Surfactant effect on electrochemical-induced synthesis of α-Ni(OH)2

Nickel hydroxide films were electrosynthesized in the presence of different diluted surfactant solutions by galvanostatic electroprecipitation. Lamellar α-Ni(OH)₂ films are obtained using cationic surfactant cetyltrimethylammonium bromide (CTAB), anionic surfactant sodium dodecyl sulfate (SDS), and also neutral surfactant Tween® 80. The films were structurally and morphologically characterized by X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy, and electrochemically by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The results evidenced that SDS remains intercalated between the lamellae of α-Ni(OH)₂. Albeit the presence of CTAB and Tween® 80, it was noticed in FTIR spectra that the surfactants did not intercalate. The morphology was affected by the presence of different surfactants. All studied surfactants displaced the oxidation potential (E _O) of Ni²⁺/Ni³⁺ process to less positive values. Also, the presence of surfactants improved the electrode charge efficiency and the charge response for the same number of moles of nickel ions deposited. The ratio of the charge and frequency change is 4.4 times bigger for films deposited with SDS when compared with pure α-Ni(OH)₂ films.     

Study of the ligand substitution reaction Fe (CN)5H2O3− + pyrazine in micellar solutions

The ligand substitution reaction Fe(CN)₅H₂O³⁻ + pyrazine → Fe(CN)₅ pyrazine³⁻ + H₂O has been studied in sodium dodecyl sulfate SDS, hexadecyltrimethylammonium bromide, CTAB, and salt aqueous solutions at 298.2 K. Kinetics were studied in dilute and concentrated salt solutions and in SDS and CTAB solutions at surfactant concentrations below and above the critical micelle concentration. Experimental results show that salt effects can be explained by considering the interaction between the cations present in the working media which come from the background electrolyte, and the Fe(CN)₅H₂O³⁻ species in the vicinity of the cyanide ligands. This interaction makes the release of the aqua ligand from the inner-coordination shell of the iron(II) complex to the bulk more difficult resulting in a decrease of the reaction rate when the electrolyte concentration increases. Kinetic data in surfactant solutions show that not only micellized surfactants are operative kinetically, but also nonmicellized surfactants are influencing the reactivity. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 377–384, 1997     

Interaction studies of styrene—ethylene oxide block copolymers with ionic surfactants in aqueous solution

The interaction of styrene—ethylene oxide block copolymers with four anionic surfactants (sodium dodecyl sulfate, sodium dodecanoate, sodium dodecylbenzenesulfonate, and sodium dodecanoyl sarcosinate), and two cationic surfactants (tetradecyl- and hexadecyl-trimethylammonium bromide), was studied and each surfactant showed a distinct interaction with the copolymer in aqueous solution. Usually two transitions, one below and one above the critical micelle concentration, CMC, of the surfactants, were observed from conductance, surface tension, and dye solubilization measurements. These transitions indicate the beginning and completion of polymer—surfactant interaction. The viscometric results showed the formation of a polyelectrolyte complex. The interaction between copolymer and sodium dodecyl sulfate was also examined by ¹H NMR. The influence of the molecular characteristics of the block copolymers, the nature and type of surfactants, temperature and added salt on the interaction is described. A possible mechanism for such an interaction is proposed.     

Physicochemical Properties of Aqueous Solutions of Binary Mixtures of Lignin Derivatives and Sodium Dodecyl Sulfate

Physicochemical properties of aqueous solutions of binary mixtures of lignosulfonates and sodium dodecyl sulfate were studied. Introduction of sodium dodecyl sulfate into solutions of high-molecular-mass lignosulfonates at certain ratios causes macrophase separation of the systems with the formation of loose precipitates. A synergistic effect of a decrease in the surface tension is observed in the mixed solutions. This effect increases with increasing lignosulfonate molecular mass and temperature. The revealed relationships are caused by hydrophobic interactions of hydrocarbon radicals of sodium dodecyl sulfate with hydrophobic segments of lignosulfonate polymer chains with the formation of micellar associates. Aqueous solutions of binary mixtures of lignosulfonates (с_LS ≥ 0.2 g dm^–3) and sodium dodecyl sulfate (с_DSNa ≥ 0.08 g dm^–3) can be recommended for use as surfactant formulations for high-temperature autoclave leaching of polymetal ores.     

