Surfactant Cetylpyridinium Chloride Research Articles

Selective Synthesis of Single-Crystalline Rhombic Dodecahedral, Octahedral, and Cubic Gold Nanocrystals

This paper reports a versatile seed-mediated growth method for selectively synthesizing single-crystalline rhombic dodecahedral, octahedral, and cubic gold nanocrystals. In the seed-mediated growth method, cetylpyridinium chloride (CPC) and CPC-capped single-crystalline gold nanocrystals 41.3 nm in size are used as the surfactant and seeds, respectively. The CPC-capped gold seeds can avoid twinning during the growth process, which enables us to study the correlations between the growth conditions and the shapes of the gold nanocrystals. Surface-energy and kinetic considerations are taken into account to understand the formation mechanisms of the single-crystalline gold nanocrystals with varying shapes. CPC surfactants are found to alter the surface energies of gold facets in the order {100} > {110} > {111} under the growth conditions in this study, whereas the growth kinetics leads to the formation of thermodynamically less favored shapes that are not bounded by the most stable facets. The competition between AuCl(4)(-) reduction and the CPC capping process on the {111} and {110} facets of gold nanocrystals plays an important role in the formation of the rhombic dodecahedral (RD) and octahedral gold nanocrystals. Octahedral nanocrystals are formed when the capping of CPC on {111} facets dominates, while RD nanocrystals are formed when the reduction of AuCl(4)(-) on {111} facets dominates. Cubic gold nanocrystals are formed by the introduction of bromide ions in the presence of CPC. The cooperative work of cetylpyridinium and bromide ions can stabilize the gold {100} facet under the growth condition in this study, thereby leading to the formation of cubic gold nanocrystals.

Role of naphthenic acid contaminants in the removal of p-xylene from synthetic produced water by MEUF

The high demand for water in oil sands operations in addition to the shortage of fresh water resources mandate continuous search for reliable and cost effective water treatment technologies. Micellar-enhanced ultrafiltration (MEUF) is potentially applicable to produced water treatment. MEUF is, however, susceptible to membrane plugging and back contamination, especially at high surfactant dosages. Recent investigations showed that addition of small amounts of a non-ionic surfactant to an ionic surfactant solution reduces the critical micellar concentration (CMC) of the mixed surfactant solution, and consequently reduces the surfactant dosage required to achieve certain removal of contaminants using MEUF. In the present study a naphthenic acid, octanoic acid, typically existing in produced water is shown to play a similar role as the non-ionic surfactant when added to the cationic surfactant cetylpyridinium chloride (CPC). Cross-flow MEUF using three different molecular weight cutoffs (MWCOs) of polyacrylonitrile (PAN) hollow fiber membranes was used to treat synthetic produced water containing p-xylene. The mixed CPC/octanoic acid solution removed comparable percentages of p-xylene contaminant at much lower concentrations of CPC. Decreasing CPC concentration in the feed resulted in less fouling and higher permeate flux and reduced back contamination. This, in turn, enhanced the performance of MEUF.

Effect of the micellar surfactant nanoreactors on the reactions of 2,4-dinitrophenylhydrazine with some aldehydes

By thermogravimetry, the IR and electronic spectroscopy physicochemical characteristics of systems including aromatic aldehydes, 2,4-dinitrophenylhydrazine, and a surfactant were investigated. Selective solubilization effect of the cationic surfactant (cetylpyridinium chloride) micelles on the aci-form of hydrazone arising in the alkaline medium was found. The universal character of solubilization by the cationic surfactant micelles in the aromatic aldehyde—2,4-dinitrophenylhydrazine systems was shown by an example of the benzaldehyde derivatives with substituents of different nature. This effect leads to the increase in solubility of the reaction products and the aggregative stability of solutions.

