Surface modification of coconut shell based activated carbon for the improvement of hydrophobic VOC removal

In this study, coconut shell based carbons were chemically treated by ammonia, sodium hydroxide, nitric acid, sulphuric acid, and phosphoric acid to determine suitable modification for improving adsorption ability of hydrophobic volatile organic compounds (VOCs) on granular activated carbons (GAC). The saturated adsorption capacities of o-xylene, a hydrophobic volatile organic compound, were measured and adsorption effects of the original and modified activated carbons were compared. Results showed that GAC modified by alkalis had better o-xylene adsorption capacity. Uptake amount was enhanced by 26.5% and reduced by 21.6% after modification by NH₃H₂O and H₂SO₄, respectively. Compared with the original, GAC modified by acid had less adsorption capacity. Both SEM/EDAX and BET were used to identify the structural characteristics of the tested GAC, while IR spectroscopy and Boehm's titration were applied to analysis the surface functional groups. Relationships between physicochemical characteristics of GAC and their adsorption performances demonstrated that o-xylene adsorption capacity was related to surface area, pore volume, and functional groups of the GAC surface. Removing surface oxygen groups, which constitute the source of surface acidity, and reducing hydrophilic carbon surface favors adsorption capacity of hydrophobic VOCs on carbons. The performances of modified GACs were also investigated in the purification of gases containing complex components (o-xylene and steam) in the stream.     

Particle size effect of raw material on the pore structure of carbon support and its adsorption capability

In this study, a series of activated carbons were prepared from Tuncbilek lignite with different particle size by chemical activation. The effect of particle size of lignite on the pore structure of activated carbon and the adsorption kinetics of crystal violet (CV) onto these activated carbons was investigated. BET surface area values of activated carbon samples were determined in the range of 940–1054 m² g^?1. Adsorption capacity of CV onto activated carbons was investigated in a batch system by considering the effects of various parameters such as initial dye concentration, agitation time and adsorption temperature. The Langmuir and Freundlich isotherms were used to describe the adsorption equilibrium studies. The adsorption kinetics of CV has been discussed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion models. Results show that the pseudo-second-order kinetic equation could describe the adsorption kinetics for CV onto activated carbons. Using the thermodynamic equilibrium coefficient obtained at different temperatures and for the initial dye, the thermodynamic constants of adsorption (ΔG°, ΔH° and ΔS°) were also evaluated.     

One-pot synthetic method to prepare highly N-doped nanoporous carbons for CO2 adsorption

A one-pot synthetic method was used for the preparation of nanoporous carbon containing nitrogen from polypyrrole (PPY) using NaOH as the activated agent. The activation process was carried out under set conditions (NaOH/PPY = 2 and NaOH/PPY = 4) at different temperatures in 600–900 °C for 2 h. The effect of the activation conditions on the pore structure, surface functional groups and CO₂ adsorption capacities of the prepared N-doped activated carbons was examined. The carbon was analyzed by X-ray photoelectron spectroscopy (XPS), N2/77 K full isotherms, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The CO₂ adsorption capacity of the N-doped activated carbon was measured at 298 K and 1 bar. By dissolving the activation agents, the N-doped activated carbon exhibited high specific surface areas (755–2169 m² g⁻¹) and high pore volumes (0.394–1.591 cm³ g⁻¹). In addition, the N-doped activated carbons contained a high N content at lower activation temperatures (7.05 wt.%). The N-doped activated carbons showed a very high CO₂ adsorption capacity of 177 mg g⁻¹ at 298 K and 1 bar. The CO₂ adsorption capacity was found to be dependent on the microporosity and N contents.     

Removal of lead (II) and nickel (II) ions from aqueous solution using activated carbon prepared from rapeseed oil cake by Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> activation

In this study, rapeseed oil cake as a precursor was used to prepare activated carbons by chemical activation with sodium carbonate (Na₂CO₃) at 600 and 800 °C. The activated carbon with the highest surface area of 850 m² g^?1 was produced at 800 °C. The prepared activated carbons were mainly microporous. The activated carbon having the highest surface area was used as an adsorbent for the removal of lead (II) and nickel (II) ions from aqueous solutions. The effects of pH, contact time, and initial ion concentration on the adsorption capacity of the activated carbon were investigated. The kinetic data of adsorption process were studied using pseudo-first-order, pseudo-second-order kinetic models and intraparticle diffusion model. The experimental data were well adapted to the pseudo-second-order model for both tested ions. The adsorption data for both ions were well correlated with Langmuir isotherm. The maximum monolayer adsorption capacities of the activated carbon for the removal of lead (II) and nickel (II) ions were determined as 129.87 and 133.33 mg g^?1, respectively.     

