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In the presented research, activated carbons from wheat bran were obtained as a result of pyrolysis and physical activation (CO2 or/and steam). In addition, the obtained materials were subjected to additional modification with superheated steam using the microwave radiation as an energy source. The detailed materials characterization was performed using low-temperature nitrogen adsorption/desorption, Raman spectroscopy, X-ray diffraction, thermal analysis (TG), Boehm's titration, point of zero charge (pHpzc), scanning electron microscopy (SEM) and FT-IR/ATR methods. Moreover, the sorption capacity towards methylene blue (MB) was determined. The activated carbons were characterized with a well-developed surface and pore structure (SBET = 339.6–594.0 m2/g; Vp = 0.157–0.356 cm3/g). Activation in the presence of steam and additional modification with microwave radiation resulted in much better development of the porous structure (SBET = 600.4 m2/g; Vp = 0.380 cm3/g). The materials were shown to possess amorphous structure and thermal stability up to the temperatures of ~450–500 °C. They have good adsorption capacity towards MB varying from 150 mg/g to 241 mg/g depending on activation manner. The adsorption can be described by the pseudo-second order model (R2 = 0.99) and fitted to the Langmuir isotherm. [ABSTRACT FROM AUTHOR]

In the work, water caltrop husk (WCH), locally agricultural residue generated in large quantities, was evaluated as a potential precursor for preparing mesoporous activated carbon (AC) by physical activation under the matrix of activation temperature (600–900℃) and holding times (i.e., 0–150 min). The pore and chemical properties of the resulting AC products, including porosity, true density, elemental analysis (EA), scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS), and Fourier-transform infrared spectroscopy (FTIR), were determined to find the optimal activation conditions. From the data on the analysis of AC properties, the activation temperature at around 800℃ for holding time of 45 min was observed to produce the optimal WCH-AC product with the Brunauer–Emmett–Teller (BET) surface area of 972.56 m2/g, total pore volume of 0.55 cm3/g, and porosity of 0.476. Its corresponding mesopore volume and mesopore percentage reached up to 0.19 cm3/g and 35%, respectively. In addition, the opposite effect was also observed for the resulting AC products activated at 800℃ under different holding times, indicating the pore enlargement and/or collapse at holding time increased from 45 to 60 min. Based on the chemical analyses, the high oxygen content was found on the surface of the resulting AC product, which could be indicative of slight polar nature (i.e., hydrophilicity) due to the oxygen-containing functional groups. [ABSTRACT FROM AUTHOR]

Coal and biomass are two important carbonaceous feedstocks for producing carbon materials. Distinct composition of them might affect pore development of resulting activated carbon (AC) during activation. This was investigated herein via activating anthracite coal and poplar biomass via physical activation (activators: CO 2 and H 2 O) and chemical activation (activators: K 2 C 2 O 4 and ZnCl 2) under the same conditions. The results indicated that the activation of highly aromatic coal produced much higher yield of AC than that from poplar sawdust (ca. 90 % versus ca. 25–37 %). Nonetheless, this was at the cost of limited development of pore structure of AC-coal (121.1 m2g-1 with K 2 C 2 O 4 and 190.8 m2g-1 with H 2 O as an activator). Conversely, abundant aliphatics in poplar created more developed pore structures in AC-poplar (949.0 m2g-1 with K 2 C 2 O 4 and 588.6 m2g-1 with H 2 O), which also enhanced yields of AC-poplar through condensation reactions catalyzed with ZnCl 2 (AC yield: 33.7 % vs 22.8 % from blank experiment). The fused ring structures in coal were hardly activated via cracking with K 2 C 2 O 4. However, H 2 O could oxidize some carbonaceous organics on AC-coal, introducing oxygen-containing species, further cracking of which formed pores. This was an important route for generating pore structures in AC-coal. [Display omitted] • Highly fused aromatic rings in coal inhibit pore development via physical/chemical activation. • Aliphatic structures in poplar are main contributor to pores but diminishes solid yield. • H 2 O is more active than CO 2 for creating pores via cracking/gasification of poplar or coal. • H 2 O oxidizes coal to generate aliphatic O-containing species and then forms pores via cracking. • Ethers, ketones and esters/lactones in coal are cracked over K 2 C 2 O 4 or ZnCl 2 , forming limited pores. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CO 2 /H 2 O co-activation and the NO-char reaction are systematically studied. • The mechanism of the synergistic activation of CO 2 and H 2 O is described. • C − O promotes the conversion of NO. • The co-activated carbon has many micropores, oxygen groups and ordered structures. • The co-activated carbon has high adsorption and reducing properties. Adsorption and reduction of NO by coal-based activated carbon has the advantages of cleanliness, wide distribution of raw materials and low cost. In this paper, activated carbons with 30, 50 and 70 wt% burn-off rates were prepared via physical activation of Zhundong coal by CO 2 , H 2 O and 40 % H 2 O/60 % CO 2 at 700 °C, and NO removal rates were tested in both temperature-programmed and isothermal experiments. The synergistic effects of CO 2 /H 2 O co-activation on the morphology, pore and chemical structures of activated carbons and the adsorption and reduction of NO by activated carbon are systematically investigated for the first time. The results show that the pore size distribution and functional group contents of activated carbons varied with the burn-off rate. At a low burn-off rate of 30 wt%, the H 2 O/CO 2 co-activated carbon exhibits the best adsorption and reduction performance for NO among all samples, which may be attributed to its largest microporous area and abundant oxygen-containing functional groups. As the burn-off rate increased, the micropores were deeply etched, enlarged and/or merged to form mesoporous structures, leading to a decrease in the number of micropores and the NO conversion. At the same burn-off rate and similar specific surface area, the NO conversion increases with increasing C − O content, suggesting that NO reduction is encouraged by C − O enrichment. Coal-based porous carbons from H 2 O/CO 2 co-activation at a low burn-off rate has the advantage of high adsorption and reduction performance for NO. In addition, the effect of active metal elements in coal-based activated carbon on the catalytic reduction of NO was briefly discussed. A novel synergistic activation method was used to prepare activated carbon for reduction of NO at moderate temperatures and the synergistic mechanism is proposed. [ABSTRACT FROM AUTHOR]

