Activated carbon from cherry stones by chemical activation: Influence of the impregnation method on porous structure

Cherry stones are utilized as a precursor for the preparation of activated carbons by chemical activation with phosphoric acid (H₃PO₄). The activation process typically consists of successive impregnation, carbonization, and washing stages. Here, several impregnation variables are comprehensively studied, including H₃PO₄ concentration, number of soaking steps, H₃PO₄ recycling, washing of the impregnated material, and previous semi-carbonization. The choice of a suitable impregnation methodology opens up additional possibilities for the preparation of a wide variety of activated carbons with high yields and tailored porous structures. Microporous activated carbons with specific surface areas of ～800 m² g^?1 are produced, in which > 60% of the total pore volume is due to micropores. High surface areas of ～1500 m² g^?1 can be also developed, with micropore volumes being a 26% of the total pore volume. Interestingly, using the same amount of H₃PO₄, either carbons with surface areas of 791 and 337 m² g^?1 or only one carbon with a surface area of 640 m² g^?1 can be prepared. The pore volumes range very widely between 0.07–0.55, 0.01–0.90, and 0.09–0.79 cm³ g^?1 for micropores, mesopores, and macropores, respectively.     

Nanoporous rice husk derived carbon for gas storage and high performance electrochemical energy storage

We report on the gas storage behaviour and electrochemical charge storage properties of high surface area activated nanoporous carbon obtained from rice husk through low temperature chemical activation approach. Rice husk derived porous carbon (RHDPC) exhibits varying porous characteristics upon activation at different temperatures and we observed high gas uptake and efficient energy storage properties for nanoporous carbon materials activated even at a moderate activation temperature of 500 °C. Various experimental techniques including Fourier transform-infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and pore size analyser are employed to characterise the samples. Detailed studies on gas adsorption behaviour of CO₂, H₂ and CH₄ on RHDPCs have been performed at different temperatures using a volumetric gas analyser. High adsorption capacities of ~9.4 mmol g^?1 (298 K, 20 bar), 1.8 wt% (77 K, 10 bar) and ~5 mmol g^?1 (298 K, 40 bar) were obtained respectively for CO₂, H₂ and CH₄, superior to many other carbon based physical adsorbents reported so far. In addition, these nanoporous carbon materials exhibit good electrochemical performance as supercapacitor electrodes and a maximum specific capacitance of 112 F g^?1 has been obtained using aqueous 1 M Na₂SO₄ as electrolyte. Our studies thus demonstrate that nanoporous carbon with high porosity and surface area, obtained through an efficient approach, can act as effective materials for gas storage and electrochemical energy storage applications.     

Synthesis of hollow porous carbon nanospheres from coal tar for adsorption of Direct Black 38 dye

A hollow porous carbon nanospheres (HPCNs) material which suits for adsorption of Direct Black 38 (DB38) was prepared from coal tar using zinc acetate as a template coupled with KOH activation. The synthesized HPCNs features with nanospheres structure and contains both micropores and a lot of mesopores. The HPCN_1?4?2 made with the mass weight ratio of coal tar/zinc acetate/KOH at 1:4:2 shows a large surface area of 1374 m² g^?1 with an average pore size of 7.41 nm. The HPCN_1?4?2 exhibits excellent adsorption capacity for DB38 dye, which has big molecular size at room temperature. This is mainly due to its large surface area and pore volumes contributed by its mesopores. This work suggests an effective way to synthesize a high performance adsorbent for large molecular size dyes from low-cost coal tar.     

Adsorption Characteristics of Microporous Carbons from Apricot Stones Activated by Phosphoric Acid

Crushed apricot stone shells were impregnated with varying H₃PO₄ acid concentrations (20–50 wt%), followed by carbonisation at 573–773 K. The products were characterised by nitrogen gas adsorption. Analysis of the nitrogen isotherms by the DR and α_s methods proved that most of the obtained carbons are highly microporous, with high surface areas (⩾1000 m² g^-1) and very low mesoporosity. Increasing acid concentration, at 573 and 673 K, increases surface area and pore volume, whereas at 733 K a small decrease in both parameters appears at higher H₃PO₄ concentrations. Whole apricot stones produce activated carbon of inferior porous characteristics. Development of the extensive pore structure was described in light of the effect of H₃PO₄ on the lignocellulosic mataerial during carbonisation.     

