Preparation of activated carbon derived from Jatropha curcas fruit shell by simple thermo-chemical activation and characterization of their physico-chemical properties

High surface area activated carbons were prepared by simple thermo-chemical activation of Jatropha curcas fruit shell with NaOH as a chemical activating agent. The effects of the preparation variables, which were impregnation ratio (NaOH:char), activation temperature and activation time, on the adsorption capacity of iodine and methylene blue solution were investigated. The activated carbon which had the highest iodine and methylene blue numbers was obtained by these conditions as follows: 4:1 (w/w) NaOH to char ratio, 800 °C activation temperature and 120 min activation time. Characterization of the activated carbon obtained was performed by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption isotherm as BET. The results present that the activated carbon possesses a large apparent surface area (S_BET = 1873 m²/g) and high total pore volume (1.312 cm³/g) with average pore size diameter of 28.0 Å.     

Production of activated carbon from olive bagasse by physical activation

Activated carbons were produced from olive bagasse and their characteristics were investigated. Olive bagasse was first carbonized at 500 °C in N₂ atmosphere. Then, the obtained chars were activated with steam. The effects of activation temperature and duration were examined. The resultant activated carbons were characterized by measuring their porosities and pore size distributions. The activated carbons produced had the BET surface areas ranging from 523 to 1106 m²/g. The total pore volume was increased from 0.2981 to 0.6067 cm³/g. Adsorption capacity was demonstrated by the iodine numbers. The surface chemical characteristics of activated carbons were determined by FTIR spectroscopic method and Boehm's titration method. The microstructure of the activated carbons prepared was examined by scanning electron microscopy (SEM). The experimental data was proved that the properties of activated carbons depend on the final temperature of the process and duration of treatment at the final temperature.     

Removal of mercury from natural gas by a new activated adsorbent from olive stones

This study was devoted to the valorization of a plant waste (olive stones): that is widely available in Mediterranean countries in order to remove mercury from natural gas. The raw material from olive stones was prepared by pyrolysis, chemical activation with phosphoric acid, and physical activation under steam. Two olive stone‐based granular activated carbons were prepared: one with the virgin stones, while the other was impregnated with sulphur. After treatment, the adsorbents obtained were characterized by determining the iodine number, the methylene blue index, and by estimating the porous properties by N₂ adsorption at 77 K. Thermogravimetric analysis and infrared spectroscopy analysis were carried out to determine the functional groups before and after mercury adsorption. An experimental study of vapour‐phase mercury adsorption by the activated carbons (virgin and sulphur‐impregnated) and a comparison with a commercial material (HGR) were performed. The comparison, made by analyzing the adsorption in a continuous mode, showed that the proportion of sulphur and the porosity were important for the removal of mercury. In the conditions used, the mercury adsorption on the ACs studied follows a physisorption mechanism. The results showed that granular activated carbon‐based olive stones (sulphur‐impregnated) are very efficient to remove mercury (with 2864 μg/g) and also less expensive than commercial activated carbon due to their local availability.     

Surface chemistry of phosphorus-containing carbons of lignocellulosic origin

Activated carbon adsorbents were prepared by phosphoric acid activation of fruit stones in an argon atmosphere at various temperatures in the 400-1000 °C range and at different acid/precursor impregnation ratios (0.63-1.02). The surface chemistry of the carbons was investigated by elemental analysis, cation exchange capacity (CEC, measured by neutralization of NaOH with acidic surface groups), infrared spectroscopy and potentiometric titration. Porous structure was derived from adsorption isotherms (N₂ at −196 °C and CO₂ at 0 °C). It was demonstrated that all carbons show considerable cation exchange capacity, the maximum (CEC = 2.2 mmol g⁻¹) being attained at 800 °C, which coincides with the maximum contents of phosphorus and oxygen. The cation exchange properties of phosphoric acid activated carbons from fruit stones are chemically stable in very acidic and basic solutions. Proton affinity distributions of all carbons show the presence of three types of surface groups with pK at 2.0-3.3, 4.6-5.9 and 7.6-9.1. These pK ranges were ascribed primarily to: (a) phosphorus-containing and carboxylic groups; (b) lactonic groups, and (c) phenolic groups, respectively. Phosphoric acid activated carbons are microporous with a relatively small contribution of mesopores. A maximum BET surface area of 1740 m² g⁻¹ was attained at 400 °C.     