As the most commonly used method for industrial activated carbon preparation, physical activation is usually accompanied by significant loss of raw materials, especially when the pore structure of activated carbon is well developed. This not only reduces yields, but also increases costs. To enhance both yield and pore structure of activated carbon, we proposed a facile and scalable method called "fast pyrolysis-physical activation". After fast pyrolysis, although the initial pore volume of the semi-coke decreases, the rapid release of volatiles promotes the increase of mesopore and macropore volumes and the development of micron-scale cracks, which is beneficial for CO 2 mass transfer and reduces diffusion resistance. Therefore, compared to slow pyrolysis, the activated carbon produced through this method has a higher pore volume (increased by 25.9 %–30.0 %) and a larger S BET (increased by 26.7 %–38.3 %), while the yield remains almost unchanged. Consequently, due to the increase in pore volume and high yield of the activated carbon, the CO 2 adsorption capacity (25 °C, 1 bar) of ACB-K700 increases from 2.02 mmol/g to 2.37 mmol/g compared to ACB-M700, and the total CO 2 adsorption capacity of activated carbon prepared from the same mass of raw coal (1 g) increases from 1.07 mmol to 1.16 mmol. Due to the pre-formed pores inside the semi-coke, the gas activator molecules are able to penetrate deep into the particles, which not only reduces the ineffective etching that occurs on the surface, but also promotes the development of pore structure. In conclusion, this study provides a new pore development model for physical activation, and also provides a new method to produce activated carbon rapidly and massively, while the pore structure is well developed. • A new pore-forming mechanism is proposed based on fast pyrolysis-physical activation. • The S BET significantly increases by 26.7–38.3 % at similar yields (49.12–53.01 %). • The rapid escape of volatiles increases the pore volume for semi-coke. • Pre-formed pores in the semi-coke reduces ineffective etching of activator. • The CO 2 absorption capacity at 25 °C and 1 bar can be up to 2.37 mmol/g. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) is produced by a physical or chemical activation process. Physical activation methods are commonly adopted in industry because of their low production costs, but the insufficiency of activating agent diffusibility into core parts of the particles and microdomains of carbon materials causes a lower activation yield and degree of pore development, compared with chemical activation methods. To increase the activating agent diffusibility and corresponding degree of pore development, we propose a novel pressurized physical activation method. Pressurization afforded remarkable increases in specific surface area and total pore volume of the prepared AC, compared with atmospheric pressure. Additionally, in AC prepared by this method, pore size distribution analysis revealed characteristic development of micropores of about 1.6 nm; such micropores did not appear in AC under conventional atmospheric physical activation. Furthermore, observations of particles and their microdomains showed that pressurization increased the activating agent diffusibility in carbon particles, but not at the microdomain level. This innovative pressurized physical activation can produce AC with highly developed pores (specific surface area >2600 m2/g) and a unique pore size distribution due to the improved activating agent diffusibility in carbon particles. [Display omitted] • Pressurized physical activation promoted pore development of activated carbons. • Specific surface area >2600 m2/g was achieved by pressurized physical activation. • Pressurization can afford unique pore size distribution. • Pressurization improved gas diffusibility in carbon particle, but not in microdomain. [ABSTRACT FROM AUTHOR]