Surface-Enhanced Raman Spectroscopy Studies of Surfactant Adsorption to a Hydrophobic Interface

Surface-enhanced Raman spectroscopy is used to investigate the kinetics of adsorption of the cationic surfactant cetylpyridinium chloride (CPC) to hydrophobic surfaces from water. A hydrophobic surface, with stable and reproducible SERS activity, is produced by binding gold colloids to an amine-terminated glass slide and then modifying this surface with octadecyltrimethoxysilane. In situ SERS-detected adsorption of CPC from aqueous solution is found to follow a Frumkin isotherm. Interactions between the charged head groups could be detected in frequency shifts in the symmetric ring breathing mode, consistent with an interfacial surfactant environment similar to a CPC micelle. Rates of surfactant adsorption were determined by time-resolved SERS measurements and were found to be much slower than the diffusion-controlled limit, indicating a significant kinetic barrier to adsorption. Desorption kinetics were heterogeneous, consistent with the spectroscopic results. Alkylsilane-modified gold colloids were shown to be useful substrates for investigating amphiphile adsorption from aqueous solutions to hydrophobic surfaces, where the adsorption kinetics could also be used to determine analyte concentrations in solution.

A rheo-optical study of shear rate and optical anisotropy in wormlike micelles solutions.

The flow behaviour of wormlike micelles solutions composed of the surfactant cetylpyridinium chloride (CPCl) and counter-ion sodium salicylate (NaSal) at a molar ratio [CPCl]/[NaSal] = 2 in brine [NaCl] = 0.5 M in a cylindrical Couette geometry was examined using homodyne PCS and ellipsometry. Homodyne PCS was used to profile local shear rate and ellipsometry to concurrently profile local optical anisotropy of the fluid. Shear thinning was observed and was correlated to an increase in turbidity and a breakdown in the stress-optic law. A stress plateau observed in mechanical measurements was correlated with the partitioning of the fluid into regions of low shear rate/low turbidity/high birefringence and high shear rate/high turbidity/low birefringence. The partitioning observed was inconsistent with a simple interpretation of the lever rule.

Energetics of the interactions of human serum albumin with cationic surfactant

The heat capacity changes for interaction of human serum albumin (HSA) and a cationic surfactant—cetylpyridinium chloride (CPC), were studied at conditions close to physiological (50 mM HEPES or phosphate buffer, pH 7.4 and 160 mM NaCl) carrying out isothermal calorimetric titrations (ITC) at various temperatures (20–40 °C). ITC measurements indicated that the small endothermic changes associated with CPC demicellization were temperature independent at these conditions. Surprisingly, important enthalpy changes associated with binding of CPC to HSA were exothermic and temperature independent at lower concentrations (below 0.022 mM) of CPC and endothermic and temperature dependent at higher concentrations of CPC. The values of heat capacity changes were obtained for each studied concentration of CPC from the plot of enthalpy changes vs temperature. The obtained results demonstrate the temperature independence of heat capacity changes at entire range of studied CPC concentrations. Both enthalpograms and heat capacity curves indicate the two-step mechanism of HSA folding changes due to its interactions with CPC. The first step corresponds to transition from native state to partially unfolded state and the second to unfolding and to the loss of tertiary structure. The analysis of the results indicates that predominant cooperative unfolding occurs at CPC/HSA molar ratio region between 25 and 30. Such information could not be extracted from thermograms and describes the role of heat capacity as a major thermodynamic quantity giving insight on physical, mechanistic and even atomic-level into how HSA may unfold and interact with CPC. The effect of CPC binding on HSA intrinsic fluorescence, UV-Vis and CD spectra were also examined. Hence, the analysis of spectral data confirms the ITC results about the biphasic mechanism of HSA folding changes induced by CPC. The CD measurement also represents the conservation of considerable secondary structure of HSA due to interaction with CPC.

