Preparation and characterization of mesoporous activated carbon from waste tires

Activated carbons were produced from waste tires and their characteristics were investigated. Rubber separated from waste tires was first carbonized at 500 °C in N₂ atmosphere. Next, the obtained chars were activated with steam at 850 °C. As a result, fairly mesoporous activated carbons with mesopore volumes and BET surface areas up to 1.09 cm³/g and 737 m²/g, respectively, were obtained. To further improve the porous properties of the activated carbons, the char was treated with 1 M HCl at room temperature for 1 day prior to steam activation. This treatment increased mesopore volumes and BET surface areas of the activated carbons up to 1.62 cm³/g and 1119 m²/g, respectively. Furthermore, adsorption characteristics of phenol and a dye, Black 5, on the activated carbon prepared via acid treatment were compared with those of a commercial activated carbon in the liquid phase. Although the prepared carbon had a larger micropore volume than the commercial carbon, it showed a slightly lower phenol adsorption capacity. On the other hand, the prepared carbon showed an obviously larger dye adsorption capacity than the commercial carbon, because of its larger mesopore volume.     

Controlling carbon microporosity: the structure of carbons obtained from different phenolic resin precursors

Carbons were prepared from resins synthesised using the phenolic precursors phenol, para methylphenol, para ethylphenol, para n-propylphenol, para isopropylphenol and 3,5-dimethylphenol. Loss of phenolic OH from these materials was followed using solid-state nuclear magnetic resonance. The surface areas of the carbons were determined using N₂ and CO₂ adsorption. No significant differences in the loss of phenolic OH were observed. Under the same carbonisation conditions, the para alkyl phenols gave carbons with wide micropores, while the phenol and 3,5-dimethylphenol gave carbons with narrow micropores. Grinding the cured resins prior to carbonisation was found to significantly increase the surface area of the carbons obtained, with the microporous surface area increasing rapidly with a fall in particle size, without a significant increase in burn-off. Higher carbonisation temperatures widened the micropore size distribution, as shown by fitting the CO₂ adsorption isotherm with the Dubinin-Astakhov equation. The ability to change the carbon micropore structure obtained from a simple, well defined precursor, has many potential applications in carbon molecular sieves, catalyst supports and the investigation of adsorption processes.     

Importance of activated carbon's oxygen surface functional groups on elemental mercury adsorption

The effect of varying physical and chemical properties of activated carbons on adsorption of elemental mercury (Hg⁰) was studied by treating two activated carbons to modify their surface functional groups and pore structures. Heat treatment (1200 K) in nitrogen (N₂), air oxidation (693 K), and nitric acid (6N HNO₃) treatment of two activated carbons (BPL, WPL) were conducted to vary their surface oxygen functional groups. Adsorption experiments of Hg⁰ by the activated carbons were conducted using a fixed-bed reactor at a temperature of 398 K and under N₂ atmosphere. The pore structures of the samples were characterized by N₂ and carbon dioxide (CO₂) adsorption. Temperature-programmed desorption (TPD) and base-acid titration experiments were conducted to determine the chemical characteristics of the carbon samples. Characterization of the physical and chemical properties of activated carbons in relation to their Hg⁰ adsorption capacity provides important mechanistic information on Hg⁰ adsorption. Results suggest that oxygen surface complexes, possibly lactone and carbonyl groups, are the active sites for Hg⁰ capture. The carbons that have a lower carbon monoxide (CO)/CO₂ ratio and a low phenol group concentration tend to have a higher Hg⁰ adsorption capacity, suggesting that phenol groups may inhibit Hg⁰ adsorption. The high Hg⁰ adsorption capacity of a carbon sample is also found to be associated with a low ratio of the phenol/carbonyl groups. A possible Hg⁰ adsorption mechanism, which is likely to involve an electron transfer process during Hg⁰ adsorption in which the carbon surfaces may act as an electrode for Hg⁰ oxidation, is also discussed.     

