were prepared and the corresponding residual black carbons were also obtained by the ultrasonic dissolution process. It was found the chemical and structure properties of residual black carbon changed a lot compared to black carbon. Using methylene blue as a target contaminant, the adsorption capacity of methylene blue by the residual black carbon was greater than that of black carbon. The adsorption capacity of black carbon-bamboo for methylene blue increased from 11.1 mg/g to 16 mg/g after the dissolution process, and the adsorption capacity of black carbon-peanut shell for methylene blue increased from 14 mg/g to 23 mg/g. The various influencing factors, such as the pH, initial concentration, temperature and adsorbent dosage, were systematically studied. The black carbons derived from peanut shell before and after the ultrasonic dissolution process both showed greater adsorption capacities for methylene blue. To further elucidate the methylene blue adsorption process, different kinds of isotherm and kinetics models were applied to simulate the experimental data. The results indicated that the Langmuir isotherm model was suitable to all the carbons before and after the ultrasonic dissolution process, and the pseudo-second-order model showed great simulation for the adsorption of methylene blue. In addition, the analysis of the thermodynamic study revealed that the adsorption processes of methylene blue were endothermic and spontaneous. Overall, results obtained from this work revealed the black carbon after been dissolved showed better adsorption capacity for contaminant.

Carbon-supported hydroxyapatite hybrid catalysts for butan-1-ol conversion: Effect of the nature of carbon support on process selectivity

Hybrid systems of hydroxyapatite supported on carbonaceous materials of different nature (activated charcoals, acetylene black, carbon black, graphite flake, synthesized microporous and mesoporous carbons) are investigated as catalysts for vapor-phase Guerbet condensation of butan-1-ol. The structure, morphology, and acid–base characteristics of hydroxyapatite, carbon supports, and the hybrid systems have been characterized by XRD, SEM-EDX, low-temperature (77 K) nitrogen ad(de)sorption, NMR, XPS, EPR, Raman spectroscopy, and TPD-NH3/CO2 techniques. The butan-1-ol conversion and selectivity towards the reaction products are found to be highly dependent on carbonaceous supports of the hybrid catalysts. The important role of acid–base capacity ratio is highlighted to achieve high selectivity in vapor-phase Guerbet condensation of butan-1-ol to 2-ethylhexan-1-ol. In particular, the surface’s strong basic sites are preferable for elongating the carbon chain. The high selectivity towards 2-ethylhexan-1-ol of about 75% is achieved over HAP/graphite flake and up to 57% over HAP/activated coconut charcoal. Compared to the bulk hydroxyapatite, the enhanced performance of the hybrid catalysts (initial activity and target product yield) is associated with the redistribution of active sites over carbon supports by strength and location.

Towards Sustainable Hydrogen Peroxide Electroproduction: Activated Carbon from Sewage Sludge As an Eco-Friendly Electrode Material