Separation and preconcentration of ultra trace amounts of beryllium in water samples using mixed micelle-mediated extraction and determination by inductively coupled plasma-atomic emission spectrometry

In the present study a cloud point extraction process using mixed micelle of the cationic surfactant cetyl-pyridinium chloride (CPC) and non-ionic surfactant Triton X-114 for extraction of beryllium from aqueous solutions is developed. The extraction of analyte from aqueous samples was performed in the presence of 1,8-dihydroxyanthrone as chelating agent in buffer media of pH 9.5. After phase separation, the surfactant-rich phase was diluted with 0.4 mL of a 60:40 methanol–water mixture containing 0.03 mL HNO 3. Then, the enriched analyte in the surfactant-rich phase was determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The different variables affecting the complexation and extraction conditions were optimized. Under the optimum conditions (i.e. 1.6 × 10 −4 mol L −1 1,8-dihydroxyanthrone, 1.2 × 10 −4 mol L −1 CPC, 0.15% (v/v) Triton X-114, 50 °C equilibrium temperature) the calibration graph was linear in the range of 0.006–80 ng mL −1 with detection limit of 0.001 ng mL −1 and the precision (R.S.D.%) for five replicate determinations at 18 ng mL −1 of Be(II) was better than 2.9%. In this manner the preconcentration and enrichment factors were 16.7 and 24.8, respectively. Under the presence of foreign ions no significant interference was observed. Finally, the proposed method was successfully utilized for the determination of this cation in water samples.

On-site spectrophotometric determination of antimony in water, soil and dust samples of Central India

A new, selective and sensitive on-site spectrophotometric method for the determination of antimony at trace level in water, soil and dust samples of Central India has been demonstrated. It is based on the color reaction of Sb(III) with I − ions in the presence of a cationic surfactant cetylpyridinium chloride (CPC) in acidic media, and subsequent extraction of the complex with N-phenylbenzimidoylthiourea (PBITU) into chloroform to give a yellow colored complex. The value of apparent molar absorptivity of the complex in the terms of Sb is (7.84) × 10 4 l mol −1 cm −1 at 440 nm. The detection limit of the method is 5 ng ml −1. In addition, the present method is free from interferences of all metal ions that are associated during the determination of antimony in environmental samples.

Two different mechanisms for adhesion of Gram-negative bacterium, Pseudomonas fluorescens LP6a, to an oil–water interface

Microbial adhesion to the oil–water interface is an important parameter in biodegradation of hydrocarbons to enhance uptake and metabolism of compounds with very low aqueous solubility, but the mechanisms of adhesion are not well understood. Our approach was to study a range of compounds and mechanisms to promote the adhesion of a hydrophilic bacterium, Pseudomonas fluorescens strain LP6a, to an oil–water interface. The cationic surfactants cetylpyridinium chloride (CPC), poly- l-lysine and chlorhexidine gluconate (CHX) and the long chain alcohols 1-dodecanol and farnesol increased the adhesion of P. fluorescens LP6a to n-hexadecane from ca. 30 to 90% of suspended cells adhering. In contrast, adjusting the ionic strength of the suspending medium only increased the adhesion from about 8 to 30%. The alcohols, 1-dodecanol and farnesol, also caused a dramatic change in the oil–water contact angle of the cell surface, increasing it from 24° to 104°, whereas the cationic compounds had little effect. In contrast, cationic compounds changed the electrophoretic mobility of the bacteria, reducing the mean zeta potential from −23 to −7 mV in 0.01 M potassium phosphate buffer, but the alcohols, 1-dodecanol and farnesol, had no effect on zeta potential. Even though both types of compounds promoted cell adhesion to the n-hexadecane interface, the mechanisms were different. Alcohols acted through altering the cell surface hydrophobicity, whereas cationic surfactants changed the surface charge density.

Cloud-Point Formation Based on Mixed Micelles for the Extraction, Preconcentration and Spectrophotometric Determination of Trace Amounts of Beryllium in Water Samples

A cloud-point extraction process using a mixed micelle of the cationic surfactant cetyl pyridinium chloride (CPC) and non-ionic surfactant Triton X-114 to extract beryllium from aqueous solutions was investigated. The method is based on the color reaction of beryllium with Chrome Azurol S (CAS) in acetate buffer and the mixed micelle-mediated extraction of the complex. This complex was concentrated in a surfactant-rich phase after separation. The optimal extraction and reaction conditions (e.g. pH, reagent and surfactant concentrations, temperature, incubation and centrifuge times) were evaluated and optimized. Under the optimized conditions, the analytical characteristics of the method (e.g. limit of detection, linear range and preconcentration factor) were obtained. Linearity was obeyed in the range of 0.30 - 18 ng mL(-1) of beryllium and the detection limit of the method was 0.05 ng mL(-1). The interference effect of some cations and anions was also studied. The proposed method was successfully applied to the determination of beryllium in real water samples.

