Textural characteristics of activated carbon by single step CO2 activation from coconut shells

Synthesis and optimization of biobased carbon adsorbent monoliths from chitosan-polybenzoxazine for efficient CO2 capture

The present study introduces a novel method for the preparation of a CO2 carbon adsorbent derived from biobased precursors. Porous carbon adsorbents were synthesized through the carbonization and thermal activation of biobased chitosan-polybenzoxazine. First, the study explored the influence of varying amounts of the key polymer precursors, lysine (0.05-0.1 g) and chitosan (0.6-0.12 g), on the surface and adsorption characteristics of the obtained carbons. This aimed to identify the most favourable amounts of these precursors that resulted in the highest CO2 adsorption performance. In the subsequent stage, the study investigated the impact of different activation times (1-7 h) to enhance the surface characteristics and CO2 adsorption capacity of the activated carbon. Both carbonization and activation processes were conducted in a tubular furnace at 900 °C under N2 and CO2 atmospheres, respectively. After carbonization, the resulting carbon monoliths exhibited a char yield of approximately 49 wt%, with a BET surface area of up to 541 m2 g-1 and a CO2 uptake of 4.0 mmol g-1 at 0 °C and 1 bar. After activation, the obtained samples displayed a surface area in the range of 650-1000 m2 g-1, with CO2 adsorption capacities at 1 bar ranging from 4.5 to 5.6 mmol g-1 at 0 °C and 3.2 to 4 mmol g-1 at 25 °C. The activated carbons also demonstrated excellent selectivities for CO2/N2 and CO2/CH4 mixtures, along with a stable CO2 adsorption-desorption performance after 10 cycles.

The Significance of Lignocellulosic Raw Materials on the Pore Structure of Activated Carbons Prepared by Steam Activation

Five different lignocellulosic raw materials (coconut shells, Moso bamboo, sawtooth oak, Chinese fir, and Masson pine) were used to prepare activated carbons by steam activation at 850 °C to evaluate the effects of their structures on physical activation. The chemical compositions, botanic forms, and pore structures of the lignocellulose-based charcoal samples were systematically characterized by proximate and ultimate analyses, scanning electron microscopy, and mercury injection porosimetry. It was found that the rate of the activation reaction between charcoal and steam is determined by the porosity of the precursor. Pore structure results show that the steam activation of coconut shell and bamboo charcoals primarily produced micropores, thus yielding microporous activated carbon materials with just a few mesopores, even following a high burn-off of >66%. The steam activation of sawtooth oak charcoals produced mainly micropores at a low burn-off of <50% and both micropores and mesopores at a high burn-off of >50%. The steam activation of Chinese fir and Masson pine charcoals produced mainly mesopores at a burn-off of 0-80%. These mesopores were remarkably broadened to >20 nm on extending the activation time, resulting in a high vitamin B12 (VB12) adsorption capacity of ~530 mg/g. In conclusion, the raw lignocellulosic materials used as precursors have a decisive effect on the development of pore structures in activated carbon materials obtained through physical activation.

Comparative Study of Three Dyes' Adsorption onto Activated Carbon from Chenopodium quinoa Willd and Quillaja saponaria

The present study shows porous activated carbon obtained from Chenopodium quinoa Willd and Quillaja saponaria and their use as potential adsorbents to remove three types of dyes from aqueous solutions. The adsorption results were compared with commercial charcoal to check their efficiency. All porous carbon materials were activated using carbon dioxide and steam and fully characterized. Moreover, the steam-activated samples exhibited a high total pore volume with a BET surface area of around 800 m2 g−1. Batch adsorption experiments showed that commercial charcoal is the charcoal that offered the best adsorption efficiency for tartrazine and sunset yellow FCF. However, in the case of crystal violet, all activated carbons obtained from Chenopodium quinoa Willd and Quillaja saponaria showed the best captures, outperforming commercial charcoal. Molecular dockings of the dyes on the commercial charcoal surface were performed using AutoDock Vina. The kinetic results of the three isotherm’s models for the present data follow the order: Langmuir~Freundlich > Temkin.

