Thermal Carbon Research Articles

Operative Temperature Variance and Life Cycle Assessment Impacts of Wall Construction Materials

The overdependence on concrete in the construction industry in sub-Saharan African countries limits the potential use of sustainable materials in the construction of buildings. Hollow Concrete Block (HCB), the industry’s most widely used wall material, contributes to excessive carbon emissions and environmental degradation. Moreso, constructions that employ HCBs, specifically in Nigeria, severely threaten the indoor comfort levels in Naturally Ventilated Spaces NVSs. This study relies on quantitative data to analyse the impact of alternative wall materials in a case building in northern Nigeria. Mud bricks (MB) and Timber/brick (TB) were compared with the existing concrete (CW) case building. The study uses Meteonorm 8 and Climate Consultant 6.0 for EPW file generation. At the same time, dynamic thermal simulation and comparative experiments for thermal comfort and carbon emissions were conducted using DesignBuilder V6 and OneClick Lifecycle assessment tools, respectively. Modelled and simulated under NVS conditions using ASHRAE’s PMV model, the result of the study suggests that the MB alternative, although with an intermediate U-value of 0.318 W/m²k, accounts for the best indoor comfort temperature annually. While the CW building accounts for 41.31% of hours above the comfort temperature of 28⁰C, the TB and MB alternatives account for 29.99% and 27.37% of hours, respectively. Furthermore, the MB alternative is the most environmentally friendly material with 510 KgCO₂/m² emissions, a value 26% less than the CW building with an embodied carbon benchmark of 690 KgCO₂/m² during the building’s life cycle stages. The author suggests that mud construction’s thermal properties and Global Warming Impact (GWI) make it a better alternative to concrete and timber buildings in the tropics.

Divergence in Antiviral Activities of Carbon Dots versus Nano-Carbon/Organic Hybrids and Implications

Carbon dots (CDots) are generally defined as small carbon nanoparticles (CNPs) with effective surface passivation, for which the classical synthesis is the functionalization of pre-existing CNPs with organic molecules. However, “dot” samples produced by “one-pot” thermal carbonization of organic precursors are also popular in the literature. These carbonization-produced samples may contain nano-carbon domains embedded in organic matters from the precursors that survived the thermal processing, which may be considered and denoted as “nano-carbon/organic hybrids”. Recent experimental evidence indicated that the two different kinds of dot samples are largely divergent in their photo-induced antibacterial functions. In this work, three representative carbonization-produced samples from the precursor of citric acid–oligomeric polyethylenimine mixture with processing conditions of 200 °C for 3 h (CS200), 330 °C for 6 h (CS330), and microwave heating (CSMT) were compared with the classically synthesized CDots on their photo-induced antiviral activities. The results suggest major divergences in the activities between the different samples. Interestingly, CSMT also exhibited significant differences between antibacterial and antiviral activities. The mechanistic origins of the divergences were explored, with the results of different antimicrobial activities among the hybrid samples rationalized in terms of the degree of carbonization in the sample production and the different sample structural and morphological characteristics.

Thermal Air Oxidation-Mediated Synchronous Coordination and Carbonation of Lanthanum on Biochar toward Phosphorus Adsorption from Wastewater.

