Adsorption of phenolic compounds onto trimethylstearylammonium surfactant-immobilized cation-exchange membranes

Trimethylstearylammonium hydroxide/methoxide surfactants were immobilized onto two kinds of cation-exchange membranes (P81 and S2001) for the adsorption of phenolic compounds in the present study. The results indicate that the membrane with a doubled cation-exchange capacity (S2001) could attain nearly twice of the immobilized surfactant amount, but its surfactant immobilization % was close to or lower than the one with a smaller cation-exchange capacity (P81). By manipulating the feed surfactant concentration, different surfactant arrangements on the membrane surfaces (such as hemimicellar, admicellar, or mixed structure) could be produced. The membranes with theoretically 100% surfactant immobilization revealed the highest hydrophobicity level, and thus they were applied in the batch adsorption of phenolic compounds. According to the batch adsorption results of four phenolic compounds onto the surfactant-immobilized membranes (100% immobilization), the main adsorption mechanism should be hydrophobic interaction and the order of phenolic compound adsorptivity was phenol < 4-nitrophenol < 4-chloro-3-methylphenol ≤ bisphenol A, identical to their log K_ow order. Moreover, in a batch adsorption/desorption cycle with 100 mL of 1 ppm bisphenol A aqueous sample tested and 5 mL of 2-propanol as the desorbent, the S2001 membrane (100% surfactant immobilization) could completely recover bisphenol A from water at a 20-fold enrichment.     

Octadecyltrimethylammonium surfactant-immobilized cation exchange membranes for solid-phase extraction of phenolic compounds

In this study, octadecyltrimethylammonium surfactant was immobilized onto a cation exchange membrane for the application in solid-phase extraction of phenolic compounds. The results indicate that an HCl prewashing step and the use of hydroxide (or methoxide) counter ion could greatly improve the immobilized surfactant capacity. Through elemental and thermogravimetric analyses, the resulted immobilization percentage on the membrane (compared to membrane ion exchange capacity) was about 50, 100, and 150%, respectively, for the feed surfactant amount of 150, 2000, and 5000 μmol (volume = 20 mL). Phenol, 4-nitrophenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, and bisphenol A were the tested compounds in a breakthrough volume experiment. The order of the obtained breakthrough volume values is similar to that of K_ow values of the phenolic compounds. In the solid-phase extraction process from a feed mixture of 0.1 ppm for 4-nitrophenol, 2,4-dichlorophenol, and 4-chloro-3-methylphenol, high concentration factors and almost complete recoveries were achieved. Moreover, by increasing the membrane volume, a larger sample volume could be processed without any deterioration in performance.     

Octadecyltrimethylammonium surfactant-immobilized cation exchange membranes for solid-phase extraction of phenolic compounds

In this study, octadecyltrimethylammonium surfactant was immobilized onto a cation exchange membrane for the application in solid-phase extraction of phenolic compounds. The results indicate that an HCl prewashing step and the use of hydroxide (or methoxide) counter ion could greatly improve the immobilized surfactant capacity. Through elemental and thermogravimetric analyses, the resulted immobilization percentage on the membrane (compared to membrane ion exchange capacity) was about 50, 100, and 150%, respectively, for the feed surfactant amount of 150, 2000, and 5000 μmol (volume = 20 mL). Phenol, 4-nitrophenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, and bisphenol A were the tested compounds in a breakthrough volume experiment. The order of the obtained breakthrough volume values is similar to that of K_ow values of the phenolic compounds. In the solid-phase extraction process from a feed mixture of 0.1 ppm for 4-nitrophenol, 2,4-dichlorophenol, and 4-chloro-3-methylphenol, high concentration factors and almost complete recoveries were achieved. Moreover, by increasing the membrane volume, a larger sample volume could be processed without any deterioration in performance.     

