Adsorption of valeric acid from aqueous solution onto activated carbons: role of surface basic sites

Adsorption of valeric acid was studied on two activated carbons of different origins, wood and bituminous coal. The effect of oxidation on the adsorption uptake was investigated. Both initial samples were oxidized with nitric acid, which caused the introduction of a significant number of oxygen-containing groups onto the carbon surface. Boehm titration, potentiometric titration, thermal analysis, and sorption of nitrogen were used for detailed surface characterization. Valeric acid adsorption from aqueous solution was measured at 333 K. The calculated isotherms showed a good fitting to the Freundlich equation. The capacity coefficients revealed a direct correlation with the number of basic groups present on the surface. The amount of valeric acid adsorbed at its low concentration is dependent on the number of basic groups, whereas at high concentration the amount adsorbed depends on the volume of micropores smaller than 10 A, where the adsorption potential is the strongest.     

Adsorption of strontium from aqueous solution using activated carbon produced from textile sewage sludges

Different types of activated carbons were prepared by changing the activation temperatures (400–700 °C) and impregnation ratio (sewage sludge: KOH; 1:1, 1:2) and the removal of Sr⁺² from aqueous solution was determined. The maximum adsorption yield (12.11 mg/g) was obtained at 500 °C for 1 h carbonization conditions with impregnation ratio of 1:1. The affecting parameters were analyzed by using central composite design method. The selected parameters were initial pH, temperature, initial strontium concentration and carbon dosage. The analysis of variance was performed in 95% confidence level and checked to fitting of experimental value and predicted value. The significant F was P < 0.05 with a model F value of 19.94 which revealed that this regression is statistically significant. The results of regression analysis indicated that pH and temperature parameters were not individually statistically significant for Sr⁺²sorption. However, the efficiency of strontium sorption increases with the increase in carbon dosage and decreases with the Sr⁺² concentration. Influences of initial pH and temperature, pH and Sr⁺² concentration, temperature and carbon dosage and Sr⁺² concentration and carbon dosage on the adsorption process were considered statistically significant. Adsorption of strontium was described by Freundlich isotherm as a physical adsorption (E = 7.2 kJ/mol). The adsorption reactions were calculated as endothermic, spontaneous and favorable reactions.     

Adsorption of gadolinium on activated charcoal from electrolytic aqueous solution

Adsoprtion of gadolinium on activated charcoal has been studied as a function of shaking time, pH, concentration of adsorbate and temperature. Gadolinium adsorption obeys the Langmuir isotherm. H^o and S^o were calculated from the slope and intercept of the In K_D 1/T plot. The influence of different cations and anions on gadolinium adsorption has been examined. The adsorption of other metal ions on activated charcoal has been studied under optimum conditions to check the selectivity of gadolinium adsorption. Consequently, gadolinium was removed from Ni, V, Zn, Cu, Rb, Sr and Mn. More than 97% of the adsorbed gadolinium on activated charcoal can be recovered with 35 ml of 3M HNO₃ solution. Wavelength dispersive X-ray fluorescence spectrometer was used for measuring gadolinium concentration.     

Adsorption of 18-crown-6 from aqueous solution on granular activated carbon: a kinetic modeling study

Granular activated carbon was used for the removal of 18-crown-6 from aqueous solution by adsorption. The influence of two experimental parameters, initial 18-crown-6 concentration and temperature, on the adsorption kinetics was evaluated. The kinetics data obtained were modeled by pseudo-first-order and pseudo-second-order models, respectively. The process of adsorption follows a pseudo-second-order rate model. The most important result of the present study is that the correlation coefficient is not a sufficient criterion for selection of a kinetic model, and therefore several criteria are suggested for its selection.     

Adsorption of selected herbicides from aqueous solutions on activated carbon

The adsorption of MCPA and 2,4-D on the activated carbon Filtrasorb 300 was studied. The adsorption isotherms of herbicides from aqueous solutions were measured over a wide range of solute concentrations and at different temperatures. The experimental equilibrium data were analyzed by the Langmuir–Freundlich isotherm taking into account the energetic heterogeneity of adsorption system. The effect of temperature and herbicide properties on its uptake was discussed. The thermal analysis was applied in order to find the differences in herbicide interactions with carbon surface. The kinetic dependences were measured and the relations between solute properties and adsorption rate were discussed.     

