Evaluation of energy distribution on a heterogeneous surface from heat of adsorption and its application to the ammonia/Na-Y zeolite system

The— function (energy level function) which represents surface heterogeneity was derived from theq— function (experimental heat function) in the case of reversible adsorption. The Langmuir equation was extended and applied to the procedure of calculations. An iterative calculation led to the most probable— function by setting theq— function and adsorption temperature. As an example for actual cases, the— function of Na-Y zeolite was calculated from theq— function obtained by the measurement of heats of adsorption of ammonia at 373 K. The— function thus derived seemed to be consistent with the positional distribution of sodium ions.     

Functionalized MgO,CeO<Subscript>2</Subscript> and ZnO nanoparticles with humic acid for the study of nitrate adsorption efficiency from water

In this study, the removal of nitrate using ZnO, MgO, and CeO₂ nanoparticles (NPs) modified by humic acid from water was tested. Nanoparticles were modified by humic acid using the microwave-assisted technique and then modified ZnO (Zn–H), modified MgO (Mg–H), and modified CeO₂ (Ce–H) were characterized through SEM, EDX, FTIR, and XRD analysis. Several important parameters influencing the removal of nitrate such as contact time, pH, adsorbent dosage and temperature were explored systematically by batch experiments. Isotherm studies were set up with the following optimum conditions: pH?=?5, adsorbent concentration of 1 g L^?1, 180 min and 25 °C. The results revealed that the adsorption were best fitted to pseudo-second order and simple Elovich kinetics models. Langmuir, Freundlich and linear adsorption models were fitted to describe adsorption isotherms and constants. The isotherm analysis indicated that the adsorption data can be represented by both Freundlich and linear isotherm models. The maximum adsorption capacity (q_m) was obtained at 55.1, 74.2 and 75.8 mg g^?1 for Zn–H, Ce–H, and Mg–H, respectively. The thermodynamic parameters such as free energy, enthalpy and entropy of adsorption were obtained. From the thermodynamic parameters, it is suggested that the adsorption of nitrate on modified NPs (MNPs) followed the exothermic and spontaneous processes. The obtained results showed that the MNPs were efficient adsorbents for removing nitrate from aqueous media.     

Silicas with thiourea grafted groups for the concentration of heavy metal ions

Two methods for the chemical bonding of thiourea and its derivatives on dispersed silica have been developed as a result of a detailed study of the process of the thiourea chemisorption on silica surface. Obtained S-containing silicas possess a high extraction efficiency for heavy metal ions.     

Progress and challenges in molecularly imprinted polymers for adsorption of heavy metal ions from wastewater

Molecularly imprinted polymers (MIPs), prepared by the interaction forces such as forming covalent or non-covalent bonds by crosslinkers and initiators, are new types of specific recognition polymers with particular cavities. This is an ideal class of materials for wastewater treatment because of the particular holes left by the elution process. This review discusses the development process, classification, synthesis principles, systems, and polymerization methods of MIPs. At the same time, the adsorption mechanism of Copper (Cu), Mercury (Hg), Chromium (Cr), Silver (Ag), and Lead (Pb) in the MIPs technique are studied. Finally, some suggestions and prospects for the future development of MIPs are also put forward.     

One-pot synthesis,characterization, and drug loading of polysaccharide-based nanoparticles with carboxy functional groups

Herein, various polysaccharide-based nanoparticles were synthesized from dextran, hydroxypropyl cellulose, and hydroxyethyl cellulose, respectively, by a self-assembly assisted approach. This approach enables us to prepare stable polysaccharide-based nanoparticles with carboxy functional groups directly from monomers without using any surfactant and organic solvent. The existence of abundant carboxyls in these polysaccharide-based nanoparticles provides them obvious pH sensitivity as verified by ¹H nuclear magnetic resonance as well as the potential in loading cationic drug.     

Preparation of macroreticular chelating resins containing mercapto groups from 2,3-epithiopropyl methacrylate/divinylbenzene copolymer beads and their adsorption capacity

Macroreticular chelating resins containing mercapto groups were prepared by the reaction of 2,3-epithiopropyl methacrylate/divinylbenzene macroreticular copolymer beads with ethanolic potassium hydrogensulfide solution for 1 h at 50°C. The adsorption capacities of this resin for Ag⁺, Hg²⁺, Pb²⁺ and Cd²⁺ were determined at various pH values. In the acidic region, the resin shows a high affinity for Ag⁺ and Hg²⁺ and high resistance against air oxidation. Cadmium is readily eluted with 1 mol dm^?3 hydrochloric acid; silver, mercury and copper ions can be eluted with 1 mol dm^?3 hydrochloric acid containing 5% (w/v) thiourea. The proposed resin appears to be useful for the removal of As³⁺ from aqueous solutions.     

