Effects of Cetylpyridinium Chloride on Phase and Rheological Behavior of the Diluted C(12)E(4)/Benzyl Alcohol/Water System

The influence of the pore size distribution of activated carbon on the adsorption of phenol from aqueous solutions was explored. Activated carbons with different porous structures were prepared by gasifying a bituminous coal char to different extents of burn-off. The results of adsorption experiments show that the phenol capacity of these carbons does not proportionally increase with their BET surface area. This reflects the heterogeneity of the carbon surface for adsorption. The pore size distributions of these carbons, determined according to the Dubinin-Stoeckli equation, were found to vary with the burn-off level. By incorporating the distribution with the Dubinin-Radushkevich equation using an inverse proportionality between the micropore size and the adsorption energy, the isotherms for the adsorption of phenol onto these carbons can be well predicted. The present study has demonstrated that the heterogeneity of carbon surface for the phenol adsorption can be attributed to the different energies required for adsorption in different-size micropores. Copyright 2000 Academic Press.     

On the mechanisms of phenol adsorption by carbons

The removal of phenol and related compounds from dilute aqueous solutions by activated carbons corresponds to the coating of the micropore walls and of the external surface by a monolayer. This process is described by an analog of the Dubinin—Radushkevich—Kaganer equation. On the other hand, as suggested by immersion calorimetry at 293 K, in the case of concentrated solutions, the mechanism corresponds to the volume filling of the micropores, as observed for the adsorption of phenol from the vapor phase. The equilibrium is described by the Dubinin—Astakhov equation. It follows that the removal of phenol from mixtures with water depends on the relative concentrations, and the limiting factor for adsorption is either the effective surface area of the carbon, or the micropore volume.     

Ionic surfactant adsorption onto activated carbons

The adsorption of sodium dodecyl sulfate onto a set of activated carbons from aqueous solutions has been studied in the low concentration range. The adsorption isotherms are reasonably well fitted by a double Langmuir equation but the calorimetry of adsorption enthalpies shows a rather wide distribution of energies. This distribution is related to direct adsorbate-adsorbent interactions in pores of different size, without noticeable contributions from the chemical nature of the surface. The adsorbate-adsorbent interaction free energy through water is evaluated using the model proposed by van Oss and co-workers for the interfacial free energy. The obtained results indicate that the calculated free energy is in good agreement with that found from application of the double Langmuir equation to the adsorption isotherms.     

杉木活性炭吸附处理水溶液中的尼古丁

用不同孔径及化学性质的活性炭对尼古丁水溶液进行吸附研究. 以杉木屑为原料, 分别用氯化锌化学活化法和水蒸气物理活化法制备活性炭, 并分别命名为AC-Z和AC-H. 同时选用椰壳基商品活性炭作为对比吸附剂, 命名为AC-C. 采用比表面积孔径测定分析仪及Boehm滴定法对活性炭进行表征, 分别测定其比表面积、孔径分布和表面官能团含量. 吸附实验主要考虑吸附时间、温度和尼古丁溶液的初始浓度三个因素, 实验数据分析结果表明微孔有利于物理吸附的进行, 而表面酸性官能团及金属原子作为吸附活性位的作用更加重要. 由改变温度对各样品的吸附量影响也能说明活性位在吸附中的作用. AC-Z拥有较多的活性位, 温度变化时尼古丁的吸附量先升高后减小, 这主要是由于适合的温度能加快尼古丁分子的离解并促使其与活性位相结合, 而过高的温度会造成尼古丁分子动能增加, 导致分子间碰撞的机率和强度增大, 使吸附在活性炭表面的尼古丁分子脱落. AC-H和AC-C由较多的微孔和不同程度的活性位组成, 优先发生物理吸附, 并且伴随发生吸附剂表面分子团簇现象, 其吸附趋势与AC-Z相反. 动力学研究表明活性炭对尼古丁的吸附反应非常迅速, 并且符合准二阶动力学程模型. 各热力学参数ΔG⁰, ΔH⁰和ΔS⁰的计算结果表明吸附剂对尼古丁的吸附为吸热和自发性过程.AC-Z和AC-H的ΔH⁰值远低于AC-C, 说明吸附剂表面的活性位对尼古丁分子有强烈的吸引作用, 所以吸附相同数量吸附质分子所需的吸附热更小, 这也说明了活性位在吸附过程中发生作用.     