Use of Eggshell-Catalyzed Biochar Adsorbents for Pb Removal from Aqueous Solution

Eggshell is a cheap and environmentally friendly calcium source. In this study, Ca-modified biochar adsorbents (CEA) were prepared by 1:10, 1:2, and 1:1 mass ratio of the eggshell and Eupatorium adenophorum. The CEA-2 sample prepared with a 1:2 mass ratio showed a maximum Pb adsorption capacity (97.74 mg·g^-1) at the conditions of an initial pH of 7.0, an adsorbent dosage of 0.5 g·L^-1, and a contact time of 8.0 h. The kinetic and isotherm studies indicated that the adsorption process of the CEA-2 sample had monolayer adsorption characteristics, which was controlled together by intraparticle and interface diffusion. Thermodynamic studies indicated that the adsorption process of CEA-2 was spontaneous (ΔG ⁰ <0) and endothermic (ΔH ⁰ > 0). X-ray diffraction and scanning electron microscopy analyses showed a uniform distribution of Ca-Pb precipitation on the CEA-2 surface, which proved that chemical precipitation was the main adsorption mechanism. Fourier transform infrared spectra found that CEA-2 had abundant active groups, especially nitrogen-containing functional groups, which could adsorb Pb through a surface complexation reaction. The Brunauer-Emmett-Teller surface area of CEA-2 was found to be 621 m²·g^-1, and such developed pores could ensure the smooth diffusion of Pb. Finally, the effect of coexisting cation and anion experiment and the cyclic regeneration experiment indicated that CEA-2 had prominent stability and reusability for Pb adsorption.

Advanced Material-oriented Biomass Precise Reconstruction: A Review on Porous Carbon with Inherited Natural Structure and Created Artificial Structure by Post-treatment

Manufacturing of porous carbon with biomass resources has been intensively investigated in recent decades. The diversity of biomass species and great variety of processing methods enable the structural richness of porous carbon as well as their wide applications. In this review, we specifically focused on the structure of biomass-derived porous carbon either inherited from natural biomass or created by post-treatment. The intrinsic structure of plant biomass was briefly introduced and the utilization of the unique structures at different length-scales were discussed. In term of post-treatment, the structural features of activated carbon by traditional physical and chemical activation were summarized and compared in a wide spectrum of biomass species, statistical analysis were performed to evaluate the effectiveness of different activation methods in creating specific pore structures. The similar pore structure of biomass-derived carbon and coal-derived carbon suggested a promising replacement with more sustainable biomass resources in producing porous carbon. In summary, using biomass as porous carbon precursor endows the flexibility of using its naturally patterned micro-structure and the tunability of controlled pore-creation by post treatment. This article is protected by copyright. All rights reserved.

Effect analysis of pore wall thickness, pore size, and functional group of activated carbon on adsorption behavior based on molecular simulation

To effectively investigate the influence of activated carbon on the adsorption of volatile organic compounds (VOCs), physical and chemical factors of activated carbon including pore wall thickness, pore size, and functional groups were studied using grand canonical Monte Carlo (GCMC) simulation. In addition, benzene and acetone were taken as two representative components of VOCs. Simulation results was presented by the changes in characteristics of benzene and acetone. The results show that at the saturated vapor pressure (P₀), the adsorption density hardly varies with the mentioned factors of activated carbon. Differently, the saturated adsorption capacity increases considerably with the rise of pore size or the reduction of pore wall thickness, and the rise of pore size also leads to a dramatic increase in adsorption layer and a subsequent fall in ordering. However, when the pressure is less than 0.001P₀, the monomolecular interaction energy and the isosteric heat are strengthened greatly with the addition of carboxyl and amino groups, while the threshold pressure shows an opposite change to the monomolecular interaction energy. In the meantime, the decrease of pore size or the increase of pore wall thickness will result in the same results. Findings in this paper can provide valuable insights into the microscopic mechanisms of the adsorption between activated carbon and VOCs.