Adsorption of aqueous metal ions on cattle-manure-compost based activated carbons

The objective of this study is to examine the suitability and performance of cattle-manure-compost (CMC) based activated carbons in removing heavy metal ions from aqueous solution. The influence of ZnCl₂ activation ratios and solution pH on the removal of Cu(II) and Pb(II) were studied. Pore texture, available surface functional groups, pH of point zero charge (pH_PZC), thermogravimetric analysis and elemental compositions were obtained to characterize the activated carbons. Batch adsorption technique was used to determine the metal-binding ability of activated carbons. The equilibrium data were characterized using Langmuir, Freundlich and Redlich–Peterson models. It was found that the uptake of aqueous metal ions by activated carbons could be well described by Langmuir equation. It is suggested that the increase of surface area and mesopore ratio as a result of increasing activation ratios favored the removal of Cu(II), while activated carbon rich in acidic groups showed selective adsorption towards Pb(II). The preferable removal of Cu(II) over Pb(II) could be due to the rich nitrogen content as well as the higher mesoporous surface area in the CMC activated carbons. The impregnated CMC activated carbons also showed a better performance for Cu(II) removal at varying solution pH than Filtrasorb 400 (F400), while a similar performance was observed for Pb(II) removal.     

Effect of the surface chemical groups of activated carbons on their surface adsorptivity to aromatic adsorbates based on π-π interactions

Three activated carbons with different surface chemical groups were used to analyse the influence of these groups on their adsorption capacities towards aromatic-type molecules whose adsorption is based on π-π interactions with surface arene centres. The three activated carbons studied were a low-functionalized carbon (Merck), an oxygen-rich carbon obtained by HNO₃ oxidation of Merck, and a nitrogen-rich carbon also prepared from Merck by mild HNO₃ oxidation followed by treatment with a dicyanodiamide/dimethyl formamide mixture at 300 °C. The nature of the surface chemical groups of the three activated carbons was investigated by both physical and chemical techniques (TPD, XPS, Boehm analysis and pH potentiometric titration). A systematic study of the adsorptions of a series of analogous aromatic adsorbates on the three activated carbons was carried out to study the adsorption mechanisms. In all cases the adsorption mechanism is based on π-π interactions between the aromatic moiety of the adsorbates and the arene centres of the graphite sheets. The differences in the normalized adsorption capacities of the adsorbents for a set of adsorbates indicate that the π-donor or π-withdrawing character of the functional groups have a clear influence on the basicity of the arene centres.     

Effect of activated carbons modification on porosity, surface structure and phenol adsorption

The primary objective of this work was the examination of modified activated carbons with tailored adsorption capacity properties. Production of activated carbons with desired properties was accomplished by modification of surface functional groups and introduction of acidic/basic properties. Modification of an activated carbon was performed using partial oxygen gasification, nitric acid treatment, urea impregnation followed by pyrolysis and pyrolysis in a urea saturated stream. The surface properties of the produced samples were estimated by the multibasic titration method of Boehm and by the CO/CO2 gas evolution profiles, while pore structure development was measured by the N2 and CO2 gas adsorption isotherms. Oxygen gasification resulted in samples with surface area slightly lower that the raw activated carbon; the introduction of surface functional groups depended upon the severity of the treatment: carbonylic and phenolic type groups were introduced in all partially gasified samples, while low temperatures and short reaction times enhanced the basic character of the carbon. However, nitric acid treatment resulted in the introduction of high nitrogen amounts in the samples, the reduction of surface area and the development of a surface containing carboxylic, lactonic, phenolic and carbonylic groups with negligible HCl neutralization capacity. Treatment of activated carbon by urea supported the formation of basic groups and carbonyls. The presence of surface functional groups affected the adsorption capacity of the produced samples for the removal of specific pollutants such as phenols. Urea treated samples with a basic character and high nitrogen content presented the highest phenol uptake capacity; nitric acid treated carbons and oxygen gasified samples presented an acidic surface functionality and a low phenol adsorption capacity. The beneficial role of nitrogen on phenol adsorption was attributed to adsorbate-adsorbent interactions.     