自溶液中的吸附XII.活性炭自水中吸附芳香化合物的热力学研究

测定了25℃和35℃时活性炭自水中吸附苯甲酸,邻苯二甲酸,邻羟基苯甲酸,间羟基苯甲酸,对羟基苯甲酸,苯酚和邻苯二酚共七种芳香化合物的等温线,计算了吸附过程的△G,△H和△S.七种芳香化合物的-△G都在5.9～7.7kcal.mol[-1]的范围内,差别不大;-△h都小于-△g的值;△s则都是正的。这些结果表明熵变是这类体系的吸附过程的重要驱动力,而且往往是主要驱动力,在液相吸附中,溶质的吸附必伴随着溶剂的脱附,前者是熵减少的过程,后者是熵增加的过程。因为上述芳香化合物的摩尔体积约是水(溶剂)的5～7倍,也就是说,吸附1摩尔的溶质将伴随5～7摩尔的水由表面脱附。因此,由于水的脱附引起的熵增加远远超过溶质吸附所引起的熵减少,这可以解释为何这类体系的吸附过程的熵变总是相当大的正值,根据这个理论,可以设想倘若溶剂的摩尔体积与溶质的相近或比溶质的更大时,吸附过程的熵变可能出现负值,文献中的一些数据支持了这一推测。     

Adsorption of phenol on supercritically activated carbon fibres: effect of texture and surface chemistry

The influence of texture and surface chemistry on the phenol adsorption capacity of activated carbon fibres (ACFs) was studied. ACFs were prepared by carbonization of a phenolic textile fibre under nitrogen flow, followed by activation with H(2)O and CO(2) (under atmospheric pressure and supercritical state). The materials were characterised by N(2) and CO(2) adsorption, and by temperature programmed desorption studies. A strong correlation between the amount of adsorbed phenol and the micropore volume has been observed. The relationship between surface oxygen concentration and amount of physisorbed and chemisorbed phenol was assessed, and it was shown that higher amounts of surface oxygen groups decreased the phenol chemisorption capacity of ACFs.     

Adsorption of roxarsone from aqueous solution by multi-walled carbon nanotubes

Molecularly imprinted particle for bisphenol A (BPA-MIP) was prepared using the surface molecular imprinting technique with a sol-gel process on the surface of silica nanoparticles. The dosages of diethylenetriaminepentaacetic acid (DTPA) as a functional monomer and teraethyl orthosilicate (TEOS) as a cross-linker were optimized, respectively. The prepared BPA-MIP was characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared spectrometer (FTIR), thermogravimetric analysis (TGA), and a standard Brunauer-Emett-Teller (BET) analysis. Moreover, the proper binding and selective recognition ability were also investigated by a single batch binding experiment. The equilibrium data fitted well to the pseudo-second-order kinetic and the Langmuir model for BPA binding onto BPA-MIP, respectively. The saturate binding capacity of BPA-MIP was found to be 30.26 μmol g(-1), which was three times higher than that of BPA non-molecular imprinted particle (BPA-NIP). The satisfactory results demonstrated that the obtained BPA-MIP showed an appreciable binding specificity toward BPA than similar structural compounds in water phase. The BPA-MIP could serve as an efficient selective material for determining or removing BPA from water environment.     

A radiotracer study of adsorption on activated carbon cloth from aqueous solution

A study has been made on the effect of pH upon the equilibrium adsorption capacity of triethyl phosphate, dimethyl phosphate and orthophosphate on to activated carbon cloth. It is shown that for molecular phosphates no dependence upon pH exists, whilst the adsorption of ionic phosphates exhibit a strong pH dependence. These adsorption trends may be explained in terms of pKa values, ionic strength and the surface charge of the activated carbon cloth is aqueous solution.     

Adsorption of methyl mercaptan on surface modified activated carbon

The influence of surface modification of activated carbon on the adsorption of methyl mercaptan in N(2) was investigated. The modification of the activated carbon was carried out by treatment with HNO(3)/H(2)SO(4) solutions, heat-treatment in Ar, and adsorption of cetylamine. Acid-treatment increased the adsorption of methyl mercaptan compared with the original activated carbon, and the adsorbed amounts increased with ratio of H(2)SO(4) in HNO(3)/H(2)SO(4) solutions. This result suggests that hydrogen bonding between acidic groups formed by acid-treatment and thiol groups of methyl mercaptan plays a role in adsorption of methyl mercaptan on activated carbon.     