Adsorption calorimetry

The efficiency of activated carbons prepared from corncob, to remove asphaltenes from toluene modeled solutions, has been studied in this work. The activating agent effect over carbonaceous solid preparation , and also temperature effect on the asphaltenes adsorption on the prepared activated carbons, was studied. The asphaltene adsorption isotherms were determined, and the experimental data were analyzed applying the Langmuir, Freundlich, Redlich–Peterson, Toth and Radke–Prausnitz and Sips models. Redlich–Peterson model described the asphaltenes isotherm on the activated carbons better. The asphaltenes adsorption capacities at 25° for activated carbons were: 1305 mg g^?1, 1654 mg g^?1 and 559.1 mg g^?1 for GACKOH, GACKP and GACH₃PO₄, respectively. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were also evaluated from the adsorption isotherms in asphaltene solutions from toluene solutions, and it was found that the adsorption process was spontaneous and exothermic in nature. Kinetic parameters, reaction rate constant and equilibrium adsorption capacities were evaluated and correlated for each kinetic model. The results show that asphaltene adsorption is described by pseudo-second-order kinetics, suggesting that the adsorption process is chemisorption. The adsorption calorimetry was used to analyze the type of interaction between the asphaltenes and the activated carbons prepared in this work, and their values were compared with the enthalpic values obtained from the Clausius–Clapeyron equation.

     

The physical and surface chemical characteristics of activated carbons and the adsorption of methylene blue from wastewater

Adsorption of a basic dye, methylene blue, from aqueous solutions onto as-received activated carbons and acid-treated carbons was investigated. The physical and surface chemical properties of the activated carbons were characterized using BET-N(2) adsorption, X-ray photoelectron spectroscopy (XPS), and mass titration. It was found that acid treatment had little effect on carbon textural characteristics but significantly changed the surface chemical properties, resulting in an adverse effect on dye adsorption. The physical properties of activated carbon, such as surface area and pore volume, have little effect on dye adsorption, while the pore size distribution and the surface chemical characteristics play important roles in dye adsorption. The pH value of the solution also influences the adsorption capacity significantly. For methylene blue, a higher pH of solution favors the adsorption capacity. The kinetic adsorption of methylene blue on all carbons follows a pseudo-second-order equation.     

Adsorption of neodymium ions on activated charcoal from aqeous solutions

Summary A commercial activated charcoal has been tested as an adsorbent for the removal of neodymium ions from aqueous solutions. The adsorption behavior of neodymium ions on activated charcoal from aqueous solutions has been studied as a function of shaking time, neodymium ions concentration and concentration of different acids. Results reveal that the adsorption equilibrium is attained within 30 minutes, and diffusion of neodymium ions into the pores of activated charcoal controls the adsorption process. The adsorption process follows the first order kinetics. The Langmuir isotherm equation was obeyed well in the whole range of concentration studied. The influence of different cations and anions on the adsorption of neodymium ion from aqueous solutions have also been investigated. Approximately 98% of neodymium ions adsorbed onto activated charcoal could be recovered with 40 ml of 3M HNO₃ solutions.     

Mercury removal from aqueous solution by adsorption on?activated carbons prepared from olive stones

The textural characterization of a series of activated carbons prepared from olive stones, by carbonization at different temperatures (400, 550, 700 and 850 °C) and thermal activation with CO₂, has been investigated using N₂ adsorption at −196 °C and CO₂ adsorption at 0 °C. The effect of pre-oxidation of the carbonized precursor has also been studied, using temperature-programmed decomposition (TPD), to evaluate the effect of oxygen content of the chars in the performance of the obtained activated carbons for mercury removal. The adsorption of Hg(II) cations from aqueous solutions at room temperature by the prepared activated carbons was studied. Experimental results show that all samples exhibit a large microporosity (pore diameter below 0.56 nm). The amount of surface oxygen groups increased after pre-oxidation treatment, this enhancing the Hg(II) uptake (up to 72%). It can be concluded that these groups make the support more hydrophilic, thus providing a more efficient adsorption of Hg(II). The formation of a great amount of surface oxide groups such as carboxyl, phenol and lactone alters the surface charge properties of the carbon, this enhancing the surface-Hg(II) interaction.     