Synthesis of new activated carbons produced from polymer waste

In this study activated carbons were prepared from polymer waste, which is side product and waste in textile industry; by chemical activation with KOH. The influence of chemical ratio onto pore structure was investigated. Activation temperature was selected as 800°C. The impregnated sample was raised to the activation temperature under N₂ (100 mL. min^?1) atmosphere with 10°C. min^–1 heating rate and hold at this temperature for 1 h. Determined BET surface area were in the range of 817–1889 m²·g^–1. Impregnation ratio; 5:1 was found to be the optimal condition for producing high surface area carbons with KOH activation. Activated carbon samples and raw material were characterized by Boehm titration, XRD, FT-IR, DTA and TGA. Adsorption capacity for selected model compound, such as naproxen sodium, caffeine and tannic acid, has been investigated.     

Kinetic,thermodynamic, and isosteric heat of dibutyl and diethyl phthalate removal onto activated carbon from Albizzia julibrissin pods

The adsorption performance of diethyl and dibutyl phthalates on a new activated carbon prepared from an abundant biomass “Albizzia julibrissin Pods,” treated chemically by H₃PO₄ is investigated through the equilibrium and kinetic study. The effect of different parameters like contact time, initial phthalate concentrations, and temperature on the adsorption capacities was studied in batch mode to evaluate the optimal conditions. Adsorption isotherms for both phthalates were fit at different temperatures using the Langmuir and Freundlich nonlinear regression. Adsorption kinetics were adjusted to various linear models, such as pseudo-first-order, pseudo-second-order, liquid film diffusion, intraparticle diffusion, and Boyd. The thermodynamic analysis indicated that the adsorption was spontaneous and exothermic in nature. The adsorption isosteric heat revealed a heterogeneous surface with different adsorption sites activities.     

不同结构活性炭对甲苯的吸附性能

考察了不同结构的活性炭样品对高浓度和低浓度甲苯蒸汽的吸附行为,采用低温(77 K)氮气吸附和129Xe-核磁共振方法对所用活性炭的结构进行了表征.并将活性炭对甲苯的吸附性能与其结构进行了关联.结果表明孔容积大的活性炭对高浓度甲苯蒸汽吸附容量大,而具有丰富微孔和较小平均孔径的活性炭对低浓度(2×10-5)甲苯蒸汽具有高的吸附容量.沥青基活性炭纤维对低浓度(2×10-5)甲苯蒸汽表现出较好的吸附能力.随着比表面积的增大,活性炭纤维对低浓度(2×10-5)甲苯蒸汽的吸附容量略有增加.OG5A,OG10A,OG15A和OG20A在30 ℃下对2×10-5甲苯蒸汽的饱和吸附容量分别为202 mg/g,219 mg/g,221 mg/g和235 mg/g.     

活性炭物理结构与其变压吸附分离瓦斯性能

活性炭(AC)在煤层瓦斯气体吸附分离上具有良好的应用前景。选用4种活性炭,利用77K氮气吸附表征了活性炭的物理性质。在自制的静态吸附装置上,测量了4种活性炭样品对瓦斯气(CH4/N2混合气体)在298K和318K时的平衡吸附量,结果发现4种活性炭对CH4/N2吸附能力有较大的差异。用Langmuir吸附方程关联实验数据,计算出4种活性炭在不同温度下对CH4/N2的分离因子。结合4种活性炭的物理性质以及其对CH4/N2的吸附量,分析了影响活性炭对CH4/N2的吸附量的因素。活性炭在变压吸附分离浓缩瓦斯时,应具备合适的孔径,比表面积和孔容越大越好。     

微孔结构与表面改性对活性炭吸附储氢能力的影响

研究了椰壳基活性炭微孔结构和化学改性对其储氢能力的影响。结果表明,物理活化的椰壳基活性炭用HF或NH3.H2O处理后可提高活性炭的吸氢能力,用HNO3处理后吸氢能力几乎没有什么变化,而用H3PO4处理后吸氢能力却有明显的下降。活性炭的比表面积、孔径分布和表面性质都会影响其吸附氢气的能力,其中,比表面积是最主要的影响因素。     

Utilization potential lignocellulosic waste biomass to produce carbon support by using new activation reagent (H3BO3 and SrCl2): structural and adsorptive properties

ABSTRACT

Activated carbons series were produced from the orange peel by chemical activation using strontium chloride (SrCl₂) and boric acid (H₃BO₃). The activation temperature effects and type of activation reagents on the surface and chemical properties of activated carbon have been investigated. The surface area of the activated carbons is 577 and 290 m² g^?1 for H₃BO₃ and SrCl₂ activation_, respectively. An increase in the temperature for both H₃BO₃ and SrCl₂ led to a decrease in the yields of the activated carbons. The yield of H₃BO₃ series is higher than the yield of SrCl₂. The obtained activated carbons were heteroporous with the mesopore. Orange peel can be used alternative waste biomass for the mesoporous activated carbon productions. Samples were characterized by XRD, SEM, FTIR, and TGA analysis.     

