Effect of surface modification of an engineered activated carbon on the sorption of 2,4-dichlorophenoxy acetic acid and benazolin from water

The performance of a conventional (F400) and a surface modified activated carbon (F400AN) has been investigated for the sorption of benazolin and 2,4-dichlorophenoxy acetic acid (2,4-D) from water. It was observed that the modified carbon, F400AN, which was obtained by annealing the conventional sample had a higher BET surface area (960 m2 g(-1) compared to 790 m2 g(-1)) and it had a higher proportion of micropores. This was attributed to the loss of oxygen containing functional groups during the thermal treatment. Zeta potential and pH titration measurements also showed that acidic functionality had been lost on the F400AN sample. The adsorption data were analysed and were fitted well using the Langmuir isotherm. The modified carbon marginally out-performed the conventional activated carbon for sorption of these two herbicides. Thermodynamic parameters (DeltaG0, DeltaH0, and DeltaS0) were determined and their values indicated that the sorption process was spontaneous and endothermic for both herbicides. A pseudo-second-order kinetic model was employed for analysing the kinetic data. It was concluded that the herbicide sorption process was controlled by a film diffusion mechanism.     

Adsorption of Safranin-T from wastewater using waste materials- activated carbon and activated rice husks

Textile effluents are major industrial polluters because of high color content, about 15% unfixed dyes and salts. The present paper is aimed to investigate and develop cheap adsorption methods for color removal from wastewater using waste materials activated carbon and activated rice husk-as adsorbents. The method was employed for the removal of Safranin-T and the influence of various factors such as adsorbent dose, adsorbate concentration, particle size, temperature, contact time, and pH was studied. The adsorption of the dye over both the adsorbents was found to follow Langmuir and Freundlich adsorption isotherm models. Based on these models, different useful thermodynamic parameters have been evaluated for both the adsorption processes. The adsorption of Safranin-T over activated carbon and activated rice husks follows first-order kinetics and the rate constants for the adsorption processes decrease with increase in temperature.     

Removal of nickel (II) ions from aqueous solutions using modified activated carbon: A kinetic and equilibrium study

Removal nickel from the aquatic environment is a serious environmental problem in view of public health. The present article studies the applicability of activated carbon, obtained from graphite, as a source of adsorbents to remove nickel from the aqueous polluted water. Activated carbon was obtained by steam activation of graphite and then was oxidized by nitric acid followed by modification with Tetraethylenepentamine (TEPA). The applicability of graphite activated carbon (GAC), and modified activated carbon by Tetraethylenepentamine (GACA) to remove nickel ions Ni(II) from aqueous media was studied. The effect of pH, initial concentration, contact time, and the temperature was evaluated during Ni(II) removal operating in a batch process. Experimental results show that the studied activated carbon have a good adsorption capacity for Ni(II) ions and could reduce the concentrations of it in the groundwater. A maximum removal efficient of Ni(II) was observed at 55°C. The experimental data showed an endothermic and spontaneous process, which was fitted to Langmuir isotherm. Based on our results, we can conclude that it is possible to use GAC and GACA for removing Ni(II) effectively from groundwater.     

Oxygen adsorption by fullerenes and carbon nanostructures

The dependences of oxygen sorption on time, gas pressure (up to 760 torr), and sample temperature were determined experimentally for three adsorbents (fullerene, astralene, and activated carbon). The difference in their adsorption abilities was shown to be related to the special features of their structures, primarily to the differences in surface area and pore volume. This conclusion was substantiated by X-ray studies of the structure of the powders. The characteristic heats of adsorption, specific surface areas, pore volumes and sizes, and characteristic energies of adsorption, which are responsible for the sorption properties of the adsorbents studied, were determined.     

