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The increase in burning, deforestation, and the exorbitant use of fossil fuels have contributed to the increase in carbon dioxide emissions; this gas is responsible for the intensification of the greenhouse effect and radical climate changes. In this way, it becomes necessary to find alternatives to reduce its emission. Porous carbon materials synthesized from lignocellulosic waste can be employed in technologies for capture and utilization of CO 2 due to the advantages such as selectivity, low-cost synthesis, high surface area and pore volume, and thermal and chemical stability. Considering the availability of Brazil nut biomass residues in the Amazon region, this article proposes to synthesize activated carbon from the lignocellulosic residue using physical and chemical activation methods for CO 2 capture. The analysis of N 2 adsorption-desorption isotherms proves the predominance of a microporous structure when using the two synthesis methods described here. In physical activation, the surface area was 912 m 2 /g, while, in chemical activation, it was 1421 to 2730 m 2 /g. The sample treated via the chemical method (BS6-K1) showed better performance in CO 2 adsorption, with adsorption results of 3.8 and 6 mmol/g of CO 2 at 25 ℃ and 0 °C, respectively, at 101 kPa. CO 2 adsorption capacity is due to the high volume of ultramicropores. It is believed that the microporous carbon material synthesized from Brazil nut residues is an alternative precursor for carbon materials used as CO 2 capture., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Pore development and the formation of oxygen functional groups were studied for activated carbon prepared from bamboo ( Bambusa bambos ) using a two-step activation with CO 2 , as functions of carbonization temperature and activation conditions (time and temperature). Results show that activated carbon produced from bamboo contains mostly micropores in the pore size range of 0.65 to 1.4 nm. All porous properties of activated carbons increased with the increase in the activation temperature over the range from 850 to 950 °C, but decreased in the temperature range of 950 to 1000 °C, due principally to the merging of neighboring pores. The increase in the activation time also increased the porous properties linearly from 60 to 90 min, which then dropped from 90 to 120 min. It was found that the carbonization temperature played an important role in determining the number and distribution of active sites for CO 2 gasification during the activation process. Empirical equations were proposed to conveniently predict all important porous properties of the prepared activated carbons in terms of carbonization temperature and activation conditions. Oxygen functional groups formed during the carbonization and activation steps of activated carbon synthesis and their contents were dependent on the preparation conditions employed. Using Boehm's titration technique, only phenolic and carboxylic groups were detected for the acid functional groups in both the chars and activated carbons in varying amounts. Empirical correlations were also developed to estimate the total contents of the acid and basic groups in activated carbons in terms of the carbonization temperature, activation time and temperature.

The present work reports the preparation of CO 2 -activated carbon (AC) using Stevia rebaudiana (Bertoni) residue as a new carbon precursor. The experimental parameters were optimized via chemometrics tools to obtain an AC with high BET surface area (S BET ). The found optimum condition was: activation temperature of 900 °C, CO 2 flow of 165 cm 3 g -1 and activation time of 60 min, providing an AC op with S BET of 874 m 2 g -1 . The AC op was characterized from several analytical techniques, which showed that it has heterogeneous morphology features and different surface chemical groups, predominating the acidic character. The adsorption performance of AC op for triclosan (TCS) removal from solution was investigated by kinetic, equilibrium and thermodynamic studies. The results showed that TCS adsorption process onto AC op is spontaneous and endothermic, wherein the mechanism occurs by different steps, which equally play important roles. Additionally, the monolayer adsorption capacity (Q m ) was found to be 117.00 mg g -1 ., (Copyright © 2019 Elsevier Inc. All rights reserved.)

In this work, the Honduras Mahogany (Swietenia macropnylla King, SMK) seed husk was used as a novel biomass resource for producing activated carbon by physical activation. The texture characteristics and chemical characterization of resulting products were investigated in correlation with the process parameters. Based on the thermochemical properties of the SMK biomass, the process conditions were set to a rate of about 10 °C/min under nitrogen (N2) flow of 500 cm3/min heated to 500 °C, then switched to carbon dioxide (CO2) flow of 100 cm3/min in the specified activation conditions (i.e., temperature of 700–850 °C for holding times of 0–60 min). Our findings showed that the texture characteristics (i.e., surface area and pore volume) increased with an activation temperature increase from 700 to 800 °C for a holding time of 30 min but gradually decreased as the temperature increased thereafter. Similarly, the texture characteristics also indicated an increasing trend with the residence time extending from 0 min to 30 min but slightly decreased as the time was extended to 60 min. Therefore, the optimal activation conditions for producing SMK-based activated carbon should be set at 800 °C for a holding time of 30 min to obtain the maximal texture characteristics (i.e., BET surface area of 966 m2/g and total pore volume of 0.43 cm3/g). On the other hand, the chemical characteristics were analyzed by energy dispersive X-ray spectroscopy (EDS) and Fourier Transform infrared spectroscopy (FTIR), showing oxygen complexes contained on the hydrophilic surface of the resulting activated carbon. [ABSTRACT FROM AUTHOR]

