Disordered Carbon Structure Research Articles

Impacts of temperatures and phosphoric-acid modification to the physicochemical properties of biochar for excellent sulfadiazine adsorption

The textural properties and surface chemistry of phosphoric acid-modified biochars (PABCs) prepared at different pyrolysis temperatures (500–700 °C) were studied based on the results obtained from XRD, SEM, BET, FT-IR, Raman, XPS and elements analyses. PABCs prepared at higher temperatures tended to possess a bigger proportion of microporous structure. The adsorption capacity and initial rate of PABCs for sulfadiazine (SDZ) were notably improved to 139.2 mg/g and 9.66 mg/(g min) as calculated from the Langmuir model. The adsorption equilibrium time was only one quarter of that without modification. The H3PO4 modification was advantageous to produce phosphate and break functional groups to form disordered carbon structure abundant of micropores. The enhancement in the adsorption of SDZ was due to the confinement effect of hydrophobic cavities from the mircoporous structure and the π–π electron–donor–acceptor interaction. Specially, PABCs exhibited stable adsorption capacities at a wide pH range (3.0–9.0) or relatively high concentrations of coexisting ions.

Process Parameters Optimization, Characterization, and Application of KOH-Activated Norway Spruce Bark Graphitic Biochars for Efficient Azo Dye Adsorption

In this work, Norway spruce bark was used as a precursor to prepare activated biochars (BCs) via chemical activation with potassium hydroxide (KOH) as a chemical activator. A Box–Behnken design (BBD) was conducted to evaluate and identify the optimal conditions to reach high specific surface area and high mass yield of BC samples. The studied BC preparation parameters and their levels were as follows: pyrolysis temperature (700, 800, and 900 °C), holding time (1, 2, and 3 h), and ratio of the biomass: chemical activator of 1: 1, 1.5, and 2. The planned BBD yielded BC with extremely high SSA values, up to 2209 m2·g−1. In addition, the BCs were physiochemically characterized, and the results indicated that the BCs exhibited disordered carbon structures and presented a high quantity of O-bearing functional groups on their surfaces, which might improve their adsorption performance towards organic pollutant removal. The BC with the highest SSA value was then employed as an adsorbent to remove Evans blue dye (EB) and colorful effluents. The kinetic study followed a general-order (GO) model, as the most suitable model to describe the experimental data, while the Redlich–Peterson model fitted the equilibrium data better. The EB adsorption capacity was 396.1 mg·g−1. The employment of the BC in the treatment of synthetic effluents, with several dyes and other organic and inorganic compounds, returned a high percentage of removal degree up to 87.7%. Desorption and cyclability tests showed that the biochar can be efficiently regenerated, maintaining an adsorption capacity of 75% after 4 adsorption–desorption cycles. The results of this work pointed out that Norway spruce bark indeed is a promising precursor for producing biochars with very promising properties.

Tridax procumbens flowers derived carbon as electrode material in aqueous supercapacitor

Microwave synthesized activated carbon utilizing Tridax procumbens flowers is reported as supercapacitor electrode. Incomplete graphitization with disordered carbon structure and honeycomb-like surface morphology is achieved. In aqueous H2SO4 electrolyte, the material exhibits charge storage through non-faradaic, electrostatic accumulation/adsorption of charges at electrode-electrolyte interface. The charge/discharge curves confirm the capacitive behavior of the material with a specific capacitance of 168 F g−1 at a current density of 0.5 A g−1. A notable energy density of 2.46 W h kg−1 at a 163 W kg−1 power density is achieved in the assembled symmetric device making it a pertinent electrode material for supercapacitors.

Investigation of MXenes Oxidation Process during SPS Method Annealing.

