Homogeneous and heterogeneous micropore structures in carbonaceous adsorbents--twenty years later

The major aim of this study is to show that, developed by Dubinin and Stoeckli, the relation between the parameters of DA (Dubinin-Astakhov) and DRS (Dubinin-Radushkevich-Stoeckli) equations is an approximation. It is shown that the parameter B(0) of DRS isotherm should be taken into account in such a relationship; strictly speaking, the parameter n(DA) of DA adsorption isotherm equation is not only the function of the dispersion of the heterogeneity of carbon, it also depends on the location of the maximum of the distribution of this heterogeneity. Moreover, taking into account that the DR isotherm rather does not describe the adsorption in a homogeneous micropore system, the analogous relationship, however, for DA adsorption isotherm as a local equation in GAI (General Adsorption Isotherm) is proposed.     

The effect of the physical and chemical characteristics of activated carbons on the adsorption energy and affinity coefficient of Dubinin equation

The dependency of adsorption energy (E) and affinity coefficient (beta) of Dubinin equations (Dubinin-Radushkevich (DR) or Dubinin-Astakhov (DA)) on surface chemistry and porosity of activated carbons was investigated by analyzing adsorption of nitrogen, benzene, trichloroethylene (TCE), and water vapor by several surface-modified activated carbons and carbon fibers. For all studied nonpolar adsorbates, carbons with smaller average micropores showed higher adsorption energies independent of their surface chemistry. For water vapor, carbons with higher surface polarities showed higher adsorption energies due to specific adsorbate-adsorbent interactions. Adsorption energies increased with decreasing average micropore widths. betaN2,DR for different carbons were observed to vary in the 0.292-0.539 range. Carbons with higher degrees of mesoporosity had higher betaN2,DR values, while no dependency was observed between betaN2,DR and surface chemistry. A comparison of DR and DA cases indicates that: (1) the average value of betaN2,DA is considerably above the classical value of this parameter; and (2) the range of betaN2,DA values were smaller compared to betaN2,DR, despite a wide range of mesoporosity of carbons examined. Obtained beta(TCE,DR) values varied in the 0.952-1.243 range, with an average value of 1.085+/-0.083, independent of surface chemistry or porosity of activated carbons. A similar result was observed for beta(TCE,DA). betaH2O,DR values of different granular and fibrous activated carbons changed in the range of 0.081-0.271. They depended more on the carbon surface chemistry and less on the porosity. A similar result was obtained when DA equation was considered.     

Detection of dopamine using self-assembled diazoresin/single-walled carbon nanotube modified electrodes

Ultrathin films of diazoresin(DR)/single-walled carbon nanotube(SWNT) were fabricated on thioglycollic acid(TGA) decorated gold(Au) electrodes by the self-assembly method combined with the photocrosslinlcing technique.The electrochemical behavior of dopamine(DA) at the DR/SWNT modified electrodes was studied using the cyclic voltammetry(CV) and differential pulse voltammetry(DPV) methods.Under the optimal conditions,a linear CV response to DA concentration from 1 μmol/L to 40 μmol/L was observed,and the detection limit of DA was 2.1 ×10~(-3) μmol/L via the DPV method in the presence of 10 μmol/L of uric acid(UA) or 2.5 × 10~(-3) μmol/L via the DPV method in the presence of10 μmol/L of ascorbic acid(AA).Moreover,the modified electrodes exhibited good reproducibility and sensitivity,demonstrating its feasibility for analytical purposes.     

Adsorption of 1-tetradecene/dodecane mixtures on different types of zeolites

The influence of heterogeneity parameters on the shape of excess adsorption isotherms has been discussed. These isotherms have been calculated according to the equations corresponding to different energy distributions. Next, the isotherm equations have been applied to examine the experimental excess isotherms for 1-tetradecene/dodecane mixture adsorption on different types ofX-zeolites at 293 K, 313 K and 333 K. The zeolite samples have been prepared from NaX-zeolite by exchanging the sodium ions for ions of alkalines and calcium group. Analysis of the above adsorption data by means of different isotherm equations showed that the parameters of aDubinin-Radushkevich-type equation change correctly with temperature and the contents of alkalines in the zeolite samples.     

