Adsorption of NH3 onto activated carbon prepared from palm shells impregnated with H2SO4

Adsorption of ammonia (NH3) onto activated carbons prepared from palm shells impregnated with sulfuric acid (H2SO4) was investigated. The effects of activation temperature and acid concentration on pore surface area development were studied. The relatively large micropore surface areas of the palm-shell activated carbons prepared by H2SO4 activation suggest their potential applications in gas adsorption. Adsorption experiments at a fixed temperature showed that the amounts of NH3 adsorbed onto the chemically activated carbons, unlike those prepared by CO2 thermal activation, were not solely dependent on the specific pore surface areas of the adsorbents. Further adsorption tests for a wide range of temperatures suggested combined physisorption and chemisorption of NH3. Desorption tests at the same temperature as adsorption and at an elevated temperature were carried out to confirm the occurrence of chemisorption due to the interaction between NH3 and some oxygen functional groups via hydrogen bonding. The surface functional groups on the adsorbent surface were detected by Fourier transform infrared spectroscopy. The amounts of NH3 adsorbed by chemisorption were correlated with the contents of elemental oxygen present in the adsorbents. Mechanisms for chemical activation and adsorption processes are proposed based on the observed phenomena.     

Preparation of highly porous carbon from fir wood by KOH etching and CO2 gasification for adsorption of dyes and phenols from water

Fir wood was first carbonized for 1.5 h at 450 degrees C, then soaked in a KOH solution KOH/char ratio of 1, and last activated for 1 h at 780 degrees C. During the last hour CO2 was poured in for further activation for 0, 15, 30, and 60 min, respectively. Carbonaceous adsorbents with controllable surface area and pore structure were chemically activated from carbonized fir wood (i.e., char) by KOH etching and CO2 gasification. The pore properties, including the BET surface area, pore volume, pore size distribution, and pore diameter, of these activated carbons were first characterized by the t-plot method based on N2 adsorption isotherms. Fir-wood carbon activated with CO2 gasification from 0 to 60 min exhibited a BET surface area ranging from 1371 to 2821 m2 g(-1), with a pore volume significantly increased from 0.81 to 1.73 m2 g(-1). Scanning electron microscopic (SEM) results showed that the surfaces of honeycombed holes in these carbons were significantly different from those of carbons without CO2 gasification. The adsorption of methylene blue, basic brown 1, acid blue 74, p-nitrophenol, p-chlorophenol, p-cresol, and phenol from water on all the carbons studied was examined to check their chemical characteristics. Adsorption kinetics was in agreement with the Elovich equation, and all equilibrium isotherms were in agreement with the Langmuir equation. These results were used to compare the Elovich parameter (1/b) and the adsorption quantity of the unit area (q(mon)/Sp) of activated carbons with different CO2 gasification durations. This work facilitated the preparation of activated carbon by effectively controlling pore structures and the adsorption performance of the activated carbon on adsorbates of different molecular forms.     

Comparisons of porous and adsorption properties of carbons activated by steam and KOH

In this work, fir woods and pistachio shells were used as source materials to prepare porous carbons, which were activated by physical (steam) and chemical (KOH) methods. Pore properties of these activated carbons including the BET surface area, pore volume, pore size distribution, and pore diameter were first characterized by a t-plot method based on N(2) adsorption isotherms. Highly porous activated carbons with BET surface area up to 1009-1096 m(2)/g were obtained. The steam and KOH activation methods produced carbons with mesopore content in the range 9-15 and 33-49%, respectively. The adsorption equilibria and kinetics of tannic acid, methylene blue, 4-chlorophenol, and phenol from water on such carbons at 30 degrees C were then investigated to check their chemical characteristics. The Freundlich equation gave a better fit to all adsorption isotherms than the Langmuir equation. On the other hand, the intraparticle diffusion model could best follow all adsorption processes. In comparison with KOH-activated carbons, it was shown that the rate of external surface adsorption with steam-activated carbons was significantly higher but the rate of intraparticle diffusion was much lower.     