Syntheses,characterization, and functionalization of poly(ester amide)s with pendant amine functional groups

Poly(ester amide)s (PEAs) comprising α‐amino acids, diols, and diacids are promising materials for biomedical applications such as tissue engineering and drug delivery because of their tunability and potential for either hydrolytic or enzymatic degradation. Although a number of PEAs of different compositions have been reported, there is a significant need for the incorporation of amino acids with functional side chains. This will allow for the conjugation of drugs or cell signaling molecules in tissue engineering scaffolds, thus expanding the potential applications of these materials. The objective of this work was the incorporation of l ‐lysine into PEAs to provide functionalizable pendant amine groups. Thus, varying percentages of lysine were incorporated into PEAs comprised of l ‐phenylalanine, 1,4‐butanediol, and succinic acid by tuning the ratio of ε‐protected‐l ‐lysine and l ‐phenylalanine derived monomers. The polymers were characterized by nuclear magnetic resonance spectroscopy, infrared spectroscopy, size exclusion chromatography, and differential scanning calorimetry. The lysine ε‐protecting group was removed, then the reactivity of the pendant amines was demonstrated by reaction with amino acid and tri(ethylene glycol) derivatives. The degradation of thin films of polymers were studied using scanning electron microscopy and the incorporation of lysine was found to significantly accelerate both the hydrolytic and enzymatic degradation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6376–6392, 2008     

A continuous flow system design for simultaneous determination of heavy metals in river water samples

A new design of a continuous flow system applied to the simultaneous determination of the concentration of zinc(II), cadmium(II), lead(II), copper(II), nickel(II), cobalt(II) and chromium(VI) in river water is described. A flow cell made in the laboratory, which has been patented, based on a 'wall-jet' configuration with a three-electrode system is described. Optimum conditions for the determination of the metal ions are reported. The detection limits and relative standard deviation values were 4.01x10(-9) M and 0.078 for Zn(II), 1.76x10(-10) M and 0.056 for Cd(II), 4.69x10(-10) M and 0.134 for Pb(II), 2.29x10(-10) M and 0.138 for Cu(II), 1.61x10(-9) M and 0.093 for Ni(II), 1.91x10(-9) M and 0.113 for Co(II), and 1.35x10(-9) M and 0.081 for Cr(VI). The procedure was applied to a sample of water from the Arlanzón river and the results were compared with inductively coupled mass plasma spectrometry (ICP-MS) as reference method. The final aim of this work is to design a flow system, which can be automated.     

Enthalpies of alkyl sulfonates in water,heavy water,and water-alcohol mixtures and the interaction of water with methylene groups

The heats of solution of the sodium n-alkyl sulfonates from methyl to octyl have been measured at 25°C in water, D₂O, and three alcohol-rich mixtures with water, all at solute concentrations low enough so that solute-solute interaction is negligible. Methylene-group contributions to the enthalpies of transfer are readily identified. Collation with the results of earlier studies of enthalpies of transfer leads to the conclusion that methylene-group enthalpies of transfer can be identified as follows: 0.87 kcal-mole^–1 for transfers to the gas phase from water and –0.035 kcal-mole^–1 for transfers to D₂O from H₂O, independent of the solute type provided only that methylene-group contributions can be identified in the data. Compared to other solvents, water is about as lipophilic as dimethylsulfoxide or a mixture of 27 moles of water with 73 moles of methanol. However, the range of the interactions between different groups on a given solute molecule seems to be much greater in water than in any of the other solvents studied, making it more difficult to identify group contributions to solvation in water. Another example of the complexity of the solvation of alkyl groups in water is encountered when one compares the solvation enthalpy of hexane in various solvents with some of the above results.     

A single-site model for divalent transition and heavy metal adsorption over a range of metal concentrations

Metal adsorption data over a range of surface coverages typically are characterized by curvilinear metal adsorption isotherms. These isotherms generally have a slope of 1 at low surface coverage and a shallower slope at higher surface coverages. The curvature of metal adsorption isotherms with increasing surface coverage is frequently interpreted in terms of sequential adsorption onto different types of surface sites, multinuclear surface complexation, or nonideality of metal adsorption. We demonstrate that the curvature of metal adsorption isotherms can also be attributed to changes in surface charge and potential that depend on the predominant type of metal surface complex. A single-site extended triple-layer model is used to reinterpret previously studied metal adsorption isotherms and pH edges for a wide variety of metals (Cd2+, Co2+, Cu2+, Pb2+, and Zn2+) and solids (goethite, hydrous ferric oxide, corundum, and magnetite) in different electrolyte solutions (NaNO3 and NaClO4). Only metal adsorption on ferrihydrite at very low surface coverages is not consistent with the single-site triple-layer model. This discrepancy might be explained if ferrihydrite is in fact not a single phase but a mixture of two or more phases. Metal surface coverages ranging from 10(-4) to 10.2 mmol/m2 on the other minerals can be accounted for with a single-site extended triple-layer model if appropriate metal adsorption reactions are chosen. In addition, several examples suggest that, within the context of the model, surface complexation schemes can be established that describe metal adsorption over both a wide range of surface coverage and a wide range of ionic strength.     