Recent Progress in Amorphous Carbon-Based Materials for Anodes of Sodium-Ion Batteries: Synthesis Strategies, Mechanisms, and Performance

Sodium-ion batteries (SIBs) are gaining renewed interest as a promising alternative to the already commercialized lithium-ion batteries. The large abundance, low cost, and similar electrochemistry of sodium (compared with lithium) is attracting the attention of the research community for their deployment in energy storage devices. Despite the fact that there are adequate cathode materials, the choice of suitable anodes for SIBs is limited. Graphite, the most versatile anode for LIBs, exhibits poor performance in case of SIBs. Amorphous or disordered carbons (hard and soft carbon) have been the most promising and cost-effective anode materials for SIBs. This Review discusses the recent advances of various forms of amorphous or disordered carbons used in SIBs with emphasis on their synthesis processes and relationship between microstructure, morphology, and performance. A profound understanding of the charge storage mechanisms of sodium in these carbon materials has been deliberated. The performance of these anode materials also depends upon electrolyte optimization, which has been aptly conferred. However, these anodes are often plagued with large voltage loss, low initial coulombic efficiency, and formation of solid electrolyte interphase. In order to overcome these challenges, several mitigation strategies have been put forward in a concise way to offer visions for the deployment of these amorphous carbon materials for the progress and commercial success of SIBs.

Microwave-Assisted Hydrothermal Preparation of Corn Straw Hydrochar as Supercapacitor Electrode Materials

In this work, we propose the microwave-assisted hydrothermal activation method to synthesize supercapacitor electrode materials from corn straw under a small amount of the potassium catalyst (30 wt %), which can meet the environmental protection and low-cost requirement. With the extension of radiation time from 40 to 100 min, the pore structure of hydrochar expands from the micropore to hierarchical pore, and the microstructure evolves from an amorphous structure to graphene-like sheets. Microwave-assisted hydrothermal activation can control the synergistic development of hierarchical pore and graphene-like sheets of hydrochar under the condition of using a lesser amount of the catalyst. The as-obtained HTC-40/70/100 shows an excellent graphitization degree and the developed hierarchical pores. By comparing the electrochemical performance of the symmetrical capacitor devices composed of corn straw hydrochar and pyrochar in organic electrolytes, we have found that the hydrochar is suitable for organic system symmetric capacitance, and the pore structure and graphitization degree are closely related to the transmission of ions and electrons in the electrolyte. Therefore, HTC-100 with a high specific surface area (1781 m²/g) and highly ordered microstructure has the best electrochemical performance.

Wood-based activated biochar to eliminate organic micropollutants from biologically treated wastewater

Implementing advanced wastewater treatment (WWT) to eliminate organic micropollutants (OMPs) is a necessary step to protect vulnerable freshwater ecosystems and water resources. To this end, sorption of OMP by activated carbon (AC) is one viable technology among others. However, conventional AC production based on fossil precursor materials causes environmental pollution, including considerable emissions of greenhouse gases. In this study, we produced activated biochar (AB) from wood and woody residues by physical activation and evaluated their capability to eliminate OMPs in treated wastewater. Activated biochar produced under optimized conditions sorbed 15 model OMPs, of which most were dissociated at circumneutral pH, to the same or higher extent than commercial AC used as a reference. While wood quality played a minor role, the dosage of the activation agent was the main parameter controlling the capacity of ABs to eliminate OMP. Our results highlight the possibility for local production of AB from local wood or woody residues as a strategy to improve WWT avoiding negative side effects of conventional AC production.

Biochar as potential precursors for activated carbon production: parametric analysis and multi-response optimization

Accelerating greenhouse gas emission particularly carbon dioxide (CO₂) in the atmosphere has become a major concern. Adsorption process has been proposed as a promising technology for CO₂ adsorption from flue gas, and the carbonaceous adsorbent is a potential candidate for CO₂ adsorption at atmospheric pressure and ambient temperature. Biochar derived from palm kernel shell waste was applied as a potential precursor for activated carbon production. This research study employed the response surface methodology coupled with Box-Behnken design to optimize the parameters involved in producing exceptional activated carbon with high yield (Y₁) and CO₂ adsorptive characteristics (Y₂). Specifically, parameters studied include the activation temperature (750-950 °C), holding time (60-120 min), and CO₂ flow rate (150-450 mL/min). The activated carbon at the optimum conditions was characterized using various analytical instruments, including elemental analyzer, nitrogen (N₂) physisorption analyzer, and field emission scanning electron microscopy. Overall, utilization of biochar as the activated carbon precursor is practical compared with the traditional non-renewable materials, due to its cost efficiencies and it being more environment-friendly ensuring process sustainability. Besides, this research study that incorporates physical activation with CO₂ as the activating agent is attractive, because it directly promotes CO₂ utilization and capture, in addition to the absence of any chemicals that may result in the secondary pollution problems.