Pore structure and adsorption performance of the KOH-activated carbons prepared from corncob

Carbonaceous adsorbents with controllable surface area were chemically activated with KOH at 780 degrees C from chars that were carbonized from corncobs at 450 degrees C. The pore properties, including BET surface area, pore volume, pore size distribution, and mean pore diameter of these activated carbons, were characterized by the t-plot method based on N(2) adsorption isotherms. Two groups are classified according to the types of adsorption/desorption isotherms. Group I corncob-derived activated carbons, with KOH/char ratios from 0.5 to 2, exhibited BET surface area ranging from 841 to 1221 m(2)/g. Group II corncob-derived activated carbons, with KOH/char rations from 3 to 6, showed high BET surface areas, from 1976 to 2595 m(2)/g. From scanning electron microscopic (SEM) results, the surface morphology of honeycombed holes on corncob-derived activated carbons was significantly influenced by the KOH/char ratios. The adsorption kinetics of methylene blue, basic brown 1, acid blue 74, 2,4-dichlorophenol, 4-chlorophenol, and phenol from water at 30 degrees C were studied on the two groups of activated carbons, which were suitably described by two simplified kinetic models, pseudo-first-order and pseudo-second-order equations. The effective particle diffusivities of phenols and dyes at the corncob-derived activated carbons of group II are higher than those of ordinary activated carbons. The high-surface-area activated carbons were demonstrated to be promising adsorbents for pollution control and for other applications.     

Influence of MgO template on carbon dioxide adsorption of cation exchange resin-based nanoporous carbon

In this work, porous carbons with well-developed pore structures were directly prepared from a weak acid cation exchange resin (CER) by the carbonization of a mixture with Mg acetate in different ratios. The effect of the Mg acetate-to-CER ratio on the pore structure and CO(2) adsorption capacities of the obtained porous carbons was studied. The textural properties and morphologies of the porous carbons were analyzed via N(2)/77K adsorption/desorption isotherms, SEM, and TEM, respectively. The CO(2) adsorption capacities of the prepared porous carbons were measured at 298 K and 1 bar and 30 bar. By dissolving the MgO template, the porous carbons exhibited high specific surface areas (326-1276 m(2)/g) and high pore volumes (0.258-0.687 cm(3)/g). The CO(2) adsorption capacities of the porous carbons were enhanced to 164.4 mg/g at 1 bar and 1045 mg/g at 30 bar by increasing the Mg acetate-to-CER ratio. This result indicates that CER was one of the carbon precursors to producing the porous structure, as well as for improving the CO(2) adsorption capacities of the carbon species.     

Effects of Burn-off and Activation Temperature on Preparation of Activated Carbon from Corn Cob Agrowaste by CO(2) and Steam

Previous studies have successfully demonstrated that corn cob is a suitable precursor for production of good activated carbon by chemical activation. However, respond to the need for cleaner production, this study focuses on the physical activation by gasifying agents such as CO(2) and steam. The activation temperatures under investigation are 1073 and 1173 K. Within the limit of 50 wt% burn-off, experimental results reveal that the BET surface area, pore volume, and average pore diameter of the resulting activated carbon generally increase with the extent of burn-off in both gasifying agents and at both temperatures. The higher activation temperature can overcome the drawbacks of a longer period of activation required to attain larger surface area and can offer higher potential to produce activated carbon of greater adsorption capacity from agriculture wastes such as corn cobs. Additionally, the BET surface areas of properly prepared activated carbons can satisfy commercial requirements, when compared with commercial activated carbon. The BET surface areas of the activated carbons after about 71 and 59 wt% burn-off of CO(2) and steam activations at 1173 K are 1705 and 1315 m(2)/g, respectively, indicating high adsorption capacities. Thus, it is feasible to produce high-quality microporous activated carbon from corn cob agrowaste using N(2) carbonization followed by physical activation with CO(2) or steam. Copyright 2000 Academic Press.     