Hemimicelle capped functionalized carbon nanotubes-based nanosized solid-phase extraction of arsenic from environmental water samples

The end functionalization of CNTs can introduce oxygen-containing negatively functional groups such as -COOH, -OH, or -CO on their surface site. If cationic surfactant such as cetyltrimethylammonium chloride (CTAC) was added to the functionalized CNTs, then interactions such as hydrophobic and ionic may lead to formation of hemimicelle/admicelle aggregates on the CNTs, a new kind of adsorbents, namely, the hemimicelle capped CMMWCNTs, is obtained. The application of the hemimicelle capped carbon nanotubes-based nanosized solid-phase extraction (SPE) adsorbents in environmental analysis is reported for the first time using arsenic as model target. The effect of adsorption and desorption conditions for arsenic including the amount of surfactant, initial pH of sample solution, the ultrasonic time of sample solution, the amount of electrolyte, flow rate, eluent and its amount were investigated and optimized prior to its determination by atomic fluorescence spectrophotometry (AFS). Arsenic can be quantitatively retained on the hemimicelle capped CMMWCNTs at pH 5-6 from sample volume up to 500 mL and then eluted completely with 2 mol L⁻¹ HNO₃ in the presence of 10 mg L⁻¹ CTAC. The method detection limit for arsenic determination with AFS detection was 2 ng L⁻¹, and the relative standard deviation (RSD, n = 11) was 5.3% at the 0.5 μg L⁻¹ level. The recoveries of arsenic in the spiked environmental water samples ranged from 94% to 104.29% with 500 mL of water sample. The proposed method has been applied successfully to the analysis of arsenic in aqueous environmental samples, which demonstrates the hemimicelle capped CMMWCNTs can be an excellent SPE adsorbents for arsenic pretreatment and enrichment from real water samples.     

Adsorption and adsolubilization of surfactants on titanium dioxides with functional groups

Adsorption of ionic surfactants on titanium dioxide with dodecyl chain groups or quaternary ammonium groups (XNm, where m is the carbon number of the alkyl chain, 4–16) was investigated. The adsorbed amount of cationic surfactants (dodecyltrimethylammonium bromide, DTAB; 1,2-bis(dodecyldimethylammonio)ethane dibromide, 2RenQ) on titanium dioxide with dodecyl chain groups increased with increasing concentration of the dodecyl chain due to hydrophobic interaction, where the adsorbed amounts of DTAB at saturation was considerably greater than those of 2RenQ. Adsorption of an anionic surfactant (sodium dodecyl sulfate, SDS) on XNm occurred mainly due to both electrostatic attraction force and hydrophobic interaction, depending on the alkyl chain length on XNm. On the other hand, adsorption of cationic surfactants, DTAC and 2RenQCl (their counter ions are chloride ions), on XNm was quite smaller compared with that of SDS due to electrostatic repulsion force. Adsolubilization of 2-naphthol in the surfactant-adsorbed layer on the titanium dioxides with the functional groups was also studied. The adsolubilized amounts of 2-naphthol on titanium dioxide with dodecyl chain groups were enhanced by adsorption of DTAB, but no distinct increase in the adsolubilization was observed by adsorption of 2RenQ. In the case of XNm, the amount of 2-naphthol adsorbed in the absence of surfactants increased with increasing alkyl chain length on XNm. Further, an appreciable increase in the adsolubilization of 2-naphthol on XNm with adsorption of 2RenQCl was observed. It was found from the admicellar partitioning coefficients that the adsolubilization of 2-naphthol preferably occurs on XNm by adsorption of SDS or 2RenQCl compared with that by DTAC. These differences in the adsolubilization were discussed by microproperties of the surfactant-adsorbed layers estimated using a spin probe.     

Investigation of elutions from a surfactant immobilized solid phase extraction sorbent based upon the hydrophobicity of the trapped species

