A simple isotherm equation for describing gas adsorption on heterogeneous microporous solids

A simple isotherm equation for describing gas adsorption on solids showing heterogeneity of microporous structure is proposed. It is shown that this equation gives a good representation of the experimental data of argon, nitrogen and benzene adsorption on different types of activated carbons. Its parameters may be used to characterize heterogeneity of microporous structure of the solids.

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Eine einfache Isotherme zur Beschreibung der Gas-Adsorption an heterogenen mikroporösen Feststoffen

Zusammenfassung Es wird eine einfache Isotherme zur Beschreibung der Gasadsorption an Feststoffen mit heterogener mikroporöser Struktur vorgeschlagen. Es wird gezeigt, daß diese Gleichung die experimentellen Daten für die Adsorption von Argon, Stickstoff und Benzol an verschiedenen Typen von Aktivkohle gut beschreibt. Die Parameter der Isotherme können zur Charakterisierung der Heterogenität der mikroporösen Struktur von Festkörpern herangezogen werden.

     

A simple adsorption model for ionic surfactants

In the past, few theoretical attempts have been made to describe quantitatively the adsorption of ionic surfactants at liquid interfaces. Well-known adsorption isotherms due to Frumkin or Hill–de Boer cannot respond to the specific electrostatic and geometric properties of the surfactant molecules. Our approach is based on a combination of the Gouy–Chapman theory with a modified Frumkin isotherm. The modification implies that the system is free to choose an optimal head group area and an optimal arrangement of the surfactant molecules in the interface as a function of bulk concentration. Interaction energies between neighbouring adsorbed surfactant molecules and between surfactant and water molecules are taken into consideration. The minimum of the Gibbs free energy of the system is equivalent to a minimal interfacial tension. Thus, the thermodynamically stable isotherm can be obtained as the lower envelope of the family of σ versus ln c isotherms resulting from different choices of the model parameters, including the area per molecule. According to the Gibbs equation, the Γ versus ln c adsorption isotherm is obtained as the derivative of this envelope. By variation of the model parameters, the envelope of the calculated adsorption isotherms can be fitted to experimental data of the interfacial tension versus bulk concentration. A computer program is used to calculate the σ versus c and the Γ versus ln c curves as well as to fit the parameters. Received: 28 October 1999/Accepted: 8 February 2000     

Adsorption and Equilibrium Isotherm Study of Removal of Copper (II) Ions from Aqueous Solution by Chemically Modified Abelmoschus esculentus Fibers

The present study explores surface modification of Abelmoschus esculentus by graft copolymerization reaction using acrylonitrile as a monomer and ascorbic acid/H₂O₂ as a redox initiator. Further, polyacrylonitrile grafted fibers were treated with hydroxylamine to convert the nitrile group of the grafted fiber into the amidoxime group to enhance adsorption of copper ions from wastewater. The graft copolymers and amidoximated fibers were characterized by FT-IR and FE-SEM. The effects of physicochemical parameters such as pH of the solution, initial metal ion concentration, and time on Cu(II) adsorption were studied to optimize condition for maximum adsorption. In addition, Langmuir, Freundlich, and Tempkin models were applied to describe the adsorption isotherm of Cu²⁺ ions.     

Insight into the performance of novel kaolinite-cellulose/cobalt oxide nanocomposite as green adsorbent for liquid phase abatement of heavy metal ions: Modelling and mechanism

A cost-efficient kaolinite-cellulose/cobalt oxide green nanocomposite (Kao-Cel/Co₃O₄ NC) was successfully synthesized, and utilized as a promising material for removing Pb²⁺ and Cd²⁺ from aqueous solution. The fabricated nanocomposite has been characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy-energy dispersive X-ray, high-resolution transmission electron microscopy, and Brunauer-Emmett-Teller analysis. The batch methodology was exploited for optimization of process parameters and the optimized conditions were found to be adsorbent dosage (2.0 g/L), extraction time (50 min), initial concentration (60 mg/L), and initial solution pH (6). Kao-Cel/Co₃O₄ NC displayed excellent adsorption properties and achieved maximum saturation capacity (Q_m) of 293.68 mg Pb²⁺/g and 267.85 mg Cd²⁺/g, with an equilibration time of 50 min at 323 K. The Langmuir model best expressed the isotherm data recommending the adsorption onto energetically homogeneous NC surface, while the compatibility of kinetics data with pseudo-second-order model revealed the dependency of adsorption rate on adsorption capacity, and probable involvement of chemisorption in the rate-controlling step. Electrostatic interaction and ion exchange mechanism were responsible for the uptake of Pb²⁺ and Cd²⁺ by Kao-Cel/Co₃O₄ NC as demonstrated by Fourier transform infrared spectroscopy and pH studies. Thermodynamic parameters confirmed the physical, spontaneous, and endothermic sequestration processes. Real water investigation specified that the present adsorbent could be effectively used for liquid phase decontamination of Pb²⁺ and Cd²⁺. The nanocomposite exhibited high reusability, which could be utilized efficiently for five runs with sustainable results. In summary, this study portrayed the present nanocomposite as an emerging material for the adsorption of heavy metal ions particularly Pb²⁺ and Cd²⁺.     