Comparative study for the removal of methylene blue via adsorption and photocatalytic degradation

Physically and chemically activated carbons were prepared from date pits and olive stones. Titania and WO(x)-TiO(2)/MCM-41 were prepared as photoactive catalysts. Surface characterizations were investigated from ash content, pH, base neutralization capacities and FT-IR techniques. The textural characteristics, namely specific surface area (S(BET)) and pore texture, were determined from low temperature adsorption of N(2) at 77 K. The decolorization of aqueous solution of methylene blue was performed by means of two alternative methods. Steam-activated carbons own higher surface area compared with ZnCl(2)-activated carbons, and the micropore surface area represents the major contribution of the total area. Steam-activated carbons were the most efficient decolorizing adsorbents owing to its higher surface area, total pore volume and the basic nature of the surface. The calculated values of DeltaG(0), DeltaH(0) and DeltaS(0) indicate the spontaneous behavior of adsorption. The photocatalytic degradation is more convenient method in decolorizing of methylene blue compared with the adsorption process onto activated carbons.     

微波辐射紫茎泽兰制备优质活性炭的研究

以紫茎泽兰为原料,碳酸钾为活化剂,采用超声波浸渍,微波辐射法制备活性炭.研究了浸渍方式与时间、微波功率、微波辐射时间、剂料比对活性炭吸附性能和得率的影响.得到了本实验条件下的优化工艺条件:超声波浸渍20min、120℃脱水2h,微波功率700W、微波辐射时间12min、剂料比1.25∶1.优化工艺条件下制备的活性炭碘吸附值为1470.27mg/g,亚甲基蓝吸附值为300mL/g,得率为16.35%.浸渍时间极大的缩短,微波辐射时间只有传统法活化时间的1/15左右,活性炭的吸附指标超过了国标GB/T 13803.1-1999和GB/T 13803.2-1999一级品的标准,其中碘吸附值是国家一级标准的1.47倍,亚甲基蓝吸附值是国家一级标准的2.73倍.同时,测定了该活性炭氮吸附,其BET比表面积为1540.97m2/g,总孔容为0.7393mL/g,并通过DFT表征了活性炭的孔径分布,结果表明该活性炭为微孔型活性炭.     

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.     

ZrO2酸碱性质的TPD表征 III.苯酚和CO2或NH3共吸附

用TPD－MS技术对ZrO2上PhOH和CO2或NH3双组分共吸附效应进行了研究．当有CO2或NH3预先吸附时，PhOH的吸附状态和脱附温度并不发生改变．PhOH一方面可以取代与表面酸－碱对中心有关的强吸附CO2或NH3物种而吸附，另一方面表面剩余的CO2或NH3吸附物种又能通过表面键诱导极化使一些“潜在的酸碱中心”得到活化，组成能够吸附PhOH的酸－碱对中心．后一种作用可导致PhOH吸附量增加一倍，表明ZrO2表面具有很高的可极化度．     

Sulfur fixation on bagasse activated carbon by chemical treatment and its effect on acid dye adsorption

Heteroatoms are known to introduce specific surface functionalities that can enhance the adsorption properties of carbons. Sulfur fixation on bagasse-activated carbon was conducted by a low temperature chemical treatment with sulfuric acid followed by physical activation with CO₂ at 900?°C. The effect of sulfur fixation on the surface chemical properties of bagasse-activated carbons were investigated and on their subsequent acid dye removal (CIBA AB80) behavior. Surface chemical development were examined and followed using Fourier transform infrared spectroscopy (FTIR), heteroatom analysis and carbon surface acidity. Functional group stability with thermal treatment was also investigated. The textural properties of the activated carbons were characterized by nitrogen adsorption. Chemical pre-treatment and gasification was able to fix up to 0.2 wt% of sulfur on the activated carbon. Although the sulfur fixed by chemical treatment is low, this method introduced several advantages in comparison to fixation by thermal methods. The chemical method did not interfere with the textural development of the carbon, as found in thermal methods. In addition, the surface chemistry generated by these levels of sulfur groups was sufficient to increase the uptake of acid blue dyes by more than 700% based on adsorption capacities normalized by the surface area of the carbon.     