HEMP-derived activated carbon fibers by chemical activation with phosphoric acid

Activated carbon fibers were prepared by chemical activation of hemp fibers with phosphoric acid at different carbonization temperatures and impregnation ratios. Surface properties of the activated carbons fibers were significantly influenced by the activation temperature and the impregnation ratio. An increase of either of these parameters produced a high development of the porous structure of the fibers. Activated carbon fibers with apparent surface area of 1350 m²/g and mesopore volume of 1.25 cm³/g were obtained at 550 °C with an impregnation ratio of 3. The activated carbon fibers presented a high oxidation resistance, due to the presence of phosphorus compounds on the carbon surface. The oxidation resistance results suggest that C-O-PO₃ and mainly C-PO₃ and C-P groups act as a physical barrier, blocking the active carbon sites for the oxidation reaction.     

Preparation and characterization of mesoporous activated carbon from waste tires

Activated carbons were produced from waste tires and their characteristics were investigated. Rubber separated from waste tires was first carbonized at 500 °C in N₂ atmosphere. Next, the obtained chars were activated with steam at 850 °C. As a result, fairly mesoporous activated carbons with mesopore volumes and BET surface areas up to 1.09 cm³/g and 737 m²/g, respectively, were obtained. To further improve the porous properties of the activated carbons, the char was treated with 1 M HCl at room temperature for 1 day prior to steam activation. This treatment increased mesopore volumes and BET surface areas of the activated carbons up to 1.62 cm³/g and 1119 m²/g, respectively. Furthermore, adsorption characteristics of phenol and a dye, Black 5, on the activated carbon prepared via acid treatment were compared with those of a commercial activated carbon in the liquid phase. Although the prepared carbon had a larger micropore volume than the commercial carbon, it showed a slightly lower phenol adsorption capacity. On the other hand, the prepared carbon showed an obviously larger dye adsorption capacity than the commercial carbon, because of its larger mesopore volume.     

Preparation of porous carbons from thermoplastic precursors and their performance for electric double layer capacitors

Porous carbons with high surface area were successfully prepared from thermoplastic precursors, such as poly(vinyl alcohol) (PVA), hydroxyl propyl cellulose and poly(ethylene terephthalate), by the carbonization of a mixture with MgO at 900 °C in an inert atmosphere. After carbonization the MgO was dissolved out using a diluted sulfuric acid and the carbons formed were isolated. The mixing of the PVA carbon precursor with the MgO precursors (reagent grade MgO, magnesium acetate or citrate) was done either in powder form or in an aqueous solution. The BET surface area of the carbons obtained via solution mixing could reach a very high value, such as 2000 m²/g, without any activation process. The pore structure of the resultant carbons was found to depend strongly on the mixing method; the carbons prepared via solution mixing were rich in mesopores, but those produced via powder mixing were rich in micropores. The size of mesopores was found to be almost the same as that of the MgO particles, suggesting a way of controlling the mesopore size in the resultant carbons. Measurement of capacitance was carried out in 1 mol/L H₂SO₄ electrolyte. The porous carbon with a BET surface area of 1900 m²/g prepared at 900 °C through solution mixing of Mg acetate with PVA showed a fairly high EDLC capacitance, about 250 F/g with a current density of 20 mA/g and 210 F/g with 1000 mA/g. The rate performance was closely related to the mesoporous surface area.     

Characterisation of lignite as an industrial adsorbent

An alternative use of the abundant and inexpensive lignite (also known as brown coal) as an industrial adsorbent has been characterised. The adsorptive properties of two Victorian lignite without any pre-treatment were investigated using the cationic methylene blue dye as a model compound in aqueous solutions. Two commercial activated carbon products were also studied for comparison. The adsorption equilibrium of the four adsorbents was better described by the Langmuir isotherm model than the Freundlich model. The adsorption capacities of the two untreated lignite adsorbents, Loy Yang and Yallourn, calculated using Langmuir isotherms were 286 and 370 mg/g, respectively, higher than a coconut shell-based activated carbon (167 mg/g), but lower than a coal-based activated carbon (435 mg/g). Surface area results suggested that larger micropores and mesopores were important for achieving good methylene blue adsorption by the activated carbons. However, FTIR and cation exchange capacity analyses revealed that, for the lignite, chemical interactions between lignite surface functional groups and methylene blue molecules occurred, thereby augmenting its adsorption capacity.     