Hydrogen peroxide (H2O2) has emerged as a chemical of paramount importance, finding diverse applications as a bleaching agent, medical disinfectant, and environmentally benign oxidant [1]. The industrial production of H2O2 currently relies on the anthraquinone oxidation process, primarily executed within large-scale industrial plants [1]. Herein lies a challenge— H2O2, typically concentrated to an 80% level, introduces inherent hazards concerning storage and transportation, prompting a quest for a safer alternative. One way to overcome such problems is by the in-situ electrogeneration of H2O2, which would allow an adjustable production of the chemical on demand directly for its application, avoiding storing costs and safety issues. The in-situ electrogeneration can be done by using a gaseous-diffusion electrode (GDE), which typically enables the application of elevated current densities or substantial overpotentials, consequently facilitating the generation of high concentrations of H2O2, since there is less limitation due to O2 mass transport to the electrode surface [2]. Commonly, these electrodes are constructed from amorphous carbon materials, due to their highly active surface area with oxygenated functional groups, excellent conductivity, and innate selectivity for H2O2 electroproduction. However, a notable challenge emerges – bare carbon's selectivity for H2O2 presents its highest response at high overpotentials, entailing heightened energy consumption. The studies in this field are currently focused on using these types of carbon as support for other catalytic materials that are more active and selective towards H2O2 electroproduction [3, 4]. Numerous studies in the literature have explored the use of carbon materials, with the most commonly employed carbon supports for such applications being Printex 6L (Orion) and Vulcan XC 72R (Cabot). These materials are obtained from the incomplete combustion of heavy petroleum products at high temperatures, being non-sustainable and environmentally unfriendly. A potential solution lies in the use of environmentally conscious carbon sources. While amorphous carbon can be obtained from various carbon-rich wastes through an activation process, their utility in H2O2 electrogeneration remains underexplored. This study sought to obtain activated carbon from sewage sludge, focusing on its efficacy in H2O2 electrogeneration. Acid (H3PO4) and alkaline (KOH/NaOH mixture) carbon activators were analyzed in concentrations ranging from 0 – 30 %m/v, temperatures of 400 – 900 ºC, and activation time from 0 – 2 h at the selected temperature. The obtained materials were analyzed through linear sweep voltammetry using an RRDE setup in N2-saturated and O2-saturated, in a 0.05 M K2SO4 (pH 3) electrolyte solution. Results have shown that the most successful materials for H2O2 electrogeneration were those produced under 900 ºC for 2h impregnated with 5 % m/v H3PO4 and 597 ºC, zero of plateau time impregnated with 20 % m/V mixture of KOH/NaOH in the ratio of 50.5 KOH: NaOH. These optimized materials exhibited remarkable selectivities of ≈ 90% and ≈ 81% at -0.8 V vs. Ag/AgCl, respectively. This level of electrocatalytic performance is on par with that of the commercial reference material, Printex 6L. These findings highlight the promise of our material as a viable carbon support for in-situ H2O2 electrogeneration, offering a more sustainable alternative compared to commercial black carbons. Acknowledgments The authors are sincerely grateful to the Brazilian research funding agencies, including the Brazilian National Council for Scientific and Technological Development - CNPq (grants no. 465571/2014-0, 302874/2017-8, and 427452/2018-0), São Paulo Research Foundation (FAPESP – grants no. #2023/04230-2, #2023/07750-7, 2022/04058-2, #2021/12053-8, #2019/04421-7, #2017/10118-0, and #2013/02762-5).

Dissolved black carbon mediated photo-oxidation of arsenic(III) to arsenic(V) in water: The key role of triplet states

Arsenic is a common contaminant found in natural waters, and has raised significant environmental concerns due to its toxicity and carcinogenicity. In this study, we investigated the mediated photo-oxidation of arsenite (As(III)) under simulated sunlight by dissolved black carbon (DBC), an important dissolved organic matter (DOM) constituent released from black carbon. Five DBC were collected from the water extracts of black carbons that were derived by pyrolyzing different biomass (i.e., bamboo, rice, peanuts, corn, and sorghum stalks), and four well-studied dissolved humic substances (DHS) were selected for benchmarking. The presence of DBC (i.e., 5 mg C−1) significantly accelerated the photo-oxidation of As(III) to arsenate (As(V)), with the observed pseudo-first-order rate constant of reaction increased by 5∼11 times. Quenching experiments of photochemically produced reactive intermediates suggested that As(III) was mainly oxidized by triplet-excited DBC (3DBC*, contribution of 48%), singlet oxygen (1O2, 18%) and superoxide anions (O2•-, 28%) in sunlight-irradiated DBC solutions. The average apparent quantum yield of As(III) photo-oxidation for DBC was found to be more than 4 times higher in comparison with DHS. Such a strong mediation efficiency of DBC was due to its smaller molecular size and higher aromaticity than DHS, which facilitated the non-charge-transfer process to produce triplet-excited states and their sensitized 1O2. Consistently, DBC exhibited a higher apparent quantum yield and a longer lifetime of triplet states as compared with DHS. The results imply that DBC may play a previously unrecognized important role in the fate of arsenic in aquatic environments.