Preparation of Highly Porous Graphitic Activated Carbon as Electrode Materials for Supercapacitors by Hydrothermal Pretreatment-Assisted Chemical Activation

The obstruction of traditional chemical activation lies in the addition of excessive catalysts to prepare the highly porous graphitic activated carbon (HPGAC), we propose the hydrothermal pretreatment-assisted chemical activation method to synthesize HPGAC as electrode materials using a small amount of Na-based catalysts (20 wt %). Hydrolysis accompanied by the strong depolymerization and reorganization of the coal framework is beneficial to the removal of different kinds of oxygen-containing structures (including cross-linking bonds, functional groups, and heterocycles) from lignite; thus, the deoxidization effect of hydrothermal carbonization (HTC) on hydrochar gradually strengthens with the increase in pretreatment temperature from 180 to 300 °C, resulting in the formation of a lot of disordered nanostructures and a smooth and compact surface. In the subsequent chemical activation stage, the microstructure of hydrochar is beneficial to the formation of a lot of graphene-like sheets and developed micropores even under a small amount of Na-based catalysts (20 wt %). The as-obtained C-HTC-300 with a highly ordered microstructure and a high specific surface area (S BET) of 1945.33 m2/g has an excellent electrochemical performance. Compared with a large consumption of catalyst for synthesizing HPGAC in traditional chemical activation, the hydrothermal pretreatment-assisted method meets the environmental protection and low-cost preparation requirements.

Microwave-assisted production of CO2-activated biochar from sugarcane bagasse for electrochemical desalination

A high-performance carbon electrode is desirable for promoting electrochemical desalination efficiency in the membrane capacitive deionization (MCDI). Sugarcane bagasse (food waste) was employed in this study to prepare hierarchically porous biochars by microwave-assisted carbonization and activation with potassium hydroxide in N₂ or CO₂ atmosphere under varying flow rates (100-600 cm³ min^-1). The sugarcane bagasse-derived biochars activated under CO₂ flow of 300 cm³ min^-1 (denoted as SBB-CO₂-300) possessed the ratio of mesopores to total pore volume (V_meso/V_total) of 56.7% with a specific surface area of 1019 m² g^-1. The electrochemical behavior of SBB-CO₂-300 was demonstrated by a surpassing specific capacitance of 208 F g^-1 at 5 mV s^-1 by means of cyclic voltammetry. The desalination tests using a batch-mode MCDI at 1.2 V in a 5 mM NaCl solution indicated that the SBB-CO₂-300 electrode exhibited an excellent electrosorption capacity of 28.9 mg g^-1. The improvement in the electrochemical deionization performance of SBB-CO₂-300 was attributed to the superior V_meso/V_total ratio, high surface area, excellent capacitance behavior, and hierarchical pore structure. The biowaste-derived biochars prepared via facile microwave-assisted carbonization and CO₂ activation route can provide a sustainable and high-efficiency carbon electrode for electrochemical deionization of brackish water.

A Review on the Transformation of Furfural Residue for Value-Added Products

As a by-product of lignocellulosic depolymerization for furfural production, furfural residue (FR) is composed of residual cellulose, lignin, humic acid, and other small amounts of materials, which have high reuse value. However, due to the limitation of furfural production scale and production technology, the treatment of FR has many problems such as high yield, concentrated stacking, strong acidity, and difficult degradation. This leads to the limited treatment methods and high treatment cost of furfural residue. At present, most of the furfural enterprises can only be piled up at will, buried in soil, or directly burned. The air, soil, and rivers are polluted and the ecological balance is destroyed. Therefore, how to deal with furfural residue reasonably needs to be solved. In this review, value-added products for furfural residue conversion are described in detail in the fields of soil culture, catalytic hydrolysis, thermal decomposition, and porous adsorption. The future studies reporting the FR to convert value-added products could find guidance from this review to achieve specific goals.