High-Voltage Supercapacitive Swing Adsorption of Carbon Dioxide

Supercapacitive swing adsorption (SSA) with garlic roots-derived activated carbon achieves a record adsorption capacity of 312 mmol kg⁻¹ at a low energy consumption of 72 kJ mol⁻¹ and high mass loadings (>30 mg cm⁻²) at 1.0 V for 85%N₂/15%CO₂ mixtures. The activated carbons are inexpensively prepared in a one-step process using potassium carbonate, and air as activators. The adsorption capacity further increases with increasing voltage. At a voltage of 1.4 V, a sorption capacity of 524 mmol kg⁻¹ at an energy consumption of 130 kJ mol⁻¹ can be achieved. The volumetric sorption capacity is also enhanced and reaches values of 85.7 mol m⁻³ at 1.0 V, and 126 mol m⁻³ at 1.4 V. Cycle stability for at least 130 h is demonstrated.     

A simple and highly effective process for the preparation of activated carbons with high surface area

Activated carbons with high surface area were prepared by phosphoric acid as activation agent and rice husks as precursors. It was found that the characteristics of the activated carbons were influenced not only by the preparation but also by the post-processing method. The high surface area of the activated carbons was prepared under the optimum condition (50% H₃PO₄ with impregnation ratio of 5:1, activation temperature of 500 °C, activation time of 0.5 h, wash water temperature of 100 °C). SiO₂ content could affect the surface area of activated carbons, either. The lower SiO₂ content of the activated carbons, the higher pore volume the carbons had. The SiO₂ content was 11.2% when used the optimum condition. The explanation was that silicon element in rice husks reacted with H₃PO₄ to form silicon phosphate (SiP₂O₇), and it could be proved further by X-ray diffraction analysis, SiP₂O₇ could be removed by post-process.     

Liquid phase adsorption of selected chloroaromatic compounds over metal organic frameworks

The adsorption behavior of selected chloroaromatic compounds (chlorobenzene, 2-chlorotoluene, 1,3-dichlorobenzene, and 2-chloroanisole) over metal organic frameworks (MOFs) of MIL-125, NH₂-MIL-125, UiO-66, MIL-101, and Cu₃(BTC)₂ were investigated. NH₂-MIL-125 showed the highest adsorption capacity at 0.1 M, whereas MIL-101 showed the highest adsorption at 1.0 M, which was significantly higher than that of activated carbon under the given conditions. The equilibrium adsorption and kinetics data could be fitted well by the Langmuir model and pseudo-second-order kinetic model, respectively. The adsorption of 2-chloroanisole over NH₂-MIL-125, MIL-101, and activated carbon was spontaneous and exothermic, and the randomness increased after adsorption. The adsorption rate constants increased with temperature and showed a dependence on the pore window size and surface functionality of the MOFs. NH₂-MIL-125 and MIL-101 showed a preference for 2-chloroanisole in a mixture with other chloroaromatic compounds. The surface area and microporosity of the MOFs appear to be major factors governing the adsorption capacity of 2-chloroanisole.     

Uniformly dispersed platinum nanoparticles loading on porous carbons without using reduction agents

Platinum nanoparticles loading on carbon nanotube, activated carbon, and activated carbon fiber was carried out by impregnation of hexachloro palatinate ion(IV) from hydrogen hexachloro platinate hydrate [H₂PtCl₆·5.7H₂O] dissolved solution without using reduction agents, and heating the hexachloro platinate(IV) impregnated carbons up to 800 °C. When the initial platinum content was controlled to 1000 ppm in the solution, the adsorption capacities of hexachloro platinate(IV) on carbon nanotube, activated carbon and activated carbon fiber were 24%, 47%, and 76%, respectively at the equilibrium state. The adsorption isotherm type of hexachloro platinate(IV) on carbon nanotube was two-step linear and quite different from Langmuir model of activated carbon fiber due to the uniformly developed cylindrical pore structure and size distribution. The average platinum particle size on porous carbons was under 2 nm by heating the hexachloro platinate(IV) up to 400 °C in spite of non-using reduction agents, while the average size increased due to the agglomeration of some particles by heating them up to 800 °C. Therefore, uniformly distributed platinum nanoparticles loading on porous carbons can be obtained from simple impregnation of hexachloro palatinate ion(IV) from solution and heating it up to 400 °C.     