Electron rich porous carbon/silica matrix from rice husk and its characterization

Free electron rich porous carbon/silica matrix (ECS₈₀₀) was prepared from rice husk by carbonization at 400 °C and activation by phosphoric acid (H₃PO₄) at 800 °C. The ratio of H₃PO₄ to pre-carbonized carbon was fixed at 2.3. The surface area, pore volume, and pore size distribution of ECS₈₀₀ was measured, using nitrogen adsorption isotherms at 77 K. The unpaired electron density of ECS₈₀₀ was measured in electron spin resonance spectroscopy, using 4-hydroxy 2,2,6,6-tetramethyl piperidine-1-oxyl as the reference spin probe. ECS₈₀₀ was further characterized, using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscope, and ²⁹Si-nuclear magnetic resonance spectroscope to study crystallization, surface morphology, functional group and different types of silicon species.     

Activated Carbon Preparation from Lignin by H3PO4 Activation and Its Application to Gas Separation

Activated carbons were produced from corn straw lignin using H₃PO₄ as activating agent. The optimal activation temperature for producing the largest BET specific surface area and pore volume of carbon was 500 °C. The maximum BET specific surface area and pore volume of the resulting carbon were 820 m²g^–1 and 0.8 cm³g^–1, respectively. The adsorption isotherm model based on the Toth equation together with the Peng‐Robinson equation of state for the determination of gas phase fugacity provide a satisfactory representation of high pressure CO₂, CH₄ and N₂ adsorption. The kinetic adsorption results show that the breakthrough difference between CO₂ and CH₄ is not obvious, indicating that its kinetic separation performance is limited.     

Porous carbonaceous materials from hydrothermal carbonization and KOH activation of corn stover for highly efficient CO2 capture

Sustainable biomass-derived carbon materials were produced by hydrothermal carbonization of corn stover that was followed by chemical activation with KOH. The prepared carbon materials were used for CO₂ adsorption and had a CO₂ uptake of 7.14?mmol/g at a pressure of 1?bar and at 0°C that was much higher than CO₂ uptake by activated carbon that was prepared from direct activation of corn stover (2.78?mmol/g). The porous corn stover-derived carbonaceous material had high surface area (2442?m²/g) and large pore volume (1.55?cm³/g). Product yields obtained by the activation of hydrothermally carbonized corn stover were significantly higher than those obtained by the direct activation of corn stover (36–75?vs. 8%). The prepared corn stover-derived porous carbon had a high CO₂/N₂ selectivity of 15.5 and exhibited constant CO₂ uptake for five successive reuse cycles. The hydrothermal carbonization step plays an important role for producing porous carbons from biomass that have high and specific adsorption properties.     

Treating contaminated soil by conversion into carbonaceous adsorbents: an investigation of activation procedures

The well established activated carbon manufacturing process has been investigated as a novel treatment for contaminated soil from gaswork sites by converting it into a porous carbonaceous solid with adsorbent properties. Several activation methodologies were evaluated: CO₂, air, ZnCl₂, H₂SO₄, H₃PO₄, FeSO₄ and HNO₃. Thermal analysis of the soil provided information regarding appropriate carbonisation and activation conditions. Bulk samples were prepared using contaminated soil samples, with ZnCl₂ being found to be the most effective agent for the process, producing an adsorbent which possessed a BET surface area of 131m²g⁻¹. The aqueous adsorption ability of the soil carbons was studied using phenol and 4‐nitrophenol as representative micropollutant organic molecules. The Langmuir monolayer capacity of the ZnCl₂‐activated soil was found to be 0.12 mmg⁻¹ for phenol and 0.23 mmg⁻¹ for 4‐nitrophenol. © 2000 Society of Chemical Industry     

Preparation and molten salt-assisted KOH activation of porous carbon nanofibers for use as supercapacitor electrodes

Carbon nanofiber paper was prepared by electrospinning from thermosetting phenolic resin, followed by activation via KOH-containing molten salt at high temperature. By adding a small dosage of KOH in the molten salt the porous volume and specific surface area could be greatly improved. The obtained porous carbon nanofibers had a specific surface area of 1007 m² g^?1, total pore volume of 0.363 cm³ g^?1, micropore volume of 0.247 cm³ g^?1. The electrochemical measurements in 6 M KOH aqueous solution showed that the porous carbon nanofibers possessed high specific capacitance and considerable rate performance. The maximal specific capacitance of 288 F g^?1 was achieved at 0.2 A g^?1 and the specific capacitance could still remain 204 F g^??1 at 20 A g^?1 with the retention of 71%. In the molten salt system, the reaction between activating agent and carbon could be more efficient, hence, such molten salt-assisted activation method was considered as a general activation method for the high-specific-surface-areaed carbons.     