Different photoreduction processes of Cr(VI) on cellulose-rich and lignin-rich biochar

In this study, a series of biochar were prepared via pyrolyzing cellulose-rich pakchoi (PBC) and lignin-rich corncob (CBC) to explore the photoreduction process of Cr(VI). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy confirmed higher oxygenated functional groups in PBC (48.9%–57.1%), whereas CBC exhibited more aromatization properties due to the stable aromatic network in lignin. For PBC, the valence bands decreased from 1.42 eV to 1.20 eV with the increase of pyrolysis temperature from 300 °C to 500 °C; however, an opposite trend was observed for CBC. The photoreduction of Cr(VI) clearly showed that both PBC and CBC had the best performance at the carbonization temperature of 300 °C (named PBC300 and CBC300). It is noted that PBC300 exhibited the most effective photoreduction of Cr(VI), which was about 1.3 times higher than that of CBC300. The maximum reduction capacities of Cr(VI) were 68.2 mg g−1 on PBC300 and 66.1 mg g−1 on CBC300 at pH∼2.0. Compared with the insoluble char substances, dissolved black carbons made more contributions for Cr(VI) photoreduction, ∼70% in PBC and almost 100% in CBC, which suggested that in the case of PBC, the insoluble char and the corresponding dissolved black carbons play an important role in the photoreduction of Cr(VI). However, only dissolved black carbons contributed to Cr(VI) photoreduction on CBC. As the key reaction pathway, the interfacial electron transport dominated Cr(VI) reduction on PBC and CBC. Moreover, the radical of •O2− had some contribution to the reduction of Cr(VI) only in the PBC system. Interestingly, •OH could promote the photoreduction of Cr(VI) in both PBC and CBC systems, which might be due to the fact that •OH facilitated the formation of small molecule fragments. These findings provide an essential basis for evaluating the environmental impact of photocatalytic behaviors of biochar.

Enhanced microbial degradation mediated by pyrogenic carbon toward p-nitrophenol: Role of carbon structures and iron minerals

Pyrogenic carbon (PC) including black carbons and engineered carbons can mediate the extracellular electron transfer to facilitate the biogeochemical reaction with organic pollutants. Yet, the role of carbon structures and iron minerals on PC-mediated microbial degradation is still lacking of understanding. Herein, we studied the electrochemical properties of PCs produced from varied feedstock with regards to the mediated degradation of p-nitrophenol (PNP) by Shewanella putrefaciens CN32 in anoxic system. Mediated degradation by PCs was enhanced by facilitating extracellular electron transfer through oxygenated group and graphitic structure. Graphitic crystallites improved the electron-accepting capacity (as suggested by ID/IG and EAC) and diminished the electrochemical impedance (as suggested by Rct), contributing to PNP degradation under the anoxic system. Furthermore, more interfacial adsorption was conducive to the mediated reduction by the graphitic structure on PCs of high-temperature. In the presence of iron minerals, both hematite and goethite significantly facilitated PC-mediated degradation, which could be ascribed to the enhancement of the electron-donating capacity of microorganism and the accumulation of the reductive-state PCs by the interaction with generated Fe(II). This work paves a feasible way to the technical design on the remediation of phenolic contaminants by PC-mediated microbial degradation in environment.

Conductive carbon additives: Friend or foe of capacitive deionization with activated carbon?