This paper discusses the effects of the environment and temperature of the Ti3C2 (MXene) oxidation process. The MXene powders were annealed at temperatures of 1000, 1200, 1400, 1600, and 1800 °C in argon and vacuum using a Spark Plasma Sintering (SPS) furnace. The purpose of the applied annealing method was to determine the influence of a high heating rate on the MXene degradation scheme. Additionally, to determine the thermal stability of MXene during the sintering of SiC matrix composites, SiC–C–B–Ti3C2 powder mixtures were also annealed. The process parameters were as follows: Temperatures of 1400 and 1600 °C, and pressure of 30 MPa in a vacuum. Observations of the microstructure showed that, due to annealing of the SiC–C–B–Ti3C2 powder mixtures, porous particles are formed consisting of TiC, Ti3C2sym, and amorphous carbon. The formation of porous particles is a transitional stage in the formation of disordered carbon structures.

CHARACTERIZATION OF CARBON FIBERS DERIVED FROM THERMALLY STABILIZED POLY(HEXAMETHYLENE ADIPAMIDE) PRECURSOR FIBERS

The thermal oxidative stabilization and carbonization processes of poly(hexamethylene adipamide) or (polyamide 66) fibers were accomplished to transform into carbon fibers. Polyamide 66 fibers were pretreated with a ethanol solution of cupric chloride followed by a stabilization process in the air atmosphere. Carbonization experiments were executed at temperatures of 500, 700, 900, and 1100°C utilizing heating rate of 2.5 °C/min. Carbonization experiments were performed at temperatures between 500 and 1100°C employing the rises of 100°C. X-ray diffraction analysis of the carbon fibers shown a highly disordered carbon structure developed during the carbonization process. The values of fiber diameter, linear density, volume density, carbon fiber yield, elemental analysis, and electrical properties revealed a strong dependence on the carbonization temperature. As an insulating material, the polyamide 66 or PA66 precursor was transformed to a semiconducting stage after the thermal stabilization and carbonization processes. The current study demonstrated how processing parameters influence the structure and characteristics of carbon fibers produced from poly(hexamethylene adipamide) fibers.

Application of design of experiments (DoE) for optimised production of micro- and mesoporous Norway spruce bark activated carbons

In this work, Norway spruce (Picea abies (Karst) L.) bark was employed as a precursor to prepare activated carbon using zinc chloride (ZnCl2) as a chemical activator. The purpose of this study was to determine optimal activated carbon (AC) preparation variables by the response surface methodology using a Box–Behnken design (BBD) to obtain AC with high specific surface area (SBET), mesopore surface area (SMESO), and micropore surface area (SMICR). Variables and levels used in the design were pyrolysis temperature (700, 800, and 900 °C), holding time (1, 2, and 3 h), and bark/ZnCl2 impregnation ratio (1, 1.5, and 2). The optimal conditions for achieving the highest SBET were as follows: a pyrolysis temperature of 700 °C, a holding time of 1 h, and a spruce bark/ZnCl2 ratio of 1.5, which yielded an SBET value of 1374 m2 g−1. For maximised mesopore area, the optimal condition was at a pyrolysis temperature of 700 °C, a holding time of 2 h, and a bark/ZnCl2 ratio of 2, which yielded a SMESO area of 1311 m2 g−1, where mesopores (SMESO%) comprised 97.4% of total SBET. Correspondingly, for micropore formation, the highest micropore area was found at a pyrolysis temperature of 800 °C, a holding time of 3 h, and a bark/ZnCl2 ratio of 2, corresponding to 1117 m2 g−1, with 94.3% of the total SBET consisting of micropores (SMICRO%). The bark/ZnCl2 ratio and pyrolysis temperature had the strongest impact on the SBET, while the interaction between temperature and bark/ZnCl2 ratio was the most significant factor for SMESO. For the SMICRO, holding time was the most important factor. In general, the spruce bark AC showed predominantly mesoporous structures. All activated carbons had high carbon and low ash contents. Chemical characterisation indicated that the ACs presented disordered carbon structures with oxygen functional groups on the ACs’ surfaces. Well-developed porosity and a large surface area combined with favourable chemical composition render the activated carbons from Norway spruce bark with interesting physicochemical properties. The ACs were successfully tested to adsorb sodium diclofenac from aqueous solutions showing to be attractive products to use as adsorbents to tackle polluted waters.Graphical abstract

Effect of the methane flow ratio on the structural and mechanical properties of high-entropy alloy co-doped DLC films

