Hydrogen adsorption on activated carbons prepared from olive waste: effect of activation conditions on uptakes and adsorption energies

Two series of activated carbon samples have been prepared from olive waste, using ZnCl₂ and H₃PO₄ as chemical activation agents. The porous structure characteristics of all samples are determined by nitrogen adsorption at ?196 °C. Hydrogen adsorption at ?196 °C is followed using both manometry and calorimetry. The results show that the highest areas are observed for the samples prepared with larger diameter of precursors and that the hydrogen uptake is strongly influenced by the available BET area. Furthermore, the adsorption energies do not vary significantly for any activation protocol and therefore seem to play only a minor role to the hydrogen adsorption behavior. However, the chemical activation does have a strong role on hydrogen uptake. Samples prepared with H₃PO₄ show a greater hydrogen uptake per unit area such that comparable uptakes are observed for the samples prepared with larger diameter of precursor even though the sample prepared with ZnCl₂ shows a 30 % higher BET area. This work highlights the non-trivial role of each activation protocol on hydrogen uptake.     

Comparison study of naphthalene adsorption on activated carbons prepared from different raws

Five activated carbons (ACs) from apricot shells (ACAS), mixture of lignin and cellulose (ACLC), wood (ACW), walnut shells (ACWS), and coal (CAC) were prepared and used as adsorbents to study the adsorption behavior of naphthalene. All ACs were characterized by scanning electron microscopy, N2 adsorption-desorption method, Xray photoelectron spectroscopy, and elemental analysis. The effects of initial concentration, contact time, ionic strength, pH, and temperature on the adsorption of ACs for naphthalene were examined. Results show that CAC exhibit higher micropore specific surface area and contain more C-O bond than other ACs. Except for ACW, CAC is the least polar or the most hydrophobic adsorbent among ACs. This finding may be helpful in the formation of hydrogen bonding between CAC and naphthalene. The adsorption quantity of CAC was 227.03mg g^-1 at 303 K, which was considerably higher compared with that of other ACs. The kinetics process of naphthalene on all ACs was controlled by pseudo-second-order kinetic model. The adsorption equilibrium of naphthalene on ACs was reached at 40min. The adsorption isotherms of naphthalene to ACs were consistent with the Freundlich isotherm model. The result of thermodynamic analysis shows that the adsorption occurs spontaneously. Moreover, the higher starting naphthalene concentration and lower adsorption temperature significantly can enhance the adsorption capacity of CAC. The maximum adsorption value of naphthalene on ACs was also observed at pH 4 under the same conditions. Moreover, the increase in ionic strength slightly promotes the adsorption of naphthalene on ACs. The microporous structure, element content and surface functional group of ACs affect its adsorption capacity.     

Enhanced mercury adsorption in activated carbons from biomass materials and waste tires

Agricultural residues and waste tires constitute an important source of precursors for activated carbon production. Activated carbons offer a potential tool for mercury emissions control. In this work, pine and oak wood, olive seed and tire wastes have been used for the preparation of activated carbons, in order to be examined for their mercury removal capacity. In the case of activated carbons produced from pine/oak woods and tire wastes, a two stage physical activation procedure was applied. Activated carbons derived from olive seeds were prepared by chemical activation using KOH. Pore structure of the samples was characterized by N₂ and CO₂ adsorption, while TPD-IR experiments were performed in order to determine surface oxygen groups. Hg° adsorption experiments were realized in a bench-scale adsorption unit consisting of a fixed-bed reactor. The influence of activation technique and conditions on the resulted activated carbon properties was examined. The effects of pore structure and surface chemistry of activated carbons were also investigated. Activated carbons produced from olive seeds with chemical activation possessed the highest BET surface area with well-developed micropore structure, and the highest Hg° adsorptive capacity. Oxygen surface functional groups (mainly lactones) seem to be involved in Hg° adsorption mechanism.     