Adsorption of uranium from crude phosphoric acid using activated carbon

The adsorption of uranium from crude phosphoric acid has been investigated using conventional activated carbons. It was found that treatment with nitric acid oxidized the surface of activated carbon and significantly increased the adsorption capacity for uranium in acidic solutions. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated. Equilibrium data were fitted to a simplified Langmuir and Freundlich isotherms for the oxidized samples which indicate that the uranium adsorption onto the activated carbon fitted well with Langmuir isotherm than Freundlich isotherm. Equilibrium studies evaluate the theoretical capacity of activated carbon to be 45.24 g kg^?1.     

Adsorption of phenylalanine from aqueous solution onto active carbon and silica gel

The adsorption isotherms of phenylalanine from aqueous solution on active carbon andsilica gel at varying pH,and the influence of inorganic salt upon the ad rption have been studied(at 25℃).The adsorption amount of phcnylalanine on the silica gel is very low due to the strong ad-sorption of water by silica gel.The results on the active carbon show:(1)The adsorption is found to bepH-dependent,within pH 4.1—5.1 it increases with pH,within pH 5.1—11.8 it decreases with pH,atpH 5.1 the adsorption reaches its maximum;(2)The phenylalanine is adsorbed mainly in the formof zwitterion;(3)A certain amount of cations and anions of phenylalanine are also adsorbed with vander Waals interaction;(4)After adding NaCl,the adsorption of phenylalanine increases markedly.     

Removal of 2.4-dichloro phenoxyacetic acid from aqueous solution by adsorption on activated carbon. A kinetic study

The sorption of 2.4-dichloro phenoxyacetic acid (2.4-D) on two different activated carbons was determined using the batch equilibration technique. The calculated slopes of the Freundlich sorption isotherms were significantly less than 1. The (K) values were higher for the activated carbon which has the higher specific surface, and increased with NaCl concentration. The rate of attaining equilibrium of 2.4-D increased with a decrease in absorbent concentration. Dynamic modelling of the adsorption showed that a first order reversible kinetic model was followed for the adsorption process. The overall rate constant K′, the adsorption rate K₁, the desorption rate constant K₂, and the equilibrium constant K_c for the adsorption process were calculated.     

Kinetics and thermodynamic study of aniline adsorption by multi-walled carbon nanotubes from aqueous solution

Multi-walled carbon nanotubes (MWCNTs) were used in the adsorptive removal of aniline, an organic pollutant, from an aqueous solution. It was found that carbon nanotubes with a higher specific surface area adsorbed and removed more aniline from an aqueous solution. The adsorption was dependent on factors, such as MWCNTs dosage, contact time, aniline concentration, solution pH and temperature. The adsorption study was analyzed kinetically, and the results revealed that the adsorption followed pseudo-second order kinetics with good correlation coefficients. In addition, it was found that the adsorption of aniline occurred in two consecutive steps, including the slow intra-particle diffusion of aniline molecules through the nanotubes. Various thermodynamic parameters, including the Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°), were calculated. The results indicated that the spontaneity of the adsorption, exothermic nature of the adsorption and the decrease in the randomness reported as ΔG°, ΔH° and ΔS°, respectively, were all negative.     

Adsorption of Cu(II) ions from aqueous solution by hazelnut husk activated carbon prepared with potassium acetate

Hazelnut husk (HH), an agricultural waste, was converted to carbonaceous material by chemical activation using potassium acetate. The produced activated carbon (KAHHAC) was characterized by FTIR, SEM, N₂ adsorption–desorption experiments, CHN elemental analysis, and determination of moisture, ash, and point of zero charge. KAHHAC was used for the batch adsorption of Cu(II) ions from aqueous solutions. Optimum pH and contact time were found to be 5.0 and 240 minutes, respectively. The adsorption equilibrium data were described well by the Langmuir equation providing 105.3?mg?g^?1 Cu(II) adsorption capacity. The pseudo-second-order model successfully described the kinetic of Cu(II) adsorption by KAHHAC. The adsorbed Cu(II) onto KAHHAC was completely desorbed by 0.5?M nitric acid. In conclusion, HH activated carbon (AC) produced by the potassium acetate activation method is a very useful and efficient sorbent material for the removal of Cu(II) from aqueous solution.     