Adsorption of methyl orange using activated carbon prepared from lignin by ZnCl2 treatment

Lignocellulosic materials are good and cheap precursors for the production of activated carbon. In this study, activated carbons were prepared from the lignin at different temperatures (200 to 500°C) by ZnCl₂. The effects influencing the surface area of the resulting activated carbon are activation temperature, activation time and impregnation ratio. The optimum condition, are found an impregnation ratio of 2, an activation temperature of 450°C, and an activation time of 2 h. The results showed that the surface area and micropores volume of activated carbon at the experimental conditions are achieved to 587 and 0.23 cm³ g^?1, respectively. The adsorption behavior of methyl orange dye from aqueous solution onto activated lignin was investigated as a function of equilibrium time, pH and concentration. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. A maximum adsorption capacity of 300 mg g^?1 of methyl orange by activated carbon was achieved.     

Adsorption Characteristics of Chromium(VI) on Granular Activated Carbon

The adsorption of Chromium(VI) from aqueous solutions was studied on different commercial grades of granular activated carbon namely Filtrasorb F‐400, F‐300, F‐200 and F‐100. The adsorption of Chromium (VI) on F‐400 carbon was found to be maximum in comparison to the other grades of carbon. The Chromium (VI) adsorption process in dilute aqueous solutions agreed with the Langmuir and Freundlich models and also obeyed first order kinetics. Metal sorption characteristics of as received activated carbons were measured in batch experiments. The maximum removal (60–65%) for different grades of raw carbon was observed at 25 °C with an initial concentration of 15.16 mg dm^?3. It is evident from the study that granular activated carbon holds a particular promise in the removal of metal ions from aqueous solutions.     

Benzene and toluene adsorption at low concentration on activated carbon fibres

The present study analyses the preparation of activated carbon fibres (ACFs) by the so-called “physical” activation method with steam or carbon dioxide and their application for benzene and toluene adsorption at low concentration (200 ppmv). ACFs have been scarcely studied for the adsorption of these pollutants at low concentration in gaseous phase, despite their interesting features regarding adsorption kinetics, bed pressure drop, possibility of conformation and others. Our results have shown that the preparation method used is suitable to produce ACFs with high adsorption capacities for benzene and toluene at the low concentration used. The fibre morphology of the ACFs does not enhance their performance, which results to be similar to other non-fibrous activated carbons such as granular, pellets and powders. Such good performance of the ACFs, leading to benzene and toluene adsorption capacities as large as 31 g benzene/100 g ACF or 53 g toluene/100 g ACF, can be explained due to their large volume of narrow micropores (<0.7 nm) developed upon activation and their low content in surface oxygen groups. Our results have also shown very good agreement between the adsorption results derived from dynamic adsorption experiments and from adsorption isotherms. As the relative pressure of the organic compound increases the corresponding fraction of narrow micropore volumes filled by benzene and toluene increases. For a given low and comparable relative pressure, toluene always occupies a larger fraction of narrow micropores than benzene.     

Prediction of Carbon Dioxide Adsorption via Deep Learning

Porous carbons with different textural properties exhibit great differences in CO₂ adsorption capacity. It is generally known that narrow micropores contribute to higher CO₂ adsorption capacity. However, it is still unclear what role each variable in the textural properties plays in CO₂ adsorption. Herein, a deep neural network is trained as a generative model to direct the relationship between CO₂ adsorption of porous carbons and corresponding textural properties. The trained neural network is further employed as an implicit model to estimate its ability to predict the CO₂ adsorption capacity of unknown porous carbons. Interestingly, the practical CO₂ adsorption amounts are in good agreement with predicted values using surface area, micropore and mesopore volumes as the input values simultaneously. This unprecedented deep learning neural network (DNN) approach, a type of machine learning algorithm, exhibits great potential to predict gas adsorption and guide the development of next‐generation carbons.     

Adsorption of mercury from single and multicomponent metal systems on activated carbon developed from cherry stones