Heterogeneity of the surface energy on unused C18-chromolith adsorbents in reversed-phase liquid chromatography

Single-component adsorption isotherm data were acquired by frontal analysis (FA) for phenol and caffeine on a new C18-Chromolith column (Merck, Darmstadt, Germany), using a water-rich mobile phase (methanol/water, 15/85, v/v). These data were modeled for best agreement between the experimental data points and the adsorption isotherm model. The adsorption-energy distributions, based on the expectation-maximization (EM) procedure, were also derived and used for the selection of the best isotherm model. The adsorption energy distributions (AEDs) for phenol and caffeine converged toward a trimodal and a quadrimodal distribution, respectively. Energy distributions with more than two modes had not been reported before for the adsorption of these compounds on packed columns. The third high energy mode observed for both phenol and caffeine seems to be specific of the surface of the monolithic column while the first and second low energy modes have the same physical origin as the two modes detected on packed columns. These results suggest significant differences between the structures of the porous silica in these different materials.     

Studying the uptake of aniline vapor by active alumina through in-line monitoring a differential adsorption bed with near-infrared diffuse reflectance spectroscopy

Through non-invasive monitoring the uptake of aniline vapor by active alumina in a differential adsorption bed (DAB) with near-infrared diffuse reflectance spectroscopy (NIR-DRS), we have studied several features of the adsorption, including isotherm, kinetics and the chemical state of aniline molecules in aniline-alumina system. What is perhaps more important, since the information above is obtained synchronously, the proposed methodology could provide information about the type of adsorption (chemical or physical adsorption), the change of chemical state of aniline in the system during the adsorption process, whether the chemical adsorption and physical adsorption took place simultaneously, the rate of the chemical and physical adsorption, and so on.     

Evaluation of selective composite cryogel for bromate removal from drinking water

Bromate, which is a potential carcinogen, should be removed from drinking water to levels of less than 10 μg/L. A chitosan‐based molecularly imprinted polymer (MIP) and a sol–gel ion‐exchange double hydrous oxide (Fe₂O₃·Al₂O₃·xH₂O) adsorbent (inorganic adsorbent) were prepared for this purpose. The sorption behavior of each adsorbent including sorption kinetics, isotherms, effect of pH and selective sorption were investigated in detail. Sorption experimental results showed that the MIP adsorbents had better selectivity for bromate, even in the presence of high concentrations of nitrate, as compared to the inorganic adsorbent. It was found that pH does not affect the adsorption of bromate when using the inorganic adsorbent. Additionally, both adsorbents were immobilized in a polymeric cryogel inside plastic carriers to make them more practical for using in larger scale. Regeneration of the cryogels either containing MIP or inorganic adsorbents were carried out by 0.1 M NaOH and 0.1 M NaCl, respectively. It was found that the regenerated MIP and inorganic adsorbents could be used at least three and five times, respectively, without any loss in their sorption capacity.     

Tween-20与牛血清白蛋白的相互作用

通过表面张力和等温滴定量热方法，研究了非离子表面活性剂Tween-20与牛血清白蛋白(BSA)的相互作用. 结果表明，BSA与Tween-20的相互作用较弱，当Tween-20浓度增大时，能将吸附于表面上的BSA分子取代. BSA/Tween-20混合体系的性质随温度的变化趋势与单一非离子型表面活性剂相似. BSA浓度在3.7×10^-5～11.1×10^-5 kg•L^-1范围内，Tween-20的cmc不随BSA浓度的变化而变化. 当Tween-20的含量一定时，Tween-20与BSA相互作用过程的热效应也与BSA 的浓度无关. BSA/Tween-20混合体系的热力学参数表明， BSA的存在使Tween-20的cmc减小，体系的熵变增大.     

超高交联树脂对壬基酚聚氧乙烯醚的吸附机理(英文)

研究了壬基酚聚氧乙烯醚(NPEO-10)在3种具有不同比表面积和孔径大小的超高交联树脂上的吸附行为与机理.3种超高交联树脂对壬基酚聚氧乙烯醚的吸附量受它们的比表面积和孔径大小以及溶液温度的影响.壬基酚聚氧乙烯醚在3种超高交联树脂上的吸附等温线可以用Langmuir和双Langmuir模型很好地拟合,而用Freundlich模型拟合则效果不好,但这些拟合曲线都具有相似的形状.热力学分析表明吸附过程主要表现为吸附质分子的疏水部分和吸附剂表面的作用以及吸附质分子在其表面形成胶束状的聚集体,即分散的、单层及双层聚集体的混合分布.吸附动力学曲线中的两个平台也证明了吸附过程存在单层和双层聚集体.脱附研究为实现超高交联树脂吸附分离水溶液中的壬基酚聚氧乙烯醚提供了合适的操作条件.