Biochar has attracted increasing attention as the sustainable and structure-tunable carrier for lanthanum (La) species for diverse applications. Carbonated La species possesses a higher biocompatibility and a lower leaching potential than other commonly used La species, while less attention is paid on the application of carbonated La in phosphorus (P) adsorption. Herein, thermal air oxidation (TAO) was applied as a novel strategy for synchronously tuning the coordination environment and chemical species of La on biochar surface. The results demonstrated that TAO induced the coordination of La with oxidation-generated oxygenated functional groups (OFGs) and carbonation of La species by the oxidation-generated CO2 on the biochar surface. The batch adsorption results showed that the Qm of resultant biochar remarkably increased from 68.92 to 132.49 mg/g at 1 g/L dosage. It also showed a robust adsorption stability in pH 2-6, a strong resistance to the co-existing Cl-, SO42-, NO3-, CO32-, or HCO3-, a stable adsorption recyclability, and an ultralow La leaching potential. The P adsorption was dominated by ligand exchange-induced inner-sphere complexation. In practical swine wastewater, the resultant biochar composite (1 g/L) removed 99.87% of P from 92.3 to 0.12 mg/L at a practical pH of 7.12. The density functional theory calculation further revealed the significant role of the binding of carbonated La by the biochar surface OFGs in reducing the P adsorption energies, indicating the synergism between the oxygenated biochar carrier and the carbonated La in P adsorption. Finally, this study provided a novel route to synchronously tune the coordination environment and chemical species of La on biochar via a facile TAO process for high-efficient P adsorption from wastewater.

Enhancement of combustion effect leading to improved performance and exhaust emissions of an SI engine with ferrous oxide and graphite nanoparticles.

The present study was conducted to investigate the effectiveness of new, less toxic, less harmful, and nonmetallic graphite (G) and metallic iron oxide (Fe2O3) nanofuel additives by analyzing experimentally their consequences on exhaust emissions and performance of an air cooled, single cylinder, 4-stroke gasoline engine. Fe2O3 and graphite nanoparticles at 40, 80, and 120 mg/l of gasoline concentrations were mixed with gasoline by means of a magnetic stirrer. Brake power (BP), brake-specific fuel consumption (BSFC), torque (T), brake thermal efficiency (BTE), nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and carbon dioxide (CO2) emissions were the investigated parameters. Experimental results indicated that G-blends showed a higher rise in brake power, brake thermal efficiency and torque and a greater reduction in the brake-specific fuel consumption as compared to that of Fe2O3 fuel blends. Moreover, the G-blends produced less NOx and CO2 than Fe2O3 blends but produced more emissions of CO and HC than that of Fe2O3 blends. On average, G-blends produced 0.46%, 0.71%, and 1.71% more torque, power, and BTE and 2.43%, 1.87%, and 13.39% less brake-specific fuel consumption (BSFC), NOx, and CO2 than Fe2O3 blends, respectively. So, in terms of the eight parameters, four performance parameters (i.e., T, BP, BSFC, BTE), and four engine emission exhaust indicators (i.e., CO, NOx, HC, CO2), graphite nanoparticles showed more positive results for 6 parameters (T, BP, BSFC, BTE, NOx, CO2), while two parameters HC and CO showed negative results with graphite as compared to that of Fe2O3 nanoparticles. So, overall, we conclude that nanoparticles of graphite are more engine and environment friendly than that of iron oxide fuel additives.

Detection of Carbonization of Paper in Transformers Using Duval Pentagon 2 and Triangle 5

The two most dangerous faults in transformers are arcing in paper insulation and thermal carbonization of paper inside windings. Both may result in catastrophic failures of the transformers. However, these faults are very difficult to detect. Furans content and the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CO ratio can be used, but they are often unreliable or not sensitive enough when small amounts of paper are involved. Furthermore, they cannot identify the exact location of the fault. Acoustic tests may be used for that purpose, but they are expensive and can be applied only to a small number of transformers. New inexpensive methods have been developed recently, using DGA and Duval Pentagon 1 and Triangle 1, to detect arcing in paper and differentiate it from arcing in oil. Duval Pentagon 2 and Triangle 5 have been used in the present article to detect faults C with thermal carbonization of paper and their location in transformers, i.e., in windings turns (the most dangerous) or in leads entering or exiting the windings. This offers the practical advantage of concentrating maintenance efforts of transformer operators on possible faults C with carbonization of paper in windings turns, which occur in a small number of transformers but may result in severe failures and outages.

