Monolayer adsorption of hard-sphere fluids monolayer profile and adsorption isotherm

A graphical decomposition theorem is proven which allows an exact summation of the one-particle distribution function ρ₁(1). Using the superposition approximation, a monolayer density profile and adsorption isotherm are calculated numerically for krypton at 100 K. The monolayer profile illustrates the structure due to hard-sphere geometrical exclusion in the adsorbate. The adsorption isotherm is compared with one derived using the Percus-Yevick approximation.     

Kinetic and theoretical studies of metal ion adsorption in KDP solution

Metal ion adsorption in saturated aqueous potassium dihydrogen phosphate solution was analyzed using kinetic, equilibrium model and computational chemistry approaches. The isotherm constants (K_F and n) in the Freundlich model and the first order Lagergren kinetic model parameter k assist with a general understanding of the fundamental adsorption behavior of trivalent and divalent metal ions. The electrostatic force based on electrostatic potential distribution was found to be an essential feature for metal ion adsorption via a correlation between the ESP values of each metal ion and these experimental parameters.     

水合金属氧化物对氟的吸附机理研究

通过碱沉淀法制备了Ce,Al,Ni,Cu的水合氧化物,研究了它们的Langmuir吸附等温线,并利用BET法通过吸附-脱附氮气测定了其比表面积,同时对其吸附氟离子前后的变化进行了IR谱图的表征.结果表明不同水合金属氧化物具有不同的比表面积,其孔径分布也不尽相同,吸附量与比表面积之间没有直接相关的正比关系.吸附等温线均符...     

Removal of Congo red dye from aqueous solution with nickel-based metal-organic framework/graphene oxide composites prepared by ultrasonic wave-assisted ball milling

Metal-organic frameworks (MOFs) were successfully synthesized by ultrasonic wave-assisted ball milling. In the absence of organic solvent, the coupling effect of ultrasonic wave and mechanical force played an significant role in the synthesis of MOFs. Adsorption of Congo red (CR) was studied in view of adsorption kinetic, isotherm and thermodynamics. The adsorbent was carried out using X-ray diffraction (XRD), thermogravimetric analysis (TGA), N₂ adsorption-desorption isotherms, Raman spectroscopy and scanning electron microscope (SEM) methods. It was found that pseudo-second-order kinetic model and Freundlich adsorption isotherm matched well for the adsorption of CR onto nickel-based metal-organic framework/graphene oxide composites (Ni-MOF/GO). The results of the adsorption thermodynamics indicated that the adsorption process was a spontaneous and endothermic process. The adsorption capacity of graphene oxide/metal-organic frameworks (GO/MOFs) for CR reached 2489 mg/g, much higher than previous reports. It was demonstrated that an increase in the number of active metal sites can dramatically improve the adsorption capacity of dye. A suitable dry temperature is beneficial for the improvement of adsorption capacity for dye. In this paper, the adsorption results indicated that ultrasonic wave-assisted ball milling has a good prospect for synthesis of MOFs with excellent adsorption performance.     

Adsorption of Hydrogels Based on Cellulose for Cu(II) and Ni(II): Behaviors and Mechanisms

Hydrogels based on cellulose-graft-poly (acrylic acid) copolymers (C-g-AA) were synthesized by graft copolymerization in a phosphoric acid solvent. Fourier transform infrared (FT-IR) spectra confirmed the structure of the C-g-AA. The adsorption behaviors of the hydrogels for Cu(II) and Ni(II) were investigated. The results showed that their adsorption capacity increased as the initial concentrations of metal ions and the pH value of the solution increased. Freundlich and Langmuir isotherm models were employed to analyze the data from batch adsorption experiments. The results indicated that there were very good correlation coefficients for their linearized equations. The maximum adsorption amounts of the hydrogels for the metal ions, based on the Langmuir model, were 182 and 200 mg/g for Cu(II) and Ni(II), respectively. When the initial concentration of metal ions was 1000 mg/g the actual adsorption amounts of the hydrogels for Cu(II) and Ni(II) were 181 and 183 mg/g, respectively.     