Microwave-assisted preparation of mesoporous-activated carbon from coconut (Cocos nucifera) leaf by H3PO4 activation for methylene blue adsorption

Mesoporous-activated carbon was prepared from fallen coconut (Cocos nucifera) leaf, an agricultural waste through a microwave-induced H₃PO₄ activation process. The characterization of the coconut leaf–activated carbon (CAC) was evaluated through the iodine number, ash content, bulk density, and moisture content. Fourier transform infrared spectroscopy, scanning electron microscope, Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction, and pH_PZC. CAC has a mesopore content of 84% with an average pore size of 36.5?Å and a large BET surface area of 632?m²/g. The uptake properties of the CAC with methylene blue was evaluated at different CAC dosage levels (0.2–10?g/L), initial pH (3–10), methylene blue concentration (50–350?mg/L), and time (0–360?min) using batch mode operation. The kinetic profiles were described by the pseudo-second-order kinetics. The equilibrium data were well fitted to the Langmuir model with a maximum monolayer adsorption capacity of 250?mg/g at 30°C. Thermodynamic functions indicate a spontaneous and exothermic nature of the adsorption process. This study indicates that coconut leaves are a promising renewable precursor that can be utilized to develop an efficient mesoporous-activated carbon.     

Equilibrium modeling,kinetic and thermodynamic studies on the adsorption of Cr(VI) using activated carbon derived from matured tea leaves

A new porous carbon with high surface area of 1,313.41 m² g^?1 with pore volume 1.359 cm³ g^?1 has been synthesized from matured tea leaves by chemical activation method using phosphoric acid. The carbon was found to be highly efficient for removal of Cr(VI) from aqueous solution. The effects of various parameters such as contact time, initial metal ion concentration, pH, temperature and amount of adsorbent on the extent of adsorption were studied. Langmuir, Freundlich and Temkin adsorption models were used to interpret the experimental data. The adsorption data were best fitted with Langmuir isotherm model. The adsorption capacity of Cr(VI) onto the activated carbon calculated from Langmuir isotherm was found to be 30.8 mg g^?1 at pH 4.8 and temperature 303 K. The adsorption capacity increases from 25.36 to 32.04 mg g^?1 with an increase in temperature from 303 to 323 K at initial Cr(VI) concentration of 60 mg L^?1. The adsorption process followed a pseudo second order kinetic model. Thermodynamic parameters ΔH⁰ (28.6 KJ mol^?1), ΔG⁰ at three different temperatures [(?0.145, ?1.09, ?2.04) KJ mol^?1] and ΔS⁰ (94.87 J mol^?1 K^?1) were calculated. These values confirm the adsorption process to be endothermic and spontaneous in nature.     

Nanoarchitectonics of Nanoporous Carbon Materials from Natural Resource for Supercapacitor Application

Nanoarchitectonics of nanoporous carbon materials (NCMs) derived from natural resource; Areca Catechu Nut (ACN) with enhanced electrochemical supercapacitance properties is reported. ACN powder is chemically activated in a tubular furnace at 400?°C and the effect of activating agent sodium hydroxide (NaOH), zinc chloride (ZnCl₂) and phosphoric acid (H₃PO₄) on the textural properties, surface functional groups and electrochemical supercapacitance properties was thoroughly examined. We found that ACN derived NCMs are amorphous in nature comprising of macropores, micropores and hierarchical micro- and mesopore architecture depending on the activating agent. Surface area and pore volume are found in the range 25–1985 m² g^?1 and 0.12–3.42 cm³ g^?1, respectively giving the best textural properties for H₃PO₄ activated NCM. Nevertheless, despite the different chemical activating agent used, all the prepared NCMs showed similar oxygen-containing surface functional groups (carboxyl, carboxylate, carbonyl and phenolic groups). The H₃PO₄ activated NCM showed excellent supercapacitance properties giving a high specific capacitance of ca. 342 F g^?1 at a scan rate of 5 mV s^?1 together with the high cyclic stability sustaining capacitance retention of about 97% after 5000 charging/discharging cycles. Electrochemical supercapacitance properties have demonstrated that the ACN derived novel nanoporous carbon material would be a potential material in energy storage application.     