Influence of metal ion on sorption of p-nitrophenol onto sediment in the presence of cetylpyridinium chloride

Heavy metals and surfactants have a significant effect on the sorption of organic contaminants. In this study, batch equilibrium experiments were carried out to investigate the influence of Pb(NO(3))(2) on the sorption of p-nitrophenol (PNP) onto sediments in the presence of cationic surfactant cetylpyridinium chloride (CPC). Results indicated that in the complex system containing PNP, Pb(NO(3))(2) and CPC, the sorption of PNP decreased with increasing concentration of Pb(NO(3))(2) due primarily to competing for adsorption sites. Likewise, partitioning of PNP in adsorbed surfactant layers and micelles decreased with increasing level of Pb(NO(3))(2). Moreover, the influence of different metal ions (Pb(2+), Cd(2+), Zn(2+)) was examined and results indicated that the presence of heavy metals inhibited the sorption of PNP in the order: Pb(2+)>Cd(2+)>Zn(2+). The competitive effect of the heavy metals was in agreement with the hydration energy and hydrated radius. The results are believed to provide a useful insight into describing the transport and fate of PNP in natural environments.

Molecular exciton theory calculations based on experimental results for Solophenyl red 3BL azo dye–surfactants interactions

The influence of anionic surfactant: sodium dodecyl sulfate (SDS) and cationic surfactants: cetyltrimethylammonium bormides (C 16TAB) and cetylpyridinium chloride (CPC) on the electronic spectrum of Solophenyl red 3BL azo dye (C.I. Direct 80) in aqueous solution was studied by means of UV–vis spectroscopy. Since, Solophenyl red 3BL azo dye was an anionic soluble dye, therefore, did not observed any interaction between SDS and 3BL dye. On the other hand, in the case of C 16TAB, aggregation was reflected by a hyosochromic shift of the main absorption band and dye H-aggregation was responsible for the short wavelength absorption band. Also, UV–vis spectra showed that micelle formation occurs for C 16TAB surfactant in 3BL dye aqueous solution in lower concentration in comparison with C 16TAB in aqueous solution lonely. Micelle formation was indicated by a red shift of the whole spectra with respect to monomer location. The importance of hydrophobic interactions was revealed by the dependence of aggregation on the cationic surfactant structure. Further results showed that dye H-aggregation was occurred under the cationic surfactant CPC as well, but in this case micelle formation could not occur. Addition of CPC surfactant into the J-aggregate dye solution in highly acidic aqueous solution was also caused completely disaggregating of dimer molecules, which may be related to occuring an acid–base reaction between them. Applicability of the molecular exciton (Kasha) theory in order to interpret of aggregation results and to estimate dimer structure of 3BL dye under C 16TAB and CPC surfactants addition was very poor and the calculated data based on this model showed that this simple point-dipole model could not describe our experimental results.

Influence of Stereoregularity of the Polymer Chain on Interactions with Surfactants: Binding of Cetylpyridinium Chloride by Isotactic and Atactic Poly(methacrylic acid)