Influence of HNO3 oxidation on the structure and adsorptive properties of corncob-based activated carbon

An investigation of the impact of strong oxidation with HNO₃ on the porosity and adsorption characteristics of char and activated carbons, derived from corncobs, is presented. Texture parameters, as obtained from N₂ adsorption at 77 K, showed a considerable decrease in surface area of the activated carbons with enhanced pore widening. The extent of porosity modification was found to depend on the scheme of activation of the precursor, simple carbonization, steam pyrolysis, steam gasification of the char, or chemical activation with H₃PO₄. Surface-chemical changes were detected by FTIR spectroscopy, where absorption bands assigned to carboxyl, carboxylate, carbonyl, and phenolic groups were observed. A SEM study demonstrated the erosive effect of HNO₃, detected by the presence of disintegration of the carbon grains, with the porous structure probably containing very large macropores. As a consequence of the oxidation process, elemental analysis showed high contents of O, H and N, and TG confirmed that the weight loss distribution in the thermogram becomes slower at higher temperatures. The removal of phenol decreased as a result of the formation of oxygen functionalities. Mono-nitrophenols were adsorbed in smaller amounts than phenol, and p-nitrophenol showed a relatively higher uptake than the other two mono-nitrophenols, whereas the uptake of Methylene Blue was improved. Removal of Pb²⁺ from aqueous non-buffered solution was considerably enhanced by chemical oxidation, which may be related to pore widening, increased cation-exchange capacity by oxygen groups, and the promoted hydrophilicity of the carbon surface.     

Characteristics of Cobalt Adsorption on Prepared TiO2 and Fe-Ti-O Adsorbents in High Temperature Water

Abstract

TiO₂ and Fe-Ti-O adsorbents were prepared by hydrolysis of Ti(OC₃H₇)4 and by alkalizing an equimolar mixed solution of TiCl₄ and FeCl₂, followed by heat treatment of their hydroxides. Their structures were studied by x-ray diffractometry and TG-DTA. The Co²⁺ adsorption characteristics of the adsorbent in high temperature water were investigated in a stirred autoclave. The prepared Fe-Ti-O adsorbent was found to be a stable nonstoichiometric ferrous/ferric titanium oxide with pseudobrookite and rutile structures. The Co²⁺ adsorption capacity of the Fe-Ti-O adsorbent was determined to be larger (0.38 meq Co²⁺/g adsorbent at 280[ddot]C) than that of TiO₂ at high temperature. The enthalpy changes (ΔH[ddot]) of about 34 and 49 kJ·mol^?1 due to the adsorption of Co²⁺ on the TiO₂ and Fe-Ti-O adsorbents, respectively, indicates that the adsorption is endothermic in the experimental temperature range (150–280[ddot]C). It is shown that the specific surface areas of these adsorbents are not dominant factors for Co²⁺ adsorption on oxides at high temperature.     

Removal of Chlorophenols from Aqueous Solution by Anion-Exchange Resins

Abstract

The effects of pH value and chloride ion concentration on the removal of chlorophenols from aqueous solutions by Purolite A-510 resin [macroreticular polystyrene-divinylbenzene resin with R(CH₃)₂(C₂H₄OH)N⁺ group] are discussed by the species distributions of chlorophenols. Those chlorophenols include phenol, 2-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol. The investigations showed that the chlorophenols could be removed effectively at alkaline conditions where the ion-exchange reaction was dominant. Also, the removal of chlorophenols increased with the number of chlorine atoms on the chlorophenols. The removal of chlorophenols via the ion-exchange reaction was hindered by the presence of chloride ions. The effect of chloride ions, however, was diminished in acidic solutions where the adsorption reaction was dominant. The proposed equilibrium model, which considers both adsorption and ion-exchange reactions, adequately describes the sorption behavior of chlorophenols. The partition constants of the protonated chlorophenols can be estimated from the octanol/water partition coefficients of the phenolic compounds.     

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.     

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     

Studies on Cesium Uptake by Phenolic Resins

Abstract

The selective removal of cesium by phenolic ion-exchange resins from highly salted alkaline radioactive solutions was studied. The resins were synthesized by alkaline polycondensation of phenol, resorcinol, catechol, and a resorcinol-catechol mixture with formaldehyde and characterized for their moisture regain, ion-exchange (H⁺→Na⁺) capacity, and distribution coefficient (K_D ) for cesium. The effects of open and sealed curing of the polymers on their properties were studied. The effect of Na⁺, NaOH, and Cs⁺ concentration on the uptake of cesium by resorcinol-formaldehyde resin was investigated, in particular. The chemical, thermal, and radiation stabilities of the polymers were also studied.     