Influence of preparation conditions on porous structures of olive stone activated by H3PO4

An olive factory residue was used as a precursor in the preparation of granular activated carbon by chemical activation with H₃PO₄. Effects of final activation temperature, time, and H₃PO₄ concentration used in the impregnation stage on the porous development were investigated. SO₂ adsorption experiments were also performed for some of the activated carbon samples to represent their adsorption performance. Activation at low temperature represented that micropores were developed first at early stages of the temperatures. Mesoporosity developed at around 250 °C, enhanced up to 400 °C, and then started to decrease due to possibly shrinking of pores. The optimum temperature for olive stone was found to be around 400 °C on the basis of total pore volume and BET surface area. It was clearly demonstrated that H₃PO₄ concentration used in the impregnation stage was not only effective for development of surface area and pore volumes but also an effective tool for tailoring the pore structure and size distribution.     

Structural evolution of hierarchical porous NiO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites and their application for removal of dyes by adsorption

Hierarchical porous NiO/Al₂O₃ composites were successfully prepared by two-steps. First, the core-shell structured Al₂O₃ microspheres were prepared via a template-free hydrothermal route using KAl(SO₄)₂·12H₂O and Al₂(SO₄)₃·18H₂O as aluminum source. Then, the NiO/Al₂O₃ composites with micro- and nano-hierarchical structures were prepared by a hydrothermal method combining the subsequent calcination process. The obtained characterization result presented that the morphology of hierarchical Al₂O₃ microsphere tuned to irregular platelets by simply varying Ni/Al ratios. The BET analysis showed that the special surface area from 52.12m² g^?1 to 214.8m² g^?1 after two hydrothermal complex process. Effects of Ni/Al ratio, adsorbent dosage, Congo red (CR) concentration, coexisting ions, adsorption time and temperature were investigated. The obtained results indicated that NiO/Al₂O₃ composite had the high adsorption efficiency (99.6%) and great adsorption capacity (186.9mg g^?1) under the optimum conditions. The adsorption isotherm and kinetics data were found to be well fitted and in good agreement with the Langmuir isotherm model and pseudo-second order model, respectively. The hierarchical porous NiO/Al₂O₃ composites presented remarkably higher adsorption efficiency during five recycling, which showed their potential as the highly efficient adsorbent for removal of CR in wastewater.     

Aloe peel-derived honeycomb-like bio-based carbon with controllable morphology and its superior electrochemical properties for new energy devices

In this study, aloe peel-derived honeycomb-like porous carbons (AP-HC) are controllably prepared by combining simple hydrothermal carbonization with chemical activation. A morphology transformation from the spherical structure (AP-SC) to the honeycomb-like structure (AP-HC) is achieved for biomass-derived carbon materials and is accompanied by an increase in the specific surface area from 13 to 1286?m² g^?1. The AP-HC as a counter electrode (CE) for dye-sensitized solar cells (DSSCs) exhibits remarkable catalytic activity for I₃^- ion reduction and a high power conversion efficiency (PCE) of 6.92% that matches the Pt-based DSSC's performance (7.19%). As a working electrode in supercapacitors (SCs), a high specific capacitance of 264?F?g^?1 at 0.5?A?g^?1 is achieved in a three-electrode system. Additionally, a high retention rate of ～77.45% (ranging from 0.5 to 30.0?A?g^?1) and superior cycling performance (91% capacitance retention after 5000 cycles) are also demonstrated. This study provides an efficient strategy for fabricating morphology-controllable porous bio-based carbon with higher specific surface area (1286?m² g^?1) that exhibits significant potential for new energy devices.     

Hydrogen adsorption on activated carbons prepared from olive waste: effect of activation conditions on uptakes and adsorption energies

Two series of activated carbon samples have been prepared from olive waste, using ZnCl₂ and H₃PO₄ as chemical activation agents. The porous structure characteristics of all samples are determined by nitrogen adsorption at ?196 °C. Hydrogen adsorption at ?196 °C is followed using both manometry and calorimetry. The results show that the highest areas are observed for the samples prepared with larger diameter of precursors and that the hydrogen uptake is strongly influenced by the available BET area. Furthermore, the adsorption energies do not vary significantly for any activation protocol and therefore seem to play only a minor role to the hydrogen adsorption behavior. However, the chemical activation does have a strong role on hydrogen uptake. Samples prepared with H₃PO₄ show a greater hydrogen uptake per unit area such that comparable uptakes are observed for the samples prepared with larger diameter of precursor even though the sample prepared with ZnCl₂ shows a 30 % higher BET area. This work highlights the non-trivial role of each activation protocol on hydrogen uptake.     