Application of different equations to adsorption isotherms of phenolic compounds on activated carbons prepared from cork

Activated carbons were prepared from solid cork wastes by physical activation with carbon dioxide or steam, and chemical activation by impregnation with phosphoric acid. In this work we show the possibility of using these activated carbons for the adsorption of phenolic compounds from the aqueous phase. The materials present a different response to the adsorptives used (p-nitrophenol, p-chlorophenol, p-cresol and phenol), depending on the type of activation and the parameters (burn-off, absolute concentration) used in each case. All the samples were capable of retaining the contaminants, with the best result being reached by the sample with higher burn-off and the worst with the carbonised, while intermediate values were reached with the remaining samples. The experimental isotherms were analysed with two and three parameters equations (Freundlich, Langmuir, Dubinin-Radushkevich-Kaganer and Redlich-Peterson). The results obtained from the application of the equations are similar in some aspects, but the degree of confidence is quite different. The best fit was achieved with the Redlich-Peterson equation, which can be explained by the fact that this has three adjustable parameters. However, overall the Freundlich and DRK equations appear to be more useful and provide parameters which can be correlated with the structural characteristics of the solids obtained from N₂ adsorption measurements.     

Liquid-phase adsorption of phenol by activated carbons prepared from bituminous coals with different oxygen contents

Activated carbons prepared from two bituminous coals were used to adsorb phenol in aqueous solutions. The major difference between the coal precursors is the oxygen content. The carbon preparation consisted of carbonization of the coals followed by activation in CO ₂ to various extents of burn-off. Experimental results show that the amount of phenol adsorbed generally increases with the BET surface area of the carbon. The carbons prepared from the coal with a higher oxygen content have larger surface areas, and, therefore, exhibit higher capacities for phenol. The surface area of the carbon increases with the extent of carbon burn-off, whereas the increase in the adsorptive capacity due to the increasing burn-off level does not show a linear relationship with the increase in area; the ratio of the capacity to BET surface area is not constant and decreases with the burn-off level. This has been attributed to the accessibility of phenol to the surface being affected by the length of diffusion path, which is an increasing function of the burn-off level or the particle size. The amount of phenol adsorbed decreases with the temperature for these carbons. It was found, according to the Langmuir model, that the adsorption process was significantly affected by the oxygen content in the coal precursors. © 1999 Society of Chemical Industry     

油茶果壳活性炭对铜离子的动态吸附

利用油茶果壳活性炭填料柱对水中铜离子进行动态吸附。探讨了pH值、初始质量浓度、床层高度等因素对穿透曲线的影响。结果表明,油茶果壳活性炭能有效去除水中的铜离子,随着床层高度的增高、pH的增大和初始浓度的减小,油茶果壳活性炭填料柱对水中铜离子的吸附穿透曲线位点向右移。通过数学模型得到的速率常数、相关系数、平衡吸附量和动力学参数,能较好地描述油茶果壳活性炭填料柱吸附铜离子的吸附动力学。     

Textural characteristics of activated carbons prepared from agricultural residues-review

Agricultural residues are the most available biomass resources in the world and can be exploited to produce various activated carbons at low cost. The textural properties of activated carbon, including surface area, pore size, pore size distribution, and certain surface functionalities are the main factors in the application of bio-based electrode materials for energy storage devices and electrochemical catalyst for CO₂ reduction reactions, gas adsorption and separation, in water and wastewater treatment. This paper reviews the physical characteristics of activated carbons produced from various biomass resources using different methods. The effects of different activation methods, sources of biomass, and other parameters on the surface properties such as specific surface area and pore volume of activated carbon are discussed. The differences in the characteristics of activated carbon made from different agricultural biomass resources under the same parameters are evaluated. Eventually, the application of abundant agricultural residues for fabricating supercapacitors' electrode materials is also discussed.     

