Preparation and characteristics of rice-straw-based porous carbons with high adsorption capacity

To prepare porous carbons with high adsorption capacity from rice straws, two different kinds of precursors, i.e. one as the raw rice straws (one-stage process) and the other as pre-carbonized rice straws (two-stage process), were activated with KOH of various impregnation ratios. The two-stage process was found very effective for manufacturing porous carbons with high surface area and adsorption capacities for MB and I₂. For example, the porous carbon that was carbonized at 700°C and subsequently activated at 900°C exhibited the surface area of 2410 m²/g, the adsorption capacities of 800 and 1720 mg/g for MB and I₂, respectively, and the total pore volume of 1.4 ml/g. In the two-stage method, there was a preferential optimum impregnation ratio of KOH to a precursor carbon, i.e. 4:1, with which high surface area of porous carbons could be achieved. The formation of uni- and bidentate carboxylic salt structure, induced by reaction between KOH and oxygen containing carbon, that facilitates the formation of azo group (-NN-) on a subsequent heat treatment was considered as one of the key factors for the presence of optimum impregnation ratio of KOH. In contrast, the porous carbons of only moderate adsorption capacity could be obtained from the one-stage method. The original morphology of rice straw was sustained during the two-stage process, yet not during the one-stage process.     

Activated carbon from bacterial cellulose as an effective adsorbent for removing dye from aqueous solution

ABSTRACT

Novel activated carbon (AC) derived from bacterial cellulose (BC-AC) was produced by phosphoric acid activation at a carbonization temperature of 500 °C. BC-AC possesses mesoporous structures of 2.3 nm in diameter, porosity of 1.0 cm³/g and surface area of 1734 m²/g with high thermal stability between 100 and 500 °C. BC-AC could be used as an effective adsorbent for removing methylene blue (MB) from aqueous solutions with the maximum adsorption capacity of 505.8 mg/g. BC-AC presented physisorption and the adsorption of MB was most likely to be a monolayer adsorption. The Redlich–Peterson model displayed the best fit with the experimental data.     

Process optimization of K2C2O4-activated carbon from kenaf core using Box–Behnken design

Potassium oxalate was evaluated as a new activating agent for preparation of kenaf core-based activated carbons. The preparation conditions were optimized through Box–Behnken design (BBD) to maximize I₂ and methylene blue (MB) adsorption values. Two quadratic models were developed to correlate the preparation variables namely activation temperature, impregnation ratio and activation time for both responses. The activated carbon produced at the optimum combination of process parameters showed 1161 mg/g and 330 mg/g of I₂ and MB uptakes, which were in excellent agreement with the predicted values from the models. Porosity parameters and scanning electron microscopy were used to investigate the obtained optimal sample. The results reveal that K₂C₂O₄ could be recommended as a promising effective activating agent for producing activated carbons from kenaf core with high surface area and potentially desirable dye removal capacity.     

Activated Carbons from Lignin: Their Application in Liquid Phase Adsorption

Abstract

The extent of the methylene blue (MB) adsorption from an aqueous solution is a convenient indicator in the evaluation of activated carbons. The adsorption of MB (cationic dye) from aqueous solution has been studied using twenty activated carbons. The activated carbons were prepared from acid‐precipitated eucalyptus kraft lignin following a two‐step process consisting of CO₂ partial gasification after carbonization in N₂ atmosphere. The adsorbed amount was studied as a function of the contact time, temperature, pH, concentration of adsorbate, and burn‐off of the activated carbons. The equilibria results obtained in a batch contactor were fitted by the Langmuir equation. The calculated values of ΔG demonstrate that the adsorption of the dye onto these activated carbons occurs by physical adsorption. Both the apparent values of ΔH and ΔS are positive, indicating that the adsorption process is endothermic and can produce spontaneously in our experimental conditions. The kinetic study was developed using a second‐order exponential decay equation and the results were correlated using the Lagergren first‐order equation relative to the concentration on the solid phase. The intraparticle diffusion coefficients have been estimated on the basis of an internal diffusion controlling mechanism for the net adsorption rate.     