Application of Experimental Design to Hydrogen Storage: Optimisation of Lignin-Derived Carbons

Lignin is a significant by-product of the paper pulping and biofuel industries. Upgrading lignin to a high-value product is essential for the economic viability of biorefineries for bioethanol production and environmentally benign pulping processes. In this work, the feasibility of lignin-derived activated carbons for hydrogen storage was studied using a Design of Experiments methodology, for a time and cost-efficient exploration of the synthesis process. Four factors (carbonisation temperature, activation temperature, carbonisation time, and activation time) were investigated simultaneously. Development of a mathematical model allowed the factors with the greatest impact to be identified using regression analysis for three responses: surface area, average pore size, and hydrogen uptake at 77 K and 1 bar. Maximising the surface area required activation conditions using the highest settings, however, a low carbonisation temperature was also revealed to be integral to prevent detrimental and excessive pore widening. A small pore size, vital for efficient hydrogen uptake, could be achieved by using low carbonisation temperature but also low activation temperatures. An optimum was achieved using the lowest carbonisation conditions (350 °C for 30 min) to retain a smaller pore size, followed by activation under the severest conditions (1000 °C for 60 min) to maximise surface area and hydrogen uptake. These conditions yielded a material with a high surface area of 1400 m2 g−1 and hydrogen uptake of 1.9 wt.% at 77 K and 1 bar.

Effect of Ammonia Activation and Chemical Vapor Deposition on the Physicochemical Structure of Activated Carbons for CO2 Adsorption

Focusing on the bottlenecks of traditional physical activation method for the preparation of activated carbons (ACs), we established a simple and scalable method to control the physicochemical structure of ACs and study their CO2 adsorption performance. The preparation is achieved by ammonia activation at different volume fractions of ammonia in the mixture (10%, 25%, 50%, 75%, and 100%) to introduce the nitrogen-containing functional groups and form the original pores and subsequent chemical vapor deposition (CVD) at different deposition times (30, 60, 90, and 120 min) to further adjust the pore structure. The nitrogen content of ACs-0.1/0.25/0.5/0.75/1 increases gradually from 2.11% to 8.84% with the increase of ammonia ratio in the mixture from 10% to 75% and then decreases to 3.02% in the process of pure ammonia activation (100%), during which the relative content of pyridinium nitrogen (N-6), pyrrolidine (N-5), and graphite nitrogen (N-Q) increase sequentially but nitrogen oxygen structure (N-O) increase continuously. In addition, ACs-0.5 and ACs-0.75, with a relatively high nitrogen content (6.37% and 8.84%) and SBET value (1048.65 m2/g and 814.36 m2/g), are selected as typical samples for subsequent CVD. In the stage of CVD, ACs-0.5-60 and ACs-0.75-90, with high SBET (1897.25 and 1971.57 m2/g) value and an appropriate pore-size distribution between 0.5 and 0.8 nm, can be obtained with the extension of deposition time from 60 to 90 min. The results of CO2 adsorption test indicate that an adsorption capacity of ACs-0.75-90, at 800 mmHg, is the largest (6.87 mmol/g) out of all the tested samples. In addition, the comparison of CO2 adsorption performance of tested samples with different nitrogen content and pore structure indicates that the effect of nitrogen content seems to be more pronounced in this work.

Production of palm kernel shell-based activated carbon by direct physical activation for carbon dioxide adsorption

The feasibility of biomass-based activated carbons has received a huge attention due to their excellent characteristics such as inexpensiveness, good adsorption behaviour and potential to reduce a strong dependency towards non-renewable precursors. Therefore, in this research work, eco-friendly activated carbon from palm kernel shell that has been produced from one-stage physical activation by using the Box-Behnken design of Response Surface Methodology is highlighted. The effect of three input parameters-temperature, dwell time and gas flow rate-towards product yield and carbon dioxide (CO₂) uptake at room temperature and atmospheric pressure are studied. Model accuracy has been evaluated through the ANOVA analysis and lack-of-fit test. Accordingly, the optimum condition in synthesising the activated carbon with adequate CO₂ adsorption capacity of 2.13 mmol/g and product yield of 25.15 wt% is found at a temperature of 850 °C, holding time of 60 min and CO₂ flow rate of 450 cm³/min. The synthesised activated carbon has been characterised by diverse analytical instruments including thermogravimetric analyser, scanning electron microscope, as well as N₂ adsorption-desorption isotherm. The characterisation analysis indicates that the synthesised activated carbon has higher textural characteristics and porosity, together with better thermal stability and carbon content as compared to pristine palm kernel shell. Activated carbon production via one-step activation approach is economical since its carbon yield is within the industrial target, whereas CO₂ uptake is comparable to the synthesised activated carbon from conventional dual-stage activation, commercial activated carbon and other published data from literature.