Mercury (II) adsorption by activated carbon made from sago waste

The preparation of activated carbon (AC) from sago industry waste is a promising way to produce a useful adsorbent for Hg (II) removal, as well as dispose of sago industry waste. The AC was prepared using sago industry waste with H₂SO₄ and (NH₄)₂S₂O₈ and physico-chemical properties of AC were investigated. Adsorptive removal of mercury (II) from aqueous solution onto AC prepared from sago industry waste has been studied under varying conditions of agitation time, metal ion concentration, adsorbent dose, particle size and pH to assess the kinetic and equilibrium parameters. Adsorption equilibrium was obtained in 105 min for 20 mg l⁻¹ and 120 min for 30, 40, and 50 mg l⁻¹ Hg (II) concentrations. The Langmuir and Freundlich equilibrium isotherm models were found to provide an excellent fitting of the adsorption data, with r² 0.9999 and 0.9839, respectively. The adsorption capacity of Hg (II) (Q_o) obtained from the Langmuir equilibrium isotherm model was found to be 55.6 mg g⁻¹ at pH 5.0 for the particle size range of 125-250 μm. The percent removal increased with an increase in pH from 2 to 10. This adsorbent was found to be effective and economically attractive.     

Adsorption of Hg(II) ions from aqueous chloride solutions using powdered activated carbons

Activated carbons were developed from Casurina equisetifolia leaves, by chemically treating with sulfuric acid (1:1) or zinc chloride (25%), at low (425 °C) and high (825 °C) temperatures. The resulting powdered activated carbons were applied for removing mercuric ions from aqueous solution at different agitation times and mercuric ion concentrations. The equilibrium data fitted well the Langmuir adsorption isotherm. The Langmuir adsorption capacities were 12.3 and 20.3 mg g⁻¹ for low temperature carbons and 43.9 and 38.5 mg g⁻¹ for high temperature carbons impregnated with H₂SO₄ and ZnCl₂, respectively. Studies of the effects of carbon dosage, NaCl concentrations and solution pH values were carried out for the more effective, high temperature carbons. Increasing NaCl concentration resulted in a significant decrease in the adsorption efficiency. Adsorption was high from solutions with low and neutral pH values and lower for solutions with alkaline pH values for the high temperature carbons.     

Iodine adsorption and structure of activated carbons

Studies were conducted on the adsorption of iodine from saturated aqueous solutions and from saturated vapor by eight activated carbons of greatly diverse pore structures. Water adsorption data were used to determine the pore size distribution curves which provided both the distributions of the pore constriction (desorption) and cavity (adsorption) diameters. Adsorption from aqueous phase formed a unimolecular layer on the carbon surface while adsorption from saturated vapor produced pore-filling of micropores (pores less than 30 Å diameter) and surface coverage of the macropores. A great deal of steric interference was present because of the small difference in the diameter of iodine molecule (4.94 Å) relative to the 10–30 Å diameter pores. Good correlation was attained between adsorption and pore structure when corrections were made for the steric effect and the mean diameter distributions of the constrictions and cavities were used. The model for the iodine-on-carbon adsorption resembles packing of spheres into cylinders.     

Cationic dyes removal by multilayer adsorption on activated carbons from lignin

The adsorption of two cationic dyes: fuchsine (FS) and malachite green (MG), from aqueous solutions has been studied using activated carbons (ACs) prepared from eucalyptus kraft lignin. The great specific surfaces of these activated carbons have led to high capacities of adsorption in the equilibrium. They were in the ranges from 1.8 to 3 mmol/g for FS, and 1.7 to 4 mmol/g for MG. The Guggenheim–Anderson–de Boer isotherm model has been applied to explain the experimental data. We have developed the thermodynamic studies from the equilibrium data. Both the first and the second adsorption layers involved apparent endothermic physical adsorption processes. The kinetic tests ranged the main variables. The ACs showed high adsorption rates and yields for the first 10 min of contact time suggesting interesting practical possibilities to be used at a field scale. A hyperbolic equation has been used to reproduce the experimental decay curves. Because of the controlling mass transfer inside the pores, the effective diffusivities were very low, in the range from 10⁻¹³ to 10⁻¹¹ cm²/s. Their estimated values have been reported for various selected cases.     