Supply-demand balance of natural gas pipeline network integrating hydraulic and thermal characteristics, energy conservation and carbon reduction

Under the background of “One national network”, the balance between the natural gas supply side and the demand side is prominent. This paper proposes a supply-demand balance method of natural gas pipeline network coupled with the hydraulic and thermal characteristics, and decides the transportation scheme through flow rate allocation. This paper designs a two-stage relaxation optimization algorithm, coupled the thermal process into the hydraulic calculation to improve the hydraulic calculation accuracy, making the natural gas transportation scheme more applicable to engineering. The result shows the feasibility of transportation decision-making and the accuracy of hydro thermal calculation of the proposed model through a real case. The relative error of thermal calculation and TGNET is below 2%, and the hydraulic calculation error of coupled thermal can also be within 10%. After optimization, the carbon emissions decrease from 418,100 tons to 260,000 tons, reducing by about 37.81%. This study also analyzes the impact of hydraulic calculation on carbon emissions calculation, and further illustrates the necessity of coupled thermal characteristics in transportation scheme. This study can provide decision support for the transportation operation and help the natural gas pipeline network to meet the dual carbon requirements and achieve sustainable development.

Experimental study on the influence of surface modification methods of carbon fiber felt on the operation and heat transfer characteristics of loop heat pipes

Under high heat flux, the heat leakage rate of the compensation chamber in a small loop heat pipe is large, which affects the operational stability and heat transfer efficiency of the loop heat pipe. It was proposed for the first time to locally modify the capillary wick thermal conductivity through surface modification, thereby reducing the heat leakage from the compensation chamber. By spraying a high thermal conductivity metal coating on the surface of a low thermal conductivity carbon fiber felt, the contradiction between the heat dissipation rate of the heat source and the heat leakage of the compensation chamber was solved. Static wicking height showed that the metal coating increased the suction force of the carbon fiber felt. Start-up and operation experiments showed that the modified wick significantly improved the start-up stability of the loop heat pipe and reduced the temperature of the heat dissipation surface. The loop heat pipe with a single-sided-coated wick showed the lowest heat dissipation surface temperature, thermal resistance, and heat leakage rate. The loop heat pipe with an aluminum single-sided-coated wick exhibited a heat source temperature of 82.81 ℃, a thermal resistance of 0.26 K/W, and a heat transfer coefficient of 26.44 kW/(m2·K) under a load of 150 W (37.5 W/cm2). This study has significantly contributed to the future application of loop heat pipes in high heat flux electronic cooling.

Incentive Mechanisms for Thermal Power Generation Enterprises with Conflicting Tasks: Electricity Production versus Carbon Emission Reduction

Coal combustion remains the primary source of thermal power generation, contributing to approximately half of China’s electricity supply. As China strives towards the goals of “carbon peaking and carbon neutrality”, the issue of carbon emissions ascends to critical importance in the thermal power industry. The delicate balance between preserving electricity production capacity and curbing carbon emissions presents a considerable challenge to thermal power enterprise management. This paper models the incentive and organizational dilemmas arising from these conflicting tasks in thermal power generation enterprises, and compares the advantages and disadvantages of single-agent and multi-agent systems. Two practical scenarios are examined: (1) the “Two Mountains” theory propounded by the Chinese government, which attaches equal importance to thermal power production and carbon emission control, and (2) the 2022 Chinese summer electricity crisis, in which thermal power production takes on a dominant role. Through comparative static analysis of both single-agent and multi-agent models under these circumstances, this study concludes that, in the first scenario, the multi-agent model outperforms the single-agent model by enhancing agent effort levels and bolstering government revenue. However, when power supply emerges as the chief concern of thermal power enterprises, centralized management of a single-agent is more effective.