Adsorption on heterogeneous surfaces: The exponential equation for the overall adsorption isotherm

The adsorption isotherm for heterogeneous surfaces can be very well approximated by the exponential higher degree polynomial of variable In (p/p₀). This equation is obtainable by statistical thermodynamics methods. On some simplifying assumptions one can obtain the Dubinin-Radushkevich and Freundlich adsorption isotherms from the exponential isotherm. The energy distribution function corresponding to the exponential adsorption isotherm can be calculated in the way analogous to that for DR isoterm.     

Optimization parameters for adsorption and desorption of Zn(II) and Se(IV) using rice husk ash: kinetics and equilibrium

An attempt at the use of rice husk ash, an agricultural waste, as an adsorbent of Zn(II) and Se(IV) from their aqueous solution is studied. Studies are carried out as a function of contact time, metal ion concentration, adsorbent dose, and pH at 25 °C. Its adsorption capability and adsorption rate are considerably higher and faster for Zn(II) ions than for Se(IV) ions. Zn(II) adsorption was found fast reaching equilibrium within ≃1 h while Se(IV) adsorption was slow reaching equilibrium within ≃100 h. The Bangham equation can be used to express the mechanism for adsorption. The experimental isotherm data were analyzed using Langmiur, Freundlich, and Temkin models. Desorption experiments were carried out using different media with a view to regenerate the spent adsorbent and to recover the adsorbed metal ion.     

Application of bifunctional Saccharomyces cerevisiae to remove lead(II) and cadmium(II) in aqueous solution

A magnetic adsorbent, EDTAD-functionalized Saccharomyces cerevisiae, has been synthesized to behave as an adsorbent for heavy metal ions by adjusting the pH value of the aqueous solution to make carboxyl and amino groups protonic or non-protonic. The bifunctional Saccharomyces cerevisiae (EMS) were used to remove lead(II) and cadmium(II) in solution in a batch system. The results showed that the adsorption capacity of the EMS for the heavy metal ions increased with increasing solution pH, and the maximum adsorption capacity (88.16 mg/g for Pb²⁺, 40.72 mg/g for Cd²⁺) at 10 °C was found to occur at pH 5.5 and 6.0, respectively. The adsorption process followed the Langmuir isotherm model. The regeneration experiments revealed that the EMS could be successfully reused.     

Silver‐capped silicon nanopillar platforms for adsorption studies of folic acid using surface enhanced Raman spectroscopy and density functional theory

The study of the interactions of folic acid (FA) with surface enhanced Raman scattering substrates is relevant for understanding its adsorption mechanism and for fabricating analytical devices for detection of malignant cells over‐expressing folate receptors. This paper presents a study of the adsorption of FA on silver‐capped silicon nanopillar substrates employing surface enhanced Raman scattering spectroscopy and density functional theory calculations. The experimentally observed vibrations from free FA and FA bound to the Ag surface display different vibrational spectra indicating chemical interaction of the molecule with the metal surface. Density functional theory calculations show that the Ag–FA interaction is primarily through the nitrogen from the pteridine ring anchoring to the Ag metal surface. To investigate the Ag–FA binding behavior further, the adsorption isotherm of FA on the silver‐capped silicon nanopillar surface is estimated. The results show a positive cooperative Ag–FA binding mechanism. That is, adsorbed FA increases the affinity of new incoming FA molecules. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermodynamics of curved boundary layers

A thermodynamic treatment of curved boundary layers is given which closely parallels the conventional theory of curved interfacial layers. The boundary analogs to the Gibbs adsorption isotherm and the Gibbs-Tolman-Koenig-Buff equation are derived.     