A unique solid phase extraction (SPE) sorbent having a removable “stationary phase” is presented. This removable phase consists of alkyltrimethylammonium surfactant, which is initially immobilized onto hydrophilic strong cation exchange resin. The surfactant chain through hydrophobic interactions extracts hydrophobic analytes in the same manner as conventional bonded alkyl moieties on silica-based non-polar sorbents. For the extraction of very hydrophobic species with conventional sorbents, solvents such methylene chloride and benzene are needed to break strong hydrophobic interactions for efficient elutions. These solvents however are toxic to the analyst and present a significant environmental concern. Using a removable “stationary phase”, hydrophobic interactions need not be broken between the analyte and the sorbent. In the presented approach, the surfactant (“stationary phase”) is removed via ion exchange with exchange ions in very mild aqueous-based and instrument compatible solutions. The analyte, being associated with the surfactant, is also removed in the process. Very efficient elutions of analytes, regardless of hydrophobicity, under mild and more favorable environmental conditions are a direct benefit of having a removable “stationary phase”. Rinse solution parameters explored include exchange cation type and concentration, and alcohol type and concentration. The extraction of three test molecules of varying hydrophobicity, naphthalene, pyrene and benzo(ghi)perylene, is investigated using this sorbent material.     

Self-aggregation of cationic surfactants onto oxidized cellulose fibers and coadsorption of organic compounds

In this work, the adsorption of cationic surfactant and organic solutes on oxidized cellulose fibers bearing different amounts of carboxylic moieties was investigated. The increase in the amount of -COOH groups on cellulose fibers by TEMPO oxidation induced a general rise in surfactant adsorption. For all tested conditions, that is, cellulose oxidation level and surfactant alkyl chain length (C12 and C16), adsorption isotherms displayed a typical three-region shape with inversion of the substrate zeta-potential which was interpreted as reflecting surfactant adsorption and aggregation (admicelles and hemimicelles) on cellulose fibers. The addition of organic solutes in surfactant/cellulose systems induced a decrease in surfactant cac on the cellulose surface thus favoring surfactant aggregation and the formation of mixed surfactant/solute assemblies. Adsorption isotherms of organic solutes on cellulose in surfactant/cellulose/solute systems showed that solute adsorption is strictly correlated to (i) the surfactant concentration, solute adsorption increases up to the surfactant cmc, where solute partitioning between the cellulose surface and free micelles causes a drop in adsorption, and to (ii) solute solubility and functional groups. The specific shape of solutes adsorption isotherms at a fixed surfactant concentration was interpreted using a Frumkin adsorption isotherm, thus suggesting that solute uptake on cellulose fibers is a coadsorption and not a partitioning process. Results presented in this study were compared with those obtained in a previous work investigating solute adsorption in anionic surfactant/cationized cellulose systems to better understand the role of surfactant/solute interactions in the coadsorption process.     

Effect of operating variables on the flux and selectivity in sweep gas membrane distillation for dilute aqueous isopropanol

Sweep gas membrane distillation was examined as a possible technique for isopropanol (IPA)–water separation using PTFE hollow fiber membrane module. The composition and flux of the permeate were monitored when feed concentration, operating temperature and flow rate were varied. The upper feed concentration tested was 10 wt.% IPA. Within the feed temperature range of about 20–50°C, IPA selectivity of 10–25 was achieved. Since the concentration near the surface on the membrane increased by the selective adsorption of IPA on the hydrophobic membrane, the selectivity increases. The permeate flux and IPA selectivity increase as feed temperature increase. The flux and selectivity increase at higher flow rates is mainly due to the reduced effects of concentration and temperature polarization. The effect of salt addition to the feed mixture was also examined.     

Preparation of solid alkaline fuel cell binders based on fluorinated poly(diallyldimethylammonium chloride)s [poly(DADMAC)] or poly(chlorotrifluoroethylene‐co‐DADMAC) copolymers