CO2 adsorption by activated templated carbons

Highly porous carbons have been prepared by the chemical activation of two mesoporous carbons obtained by using hexagonal- (SBA-15) and cubic (KIT-6)-ordered mesostructured silica as hard templates. These materials were investigated as sorbents for CO(2) capture. The activation process was carried out with KOH at different temperatures in the 600-800°C range. Textural characterization of these activated carbons shows that they have a dual porosity made up of mesopores derived from the templated carbons and micropores generated during the chemical activation step. As a result of the activation process, there is an increase in the surface area and pore volume from 1020 m(2)g(-1) and 0.91 cm(3)g(-1) for the CMK-8 carbon to a maximum of 2660 m(2)g(-1) and 1.38 cm(3)g(-1) for a sample activated at 800°C (KOH/CMK-8 mass ratio of 4). Irrespective of the type of templated carbon used as precursor or the operational conditions used for the synthesis, the activated samples exhibit similar CO(2) uptake capacities, of around 3.2 mmol CO(2)g(-1) at 25°C. The CO(2) capture capacity seems to depend on the presence of narrow micropores (<1 nm) rather than on the surface area or pore volume of activated carbons. Furthermore, it was found that these porous carbons exhibit a high CO(2) adsorption rate, a good selectivity for CO(2)-N(2) separation and they can be easily regenerated.     

ZrO2酸碱性质的TPD表征 II. NH3和CO2共吸附研究

用NH_3和CO_2双组分并吸附TPD-MS和IR技术对ZrO_2催化剂表面酸中心和碱中心的相互关系进行了表征. 先吸附NH_3（或CO_2）对在其后吸附的CO_2（或NH_3）不仅无阻碍，反而导致后吸附CO_2（或NH_3）在最高程脱峰温区（＞510 K）的脱附量增加．这种双组分并吸附效应在IR谱图上表现为NH_3共吸附诱发生成了一种新的CO_2吸附态，即在碱中心上形成单齿碳酸根物种．同时CO_2共吸附又强化NH_3与Zr~(4＋)（Lewis酸中心）的配位键合．这表明ZrO_2表面存在相互邻接的酸中心和碱中心，它们通过表面键诱导极化而令酸－碱相互作用加强．这类双组分共吸附效应可归结为表面键诱导酸－碱相互作用．     

活性炭孔隙结构对催化氧化脱除单质汞的影响

研究活性炭在硫化氢存在条件下催化氧化脱除煤气中单质汞的吸附机理和探讨提高其吸附能力的方法,在模拟煤气气氛下对3种活性炭和一种活性焦进行汞的吸附性能实验,并进一步分析活性炭(焦)的孔隙结构。用BET方程处理N₂等温吸附数据,计算比表面积;用HK法进行微孔分析;用BJH法计算中孔孔径分布。结果表明,硫化氢被催化氧化后,生成吸附在活性炭孔壁上的活性硫促进了对汞的吸附;随着活性炭微孔和中孔体积的增大,活性炭对汞的吸附能力得到提高。     

The use of microwave radiation for obtaining carbonaceous adsorbents from biomass and their use in elimination of inorganic pollutants

A new technology of obtaining activated carbons by physical and direct activation of biomass with the use of microwave radiation is described. The effect of activation temperature (700 and 800 °C) and two periods of time (15 and 30 min) on the textural parameters, acid–base character of the surface and sorption properties of activated carbons was tested. The resulting carbons were characterized by low-temperature nitrogen sorption and determination of pH as well as the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide adsorption in dry and wet conditions as well as by iodine removal from aqueous solution. The final products were adsorbents of surface area ranging from 291 to 368 m²/g and pore volume from 0.20 to 0.26 cm³/g, showing basic character of the surface. The results obtained in our study have proved that suitable choice of the pyrolysis and activation procedure for hay with the use of microwave radiation permit producing adsorbents with good capacity toward toxic gases of acidic character as well as inorganic pollutants of molecules of size similar to that of iodine molecules.     