Synthesis of Tapioca Cellulose-based Poly(amidoxime) Ligand for Removal of Heavy Metal Ions

Poly(acrylonitrile)/cellulose block copolymer (PAN-b-cell) was prepared by using a free radical initiating process and then the nitrile functional groups of the PAN blocks of the copolymers were transformed into amidoxime ligands. The resulting poly(amidoxime) ligands could complex with heavy metal ions; for example, the reflectance spectra of the [Cu -ligand]ⁿ⁺ was found to be at the highest absorbance, about 94%, at pH 6. The pH was the key parameter for metal ions sensing by the ligand. The adsorption capacity for copper was very good, 272 mg g^?1, with a fast adsorption rate (t_1/2 = 10 min). The adsorption capacities for other heavy metal ions such as Fe³⁺, Cr³⁺, Co³⁺ and Ni²⁺ were also good, being 242, 219, 201 and 195 mg g^?1, respectively, at pH 6. The heavy metal ions removal efficiency from water was 98% at low concentration. The data proved that the heavy metal ions adsorption onto the polymer ligands were well fitted with the Langmuir isotherm model (R²>0.99), which suggests that the cellulose-based adsorbent surface namely the poly(amidoxime) ligand, was homogenous and a monolayer. The reusability was examined by a sorption/desorption process for six cycles and the extraction efficiency was determined. This new adsorbent could be reused for 6 cycles without any significant loss in its original removal function.     

Adsorption kinetics,isotherms, and thermodynamic studies for the adsorption of Pb<Superscript>2+</Superscript> and Hg<Superscript>2+</Superscript> metal ions from aqueous medium using Ti(IV) iodovanadate cation exchanger

In the current study, Ti(IV) iodovanadate cation exchanger (TIV) was synthesized and applied for the removal of Pb²⁺ and Hg²⁺ metal ions from the aqueous medium. The adsorption studies were performed by the batch techniques and adsorption parameters viz. contact time, pH, initial metal ion concentration, and temperature were also investigated. The optimum adsorption of Pb²⁺ (95 %) and Hg²⁺ (65 %) were observed at pH 6. The pseudo-second order equation represented the adsorption kinetics with high correlation coefficient. Langmuir model showed the best fitting to the isotherm equilibrium data, with a maximum adsorption capacity of 18.8 mg g^?1 for Pb²⁺ and 17.2 mg g^?1 for Hg²⁺. Furthermore, thermodynamic factors, i.e., ΔG, ΔH, and ΔS, indicated that adsorption of Pb²⁺ and Hg²⁺ onto TIV were spontaneous, endothermic, and feasible in the temperature range of 293–323 K.     

Anti-corrosive properties of natural honey on Al–Mg–Si alloy in seawater

Anti-corrosive properties of natural honey on Al–Mg–Si alloy in seawater were evaluated by potentiodynamic polarization (PP), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements. All the studied parameters showed good anti-corrosive properties against the corrosion of Al–Mg–Si alloy in the tested solution and their performance increases with corrosion resistant concentration. Polarization data indicated that natural honey is a mixed-type corrosion resistant. LPR and EIS studies showed that there were significant increases in the overall resistance after the addition of natural honey. The adsorption of natural honey on the metal surface obeys Langmuir adsorption isotherm. The analysis of morphology studies confirmed the formation of precipitates of natural honey on the metal surface, which reduced the overall corrosion reaction.     

Improvement of corrosion resistance of AA6061 alloy by tapioca starch in seawater

This study examines the use of tapioca starch for improvement of corrosion resistance of AA6061 alloy in seawater. Gravimetric, potentiodynamic polarization, linear polarization resistance and electrochemical impedance measurements were employed to study the corrosion behavior of AA6061 alloy in seawater. The electrochemical measurements for AA6061 alloy in seawater showed that the presence of tapioca starch significantly decreases the corrosion rates, corrosion current densities (i_corr), and double layer capacitance (C_dl), simultaneously increases the values of polarization resistance (R_p). The inhibition efficiencies increase with increasing of tapioca starch concentration. The Langmuir adsorption isotherm fits well with the experimental data. The nature of adsorption of tapioca starch on the metal surface has also been examined. The analysis of SEM and EDS confirmed the formation of precipitates of tapioca starch on the metal surface, which reduced the overall corrosion reaction.     