Preparation and Phosphine Adsorption of Activated Carbon Prepared from Walnut Shells by KOH Chemical Activation

Walnut-shell activated carbons (WSACs) with high surface area and predominant micropore development were prepared by KOH chemical activation. The effects of carbonization temperature, activation temperature, and ratio of KOH to chars on the pore development of WSACs and PH₃ adsorption performance of the modified walnut-shell activated carbons (MWSACs) were studied. Criteria for determining the optimum preparation conditions were pore development of WSACs and PH₃ breakthrough adsorption capacity of MWSAC adsorbents. The result shows that the optimum preparation conditions are a carbonization temperature of 700°C, an activation temperature of 700°C, and a mass ratio of 3. The BET surface area and the micropore volume of the optimal WASC are 1636m²/g and 0.641cm³/g, respectively. The micropore volume percentage of WSAC plays an important role in PH₃ adsorption when there is a slight difference in BET surface areas. High-surface-area WSACs with predominant micropores are suitable for PH₃ adsorption removal. The MWSAC adsorbent owns the biggest PH₃ breakthrough adsorption capacity (284.12mg/g) due to the biggest specific surface area, total pore volume, and micropore volume percentage. The MWSAC adsorbent will be a potential adsorbent for PH₃ adsorption removal from yellow phosphorus tail gas.     

Wastewater Treatment by Chemically Activated Carbons from Giant Reed: Effect of the Activation Atmosphere on Properties and Adsorptive Behavior

Abstract

Uptake of nickel and benzene from dilute single‐solute solutions, mimicking wastewater with low concentrations of heavy metals or volatile organic compounds, was examined using activated carbons with similar good surface properties (BET surface area of ≈1100 m²/g). They were developed through H₃PO₄ acid activation of giant reed (Arundo donax L.) under flowing air or N₂. The carbons obtained in air proved more effective to capture Ni(II) ions under pre‐established equilibrium conditions. Inversely, the N₂‐derived carbons exhibited a better ability for benzene adsorption. The behavior was related to the smaller total content of acidic/polar surface oxygen functionalities of the carbons developed under N₂ (1.9 meq/g), compared to that of the air‐derived ones (3.3 meq/g). Two‐, three‐parameter models described properly the isotherms, predicting similar maximum adsorption capacities (X_m ) for the investigated systems. The X_m parameter in the Langmuir's model was 0.44 mmol/g for the adsorption of Ni(II) ions on the air‐derived carbons, and 0.45 mmol/g for benzene adsorption on those obtained in N₂. Present results highlight the relevance of the surface chemistry developed upon activation to optimize the performance of activated carbons for wastewater treatment according to the pollutants' nature.     

Magnetically-separable hierarchically porous carbon monoliths with partially graphitized structures as excellent adsorbents for dyes

Magnetically-separable hierarchically porous carbon monoliths with partially graphitized structures were synthesized through confinement self-assembly in polyurethane (PU) foam associated with a direct carbonization process from triblock copolymer F127, phenolic resol and ferric nitrate. It was observed that the magnetic Fe nanoparticles were embedded in the walls of graphitic porous carbon matrix, and the resulting materials exhibited hierarchically porous structure with macropores of 100–450 μm, mesopore size of 4.8 nm, BET surface area of 723 m²/g, pore volume of 0.46 cm³/g, and saturation magnetization of 3.1 emu/g. Using methylene blue as model dye pollutant in water, the carbon monolith materials showed high adsorption capacity of 190 mg/g, exhibiting excellent adsorption characteristics desirable for the application in adsorption of dyes and easy separation under an external magnetic field.     

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

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

Solvothermal polycondensation of novolacs phenolic-resin to nanopowders and their derived activated nanocarbons as efficient adsorbents for water cleaning

Novolacs phenolic-resin (PF) was easily polycondensed into polymeric powders with sizes and morphologies ranging from microspheres to nanoparticles by a simple solvothermal process without adding any crosslinking agent. Activating the highly divided PF powders by CO₂ resulted in nanosize activated carbons with high specific surface area (2092 m² g^?1) and large pore volume (1.33 cm³ g^?1) while preserving a high carbon yield of about 38 wt%. As for adsorption tests, the micropore-dominated activated nanocarbons exhibited fast and high adsorption capabilities towards both Cr(VI) ions and bulky rhodamine B molecules due to their much improved external surface area and the greatly shortened intra-particle diffusion distance. The equilibrium adsorption amounts of Cr(VI) and RB on the activated nanocarbons as estimated by the Langmuir model were 200 and 990 mg g^?1, achieved within an adsorption time of 30 and 360 min, respectively.     