A Simple Aqueous Solution Based Chemical Methodology for Preparation of Mesoporous Alumina: Efficient Adsorbent for Defluoridation of Water

In this paper, we report a simple aqueous solution based chemical method for preparation of mesoporous γ-Al₂O₃ which can be used for removal of fluoride ions from water. The synthesized Al₂O₃ and commercial Al₂O₃(Grade AD101-F, ACE Manufacturing and Marketing, Baroda, India) were characterized by using powder x-ray diffractometer, N₂ adsorption–desorption surface area and pore size analyzer, and high resolution transmission electron microscope. Synthesized Al₂O₃ contains a wormhole-like mesoporous structure with 358.7 m² g^?1 Brunauer–Emmett–Teller (BET) surface area and 0.8 cm³ g^?1 pore volume. Batch adsorption studies were performed to determine the fluoride adsorption capacity of Al₂O₃. The effect of different parameters such as contact time, initial fluoride concentration, pH, and adsorbent dose was studied to understand the fluoride adsorption behavior of the synthesized Al₂O₃ under various conditions. The kinetics results showed that the fluoride adsorption on synthesized Al₂O₃ followed pseudo-second-order kinetics. Adsorption equilibrium data fitted well to the Freundlich equation and indicated multilayer adsorption of fluoride on the surface of Al₂O₃. Synthesized Al₂O₃ demonstrated significantly improved fluoride adsorption capacity and faster kinetics than commercial Al₂O_3.     

Effect of thermal pretreatment on porous structure of asphalt-based carbon

The effect of thermal pretreatment on the porous structure and adsorption properties of asphalt-based carbons activated with potassium hydroxide was investigated by FTIR, Raman spectroscopy, TEM, N₂ and CO₂ adsorption. Two series of the activated carbons were prepared by a one-stage method using KOH as the activating agent and a two-stage method including pretreatment of asphalt at 450 °C. A cross-effect of the KOH/asphalt ratio and pretreatment conditions on the characteristics of the porous structure of the activated carbons was revealed. The pretreatment of asphalt before activation is demonstrated to be a necessary stage for the effective control of the carbon porous structure by variation the KOH/asphalt ratio from 2 to 4. The porous carbon derived from petroleum asphalt exhibited the high CO₂ adsorption capacity of 3.8 mmol/g at 25 °C and 1 atm and good selectivity for CO₂ over N₂, indicating possible applications in CO₂ capture technology.

Graphical abstract

     

Study on adsorption refrigeration cycle utilizing activated carbon fibers. Part 1. Adsorption characteristics

Thermal heat driven adsorption systems using natural refrigerants have been focused on the recent energy utilization trend. However, the drawbacks of these adsorption systems are their poor performance in terms of system cooling capacity and coefficient of performance (COP). The objective of this paper is to improve the performance of thermally powered adsorption cooling system by selecting new adsorbent–refrigerant pair. Adsorption capacity of adsorbent–refrigerant pair depends on the thermophysical properties (pore size, pore volume and pore diameter) of adsorbent and isothermal characteristics of the pair. In this paper, the thermophysical properties of two PAN types of activated carbon fibers (FX-400 and KF-1000) are determined from the nitrogen adsorption isotherms. The standard nitrogen gas adsorption/desorption measurements on various adsorbents at liquid nitrogen of temperature 77.3 K were performed. Surface area of each adsorbent was determined by the Brunauer, Emmett and Teller (BET) plot of nitrogen adsorption data. Pore size distribution was measured by the Horvath and Kawazoe (HK) method. As of the adsorption/desorption isotherms, FX-400 shows very small hysteresis when the value of P/P_o exceeds 0.4, while KF-1000 has no hysteresis in the whole range of P/P_o. The adsorption capacity of FX-400 is about 30% higher than that of KF-1000. The adsorption equilibrium data of activated carbon fiber (ACF)-methanol are presented and correlated with simple equations. The adsorption equilibrium data of ACF (KF-1000)-water also presented in order to facilitate comparison with those of ACFs-methanol pair. The results will contribute significantly in designing the adsorber/desorber heat exchanger for thermally driven adsorption cooling system.