In this study, we systematically study the efficient production method and electrochemical characteristics of activated carbons (AC) derived from rice husk (RH) and walnut shell (WS). In particular, the effectiveness of physical activation using carbon dioxide (CO2) was investigated and compared with the more common chemical activation method using potassium hydroxide (KOH). The results show that the KOH–activated samples have remarkable specific capacities, reaching 157.8 F g−1 for RH and 152 F g−1 for WS at 1 A g−1. However, the rate capability of AC obtained via KOH decreases significantly as the scanning rate increases, retaining only 51.5% and 68% of their original capacities for RH–KOH and WS–KOH, respectively, at 20 A g–1. In contrast, CO2–activated samples show a superior rate performance with a capacity retention of 75.6% for WS and 80% for RH at the same current density. In addition, electrochemical impedance spectroscopy (EIS) analysis shows that AC obtained via CO2 has a lower charge transfer resistance compared to its KOH counterparts. CO2–activated RH and WS electrodes show Rct values of 0.1 Ω and 0.24 Ω, respectively, indicating improved ion transport kinetics and surface area utilization. These results highlight the importance of activation techniques in tailoring the electrochemical behavior of biomass–derived carbon. This study not only expands the understanding of the interaction between activation, morphology, and performance but also indicates the potential of CO2 activation as an environmentally friendly and efficient alternative. As the field of sustainable energy storage advances, this work provides valuable guidance for the development of high–performance supercapacitor electrodes with less environmental impact. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly porous activated carbon was synthesized through physical method. • Biomass from Strychnos Potatorum was used as a raw material. • Symmetric supercapacitor devices exhibit a specific capacitance of 281 F g−1 at 0.2 A g−1. • Excellent retention of more than 98.2 % after 5000 cycles. Herein, low-cost activated carbon (AC) prepared from Strychnos Potatorum shells using CO 2 as an activating agent via physical activation technique. Waste biomass-derived AC have the merits of excellent conductivity and highly porous with high-surface area. Electrochemical assessments indicated that the prepared Strychnos Potatorum derived activated carbon (SPAC) electrode exhibited superior electrochemical performance. The experimental data showed that the specific capacitance of 352.5 F g−1 at 0.5 A g−1 and retained 140 F g−1 at 20 A g−1. Symmetric supercapacitors SPAC//SPAC device displayed an impressive specific capacitance of 147 F g−1 at 0.1 A g−1 and an energy density of 20.41 W h kg−1 at 100 W kg−1 and retained 2.7 Wh kg−1 at 10000 W kg−1. Furthermore, these supercapacitors demonstrated exceptional cyclability, maintaining capacity retention of 92.3 % over 10,000 charge–discharge cycles at 1 A g−1. This research work underscores the promising potential of AC materials derived from Strychnos Potatorum shells in development of high-performance supercapacitors. [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]

• Residue after supercritical extraction of hops as precursor for activated bio-carbons production. • This study developed activated bio-carbons to remove NO 2. • The most favorable conditions for NO 2 removal from air stream were specified. • The maximum adsorption capacity obtained 79.2 mg/g ads. Production of activated bio-carbons from the residue of supercritical extraction of hops has been described. The precursor was first subjected to pyrolysis at 500 and 700 °C in nitrogen atmosphere. The bio-chars were next subjected to physical activation at 700 and 800 °C in carbon dioxide atmosphere. The effects of pyrolysis and activation temperature on the physicochemical properties and sorption capacity toward NO 2 were established. The results have shown that by physical activation of residue of supercritical extraction of hops it is possible to produce bio-sorbents with very high capacity towards NO 2, reaching maximum 79.2 mg/g. It has been proved that the effectiveness of NO 2 removal to large extent depends on the conditions of adsorption. The presence of steam in the stream of gases and preliminary wetting of the adsorbent bed have positive effect on the adsorption of NO 2 by the bio-sorbents obtained. [ABSTRACT FROM AUTHOR]