Association of a cationic surfactant cetylpyridinium chloride, CPC, with isotactic and atactic poly(methacrylic acid), i-PMA and a-PMA, respectively, in aqueous 0.01 M NaCl solutions was studied by pH and fluorescence measurements in conjunction with potentiometric studies using a surfactant-sensitive membrane electrode. pH measurements have demonstrated that the presence of an oppositely charged surfactant increases ionization of carboxyl groups on PMA at low degrees of neutralization. The increase is more pronounced in the case of i-PMA. The isotactic form of PMA is not soluble in water at zero degrees of neutralization but can be rendered soluble by the addition of CPC at the surfactant to a polyion molar ratio of around 0.4. In the solubilized complex, the positive charge of the CPC molecule is facing the polar solvent, whereas surfactant tails are oriented toward the i-PMA compact coil. Binding isotherms and cooperativity parameters show that chain tacticity has an important influence on the interaction of cetylpyridinium cation with polymethacrylate anion. At the onset of cooperative binding, the association is stronger with i-PMA than with the atactic form, as demonstrated by lower CAC values and higher values of the cooperativity parameters. In contrast, more surfactant is bound by a-PMA in the region where polyion becomes saturated with surfactant ions. Results are interpreted by taking into account local chain conformations as obtained from quantum mechanical semiempirical molecular orbital calculations. Greater hydrophobicity and possibly higher charge density of i-PMA on one hand and more flexibility of the a-PMA chain on the other are held responsible for these observations.

Effects of cationic and anionic surfactants on the adsorption of toluidine blue onto fly ash

The adsorption of cationic dye toluidine blue (TB) onto fly ash has been studied from aqueous solution, in the presence of cationic surfactant cetyl pyridinium chloride (CPC) and anionic surfactant sodium dodecyl sulfate (SDS) at three different temperatures. Two-step adsorption isotherms are observed for TB adsorption in aqueous solution. Isotherm shape is also preserved in the presence of CPC. The equilibrium saturation adsorption capacities of fly ash for TB decreased in the presence of CPC as a result of the competitive adsorption for the same sites between the same charged dye and surfactant molecules. Four-region adsorption isotherms are obtained in the presence of SDS. The adsorption of the cationic dye at low SDS concentration is enhanced by adsolubilization phenomenon because of the favorable interaction with the negatively charged adsorbed micelles. Above the critical micelle concentration free micelles are formed, TB is distributed between the free and the adsorbed aggregates, and therefore the global adsolubilization decreases. The order of changing of Freundlich isotherm constant (n) gives information about isotherm shape whether two-step or four-region adsorption isotherm. Adsorption isotherms of SDS and CPC in aqueous solution have also been constructed for interpreting adsorption results of TB in the presence of surfactants.

Mechanism of Smectic Arrangement of Montmorillonite and Bentonite Clay Platelets Incorporated in Gels of Poly(Acrylamide) Induced by the Interaction with Cationic Surfactants

Structure transitions, induced by the interaction with the cationic surfactant cetylpyridinium chloride in nanocomposite gels of poly(acrylamide) with incorporated suspensions of the two closely related layered clays bentonite and montmorillonite, were studied. Unexpectedly, different behaviors were revealed. X-ray diffraction measurements confirm that, due to the interaction with the surfactant, initially disordered bentonite platelets arrange into highly ordered structures incorporating alternating clay platelets and surfactant bilayers. The formation of these smectic structures also in the cross-linked polymer gels, upon addition of the surfactant, is explained by the existence of preformed, poorly ordered aggregates of the clay platelets in the suspensions before the gel formation. In the case of montmorillonite, smectic ordering of the disordered platelets in the presence of the surfactant is observed only after drying the suspensions and the clay-gel composites. Rheology studies of aqueous suspensions of the two clays, in the absence of both surfactant and gel, evidence a much higher viscosity for bentonite than for montmorillonite, suggesting smaller clay-aggregate size in the latter case. Qualitatively consistent results are obtained from optical micrographs.