Capacitive deionization with activated carbon (AC) electrodes has been widely applied for removing charged ions from aqueous solutions. Such carbon electrodes commonly contain a minor polymer binder and a minor carbon additive content. The choice of carbon additives is rarely investigated in depth regarding the performance enhancement/deterioration they might bring. In this work, we explored the influence of various carbon types, namely, onion-like carbon, carbon black, and micro-mesoporous carbons, on the desalination capacity and rate. Based on the cycling performance of 100 cycles, we draw relationships between the physicochemical properties of different carbon types and their results on electrochemical desalination performance. The results indicate that the direct use of the activated carbon electrode without additives leads to a higher desalination capacity of approximately 10 mg/g in early cycles, though at the cost of a lower desalination rate of 6 μg/g/s. The larger AC particles limit the intraparticle ion transportation due to the increased diffusion path length. The highest desalination rate (20 μg/g/s) is enabled by the incorporation of small and less porous additives, as it shortens the ion diffusion path length due to the increased size dispersion, hence improving the overall ion transport and desalination rates.

Conductive black carbon promoted biotransformation of undissolved 2, 2′-dinitrobiphenyl by mediating electron transfer

With low bioaccessbility, persistence of the undissolved organic pollutants in soil and sediments poses threat to health of the resident. Although ubiquitous black carbon catalyzes a wide range of biogeochemical reactions in nature, its role in biotransformation of the compounds in non-aqueous phase like 2, 2′-nitrobiphenyl remains unclear. Reduction rate constants of 2, 2′-dinitrobiphenyl by Shewanella oneidensis MR-1 increased from 0.0044 h−1 by 7-fold to 0.035 h−1 in the presence of black carbons produced at pyrolysis temperature of 250–900 °C. Accordingly, electrical conductivity of black carbon was enhanced from 0 to 5.56 S∙cm−1. The reactivity of black carbon for catalyzing the biotransformation positively correlated with its electrical conductivity (R2 > 0.89), which was strongly associated with conductive graphitic clusters in it. The surface oxygenated groups in black carbon were likely not involved in the bioreduction. This work attaches importance to role of the ubiquitous black carbon in natural biotransformation of the undissolved pollutants, and elucidates new mechanism for the biotransformation.

Characterisation of bushfire residuals in source water and removal by coagulation

A bushfire is a spontaneous vegetation fire that can fundamentally affect lives, property, the environment, and even the global climate. Ash from fire carries hazardous pollutants like metal oxides/hydroxides, minerals, black carbons, and by-products of partial combustion, such as hydrocarbons and colloidal charcoal. Bushfire gases and residues can heavily pollute surface and groundwater resources.This paper focuses on the impact of bushfire residue on water quality and explores methods to remediate impacted water supplies. Soils burned in controlled furnace conditions between 150 °C, and 600 °C were characterised, suspended in water, and changes in water quality was measured following leaching from the burned residues. Results indicate that once the soil is burned at temperatures above 300 °C, there is little evidence of leached organic matter. At temperatures below 300 °C, the water discolouration was evident after 24 h leaching, and much higher quantities of leached organic matter were measured. Higher burning temperatures resulted in more alkaline residues.Leachate and charred sample characterisation data shows that the charcoal is highly porous and mainly consists of- amorphous material. The ash is a heterogeneous concoction of smaller particles and comprises significant mineral content. The results also indicate that the primary pollutant among the brushfire residuals is ash which increases pH, alkalinity, turbidity, and UV254. Coagulation experiments reveal that dual coagulation systems with metal salts- organic polyelectrolyte reduced the turbidity by 84 %, and dissolved organic carbon (DOC) reduced by 68 % of water containing ash residues. However, some other treatments are needed to reduce the alkalinity.

Techniques for monitoring bioavailable organic pollutants in sediment: Application of poly(methyl methacrylate) as a passive sampler

A poly(methyl methacrylate) (PMMA) passive sampler was applied to harbor sediment to examine whether the substrate could be used as a tool to measure freely dissolved concentrations of contaminants. An ex situ method required at least 1g of PMMA to detect freely dissolved polycyclic aromatic hydrocarbons (PAHs) in sediment with <100ng/g dry weight. Two weeks were sufficient to reach equilibrium under 180rpm for PAHs with a molar volume of <250cm3/mol. For the in situ method, a deployment time of four months was sufficient to measure PAHs with a molar volume up to 250cm3/mol in the sediment bed. The PMMA passive sampler could be used to measure the bioavailable fraction of PAHs in porewater, reflecting the complex properties of sediment with strong sorption such as black carbons.