Nafion修饰电极计时电位溶出法测定多巴胺的研究

本文提出了Nafion 修饰电极计时电位溶出分析方法,讨论了测定多巴胺(DA)的实验条件,研究了修饰电极的富集作用及其电极反应机理。去甲肾上腺素(NE)、抗坏血酸(AA)等均不干扰测定DA,选择性好。     

改性土壤对水中苄黄隆的吸附行为研究

研究了季铵盐阳离子表面活性荆四甲基铵离子(TMA)和十六烷基三甲基铵离子(HDTMA)改性的黄土l,黄土2，沉积物对水中苄黄隆的吸附作用．结果表明：改性后土壤对苄黄隆的吸附能力提高．同时考察了改性土壤对苄黄隆吸附的热力学行为．结果表明：HDTMA改性的土壤对苄黄隆的吸附等温线为线性，吸附类型以分配为主．HDTMA改性黄土1吸附热为-6．12kJ/mol，HDTMA改性黄土2的吸附热为-8．44kJ/mol。HDTMA改性沉积物的吸附热为-4．04kJ／mol．结合力以疏水作用力为主：TMA改性的土壤对苄黄隆的吸附等温线符合Freundlich方程．考察了溶液pH对吸附量的影响．结果表明在酸性条件下．改性土壤的吸附能力较大．     

Removal of dyes from colored textile wastewater by orange peel adsorbent: equilibrium and kinetic studies

The use of low-cost and ecofriendly adsorbents has been investigated as an ideal alternative to the current expensive methods of removing dyes from wastewater. Orange peel was collected from the fields of orange trees in the north of Iran and converted into a low-cost adsorbent. This paper deals with the removal of textile dyes from aqueous solutions by orange peel. Direct Red 23 (DR23) and Direct Red 80 (DR80) were used as model compounds. The adsorption capacity Q0 was 10.72 and 21.05 mg/g at initial pH 2. The effects of initial dye concentration (50, 75, 100, 125 mg/l), pH, mixing rate, contact time, and quantity of orange peel have been studied at 25 degrees C. The Langmuir and Freundlich models were used for this study. It was found that the experimental results show that the Langmuir equation fit better than the Freundlich equation. The results indicate that acidic pH supported the adsorption of both dyes on the adsorbent. Orange peel with concentrations of 8 and 4 g/l has shown adsorption efficiencies of about 92 and 91% for DR23 and DR80, respectively. Furthermore, adsorption kinetics of both dyes was studied and the rates of sorption were found to conform to pseudo-second-order kinetics with a good correlation (R > or = 0.998). Maximum desorption of 97.7% for DR23 and 93% for DR80 were achieved in aqueous solution at pH 2. Finally, the effect of adsorbent surface was analyzed by scanning electron microscope (SEM). SEM images showed reasonable agreement with adsorption measurements.     

Simultaneous determination of dopamine and ascorbic acid on poly (3,4-ethylenedioxythiophene) modified glassy carbon electrode

Detection of dopamine (DA) in the presence of excess of ascorbic acid (AA) has been demonstrated using a conducting polymer matrix, poly (3,4-ethylenedioxythiophene) (PEDOT) film in neutral buffer (PBS 7.4) solution. The PEDOT film was deposited on a glassy carbon electrode by electropolymerization of EDOT from acetonitrile solution. Atomic force microscopy studies revealed that the electrodeposited film was found to be approximately 100 nm thick with a roughness factor of 2.6 nm. Voltammetric studies have shown catalytic oxidation of DA and AA on PEDOT modified electrode and can afford a peak potential separation of ∼0.2 V. It is speculated that the cationic PEDOT film interacts with the negatively charged ascorbate anion through favorable electrostatic interaction, which results in pre-concentration at a less anodic value. The positively charged DA tends to interact with the hydrophobic regions of PEDOT film through hydrophobic–hydrophobic interaction thus resulting in favorable adsorption on the polymer matrix. Further enhancement in sensitivity to micro molar level oxidation current for DA/AA oxidation was achieved by square wave voltammetry (SWV) which can detect DA at its low concentration of 1 μM in the presence of 1000 times higher concentration of AA (1 mM). Thus the PEDOT modified electrode exhibited a stable and sensitive response to DA in the presence of AA interference.     