High-entropy alloy is co-doped in diamond-like carbon films by sputtering using a single (AlCrNbSiTiV) target. This study analyzed the effects of methane flow rates [Rm = CH4/(Ar + CH4) flow ratio], which varied in the range from 16 to 24%, on the morphological, phase structures, mechanical characteristics and tribological behavior of diamond-like carbon films. The diamond-like carbon film is characterized using Raman spectroscopy, nano-indentation, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and scratch testing. As a result, the element concentration in the diamond-like carbon films is quite near to the High-entropy alloy target composition, and the metal content of co-doped diamond-like carbon films decreases as the fraction of the methane reactive gas increases. For a monotonically increasing Rm flow ratio, the position of the G-peak is downshifted to a low wavenumber, a decrease in ID/IG ratio suggests a decrease in sp2/sp3 ratio, which is associated with the decrease in the fraction of graphite and the more disordered carbon structure. An increase in the Rm flow ratio results in increased hardness (H) and elastic modulus (E) and a decreased friction coefficient, wear rate, H3/E2 and H/E. Cutting tests using a tool coated in a diamond-like carbon film shows the cutter life was extended.

NMR studies of adsorption and diffusion in porous carbonaceous materials

Porous carbonaceous materials have many important industrial applications including energy storage, water purification, and adsorption of volatile organic compounds. Most of their applications rely upon the adsorption of molecules or ions within the interior pore volume of the carbon particles. Understanding the behaviour and properties of adsorbate species on the molecular level is therefore key for optimising porous carbon materials, but this is very challenging owing to the complexity of the disordered carbon structure and the presence of multiple phases in the system. In recent years, NMR spectroscopy has emerged as one of the few experimental techniques that can resolve adsorbed species from those outside the pore network. Adsorbed, or “in-pore” species are shielded with respect to their free (or “ex-pore”) counterparts. This shielding effect arises primarily due to ring currents in the carbon structure in the presence of a magnetic field, such that the observed chemical shift differences upon adsorption are independent of the observed nucleus to a first approximation. Theoretical modelling has played an important role in rationalising and explaining these experimental observations. Together, experiments and simulations have enabled a large amount of information to be gained on the adsorption and diffusion of adsorbed species, as well as on the structural and magnetic properties of the porous carbon adsorbent. Here, we review the methodological developments and applications of NMR spectroscopy and related modelling in this field, and provide perspectives on possible future applications and research directions.

Study on the effect of inherent AAEM on char structure evolution during coal pyrolysis by in-situ Raman and TG

Inherent minerals, especially alkali and alkaline earth metals (AAEM), are reactive constituents that interact with organic matter during pyrolysis and have significant effects on thermal characteristics and carbon structure evolution of char. The pyrolysis of raw and leached coal samples was conducted by using thermogravimetric analyzer and in-situ Raman system to explore the effects of content and chemical form of AAEM on pyrolysis characteristics and carbon structure evolution of single char particle. The water-soluble and ion-exchangeable AAEM promoted continuous breaking/reforming of bonds between alkyl substitutional groups and aromatic ring systems, resulting in the delay of volatiles release and orderly evolution of carbon structure during pyrolysis. The effects of water-soluble AAEM was more severe, because the divalent alkaline earth metal bonds to carbon was much more stable than the monovalent alkali metal for the inherent AAEM participated in the polycondensation reaction. Besides, the ion-exchangeable AAEM inhibited the generation of cross-linked structures more effectively than water-soluble AAEM, because ion-exchangeable AAEM existed in the form of AAEM-carboxylates and delayed the thermal decomposition. Moreover, the inherent AAEM promoted the miniaturization of carbon crystal structure in the carbon matrix, forming char with disordered carbon structure.