Characteristics of typical dissolved black carbons and their influence on the formation of disinfection by-products in chlor(am)ination

Characteristics of typical dissolved black carbons and their influence on the formation of disinfection by-products in chlor(am)ination

New insights into the enhanced transport of uncoated and polyvinylpyrrolidone-coated silver nanoparticles in saturated porous media by dissolved black carbons

Silver nanoparticles (AgNPs) are among the most applied nanomaterials and have great potential to be present in the environment. Dissolved black carbon (DBC) is ubiquitous in soil as a result of large-scale application of biomass-derived black carbon as soil amendments, while its impacts on the transport of AgNPs remain unclear. In this study, two DBCs with different functional groups were prepared at 300 and 500 °C (DBC300 and DBC500), and their impacts on the transport of uncoated AgNPs (Bare-AgNP) and polyvinylpyrrolidone-coated AgNPs (PVP–AgNP) in saturated quartz sand were investigated. The transport of PVP-AgNP was much higher than Bare-AgNP under the same conditions because of the increased steric hindrance provided by PVP surface coating. The transport of two kinds of AgNPs was both enhanced by the DBCs under all the experimental conditions. DBC500 displayed a stronger enhancement effect than DBC300 on PVP-AgNP transport, but DBC300 facilitated the migration of Bare-AgNP more significantly than DBC500. The higher aromaticity and stronger hydrophobicity of DBC500 drove it to be adsorbed on the surface of PVP-AgNP, thus providing stronger steric hindrance and promotion effect on PVP-AgNP transport. However, DBC300 contained surface sulfhydryl groups, which bound with the Bare-AgNP tightly, therefore it greatly promoted Bare-AgNP transport via enhanced steric hindrance. (X)DLVO calculations indicated DBCs generally increased the energy barrier between the AgNPs and sand grains. The results shed light on the vital roles of both the properties of AgNPs and DBCs on the fate and environmental behaviors of silver nanomaterials in complex environments.

Sorption mechanisms of lead on soil-derived black carbon formed under varying cultivation systems

The knowledge about lead (Pb) sorption on soil-derived black carbons (SBCs) under different cultivation intensities of soils is limited. In this study, chemical and spectroscopic methods were applied to investigate the Pb sorption mechanisms on SBCs in soils from a forest land, a rubber plantation area, and a vegetable farm with none, less and highly intensive cultivation, respectively, that are located in the Hainan Island of China. Results showed that the specific surface area and cation exchange capacity of the SBCs from the less and highly intensive cultivation soils were 4.5- and 2.7-fold, and 1.3- and 1.8-fold higher compared to that of SBC from the no-cultivation soil, which subsequently enhanced the Pb sorption capacities of SBCs in iron exchange fraction. Ion exchange and hydrogen bonded Pb fractions together accounted for about 80% of total Pb sorbed on all SBCs at an externally added 1000 mg L−1 Pb solution concentration. The OC–O groups also played key roles in Pb sorption by forming complexes of OC–O–Pb–O and/or OC–O–Pb. Overall, SBCs in soils under all studied cultivation intensities showed high potential to sorb Pb (with the maximum absorbed Pb amount of 46.0–91.3 mg g−1), and increased Pb sorption capacities of the studied soils by 18.7–21.1 mg kg−1 in the stable fraction (complexation). Therefore, SBC might be a potential environment-friendly material to enhance the Pb immobilization capacity of soil.