Dynamic Surface Tension and Adsorption Kinetics of Sodium Lignosulfonate Aqueous Solutions

In the article, the dynamic surface tension of sodium lignosulfonate (SL) aqueous solutions are investigated using an axisymmetric drop shape analysis-profile method. The data are analyzed by the Langmuir, Frumkin, modified Frumkin, and modified Flory-Huggins equations. The results indicate that the Langmuir model's results with two adjustable parameters are comparable to that of other models with three or four adjustable parameters. Based on the simplicity of simulation, the Langmuir adsorption equation is used to correlate the dynamic adsorption processing. The aggregation between SL molecules and the variation of adsorption configuration are proposed to interpret the results of dynamic surface tension.      

Energetic heterogeneity of the surface of a micro/mesoporous zeolite adsorbent

A complex approach based on treatment of calorimetric data using the Guggenheim–Andersen–de Boer and modified Jovanović equations was developed to evaluate the energetic and structural heterogeneity of microporous and mixed micro/mesoporous zeolite adsorbents. The calculated dependence of the hexane adsorption energy distribution function for the Y-US-Ex micro/mesoporous zeolite on the adsorbate pressure is in good accord with the calorimetric curves for the differential heats of adsorption, which indicates the suitability of this theoretical approach.     

Surface morphology of nanostructured polymer-based activated carbons

Complementary techniques, including nitrogen adsorption, small-angle X-ray scattering (SAXS), and atomic force microscopy (AFM), have been utilized to characterize the surface features of highly microporous carbon materials prepared from highly aromatic polymers. Nitrogen adsorption measurement interpreted by BET, DR, HK, and NLDFT methods reveals these nanostructured activated carbons exhibit a high surface area of up to 4000 m2/g, a micropore volume up to approximately 1.75 mL/g, and an average pore size of approximately 10-20 angstroms. A modified equation, based on Porod's law, the Debye-Bueche equation, and fractal dimension theories, has been proposed and successfully applied to analyze the SAXS spectra and to extract the porous texture of these unique activated carbons. AFM 3D imaging combined with the Fourier transform technique has been applied to statistically quantify pore sizes on the carbon surface.     

甲烷在活性炭上吸附平衡模型的研究

比较吸附模型分析甲烷在活性炭上吸附平衡的适用性,为吸附式天然气(ANG)的工程应用提供准确的预测模型。基于在温度268.15～338.15 K、压力0～12.5 MPa测试的甲烷在Ajax活性炭上的吸附平衡数据,选择Langmuir、Langmuir-Freundlich和Toth方程,应用非线性回归拟合方程参数后,确定绝对吸附量和甲烷吸附相态,并比较方程在不同压力区域内的预测精度。结果表明,甲烷吸附相密度随平衡温度和压力变化;由绝对吸附量确定的甲烷在Ajax活性炭上的平均等量吸附热为15.72 kJ/mol,小于由过剩吸附量的标绘结果;Langmuir、Langmuir-Freundlich和Toth方程预测结果在0～0.025 MPa的累积相对误差为6.449 8%、7.918 4%和0.910 0%,在1～10 MPa为0.491 1%、0.161 3%和0.369 4%。Toth方程在整个压力范围内的预测结果最为准确,但Langmuir-Freundlich方程在较高压力区域内具有较高的预测精度。     

Dissociative Adsorption of Water Molecules on Uncharged Surfaces of Indium(111) and Gallium