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.     

Oxygen-containing functional group-facilitated CO2 capture by carbide-derived carbons

A series of carbide-derived carbons (CDCs) with different surface oxygen contents were prepared from TiC powder by chlorination and followed by HNO₃ oxidation. The CDCs were characterized systematically by a variety of means such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ultimate analysis, energy dispersive spectroscopy, N₂ adsorption, and transmission electron microscopy. CO₂ adsorption measurements showed that the oxidation process led to an increase in CO₂ adsorption capacity of the porous carbons. Structural characterizations indicated that the adsorbability of the CDCs is not directly associated with its microporosity and specific surface area. As evidenced by elemental analysis, X-ray photoelectron spectroscopy, and energy dispersive spectroscopy, the adsorbability of the CDCs has a linear correlation with their surface oxygen content. The adsorption mechanism was studied using quantum chemical calculation. It is found that the introduction of O atoms into the carbon surface facilitates the hydrogen bonding interactions between the carbon surface and CO₂ molecules. This new finding demonstrated that not only the basic N-containing groups but also the acidic O-containing groups can enhance the CO₂ adsorbability of porous carbon, thus providing a new approach to design porous materials with superior CO₂ adsorption capacity.     

Advances in the study of methane storage in porous carbonaceous materials

This paper presents an overview of the results of our research group in methane storage, in which the behaviour of different carbon materials in methane storage has been studied. These materials include physically activated carbon fibres (ACFs), chemically activated carbons (ACs) and activated carbon monoliths (ACMs), all of them prepared in our laboratories. These results have been compared with those corresponding to commercial ACFs, commercial activated carbon cloths and felts, and a commercial activated carbon.An in depth analysis (different raw materials, activating agent and preparation variables) has been done in order to obtain the carbon material with the best methane adsorption capacity by unit volume of adsorbent. The important effect of the micropore volume, micropore size distribution (MPSD) and packing density of the carbon materials in the methane adsorption capacity and delivery has been analysed. After this study, activated carbons with volumetric methane uptake as high as 166 v/v and delivery of 145 v/v have been prepared. In addition, ACM with methane uptake of 140 v/v and a delivery of 126 v/v has also been obtained.Moreover, the results corresponding to preliminary in situ small angle neutron scattering (SANS) study of CD₄ adsorption under pressure in different porous carbons and a zeolite are also included. These experiments have established SANS as a viable technique to investigate high-pressure methane adsorption. CD₄ adsorption at supercritical conditions produces changes in the SANS curves. The changes observed are in agreement with theoretical speculations that the density of the adsorbed phase depends upon the pore size.     

多级孔的氮掺杂葡萄糖衍生碳的催化氧化应用

碳材料是以过硫酸氢钾（PMS）为氧化剂的高级氧化法（AOPs）的一种重要催化剂。以葡萄糖为碳源，NaNO3为模板和造孔剂，通过高温炭化法以及NH3高温后处理合成了氮掺杂多级孔碳材料NC-X-T〔X为NaNO3与葡萄糖的质量比，T为温度（℃）〕。采用氮气吸附-脱附、XRD、XPS、SEM、TEM对NC-X-T材料的比表面积、孔径分布、晶体结构、化学组成以及形貌进行了表征与测试。以NC-X-T为催化剂，以PMS为氧化剂，在不同实验条件下进行了苯酚的降解实验。结果表明，造孔和掺氮过程的协同可极大提升NC-X-T材料的催化性能（0.005 g NC-0.5-800，1.0 g/LPMS，在40 min内可将5.3×10-4 mol/L苯酚（100 mL）完全降解，反应速率常数高达0.397 min-1），优于大多数金属及非金属催化剂。利用XPS对降解过程中NC-X-T的稳定性进行了研究，证实碳材料的氧化是其失活的主要原因，经过高温无氧处理可以恢复其部分催化活性。关键词：生物质；过硫酸氢钾；硝酸钠；多级孔结构；氮掺杂；协同效应；水处理技术中图分类号：X703 文献标识码： 文章编号：     