The effect of small green walls on reduction of particulate matter concentration in open areas

A major concern in urban areas is the low quality of air, with high levels of particulate matter (PM), consisting of black carbons, volatile organic compounds and various pollutants that are hazardous for the human health and the global environment. Thus, there is an urgent need to decrease air pollution by implementing various short and long-term measures. One of the methods for decreasing air pollution in urban areas is increasing the green infrastructure as plants absorb the particulate matter through their leaves and stems. The initial step in dealing with this problem is raising the public awareness, which is generally low in Skopje and the Balkan region.The aim of the research is to quantify the positive effects on green infrastructure on air pollution and provide research-based inputs that can be used by local governments and decision makers. This paper presents data from continuous measurements on a location in Skopje, provides an assessment of the influence of green zones on air quality in urban areas and correlates it with meteorological factors. This is achieved by using an innovative, low-cost, easy replicable and energy-efficient system, consisted of green wall and stations for monitoring the air quality which are based on wireless sensor network technology.By using statistical tools as Freidman and Mann-Whitney tests, the impact of the relative position of the measurement sensors and the green areas and other objects to the PM concentrations is quantified. The performed analyses confirm that green areas, including green walls, have a high impact in the reduction of PM concentrations in their proximity.The differences in measured values obtained by measurement nodes positioned in relatively small distances are not negligible, thus implying that the relative position of the measurement nodes to the green infrastructure influences the measured PM concentrations. Therefore, the measurement location should be carefully considered for any air quality monitoring system. Measurements with higher spatial granularity should be used for modelling and air quality forecasting purposes.The results in this paper show that the green area mitigates the PM of 2.5 or less micrometers (PM2.5) on average by 25% and PM of 10 or less micrometers (PM10) on average by 37% compared to the neighboring non-green areas. The results show a strong correlation between PM2.5 and PM10. In Skopje, the combination of low temperatures, high humidity and no, or low wind speed lead to high PM concentrations.The presented algorithm compares the statistically obtained data to the reference categories from WHO (from very low to very high, with reference to PM2.5). The described methodology is used to develop a simple decision-making support algorithm for local governments to support their decisions on applying PM mitigation measures.

Oxidative transformation of 1-naphthylamine in water mediated by different environmental black carbons

Black carbons (BCs) are ubiquitous in the natural environment and can significantly influence the environmental behavior of pollutants. This work examined the mediating effects of graphite, soot, and biochar on 1-naphthylamine (1-NA) oxidation under aerobic conditions. It was shown that the three BCs significantly promoted the oxidation of 1-NA in the dark, and the mediation efficiency of graphite was much greater than that of soot or biochar. The oxidation products were the coupling oligomers (dimers and trimers) and the oxygen-containing oligomers of 1-NA (di-OH-1-NA, OH-azo naphthalene, OH-trimers and amino-naphthoquinone derivatives etc.). The phenolic OH on BCs were identified as the active sites for 1-NA oxidation, which could stimulate O2 to produce reactive oxygen species through successive single electron transfer and then cause 1-NA oxidation. Moreover, the superior catalytic performance of graphite was also related to its high electrical conductivity. The synergies between the sp2-hybridized carbon surface and the active sites (such as phenolic OH and defects) facilitated the oxidation of 1-NA on graphite. Findings in this study not only are helpful for better understanding the reactivity of environmental BCs, but also provide new insights into the risk assessment of 1-NA in the natural environment.

Impact of Carbon Porosity on the Performance of Cathode Microporous Layers in Proton Exchange Membrane Fuel Cells

AbstractAcetylene black carbons were activated under flowing CO2 atmosphere at 900 °C for different treatment times. The impact of this heat treatment on the porosity, hydrophilicity, and surface oxygen groups was carefully examined. Longer periods of activation led to increases in the surface area and porosity of the samples. Pore size distributions of the samples showed an increase in micropores, followed by a rise in mesopores, which indicated the occurrence of pore widening with a longer activation period. When used as a microporous layer for H2/air fuel cells, samples with higher levels of porosity showed, in general, reduced mass transport performance due to the formation of pooling locations for water. These results highlight the importance of textural pores in carbon structures on the water management in hydrogen fuel cell when operating under high humidity conditions.