生物质和煤基活性炭制备过程的活化特性比较

分别以稻壳、木屑及褐煤为原料用水蒸气活化法制备了活性炭,比较了所得活性炭的吸附性能和炭化料的反应活性,探明了造成不同原料活化特性差异的原因。结果表明,活化过程中生物质原料的反应活性优于褐煤,炭化料的活化速率遵循脱灰稻壳>木材炭化料>稻壳炭化料>褐煤炭化料。通过对炭化料进行元素分析、气化反应活性分析、BET、SEM、XRD、FTIR、XPS等物理和化学性质的表征,揭示了不同原料表现出不同活化特性的原因。结果表明,在相同炭化和活化条件下,原料挥发分越高,灰分越低,炭化料有机含氧量越高,则水蒸气的活化速率越快,更容易在短时间内制备出高性能的活性炭。     

Study of cobalt adsorption from aqueous solution on activated carbons from almond shells

The adsorption of cobalt from aqueous solutions in a series of activated carbons obtained from almond shells has been studied. The chemical nature and textural characteristics of those activated carbons were investigated. Both surface basicity and porosity increase with increasing activation time. The cobalt uptake on those activated carbons also increases with the activation time. A great enhancement of the cobalt uptake was found when those activated carbons were treated with concentrated nitric acid. The influence of the pH on the cobalt adsorption process was also studied.     

Synthesis and characterization of activated carbons prepared from benzene CVD on zeolite Y

Microporous activated carbons were prepared using zeolite NaY as the template and benzene as the carbon precursor. Chemical vapor deposition of benzene was conducted in the temperature range of 600–950 °C and under different flow rates of benzene. The structural properties of the derived carbons were characterized with various experimental techniques. It was found that the CVD temperature of 650 °C results in carbons with the highest surface area of 1,511 m²/g, a pore volume of 0.93 cm³/g, and a good structural regularity. The higher CVD temperatures (e.g. ~900 °C) were found to result in carbons with lower surface area and poor structural regularity. The increased benzene flow rate will result in carbons with lower surface area and larger pore sizes.     

微生物法处理含铬废水

采用大肠杆菌对含铬废水进行生物处理，研究其在不同条件下除铬(Ⅵ)的能力。实验结果表明，该菌的适用范围广，处理含铬废水功能强。在菌废比为1：1时，温度为37℃，pH值在7左右，48h后对100mg/L的含铬废水去除率可达99％。     

Mechanisms of Cr(VI) removal from water by various types of activated carbons

The removal mechanisms of Cr(VI) from water using different types of activated carbons, produced from coconut shell, wood and dust coal, were investigated in this project. Different types of activated carbons have different surface characteristics. The coconut shell and dust coal activated carbons have protonated hydroxyl groups on the surface (H‐type carbons), while the surface of the wood‐based activated carbon has ionised hydroxyl groups (L‐type carbons). The adsorption kinetics of chromium onto the activated carbons at pH values ranging from 2 to 6 were investigated. It was found that the optimum pH to remove total chromium was 2 for wood‐based activated carbon, while for coconut shell and dust coal activated carbons, the optimum pH was around 3–4. The difference in the optimum pH for different activated carbons to remove Cr(VI) from water can be explained by the different surface characteristics and capacity of the activated carbons to reduce Cr(VI) to Cr(III). © 1999 Society of Chemical Industry     

Influence of activated carbons porous structure on iopamidol adsorption

In the present study the adsorption of iopamidol (a pharmaceutical compound used in soft tissues diagnostic imaging based on X-ray radiography) onto activated carbons was assessed, since this is an effective technology to remove pharmaceutical compounds that fail to be degraded in conventional wastewater treatments. Three sisal-based carbons prepared by chemical activation with KOH, and two commercial carbons, were selected in order to understand the role of the porous structure in the removal of iopamidol from aqueous phase. The kinetic and equilibrium adsorption results indicate that iopamidol is adsorbed in mesopores and also in larger micropores (supermicropores). The adsorption isotherms reflect a complex mechanism originating unusual two-step isotherms, which highlights the influence of the porous structure. As proven using conductivity measurements and computational calculations, iopamidol can be adsorbed as a single molecule or in the form of aggregates, filling either small or much larger pores in a discontinuous way. By conjugating the molecular dimensions of the iopamidol species and the micropore size distribution of the samples, it was demonstrated that the unusual two-step isotherms are related with the absence of pores with width between 1.2 and 2.0 nm.