A membrane or an electrode binder to be used in a solid alkaline fuel cell (SAFC) needs to (i) be insoluble in both aqueous solutions and the required fuels, and (ii) exhibit an hydroxide ion conductivity. To achieve these goals, two pathways were employed: (i) one consists of the radical copolymerization of diallyldimethylammonium chloride (DADMAC) with chlorotrifluoroethylene (CTFE) while (ii) the other one is based on the counter‐ion exchange of a poly(DADMAC) by fluorinated anions. First, the radical copolymerization of CTFE with DADMAC under various experimental conditions was achieved in yields up to 85%, and DADMAC percentages in the copolymers were higher than those in the feed compositions. To obtain insoluble copolymers, high CTFE feed contents (>70 mol %) were required. The other route consisting in the partial replacement of the Cl^? counter‐ions in the water‐soluble poly(DADMAC) by bistrifluoromethanesulfonimide (TFSI^?) did confer the starting material insolubility in water while maintaining its conductivity. When the fluorinated poly(DADMAC) was obtained from concentrated solutions of fluorinated surfactant, it was observed that the amount of counter‐ions exchanged was difficult to control, which limits optimization. Nevertheless, under diluted conditions, membranes with ion exchange capacity up to 0.7 meq g^?1, and conductivities close to 1 mS cm^?1 were obtained. Although their conductivities were low, these membranes fulfill the requirements for a SAFC membrane in terms of solubility in DMSO, water insolubility, and thermal stability (T_d,10% > 320 °C). When used in a fuel cell, as a binder in the membrane‐electrode assembly (MEA), significant improvements were noted (+50% of the open circuit voltage, +580% in current density, and +540% in accessible power). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2043–2058, 2009     

Adsorption of cationic surfactants and subsequent adsolubilization of organic compounds onto cellulose fibers

Cationic surfactants with different hydrophobic chain length were adsorbed onto cellulose fibers in an aqueous medium. The adsorption isotherms exhibited three characteristic regions which were interpreted in terms of the mode of aggregation of the surfactant molecules at the solid–liquid interface. The hydrophobic layers were used as a reservoir to trap various slightly water soluble organic molecules. A quantitative study of these phenomena suggested typical partition behavior of the organic solutes between the aqueous phase and the surfactant layer. The surfactant chain length (from C12 to C18) was shown to play an important role in terms of the capacity to retain the organic solute and the capacity increased with the number of carbon atoms.     

The adsorption of alkylpyridinium chlorides and their effect on the interfacial behavior of quartz

This research was directed at understanding cationic surfactant adsorption phenomena on wet-ground natural quartz, mainly with dodecylpyridinium chloride as the model surfactant. How these surfactant ions adsorb at the interface was delineated through measurements of adsorption isotherms, zeta potentials, suspension stability, contact angles, induction times, and flotation response. Hydrocarbon chain association of adsorbed surfactant ions (or self-association) leads to four distinct adsorption regions as the concentration of surfactant is increased in solution. The same four regions manifest themselves in the behavior of all of the interfacial processes studied. At low concentrations, adsorption is controlled primarily by electrostatic interactions, but when the adsorbed surfactant ions begin to associate into hemimicelles at the surface, hydrophobic chain interactions control the adsorption process. The results of experiments with alkylpyridinium chlorides of 12, 14 and 16 carbon atoms can be normalized in terms of their CMCs, which clearly show that surface aggregation phenomena are driven by the same hydrophobic interactions that lead to micelle formation in bulk solution.     

Propriétés de transport de membranes échangeuses d'anions en présence d'ions organiques. Partie I. Influence de la longueur de la chaı̂ne aliphatique

Transport properties of anion exchange membranes in contact with organic ions. Part I. Influence of the length of the aliphatic chain. The physico-chemical properties of an anion-exchange membrane (AMV, Asahi Glass) were studied in aqueous solutions containing both a mineral salt (NaCl) and an organic salt at the same concentration (10^–1 M). The organic salt was a sodium carboxylate with an aliphatic chain varying from C₁ to C₈. Measurements of ion exchange, water content, electric resistance, self-diffusion and electrodiffusion fluxes were performed. Changes in the membrane parameters were related to the increase in the hydrophobic character of the organic ion.     

Single-chain surfactant monolayer on carbon paste electrode and its application for the studies on the direct electron transfer of hemoglobin