Effect of agitation on removal of acetic acid from pretreated hydrolysate by activated carbon

The effect of agitation on the adsorption of acetic acid by activated carbon was tested utilizing an external mass transfer-diffusion model. Simulated pretreated biomass was contacted with activated carbon under prescribed conditions of temperature and agitation. Adsorption isotherm studies are presented as well as batch kinetic rate studies. Use of these data enabled the determination of isotherm constants, an external mass transfer coefficient, and an effective diffusivity for each agitation rate studied. The external film coefficient results ranged from 33.62 μm/s to a complete absence of external mass transfer resistance, and the diffusivity results ranged from 0.8625 to 10.70 μm²/s. The optimum combination of no external film resistance, and highest diffusivity, 10.70 μm²/s, occurred at 250 rpm and 25°C. The results of these models and the experimental parameters suggested an efficacious method and conditions for the removal of this undesirable chemical.     

Adsorption of a reactive dye on chemically modified activated carbons--influence of pH

The surface chemistry of a commercial activated carbon with a slightly basic nature was modified by appropriate treatments in order to obtain two additional samples, respectively with acidic and basic properties, without changing its textural parameters significantly. Different techniques (N2 adsorption at 77 K, temperature programmed desorption, and determination of acidity, basicity, and pH at the point of zero charge) were used to characterize the adsorbents. Kinetic and equilibrium adsorption data of a selected textile reactive dye (Rifafix Red 3BN, C.I. reactive red 241) on the mentioned materials were obtained at the pH values of 2, 7, and 12. The kinetic curves are fitted using the second-order model. The respective rate constants seem to diminish progressively with the initial concentration for the more diluted solutions tested, reaching a constant value at higher concentrations, which depends on the experimental system under consideration (adsorbent and pH). In general, the Langmuir model provides the best fit for the equilibrium data. The different uptakes obtained are discussed in relation to the surface chemical properties of the adsorbents. It is shown that the adsorption of the reactive (anionic) dye on the basic sample (prepared by thermal treatment under H2 flow at 700 degrees C) is favored. This conclusion is explained on the basis of the dispersive and electrostatic interactions involved. Moreover, it is also shown that the optimal adsorption condition for all the activated carbons tested corresponds to solution pH values not higher than the pH(pzc) of the adsorbents, which may be interpreted by taking into account the electrostatic forces present.     

Adsorption of Reactive Blue 4 dye from water solutions by carbon nanotubes: experiment and theory

Multi-walled and single-walled carbon nanotubes were used as nanoadsorbents for the successful removal of Reactive Blue 4 textile dye from aqueous solutions. The adsorbents were characterised by infrared and Raman spectroscopy, N(2) adsorption/desorption isotherms and scanning and transmission electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium isotherms at 298-323 K was fixed at 4 hours for both adsorbents. The general order kinetic model provided the best fit to the experimental data compared with pseudo-first order and pseudo-second order kinetic adsorption models. For Reactive Blue 4 dye, the equilibrium data (298 to 323 K) were best fitted to the Liu isotherm model. The maximum sorption capacity for adsorption of the dye occurred at 323 K, attaining values of 502.5 and 567.7 mg g(-1) for MWCNT and SWCNT, respectively. Simulated dyehouse effluents were used to check the applicability of the proposed nanoadsorbents for effluent treatment (removal of 99.89% and 99.98%, for MWCNT and SWCNT, respectively). The interaction of Reactive Blue 4 textile dye with single-walled carbon nanotubes (SWCNTs) was investigated using first principles calculations based on density functional theory. Results from ab initio calculations indicated that Reactive Blue 4 textile dye could be adsorbed on SWCNT through an electrostatic interaction; these results are in agreement with the experimental predictions.     