The adsorption of mercury from a single/multi-solute aqueous solution by activated carbon (AC) prepared from cherry stones (CS) by chemical activation with H₃PO₄, ZnCl₂ or KOH is studied. Three series of AC (i.e., P, H₃PO₄; Z, ZnCl₂; K, KOH) were prepared by controlling the impregnation ratio and carbonization temperature. The textural characterization of AC was carried out by gas adsorption, mercury porosimetry and density measurements. The surface chemistry was analyzed by the pH of the point of zero charge (pH_zpc), FT-IR spectroscopy and Boehm’s method. Experiments of mercury adsorption were conducted by the batch method, using aqueous solutions of mercury and of mercury, cadmium and zinc without pH adjustment. The ACs possess a wide range of pore volumes and sizes. Their microporosity is usually well developed. The meso- and macropore volumes are higher for the P carbons and K carbons, respectively. BET surface areas as a rule range between 1000 and 2000 m²?g^?1. The pH_zpc is much lower for the P carbons. The content of acidic oxygen surface groups is lower for the K carbons, whereas the content of basic groups is higher for these carbons. The kinetics of the adsorption process of mercury is faster for ACs with high volumes of large size pores. However, the surface groups have a marked unfavorable influence on the kinetics. The pseudo-second order rate constant (k₂×10^?3, g/mol?h) is higher by the order Z-4-800 (67.69)>K-3-800 (43.45)>P-3.44-400 (36.98). The incorporation of zinc and cadmium to the mercury solution usually decelerates the adsorption process for the P carbons and Z carbons and accelerates it for the K carbons. The amount adsorbed of mercury is much larger for the K carbons than for the other ACs. For the Z carbons, competition effects of zinc and cadmium on the adsorption of mercury are negligible, which indicates that mercury adsorbs specifically on surface active sites of these adsorbents.     

Porosity characteristics and pore developments of various particle sizes palm kernel shells activated carbon (PKSAC) and its potential applications

The adsorption behaviour and the micro- and mesopore size distributions of commercial palm kernel shell activated carbons (PKSAC) and other commercial activated carbon are characterized. The results showed that PKSAC are predominantly microporous materials, where micropores account 68–79% of total porosity. On the other hand, commercial activated carbons: Norit SX Plus, Calgon 12×40, and Shirasagi “A” activated carbons contained high mesopore fraction ranging from 33 to 52%. The analysis showed that the degree of mesoporosity of PKSAC is increased steadily with the decrease of particle size. This is due to the presence of channels interconnect the smaller pores in the interior of smaller particle size PKSAC. The smaller size PKSAC particle that is highly mesoporous has preformed better on the adsorption of larger molecules such as methylene blue. On the other hand, bigger size PKSAC particle has better performance on the adsorption of smaller adsorbates such as iodine.     

Removal of lead(II) and zinc(II) ions from aqueous solutions by adsorption onto activated carbon synthesized from watermelon shell and walnut shell

Activated carbons from watermelon shell (GACW) and walnut shell (GACN) were synthesized through chemical activation with phosphoric acid 40 % w/w, as an alternative low-cost adsorbent for the removal of lead(II) and zinc(II) ions from aqueous solutions. The yield of production was 85 and 80 % for GACW and GACN respectively. To compare the differences and similarities between the two activated carbons the following tests were performed: surface and pore width with SEM, nitrogen adsorption isotherms at ?196 °C (77 K), IR spectroscopy, TGA, point of zero charge (PZC) and Boehm titration. The GACN has 10 % more surface area (789 m² g^?1 for GACN and 710 m² g^?1 for GACW) and 13 % more pore volume than GACW. Also, GACN has a better resistance to high temperatures than GACW (the loss of mass at 900 °C was 20 % for GACN, while for GACW was 31 %). The effect of the initial concentration of lead(II) and zinc(II) ions on the adsorption process was studied in a batch process mode. To quantify the adsorption of lead and zinc adsorption isotherms of both metals in aqueous solution were performed for each carbon using analytic technique of atomic absorption. The adsorption isotherm data were better fitted by Langmuir model. Experimental results suggests that one gram of GACW adsorbs more milligrams of lead(II) and zinc(II) than one gram of GACN; it is suggest that the pore distribution is a significant variable in the adsorption process because GACW present mesopores and micropores, while GACN has only micropores. Also, the surface chemistry is an important variable in the adsorption process because GACW presents a lower pH_PZC than GACN (3.05 for GACW and 4.5 for GACN) and the solution’s pH of each metal was adjusted in 4.5, for that it could be suggested that the electrostatic interactions were increased between the ion and the carbon surface.     