Application of modified magnetic nanoparticles with amine groups as an efficient solid sorbent for simultaneous removal of 2,4-Dichlorophenoxyacetic acid and 2-methyl-4-chlorophenoxyacetic acid from aqueous solution: optimization and modeling

In the present work, functionalized magnetic nano-adsorbent with amine groups (Fe₃O₄@SiO₂@NH₂) was prepared for the simultaneous removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) from aqueous solution. Characterization such as Fourier transform infrared spectroscopy, vibrating sample magnetometry, and scanning electron microscope confirmed that the magnetic nanoparticles structure of Fe₃O₄@SiO₂ nano-adsorbent was successfully functionalized by amine groups. The impact of some influencing parameters such as contact time, pH, adsorbent dosage, 2,4-D and MCPA initials concentration and solution temperature were studied. The equilibrium data were analyzed by Langmuir and Freundlich adsorption isotherms and also two models kinetically of pseudo-first-order and pseudo-second-order. Findings of the present study showed that the synthesized amino-functionalized MNPs will be helpful in use as an effective recyclable adsorbent for the removal of phenoxy acid herbicides from aqueous solution due to its advantages such as facile and rapid separation of target molecules from solution.     

螯合吸附材料PAO/SiO_2对重金属离子的螯合吸附行为

将丙烯腈接枝聚合在微米级硅胶微粒表面,经偕胺肟化转变,制得了接枝有聚偕胺肟(PAO)的复合型螯合吸附材料PAO/SiO2。本文重点考察了螯合吸附材料PAO/SiO2对几种重金属离子的螯合吸附行为,深入地研究了吸附机理。研究结果表明,偕胺肟基团与重金属离子之间的静电作用与配位螯合作用的协同,导致PAO/SiO2对重金属离子产生强的螯合吸附作用。在可抑制金属离子水解的pH范围内,介质的pH值越高,PAO/SiO2的螯合吸附能力越强;PAO/SiO2对性质不同的金属离子的吸附性能是有差别的,吸附容量的顺序为Cu2+Ni2+Pb2+Cd2+。     

Decoration of electrospun polyacrylonitrile nanofibers with ZnO nanoparticles and their application for removal of Pb ions from waste water

The adsorption behavior of lead (II) from aqueous solutions utilizing ZnO/polyacrylonitrile (PAN) nanofibers was studied. ZnO/PAN nanofibers were prepared by electrospinning method. The changes of the parameters of adsorbent amount, pH, contact time, and temperature were tested in the adsorption experiments. The adsorption was well described by the Langmuir adsorption isotherm model. The thermodynamic parameters indicate that the adsorption process is exothermic. The dynamic behavior of the lead (II) ions adsorption by PAN/ZnO nanofibers was well described by the pseudo-second-order kinetic model. The adsorbent can be regenerated by suitable desorption processes for multiple uses without significant loss of its adsorption capacity.     

油页岩飞灰对重金属离子的吸附动力学及热力学

采用批式振荡吸附法研究了燃油页岩电厂循环流化床锅炉飞灰对重金属离子Pb²+、Cu²+、Zn²+、Cd²+的吸附动力学及吸附热力学特性,并提出了吸附机理。结果表明,油页岩飞灰对Pb²+、Cu²+、Zn²+、Cd²+的吸附平衡数据符合Langmuir和Freundlich吸附等温方程,但Freundlich方程能够更好地描述吸附等温线。在油页岩飞灰对重金属离子吸附的初始阶段,拉格朗日准一级动力学方程、准二级动力学方程、Elovich方程、粒子内扩散模型均能很好地反映吸附模式,而整个吸附过程则遵循二级反应动力学方程,其吸附过程是液膜扩散和粒子内扩散共同作用的结果。油页岩飞灰对Pb²+、Cu²+、Zn²+、Cd²+的吸附是吸热反应。     

Solid-phase extraction for the decontamination of alkali metal, alkaline Earth metal, and ammonium salts from heavy metal ions

Salicylaldoxime-immobilized silica gel was characterized and used as a potential sorbent for heavy metal ions, viz. Cu(II), Ni(II), Co(II), and Zn(II). The experimental conditions were optimized both in batch and column processes to achieve the maximum efficiency. Kinetic and thermodynamic parameters as well as isotherm constants were evaluated to test the feasibility of the process. The role of various metal ions and different anions were tested in order to monitor the process in case of real samples. The alkali metal, alkaline earth metal, and ammonium salts do not have any effect on the said process. This differential behavior can be effectively used for the decontamination of alkali metal, alkaline earth metal, and ammonium salts from Cu(II), Ni(II), Co(II), and Zn(II) ions via solid phase extraction following AAS measurement. The purification of the salts was confirmed by voltammetric experiment.     