Prognostic Metamodel Development for Waste-Derived Biogas-Powered Dual-Fuel Engines Using Modern Machine Learning with K-Cross Fold Validation

Attention over greenhouse gas emissions has driven interest in cleaner energy sources including alternative fuels. Waste-derived biogas, which is produced by the anaerobic digestion of organic waste such as municipal solid waste, agricultural residues, and wastewater sludge, is an intriguing biofuel source due to its abundant availability and promise of lowering emissions. We investigate the potential of waste-derived biogas as an alternative fuel for a dual-fuel engine that also uses diesel as a secondary fuel in this study. We suggest using a modern machine learning XGBoost model to forecast engine performance. Data acquired with thorough lab-based text will be used to create prognostic models for each output in this effort. Control factors impacting engine performance, including pilot fuel injection pressure, engine load, and pilot fuel injection time, will be employed. The effects of these control elements on engine reaction variables such as brake thermal efficiency (BTE), peak pressure (Pmax), nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (UHC) were simulated. The created models were tested using a variety of statistical approaches, including the coefficient of determination (0.9628–0.9892), Pearson’s coefficient (0.9812–0.9945), mean absolute error (0.4412–5.89), and mean squared error (0.2845–101.7), all of which indicated a robust prognostic model. The use of the increased compression ratio helped in the improvement of BTE with a peak BTE of 26.12%, which could be achieved at an 18.5 compression ratio 220 bar fuel injection pressure peak engine load. Furthermore, our findings give light regarding how to improve the performance of dual-fuel engines that run on waste-derived biogas, with potential implications for cutting emissions in the transportation sector.

Effects of high thermal conductivity chopped fibers on ablation behavior of pressureless sintered SiC–ZrC ceramics

As one of the most promising thermal protection materials, the ablation performance of SiC–ZrC ceramics is strongly influenced by thermal conductivity. In this work, the high thermal conductivity mesophase pitch-based carbon fibers (MPCFs) were uniformly added into a mixture of SiC and ZrC powders, which were pressureless sintered to form a MPCFs modified SiC–ZrC ceramics. The relationship between thermal conductivity and MPCFs content was investigated in detail. Both theoretical calculations and experimental results showed that the SiC–ZrC ceramics modified by adding 4.81 vol% MPCFs gained the highest thermal conductivity of 68.10±0.68 W/(m⋅K). The simulation shows that the temperatures at ablation center and backside of the ceramics were 1094 °C and 446 °C, respectively, after plasma ablation at 2300 °C for 20 s. And the actual backside temperature was detected to be 438 °C and that agreed with the simulation results. The high thermal conductivity leads to a lower ablation temperature because the heat is rapidly transferred from the high temperature part to the low region. Due to the low ablation temperature, the 4.81 vol% MPCFs modified SiC–ZrC ceramics exhibited the lowest mass ablation rate (−0.048±0.007 mg/s) and linear ablation rate (−0.715±0.056 μm/s). This research presents a novel insight for designing and fabricating excellent ablation-resistance ultra-high temperature ceramics (UHTCs).

Development of a fuzzy logic model for the prediction of spark-ignition engine performance and emission for gasoline–ethanol blends

Abstract Due to the enormous of fossil fuels and the ensuing increase in automobiles, an unprecedented scenario has arisen with pollution levels that are out of human control. In this study, a fuzzy logic model is developed to predict how well a spark-ignition engine running on gasoline and ethanol mixes would operate. A test engine was operated on pure gasoline and gasoline–ethanol fuel mixtures in a range of ratios at varying engine speeds. In order to estimate outputs such as brake-specific fuel consumption (BSFC), brake thermal efficiency, nitrogen oxides (NOx), hydrocarbon emissions, and carbon monoxide, a fuzzy logic model, a sort of logic model application, has been developed using experimental data. The developed fuzzy logic model’s output was compared to the results of the trials to see how well it performed. The output parameters were indicated, including braking power, thermal, volumetric, and mechanical efficiency. The input parameters were engine speed and ethanol mixes. Regression coefficients were nearly equal for training and testing data. According to the study, a superior method for accurately forecasting engine performance is the fuzzy logic model. To eliminate proportionality signs from equations, regression analysis is used. It is accurate to develop mathematical relations based on dimensional analysis. Based on the root mean square errors, BSFC is a minimum of 6.12 and brake power is a maximum of 8.16; lower than 2% of errors occur on average.