The effect of co-occurring inorganic solutes on the removal of arsenic (V) from water using cationic surfactant micelles and an ultrafiltration membrane

The effect of co-occurring inorganic solutes existence in feed water on the removal of arsenic (V) and permeate flux was investigated for the treatment process using a cationic surfactant cetylpyridinium chloride (CPC) and a 5 kilo-Dalton (kDa) polyethersulfone (PES) membrane. Simulated water and well water (Washoe County STMGID #9 operational well, Nevada) were used for this study. The concentrations of arsenic ([As] F = 0−105 μg/L) and inorganic solutes ([HCO − 3] = 0−4.1 mg/L, [HPO 2− 4] = 0−0.3 mg/L, [H 4SiO 4] = 0−90 mg/L, and [SO 2− 4] = 0−400 mg/L) in simulated feed water were varied. The pH level of simulated feed water was adjusted to 8 since the well water pH was around 8. The arsenic concentration in the well water was 73 μg/L. The concentrations of carbonate, phosphate, silicate, and sulfate in the well water were 1 mg/L, 0.17 mg/L, 69 mg/L, and 8.2 mg/L, respectively. PES membrane without surfactant micelles was found to be ineffective for arsenic removal. The highest arsenic removal in the presence of inorganic solutes is 25%, corresponding to a permeate water arsenic concentration of 30 μg/L which is well above the new maximum contaminant level (MCL) of 10 μg/L. With the addition of 10 mM CPC to the feed water, the arsenic removal efficiency is significantly increased ranging between 78.1% and 100%. The arsenic removal efficiency was found to be dependent on the feed water arsenic and co-occurring inorganic solute concentrations. Except for one UF experiment performed with the simulated feed water containing 105 μg/L arsenic and 400 mg/L SO 2− 4 (23 μg/L arsenic in permeate water), all the other UF experiments produced permeate water with arsenic below the new MCL. The presence of HCO − 3, HPO 2− 4, and H 4SiO 4 species in feed water does not affect the arsenic removal efficiency (100%) except in one case (99% removal efficiency for the feed water containing 105 μg/L arsenic and 90 mg/L H 4SiO 4). The experiments performed with well water result in almost 100% arsenic removal (arsenic level in permeate water is below the detection limit of ICP-MS, 1 μg/L). Furthermore, absolute permeate flux was also found to be dependent on the feed water arsenic and co-occuring inorganic solute concentrations. An increase in feed water arsenic concentration results in a decrease in the permeate flux. For the experiments performed with simulated water containing CPC and arsenic, the permeate water flux is 56.5 ± 2.5% of ultra clean water flux. The permeate flux reduces further as the co-occuring inorganic solute concentration or the total dissolved solid in feed water increases. It is 43.5 ± 3.5%, 45.5 ± 7.5%, 43.5 ± 6.5%, and 37.5 ± 5.5% of the ultra clean water flux for the simulated water containing HCO − 3, HPO 2− 4, H 4SiO 4 and SO 2− 4 species, respectively. With the well water, permeate flux was found to be 33% of the ultra clean water flux. Only 1.52 ± 0.33% of the surfactant molecules used were detected in permeate water. Surfactants in permeate water can be further separated and reused in the feed stream.

Interaction of Cetylpyridinium Chloride with Giant Lipid Vesicles

The interaction of cationic surfactant cetylpyridinium chloride, CPC, with giant lipid vesicles prepared from 1-palmitoyl-2-oleoylphosphatidylcholine, POPC, was examined at various concentrations of the lipid component. The lipid concentration was determined by a spectrophotometric method. The potentiometric method based on surfactant-selective electrode was used for the determination of surfactant concentration in the external water solution. From these results, moles of surfactant incorporated in the membrane per mole of lipid (parameter beta) and two kinds of partition coefficients were calculated. Their values were found to be considerably larger than the available literature data. A three stage process of surfactant-induced solubilization of lipid vesicles was observed. First, stable mixed bilayers form, which become saturated with CPC at a value beta(sat) larger than 0.8, which then gradually disintegrate. Just prior to the breakdown of the vesicular structure, formation of ellipsoidal vesicles was observed by optical microscopy. This phenomenon was attributed to the cooperative incorporation of surfactant into the bilayer. Fluorescence measurements have shown that the second stage in the solubilization process of POPC by the C16 chain-length surfactant does not involve mixed micelles. These are formed only in the third stage, which is the complete solubilization of POPC bilayers. The corresponding critical micellization concentration decreases with increasing concentration of the lipid component.

