Adsorption characteristics of surfactants and phenol on modified zeolites from their aqueous solutions

Adsorption characteristics of anion-, cation- and nonion-type surfactants and phenol from their aqueous solution on Na-Y zeolites modified by SiCl₄ treatment and NA-ZSM-5 zeolites with several Si/Al ratios were measured. Surfactants used were sodium dodecylbenzenesulfonte (DBS), laurylpyridinium chloride (LPC), polyoxyethylenenonylphenylether (POENPE) and phenol.Adsorption of surfactants was enhanced by SiCl₄ treatment of Na-Y, which indicates an important role of the hydrophilic-hydrophobic character in the adsorption.Adsorption isotherms were in general of Langmuir type and adsorbed amount depended on the Al/(Si+Al) or Si/Al ratio of zeolite frameworks. In case of DBS adsorption of Na-ZSM-5 series, adsorption occurred only on the outer surface due to steric hindrance. LPC adsorption abilities were observed on even hydrophilic zeolites and were ascribed to ion exchange effect. In case of phenol adsorption on hydrophobic Na-Y, the adsorption isotherm was of Type V according to BDDT classification.     

Adsorption characteristics of chloroform on modified zeolites from gaseous phase as well as its aqueous solution

Adsorption characteristics of chloroform from its aqueous solution on Na–Y and Li–Na–Y modified by SiCl₄ were measured and compared with those on Na–ZSM-5 and Na-Mordenite.No adsorption occurred on Na–Y with high hydrophilicity, while the siliceous faujasites became capable of adsorption and its amount increased with increase in the Si/A1 ratio. Adsorption isotherms are of Langmuir type, suggesting that adsorption proceeds by pore filling. The adsorption amounts expressed in volume on Na–Y with high hydrophobicity corresponded to their pore volumes.Adsorption characteristics of chloroform from gaseous phase on Na–Y with different Si/A1 ratio were also measured. The adsorption capability decreased with increasing Si/A1 ratio.Immersional heats of zeolites into water or chloroform were measured in order to evaluate the surface affinity to both solvents. Immersional heats into water were almost constant (about 500 mJ·m^–2) for zeolites with their Si/A1 ratio below 10. The heats decreased with an increase in the Si/A1 ratio above 10, then became almost constant (about 120 mJ·m^–2) over 30 in their ratio. Heats of immersion of Na–Y series into chloroform were almost constant irrespective of their Si/A1 ratio, but decreased slightly when the ratio exceeded 20.Adsorption characteristics of chloroform could be well related to immersional heats into both solvents.     

Enhanced adsorption of roxarsone onto humic acid modified goethite from aqueous solution

The adsorption of roxarsone (ROX) on the humic acid modified goethite (HA-α-FeOOH) was evaluated for several potential environmental factors. Results showed that 1) ROX had a higher adsorption capacity onto HA-α-FeOOH than unmodified α-FeOOH; 2) the adsorption of ROX increased with a decrease in pH; 3) the high ionic strength significantly inhibited the adsorption capacity of HA-α-FeOOH; and 4) a higher temperature yielded greater adsorption, since the process for ROX to be adsorbed by HA-α-FeOOH was a spontaneous endothermic reaction. The maximum adsorption capacity of ROX was found to be 80.71?mg?·?g^?1, when the temperature was 308?K. Meanwhile, the inhibitory effects of ionic strength and PO₄^3? on the adsorption of ROX onto HA-α-FeOOH were enhanced with an increase in concentration. In addition, the adsorption equilibrium data obeyed Langmuir isotherm model and the kinetic data were well described by the pseudo-second-order kinetic model. From the infrared spectra of HA-α-FeOOH, it could be deduced that the ROX adsorption onto HA-α-FeOOH was achieved via the ion exchange between the arsenic acid and the carboxyl group on adsorbent, as well as the formation of As-O-Fe bond between Fe-O and arsenic acid ions.     