Abstract The present work reports the preparation of CO 2 -activated carbon (AC) using Stevia rebaudiana (Bertoni) residue as a new carbon precursor. The experimental parameters were optimized via chemometrics tools to obtain an AC with high BET surface area (S BET). The found optimum condition was: activation temperature of 900 °C, CO 2 flow of 165 cm3 g−1 and activation time of 60 min, providing an AC op with S BET of 874 m2 g−1. The AC op was characterized from several analytical techniques, which showed that it has heterogeneous morphology features and different surface chemical groups, predominating the acidic character. The adsorption performance of AC op for triclosan (TCS) removal from solution was investigated by kinetic, equilibrium and thermodynamic studies. The results showed that TCS adsorption process onto AC op is spontaneous and endothermic, wherein the mechanism occurs by different steps, which equally play important roles. Additionally, the monolayer adsorption capacity (Q m) was found to be 117.00 mg g−1. Graphical abstract fx1 Highlights • Stevia residue was used as precursor of CO 2 -activated carbon. • Activation procedure was optimized from Response Surface Methodology. • Optimized activated carbon (AC op) was employed on adsorption of triclosan. • Monolayer adsorption of triclosan over AC op was found to be 117.00 mg g−1. • Adsorption occurs via spontaneous and endothermic process. [ABSTRACT FROM AUTHOR]

Physical activation of biomass with H 2 O or CO 2 is an important method for producing activated carbon (AC). Activation of biomass with CO 2 or H 2 O follows varied mechanisms and the use of mixed CO 2 /H 2 O might show potential synergistic effects for creating pores. This was investigated by activation of lignin-derived biochar with H 2 O, CO 2 and their mixture. The results demonstrated that H 2 O as an activator was much more effective than CO 2 for generation of pores (804.1 m2g−1 versus 516.1 m2g−1in CO 2), especially mesopores (40% versus 14% in CO 2). This was achieved via enhancing cracking/gasification reactions of the biochar with H 2 O. The synergistic effect of CO 2 and H 2 O for activation of the lignin-derived biochar was insignificant as cracking/gasification reactions were not enhanced, leading to remarkably lower specific surface area of the AC (674.8 m2g−1) than that with H 2 O as an activator alone. Competitive adsorption of CO 2 and H 2 O existed and preferable adsorption of CO 2 hindered deoxygenation of the biochar with H 2 O. The in-situ IR characterization indicated that CO 2 presence suppressed decarbonylation reactions, retaining more oxygen species in form of C O, while it was the opposite in H 2 O. Additionally, activation with H 2 O formed numerous round-shape dents on surface of activated carbon, while the activation with CO 2 formed the characteristic round edges. The AC activated with H 2 O showed superior capability for adsorption of phenol than that activated with CO 2 or mixed H 2 O/CO 2. [Display omitted] • H 2 O is more effective than CO 2 for cracking, forming less activated carbon (AC). • Synergistic effect of CO 2 /H 2 O is insignificant as creating pores are not enhanced via cracking. • Competitive while preferable adsorption of CO 2 hinders activation with H 2 O. • CO 2 is not as active as H 2 O for cracking of C O in intermediates and for creating pores. • AC activated with H 2 O is superior for adsorbing phenol. [ABSTRACT FROM AUTHOR]

In this work, hierarchically porous nitrogen-doped carbon materials (PNCs) are prepared through a physical activation process by using carbon dioxide as an activating agent and polyaniline as a precursor. The morphology, porous property, and chemical attribute of PNCs are investigated through different technical methods, such as scanning electron microscopy, nitrogen adsorption–desorption measurement, and X-ray photoelectron spectroscopy. The textural property of PNCs can be tuned by varying the activation time. PNCs display high specific surface areas (1030–2900 m 2 g −1 ) and large pore volumes (0.66–1.87 cm 3 g −1 ). When taken as adsorbents for gas capture, PNCs exhibit high carbon dioxide capture capacities (17.2–21.5 wt% at 273 K and 1.0 bar) and good selective adsorption of carbon dioxide over nitrogen or methane. The superior performance can be ascribed to the high porosity, suitable pore size, and the presence of nitrogen functional groups. [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]