A variety of single-chain surfactants with different charge properties and tail lengths can spontaneously adsorb on the hydrophobic surface of carbon paste electrode and form stable monolayers on the electrode surface. Hemoglobin (Hb) was successfully immobilized on these surfactant monolayers to form stable protein-surfactant composite films regardless of the charge and the tail length of surfactants. The resulting surface-confined Hb exhibited well-defined direct electron-transfer behaviors in all positively, neutrally and negatively charged surfactant films, suggesting the important role of hydrophobic interactions in the adsorption of Hb on surfactant films. When the density of surfactant monolayers was controlled to be the same, Hb was found to possess a better direct electron-transfer behavior on monolayers of cationic surfactants with a longer tail length. This, in combination with the tunneling effect in the direct electron transfer of Hb on surfactant films, demonstrated that the adsorption of Hb on surfactant monolayers may be mainly achieved by the partial intercalation of Hb in the loose structures of surfactant films through hydrophobic interactions between the alkane chains of surfactants and the hydrophobic regions of Hb. The native conformation of Hb adsorbed on these surfactant films was proved to be unchanged, reflected by the unaltered ultraviolet-visible (UV-vis) and reflection-absorption infrared (RAIR) spectra, and by the catalytic activity toward hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) in comparison with the free Hb molecules.     

Hybrid liquid membrane (HLM) system in separation technologies

A novel liquid membrane system, denoted hybrid liquid membrane (HLM), was developed for the separation of solutes (metal ions, acids, etc.). It utilizes a solution of an extracting reagent (carrier solution), flowing between membranes. The membranes, which separate the carrier solution from feed and receiving (strip) solutions, enable the transport of solutes, but block the transfer of the carrier to the feed or to the strip. Blocking the carrier is achieved through membranes hydrophilic/hydrophobic or ion exchange properties, or through their rentention abilities, due to pore size.     

Removal of aromatic compounds in the aqueous solution via micellar enhanced ultrafiltration: Part 1. Behavior of nonionic surfactants

The effects of nonionic surfactants having different hydrophilicity and membranes having different hydrophobicity and molecular weight cut-off on the performance of micellar-enhanced ultrafiltration (MEUF) process were examined. A homologous series of polyethyleneglycol (PEG) alkylether having different numbers of methylene groups and ethylene oxide groups was used for nonionic surfactants. Polysulfone membranes and cellulose acetate membranes having different molecular cut-off were used for hydrophobic membranes and hydrophilic membranes, respectively. The concentration of surfactant added to pure water was fixed at the value of 100 times of critical micelle concentration (CMC). The flux through polysulfone membranes decreased remarkably due to adsorption mainly caused by hydrophobic interactions between surfactant and membrane material. The decline of solution flux for cellulose acetate membranes was not as serious as that for polysulfone membranes because of hydrophilic properties of cellulose acetate membranes. The surfactant rejections for the cellulose acetate membranes increased with decreasing membrane pore size and with increasing the hydrophobicity of surfactant. On the other hand the surfactant rejections for polysulfone membranes showed totally different rejection trends with those for cellulose acetate membranes. The surfactant rejections for the polysulfone membranes depend on the strength of hydrophobic interactions between surfactant and membrane material and molecular weight of surfactants.     

固定化铜离子亲和膜色谱柱吸附血红蛋白的研究

将纤维素滤纸进行碱处理及环氧活化、偶联亚氨基二乙酸、固定化铜离子等处理,并将其装入自制的色谱柱管,制得固定化铜离子亲和膜色谱柱。该柱可用于吸附血红蛋白(hemoglobin,Hb),吸附率可达到90%以上。考察了上样量、pH值、温度、上样速度等因素对固定化铜离子亲和膜吸附Hb的影响。实验结果表明,固定化铜离子亲和膜色谱柱吸附血红蛋白的最佳条件为：室温下实验,缓冲体系的pH值控制在6~8,上样速度0.5~1.0 mL/min,上样量为3.16~7.90 mg/g。     

表面活性剂对污泥脱水性能影响的机理研究:Gemini表面活性剂与聚电解质相互作用的分子动力学模拟

表面活性剂可以与污泥表面的胞外聚合物(EPS)吸附形成胶束,释放出自由水和结合水,从而达到改善污泥脱水性能的目的.本文采用粗粒化的分子动力学模拟方法,研究了Gemini表面活性剂与EPS形成复合物的过程和结构.聚电解质链的亲疏水性对吸附过程有显著影响,亲水聚电解质链与Gemini表面活性剂吸附的主要驱动力为静电吸引,Gemini表面活性剂头基吸附在链上,尾链朝向溶剂;疏水聚电解质链与Gemini表面活性剂吸附过程由静电作用与疏水作用共同促进,Gemini表面活性剂以平行于聚电解质链的构型存在.Gemini表面活性剂联结基团长度对吸附过程的影响甚微;聚电解质链的电荷密度对亲水聚电解质链的吸附产生协同作用,对疏水聚电解质链的吸附不产生作用.     