十二烷基硫酸钠与溴化正辛基三甲基铵混合表面活性剂水溶液的表面吸附及胶团形成

本文研究了盐存在时不同比例的十二烷基硫酸钠(简称12CH)和溴化正辛基三甲基铵(简称C8NBr)混合物的表面活性、表面吸附以及胶团形成等性质,结果表明:(1)正、负离子表面活性剂混合物具有很高的表面活性,不论其混合比例如何,临界胶团浓度(cmc)及cmc时溶液的表面张力(γcmc)皆较任何单一组分时小;(2)不论体相中比例如何,表面层中12CH和C8NBr的饱和吸附量的摩尔比皆～1.7且总饱和吸附量亦皆～5.2x10[-10]mol.cm[-2].由此求得表面层中分子截面积为32A[2],与由分子结构计算的数据相近,说明正、负表面活性离子排列紧密;(3)与碳链长相同的正、负离子型表面活性剂混合水溶液比较,本体系反应离子浓度对cmc有明显影响,证实表面层带电,胶团也带电;(4)计算了离子强度相同,温度不同时和温度相同、离子强度不同时的热力学量,得出离子强度大者易形成胶团。     

Adsorption of phenol from aqueous solution onto zeolites Y modified by silylation

The present work consists in studying the adsorption of phenol onto zeolites Y modified by silylation, in order to increase their hydrophobic character. The operation was carried out by chemical liquid deposition with trimethylchlorosilane (TMCS). Study of the effect of certain parameters like initial concentration, pH and ionic strength were conducted. Experimental data were fitted by the models of Langmuir, Freundlich and Dubinin-Raduskevich calculated by non-linear regression. Results obtained show that the adsorption of phenol on samples is very fast and supported at acidic values of pH. We also found that phenol uptake increases with Si/Al ratio and modification by silylation improves the percentage of adsorption by approximately 30%.     

Temperature induced restoration of fluorescence from oxidised single-walled carbon nanotubes in aqueous sodium dodecylsulfate solution

Fluorescence intensity from single walled carbon nanotubes in aqueous sodium dodecylsulfate solution is shown to be strongly temperature dependent in the range 5-60 degrees C. Emission peaks corresponding to particular nanotube species which have been quenched due to oxidation by aerated water show sharp transitions at distinct temperatures as the sample is heated. The temperature at which the transition occurs is found to be species dependent and has been interpreted as being proportional to the valence band edge potential of the nanotube. The results are explained quantitatively using the Nernst equation to measure the increase in reduction potential of the solution as the temperature is raised. The removal of dissolved O(2) and CO(2) is thought to be a significant driving force in the reversal of the redox reaction which causes oxidation of the nanotubes.     

Adsorption of sodium dodecylsulfate on chrysotile

Adsorption of sodium dodecylsulfate (SDS) onto chrysotile from aqueous solutions was investigated along with varying temperature, ionic strength and surface treatments. Commercial chrysotile fibers were treated by sonication or extensive washings. The ratio of adsorbed SDS per gram of chrysotile is approximately constant with varying chrysotile masses. A steady state is reached after about 2 h of contact between SDS and chrysotile. In general, less surfactant is adsorbed on the sonicated chrysotile than on the extensively washed chrysotile. For the sonicated chrysotile, isotherms presented an adsorption maximum in the region of the surfactant critical micelle concentration, when the experiments were carried out without ionic strength control. The adsorption maximum is due to the presence of magnesium ions in the solution, which can form complexes with dodecylsulfate ions. For the extensively washed chrysotile, the isotherm behavior is similar to that obtained with sonicated chrysotile in the presence of an inert electrolyte. No significant difference in adsorption of SDS on the extensively washed chrysotile was observed when varying temperature or ionic strength. The adsorption of SDS was found to be dependent on the prior surface treatment.     

Solubility and thermodynamics of solution of argon in aqueous solutions of sodium octanoate and sodium dodecylsulfate

The ostwald absorption coefficient of argon was measured in aqueous solutions of two surfactants; sodium n-octanoate and in sodium dodecylsulfate, at several concentrations and at a few temperatures between 10–25°C. The free energies, entropies and enthalpies of solution were computed. A tentative interpretation of the results is given, based on a competition between the solubilization and the salting-out effects of the surfactants.     