Carbon Fibers with Low Cost and Uniform Disordered Structure Derived from Lignin/Polyacrylonitrile Composite Precursors

Lignin/polyacrylonitrile (PAN) composite precursors and PAN precursors were prepared by wet spinning and then converted into carbon fibers together under different carbonization temperatures. The microscopic morphology, mechanical properties and microstructure of the carbon fibers were studied. All the carbon fibers had dense structure without any visible macrovoids. Carbon fibers with tensile strength of 2.1 GPa and tensile modulus of 224 GPa were obtained from the lignin/PAN composite precursor by carbonizing at 1200 °C. Interestingly, the lignin/PAN-based carbon fibers had a unique uniform disordered carbon structure. They were expected to be applied in the fields of electrothermal conversion and thermal insulation, besides composites.

Sagoe Starch Derived Hard Carbons As Anodes for Sodium Ion Battery

Based on the chemical similarity, large abundance and cheap price, sodium ion battery (SIB) can become a promising alternative to subsitute lithium ion battery (LIB). The main issue of the development of SIB is to look for a suitable anode material since graphite, the anodes in LIB, can not be used in SIB because of the unstable thermodynamic properties . In this work, we report the synthesis of hard carbon anodes for SIB from sagoe starch that are prepared by hydrothermal carbonization followed by the pyrolysis process at moderate temperature between 500 °C and 900 °C. Morphology studies show that the hard carbon is very porous porous with interconnected porous network. X-ray diffraction and Raman spectroscopic analysis show that the carbon materials have disordered carbon structure with large interlayer spacing pf 0.39 nm. The electrochemical characterizations reveal that hard carbon which is prepared at 700 °C (STHC-700) shows the best performance, showing 375 mAh g−1 and 290 mAh g−1, initial discharge and charge capacities, respectively. Specific capacities of about 268 mAh g−1 and 178 mAh g−1 are obtained for WHC-700 material at a current density of 50 and 200 mA g−1, respectively. The sagoe starch produce hard carbon material at moderate pyrolysis temperature with microstructural properties and large interlayer spacing. These properties are contributing for the excellent electrochemical performance as anodes for sodium ion batteries.

Investigation of the carbon structure of naturally graphitized coals from Central Hunan, China, by density-gradient centrifugation, X-ray diffraction, and high-resolution transmission electron microscopy

A suite of six naturally graphitized coals were separated by density-gradient centrifugation (DGC). The density profiles of anthracite and meta-anthracite samples show an average density increase from 1.50 g/mL to 1.93 g/mL with increased rank. Components of partially graphitized coals were separated into two distinct density peaks: a low-density peak at ~1.82 g/mL, and a high-density peak at ~2.0 g/mL; sample SL-3 also showed a shoulder at around 2.14 g/mL. The separated density fractions of the partially graphitized samples were examined by X-ray diffraction (XRD) and optical microscopy. This revealed that the lower density portions contain vitrinite and inertinite, whereas microcrystalline graphite along with needle and flake graphite are the primary components of the higher density portions, demonstrating that DGC can be used to separate components in metamorphosed coals. Carbon phases including local molecular oriented domains (LMODs) and turbostratic layers are observed in the partially graphitized coals under high-resolution transmission electron microscopy (HRTEM). The average density of the most graphitized coal is 2.18 g/mL, which together with the XRD pattern suggests a carbon structure close to that of graphite. In anthracite, basic structural units (BSUs) are distributed throughout the disordered carbon structure matrix; whereas graphitic lamellae are the primary constituent in the most graphitized coals, indicating the transformation of the carbon structure from amorphous-like anthracite to ordered graphite during natural graphitization. The co-occurrence of different carbon phases and structural units in the same sample demonstrates the heterogeneous nature of graphitized coals. The presence of novel carbon structures (such as BSUs, LMODs, turbostratic structure, and onion-like carbon, etc.) in the naturally graphitized coal series suggests potential use in the future development of new coal-based carbon materials.