Boosting electrocatalytic activity with the formation of abundant heterointerfaces and N, S dual-doped carbon nanotube for rechargeable Zn-air battery

Herein, a facile synthetic strategy is proposed to fabricate high-performance electrocatalysts for rechargeable Zn-air batteries (ZABs). Heterostructured NiCo/NiCo2S4 nanoparticles encapsulated in N-, S- co-doped CNT (NiCo/NiCo2S4@NSCNT) are synthesized via co-precipitation, thermal carbonization, and partial sulfidation processes. The strongly coupled NiCo/NiCo2S4 heterostructure can improve the redox property and charge transfer ability. Also, the CNTs with abundant foreign dopants provide high electrical conductivity and abundant defect sites for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The prepared NiCo/NiCo2S4@NSCNT electrocatalyst exhibits a low overpotential of 349 mV at a current density of 10 mA cm−2 and a half-wave potential of 0.865 V for the OER and ORR, respectively. Moreover, the ZAB assembled using as-prepared NiCo/NiCo2S4@NSCNT can provide superior specific capacity (756.16 mA h gZn−1), peak power density (155.82 mW cm−2), and long-term cyclability compared to those of the precious metal-based electrocatalyst (Pt/C + RuO2).

Potential savings in the cement industry using waste heat recovery technologies

This work describes technologies especially suitable for enhancing cement production process efficiency and overall plant performance by preheating raw material or generating electricity, thus reducing thermal losses, costs, and carbon dioxide emissions. Assessed systems for this purpose include power cycles such as the Organic Rankine Cycle, Tri-lateral Cycle, and Kalina cycle, and alternatives currently under development, such as thermoelectric generators and supercritical fluid cycles. Likewise, the zones of the cement production process with the most significant waste-heat recovery potential are pointed out, focusing on clinkerisation, which accounts for most of the thermal energy expenditure of a cement plant. In addition, the total carbon dioxide emissions related to cement manufacture and the participation of each production stage are presented. Finally, the potential for waste heat recovery in the cement industry of the first six Latin American producers is reviewed, which covers 82% of the total production in the region, based on the thermal and electrical requirements reported in the literature. The potential for emissions savings of carbon dioxide is estimated under the emission factor for the electricity system in each country.

Engineering Conductivity and Performance in Electrorheological Fluids Using a Nanosilica Grafting Approach

Carbonization is considered an effective process for the preparation of carbon-rich solids for various applications. Raw carbonaceous particles however often possess high electrical conductivity, limiting their applicability in electrorheology. To address this drawback, the carbonaceous particles prepared from glucose through hydrothermal synthesis, followed by thermal carbonization in an inert atmosphere, were subsequently coated by compact and mesoporous nanosilica, giving rise to semiconducting particles. The successful coating was confirmed using transmission electron microscopy and spectroscopic analysis, and the composite particles were further used as a dispersed phase in electrorheological (ER) fluids of concentration 5 wt %. While an ER fluid based on pure carbonized particles caused a short circuit of the measuring device at the electric field of intensity 1 kV mm–1, the ER behavior of its analogue based on mesoporous silica-coated particles was successfully measured up to 3 kV mm–1, giving a high yield stress exceeding even the values estimated for ER fluids based on similar carbonaceous particles coated with a compact silica layer. Even though the conductivity decreased only about one order of magnitude after the coating process, the dielectric properties of the prepared ER fluid differed significantly, the relaxation process was shifted to lower frequencies, and most importantly, the dielectric relaxation strength increased, indicating an increased amount of interactions. The presence of mesoporous nanosilica further enhanced the sedimentation stability of the ER fluids when compared to its analogue with the compact silica coating, expanding the scope of practical applicability.