Adsorption on heterogeneous surfaces: A new method for evaluating the energy distribution function

The well-known integral representation for the overall adsorption isotherm on heterogeneous surfaces is used to calculate the differential distribution of adsorption energy. The assumption that the isotherm of Jovanovi? governs the local adsorption reduces the problem of evaluating the energy distribution to inversion of Laplace transformation.     

Effect of biotite content of hydrogels on enhanced removal of methylene blue from aqueous solution

A series of chitosan-g-poly(acrylic acid)/biotite (CTS-g-PAA/BT) hydrogels with unique clay biotite (BT) were prepared and used to remove cationic dye methylene blue (MB) from aqueous solution by batch adsorption experiments. Variables of the system including BT content, initial pH, contact time, initial concentration, and temperature affecting the adsorption efficiency of MB by CTS-g-PAA/BT hydrogels were investigated. Kinetic studies indicated that the adsorption data well followed pseudo-second-order kinetics. Langmuir and Freundlich isotherm models were applied to experimental equilibrium data of MB adsorption depending on temperature. The adsorption equilibrium data obeyed Langmuir isotherm, and the monolayer adsorption capacity calculated from the Langmuir isotherm was 2,125.70 mg/g for CTS-g-PAA/10% BT at 30 °C. The adsorption capacity was much higher compared with other hydrogels with the same content of other clays. The introduction of BT into the hydrogel could effectively improve its adsorption properties and reduce the cost. Thermodynamic parameters were evaluated for the dye-adsorbent systems and revealed that the adsorption process was spontaneous and exothermic in nature. All the information gave an indication that CTS-g-PAA/10% BT could potentially be applied as an efficient adsorbent for cationic dye removal from aqueous solution.     

花生壳吸附水中苯酚的热力学与动力学研究

利用废弃的花生壳对水中苯酚进行吸附试验,考察了吸附的最佳条件、吸附热力学和动力学特征.采用Langmuir和Freundlich等温线对平衡数据进行了线性拟合,结果表明,花生壳对苯酚的吸附平衡符合Freundlich等温方程.在298K下,吸附焓变△H=-5.12kJ ·moL^-1,自由能变△G=-4.41 kJ·moL^-1,熵变△S=-2.38J·mo1-1·K-1.表明：该吸附过程为自发进行的放热过程,其动力学行为更好的符合Lagergren准二级动力学模型.     

Adsorption of gas mixtures on heterogeneous surfaces: The integral representation for a monolayer total adsorption isotherm

The authors extended the integral equation for a one-component adsorption isotherm on to n-component adsorption from gaseous mixtures. It appears that the n-component adsorption isotherm on heterogeneous surfaces can be presented as a multiple integral. Two methods were used for evaluation of the surface heterogeneity with regard to a gas mixture. The first method is based on the n-dimensional gaussian energy distribution. The second one concerns the extension of our method for studying adsorption systems of high surface heterogeneity. Two-component adsorption systems have been analyzed in details.     

Piperidin-1-yl-phosphonic acid and (4-phosphono-piperazin-1-yl) phosphonic acid: A new class of iron corrosion inhibitors in sodium chloride 3% media

The inhibiting effect of the piperidin-1-yl-phosphonic acid (PPA) and (4-phosphono-piperazin-1-yl) phosphonic acid (PPPA) on the behavior of iron in 3% NaCl media has been examined by electrochemical and gravimetric measurements. Potentiodynamic polarization studies clearly reveal the fact that the addition of increasing concentrations of phosphonic acids moves the corrosion potential towards negative values and reduces the corrosion rate. In uninhibited and inhibited solutions, the increasing of temperature reduces the inhibition efficiency. Changes in impedance parameters (R_t and C_dl) are indicative of adsorption of PPA and PPPA on the metal surface leading to the formation of protective films. Gravimetric measurements reveal that the presence of PPA and PPPA increases the inhibition efficiency by decreasing the corrosion rate. The results obtained by corrosion weight loss tests reveal that adsorption of compounds tested on the ARMCO iron surface obeys to Langmuir adsorption isotherm.