Removal of sulfate from wastewater via synthetic Mg–Al layered double hydroxide: An adsorption,kinetics, and thermodynamic study

Sulfate-contaminated water is a major environmental problem that alters the taste of water, disturbs the digestive systems of animals and humans, and erodes both soil and metals. In this study, the layered double hydroxide LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ were prepared using a co-precipitation technique, and applied in the adsorption of SO₄^2- from an aqueous solution. The reaction is well described by the Langmuir adsorption model. LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ afforded maximum SO₄^2- adsorption values of 135.14 and 92.59 ​mg/g, respectively. The reaction is best explained by a pseudo-second-order mechanism, which suggests that chemisorption is the rate-determining step. The activation energies of LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ indicate that the adsorption of SO₄^2- on synthetic LDHs predominantly follows an anion-exchange mechanism, wherein SO₄^2- ions in the aqueous medium replaces intercalated NO₃^- ions in the synthetic LDHs. The thermodynamic parameters (ΔH̊, ΔS̊, and ΔG̊) were also calculated. The reaction was endothermic, and the synthetic LDHs afforded feasible and spontaneous adsorption of SO₄^2-.     

软模板法制备三维花状MgAl-LDH及其吸附性能

采用软模板法,以十二烷基硫酸钠(SDS)为模板剂,经水热合成制得三维花状双金属(Mg Al)氢氧化物(3D-Mg Al LDH)。通过XRD、FT-IR、SEM及TEM等表征手段,研究了原料Mg/Al物质的量之比、SDS浓度及反应时间对产物微观结构和表面形貌的影响规律,并初步探讨了3D-Mg Al LDH的形成机理。结果表明,当n_(Mg)/n_(Al)=2,SDS浓度为0.1 mol·L~(-1),水热反应时间为6 h时,可形成结晶度良好、花球形貌完整,纳米片厚度均一的三维花状LDH。在3D-Mg Al LDH的形成过程中,SDS既以阴离子形态参与LDH形成,又因其类球状胶束特性附着在已形成的LDH表面或边缘诱导LDH纳米片交叉生长形成三维花状。吸附实验表明,3D-Mg Al LDH对非离子型有机污染物具有良好的吸附作用,最大吸附量约为31 mg·g~(-1),去除率达到100%。     

Effect of micelles on pKa* of acridine: a spectroscopic study

The effect of anionic, nonionic and cationic surfactants on the protonation reaction of acridine in an excited state has been studied. In the case of sodium decyl sulfate and sodium dodecyl sulfate, the observed shift in pK * to a more alkaline region was +0.6 and +0.9 units (from 9.9 to 10.5 and 10.8 respectively), which corresponds to a decrease in the Gibbs free energy by 3.5 and 5.0 kJ mol^–1.     

Salt Effects on the Aqueous Two-Phase System of Gemini(12-3-12, 2Br<Superscript>−</Superscript>)/SDS/PEG

The effect of added salts (NaCl, KCl and NaBr) on the aqueous two-phase system (ATPS) formed in mixtures of Gemini(12-3-12, 2Br⁻)/sodium dodecyl sulfate/polyethylene glycol has been investigated. Phase diagrams of the aqueous systems containing Gemini(12-3-12, 2Br⁻), sodium dodecyl sulfate (SDS), polyethylene glycol(PEG) and a salt have been determined experimentally at 313.15 K. The results indicate that the addition of salts not only induces the appearance of ATPS-A (in which anionic surfactant is in excess), shortens the phase separation time, enlarges the regions of ATPS-C (in which cationic surfactant is in excess), and decreases the minimum concentration required for forming an ATPS, but also alters the matching between anionic and cationic surfactants. Extractive experiments also showed that these salts notably enhance the extraction ability of ATPS; the Gemini-rich phase exhibits prominent cohesive action with xylenol orange, regardless of whether or not it is the upper phase or the lower phase.     