Activated carbon from sugar cane bagasse by carbonization in the presence of inorganic acids

Dried ground bagasse, impregnated with 50% inorganic acids and carbonized at 500°C, showed the sequence H₃PO₄ > H₂SO₄ > HCl > HNO₃, with respect to the efficiency of activation. Treatment with phosphoric acid of various concentrations (30–50 wt%) was followed by carbonization at 300–500°C for 3 h. Pore structure parameters were determined from the low-temperature adsorption of nitrogen, by applying the BET and α_s methods. Activated carbons obtained at low temperatures are essentially microporous with a low degree of mesoporosity. At higher temperatures products of higher surface area and total pore volume with developed mesoporosity and low microporosity are formed. An increase in the period of carbonization leads to a small decrease in both surface area and pore volume. Activated carbons with surface areas > 1000 m² g^?1 and mean pore dimensions around 2·0 nm, suitable for various purposes, are thus obtained.     

Surface Porosity of Lignin/PP Blend Carbon Fibers

Abstract

The surface porosities of carbon fibers derived from the polymer blend fibers of hardwood kraft lignin, HKL and polypropylene, PP, were discussed using thermal analyses, FTIR, and nitrogen adsorption. HKL/PP carbon fibers were prepared by two‐step thermal processing, thermostabilization, and carbonization. During the thermostabilization process, pores are created by oxidative degradation of the PP component. After thermostabilization some crystalline and highly oxidized PP components remained in the blend fiber. These residual PP components were subsequently pyrolyzed during carbonization, and effectively created a porous structure in the resulting carbon fibers. N₂ adsorption tests of the porous carbon fibers revealed the same type of adsorption/desorption isotherms as for activated carbon fiber. The internal surface area of the HKL/PP = 62.5/37.5 carbon fibers was calculated to be 499 m² g^?1. This value was lower than that for commercial activated carbon, 745 m² g^?1. However, these porous lignin‐based carbon fibers were not activated carbon fibers, which could be relatively easily done through steam activation. Thus, the HKL/PP blend carbon fibers appear to be promising precursors for activated carbon fibers.     

Porous carbon materials produced by the chemical activation of birch wood

It was established that the main factors responsible for the yield and specific surface area of porous carbon materials obtained by the chemical activation of the wood of birch are the nature of a modifying agent and the temperature of pyrolysis. The additional opening of the porous structure of the product of the chemical activation of wood occurs at the stage of its water treatment as a result of the removal of water-soluble compounds. The conditions of the carbonization of birch wood modified with H₃PO₄, KOH, and ZnCl₂ were chosen in order to provide the significant development of the porous structure of carbon materials. The porous carbon material with the highest specific surface area (more than 2560 m²/g) was obtained by the water washing of the product of the carbonization of birch wood modified H₃PO₄ at 400°C.     

A novel method for production of activated carbon from waste tea by chemical activation with microwave energy

This study presents the production of activated carbon from waste tea. Activated carbons were prepared by phosphoric acid activation with and without microwave treatment and carbonisation of the waste tea under nitrogen atmosphere at various temperatures and different phosphoric acid/precursor impregnation ratios. The surface properties of the activated carbons were investigated by elemental analysis, BET surface area, SEM, FTIR. Prior to heat treatment conducted in a furnace, the mixture of the waste tea and H₃PO₄ was treated with microwave heating. The maximum BET surface area was 1157 m²/g for the sample treated with microwave energy and then carbonised at 350 °C. In case of application of conventional method, the BET surface area of the resultant material was 928.8 m²/g using the same precursor and conditions. According to the Dubinin–Radushkevich (DR) method the micropore surface area for the sample treated with microwave energy was higher than the sample obtained from the conventional method. Results show that microwave heating reasonably influenced the micropore surface area of the samples as well as the BET surface area.The samples activated were also characterised in terms of the cumulative pore and micropore volumes according to the BJH, DR and t-methods, respectively.