Exploiting micellar environment for simultaneous electrochemical determination of ascorbic acid and dopamine

A simple and reliable method for simultaneous electrochemical determination of ascorbic acid (AA) and dopamine (DA) is presented in this work. It was based on the use of the cationic surfactant cetylpyridinium chloride (CPC) that enables the separation of the oxidation peaks potential of AA and DA. Cyclic voltammetry (CV) as well as pulse differential voltammetry (PDV) were used in order to verify the voltammetric behaviour in micellar media. In the cationic surfactant CPC, a remarkable electrostatic interaction is established with negatively charged AA, as a consequence, the oxidation peak potential shifted toward less positive potential and the peak current increased. On the other hand, the positively charged DA is repelled from the electrode surface and the oxidation peak potential shifts toward more positive potential in comparison to the bare electrode. Therefore, the common overlapped oxidation peaks of AA and DA can be circumventing by using CPC. Parameter that affects the E pa and I pa such as CPC concentration and pH were studied. Under optimised conditions, the method presented a linear response to AA and DA in the concentration range from 5 to 75 μmol L −1 and 10 to 100 μmol L −1, respectively. The proposed method was successfully applied to the simultaneous determination of AA and DA in dopamine hydrochloride injection (DHI) samples spiked with AA.

Molecular level separation of arsenic (V) from water using cationic surfactant micelles and ultrafiltration membrane

Removal of arsenic (V) from water using surfactant micelles and ultrafiltration membrane was investigated using simulated water and stirred cell ultrafiltration unit. The effects of membrane materials (regenerated cellulose and polyethersulfone), membrane nominal molecular weight cut-off (NMWCO, 5 and 10 kDa), feed water arsenic concentration (from 0 to 221 μg/L), and feed water pH (5.5 and 8) on the efficiency of arsenic (V) removal and the permeate flux were studied with and without the surfactant addition. Polyethersulfone (PES) membranes without the surfactant micelles were found to be ineffective for arsenic removal. Regenerated cellulose (RC) membranes provide better removal than PES membranes due to its negatively charged surface at the experimental conditions. However, the arsenic concentration in permeate water (product water) is not reduced to the new maximum contaminant level (MCL) of 10 μg/L. With the addition of 10 mM cationic surfactant cetylpyridinium chloride (CPC) to the feed water, both PES and RC membranes reduce the arsenic concentration in permeate water well below the MCL. The arsenic removal efficiency and absolute permeate flux were found to depend on the membrane materials, membrane NMWCO, and water pH. Highest arsenic removal, 100%, is achieved for the feed water arsenic concentrations of 22 and 43 μg/L using 5 kDa PES membranes at pH of 5.5 and 10 kDa RC at pH of 8. Regardless of the feed water arsenic concentration, 100% arsenic removal is obtained with 5 kDa PES membranes at pH of 8.

Characterization of pore systems of mesoporous silicas templated by cetylpyridinium under mild-alkaline condition: the effect of low-temperature ammonia post-treatment

Mesoporous silicas with ordered hexagonal MCM-41 structure were synthesized under mildly alkaline condition at room temperature in the presence of the surfactant cetylpyridinium chloride. Low-temperature post-synthesis treatment of these silicas in ammonia solution was investigated. The pore size was expanded from 2 to 4 nm by post-treatment at temperatures lower than 373 K, accompanied by a subtle change of morphology, and could be fine-tuned by varying the post-treatment temperature. A bimodal mesopore system with an interconnected three-dimensional was obtained, when the post-treatment occurred at 373 K. The control of the pore system and the creation of larger secondary mesopores, leading the unidimensional channels interconnected, are important and useful for catalysis. The role of ammonia in the extension of the pore size during low-temperature treatment and the possible generation of the secondary pore system by the decomposition of the thermally unstable cetylpyridinium surfactant are discussed in detail. The present work can serve as an excellent example for pore system engineering.