Removal of copper (II) and phenol from aqueous solution using porous carbons derived from hydrothermal chars

The feasibility of hydrothermal char (HTC), a byproduct from biomass hydrothermal liquefaction for bio-oil production, as raw material for preparation of porous carbons was investigated in the present study. The resultant HTC-derived porous carbons were characterized and utilized as adsorbents for copper (II) and phenol removal from aqueous solution. Compared with porous carbons using pyrolytic char as precursor, the HTC-derived porous carbons exhibited unique textural features, e.g., narrow pore size distribution, high surface area and large pore size. In addition, FT-IR analysis confirmed that substantial amount of ketene groups existed on the surface of the HTC-derived porous carbons. As the adsorbents, the copper (II) adsorption onto HTC-derived carbons was strongly affected by the pH value of the solution in comparison with phenol adsorption. The carbons derived from pinewood and rice husk HTC exhibited high adsorption capacity of 83.88 and 39.30 mg/g for phenol and 25.18 and 22.62 mg/g for copper (II), respectively. The adsorption data for copper (II) and phenol onto the carbon adsorbents could be well described by Langmuir and Freundlich models. In comparison with pinewood sawdust HTC-derived carbon, the adsorption onto rice husk HTC-derived carbon preferentially followed Freundlich model due to the presence of silica on the surface.     

Utilization of Raw and Activated Date Pits for the Removal of Phenol from Aqueous Solutions

Activated carbons prepared from date pits, an agricultural waste byproduct, have been examined for the adsorption of phenol from aqueous solutions. The activated carbons were prepared using a fluidized bed reactor in two steps; carbonization at 700 °C for 2 hours in N₂ atmosphere and activation at 900 °C in CO₂ atmosphere. The kinetic data were fitted to the models of intraparticle diffusion, pseudo‐second order, and Lagergren, and followed more closely the pseudo‐second‐order chemisorption model. The isotherm equilibrium data were well fitted by the Freundlich and Langmuir models. The maximum adsorption capacity of activated date pits per Langmuir model was 16 times higher than that of nonactivated date pits. The thermodynamic properties calculated revealed the endothermic nature of the adsorption process. The uptake of phenol increased with increasing initial phenol concentration from10 to 200 ppm and temperature from 25 to 55 °C, and decreased with increasing the solution pH from 4 to 12. The uptake of phenol was not affected by the presence of NaCl salt.     

Characteristics of as-prepared biochar derived from catalytic pyrolysis within moderate-temperature ionic liquid for CO2 uptake

A promising biochar as solid adsorbent for CO₂ uptake was prepared by the catalytic pyrolysis of coconut shell in moderate-temperature ionic liquid (IL). Then, it was characterized by means of SEM, EDS, BPEA, BET, NLDFT, FTIR, and TG-DSC, and a mechanism interpretation of the porous biochar formation was conducted. In addition, the adsorption characteristics of CO₂ on the as-prepared biochar, such as adsorption capacity, adsorption potential, isosteric heat, and static selectivity at different adsorption temperatures and pressures, were systematically evaluated. The results indicated that the as-prepared biochar exhibited an adequate CO₂ adsorption with a capacity of 4.5 mmol/g at 273 K and 100 kPa. Then, a significant number of slit-like pores were revealed to exist on the as-prepared biochar with a peak pore size between a range of 0.6 nm-2 nm. The porous structure formation was ascribed to the release of carbon-, hydrogen-, oxygen-, sulphur-, and nitrogen-containing compounds during biochar preparation. Meanwhile, both the adsorption potential and isosteric heat of the CO₂ uptake under the tested conditions decreased with an increase in the adsorption capacity, which ranged from 33 kJ/mol-21 kJ/mol and 23 kJ/mol-7 kJ/mol, respectively. Therefore, the isosteric heat could be considered as a piecewise function of adsorption capacity. In addition, the molar ratios of CO₂ over N₂ adsorbed under the tested conditions were above 11 and were accompanied by molar ratio peaks of 26 at 273 K and 19 at 298 K, respectively. Moreover, an interesting phenomenon occurred: the static adsorptive selectivity of CO₂ over N₂ first increased and then decreased and there was an increase in the adsorption pressure at the tested adsorption temperatures.     