Rapid Preparation of All-In-One Compressible Capacitors with Flame Carbonized Melamine Foam for AC Line Filtering

Melamine foam (MF) is a good candidate for electrochemical filter capacitors due to its 3D porous structure, flexibility, and nitrogen-containing property. However, traditional thermal carbonization would cause a severe loss of nitrogen and need several hours to perform the transition from melamine to carbon. Moreover, to construct all-in-one electrochemical capacitors, the nonconductive MF must be deposited a conductive layer on the surface of MFs. Herein, we developed a flame carbonization method to carbonize the MFs to an all-in-one structure in less than one minute. The carbonized MF exhibits 2.6 times higher nitrogen content than that of the traditional carbonized. MF-based all-in-one compressible electrochemical capacitors deliver excellent alternating current (AC) line filtering performance, such as a low phase angle of −83.1° at 120 Hz, a low resistance capacitance time constant of 157 μs, and a short relaxation time constant of 46 μs. The AC signal of 120 Hz, even a higher frequency of 2000 Hz, can be successfully converted into a stable direct current (DC) signal. Besides, the influence of electrolyte, compressive strain, and the thickness/carbonization time of MFs on the electrochemical performance has been studied. This work provides an ingenious design and effective preparation strategy for MFs-based all-in-one electrochemical capacitors.

High-enthalpy biphasic phase change organogels with shape memory function based on hydrophobic association and H-bonding interaction

Low-temperature solid–liquid organic phase change materials (OPCMs) offer tremendous opportunities in thermal management techniques but suffer from leakage problems above the melting temperature. Here, inspired with the universal hydro/organogels using three-dimensional polymer networks capable of holding large amounts of liquid solvents, a kind of form-stable high-enthalpy biphasic phase change organogels (BPCOGs) were developed by the integration of hydrophobic association for synthesizing intrinsic phase change matrices and H-bonding interaction for binding OPCM liquids. The porous phase separated poly(acrylamide-octadecyl acrylate) (P(AM-co-OA)) matrices with uniformly dispersed thermal conductive carbon nanotubes were fabricated from the hydrophobically associating hydrogels (HAHs), in which POA segments provide the phase change energy storage microdomains and the PAM network is capable of binding a series of melted OPCMs by hydrogen bond engineering. The fabricated BPCOGs possess form-stability, high phase change enthalpy (high up to 215.5 J g−1) and high energy storage efficiency (>90%), and show excellent electrical/optical-thermal energy conversion as well as shape memory performances. This study provides a universal strategy to prepare flexible biphasic OPCMs suitable for a variety of solid–liquid OPCMs including fatty alcohols, fatty acids and polyethylene glycol, and demonstrates the great potentials of these BPCOGs in solar energy utilization and functional flexible devices.

Potential of Integrating Solar Energy into Systems of Thermal Power Generation, Cooling-Refrigeration, Hydrogen Production, and Carbon Capture

Abstract Global warming due to the accumulation of CO2 in the atmosphere has directed global attention toward the adaptation of renewable energies and the use of renewable energy resources, like solar energy. Solar energy utilization could contribute to clean energy production, which is continuously needed due to increased population and industrialization. Recent increasing anxieties over energy sustainability and the preservation of the falling global ecosystem have renewed the expedition for extra efficient and economical processes for the utilization of renewable energy. Various approaches have been developed for the effective utilization of solar energy in different fields, which are highlighted in this work. In power generation, solar energy is utilized in preheating the air upstream of the combustion chamber in gas turbines and in waste heat recovery for combined-cogeneration cycles. It can also be used in Rankine cycles of thermal power plants utilizing low critical temperature gases such as CO2. In cooling and refrigeration systems, solar energy is utilized in reboilers, absorption, and mechanical cooling systems. Solar energy can also be utilized to produce clean fuels such as H2 production either from water splitting or from light and heavy fuels via fuel reforming and membrane separation. In addition, solar systems can be integrated to carbon capture applications in each of its three technologies of precombustion, oxyfuel combustion, and post-combustion. Integration of solar energy in these processes is reviewed comprehensively in this work. Thus, the solar energy in power generation, cooling-refrigeration, hydrogen production-storage, and carbon capture technologies are analyzed and evaluated.