活性炭的表面化学改性及其对有机硫化物的吸附性能的研究

活性炭； 表面化学改性； 有机硫化物； 吸附性     

Speciation of some trace elements in water samples after preconcentration on activated carbon by neutron activation analysis

A new filtering column has been developed on the covalent attachment of chelating functionalities to simple, highly hydrophilic adsorbent material, which can then complex heavy metal ions irreversibly and targeted towards toxic metals removal. The capacity of the chemically modified sorbent (modified charcoal) materials used in this work was evaluated for the above mentioned heavy metal ions in the presence of iron ions and simulated water samples. The methods are based on preconcentrations of the elements of interest on activated carbon and zirconium loaded activated carbon using specific conditions of pH and oxidation states followed by a final determination by neutron activation analysis (NAA). It has been investigated that zirconium loaded activated carbon is able to adsorb As (V), Se (VI), Cr (VI) and Hg (II) at any pH while activated carbon is able to adsorb As (III), Se (IV), Cr (III) and Hg(I) at higher pH. This revised version was published online in August 2006 with corrections to the Cover Date.     

改性碳纳米管常温下吸附分离低浓度CO2

采用浸渍法将四乙烯五胺(TEPA)和三乙烯四胺(TETA)负载至碳纳米管(CNTs)上,得到一种固态胺吸附剂CNTs-TEPA和CNTs-TETA,用以吸附低浓度下的CO2.利用扫描电镜(SEM)、透射电镜(TEM)、傅里叶红外(FTIR)光谱、N2物理吸附脱附、元素分析和热重分析(TGA)等方法表征样品.结果表明:CNTs-TEPA和CNTs-TETA形态并未发生变化,仍保留CNTs规整有序的孔道结构,但样品的比表面积和孔容都显著减小.在常温条件下,CNTs-TEPA和CNTs-TETA的CO2吸附量与CNTs相比有显著提高,同时,在胺浸渍质量相同的情况下,改性后的CNTs-TEPA效果优于CNTs-TETA.温度从20℃升至30℃,CNTs-TEPA和CNTs-TETA的CO2吸附量分别从126.7、101.2mg·g-1升至139.3、110.4mg·g-1.CNTs的吸附量随着温度的增加变化不明显.最后,采用Suyadal和Yasyerli两种模型对CO2的动态吸附穿透曲线进行拟合,结果说明Yasyerli模型对CNTs、CNTs-TEPA和CNTs-TETA的CO2吸附过程的拟合程度更高.     

Characterization and metal sorptive properties of oxidized active carbon

A commercial activated carbon Chemviron F 400 has been oxidized using nitric acid in order to introduce a variety of acidic surface functional groups. Both unoxidized and oxidized carbon samples were characterized using nitrogen porosimetry, elemental analysis, pH titration, Boehm's titration, and electrophoretic mobility measurements. Results show that oxidation treatment reduced surface area and pore volume. However, the carbon surface acquires an acidic character with carboxylic groups being the dominant surface functional groups. The modified sample displays cation-exchange properties over a wide range of pH values and exhibits polyfunctional nature. Both carbon samples were challenged for the removal of transition metals such as copper(II), nickel(II), cobalt(II), zinc(II), and manganese(II). The affinity series Mn2+Zn2+ has been found to coincide with the general stability sequence of metal complexes (the Irving-Williams series). The higher preference displayed by carbons toward copper(II) is a consequence of the fact that copper(II) often forms distorted and more stable octahedral complexes.     

Adsorption of some toxic elements from water samples on modified activated carbon,activated carbon and red soil using neutron activation analysis

A simple and sensitive method for the determination of some metalloids and heavy metals in water samples is presented. The method is based on the preconcentration of the attachment of chelating functionalities with metalloids and toxic metals irreversibly and targeted towards toxic metals adsorbed on modified activated carbon, activated carbon and red soil particles at pH 3.0–9.0±0.2, followed by quantitative determination using instrumental neutron activation analysis (INAA), on the absorbers. Attachment results from attraction that may be physical, chemical, electrical, or a combination of all three. The efficient removal of metalloids and toxic metals, especially arsenic, chromium and mercury is anticipated. The adsorption capacity of the chemically modified activated carbon materials was evaluated for the above mentioned metalloid and toxic metal ions in the presence of iron ions and simulated water samples. Red soil particles containing iron was utilized in the control of oxidation-reduction reaction with metalloids and toxic metals. The preconcentration of the elements of interest on red soil particles, activated carbon and modified activated carbon at different depths, pH and oxidation states was investigated. The results obtained showed good agreement with certified values giving relative errors of less than 10%.     