Effect of Physical and Mechanical Activation on the Physicochemical Structure of Coal-Based Activated Carbons for SO2 Adsorption

The SO2 adsorption efficiency of activated carbons (ACs) is clearly dependent on its physicochemical structure. Related to this, the effect of physical and mechanical activation on the physicochemical structure of coal-based ACs has been investigated in this work. In the stage of CO2 activation, the rapid decrease of the defective structure and the growth of aromatic layers accompanied by the dehydrogenation of aromatic rings result in the ordered conversion of the microstructure and severe carbon losses on the surfaces of Char-PA, while the oxygen content of Char-PA, including C=O (39.6%), C–O (27.3%), O–C=O (18.4%) and chemisorbed O (or H2O) (14.7%), is increased to 4.03%. Char-PA presents a relatively low SBET value (414.78 m2/g) owing to the high value of Non-Vmic (58.33%). In the subsequent mechanical activation from 12 to 48 h under N2 and dry ice, the strong mechanical collision caused by ball-milling can destroy the closely arranged crystalline layers and the collapse of mesopores and macropores, resulting in the disordered conversion of the microstructure and the formation of a defective structure, and a sustained increase in the SBET value from 715.89 to 1259.74 m2/g can be found with the prolonging of the ball-milling time. There is a gradual increase in the oxygen content from 6.79 to 9.48% for Char-PA-CO2-12/48 obtained by ball-milling under CO2. Remarkably, the varieties of physicochemical parameters of Char-PA-CO2-12/48 are more obvious than those of Char-PA-N2-12/48 under the same ball-milling time, which is related to the stronger solid-gas reactions caused by the mechanical collision under dry ice. Finally, the results of the SO2 adsorption test of typical samples indicate that Char-PA-CO2-48 with a desirable physicochemical structure can maintain 100% efficiency within 30 min and that its SO2 adsorption capacity can reach 138.5 mg/g at the end of the experiment. After the 10th cycle of thermal regeneration, Char-PA-CO2-48 still has a strong adsorptive capacity (81.2 mg/g).

Tannin-derived micro-mesoporous carbons prepared by one-step activation with potassium oxalate and CO2

Micro-mesoporous carbons (MMCs) were successfully prepared using natural polyphenolic compounds, condensed tannins, and glyoxal, a nontoxic aldehyde, in lieu of synthetic phenolic compounds like formaldehyde and resorcinol as carbon precursors. Such MMCs were fabricated by a soft-templating strategy under mild conditions. Porosity development was achieved by varying the amount of potassium oxalate as an in-situ activator coupled with one-step CO₂ activation at 700 °C. This strategy allowed for the enhancement of microporosity as well as retention of the uniform mesoporous structure of the carbons. The CO₂ uptakes of 5.2 mmol/g at 0 °C and 3.6 mmol/g at 25 °C were achieved at 1 bar pressure for the tannin-derived activated MMC sample with a surface area of 1192 m²/g, a volume of fine micropores (sizes below 1 nm) of 0.33 cm³/g, and a mesopore volume of 0.49 cm³/g. This study opens new opportunities for a facile and green synthesis of MMCs from less toxic precursors with tailored porosity by synergistic effects of chemical and physical activation. The resulting MMCs exhibit the potential applicability not only as CO₂ sorbents but also in other environmental applications such as adsorption of organic volatile compounds and dye molecules, which require slightly larger pores.