Removal of cadmium ions using micellar-enhanced ultrafiltration with mixed anionic-nonionic surfactants

Micellar-enhanced ultrafiltration (MEUF) was used to remove cadmium ions from wastewater efficiently. In this study the nonionic surfactants polyoxyethyleneglycol dodecyl ether (Brij35) and polyoxyethylene octyl phenyl ether (TritonX-100) were for micellar-enhanced ultrafiltration to lower the dosage of the anionic surfactant sodium dodecyl sulfate (SDS). The surfactant critical micelle concentration (CMC) and the degree of micelle counterion binding were investigated. The effects of nonionic surfactant addition on the efficiency of cadmium removal, the residual quantities of surfactant, the permeate flux and the secondary membrane resistance were investigated. A comparison between MEUF with SDS and MEUF with mixed anionic–nonionic surfactants was undertaken. The results show that the addition of Brij35 or TritonX-100 reduced the CMC of SDS and the degree of counterion binding for the micelles. Due to these variations the Cd²⁺ rejection efficiency was at a maximum when the Brij35:SDS and the TritonX-100:SDS molar ratio was 0.5. The Cd²⁺ rejection efficiency in MEUF with SDS is higher than for MEUF with mixed surfactants when the total dose of surfactant is constant. The permeate flux of MEUF with SDS is higher than that for MEUF with mixed surfactants while the secondary resistance of MEUF with SDS is less than that of MEUF with mixed surfactants.     

Synthesis and properties of nonylphenol-substituted dodecyl sulfonate

Nonylphenol-substituted dodecyl sulfonate (C₁₂-NPAS) was synthesized via sulfonation-alkylation-neutralization using 1-dodecene, SO₃, and nonylphenol as raw materials. The properties such as surface tension, interfacial tension (IFT), wettability, foam properties, and salinity tolerance of C₁₂-NPAS were systematically investigated. The results show that the critical micelle concentration (CMC) of C₁₂-NPAS was 0.22?mmol?·?L^?1 and the surface tension at the CMC (γ_CMC) of C₁₂-NPAS was 29.4 mN/m. When compared with the traditional surfactants sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), and linear alkylbenzene sulfonate (LAS), the surface properties of C₁₂-NPAS were found to be superior. The IFT between Daqing crude oil and a weak-base alkaline/surfactant/polymer (ASP) oil flooding system containing 0.1?wt% of C₁₂-NPAS can reach an ultralow level of 2.79?×?10^?3 mN/m, which was lower than that found for the traditional surfactant heavy alkylbenzene sulfonate (HABS). The salinity and hardness tolerance of C₁₂-NPAS were much stronger than those found for conventional surfactants, petroleum sulfonate, and LAS. C₁₂-NPAS also shows improved wetting performance, foamability, and foam stability.     

Interactions between Poly(ethylene oxide) and Sodium Alkylcarboxylates As Studied by Conductivity and Gel Permeation Chromatography

The interactions between PEO and sodium alkylcarboxylates (octyl, decyl, and dodecyl) have been investigated by conductivity measurements and gel permeation chromatography (GPC). Also included in the study was sodium dodecyl sulfate. From the conductivity measurements the critical aggregation concentration, ionization degree, and binding ratios were determined; the binding ratio was also determined from GPC. PEO–surfactant interactions were observed for all the studied surfactants, except sodium octanoate. For the polymer–surfactant complexes the ionization degree was in all cases observed to be about 0.2 higher than the ionization degree for the corresponding aqueous micelles. Further, the binding ratio decreased somewhat with decreasing chain length of the alkylcarboxylate. The Gibbs free energy showed that the polymer–surfactant interaction decreases with decreasing chain length of the alkylcarboxylates and is weaker for alkylcarboxylate compared to alkylsulfate of similar chain length.     

Electrocatalysis Oxidation of GMP Based on Layered Double Hydroxide Functionalized with Anionic Surfactant and Room Temperature Ionic Liquid Modified Glassy Carbon Electrode

The electrocatalysis oxidation of guanosine‐5′‐monophosphate (GMP) was investigated on Mg‐Al layered double hydroxide (LDH) functionalized with sodium dodecyl sulfate (SDS) and room temperature ionic liquid (RTIL) modified glass carbon electrode (GCE). The cyclic voltammogram of GMP on the modified electrode (RTIL/ LDH‐SDS/GCE) exhibited a well defined anodic peak at 1.091 V in 0.2 mol·L^?1 pH 4.4 acetate buffer solution. The GMP oxidation was enhanced in the presence of anionic surfactant in the ?lms. The results suggest that the surfactant molecules intercalate the LDH layers to preconcentrate GMP molecules and the RTIL showed good ionic conductivity. The experimental parameters were optimized, the kinetic parameters were investigated and the probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to GMP concentration in the range from 5.0×10^?7 to 1.0×10^?4 mol·L^?1 with the correlation coefficient of 0.9987 and the detection limit was 1.0×10^?7 mol·L^?1. The RTIL/LDH‐SDS/GCE showed a good electrochemical response to the oxidation of GMP and would be developed into a new biosensor.     