Preparation and Characterization of Activated Carbon from Chestnut Shell and its Adsorption Characteristics for Lead

Activated carbons were prepared from chestnut shell by phosphoric acid activation and the prepared activated carbons were used to remove lead(II) from aqueous solutions. The effects of impregnation ratio (IR) and activation temperature on activated carbon production were investigated. The produced activated carbons were characterized by N₂ adsorption, scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques. The highest surface area (1611 m²/g) and total pore volume (0.7819 cm³/g) were obtained at a carbonization temperature of 500°C with an impregnation ratio of 3/1. The resulting activated carbon was used for removal of lead(II) from aqueous solution. The effects of temperature, contact time, and adsorbent dosage were investigated. The adsorption isotherm studies were carried out and the obtained data were analyzed by the Langmuir, Freundlich, and Temkin equations. The rate of adsorption was found to conform to the pseudo-second-order kinetic model. The Langmuir isotherm equation showed better fit for all temperatures and the maximum adsorption capacities of lead(II) was obtained as 138.88 mg/g at 45°C.     

Carbonization and CO<Subscript>2</Subscript> activation of scrap tires: Optimization of specific surface area by the Taguchi method

This research demonstrates the production of activated carbon from scrap tires via physical activation with carbon dioxide. A newly constructed apparatus was utilized for uninterrupted carbonization and activation processes. Taguchi experimental design (L16) was applied to conduct the experiments at different levels by altering six operating parameters. Carbonization temperature (550–700 °C), activation temperature (800–950 °C), process duration (30–120 min), CO₂ flow rate (400 and 600 cc/min) and heating rate (5 and 10 °C/min) were the variables examined in this study. The effect of parameters on the specific surface area (SSA) of activated carbon was studied, and the influential parameters were identified employing analysis of variance (ANOVA). The optimum conditions for maximum SSA were: carbonization temperature=650 °C, carbonization time=60 min, heating rate=5 °C/min, activation temperature= 900 °C, activation time=60 min and CO₂ flow rate=400 cc/min. The most effective parameter was activation temperature with an estimated impact of 49%. The activated carbon produced under optimum conditions was characterized by pore and surface structure analysis, iodine adsorption test, ash content, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The process yield for optimized activated carbon was 13.2% with the following properties: specific surface area=437 m²/g, total pore volume=0.353 cc/g, iodine number=404.7 mg/g and ash content=13.9% along with an amorphous structure and a lot of oxygen functional groups. These properties are comparable to those of commercial activated carbons.     

Porous properties of activated carbon produced from Eucalyptus and Wattle wood by carbon dioxide activation

This work focused on the preparation of activated carbon from eucalyptus and wattle wood by physical activation with CO₂. The preparation process consisted of carbonization of the wood samples under the flow of N₂ at 400°C and 60 min followed by activating the derived chars with CO₂. The activation temperature was varied from 600 to 900°C and activation time from 60 to 300 min, giving char burn-off in the range of 20/2-83%. The effect of CO₂ concentration during activation was also studied. The porous properties of the resultant activated carbons were characterized based on the analysis of N2 adsorption isotherms at −196°C. Experimental results showed that surface area, micropore volume and total pore volume of the activated carbon increased with the increase in activation time and temperature with temperature exerting the larger effect. The activated carbons produced from eucalyptus and wattle wood had the BET surface area ranging from 460 to 1,490 m²/g and 430 to 1,030 m²/g, respectively. The optimum activation conditions that gave the maximum in surface area and total pore volume occurred at 900°C and 60 min for eucalyptus and 800°C and 300 min for wattle wood. Under the conditions tested, the obtained activated carbons were dominated with micropore structure (∼80% of total pore volume).     