Raman spectra of atmospheric particles measured in Maryland, USA over 22.5 h using an automated aerosol Raman spectrometer

Raman spectroscopy can be used to determine the vibrational frequencies of materials and from these the chemical compositions. Raman microspectroscopy (RMS) can help in understanding the chemistry of atmospheric and other aerosols. This paper describes the use of an automated Aerosol Raman Spectrometer (ARS) from Battelle to collect approximately 100,000 RS in 15-min intervals over 22.5 h in Maryland, USA. Approximately 9000 of these RS have intensities exceeding the thresholds used in this analysis. This paper describes and illustrates processing techniques used for the RS, including detection and removal of RS exhibiting charring, and estimation and removal of fluorescence and other broad features. RS exhibiting the D and G bands of soots and other black carbons (labeled DG Carbon or DGC), are especially common in the data, probably because the particles are charged to increase the collection efficiency of small particles; the Raman cross sections of DGC are large; and the sampling location is near major roads. RS consistent with calcium oxalate hydrates (C2O4)Ca·(1 + x)H2O where x = 0 (whewellite) and x = 1 (weddellite) are observed. RS with the ν(CO) frequency intermediate between the x = 0 and 1 extremes are also observed, possibly suggesting calcium oxalates with x between 0 and 1, or mixed oxalates including other metals, e.g., Fe or Mg. Other materials consistent with the measured RS are calcite, dolomite, gypsum, anhydrite, quartz, orthoclase, jadeite or muscovite, biological materials, and iron oxides. The measured RS data set and code to process these are provided.

Operando X-Ray Diffraction during Battery Cycling at Low Temperatures

Lithium-ion batteries are nowadays widely used in consumer electronics and electric vehicles. However, the application in electric vehicles poses new challenges to this battery technology. High energy and power densities, a high degree of safety and a long lifetime are important to meet the requirements of the customers. To improve lithium-ion batteries, it is necessary to gain a deeper understanding of electrochemical processes occurring during battery cycling. Operando characterization techniques are used to shed light on these processes. In particular, operando X-ray diffraction (XRD) and neutron diffraction are applied for the observation of phase changes of battery materials during cycling. Thereby, the lithiation and delithiation mechanism can be investigated depending on different factors like C-rate or temperature. The gained deeper understanding of the structural behavior of battery materials under various operating conditions leads to the improvement of battery management systems by increasing the performance and reducing degradation processes of batteries. The phase changes of state-of-the-art battery materials at room temperature are well understood but the influence of temperature on the phase evolution is barely investigated. Recent studies show that the classical staging mechanism of graphite [1, 2] does not occur at higher C-rates [3, 4] and elevated or low temperatures [5, 6] and instead, several stages coexist. During a rest period after charge or discharge, these phases can equilibrate [6]. The lithiation and delithiation mechanism does not only influence the charge and discharge behavior, but also the dimensional changes concurrently with the degradation of the electrodes [5]. Therefore, a deeper understanding of the structural behavior of battery materials under various operating conditions is needed to improve the material properties and adapt battery management systems to increase the performance of the battery and reduce degradation. At DLR, a new set-up was developed to investigate with operando XRD the phase evolution of battery materials during cycling at temperatures below room temperature. This method allows a readily characterization of battery materials at various temperatures and the identification of the temperature dependent intercalation mechanisms. [1] J. Besenhard and H.P. Fritz, The Electrochemistry of Black Carbons, Angew. Chem. Int. Ed. 22 (1983) 950-975. [2] J.R. Dahn, Phase diagram of LixC6, J. Phys. Rev. B. 44 (1991) 9170-9177. [3] H. He, C. Huang, C.-W. Luo, J.-J. Liu and Z.-S. Chao, Dynamic study of Li intercalation into graphite by in situ high energy synchrotron XRD, Electrochim. Acta. 92 (2013) 148-152. [4] N. Sharma and V.K. Peterson, Current-dependent electrode lattice fluctuations and anode phase evolution in a lithium-ion battery investigated by in situ neutron diffraction, Electrochim. Acta. 101 (2013) 79-85. [5] N.A. Cañas, P. Einsiedel, O.T. Freitag, C. Heim, M. Steinhauer, D.-W. Park and K.A. Friederich, Operando X-ray diffraction during battery cycling at elevated temperatures: A quantitative analysis of lithium-graphite intercalation compounds, Carbon. 116 (2017) 255-263. [6] V. Zinth, C. von Lüders, J. Wilhelm, S.V. Erhard, M. Hofmann, S. Seidlmayer, J. Rebelo-Kornmeider, W. Gan, A. Jossen and R. Gilles, Inhomogeneity and relaxation phenomena in the graphite anode of a lithium-ion battery probed by in situ neutron diffraction, J. of Power Sources. 361 (2017) 54-60.