Sulfur doped carbons were prepared through physical activation of sulfur containing resorcinol-formaldehyde resins. The sulfur doping level depended on the sulfuric acid addition amount during the synthesis of the resin, it was also found that the increase of sulfur content caused the enlargement of pores. The CO 2 adsorption tests were carried out at 273, 298 and 323 K, the influences of different activation conditions were investigated systematically. The adsorption amount at 1 bar reached 5.63, 3.69 and 2.33 mmol/g at 273, 298 and 323 K, respectively. The results also revealed that both sulfur doping and the porous characteristics had important influences on the CO 2 uptake. The sulfur doped carbon also showed a high initial isosteric adsorption heat of 48.8 kJ/mol, which is higher than that of undoped carbon and close to that of nitrogen doped carbon. It was concluded that sulfur doping could significantly enhance the interaction strength between CO 2 and carbon surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Free standing CO 2 activated electrode fabricated from carbonized palm tree fronds. • Enhanced specific capacitance after CO 2 activation. • CO 2 activated electrodes showed enhanced capacitive deionization of water. • Activated electrodes showed higher salt adsorption and quick regeneration. Water is essential for life and is one of the most important resources on Earth. However, pollution of water is a major concern, as it can have negative impact on both the environment and human health. Capacitive deionization (CDI) of water is being considered as one of the emerging water purification techniques for removal of ions and desalination. In this work, CDI performance of free-standing electrodes made of CO 2 activated carbon nanoparticles (AcNP) has been studied. These nanoparticles were produced from carbonized date palm fronds followed by ball milling. The AcNP were mixed with single wall carbon nanotubes and polymer binder; subsequently casted on glass substrate to fabricate highly conducting free-standing electrodes. The Brunauer–Emmett–Teller analysis of the AcNP in contrast to the un-activated carbon nanoparticles (UnAcNP) showed significant increase in the specific surface area, microspore and mesopore volume, total pore volume and average pore size. The specific capacitance values of the UnAcNP and AcNP electrodes were measured to be 8.75 and 50 Fg−1, respectively at a fixed scan rate of 5 mV/s. The electrochemical impedance spectroscopy measurement also showed that the CO 2 activation has reduced the charge transfer resistance of the fabricated electrode and enhanced its capacity. The CDI performance showed that the AcNP has a much higher salt absorption capacity of 6.30 mg/g in contrast to 0.032 mg/g for the UnAcNP sample. Moreover, average salt absorption rate was found to be 0.42 mg/g/min for AcNP in comparison to UnAcNP (0.0021 mg/g/min). The higher desalination capacity of the AcNP shows promising applications of plant-based carbon materials in water desalination and purification systems. [ABSTRACT FROM AUTHOR]

This study presents porous activated carbons, prepared by the physical activation of high-alkali Zhundong coal with CO 2 , H 2 O, or CO 2 /H 2 O, as supercapacitor electrode materials. The synergistic effect between CO 2 and H 2 O activation on the specific capacitance, morphology, pore and physicochemical structure, and supercapacitor performance of activated carbons was systematically investigated for the first time. A hierarchical porous structure is formed in carbon co-activated by CO 2 and H 2 O at 800 °C (TC C/H-800), which also has a rich graphite microcrystalline structure, long-range ordered graphite network, abundant oxygen- and nitrogen-containing functional groups and high char yield (about 70 wt%), all of which are desirable properties. Moreover, the TC C/H-800 electrode shows better electrochemical performance than electrodes based on carbon activated by CO 2 or H 2 O alone, and has an ideal coulombic efficiency (98.95% after 2000 cycles at 5 A g−1) and a good specific capacitance. The symmetrical TC C/H-800 supercapacitor reaches a 155.1 F g−1 specific capacitance at 0.5 A g−1. Meanwhile, its energy density is 21.54 Wh kg−1 at 500.00 W kg−1, with 92.97% of the initial discharge capacity retains after 10,000 cycles. Coal-based porous carbon activated by CO 2 and H 2 O synergistically has the advantages of low losses and low pollution. [Display omitted] • A synergistic effect occurs when CO 2 and H 2 O are co-activated for supercapacitors. • The mechanism of the synergistic activation of CO 2 and H 2 O is described. • The material performs better than other physical activation methods. • Co-activation of CO 2 and H 2 O has the advantages of low loss and low pollution. [ABSTRACT FROM AUTHOR]

Biochar is a carbon-rich material that is a co-product of the thermochemical conversion of biomass to liquid or gaseous products. A possible high-value application of biochar is the production of activated carbon. Biochar from biomass can be physically activated with a mild oxidant such as steam or carbon dioxide. A new model is proposed to describe the physical activation of pyrolytic biochar to activated carbon. The primary model assumption is that activation deepens but does not widen the pores. Measurements confirmed that the average pore diameter remained at about 1.9 nm. The new model successfully predicts the yield and specific surface area of activated carbon produced from olive residues. The pyrolysis conditions significantly impact the quality of the activated carbon. For example, biochar produced at higher heating rates contains more pores that, when cleared by physical activation with carbon dioxide, provide an activated carbon with a higher specific surface area, reaching about 1300 m2/g. [Display omitted] • New model for biochar physical activation to activated carbon. • Model assumes that physical activation deepens but does not widen the pores. • Model predicts yield and specific surface area of activated carbon. • Biochar production conditions affect the activated carbon specific area. [ABSTRACT FROM AUTHOR]