Catalytic Effect of NaCl on the Improvement of the Physicochemical Structure of Coal-Based Activated Carbons for SO2 Adsorption

The utilization of coal-based activated carbons focuses on improving the physicochemical structure for achieving high-capacity. Herein, the catalytic effect of NaCl (1 and 3 wt%) in the presence of oxygen functional groups on the improvement of the physicochemical structure of coal-based activated carbons is studied in this work. A large quantity of Na can be retained in 1NaJXO and 3NaJXO with the presence of oxygen functional groups to promote further its catalytic characteristics during pyrolysis, resulting in the disordered transformation of the carbon structure. In addition, the development of micropores is mainly affected by the distribution and movement of Na catalyst, whereas the growth of mesopores is mainly influenced by the evolution of oxygen functional groups. Then, the active sites of 3NaJXO-800 can no longer be consumed preferentially in the presence of Na catalyst during subsequent CO2 activation to facilitate the sustained disordered conversion of the microstructure and the rapid development of the micropores, resulting in the obvious high SBET value as activation proceeds. And the high SBET/burn-off ratio value (41.48 m2∙g−1/%) of 3NaJXO-800 with a high value of SBET (1995.35 m2∙g−1) at a low burn-off value (48.1%) can be obtained, presenting the high efficiency of pore formation. Finally, the SO2 adsorption efficiency of 3NaJXO-800-48.1 maintains at 100% within 90 min. After 180 min, 3NaJXO-800-48.1 still presents a high adsorptive capacity (140.2 mg/g). It is observed that a large micropore volume in the case of hierarchical pore structure necessarily assures optimal adsorption of SO2.

Highly Porous Graphitic Activated Carbons from Lignite via Microwave Pretreatment and Iron-Catalyzed Graphitization at Low-Temperature for Supercapacitor Electrode Materials

At present, the preparation of highly porous graphitic activated carbons (HPGACs) using the usual physical and chemical activation methods has met a bottleneck. In this study, HPGACs are directly synthesized from lignite at 900 °C. The whole process is completed by a microwave pretreatment, a graphitization conversion of the carbon framework at a low temperature using a small amount of FeCl3 (10–30 wt%), and a subsequent physical activation using CO2. Consequently, the dispersed and mobile iron species, in the absence of oxygen functional groups (removed during the microwave pretreatment), can greatly promote catalytic graphitization during pyrolysis, and, as an activating catalyst, can further facilitate the porosity development during activation. The as-obtained AC-2FeHLH-5-41.4(H) presents a low defect density, high purity, and specific surface area of 1852.43 m2 g−1, which is far greater than the AC-HLH-5-55.6(H) obtained solely by physical activation. AC-2FeHLH-5-41.4(H) as a supercapacitor electrode presents an excellent performance in the further electrochemical measurements. Such a convenient and practical method with low cost proves a scalable method to prepare HPGACs from a wide range of coal/biomass materials for industrial scale-up and applications.

Comparison of the Properties of Activated Carbons Produced in One-Stage and Two-Stage Processes

Activated carbons (ACs) can be produced from biomass in a thermal process either in a direct carbonization-activation process or by first carbonizing the biomass and later activating the bio-chars into activated carbons. The properties of the ACs are dependent on the type of process used for production. In this study, the properties of activated carbons produced in one-stage and two-stage processes are considered. Activated carbons were produced by physical activation of two types of starting materials: bio chars produced from spruce and birch chips in a commercial carbonization plant and from the corresponding raw chips. The activated carbons produced were characterized regarding specific surfaces, pore volumes, and pore size distributions. The un-activated bio chars had varying surface areas, 190 and 140 m2 g−1 for birch and spruce, respectively, and pore volumes of 0.092 and 0.067 cm3 g−1, respectively. On the other hand, 530–617 and 647–679 m2 g−1 for activated bio chars from birch and spruce, respectively, and pore volumes 0.366–0.509 and 0.545–0.555 cm3 g−1, respectively, were obtained. According to the results obtained, two slightly different types of activated carbons are produced depending on whether a one-stage or a two-stage carbonization and activation process is used. The ACs produced in the one-stage process had higher specific surface areas (SSA), according to the BET-model (Brunauer–Emmett–Teller), compared to the ones produced in a two-stage process (761–940 m2 g−1 vs. 540–650 m2 g−1, respectively). In addition, total pore volumes were higher in ACs from the one-stage process, but development of micro-pores was greater compared to those of the two-stage process. This indicates that the process can have an influence on the ACs’ porosity. There was no significant difference in total carbon content in general between the one-stage and two-stage processes for spruce and birch samples, but some differences were seen between the starting materials. Especially in the one-stage procedure with 2 and 4 h steam activation, there was nearly a 10% difference in carbon content between the spruce and birch samples.