Applicability of Activated Carbon to Treatment of Waste Containing Iodine-Labeled Compounds

Abstract

A timber industry waste was transformed to activated carbon by a one-step chemical activation process using H₃PO₄ (H). The used activated carbon (SDH) was characterized by N₂ adsorption, FTIR, density, pH, point of zero charge pH_pzc, moisture and ash content. Methylene blue (MB) and the iodine number were calculated by adsorption from the solution. The applicability of the different activated carbon produced was carried out to treatment of aqueous waste contaminated with iodine-labeled prolactin (I-PRL) Treatment processes were performed under the varying conditions; contact time, temperature, carbon type, carbon dosage, and different particle size of the activated carbon (SDH). The results indicated that 5 hours are sufficient to reach a plateau, and the amount of I-PRL adsorbed on SDH activated carbons increase with the solution temperature with thermodynamic parameter of ΔG° = ?7.962 (kJ/mol), ΔH° = 28.869 (kJ/mol) and ΔS° = 109.94 (J/mol K). The optimum adsorption results were reached using carbon dose of 0.1 gm with particle size of <0.25 mm, and a batch factor (V/M) of 7.14 mlg^?1. First- and second-order equations, intraparticle diffusion equation, and the Elovich equation have been used to test experimental data. The experimental data was found to fit the second-order model and a chemisorptions mechanism. 0.7 M NaOH can be used for regeneration of spent SDH activated carbon with the efficiency of 99.6% and the regenerated carbon can be reused for five cycles effectively.     

Capacity of activated carbon derived from pistachio shells by H3PO4 in the removal of dyes and phenolics

Two activated carbons were obtained from pistachio shells by impregnation with H₃PO₄ under standard conditions of acid concentration (50 wt%) and heat treatment at 773 K for 2 h. The soaking time was 24 and 72 h for the two samples before thermal pyrolysis. Analysis of the N₂/77 K adsorption isotherms proved that both were highly adsorbing carbons with considerable microporosity, and that the prolonged contact with activant enhanced total porosity (surface area and pore volume) and increased the amount of mesoporosity. Adsorption isotherms of probe molecules, viz methylene blue (MB), rhodamine B (RB), phenol (P) and p‐nitrophenol (PNP), were determined at room temperature, from aqueous solutions. Both the Langmuir and Freundlich model adsorption equations show satisfactory fit to experimental data. Both carbons exhibit similar adsorption parameters irrespective of their porosity characteristics. The sequence of uptake per unit weight was: PNP > MB > RB > P. Low affinity towards phenol may be associated with its competition with water molecules which are more favourably attracted to the acid surface which has a high oxygen functionality. Preferred adsorption in the order PNP > MB > RB is proposed to be a function of carbon porosity, related to the increased molecular dimensions of the solutes. Adsorption from a binary mixture of equal concentrations of MB and RB showed reduced uptake for both sorbates in comparison to the single component experiments. RB removal surpasses that of MB in the binary test and may be attributed to lower water solubility and higher molecular dimensions. Copyright © 2003 Society of Chemical Industry     

N‐doped porous carbons for CO2 capture: Rational choice of N‐containing polymer with high phenyl density as precursor

N‐doped porous carbons (NPCs) are highly promising for CO₂ capture, but their preparation is severely hindered by two factors, namely, the high cost of N‐containing polymer precursors and the low yield of carbon products. Here we report for the first time the fabrication of NPCs through the rational choice of the polymer NUT‐4, with low cost and high phenyl density, as precursor. For the material NPC‐600 obtained from carbonization at 600°C, the yield is as high as 52.1%. The adsorption capacity of CO₂ on NPC‐600 reaches 6.9 mmol/g at 273 K and 1 bar, which is obviously higher than that on the benchmarks, including 13X zeolite (4.1 mmol/g) and activated carbon (2.8 mmol/g), as well as most reported carbon materials. Our results also demonstrate that the present NPCs can be completely regenerated under mild conditions. The abundant microporosity and “CO₂‐philic” (N‐doped) sites are responsible for the adsorption performance. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1648–1658, 2017     

Study of the carbonization temperature for a chemically activated carbon: influence on the textural and structural characteristics and surface functionalities