几种植物基活性炭材料的表面结构与吸附性能比较——(II)表面化学结构与吸附性能研究

用X-射线光电子能谱对3种植物基活性炭材料:椰壳活性炭 (CAC4)、剑麻茎基活性炭(SSAC)和剑麻基活性碳纤维 (SACF) 的表面化学结构进行了表征,并研究和对比了它们的吸附性能,包括对碘、苯酚和亚甲基蓝的液相吸附性能,对有机蒸汽的吸附性能以及对Au3+的还原吸附性能等。结果表明,3个样品表面均含有多种含氧官能团,吸附能力SACF>SSAC> CAC4。样品的吸附性能主要取决于自身孔结构,与其表面化学结构也有密切的关系。     

Effects of vacuum pyrolysis conditions on the characteristics of activated carbons derived from pistachio-nut shells

Preparation of effective adsorbents from pistachio-nut shells was carried out. Optimization of the vacuum pyrolysis parameters prior to activation was carried out to study the effects of vacuum pyrolysis temperature, hold time, and heating rate on the properties of chars and activated carbons, while CO2 activation conditions were fixed at a temperature of 900 degrees C, an activation time of 30 min, a heating rate of 10 degrees C/min, a CO2 flow rate of 100 cm3/min, and a nitrogen flow rate of 150 cm3/min. The optimum vacuum pyrolysis conditions for preparing activated carbons with high surface area and pore volume were identified. The microstructure and microcrystallinity of the activated carbons prepared were examined by scanning electron microscopy and powder X-ray diffraction techniques respectively while the Fourier transform infrared spectra determined any changes in the surface functional groups produced during different preparation stages. Experimental results show that it is feasible to prepare activated carbons with high BET surface area from pistachio-nut shells.     

Roles of the textural and surface chemical properties of activated carbon in the adsorption of acid blue dye

This study has demonstrated the use of empirical modeling in resolving the effects of individual carbon properties on acid blue dye adsorption. Acid blue dye adsorption tests were conducted on activated carbons prepared from bagasse by physical (CO2) and chemical (ZnCl2, MgCl2 and CaCl2) techniques. Empirical models based on the carbon textural (surface area and pore size) properties and the surface chemistry inferred from heteroatom (C,H, N, and S) concentration and carbon surface pH were used to resolve the effects of individual carbon properties on acid blue dye adsorption. This form of analysis was conducted to optimize carbon preparation properties, forming the foundation for tailor-making adsorbents from bagasse suitable for acid dye adsorption. A series of statistical analyses (partial F-tests to establish the parameter significance) measured variants including the mean square error, r2 and adjusted r2, normality, and randomness of residuals, and formed the basis for testing the adequacy of these models. The empirical models suggest that a combination of suitable pore structure and distinct basic surface chemistry generated by sulfur- and nitrogen-based groups, which were also elucidated by Fourier transform infrared spectroscopy, is necessary to promote acid dye adsorption.     

Modeling adsorption rate of organic micropollutants present in landfill leachates onto granular activated carbon

The overall adsorption rate of single micropollutants present in landfill leachates such as phthalic acid (PA), bisphenol A (BPA), diphenolic acid (DPA), 2,4-dichlorophenoxy-acetic acid (2,4-D), and 4-chloro-2-methylphenoxyacetic acid (MCPA) on two commercial activated carbons was studied. The experimental data obtained were interpreted by using a diffusional model (PVSDM) that considers external mass transport, intraparticle diffusion, and adsorption on an active site. Furthermore, the concentration decay data were interpreted by using kinetics models. Results revealed that PVSDM model satisfactorily fitted the experimental data of adsorption rate on activated carbon. The tortuosity factor of the activated carbons used ranged from 2 to 4. The contribution of pore volume diffusion represented more than 92% of intraparticle diffusion confirming that pore volume diffusion is the controlling mechanism of the overall rate of adsorption and surface diffusion can be neglected. The experimental data were satisfactorily fitted the kinetic models. The second-order kinetic model was better fitted the experimental adsorption data than the first-order model.     

稻壳多孔碳材料的电容性能及模型计算

采用NaOH和H₃PO₄化学活化法, 由廉价的稻壳制备了2种高比表面积的介孔活性碳, 测试了其比表面积和平均孔径, 利用循环伏安、 恒流充放电和交流阻抗测试了其电化学性能, 其比电容分别达到145.8和168.5 F/g. 利用一种多分支的三级孔道模型对其进行交流阻抗谱拟合, 拟合结果符合度较高, 表明该模型对分析活性碳电极结构有一定指导意义.