We have analyzed the effects of CO 2 activation on the porosity of ultrahigh pore volume carbon aerogels. Data obtained from the new 2D-NLDFT-HS model for carbons has been compared to the results of conventional methods (BJH, t-plot, DR); all the models were applied to the desorption branch of the isotherms. Physical activation of the carbon aerogel at different burn-off degrees resulted in materials showing increasing volume of micropores and alteration of mesopore structure. The later effect manifested itself by a characteristic inflection in the desorption branch of the nitrogen isotherm at high relative pressures. Such curvatures are attributed to a non uniform activation of the carbon matrix with CO 2 that in some parts carves the surface of the precursor deeper than in others, creating bimodal/multimodal pore size distributions. The different methods applied for the assessment of the textural properties of the aerogels with ultrahigh micro-/mesoporosity showed excellent agreement in terms of pore volumes, surface areas and average pore size. [ABSTRACT FROM AUTHOR]

Sliced activated carbons were prepared from palm tree fronds, a biomass material, using a single step physical method. Effect of the synthetic parameters on the surface area, pore size and pore volume of the activated carbon were studied, pursuing by the optimization of studied parameters. The activation temperature, heating ramp rate, reaction vessel pressure and the CO 2 flowrate were found to be the influential parameters for the synthesis of sliced activated carbon with larger porosity and surface area. The optimum conditions to synthesize the porous activated carbon bearing high pore volume and surface area were studied and identified. Highest surface area of 1094 m 2 g −1 was achieved under the optimum conditions. Scanning electron microscopy (SEM) for the porosity and Fourier transform infrared spectroscopy (FTIR) for surface functional groups and transmission electron microscopy (TEM) confirms the presence of uniform nanoparticles of 2.1385 nm. [ABSTRACT FROM AUTHOR]

Amazonian andiroba shell was used as a non-expensive, renewable biomass resource to produce a porous activated carbon as a CO 2 adsorbent and a cheap supercapacitor material. Activated carbons were prepared by CO 2 physical activation of hydrochars obtained from hydrothermal carbon of biomass. The effect of activation times (1 h, 5 h, and 10 h) at 880 ºC on the physical characteristics of the activated carbons was investigated. A significant increase of surface area (from 616 to 1937 m2/g) with respect to the activation time was observed. AC-AND-5 h showed good microporosity, with the highest adsorption capacity of CO 2 was obtained as 3.2 mmol/g and 6.1 mmol/g at 25 ºC and 0 ºC up to 1 bar, respectively. The sample AND-AC-5 h shows a good CO 2 /N 2 selectivity and fast adsorption kinetics that be easily regenerated with superior cyclic stability after multiple cycles. Moreover, it proved that the photogenerated electrons and holes in wide band gap carbon can be easily transferred into carbon, resulting in a suppressed charge recombination. The best charge transfer processes was received for AC-AND-1 h sample. [Display omitted] • Activated carbons were prepared with HTC method successfully. • The textural properties can be tailored by the time carbonization. • The CO2 uptake reached up to 6.1 mmol/g and 3.2 mmol/g at 0 and 25 ºC, respectively. • AC-AND-5 h sorbent had highly stable after 15 consecutive adsorption-desorption cycles. • AC-AND-1 h had the best steady-state charge transfer process [ABSTRACT FROM AUTHOR]

Abstract: Activated carbons were prepared from raw lignite applying a physical activation method with CO2 in a rotary tube furnace. The effects of process parameters were determined namely; temperature, activation time, preoxidation time, CO2 flow rate, heating rate and rotation rate. In general micropore rich activated carbons were produced and the operating parameters had a significant influence on the product. BET surface areas were found to range from 331.5m2/g to 696.4m2/g, the total pore volume from 0.1768cm3/g to 0.4446cm3/g and yield from 61.06% to 11.06%. Raising CO2 flow rate significantly increased the BET surface area of the product. The operation mode of the reactor was important. The BET surface area of the sample produced with rotation of the reactor is approximately 16% higher than the sample produced without rotation of the reactor, although it appears insensitive to the absolute speed of rotation. It was concluded that rotation of the reactor is an effective way to enhance the production of activated carbon, in terms of increasing surface area without a significant reduction in yield. [Copyright &y& Elsevier]