Preparation of activated carbon from Jatropha hull with microwave heating: Optimization using response surface methodology

Preparation of activated carbon has been attempted using steam as the activating agent by microwave heating from Jatropha hull. The response surface methodology (RSM) technique is utilized to optimize the process conditions. The influences of the three major parameters, activation temperature, activation time and steam flow rate on the properties of activated carbon are investigated using analysis of variance (ANOVA), to identify the significant parameters. The optimum conditions for the preparation of activated carbon has been identified to be an activation temperature of 900 °C, activation time of 19 min and steam flow rate of 5 g/min. The optimum conditions resulted in an activated carbon with an iodine number of 988 mg/g and a yield of 16.56% respectively, while the BET surface area evaluated using nitrogen adsorption isotherm correspond to 1350 m²/g, with the pore volume of 1.07 cm³/g. The activated carbon is hetero porous with the micropore volume contributing to 40.8%.     

Activated carbon produced from Sasol-Lurgi gasifier pitch and its application as electrodes in supercapacitors

A pyrolysis product derived from Sasol-Lurgi gasifier pitch was activated using different proportions of KOH. The increase of the amount of KOH used for activation caused the activation degree of the carbons to increase very significantly. The activated carbons obtained using lower amounts of KOH were mainly microporous, while the amount of mesopores developed in the samples progressively increased for the carbons activated with higher proportions of KOH. The gravimetric specific capacitance of samples obtained with (2:1), (3:1) and (5:1) KOH to carbon ratio were rather similar at low current densities (∼400 F/g at low current densities), despite the significant differences observed in their textural characteristics. Supercapacitors built with the activated carbons obtained with (2:1) and (3:1) KOH to carbon ratio yielded the highest volumetric capacitance (higher than 200 F/cm³ at low current densities), while the most activated sample yielded the lowest values, due to the significant reduction in density caused by activation. The high values of capacitance observed result from the combination of two mechanisms of energy storage: double layer formation and pseudocapacitance.     

Activation of carbon nanofibres for hydrogen storage

The present study was aimed to investigate different methods of activation of carbon nanofibres, CNF, in order to determine the beneficial effect on the hydrogen sorption capacities of increasing the surface area. Two activation systems were used: physical activation with CO₂ and chemical activation with KOH. A range of potential adsorbents were thus prepared by varying the temperature and time of activation. The structure of the CNF proved more suitable to activation by KOH than by CO₂, with the former yielding higher surface area carbons (up to 1000 m² g⁻¹). The increased surface area, however, did not correspond directly with a proportional increase in hydrogen adsorption capacity. Although high surface areas are important for hydrogen storage by adsorption on solids, it would appear that it is essential that not only the physical, but also the chemical, properties of the adsorbents have to be considered in the quest for carbon based materials, with high hydrogen storage capacities.     

Removal efficiency of radioactive methyl iodide on TEDA-impregnated activated carbons

Activated carbons were prepared by different series of carbon dioxide and steam activation from walnut shells for their optimal use as radioactive methyl iodide adsorbents in Nuclear Plants. The knowledge of the most favourable textural characteristics of the activated carbons was possible by the previous study of the commercial activated carbon currently used for this purpose. In order to increase their methyl iodide affinity, the effect of triethylenediamine impregnation was studied at 5 and 10 wt.%. The results obtained indicated that in both cases the adsorption efficiency is markedly improved by the addition of impregnant, which allows the adsorbate uptake to occur not only by physical adsorption, via non-specific interactions (as in non-impregnated carbons) but also by the specific interaction of triethylenediamine with radioactive methyl iodide. Methyl iodide retention efficiencies up to 98.1% were achieved.     