This study aims at investigating the relationship between the porosity and the surface functional groups of an activated carbon during the pyrolysis process. Several activated carbons are prepared by the carbonization of a mixture of olive waste and ZnCl₂ at different temperatures, which are chosen by taking into account the different phenomena occurring during this treatment. The porosity of the prepared carbons is investigated using both N₂ and CO₂ isotherms at 77 and 273 K, respectively. Long-range and short-range orders are studied respectively by X-ray diffraction (XRD) and Raman spectroscopy. The investigation of the carbon functionalities is carried out by Boehm titration, Fourier transformed infrared spectroscopy (FTIR) and water adsorption measurements. The effect of carbonisation temperature on the adsorption of cyclohexane provides additional information on the oxygen functional groups and especially the carboxylic proups. To summarize, the results show that a carbonisation at 573 K is sufficient to obtain a well-developed porosity and to ensure already the formation of acidic surface groups and especially the carboxylic groups.     

Activated carbon from cherry stones

Fruit stones constitute a significant waste disposal problem for the fruit-processing industry. High-quality activated carbon can be produced from waste cherry stones: the activated carbon is low in impurities and has an adsorption capacity that compares favorably with commercial activated carbons. Activation at 800°C in steam for 2–3 hours, following initial carbonization, produces an activated carbon in about 10% yield (by weight) of the initial cherry stone. The activated carbons produced have surface areas (CO₂ adsorption) as high as 1200 m²/g and CCl₄ numbers of 70–80. Activation in carbon dioxide requires higher temperatures (900°C) and gives a carbon of slightly lower activity. Carbon from the hull, or hard outer portion of the fruit stone, provides essentially all of the adsorption capacity; the inner kernel does not form a microporous material. The hull structure is dominated by 0.4-micron pores which facilitate access to internal microporosity. This structure requires that the carbon be ground to less than 75 micron particles to achieve reasonable adsorption rates.     

PRODUCTION AND CHARACTERIZATION OF POROUS CARBON FROM DATE PALM SEEDS BY CHEMICAL ACTIVATION WITH H3PO4: PROCESS OPTIMIZATION FOR MAXIMIZING ADSORPTION OF METHYLENE BLUE

The potential of date palm pits to be a suitable precursor for preparation of porous carbon was explored in the present work, utilizing phosphoric acid as the activating agent. Experimental methods reported in the literature were chosen with certain modifications in order to simplify the process. Process optimization was performed using the popular response surface methodology (RSM) adopting a Box-Behnken design. Process optimization was intended to maximize the porous carbon yield and the methylene blue (MB) adsorption capacity, with the process variables being the activation temperature, impregnation ratio (IR), and activation time. The structural characteristics were assessed based on nitrogen adsorption isotherms, SEM, and FT-IR, while the adsorption capacity was estimated using MB adsorption. The optimized experimental conditions were identified to be an activation temperature of 400°C, IR of 3, and activation time of 58 min, with the resultant porous carbon having a yield of 44% and MB adsorption capacity of 345 mg/g. The structural characteristics of the porous carbon reveal the BET surface area to be 725 m²/g, with pore volume of 1.26 cc/g, an average pore diameter of 2.91 nm, and total micropore volume of 0.391 cc/g. The popular Langmuir and Freundlich adsorption isotherm models were tested, and a maximum monolayer adsorption capacity of MB was estimated to be 455 mg/g, which compares with the highest for MB reported in literature, evidencing the suitability of porous carbon for adsorption of macromolecular compounds. The low activation temperature and activation time with highest yield render the process technically and economically attractive for commercial use.     

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

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

Novel high performance magnetic activated carbon for phenol removal: equilibrium,kinetics and thermodynamics

A series of novel iron oxide based magnetic activated carbons (MAC) were fabricated through simple one-step method from Pomelo Peel using hydrochloric acid pickling water as chemical activation agent and iron oxide precursor. The characterizing results show that the MAC prepared through physiochemical activation at 973 K has a relative high surface area of 760 m²/g and can be fast separated from water under a moderate magnetic field. Batch adsorptions of phenol onto the MAC were investigated for its equilibrium, the kinetic modeling and thermodynamics. Equilibrium data were best described by Langmuir model, and the estimated maximum adsorption capacity of the MAC-973 was up to 1.1?×?10² mg/g at 298 K. Chemical reaction was found to be a rate-controlling parameter to this phenol-MAC batch adsorption system due to strong agreement with the pseudo-second-order kinetic model.