A possible mechanism of dissociative adsorption (DA) of water on the (111) surface of indium and liquid gallium is investigated within a cluster model for metal using a density functional method (B3LYP). The adsorption interaction of H and O atoms and OH group with these metals is studied. The free energy of DA of H₂ and O₂ molecules is calculated. An analysis of DA is performed both for the case of the metal/vacuum interface and with allowance made for solvation effects within a continuum approach. According to quantum-chemical calculations, DA of water on the In(111) surface is more thermodynamically probable than on gallium. In the case of indium, DA with the participation of a water dimer may have a smaller activation energy compared with DA of monomer H₂O_ads. The data obtained are used to interpret the experimentally observed nonmonotonous dependence of the work function for indium and gallium on the partial pressure of water vapor. The hypothesis about the origin of the absorption band in electroreflectance spectra for the gallium/aqueous solution interface as a result of the electron transfer from an adsorbed water molecule into the metal's conduction band is confirmed.     

Adsorption of Promethazine hydrochloride with KSF Montmorillonite

Adsorption of Promethazine hydrochloride (PHCl) onto KSF Montmorillonite from aqueous solution has been investigated. Experiments were conducted at various pH values, ionic backgrounds and solution temperatures. The pseudo-second-order equation successfully predicted the adsorption among the tried kinetics models (pseudo-first-order, pseudo-second-order and intraparticle diffusion). Langmuir, Freundlich and DR adsorption models were used to describe equilibrium isotherms and the isotherm constants were obtained. The increase in solution temperature caused a decrease in the adsorption capacity values found from Freundlich and DR isotherm. The adsorption type can be explained by combined ion exchange and physisorption. Thermodynamic parameters of adsorption of Promethazine hydrochloride (PHCl) onto KSF were also evaluated. The surface morphologies of KSF and PHCl loaded KSF were examined using a scanning electron microscope (SEM). FTIR measurements of samples were also conducted.     

吸附等温方程参数估算方法的分析

采用定容容量法,在温度6~60℃、平衡压力达106Pa的条件下,测得N2和O2在5A分子筛上系统的吸附相平衡数据。通过Langmuir和Toth等温方程关联这些相平衡数据,结果表明:线性化拟合的方法不可靠,其中用1/q~1/P形式线性化Langmuir方程,会得到误差很大的结果;用非线性法在各温度下单独拟合的等温方程和实验结果吻合很好,但是参数不符合其物理意义,进一步处理则误差较大。应当用非线性最小二乘法将所有温度下的相平衡数据一起拟合吸附等温方程。Langmuir和Toth方程都能用于描述体系的平衡吸附量随温度和压力的变化关系,而Toth方程的误差更小。     

Analytical models for describing cation adsorption/desorption kinetics as considering the electrostatic field from surface charges of particles

Surface charges of particles together with the adsorbed counter ions in diffuse layer can set up a strong electrostatic field around the particles in aqueous solution. The existent kinetic models for describing cation exchange on solid/liquid interface were either empirical or semi-empirical, and in which the electrostatic field is not considered. In this paper, as considering the important effect of electrostatic field around particles on cations adsorption/desorption, for the first time the dynamic distribution equations of cations in diffuse layer for adsorption and desorption processes in both flow method and batch technique have been established. Those equations clearly show how the cation concentration changes with time in different position of diffuse layer during the cation exchange process, and the corresponding new kinetic models have been obtained upon them. The new models indicate that, in both flow method and batch technique, for the adsorption process, experimental results should appear zero order kinetic process caused by the strong force adsorption in the initial stage of adsorption, and then transform to the first order kinetic process of the weak force adsorption; and for the desorption process, however, only first order kinetic process may exist. The new models are essentially different from the classic apparent or empirical kinetic models since all the parameters have their defined physical meanings in the new models, thus the rate parameters in the new models have the potential to theoretically predict. Theoretical analyses also indicated that, the adsorption/desorption rate in flow method experiment will be much higher than that in batch technique experiment.     