Many experimental studies have shown the feasibility of using biomass precursors to produce activated carbon, often improving the properties obtained from traditional materials. However, hardly any models focus on the development of porosity during the process. Among the so-called pore models, the random pore model (RPM) is the most popular and accurately predicts the evolution of the porous structure due to pore growth and coalescence. However, in activation processes with a low degree of conversion, in which pore formation is the dominant mechanism, the RPM does not correctly predict the evolution of the specific surface area since it does not consider the appearance and creation of new porosity. In this work, a new model is proposed that predicts the specific surface area created due to the formation of new pores. Subsequently, it is combined with the determination of the variation of the specific surface area predicted by the RPM due to the growth and coalescence of existing pores. The validation of the new pore evolution model with activated carbon samples obtained at different conversions shows that the model proposed adequately predicts the specific surface area and pore distribution evolution throughout the activation process. [Display omitted] [ABSTRACT FROM AUTHOR]

Acetylene black carbons were activated under flowing CO2 atmosphere at 900 °C for different treatment times. The impact of this heat treatment on the porosity, hydrophilicity, and surface oxygen groups was carefully examined. Longer periods of activation led to increases in the surface area and porosity of the samples. Pore size distributions of the samples showed an increase in micropores, followed by a rise in mesopores, which indicated the occurrence of pore widening with a longer activation period. When used as a microporous layer for H2/air fuel cells, samples with higher levels of porosity showed, in general, reduced mass transport performance due to the formation of pooling locations for water. These results highlight the importance of textural pores in carbon structures on the water management in hydrogen fuel cell when operating under high humidity conditions. [ABSTRACT FROM AUTHOR]

Recently, bio-based carbon foams have gained much interest in many chemical industry fields because of their unique structure and properties. This study provides new information on the effects of catalytic metals (iron, nickel, and copper) on the foaming process. Specifically, the effects of these catalysts on the density, foam growth, and cell size and then further on the pore size distribution and specific surface areas after the physical activation are considered. Furthermore, some of the activated sugar foams were used in adsorption tests using methylene blue as adsorbent. Results showed that the highest effect on foam density was obtained using the iron catalyst in the foaming process. In addition, increasing the iron amount, the development of micro-pores decreased from 95.2 to 60.3% after cabonization and activation of the foams. Nickel and iron had the highest and lowest effect on foam rise at 1375 and 500%, respectively. Interestingly, when the nickel catalyst was used, cell sizes and surface areas two times larger than those when the foams were prepared with the iron and copper catalysts was obtained. The specific surface area of activated sugar-based carbon foams changed significantly with the increased copper amount inside the foaming solution in compared with iron or nickel catalyst. Methylene blue adsorption capacity of additional series of activated sugar foams decreased from 28 to 9% when meso-pore amount decreased. [ABSTRACT FROM AUTHOR]

Two-step physical activation was used to prepare activated carbon from textile waste jute. Raw material was first carbonized under nitrogen and then activated by CO2. Based on yield and pore structure, the optimal carbonization temperature and time were 500 °C and 60 min, respectively. Carbonized sample was next activated. The development of porosity and surface chemistry was highly dependent on activation temperature and time. Activated carbon produced at 800 °C was predominantly microporous while that produced at 900 °C was more mesoporous and macroporous. The shift from microporosity to mesoporosity could be used to produce either microporous or mesoporous carbon just by changing the activation temperature. Activation also changed the surface chemistry and created a more carbonaceous structure. The jute-based activated carbon was mostly powdered in form, slightly acidic and effective in adsorbing both heavy metals and organics. [ABSTRACT FROM AUTHOR]