Water vapor adsorption and microporous structure of carbon adsorbents. 18. Effect of surface chemistry of activated carbons on water vapor adsorption

This investigation has been devoted to a study of the chemical composition of the surfaces of activated carbons. A study has been made of the way in which changes in the surface chemistry of a series of carbons, as a result of heat treatment, affects the nature of their adsorption of water vapor. A differentiation has been made between oxygen-containing groups found on the surface of activated carbons before and after their heat treatment. It has been established that the original adsorption centers, which play a determining role in water vapor adsorption by activated carbons, comprise functional groups like strongly acidic free hydrogen ions, carboxylic and phenolic groups, situated on on the pore surface of the activated carbons. The number of these functional groups on the pore surface of the activated carbons has been correlated with the parametera ₀ (the number of original adsorption centers) in the isotherm equation for water vapor adsorption. The relative pressure corresponding to the formation of an adsorption layer on the surface of the activated carbons has been shown to depend on the number of original adsorption centers, the acidic functional groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 35–40, January, 1991.     

Modification of the theory of a three-dimensional filling of micropores

Compressibility of the adsorbate has been taken into account in calculating the maximum adsorption in micropores. On this basis, an equation has been derived for improvement of the theory of three-dimensional filling of micropores in application to the calculation of micropore volume by the Dubinin-Radushkevich equation. Evaluations for the case of benzene adsorption on activated carbons at 20°C have shown that the accounting for adsorbate compressibility leads to corrections of the Dubinin-Radushkevich theory amounting to approximately 10%.Institute of Physical Chemistry, Russian Academy of Sciences, Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 13–18, January, 1992.     

Density of He adsorbed in micropores at 4.2K

The density of He adsorbed in the cylindrical micropores of zeolites NaY and KL has been determined by He adsorption at 4.2K. He adsorption isotherms were then compared with N₂ adsorption isotherms at 77K. Crystallographic considerations of the micropore volumes gave the density of the He adsorbed layer, which is necessary for assessment of ultramicroporosity of less-crystalline microporous solids, such as activated carbons. The determined density of He adsorbed in the cylindrical micropores of the zeolite was in the range 0.22 to 0.26 gml^–1, greater than that of He adsorbed on a flat surface (0.202 gml^–1). A value for the density of He between 0.20 to 0.22 gml^–1 is recommended for evaluation of ultramicroporosity of a slit-shaped microporous system such as activated carbon.     

Study of chromium(VI) adsorption onto modified activated carbons with respect to analytical application

Two different types of modification of activated carbon, by treatment with concentrated solution of HNO₃ and outgassing treatment at high temperature, were studied in order to obtain the most effective adsorption of chromium(VI) ions from water solution. The basic parameters affecting the adsorption capacity of Cr(VI) ions on modified activated carbons were studied in details and the effect of modifications of activated carbons has been determined by studying the initial runs of adsorption isotherms. The obtained Cr(VI) adsorption isotherms were well fitted in the Freundlich equation. The reduction of Cr(VI) to Cr(III) and further ion exchange mechanism of adsorption onto oxidizing activated carbon and surface precipitation to Cr(OH)₃ in case of outgassing activated carbon were found as the main adsorption mechanisms of Cr(VI) ions onto modified activated carbons. Presence of chlorides and nitrates in studied adsorption system strongly decreased the adsorption ability of Cr(VI) onto outgassing activated carbon and mechanism of this behavior is proposed.     

A comparative study on characterizations of biomass derived activated carbons prepared by both normal and inert atmospheric heating conditions

In the present study, cost effective activated carbon from wasteland biomass of Calotropis gigantea stem was prepared at 400 °C, 600 °C, 750 °C and 900 °C carbonization temperatures in normal atmosphere (NA) and at 600 °C, 750 °C in inert atmosphere (IA) of nitrogen by using Potassium Carbonate (K₂CO₃) as chemical activating agent in the impregnation ratios of 0.5, 1 and 2. Activated carbons prepared under NA and IA were characterized and compared. Field Emission Scanning Electron Microscopy (FESEM) study confirmed presence of micropores and mesopores. While Xray Diffraction (XRD) analysis confirmed presence of both disordered amorphous carbon humps and graphitic crystallite peaks. Presences of functional groups were more prominent in NAC; found from Fourier Transform Infra-Red Spectroscopy (FTIR) analysis. BET surface area at 750 °C at chemical impregnation ratio 1 under NA was recorded highest containing both micropores and mesopores. Disordered carbon structure was confirmed from RAMAN spectroscopic analysis and nanoporous structure of activated carbon was confirmed from HRTEM analysis. NA activated carbons processed from wasteland weed can be preferred for different adsorption related applications as they are reasonable with improved properties.