Preparation and characterization of Type II anion exchange membranes from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)

To separate hydrophilic anions from hydrophobic ones, Type II PPO-based anion exchange membranes were developed. Different from Type I (with both trimethylbenzylammonium and triethylbenzylammonium groups), Type II has an excellent hydrophobicity modifier as fixed groups: dimethyethanolammonium groups, which were introduced into PPO (poly(2,6-dimethyl-1,4-phenylene oxide)) by following benzyl bromination of PPO and subsequent quaternary amination with a dimethylethanolamine (DMEA) aqueous solution. The membrane's intrinsic properties are dependent on DMEA concentration and amination temperature. The optimum conditions for membrane preparation are as follows: amination temperature 70 °C, time 30–48 h, and DMEA concentration 1:3–1:5 (v/v, DMEA to water). The obtained Type II anion exchange membranes had an IEC of 1.5 mmol/g dry membrane, water content of 30%, and membrane area resistance of 30 Ω cm². The introduced dimethyethanolammonium groups can block hydrated anions from the access to membranes but let hydrophobic anions transport; hence, an effective separation between hydrophilic and hydrophobic anions can be achieved during electro-membrane operation.     

Study on the first-step adsorption of dodecyltrimethylammonium bromide solutions on silica wafer surfaces by ultramicroelectrode voltammetry

Ultramicroelectrode (UME) voltammetry is introduced to study the first-step adsorption of dodecyltrimethylammonium bromide (DTAB) solutions on silica wafer surfaces. This method is based on the exchange reaction of the surfactant molecules with hydrogen ions (H⁺) on the surfaces. In the first-step adsorption process, when a surfactant molecule is adsorbed to the hydroxylated silica surfaces, a H⁺ will be displaced. Therefore, H⁺ concentration will change with the adsorption process until it reaches saturation of the first-step adsorption. The molar adsorption amount of DTAB (mol m⁻²) before critical micelle concentration (CMC) can be calculated from the change in H⁺ concentration. The following adsorption process at higher surfactant concentrations is dominated by hydrophobic forces. Consequently, the H⁺ concentrations do not change with the adsorption process any more, which makes the measurement uninfluenced by the following hydrophobic adsorption process. The adsorption isotherms of DTAB on silica wafer surfaces under different pH are measured with this method. It is found that all the adsorption isotherms exhibit asymptote (L) shape and the equilibrium molar adsorption amounts increase with increasing the pH of the solution. These results indicate that H⁺ not only change the surface charge but also compete with surfactant for adsorption at higher proton concentrations.     

Effects of membrane hydrophilicity on the removal of a trihalomethane via micellar-enhanced ultrafiltration process

Micellar-enhanced ultrafiltration (MEUF) process was explored for obtaining pure water from an aqueous solution containing small amount of trihalomethanes (THMs). A homologous series of polyethylene glycol alkylether was used as nonionic surfactant. To understand effects of membrane hydrophilicity on the performance of MEUF process, membranes for the ultrafiltration were prepared from polysulfone blends containing various amount of a hydrophilic copolymer, poly(1-vinylpyrrolidone-co-acrylonitrile) (P(VP-AN)). An increase in the permeate flux was observed with an increase of the membrane hydrophilicity. The performance of MEUF process in removing THM and surfactant was shown to depend on the membrane characteristics, surfactant characteristics, and operating pressure. The rejections of THM and surfactant were increased with increasing hydrophobicity of surfactant and hydrophilicity of membrane. The rejections of THM examined with hydrophilic membranes were increased with increasing operating pressure, while those examined with hydrophobic membranes were decreased with increasing operating pressure. THM included in water could be removed up to 99% via MEUF process. The performance of MEUF examined with hydrophilic membranes could be explained with the rejection of micelles containing THM, while that examined with hydrophobic membranes could be explained with hydrophobic interactions between surfactant and membrane materials.