To improve the utilization value of coal resources and optimize the production process of coal-based activated carbon, an L 9 (34) orthogonal experiment was designed to study the comprehensive effects of the carbonization temperature, heating rate, activation time and activator type on the specific surface area and iodine value of activated carbon prepared by physical activation, as well as the surface chemical and crystal properties. The results showed that large amounts of C–H and oxygen functional groups from the raw materials were lost in the process of preparing the activated carbon, and CaCO 3 generated CaS through a two-step reaction. The raw materials were nonporous or macroporous materials, while the activated carbon developed a microporous structure. The same optimal working conditions were obtained when the iodine value and the specific surface area were used as the optimization target, as follows: 800 °C for carbonization, 10 °C/min for heating rate, 75 min for activation time, and steam + CO 2 as the activator. Finally, activated carbon was prepared under the optimal experimental conditions. The results showed that this activated carbon had the highest specific surface area and iodine value. In addition, the iodine value had a good linear relationship with the specific surface area. [Display omitted] • Time was the greatest factor, followed by the heating rate, temperature and activator. • Steam and CO 2 coactivation had a better activation effect. • The same results were obtained when the iodine value and BET were used as the optimization target. • Carbonization formed cracks and pits, and activation formed a developed pore structure. • CaCO 3 was converted into CaS during activated carbon preparation. [ABSTRACT FROM AUTHOR]

Activated carbons were prepared from a new lignocellulosic biomass source: date palm petioles. The activation process comprise the pyrolysis to 1000 °C under nitrogen flow and then the activation at 750, 850 and 900 °C under CO 2 flow. The samples were characterized by N 2 adsorption, scanning electron microscopy and mercury porosimetry. The activated carbons exhibited a predominant microporosity with specific surface area from 225 m 2 ·g −1 to 546 m 2 ·g −1 , and micropore volumes from 0.09 cm 3 ·g −1 to 0.23 cm 3 ·g −1 . [ABSTRACT FROM AUTHOR]

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.

In this work, waste acrylic fiber web was impregnated with iron chloride solution and another web without salt impregnation was carbonized by heating under a layer of charcoal through physical activation in a high temperature furnace to produce activated carbon and iron impregnated activated carbon (FeAC). After stabilization at heating rate 50°C.hr-1 the carbonization process was performed at the heating rate of 300°C.hr-1. Both the webs were heated to 1200°C with no holding time for getting a higher surface area and porosity. Both the samples were characterized by using BET surface area, SEM, EDX and TGA for determining the surface area, microscopic structure and content of different elements. Iron impregnated activated carbon (FeAC) was later used as adsorbent for the removal of methylene blue from an aqueous solution. The dye removal percentage and adsorption capacity was checked at different experimental parameters like different dye concentrations, adsorbent dosage, stirring speed and different pH. [ABSTRACT FROM AUTHOR]

To prepare activated carbons with a high porosity and low ash content from pyrolyzed rice husk, the method of KOH or K2CO3 solution leaching after CO2 activation was investigated. The effects of KOH or K2CO3 concentration and leaching time on the yield, ash content, and textural properties of the activated carbon were studied, and the activated carbon prepared under the best conditions was characterized. The results showed that the best leaching time was 1 h for KOH and K2CO3, and the best concentrations were 1.0 and 4.0 M, respectively. The leaching process was greatly beneficial to the development of the pore structure. The specific surface area of the activated carbon prepared under the most favorable conditions was approximately 1100 m²/g, and the iodine values were greater than 1100 mg/g. As a result of the leaching process, the ash content of the sample was notably decreased from 63% to approximately 5%, and the porosity development was attributed to the reaction of the leaching reagents with silica. [ABSTRACT FROM AUTHOR]

Abstract: Activated carbons previously used for p-Nitrophenol (PNP) adsorption were subjected to thermal reactivation in order to recover their initial porosity characteristics. Three activating agents were comparatively analysed (air, carbon dioxide and water steam). Regeneration results improved in the sequence air

Highlights: [•] Novel method of activation by cycles permits good control of porosity development. [•] S BET values above 1000m2/g can be obtained with burn-off values lower than 40%. [•] The low burn-off helps to maintain granular morphology of the activated carbons. [•] Carbons with unique hollow core structure and wall thickness of 250μm are produced. [•] The activated carbons showed a good mechanical strength during attrition test. [ABSTRACT FROM AUTHOR]

Abstract: Taixi anthracite was used as a precursor to prepare microporous activated carbons for SO2 adsorption from flue gas. In this work the activated carbons were prepared by physical activation with carbon dioxide and steam, respectively. Specifically, the effects of activation temperature and burn-off degree on the physico-chemical properties of two series were comparatively studied. The physical properties of the AC samples on the SO2 adsorption were also investigated. The surface area and porosity of sample was studied by N2 adsorption at 77K. The surface chemistry was evaluated by FTIR. The BET surface areas and micropore volumes of steam-activated carbons are always larger than those by CO2 activation except the samples with burn-off above 70%. The CO2 activation leads to samples with continuous evolution of ultramicropore volumes. At higher activation temperature, the decrease of micropore volume is attributed to an external burn-off for both series. All the activated carbons show basic properties, which makes these samples suitable for SO2 adsorption. It is observed that a large micropore volume does not necessarily assure an optimal adsorption of SO2; rather, the pore size and pore size distribution should be considered as important parameters. [Copyright &y& Elsevier]