Abstract: Activated carbons have been prepared by physical activation with H2O–CO2 in two-step pre-treatment including ZnCl2–HCl from acorn shell at 850°C. The active carbons were characterized by N2 adsorption at 77K. Adsorption capacity was demonstrated by the iodine numbers. The surface chemical characteristics of activated carbons were determined by FTIR spectroscopic method. The microstructure of the activated carbons prepared was examined by scanning electron microscopy. The maximum BET surface area of the obtained activated carbon was found to be around 1779m2/g. [Copyright &y& Elsevier]

Abstract: Fibres from oil palm empty fruit bunches, generated in large quantities by palm oil mills, were processed into self-adhesive carbon grains (SACG). Untreated and KOH-treated SACG were converted without binder into green monolith prior to N2-carbonisation and CO2-activation to produce highly porous binderless carbon monolith electrodes for supercapacitor applications. Characterisation of the pore structure of the electrodes revealed a significant advantage from combining the chemical and physical activation processes. The electrochemical measurements of the supercapacitor cells fabricated using these electrodes, using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge techniques consistently found that approximately 3h of activation time, achieved via a multi-step heating profile, produced electrodes with a high surface area of 1704m2 g−1 and a total pore volume of 0.889cm3 g−1, corresponding to high values for the specific capacitance, specific energy and specific power of 150Fg−1, 4.297Whkg−1 and 173Wkg−1, respectively. [Copyright &y& Elsevier]

Abstract: Activated carbons are commonly used in the treatment of waste water, namely as decontaminating agent of phenolic compounds. This work deals with the preparation of an activated carbon from an abundant local variety of date stones know Ghars. This natural product is largely exploited as a principal nutriment for animals alimentation. Two steps of the activation process are involved in this study, first, a physical treatment by carbon dioxide and second, the characterization of the resulting activated carbon followed by modelization procedure using 4-chlorophenol as test substrate. On the basis of the BET results, we have obtained a specific surface of 604m2/g and microspores volumes of 0.29cm3 g−1. In addition, the adsorption capacity was about 28.57mg/g according to Langmuir model. The physical activation method utilized in this task was achieved by using carbon dioxide. Textural characteristics of the resulting activated carbon were carried out by nitrogen adsorption at 77K along with application of BET equation for determination of surface area. Total volume of pores was determined by αs method. External surface area, micropore area and micropore volume were determined by t-plot method. The comparison of raw material, pyrolysât vis-à-vis the activated carbon was based on the elemental analysis of the principal elements. The adsorption capacity of the different prepared activated carbons was tested by using 4-chlorophenol as substrate. [Copyright &y& Elsevier]

Abstract: Polyethyleneterephthalate (PET), has become one of the major post-consumer plastic wastes. In this work, PET wastes were used to produce activated carbon by physical activation method, using carbon dioxide (CO2) for gasification. The effects of the production variables such as temperature, heating rate, flow rate and holding time of carbonization stage and activation stage on the adsorption capacity of activated carbon were investigated. Preparation tests for the effects of these factors were designed with Taguchi method. According to the Taguchi parameter design methodology, L16 orthogonal array was used. Analysis of experimental results showed that, the most effective factors on each experimental design response were activation temperature and holding time in both stage. The optimum conditions for activated carbons production from PET wastes were found to be as follows: carbonization temperature 800°C, carbonization time 60min, activation temperature 975°C, activation time 240min, heating rate of carbonization and activation 10k/min, flow rate N2 200ml/min and CO2 100ml/min. The properties of prepared activated carbon at optimum operating conditions such as surface area 790m2/g and iodine number 630mg I2/g C, were comparable to commercial activated carbons. [Copyright &y& Elsevier]

Abstract: Ordered mesoporous carbon (OMC) with hexagonal arrays of tubes (CMK-3) was synthesized by direct replication, using SBA-15 as template and propylene as carbon source. Microporosity was developed in these OMCs with either carbon dioxide or potassium hydroxide as activating agents; effects of these activation treatments on their pore structure were discussed. Porous texture was characterized by gas adsorption, morphology was examined by SEM and the degree of order of porous structure was evaluated by X-ray diffraction and TEM micrography. The specific surface area, microporous volume and total pore volume were markedly enhanced upon activation of CMK-3, but the long-range ordered structure gradually became more disordered. Potassium hydroxide activation develops the materials microporosity in a greater extent than with CO2, nevertheless moderate temperatures and activating agent proportions must be used in order to preserve the ordered mesoporous structure. [Copyright &y& Elsevier]