Adsorption properties of amine modified lignin-hydrogel composite for uranyl ions: Theoretical and experimental insights

A new modified material was synthesized and characterized as ethylene diamine modified (EA) Polyacrylamide (PAA)-Lignin (L). The adsorption features of EA modified PAA-L were studied for uranyl ions. The characterization experiments were evaluated by FT-IR spectroscopic techniques, scanning electron microscopy (SEM), and PZC analysis. Adsorption of UO₂²⁺ ions as a function of concentration, pH, temperature, and time of adsorption were studied. The adsorption phenomenon of UO₂²⁺ ions onto PAA-L-EA from aqueous medium was successfully evaluated by various equilibrium models such as Langmuir, Freundlich, and Dubinin-Radushkevich (DR). The (Qe) maximum adsorption capacity values for Langmuir model was calculated as 0.792 kg mol^?1 by using experimental data. The constant values of thermodynamic parameters such as (ΔG°), (ΔH°) and (ΔS°) were calculated and it has observed that the mechanism of adsorption was found compatible with endothermic and spontaneous owing to increasing disorderliness at solution/solid system. The adsorption mechanism is compatible with Elovich and intraparticle diffusion models. The power of the interaction between modified lignin and uranyl ?on was explained in the light of Hard and Soft Acid-Base Principle.     

Impact of carbon dioxide on the surface tension of 1-hexanol aqueous solutions

Effects of carbon dioxide presence on the surface tension and adsorption kinetics of 1-hexanol solutions were investigated. Experiments were performed at a range of carbon dioxide vapor pressures and varying concentrations of 1-hexanol aqueous solution. Both dynamic and steady-state surface tensions of 1-hexanol aqueous solution were found to decrease with carbon dioxide pressure, and a linear relationship was observed between the steady-state surface tension and carbon dioxide pressure. To explain the experiments, adsorption and desorption of the two species (1-hexanol and carbon dioxide) from two sides of the vapor-liquid interface were considered. A modified Langmuir isotherm, the modified Langmuir equation of state and the modified kinetic transfer equation were developed. The resulting steady-state and dynamic surface tension data were modeled using the modified Langmuir equation of state and the modified kinetic transfer equation, respectively. Equilibrium constants and adsorption rate constants of 1-hexanol and carbon dioxide were evaluated through a minimization procedure for CO₂ pressures ranging from 0 to 690 kPa. From the steady-state modeling, the equilibrium parameters for 1-hexanol and carbon dioxide adsorption from vapor phase and liquid phase were found unchanged at different pressures of carbon dioxide. From the dynamic modeling, the adsorption rate constants for 1-hexanol and carbon dioxide from vapor phase and liquid phase were found to decrease with carbon dioxide pressure. Some fluctuations in the fitting parameters of the dynamic modeling (adsorption rate constants) were observed. These fluctuations may be due to experimental errors, or more likely the limitations of the model used. A major limitation of the model is related to large differences in adsorption/desorption between initial and final stages of the process, and a single set of property parameters cannot describe both initial and final states of the system. Variations may occur depending on which set of data, of initial or final states, is used in the model predictions over the entire time range.     

Heterogeneous catalysis on solids of gases diffusing through a liquid layer,studied by inverse gas chromatography

Physicochemical parameters for heterogeneous catalytic reactions when the catalytic bed was under a liquid phase have been determined, using a non-linear adsorption isotherm by the reversed-flow version of inverse gas chromatography (RF-GC). The mathematical analysis developed in heterogeneous catalysis, mass transfer across gas-liquid boundaries, and diffusion coefficients of gases in liquids was associated with a non-linear adsorption isotherm to find the relevant equations pertaining to the problem. These equations were then used to calculate the adsorption/desorption rate constant, the rate constant for the first-order catalytic reaction and the equilibrium constant for the non-linear adsorption isotherm. The diffusion coefficients of the reactant in the liquid and gaseous phases and the partition coefficients for the distribution of the reactant between the gaseous and liquid phase were also determined.