Abstract: The use of rubber-seed shell as a raw material for the production of activated carbon with physical activation was investigated. The produced activated carbons were characterized by Nitrogen adsorption isotherms, Scanning electron microscope, Thermo-gravimetric and Differential scanning calorimetric in order to understand the rubber-seed shell activated carbon. The results showed that rubber-seed shell is a good precursor for activated carbon. The optimal activation condition is: temperature 880°C, steam flow 6kgh−1, residence time 60min. Characteristics of activated carbon with a high yield (30.5%) are: specific surface area (SBET) 948m2 g−1, total volume 0.988m3 kg−1, iodine number of adsorbent (q iodine) 1.326gg−1, amount of methylene blue adsorption of adsorbent (q mb) 265mgg−1, hardness 94.7%. It is demonstrated that rubber-seed shell is an attractive source of raw material for producing high capacity activated carbon by physical activation with steam. [Copyright &y& Elsevier]

Abstract: Grape stalk is an organic waste produced in great amounts in the industrialization processes of grape. This work presents the results of studies carried out to use this waste as raw material to prepare activated carbon through the physical and chemical route. The physicochemical characterization of this material suggests the presence of unusually high levels of ashes. Metal content was determined and high levels of potassium, sodium, iron, calcium and magnesium in carbonized and raw grape stalk were exhibited. This characteristic made difficult physical activation at high temperatures. A leaching step was included before the activation with steam, and adsorbents with surface areas between 700 and 900m2/g were obtained. Physical activation was also performed at lower temperatures using carbonized grape stalk without leaching, leading to the development of some grade of porosity, with an area of 412m2/g. These results would indicate the catalytic effect of the minerals present in this raw material. Chemical activation using phosphoric acid as activating agent seemed to be a very efficient method as final products with BET areas between 1000 and 1500m2/g were obtained. [Copyright &y& Elsevier]

Two substantially different carbonaceous precursors (Quercus Agrifolia wood and walnut shells) were processed following an identical carbonization-activation procedure, using CO2 as activating agent. Three activation temperatures were used and the evolution of micro and mesoporosity of produced samples as a function of activation yield is depicted. Differences, apparently given by intrinsic characteristics of precursors, were found in both the evolution and final status of porosity of obtained samples. It was concluded that initial properties of starting material strongly influence both course and results of the activation process under similar experimental condition. [ABSTRACT FROM AUTHOR]

A low cost-biomass, olive stone, was used as a carbon precursor to synthesize activated biochar. Experiments were carried by single step activation for two agents (steam and CO 2) using a bench scale high-pressure thermobalance. Temperature, pressure, flow rate and holding time were optimized according to the highest adsorption capacity of the biochar obtained. In this respect, activation conditions were established at 900 °C for 30 min, at 0.15 ml/min and 1 bar for H 2 O activation. The optimum activation conditions for CO 2 activation was found to be 1000 °C for 30 min, at 300 ml/min and 1 bar. The activated biochars yielded were characterized by adsorption-desorption of N 2 at −196 °C, scanning electron microscopy, Raman spectroscopy, thermogravimetric analyses and elemental analyses. Results showed that the CO 2 activation only generated microporosity developed in the biochar, whereas both meso and micropores were created after steam activation. Then, the optimum materials were evaluated as a possible CO 2 adsorbent and for this purpose, the CO 2 adsorption isotherms over the pressure range of 1–20 bar at 30 °C were studied. Moreover, the results for these isotherms results were fitted to Langmuir, Freundlich and Sips isotherm models, and the latter forecast the results most accurately. [Display omitted] • Activated carbons were synthesized from low-cost and renewable precursor materials. • Experiments were carried out by means of a single step activation with steam and CO 2. • The effect of activation conditions of activated carbon on the CO 2 uptake was studied and characterized. • The CO 2 adsorption isotherms were fitted to Langmuir, Freundlich and Sip isotherms. • Optimal activated carbons were evaluated as a possible CO 2 adsorbent. [ABSTRACT FROM AUTHOR]