Abstract: The possibility of changing waste paper sludge into valuable carbonaceous adsorbent was tested. The performance of three types of samples obtained from this waste was studied: chars (PK), activated chars (PKA) and activated initial material (PA). Pyrolysis of the initial material was carried out at 550, 600 and 700°C, while the activation of the initial material and chars obtained with CO2 at 550, 600 and 700°C. The sorption capacity of carbonaceous adsorbents obtained was evaluated on the basis of NO2 adsorption in dry and wet conditions. The NO2 sorption properties of the activates decrease with increasing temperature of activation and the maximum sorption capacity was noted for the samples activated at 550°C. On the basis of measurements in dry and wet conditions, the presence of water was found to increase the NO2 breakthrough capacity. The NO2 sorption capacity of the adsorbents obtained depended on the type and temperature of modification process and acid–base properties of the materials obtained. [Copyright &y& Elsevier]

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: In this work, platinum (Pt) metal loaded activated multi-walled carbon nanotubes (MWNTs) were prepared with different structural characteristics for hydrogen storage applications. The process was conducted by a gas phase CO2 activation method at 1200°C as a function of the CO2 flow time. Pt-loaded activated MWNTs were also formulated to investigate the hydrogen storage characteristics. The microstructures of the Pt-loaded activated MWNTs were characterized by XRD and TEM measurements. The textural properties of the samples were analyzed using N2 adsorption isotherms at 77K. The BET, D–R, and BJH equations were used to observe the specific surface areas and the micropore and mesopore structures. The hydrogen storage capacity of the Pt-loaded activated MWNTs was measured at 298K at a pressure of 100bar. The hydrogen storage capacity was increased with CO2 flow time. It was found that the micropore volume of the activated MWNTs plays a key role in the hydrogen storage capacity. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to obtain a series of activated carbons from the seeds of Mucuna mutisiana by physical activation with a mixture of steam and nitrogen in the presence of air. The effects of modulating the time and the temperature of activation were studied for samples that presented burn-off values between 33% and 86%. The samples obtained were characterised by physical adsorption of nitrogen at 77K and carbon dioxide at 273K. The apparent superficial areas were calculated by the BET method and the micropore volumes were calculated using the Dubinin–Raduskevich (DR) method and the alpha method. The results showed values of superficial area between 159 and 1106m2 g−1 and micropore volumes between 0.069 and 0.455cm3 g−1. The samples also presented mesoporosity with values between 0.023 and 0.125cm3 g−1. [ABSTRACT FROM AUTHOR]

Abstract: In this work the use of coffee endocarp as precursor for the production of activated carbons by steam and CO2 was studied. Activation by both methods produces activated carbons with small external areas and microporous structures having very similar mean pore widths. The activation produces mainly primary micropores and only a small volume of larger micropores. The CO2 activation leads to samples with higher BET surface areas and pore volumes when compared with samples produced by steam activation and with similar burn-off value. All the activated carbons produced have basic characteristics with point of zero charge between 10 and 12. By FTIR it was possible to identify the formation on the activated carbon''s surface of several functional groups, namely ether, quinones, lactones, ketones, hydroxyls (free and phenol); pyrones and Si–H bonds. [Copyright &y& Elsevier]

• Biochars were sucessfully synthesized from aquatic plant (macrophytes). • CO 2 physical activation improved the surface area of the biochar. • The activated material shows na adsorption capacity of 117.8 mg g−1. This work reports the use of macrophyte (Eichornia crassipes) as raw material for preparation activated biochar (ABC) from the physical activation, using CO 2 as activating agent. The ABC was applied in the removal of caffeine (CAF) from the aqueous solution. The characterization of ABC showed that it has micro and mesoporosity features with BET surface area (S BET) value of 740 m2 g−1 and basic character of surface with value of pH PCZ of 8.44. CAF adsorption study demonstrated that the initial pH is not a factor that directly influences the adsorption capacity, whose q e is 161.1 ± 10.56 mg g−1. The kinetic study showed that pseudo-second-order model is that better describe the adsorption process. Adsorption equilibrium study indicated the Redlich-Peterson as the best isothermal model and that ABC has high monolayer adsorption maximum capacity of CAF (Q max = 117.8 mg L−1). Thermodynamic studies indicated that the processo is spontaneous, endothermic and governed by chemisorption. [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]