Thermal analysis of the products of SCS of zinc nitrate with glycine and citric acid

The composition of powders produced in reactions of Solution Combustion Synthesis (SCS) of zinc nitrate with glycine and a mixture of glycine and citric acid has been studied. The precursors formed on completion of solution combustion reactions were established to contain ZnO and up to 7 wt% of carbonaceous fragments due to incomplete oxidation of fuel. The latter are mixtures of residual carbon (0.2−3 wt%) and the fragments of citric acid decomposition, bound carbon, (0.6–4.4 wt%), which are strongly disordered carbon structures in nature, including amorphous ones. The performed thermal analysis of precursors and modeling allow us to suppose that the process of additional oxidation takes place in two stages – at 240−280 °C (oxidation of organic fragments) and 410−424 °C (oxidation of residual carbon) and is incomplete in character. It was shown that the complete removal of the carbonaceous fragments of organic fuel needs the temperatures close or over 900 °C. The best conductivity of ZnO were 1.13·10−7 and 9.19·10−8 S/cm after SCS and annealing 650 °C, respectively.

Investigation on carbide slag catalytic effect of Mongolian bituminous coal steam gasification process

Carbide slag may pollute the environment because it is difficult to handle. In this paper, carbide slag without pretreatment served as the new source of calcium and was added to bituminous coal for gasification experiments to realize waste utilization. The gasification experiment after adding carbide slag to bituminous coal enhances H2 production, which reduced the activation energy of the gasification reaction. The results show that the catalytic effect on steam gasification was evident when the carbide slag was added to Mongolian bituminous coal. The coal char at reaction temperature was prepared and characterized by X-ray diffraction (XRD), Raman, Scanning electron microscope (SEM), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and FT-IR spectroscopy. The carbon structure evolution and calcium structure changes of coal char under reaction temperature were studied, and the influence of coal char structure changes on gasification performance was analyzed. The results show that in the coal char added with carbide slag, the oxygen-containing functional groups generated by the polycondensation reaction interacted with calcium to form a calcium-oxygen-carbon complex. The existence of this structure not only leads to the highly uniform dispersion of CaO in the char but also hinders the graphitization process of the char. Highly dispersed CaO and disordered carbon structure significantly improved the reactivity of bituminous coal steam gasification. Si and Al in the bituminous coal affected the dispersion of Ca during steam gasification.

Novel Approach Through the Harmonized Sulfur in Disordered Carbon Structure for High-Efficiency Sodium-Ion Exchange.

Sodium-ion batteries (SiBs) have recently attracted considerable interest due to the plentiful supply of raw materials for their production and their electrochemical behavior, which is similar to that of lithium-ion batteries (LiBs). However, the relatively larger radius of sodium ions than that of lithium ions is not suitable for storage in conventional graphite, which is widely used as the anode. To resolve this issue, in this study, we developed a new harmonized carbon material with a three-dimensional (3D) grapevine-like structure and a sulfur component using an efficient synthesis process. On the basis of these advantages, the harmonized sulfur-carbon material exhibited a highly reversible capacity of 146 mA h g-1 at an extremely high specific current of 100 A g-1 and long-term galvanostatic cycling stability at 10 and 100 A g-1 with superior electrochemical performance. Our results are anticipated to provide new insights into SiB anode materials that would advance their production.

Investigation of coal-biomass interaction during co-pyrolysis by char separation and its effect on coal char structure and gasification reactivity with CO2

The interaction between coal and biomass has been widely investigated. However, the mechanism is always proposed based on physicochemical structure and reactivity of char mixture. In this work, char mixture after co-pyrolysis of anthracite and biomass was separated based on different shape and size, and then structure and reactivity of the coal char were analyzed to reveal mechanism of coal-biomass interaction. Anthracite char samples with different corn straw (CS) blending ratios were prepared by pyrolysis in a fixed bed reactor at 600 and 900°C. The AAEM concentration and microcrystalline structures of coal char were examined by inductively coupled plasma-optical emission spectrometry (ICP-OES) system and X-ray diffraction (XRD). The gasification reactivity of char sample after separation was analyzed by TGA under CO2. The results show that concentration of active K and Mg in coal char samples gradually increased and more disordered carbon structure formed as the CS proportion in the blending increased from 0 to 80%. The coal char in the blending captured more AAEM species by volatile-char interactions instead of escaping with volatile from biomass during co-pyrolysis process. Meanwhile, higher pyrolysis temperature led to volatilization and inactivation of K and Na, and also decrease in graphitization degree. Moreover, both addition of CS and low pyrolysis temperature could promote gasification reactivity of coal char sample. Furthermore, a satisfactory linear correlation (R2=0.9009) between alkali index AI and R0.5 of the char samples was established. This indicated that AAEMs performed the dominate effect to enhance gasification reactivity of coal char during co-gasification of coal and biomass.