Enthalpy of solution of phenoxyalcohols solubilized in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solutions

The enthalpy of solution of phenoxy 2-ethanol, 1 phenoxy,-3 propanol and benzylalcohol was determined at 25 °C in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solution, up to 0.2 mol/kg surfactant concentration. Using the pseudo-phase model, the standard enthalpy of transfer and the partition coefficient of the alcohols between micelle and water are calculated. The latter quantity is found to be systematically larger when derived from enthalpy than from free energy measurements. Using the so-called compensation plot, the solution thermodynamics of aromatic and aliphatic alcohols in aqueous sodium dodecylsulfate and in the octane+water systems are compared. Aromatic alcohols display an anomalous behavior in the octane+ water system but not in the micellar one.The standard enthalpy of solution of various alcohols presents, when plotted against hexadecyltrimethylammonium bromide concentration, a shoulder in the region around 0.05 mol/kg; a discussion is presented on the evidence for alleged micellar structural changes in aqueous micellar systems.     

Micropore modification of zeolites with transition-metal oxides

The micropores of USY and ZSM-5 zeolites were modified with the transition-metal oxides, such as Fe₂O₃, MoO₃ and V₂O₅. The structures of the modified samples were characterized by XRD and the physical features were determined by N₂ adsorption method. The results show that the transition-metal oxides can diffuse well into the micropores of zeolites. The surface area, micropore area, pore volume and typical pore diameter of the modified samples change respectively, and the change might result in a novel process for the design of the shape-selective catalysts and special adsorbents.     

Interaction of sodium dodecylsulfate (SDS) with homoionic montmorillonites: adsorption isotherms and metal-ion release

The interaction of dodecylsulfate anions (DS^–) with homoionic Ca-, Mg-, Ni-, Cu-, Cd-, Pb- and Fe-montmorillonites were investigated. Mg- and Cd-montmorillonite do not adsorb DS^–, and an anion exchange at the edges of the clay mineral does not take place. Three different adsorption processes are identified on the other montmorillonites: i) Fe-montmorillonite is covered with amorphous iron hydroxide, and DS^–-anions are bound at positively charged sites. ii) On Ca- and Pb-montmorillonite DS^– is precipitated as Me(DS)₂. iii) On Ni- and Cu-montmorillonite DS^– forms ion pairs with the cations on the surface. In all cases DS^– is not bound above the CMC but the metal ions are mobilized from the surface either by solubilization of the precipitates or by formation of mixed micelles.     

Coarse-grained molecular dynamics simulation of self-assembly of polyacrylamide and sodium dodecylsulfate in aqueous solution

Coarse-grained molecular dynamics simulations have been performed to study the self-assembly of polymer, polyacrylamide (PAM) and surfactant, sodium dodecylsulfate (SDS) in aqueous solution. Our simulations revealed that PAM curled into clusters in the absence of SDS, while it was stretched if SDS was added. For the SDS-PAM complexes, the aggregate formation process can be divided into three stages: firstly, PAM quickly absorbs some SDS monomers until the radius of gyration (Rg) of polymer reaches a minimum; then, PAM stretches and the Rg of PAM increases due to more and more adsorbed SDS; ultimately, the commonly accepted "necklace" structure is formed with PAM located at the interface of the hydrophobic and hydrophilic regions of the SDS micelle. The main driving force for the association was hydrophobic interactions between the polymer backbone and the surfactant hydrophobic tails. As the concentration of SDS increased, the Rg of PAM increased up to a maximum, indicating the polymer was saturated with surfactant.     

Rheological properties of the aqueous solution for fluorocarbon‐containing hydrophobically modified sodium polyacrylic acid with various surfactants

The interaction of fluorocarbon‐ containing hydrophobically modified sodium polyacrylic acid (FMPAANa) (0.5 wt%) with various surfactants (anionic, nonionic and cationic) has been investigated by rheological measurements. Different rheological behaviors are displayed for ionic surfactants and nonionic surfactants. Fluorinated surfactants have stronger affinity with polyelectrolyte hydrophobes comparing with hydrogenated surfactants. The hydrophobic association of FMPAANa with a cationic surfactant (CTAB) and a fluorinated nonionic surfactant (FC171) is much stronger than with a nonionic surfactant (NP7. 5) and an anionic surfactant (FC143). Further investigation of the effects of temperature on solution properties shows that the dissociation energy E_m is correlated to the strength of the aggregated junctions.     