Bamboo and its solid residue after hydrothermal treatment were converted successfully into porous carbon by physical activation with the CO 2 agent. The solid residue exhibits a higher potential to form activated carbon thanks to its very low ash content (almost 0%). The porosity and CO 2 uptake of the carbon materials were characterized by the N 2 and CO 2 adsorption/desorption techniques. The results showed a dominant microporous structure in the carbon derived from both bamboo and solid residue. The highest BET surface area that the carbon material from bamboo could achieve was 976 m2 g−1, meanwhile, this value at the carbon prepared from solid residue activated at the same temperature was 1496 m2 g−1. The microporosity structure of activated carbon could be stimulated and enhanced at the optimal condition of CO 2 activation. The CO 2 adsorption capacity of the carbon made from bamboo and the solid residue was also analyzed with good capacity (3.4 mmol g−1) comparing to the 3 reference materials at the same condition of adsorption (293 K, 1 atm). [Display omitted] • The hydrothermal treatment reduces bamboo ash significantly. • Physical activation strongly stimulates the microporous structure in the activated carbon. • The activated carbon prepared from solid residue poses a high adsorption capacity. • Activated carbon derived from bamboo can achieve a good CO 2 uptake. [ABSTRACT FROM AUTHOR]

• CO 2 activation at 1.0 MPa and 700 °C leads to wider pose size distributions. • Chemical activation was effective at 700 °C and only dependent on the K 2 CO 3 loading. • Highly developed textural properties did not ensure high H 2 production. • K 2 CO 3 enhanced H 2 production during steam and dry reforming of pyrolysis oil. • Residual metallic potassium plays a key role in promoting reforming reactions. The main aim of the present study is to provide a comprehensive assessment of the effects of process activation conditions on the textural properties of the resulting activated carbons, which were produced from wheat straw-derived biochar through chemical activation (with K 2 CO 3 at different pressures and mass impregnation ratios) and physical activation (with CO 2 at different temperatures and pressures). For chemically activated biochars, it was found that specific surface area and pore size distribution were both only positively affected by increasing the carbonate loading. However, physically activated biochars produced at the highest pressure and lowest temperature (1.0 MPa and 700 °C) had the highest surface areas and widest pore size distributions. The materials with the most appropriate textural properties were then tested as catalysts for steam and dry reforming of the aqueous phase of pyrolysis oil. The best catalytic performance (a total gas yield of 74% and a selectivity toward H 2 of almost 40%) was observed for a physically activated biochar. This good performance was ascribed to the high availability of K0 on the catalyst surface, which could effectively promote the reactions involved in the upgrading process. [ABSTRACT FROM AUTHOR]

• Mesoporous structure promotes adsorption of CO 2 and NH 3 more significantly. • Effect of functional groups in the micropores is greater than that of pore structures. • NH 3 inhibits the construction of O-containing functional groups by H 2 O. • Combination of simulation and experiment is used for biochar adsorption research. CO 2 emission reduction has become a global consensus, and the most potential carbon emission reduction technology-Carbon Capture and Storage (CCS) is still in the development stage. In order to make up for the shortcomings of CCS technology, the idea of functionalized biochar-ammonia carbon capture system is proposed. Corn straw was used as raw materials, and activated biochar were prepared by one-step/two-step H 2 O/NH 3 ·H 2 O activation, to construct a hierarchical-functionalized structure of biochar, and explore its adsorption characteristics of CO 2 and NH 3. Various methods such as solid characterization, temperature programmed desorption, molecular dynamics and quantum chemical simulation were used to explore the structure-effect relationship between the physicochemical properties of biochar and the adsorption of CO 2 and NH 3. The results show that the pore structure of gas-physical activated biochar is dominated by micropores. The one-step method is beneficial to the construction of functional groups on biochar surface, while the two-step one is conducive to the improvement of pore formation and its aromatization. During NH 3 ·H 2 O activation, NH 3 would inhibit the formation of O-containing functional groups on the surface of biochar by H 2 O. Compared with O-containing groups, the N-containing functional groups on biochar surface have greater adsorption energy for CO 2 and NH 3 adsorption. The adsorption sites of CO 2 and NH 3 are mainly in the micropores (d < 0.7 nm), and the contribution of functional groups in the micropores to the adsorption of CO 2 and NH 3 is greater than the pore structure. This study provided theoretical basis for the development of new biochar-ammonia CO 2 capture system. [ABSTRACT FROM AUTHOR]