Suppression of surfactant interferences in anodic stripping voltammetry by sodium dodecyl sulfate

It was investigated whether interferences from surfactants in anodic stripping voltammetry (ASV) could be remedied by the anionic surfactant sodium dodecyl sulfate (SDS) which causes little or no interference in itself. Cadmium and lead were used as test analytes, and measurements were performed in acetate buffer as well as in 0.1 M HNO₃. One hundred parts per million of the interfering surfactant was added. SDS eliminated severe interference from the non-ionic surfactants Triton^© X-100 and dodecyl octaethylene glycol ether as well as from the polymer polyethylene glycol 6000 and from the cationic surfactant cetyl trimethyl ammonium bromide. SDS could not remedy the extraordinarily severe interference from the cationic surfactant cetyl pyridinium chloride. Two anionic surfactants were also tested as interferents but they had little detrimental effect on the ASV signals. The effect of SDS was explained by the formation of mixed micelles which scavenge the interferent in the bulk solution and by competitive displacement of the interferent at the electrode surface.     

镁铁水滑石的制备及其对小球藻油脂合成生物柴油的催化性能

用改良尿素法制备了镁铁水滑石(MgFe-LDH),对其在小球藻油脂合成生物柴油反应中的催化性能进行了研究。利用XRD、FT-IR、SEM及FT-IR拟合、去卷积分析等技术对所制备的MgFe-LDH进行了表征,考察了pH值、Mg/Fe摩尔比、反应温度和时间对其结构和性能的影响。结果表明,Mg/Fe摩尔比为3或4、pH值为9.5,在110 ℃条件下反应10 h,所制备的MgFe-LDH(Mg3Fe或Mg4Fe)结晶度最高,粒径均匀,结构规整。与Mg/Fe摩尔比为2的MgFe-LDH(Mg2Fe)相比,Mg3Fe或Mg4Fe在完全分解焙烧时,其层板结构保持稳定,具有较高的晶体结晶度、较多的催化活性位和较高的催化活性。以Mg3Fe金属氧化物为催化剂,在醇/油摩尔比为6时反应1.5 h,生物柴油产率可达87％;该催化剂循环使用3次,仍具一定催化活性。     

高盐油藏下两性/阴离子表面活性剂协同获得油水超低界面张力

研究了在高盐油藏中, 利用两性/阴离子表面活性剂的协同效应获得油水超低界面张力的方法. 两性表面活性剂十六烷基磺基甜菜碱与高盐矿化水具有很好的相容性, 但在表面活性剂浓度为0.07%-0.39%(质量分数)范围内仅能使油水界面张力达到10^-2 mN·m^-1量级, 加入阴离子表面活性剂十二烷基硫酸钠后则可与原油达到超低界面张力. 通过探讨表面活性剂总浓度、金属离子浓度、复配比例对油水动态界面张力的影响, 发现两性/阴离子表面活性剂混合体系可以在高矿化度、低浓度和0.04%-0.37%的宽浓度范围下获得10^-5 mN·m^-1量级的超低界面张力, 并分析了两性/阴离子表面活性剂间协同获得超低界面张力的机制.     

Surfactant media for constant-current coulometry. Application for the determination of antioxidants in pharmaceuticals

Effect of surfactant presence on electrochemical generation of titrants has been evaluated and discussed for the first time. Cationic (1-dodecylpyridinium and cetylpyridinium bromide), anionic (sodium dodecyl sulfate) and nonionic (Triton X100 and Brij^® 35) surfactants as well as nonionic high molecular weight polymer (PEG 4000) do not react with the electrogenerated bromine, iodine and hexacyanoferrate(III) ions. The electrogenerated chlorine chemically interact with Triton X100 and Brij^® 35. The allowable range of surfactants concentrations providing 100% current yield has been found. Chain-breaking low molecular weight antioxidants (ascorbic acid, rutin, α-tocopherol and retinol) were determined by reaction with the electrogenerated titrants in surfactant media. Nonionic and cationic surfactants can be used for the determination of antioxidants by reaction with the electrogenerated halogens. On contrary, cationic surfactants gives significantly overstated results of antioxidants determination with electrogenerated hexacyanoferrate(III) ions. The use of surfactants in coulometry of α-tocopherol and retinol provides their solubilization and allows to perform titration in water media. Simple, express and reliable coulometric approach for determination of α-tocopherol, rutin and ascorbic acid in pharmaceuticals using surfactant media has been developed. The relative standard deviation of the measurements does not exceed of 5%.     