Attachment of redox active molecules on the carbon additive and its effect on the cycling performance of LiFePO4 electrodes

The bis(1,10-phenanthroline)-5-amino-1,10-phenanthroline iron (II) complex (Fe2+[Phen]2[Phen-NH2]) was synthesized and characterized before covalent attachment to the surface of acetylene black carbon via diazonium chemistry. The metal complex was characterized by UV–visible spectroscopy and elemental analysis. Elemental analysis revealed a low grafting yield of approximately 3 wt%. Cycling voltammetry of modified-carbon electrode showed an apparent redox potential of 4.1 V (vs. Li) characteristic of the iron complex. The voltammetric charge associated to the redox peak corresponded to approximately 3.3 wt% of grafted groups, in agreement with the value estimated by elemental analysis. The electrochemical performance of LiFePO4 cathodes using modified and unmodified acetylene black carbons as conducting additive were compared through galvanostatic cycling and electrochemical impedance spectroscopy measurements. At a 5C rate, the electrode made with the modified carbon delivered a specific capacity of about 60 mAh.g−1 in comparison to only 25 mAh.g−1 for the composite with unmodified conductive additive. Charge/discharge cycling experiments over 200 cycles at C/2.5 revealed a capacity fade of about 0.2 and 0.14% per cycle for the LiFePO4 electrodes made with the unmodified and modified carbons, respectively. Furthermore, the charge-transfer resistance of LiFePO4 electrode using the grafted-carbon is significantly smaller (150 Ω) than the unmodified acetylene black (300 Ω).

Addition of Carbonaceous Material to Aquatic Sediments for Sorption of Lindane and p,p’-Dichlorodiphenyldichloroethylene

Isomers of hexachlorocyclohexanes (HCHs) and metabolites of dichlorodiphenyltrichloroethanes (DDTs) are still frequently detected worldwide in considerable amounts, even decades after their prohibition. Carbonaceous materials (CMs) have been shown to significantly reduce risks of propagation to humans by binding the hydrophobic organochlorine pesticides (OCPs) present in aquatic sediments. In the present study, black carbons extracted from natural sediments, and artificially produced black carbons, including black carbons by burning rice straw at 450 and 850 °C, and a commercial activated carbon were compared to investigate the factors affecting the sorption of γ-HCH (lindane) and p,p’-dichlorodiphenyldichloroethylene (p,p’-DDE) on CMs. The results indicated that when the proportion of CMs to total organic carbon (ƒCM/ƒOC) was greater than 0.35, CMs played a leading role in the sorption of lindane and p,p’-DDE by the sediments. The sorption contribution rate of CMs could reach up to 64.7%. When the ratio of ƒCM/ƒOC was less than 0.10, CMs played a minor role in the sorption. In addition, the nonlinearity of the sorption isotherms was strengthened with the increasing the proportion of CMs to total organic carbon. Our findings show that ƒCM/ƒOC value is a principal parameter for assessing the sorption capacity of sediments added by CMs for OCPs.