Production of fibrous activated carbons from natural cellulose (jute, coconut) fibers for water treatment applications

Different fibrous activated carbons were prepared from natural precursors (jute and coconut fibers) by physical and chemical activation. Physical activation consisted of the thermal treatment of raw fibers at 950 °C in an inert atmosphere followed by an activation step with CO₂ at the same temperature. In chemical activation, the raw fibers were impregnated in a solution of phosphoric acid and heated at 900 °C in an inert atmosphere. The characteristics of the fibrous activated carbons were determined in the following terms: elemental analysis, pore characteristics, SEM observation of the porous surface, and surface chemistry. As the objective of this study was the reuse of waste for industrial wastewater treatment, the adsorption properties of the activated carbons were tested towards pollutants representative of industrial effluents: phenol, the dye Acid Red 27 and Cu²⁺ ions. Chemical activation by phosphoric acid seems the most suitable process to produce fibrous activated carbon from cellulose fiber. This method leads to an interesting porosity (S_BET up to 1500 m² g⁻¹), which enables a high adsorption capacity for micropollutants like phenol (reaching 181 mg g⁻¹). Moreover, it produces numerous acidic surface groups, which are involved in the adsorption mechanisms of dyes and metal ions.     

Effects of chemical modification of petroleum cokes on the properties of the resulting activated carbon

Activated carbons have been prepared from petroleum cokes by the combination of a chemical treatment with HClO₄ or H₂O₂ and a chemical activation with KOH at a constant KOH/coke ratio of 3/1. The influence of different chemical treatments on the properties of the activated carbon precursors and final carbons activated with KOH was invested by using XRD, FTIR, and BET techniques. XRD results indicated that the value of interplanar distance d₀₀₂ increased by chemical treatment and the disappearance of the peak corresponding to 0 0 2 faces correlated to high specific surface area. FTIR studies showed that chemical modification promoted the formation of surface oxygen functionalities. Significant effects on BET surface area, pore texture and iodine adsorption capacity were evidenced. The results show that chemical modification prior to activation dramatically increased the BET surface area and total pore volume of the resulting activated carbon. Modified petroleum coke based activated carbon with chemical activation had higher specific surface area (2336 m²/g) and better iodine adsorption value (1998 mg/g).     

A study of the characteristics of activated carbons produced by steam and carbon dioxide activation of waste tyre rubber

This paper presents a study into the effect of different activation conditions on the porosity and adsorption characteristics of carbon adsorbents produced from waste tyre rubber. For the purpose of this work, three carbon series were produced using different activation temperatures (between 925 and 1100 °C) and oxidising agents (steam or carbon dioxide). Carbons produced to different degrees of burn off were characterised using gas (nitrogen) and liquid phase (phenol, methylene blue and Procion Red H-E2B) adsorption. Total micropore volumes and BET surface areas increased almost linearly with the degree of activation to 0.554 ml/g and 1070 m²/g, respectively, while the development of external surface area was particularly rapid at degrees of activation above 50 wt% burn off. Steam was observed to generate a narrower but more extensive microporosity than carbon dioxide. However, carbon dioxide produced carbons of slightly larger external surface areas. Activation at higher temperatures resulted in pores of slightly larger dimensions, although this was only evident in highly activated samples. Porosity characteristics were reflected in the capacity of the carbons to adsorb species of different molecular size from solution. In this respect, steam-activated carbons presented greater capacities for the adsorption of smaller molecular size compounds (phenol), while carbon dioxide-activated carbons adsorbed larger textile dyes more effectively.     

Importance of activated carbon's oxygen surface functional groups on elemental mercury adsorption

The effect of varying physical and chemical properties of activated carbons on adsorption of elemental mercury (Hg⁰) was studied by treating two activated carbons to modify their surface functional groups and pore structures. Heat treatment (1200 K) in nitrogen (N₂), air oxidation (693 K), and nitric acid (6N HNO₃) treatment of two activated carbons (BPL, WPL) were conducted to vary their surface oxygen functional groups. Adsorption experiments of Hg⁰ by the activated carbons were conducted using a fixed-bed reactor at a temperature of 398 K and under N₂ atmosphere. The pore structures of the samples were characterized by N₂ and carbon dioxide (CO₂) adsorption. Temperature-programmed desorption (TPD) and base-acid titration experiments were conducted to determine the chemical characteristics of the carbon samples. Characterization of the physical and chemical properties of activated carbons in relation to their Hg⁰ adsorption capacity provides important mechanistic information on Hg⁰ adsorption. Results suggest that oxygen surface complexes, possibly lactone and carbonyl groups, are the active sites for Hg⁰ capture. The carbons that have a lower carbon monoxide (CO)/CO₂ ratio and a low phenol group concentration tend to have a higher Hg⁰ adsorption capacity, suggesting that phenol groups may inhibit Hg⁰ adsorption. The high Hg⁰ adsorption capacity of a carbon sample is also found to be associated with a low ratio of the phenol/carbonyl groups. A possible Hg⁰ adsorption mechanism, which is likely to involve an electron transfer process during Hg⁰ adsorption in which the carbon surfaces may act as an electrode for Hg⁰ oxidation, is also discussed.     