The Formation of the Nanosized Surface Layers of a Titanium Alloy by Ion-Beam Mixing of Carbon with N+ Ion Implantation

The formation of nanoscale layers on the VT6 titanium alloy surface by ion-beam mixing of carbon with the N+ ion implantation is investigated in this work. Ion-beam mixing in the transition layer of a film–carbon system on the VT6 alloy surface has been found to provide conditions for the formation of titanium carbides and nitrides. The thin surface layer (~10–20 nm) of the samples after both the deposition and ion-beam mixing of a carbon film mostly consists of carbon in a disordered state with sp2 and sp3-hybridized C–C bonds. The formation of titanium carbides and nitrides in the transition layer, a disordered carbon structure in the thin surface layer, leads to a tenfold increase in the corrosion resistance of the samples.

Combustion behavior of chars derived from coal pyrolysis under a CO-containing atmosphere

The combustion behaviors of chars derived from coal pyrolysis under a CO-containing atmosphere were analyzed by thermogravimetry, and the structural changes of char samples prepared under different pyrolysis conditions (temperature and atmosphere) were characterized by scanning electron microscopy, X-ray diffraction, and CO2 adsorption methods. The apparent activation energies (Ea) of char-N2 and char−CO under non-isothermal combustion conditions were obtained by the Flynn–Wall–Ozawa method. Char-N2 exhibited higher combustion reactivity than char−CO, a more developed micropore structure, a more ordered carbon microcrystalline structure, and a higher Ea at the same pyrolysis temperature. In a CO-containing pyrolysis atmosphere, the carbon particles precipitated by the disproportionation reaction blocked the pores (inhibiting the escape of volatiles), reduced the number of active char sites, and increased the order of the carbon structure. The volatile content significantly influenced the Ea only during the initial conversion rate of char combustion. Based on the high reactivity of the disordered carbon structure, chemical reaction is the likely limiting factor of char-N2 combustion, whereas diffusion should mainly limit char−CO combustion.

Transparent magnesium aluminate spinel: Effect of critical temperature in two-stage spark plasma sintering

The discolouration of magnesium aluminate spinel caused by carbon contamination is a main drawback of fabricating transparent bodies by spark plasma sintering (SPS). In this study, a two-stage heating rate profile was used to produce transparent MgAl2O4 without using sintering aids by SPS at 1250°C. The effect of critical temperature (Tc), at which the heating rate is decreased, on transparency and carbon contamination was investigated: higher critical temperature resulted in higher contamination. Non-uniform densification indicated that fast heating results in a hot-zone formation in the centre of sintered pellets; the higher temperature of centre favoured reaction of graphite die with spinel and formation of disordered carbon structures in residual pores.

Rambutan peel based hard carbons as anode materials for sodium ion battery

Sodium (Na) ion battery (NIBs) are considered as one of the most prospective battery system to substitute lithium ion batteries (LIBs) especially for stationary applications. In this study, rambutan peels were selected as carbon precursors to prepare hard carbons as anode materials for NIBs. Hard carbons were prepared by applying hydrothermal carbonization and then continued by the pyrolysis treatment at different temperatures (800, 1000 and 1200 °C). The electrochemical studies were carried out by cyclic voltammetry (CV) and galvanostatic charge discharge (GCD). The obtained hard carbons at pyrolysis temperature of 1000 exhibited the best electrochemical performance. It showed the highest reversible capacity of 225 mAh g−1 (0.1 C-rate, 1 C = 300 mA g−1) after 100 cycles if tested as the anode materials for NIBs. It is attributed to the disordered carbon structure, low degree of graphitization, large interlayer spacing and flake-like morphology of carbon sample which can provide more space for sodium storage and facilitate sodium ion transfer.