Sequestration of Aqueous Lead(II) Using Modified and Unmodified Red Onion Skin

The efficacy of onion skins, both unmodified and chemically modified with thioglycolic acid, was investigated as alternative low-cost adsorbents for the sequestration of aqueous lead(II) ions from aqueous solution. The adsorbents were characterised using Fourier transform infrared spectroscopy and scanning electron microscopy – energy dispersive X-ray spectroscopy. Adsorption experiments were performed using batch sorption processes. The effects of contact time, pH, initial Pb(II) concentration, adsorbent dose, and temperature were investigated. Optimum sorption conditions were found at pH 4 and a 150?min equilibrium time for the modified onion skin and unmodified onion skin. The Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models were used to characterize the equilibrium experimental results. The equilibrium process was best described by the Freundlich isotherm. The maximum adsorption capacities of 4.878 and 6.173?mg/g were obtained for modified and unmodified adsorbents, respectively, using the Langmuir model. Kinetic studies indicated that the sorption of Pb(II) ions followed a pseudo-second-order model. Thermodynamic parameters such as standard enthalpy change (ΔH°), entropy change (ΔS°), and free energy change (ΔG°) were evaluated from the sorption experimental measurements. The results showed that the sorption process of Pb(II) ions on unmodified and modified onion skins was feasible and exothermic under the conditions used in this study. The sorption process followed the mechanism of physisorption.     

活性炭的表面处理对二苯并噻吩催化氧化脱除的影响

将一种木质活性炭经过三种表面处理,即高锰酸钾稀硫酸溶液液相氧化、浓硝酸液相氧化和350℃低温气相氧化处理。实验所选活性炭及相应的表面改性炭使用氮气吸附和Boehm滴定分别进行了结构性质和表面化学表征。研究了所选活性炭和相应的表面改性炭催化过氧化氢氧化脱除二苯并噻吩（DBT）。实验结果表明,活性炭表面化学对二苯并噻吩的氧化脱除影响很大;炭表面化学对DBT吸附脱除的影响不同于对DBT氧化脱除的影响,表面酸性越强越有利于DBT的吸附;表面羰基能加速过氧化氢产生自由基,表面羰基量的增加明显有利于DBT的氧化脱除。活性炭经过热处理后,在二苯并噻吩的氧化脱除中催化活性明显增加,正辛烷溶液中硫的体积质量从0.556g·L-1降到0.009g·L-1。     

Sorption of Tc(VII) and Am(III) by carbon materials: effect of oxidation

In this work we studied the effect of oxidation on the sorption properties of carbon materials, produced on the basic of activated carbons FAS and VSK in relation to radionuclides Am(III) and Tc(VII). It has been found that the oxidation increases the distribution coefficients for the extraction of radionuclides of sorption nitric acid raising agents. As to identify the mechanism of the oxidation influence on the sorption properties the physical and chemical properties of the synthesized samples (porous surface structure, IR-spectrums etc.) were studied. The possibility of removal of radionuclides from the real industrial solutions of complex composition using of the obtained carbon nanomaterials was investigated.     

Removal of malachite green from dye wastewater using mesoporous carbon adsorbent

Mesoporous carbon was synthesized for the removal of a cationic dye malachite green (MG) from aqueous solution. The studies were carried out under various experimental conditions such as contact time, dye concentration, adsorption dose and pH to assess the potentiality of mesoporous carbon for the removal of malachite green dye from wastewater. The sorption equilibrium was reached within 30 min. In order to determine the adsorption capacity, the sorption data were analyzed using linear form of Langmuir and Freundlich equation. Langmuir equation showed higher conformity than Freundlich equation. More than 99% removal of MG was reached at the optimum pH value of 8.5. From kinetic experiments, it was concluded that the sorption process followed the pseudo-first-order kinetic model. This study showed that mesoporous carbon can be recommended as an excellent adsorbent at high pH values.     