High power supercapacitors using polyacrylonitrile-based carbon nanofiber paper

Porous carbon nanofiber paper has been obtained by one-step carbonization/activation of PAN-based nanofiber paper at temperatures from 700 to 1000 °C in CO₂ atmosphere. The paper was used as supercapacitor electrode without any binder or percolator. At low temperature, e.g., ?900 °C, nitrogen enriched carbons with a poorly developed specific surface area (S_BET ? 400 m²/g) are obtained. In aqueous electrolytes, these carbons withstand high current loads without a noticeable decrease of capacitance, and the normalized capacitance reaches 67 μF/cm². At 10 s time constant, the values of energy and power densities are 3-4 times higher than for activated carbons (AC) presenting higher specific surface area. By carbonization/activation at 1000 °C, subnanometer pores are developed and S_BET = 705 m²/g. Despite moderate BET specific surface area, the capacitance reaches values higher than 100 F/g in organic electrolyte. At high power densities, the nanofiber paper obtained at 1000 °C outperforms the energy density retention of ACs in organic electrolyte. The high power capability of the carbon nanofiber papers in the two kinds of electrolytes is attributed both to the high intrinsic conductivity of the fibers and to the high diffusion rate of ions in the opened mesopores.     

A review of the control of pore structure in MgO-templated nanoporous carbons

Nanoporous carbons with a high surface area were directly prepared from various carbon precursors without any stabilization and activation processes. Various carbon precursors, including poly(vinyl alcohol), poly(ethylene terephthalate), polyimide, coal tar pitch, were used and MgO itself, Mg acetate, Mg citrate, Mg gluconate and Mg hydroxy-carbonate were employed as MgO precursor. Carbon precursor was mixed with MgO precursor in different ratios either in powder (powder mixing) or in solution (solution mixing), and heat-treated at 900 °C in inert atmosphere. MgO formed in the carbonization products was dissolved out using a diluted acid. BET surface area of the carbons obtained could be reached to high value, as high as 2000 m²/g, even though any activation process was not applied. Most carbons prepared through this method were rich in mesopores. Size of mesopores in the resultant carbons was tunable by selecting MgO precursor and relative volume between mesopores and micropores was controlled by carbon precursor.     

Role of microporosity and surface functionality of activated carbon in methylene blue dye removal from water

Activated carbons have been prepared from jute stick by both chemical and physical activation methods using zinc chloride and steam, respectively. They were characterized by evaluating surface area, iodine number, pore size distribution, and concentration of surface functional groups. The chemically activated carbon largely featured micropore structure, while the physically activated carbon mainly featured macropore structure. The specific surface area of chemically and physically activated carbons was 2,325 and 723 m ² /g, while the iodine number was 2,105 and 815mg/g, respectively. The concentration of surface functional groups was determined by Boehm titration method, which suggested that different types of surface functional groups are randomly distributed on chemical activated carbons, while it is limited for physical activated carbon. The microporosity along with surface functional groups provided a unique property to chemically activated carbon to adsorb Methylene Blue dye to a large extent. The adsorption of dye was also affected by the adsorption parameters such as adsorption time, temperature and pH. Comparatively, higher temperature and pH significantly facilitated dye adsorption on chemically activated carbon.     

Adsorption of methylene chloride vapor on activated carbons

A laboratory investigation on the adsorption of hazardous methylene chloride (METH) vapor on the commercial activated carbons BPL and PCB, which were made from bituminous coal and coconut shell, respectively, was conducted at 283, 293, 303, and 313 K. The physical properties and surface functional groups of the two activated carbons were also measured and compared with each other. The experimental results indicate that the adsorption capacity of carbon PCB is slightly higher than that of carbon BPL. It was found that the Langmuir, Freundlich, and Dubinin–Radushkevich adsorption equations were well fitted by the measured adsorption data. The values of the parameters of the adsorption equations were determined for the two adsorbents. The physical properties (e.g. micropore volume) of the adsorbents are consistent with the parameters obtained from the adsorption results.