Carboxyl-functionalized nanoparticles with magnetic core and mesopore carbon shell as adsorbents for the removal of heavy metal ions from aqueous solution

This communication demonstrates superparamagnetic nanosized particles with a magnetic core and a porous carbon shell (thickness of 11 nm), which can remove 97% of Pb(2+) ions from an acidic aqueous solution at a Pb(2+) ion concentration of 100 mg L(-1). It is suggested that a weak electrostatic force of attraction between the heavy metal ions and the nanoparticles and the heavy metal ions adsorption on the mesopore carbon shell contribute most to the superior removal property.     

Synthesis and characterization of iron oxide/polymer composite nanoparticles with pendent functional groups

We describe in this paper an approach to synthesize superparamagnetic iron oxide nanoparticles in the presence of polymerized lactic acid. The resulted particles consisted of clusters of iron oxide monocrystals, embedded inside the polymer chains. The composite particles synthesized in situ were highly dispersible in aqueous solution with good stability. X-ray diffraction and magnetometer data all confirmed the crystalline structure and super-paramagnetic property of the particles. They exhibited narrow size distribution with hydrodynamic diameters close to 80 nm. In addition, the particles were shown to have abundant surface carboxyl groups, which can be used to conjugate various biomolecules. Such a preparation would be especially useful for developing target specific MRI contrast agents or drug delivery vehicles.     

Enhancing adsorption of heavy metal ions onto biobased nanofibers from waste pulp residues for application in wastewater treatment

Biobased nanofibers are increasingly considered in purification technologies due to their high mechanical properties, high specific surface area, versatile surface chemistry and natural abundance. In this work, cellulose and chitin nanofibers functionalized with carboxylate entities have been prepared from pulp residue (i.e., a waste product from the pulp and paper production) and crab shells, respectively, by chemically modifying the initial raw materials with the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) mediated oxidation reaction followed by mechanical disintegration. A thorough investigation has first been carried out in order to evaluate the copper(II) adsorption capacity of the oxidized nanofibers. UV spectrophotometry, X-ray photoelectron spectroscopy and wavelength dispersive X-rays analysis have been employed as characterization tools for this purpose. Pristine nanofibers presented a relatively low content of negative charges on their surface thus adsorbing a low amount of copper(II). The copper adsorption capacity of the nanofibers was enhanced due to the oxidation treatment since the carboxylate groups introduced on the nanofibers surface constituted negative sites for electrostatic attraction of copper ions (Cu²⁺). The increase in copper adsorption on the nanofibers correlated both with the pH and carboxylate content and reached maximum values of 135 and 55 mg g^?1 for highly oxidized cellulose and chitin nanofibers, respectively. Furthermore, the metal ions could be easily removed from the contaminated nanofibers through a washing procedure in acidic water. Finally, the adsorption capacity of oxidized cellulose nanofibers for other metal ions, such as nickel(II), chromium(III) and zinc(II), was also demonstrated. We conclude that TEMPO oxidized biobased nanofibers from waste resources represent an inexpensive and efficient alternative to classical sorbents for heavy metal ions removal from contaminated water.     

Peculiarities of adsorption of organic compounds and water on silicas with bonded polyfluoroalkyl groups

The adsorption isotherms of benzene revealed the low adsorption potential of polyfluoroalkyl silicas compared with both initial silica and hexadecyl silica. Hydrophobicity of all modified silicas, measured by water adsorption, was rather close at p/p(s)=1 and was significantly different in the initial p/p(s) region: polyfluoroalkyl silicas did not nearly adsorb water but alkyl silica did it gradually. Thermodynamic parameters of adsorption of organic compounds of different nature were studied at a zero surface coverage by gas chromatography (GC). The high enough contributions of specific interactions as well as polar molecular group increments to the Gibbs adsorption energy were found to be characteristic of polyfluoroalkyl silica. The selectivity of polyfluoroalkyl silicas and the commonly used fluorinecontaining liquid stationary phase for GC (OV-210) toward homologous ethers, esters, and alcohols was comparable in most cases. GC data, IR spectra, and adsorption measurements were in good agreement with each other. It was shown that residual SiOH-groups of silica do not nearly take part in the adsorption process because they are effectively screened by the attached organic groups.