Unique layered double hydroxide morphologies using reverse microemulsion synthesis

We report the first controlled synthesis of a layered double hydroxide (LDH) in a water-in-oil reverse microemulsion system. This synthesis of Mg2Al-LDHs was carried out in the reverse microemulsion of NaDDS (sodium dodecyl sulfate)-water-isooctane with water/surfactant molar ratio = 24. This enables us to obtain nanometer sized LDH platelets typically with a 40-50 nm diameter and 10 nm thickness. Further modification of the reverse microemulsion using triblock copolymers during crystallization allowed us to express different growth orientations of the LDH structure. These data show that the aspect ratio of LDHs can be flexibly adjusted over a wide range.     

The effects of alkyl sulfates on the analysis of phenolic compounds by microchip capillary electrophoresis with pulsed amperometric detection

The effects of different surfactants (sodium 2-ethylhexyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate and sodium tetradecyl sulfate) on the analysis of phenolic compounds by microchip-CE with pulsed amperometric detection were investigated. Using sodium decyl sulfate as a model surfactant, the effects of concentration and pH were examined. Under the optimized conditions, the analysis of six phenolic compounds was performed and compared with control runs performed without surfactant. When these surfactants were present in the run buffer, decreases in the migration time and increases in the run-to-run reproducibility were observed. Systematic improvements in the electrochemical response for the phenolic compounds were also obtained. According to the results presented, surfactants enhance the analyte-electrode interaction and facilitate the electron transfer process. These results should allow a more rational selection of the surfactants based on their electrophoretic and electrochemical effects.     

Kinetics of the interaction of Cd(II)-histidine complex with ninhydrin in absence and presence of cationic and anionic micelles

Kinetics of the interaction of Cd(II)-histidine complex with ninhydrin has been carried out at pH 5.02 (acetic acid-sodium acetate buffer) under varying conditions of reactant concentrations, temperature, and surfactant concentrations. The order of the reaction with respect to Cd(II)-histidine complex was unity while it was fractional with respect to ninhydrin. On the basis of these studies a mechanism has been proposed. In the absence of the surfactants, the reaction followed rate equation: while, in presence of surfactants, the following rate equation was obeyed: Anionic micelles of sodium dodecyl sulphate catalyze the reaction with the rate reaching a maximum at ca. 0.10 mol dm⁻³ surfactant. The surfactant decreases activation enthalpy and makes it more negative. Cationic micelles of cetyltrimethylammonium bromide strongly inhibit the reaction and increase the activation enthalpy but make the activation entropy more positive than the SDS micelles. Added salts (KNO₃ and NaCl) inhibit the catalysis, and the effect is more with the latter. The rate constants, binding constants with surfactants, and the index of cooperativity have been evaluated. © 1997 John Wiley & Sons, Inc.     

Decomposition of di-tert-butyl nitroxide in aqueous solutions

Di-tert-butyl nitroxide (DTBN) decomposes in aqueous solutions producing 2-methyl-2-nitroso propane (MNP) and tert-butanol. The process is acid catalyzed, it is of second order in DTBN, and takes place with a rate constant of (1.0 ± 0.1) M^?2 s^?1. The reaction is also catalyzed by the anionic surfactant sodium dodecyl sulfate and by Fe(II) and Fe(III) ions. The catalysis by Fe(III) involves a very fast reduction of Fe(III) ions with concomitant formation of 2-methyl-2-nitroso propane. The reaction catalyzed by Fe(II) also produces 2-methyl-2-nitroso propane with a formation rate given by: d[MNP]/dt = (0.25 ± 0.10) [Fe(II)] [DTBN]. This reaction rate is nearly pH independent.