Studying carbon fiber composite phase change materials: Preparation method, thermal storage analysis and application of battery thermal management

Carbon fiber composite phase change material (PCM) can serve as an excellent material for thermal storage system. This work presents a new composite PCM prepared with two raw materials of KAl(SO4)2·12H2O (X) and Na2SO4·10H2O (Y), supporting materials activated carbon fibers (ACFs), and thermal conductivity agent nano carbon powder (C). The characterization results show that adding 1 wt% C can increase the thermal conductivity about 81.0 % of mixed materials (C, X, and Y) than that of mixed X, Y; Moreover, the addition of ACFs also increases the thermal conductivity by 130 %. DSC tests reveal that phase change temperatures of XY and CXY are respectively 36.47 °C and 35.67 °C, meantime the enthalpies are 220.84 J/g and 185.24 J/g, respectively. Thus, this new material is suitable for the lithium-ion battery thermal management system (BTMS) applying. The application results show that ACFs composited CXY (ACFs/CXY) tremendously cripples the battery's temperature rise rate after the melting point in comparison with no wrapping material, and the ACFs/CXY-based BTMS can effectively control the battery temperature below 60 °C for 1903 s at the high heating power of 6 W. The ACFs composite PCM has the advantages of low cost, simple preparation, and easy acquisition, which reduces the cost of energy storage system, and has remarkable capacity of temperature controlling.

Activated carbon nanofibers derived from polyimides containing aryl imidazole and hydroxyl groups for high-performance supercapacitors

In this work, the carbon nanofibers (CNFs) are first prepared by electrospinning the poly(amic acid) (PAA) solution containing aryl imidazole and hydroxyl groups, followed by thermal imidization, rearrangement and carbonization. Then, the CNFs are further treated with KOH to obtain activated CNFs. The effects of the PAA concentration, rearrangement time, carbonation temperature and mass ratio of CNFs/KOH on the electrochemical properties are investigated. The results show that the sample HPI-CNF-20-2-800 displays the best electrochemical performance. After activation, the A-HPI–CNF–1/3 exhibits a maximum specific surface area of 1762 m2 g−1 and pore volume of 0.92 cm3 g−1, leading to a high specific capacitance of 325.0 F g−1 at 0.5 A g−1. Moreover, the specific capacitance can reach 234.6 F g−1 when the current density is 20 A g−1. Furthermore, the symmetric supercapacitor fabricated by A-HPI–CNF–1/3 shows a maximum energy density of 29.17 Wh kg−1, coupled with a power density of 500.0 W kg−1. The capacitance retention rate of the supercapacitor maintains about 99.95% after 20,000 charge-discharge cycles at 1 A g−1. Therefore, this work provides a novel rearrangeable precursor for the preparation of activated CNFs with a considerable electrochemical performance, which will be considered as excellent electrode materials for supercapacitors.

Fractal characteristics of porous carbon materials obtained from walnut shells

The structural features of carbon nanoporous materials (CM) were investigated by the low-temperature porometry method. Thuse, the CM has been obtained by thermal carbonization of plant biomass (walnut shells). The parameters of the CM samples were determined. In particular, the Neimark–Kiselev method was used to calculate the fractal dimension and estimate the surface inhomogeneity of the obtained CM samples by analyzing nitrogen adsorption isotherms. It was determined that, with an increase in the carbonization temperature of the raw material, the surface fractal dimension in the range from 1.68 to 2.56. The mineral composition was determined for СM samples using chemical elemental analysis.