Enhancement adsorption of hexavalent chromium from aqueous solution on polypyrrole using ethylamine group

A novel nanospheres adsorbent was successfully prepared using functionalized 1H-Pyrrole-1-ethanamine by homopolymerization. It could be easily protonated to form double-charged repeating structural units on the surface of nanospheres. The physic-chemical properties were characterized by SEM, TGA, XPS and Zeta potential. The effects of initial pH, adsorbent dosage, contact time, initial concentration, and ionic strength were studied in detail. The maximum adsorption capacity of Chromium(VI) was about 729.09?mg?g^?1 at room temperature. Electrostatic attraction played an important role in the adsorption process and the size of the ion group had a greater effect on the adsorption performance than the charge.     

Lignite fired fly ash modified by chemical treatment for adsorption of zinc from aqueous solution

The purpose of the study described in this paper was to compare removal of Zn(II) from aqueous solutions by use of two adsorbents—alkali-modified fly ash (FAN) and alkali and dye-modified fly ash (FAN-MO). The effects of four conditions (solution pH, contact time, initial metal ion concentration, and dose of adsorbent) on removal of Zn(II) at 27 ± 5 °C were studied in batch mode. Adsorption of Zn(II) was greater at pH 4.0 for FAN (76.49 %) and at pH 5.0 for FAN-MO (24.72 %). Maximum adsorption of Zn(II) by FAN and FAN-MO was achieved after 50 min. The linear forms of the Langmuir, Freundlich, Tempkin, D–R, Harkin–Jura, and Frenkel–Halsey isotherms were used for experiments with different concentrations of the metals. Adsorption of Zn(II) ions satisfied the Langmuir isotherm model only. The adsorption capacity of both adsorbents was also investigated by column studies. Adsorption of Zn(II) ions on FAN in column studies (45.33 %) was lower than in batch mode studies. For FAN-MO, adsorption was 37.88 % in column studies, again lower than in batch mode studies. Fly ash modified by alkali had a higher adsorption capacity for Zn(II) ions than fly ash modified by alkali followed by addition of dye.     

Separation of acidic and neutral compounds by strong anion-exchange capillary electrochromatography dynamically modified with sodium dodecylsulfate

Summary Acidic and neutral compounds have been separated by strong anion-exchange capillary electrochromatography (SAXCEC) dynamically modified by addition of sodium dodecylsulfate (SDS). It was found that separation of neutral solutes by SAXCEC without addition of SDS is difficult because of the weak interaction of the solutes with the hydrophilic packing surface. The hydrophobicity of the packing surface increases on addition of SDS to the mobile phase, however, and the capacity of separating neutral solutes increases. Acidic solutes are retained, mainly because of the ion-exchange properties of this system. The influence of mobile phase composition, e.g. SDS concentration, ionic strength, and organic modifier fraction, on the retention of acidic and neutral solutes was investigated. Three acids and five neutral solutes were separated in only 5 min under optimized conditions, because the direction of the strong electroosmotic flow (EOF) was the same as that of electrophoretic migration of the acids under the conditions used. The repeatability of this system in terms of migration time relative standard deviation (RSD) is good—less than 0.48% for 10 consecutive runs of all the solutes tested. Column efficiencies for acids were > 125000 plates m⁻¹; those for neutral solutes varied from 25000 to 100000 plates m⁻¹.     

新型吸附树脂对水中苯的吸附行为

研究表明,苯对人的毒性作用表现在中枢神经系统,65g／m^3的苯可引起广泛的出血导致死亡。反复暴露的低浓度苯主要对血液及造血组织产生毒性作用。根据苯吸入致白血病的流行病学研究数据,采用定量外推法计算出饮用水苯质量浓度为0．01mg/L时终身患癌的超额危险度为10^-5,因此饮用水中的苯的限值为0．01mg／L。因此,有效去除饮水中的苯具有重要的意义。     