Preparation of a carbon-based solid acid catalyst by sulfonating activated carbon in a chemical reduction process

Sulfonated (SO(3)H-bearing) activated carbon (AC-SO(3)H) was synthesized by an aryl diazonium salt reduction process. The obtained material had a SO(3)H density of 0.64 mmol·g-1 and a specific surface area of 602 m2·g-1. The catalytic properties of AC-SO(3)H were compared with that of two commercial solid acid catalysts, Nafion NR50 and Amberlyst-15. In a 10-h esterification reaction of acetic acid with ethanol, the acid conversion with AC-SO(3)H (78%) was lower than that of Amberlyst-15 (86%), which could be attributed to the fact that the SO(3)H density of the sulfonated carbon was lower than that of Amberlyst-15 (4.60 mmol·g-1). However, AC-SO(3)H exhibited comparable and even much higher catalytic activities than the commercial catalysts in the esterification of aliphatic acids with longer carbon chains such as hexanoic acid and decanoic acid, which may be due to the large specific surface area and mesoporous structures of the activated carbon. The disadvantage of AC-SO(3)H is the leaching of SO(3)H group during the reactions.     

Thermal studies of carbonaceous electrode materials chemically modified with cyanuric chloride

A thermoanalytical investigation of chemically modified graphite and activated carbon is presented. Evaluation of thermal curves shows that radio-frequency oxygen plasma treatment is superior to electrochemical oxidation for increasing surface functional group concentrations, which when chemically reduced, can be used for cyanuric chloride binding. The amount of cyanuric chloride bound to the carbonaceous surface is determined by both potentiometric titration of hydrolyzed chloride and magnitude of weight loss at 275–290°C. The species evolved in this temperature range is identified by temperature-programmed mass spectrometry as cyanuric acid.     

Removal of aluminum from some water samples by sorptive-flotation using powdered modified activated carbon as a sorbent and oleic acid as a surfactant.

Bench-scale experiments were conducted in the laboratory, aiming to remove aluminum from water. They were based on using powdered activated carbon (PAC), which was prepared from olive stones generated as plant wastes and modified with an aqueous oxidizing agent as HNO3 as an effective sorbent and oleic acid (HOL) as a surfactant. The main parameters (namely: initial solution pHs, sorbent, surfactant and aluminum concentrations, shaking time, ionic strength and the presence of foreign ions) that influence the sorptive-flotation process were examined. Good results were obtained under the optimum conditions, according to which nearly 100% of aluminum, at pH 7 and at room temperature (approximately 25 degrees C), was removed. The procedure was successfully applied to recover aluminum spiked to some natural water samples. Moreover, a sorption and flotation mechanism is suggested.     

Heavy metals and adsorbents effects on activated sludge microorganisms

The sorption of Cu(II) and Cd(II) from synthetic solution by powdered activated carbon (PAC), biomass, rice husk (RH) and activated rice husk (ARH) were investigate under batch conditions. After activated by concentrated nitric acid for 15 hours at 60-65 degrees C, the adsorption capacity for RH was increased. The adsorbents arranged in the increasing order of adsorption capacities to the Langmuir Q degree parameter were biomass > PAC > ARH > RH. The addition of adsorbents in base mix solution had increased the specific oxygen uptake rate (SOUR) activated sludge microorganisms with and without the presence of metals. The increased of SOUR were due to the ability of PAC and RH in reducing the inhibitory effect of metals on microorganisms and provide a reaction site between activated sludge microorganisms and substrates.