Adsorption of uranium from aqueous solution using HDTMA+-pillared bentonite: isotherm, kinetic and thermodynamic aspects

The ability of hexadecyltrimethylammonium cation pillared bentonite (HDTMA⁺-bentonite) has been explored for the removal and recovery of uranium from aqueous solutions. The adsorbent was characterized using small-angle X-ray diffraction, high resolution transmission electron microscopy, and Fourier transform infrared spectroscopy. The influences of different experimental parameters such as solution pH, initial uranium concentration, contact time, dosage and temperature on adsorption were investigated. The HDTMA⁺-bentonite exhibited the highest uranium sorption capacity at initial pH of 6.0 and at 80?min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, ??G° (308?K), ??H°, and ??S° were determined to be ?31.64, ?83.84?kJ/mol, and ?169.49?J/mol/K, respectively, which demonstrated the sorption process of HDTMA⁺-bentonite towards U(VI) was feasible, spontaneous, and exothermic in nature. The adsorption on HDTMA⁺-bentonite was more favor than Na-bentonite, in addition the saturated monolayer sorption capacity increased from 65.02 to 106.38?mg/g at 298?K after HDTMA⁺ pillaring. Complete removal (??100%) of U(VI) from 1.0?L simulated nuclear industry wastewater containing 10.0?mg U(VI) ions was possible with 1.5?g HDTMA⁺-bentonite.     

Adsorption of naphthalene on zeolite from aqueous solution

Polynuclear aromatic hydrocarbons (PAHs), which are environmental hormones and carcinogens, are viewed as the priority pollutants to deal with by many countries. Most PAHs are hydrophobic with high boiling and melting points and high electrochemical stability, but with low water solubility. Compared with other PAH species, naphthalene has less toxicity and is easily found in the environment. Thus, naphthalene is usually adopted as a model compound to examine the environmental and health aspects of PAHs. This study attempted to use an adsorption process to remove naphthalene from a water environment. The adsorption equilibrium of naphthalene on zeolite from water-butanol solution, which is a surfactant-enriched scrubbing liquid, was successfully evaluated by Langmuir, Freundlich, and linear isotherms. Among the tested kinetics models in this study (e.g., pseudo-first-order, pseudo-second-order, and Elovich rate equations), the pseudo-second-order equation successfully predicted the adsorption.     

Dispergation and modification of multi-walled carbon nanotubes in aqueous solution

Multi-walled carbon nanotubes (MWCNTs) are widely applied in development of composite materials. However, their properties are directly influenced by the degree of uniformity of dispersion of MWCNTs in the material’s matrix. In this paper, the dispersing of raw MWCNTs (R-MWCNTs) and decorated MWCNTs (D-MWCNTs) was studied in aqueous solution. The D-MWCNTs were obtained by chemical modification method by treatment of initial MWCNTs with the mixture of concentrated nitric and sulfuric acids (3: 1 vol/vol). To achieve a good dispersion of the MWCNTs, a method utilizing ultrasonic processing and surfactant (polyvinylpyrrolidone, PVP) was employed. MWCNTs were characterized by Fourier transform infrared spectroscopy (FT–IR) and X-ray diffraction (XRD). The prepared MWCNTs suspensions were investigated by UV spectroscopy, zeta potential measurements, surface tension and transmission electron microscopy (TEM). The D-MWCNTs have better dispersibility in aqueous solution; this attributed to the functional groups formed on their surface during chemical modification. The PVP surfactant in a certain concentration of 0.6 g/L has the maximum dispersing effect on MWCNTs in aqueous solution, the optimum concentration ratio of PVP and MWCNTs was 3: 1.     

Adsorption of chromium ions from aqueous solution by using activated carbo-aluminosilicate material from oil shale

A novel activated carbo-aluminosilicate material was prepared from oil shale by chemical activation. The chemicals used in the activation process were 95 wt% sulfuric and 5 wt% nitric acids. The produced material combines the sorption properties and the mechanical strength of both activated carbon and zeolite. An X-ray diffraction analysis shows the formation of zeolite Y, Na-X, and A-types, sodalite, sodium silicate, mullite, and cancrinite. FT-IR spectrum shows the presence of carboxylic, phenolic, and lactonic groups on the surface of this material. The zero point of charge estimated at different mass to solution ratio ranged from 7.9 to 8.3. Chromium removal by this material showed sorption capacity of 92 mg/g.