Effects of oxygen functional groups and FeCl3 on the evolution of physico-chemical structure in activated carbon obtained from Jixi bituminous coal

It is crucial to increase the values of S_BET/burn-off ratio to achieve activated carbon (AC) with a higher SO₂ adsorption capacity at a low cost from flue gas. In this study, at first, Jixi bituminous coal was used as a raw material to prepare a series of pre-treated samples by oxidation treatment and adding different amounts of the FeCl₃ catalyst. Then, the AC samples were prepared by pyrolysis under a N₂ atmosphere and physical activation with CO₂. Finally, the change in the physico-chemical structure of different samples was determined to study the effects of oxygen functional groups and FeCl₃. The results show that the rapid growth of mesopores is mainly influenced by the evolution of oxygen functional groups, whereas the micropores are mainly influenced by the FeCl₃ catalyst during pyrolysis. These effects can also further improve the size and the carbon type of the aromatic structure from a different perspective to promote the disordered microstructure of treated chars (1FeJXO15-800H, 3FeJXO15-800H and 6FeJXO15-800H) as compared to the ordered microstructure and less pores of the un-pretreated char (JX-800). Then, the active sites can no longer be consumed preferentially in the presence of the catalyst; this results in the continuous disordered conversion of the microstructure as compared to the ordered conversion of JX-800 char during activation. On the one hand, the developed initial pores of 1FeJXO15-800H, 3FeJXO15-800H, and 6FeJXO15-800H chars promote the favorable diffusion of activated gas, following the non-hierarchical development. On the other hand, the presence of Fe-based catalysts facilitates the etching of carbon structure and the rapid and continuous development of the micropores, hindering the severe carbon losses on the particle surface. Finally, the 3FeJXO15-800H char with a high value of S_BET (1274.64 m² g⁻¹) at a low burn-off value (22.5%) has the highest S_BET/burn-off ratio value of 56.65 m² g⁻¹/%, whereas the JX-800 char with a low value of S_BET (564.19 m² g⁻¹) at a burn-off value of 58.2% has the lowest S_BET/burn-off ratio value of 9.69 m² g⁻¹/%. Therefore, the presence of oxygen functional groups and FeCl₃ has obviously changed the evolution of the physico-chemical structure in activated carbon to effectively enhance the values of S_BET/burn-off.

Effects of oxygen functional groups and FeCl₃ on evolution of physico-chemical structure in activated carbon to increase its value S_BET/burn-off.

The Properties of Activated Carbon Fiber Derived from Direct Activation from Oil Palm Empty Fruit Bunch Fiber

Oil palm empty fruit bunch (EFB) is an abundant agricultural waste available in Malaysia. More than two million tonnes (dry weight) of extracted oil palm fiber are estimated to be generated annually. Usually the EFB is used as boiler fuel to produce steam in the palm oil mills. EFB fiber can be used to prepare activated carbon fiber (ACF) by carbonization and activation. Conversion of EFB fiber to ACF will reduce the amount of agricultural waste produced annually and it represents a potential source of adsorbents used for adsorption. The ACF has many advantages as compared to the conventional activated carbon found in powder or granular form. These advantages include large surface area, high adsorption capacity and high rates of adsorption from the gas or liquid phase. In this study, ACF produced from EFB fiber by single step direct activation process (ACF-D) was compared against ACF produced by conventional 2-step carbonization and activation (ACF-ND). The different properties between ACFs produced were investigated. The raw EFB and ACFs were characterized by a SEM and EDS, FTIR and XRD. The results show that EFB has carbon content of 63.33 weight percentage (wt %) with oxygen content of 36.67 wt %. ACF-D was found to have a high carbon content of 93.63 wt%, with low oxygen content (5.19 wt %). ACF-ND gave a higher carbon content up to 95.68 wt% and accompanied by a lower oxygen content (3.85 wt %).