中孔炭材料的制备及吸附性能的研究

以正硅酸乙酯为模板硅源，酚醛树脂为炭前驱体，运用模板法制备了中孔炭材料。并用红外光谱（FT—IR）、扫描电镜（SEM）、低温N2自动吸附、甲醛和VB12饱和吸附等对样品形貌、孔结构和吸附性能进行了研究。结果表明：制备的炭材料孔径集中分布在2-7nm左右，且中孔孔隙率达到74．6％，比表面积达到1012m^2／g；材料对VB12大分子有较好的吸附性能。表明通过控制正硅酸乙酯的水解条件能制备孔径集中的中孔炭材料。     

Characteristics of unburned carbons and their application for humic acid removal from water

Two unburned carbons (UCs) were separated from coal fly ash and their physicochemical properties were characterised using N₂ adsorption, XRD, SEM, XPS, FT-IR and potentiometric mass titration. Chemical treatments using HNO₃ and KOH were also conducted on one of the unburned carbons. The adsorption of humic acid from aqueous solution was performed on these untreated and chemically treated UCs. It was found that the UCs showed different porous structure and surface chemical properties, which influenced their adsorption behaviour. UCs exhibited high adsorption capacity for humic acid. After chemical treatment, the textural structure and surface functional groups of the unburned carbon were changed and the adsorption behaviour showed significant difference. Acid treatment did not change the surface area but reduced the functional groups while basic treatment significantly enhanced the surface area in microporous section but still reduced the surface functional groups. Particle size and pH solution will also influence the adsorption capacity. The adsorption will increase with decreasing particle size for humic acid. Higher pH solution will reduce humic acid adsorption on unburned carbon. Ionic strength will also affect humic acid adsorption showing positive effect on adsorption capacity.     

Modified activated carbons for catalytic wet air oxidation of phenol

This study aims at testing several activated carbons for the catalytic wet air oxidation (CWAO) of phenol solutions. Two commercial activated carbons were used both as received and modified by treatment with either HNO₃, (NH₄)₂S₂O₈, or H₂O₂ and by demineralisation with HCl. The activated carbons were characterised by measuring their surface area, distribution of surface functional groups and phenol adsorption capacity. The parent and treated activated carbons were then checked for CWAO using a trickle bed at 140 °C and 2 bar of oxygen partial pressure. The treatments increase the acidic sites, mostly creating lactones and carboxyls though some phenolic and carbonyl groups were also generated. Only (NH₄)₂S₂O₈ treatment yields a significant decrease in surface area. CWAO tests show that catalytic activity mainly depends on the origin of the activated carbon. The modifications generally had a low impact on phenol conversion, which correlates somewhat with the increase in the acidity of the carbons. Characterisation of the used activated carbon evidences that chemisorbed phenolic polymers formed through oxidative coupling and oxygen radicals play a major role in the CWAO over activated carbon.     

Surface‐Treated Activated Carbon for Removal of Aromatic Compounds from Water

Modifications of commercial activated carbons by chemical treatment with HNO₃ or HCl and HF and the adsorption behavior of simple aromatic compounds (aniline, pyridine, phenol, and benzene) on activated carbon and modified activated carbon were investigated. The results show that the textural properties change a little after these modifications, but the surface acidity (mainly oxygen‐containing groups) of activated carbon modified with HNO₃ increases greatly. The effect of ash of activated carbon on adsorption of the organic compounds mentioned above is insignificant. However, addition of surface acidity (mainly surface oxygen‐containing groups) decreases the adsorption capacity of compounds significantly. The adsorption uptake of compounds on activated carbon with oxidation of HNO₃ is low possibly due to dispersive interaction, water cluster blocking, or competition between water and compounds adsorbed on activated carbon's surface because of hydrophilic increase of the activated carbon surface. The solubility of aromatic compounds in water has an important effect on the adsorption capacity of activated carbon. q_m and K_L (Langmuir adsorption parameters) for the aromatic compounds vary similarly.