Role of clay-based membrane for removal of copper from aqueous solution

The present study focuses on the fabrication of polysulfone (PSf)-clay minerals impregnated hybrid membrane for treatment of Cu (II) ions. Blending and phase inversion methods have been employed to develop clay-based membranes by the mixing of bentonite, sepiolite and zeolite in the matrix of PSf. Moreover, characterization of fabricated membranes was carried out using SEM, FTIR, zeta potential, pore size and water contact angle measurement. Adsorption and filtration experiments were conducted to evaluate the permeation performance of the membrane. Obtained results of permeation study reveal that the presence of clay minerals in the matrix of modified membrane not only increases the adsorption and rejection efficiency for Cu (II) but, it also improves the flux of pure water. Among all developed membranes, the membrane prepared by the mixing of zeolite demonstrates the highest adsorption (2.82 mg/g) and rejection value (97%) towards Cu (II) at low pressure (0.5 bar). Regeneration performance results confirm the reusability of membrane up to 3–5 cycles along with 82.5–90% metal recovery. Based on significant metal recovery, clay-based low-cost zeolite/PSf membrane could be used to remove Cu (II) from water at low pressure to replace current conventional membrane.     

Protein adsorption characteristics of calcium hydroxyapatites modified with pyrophosphoric acids

Protein adsorption characteristics of calcium hydroxyapatite (Hap) modified with pyrophosphoric acids (PP(a)) were examined. The PP(a) modified Hap particles (abbreviated as PP-Hap) possessed anchored polyphosphate (PP: P-{O-PO(OH)}(n)-OH) branches on their surfaces. The proteins of bovine serum albumin (BSA: isoelectric point (iep)=4.7, molecular mass (M(s))=67,200 Da, acidic protein), myoglobin (MGB: iep=7.0, M(s)=17,800 Da, neutral protein), and lysozyme (LSZ: iep=11.1, M(s)=14,600 Da, basic protein) were examined. The zeta potential (zp) of PP-Hap particles as a function of pH overlapped; zp-pH curves were independent of the concentration of pyrophosphoric acids (abbreviated as [PP(a)]) used for modifying Hap surface. The saturated amounts of adsorbed BSA (Delta n(ads)(BSA)) were increased three-fold by the surface modification with PP(a) though they were independent of the [PP(a)]. Furthermore, the fraction of BSA desorption was independent of the [PP(a)]. This enhancement of BSA adsorption onto the PP-Hap is due to the hydrogen bonding between oxygen and OH groups of the PP-branches and functional groups of BSA molecules. In the case of LSZ, a more higher adsorption enhancement was observed; the saturated amount of adsorbed LSZ (Delta n(ads)(LSZ)) for Hap modified at [PP(a)]=6 mmol/dm(3) was nine-fold than that for Hap unmodified. This remarkable adsorption enhancement was explained by a three-dimensional binding mechanism; LSZ molecules were trapped inside of the PP-branches. Hence, a fraction of LSZ desorption was decreased with an increase in the [PP(a)]; as more PP-branches are presented on the surface the higher retardation of LSZ desorption was induced. It was expected from their small size that MGB adsorb between the PP-branches as well as LSZ. However, the amounts of adsorbed MGB (Delta n(ads)(MGB)) did not vary and were independent of the [PP(a)] due to the small numbers of functional groups of MGB. In addition, no dependence of the fraction of MGB desorption on the [PP(a)] was observed. The results of zp for all the protein systems supported the mode of protein adsorption discussed. The anchored structure of the PP-branches developed on the Hap surface to provide three-dimensional protein adsorption spaces was proved by a comparative experiment that was elucidating the effect of pyrophosphate ions for BSA adsorption onto Hap.     

Adsorption behavior of organic halides on zeolites

The adsorption behavior and the differential heat of adsorption of chloroform were measured on various types of zeolite (faujasite, ZSM-5 and mordenite) with different Si/Al ratios. The results reveal that saturated adsorption is almost proportional to the micropore volume and is independent of the micropore structure or the Si/Al ratio. However, initial heat of adsorption was the highest (90 kJ mol⁻¹) on the mordenite with low Si/Al ratio, while low on the faujasite with high Si/Al ratio or ZSM-5 (50 kJ mol⁻¹). Change in initial heat of adsorption with Si/Al ratio is small for faujasite or mordenite and large for ZSM-5. For the comparison, trichloroethylene adsorption behavior of zeolite was also investigated. Saturated adsorption of trichloroethylene was almost constant for all types of zeolite, while the faujasite with high Si/Al ratio exhibited an adsorption isotherm of type V in BDDT (Brunauer, Deming, Deming and Teller) classification. The tendencies of heat of immersion are similar to the results of the initial heat of adsorption.