Mixed Cationic-Nonionic Surfactants Route to MCM-48: Effect of the Nonionic Surfactant on the Structural Properties

Structurally ordered MCM-48 silicas were facilely synthesized using the mixtures of cetyltrimethylammonium bromide (CTAB) and p-Octyl polyethylene glycol phenyl ether (OP-10) as co-templates with low molar ratio of CTAB to silica (0.139:1) and low concentration of mixed surfactants (ca. 5%) and within a wide range of OP-10/CTAB ratio (0.08–0.25). For comparison purpose, the cubic material was also prepared with only CTAB as the structure-directing agent under the same preparation conditions. The products obtained by different templating method were thoroughly characterized by XRD, N₂ sorption, TEM, TG-DSC and ²⁹Si MAS NMR. Measurement results from these techniques indicated that the introduction of nonionic OP-10 had significant effect on the structural properties of MCM-48 and the mixed surfactants' route allowed an efficient synthesis and a more condensed product compared to the only cationic CTAB templating protocol. Finally, our preliminary explanation for that why cubic MCM-48 materials could be obtained in this system and structural properties were sensitive to the OP-10/CTAB ratios was discussed in detail.     

Micellar‐accelerated hydrolysis of organophosphate and thiophosphates by pyridine oximate

Rate constants for the hydrolysis reaction of phosphate (paraoxon) and thiophosphate (parathion, fenitrothion) esters by oximate (pyridinealdoxime 2‐PyOx⁻ and 4‐PyOx⁻) and its functionalized pyridinium surfactants 4‐(hydroxyimino) methyl)‐1‐alkylpyridinium bromide ions (alkyl = C_nH_2n+1, n = 10, 12, 14, 16) have been measured kinetically at pH 9.5 and 27°C in micellar media of cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB). Acid dissociation constant, pK_a, of oximes has also been determined by spectrophotometric, kinetic, and potentiometric methods. The rate acceleration effects of cationic micelles have been explored. Cationic micelles of the pyridinium head group (CPB) showed a large catalytic effect than the ammonium head group (CTAB). The effects of pH, oximate concentration, and surfactants have been discussed.     

The α‐effect in micelles: Nucleophilic substitution reaction of p‐nitrophenyl acetate with N‐phenylbenzohydroxamate ion

Pseudo‐first‐order rate constants have been determined for the nucleophilic substitution reactions of p‐nitrophenyl acetate with p‐chlorophenoxide (4‐ClC₆H₄O^?) and N‐phenylbenzohydroxamate (C₆H₅CON(C₆H₅)O^?) ions in phosphate buffer (pH 7.7) at 27°C. The effect of cationic, (CTAB, TTAB, DTAB), anionic (SDS), and nonionic (Brij‐35) surfactants has been studied. The k_obs value increases upon addition of CTAB and TTAB. The effect of DTAB and other surfactants on the reaction is not very significant. The micellar catalysis and α‐effect shown by hydroxamate ion have been explained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 26–31, 2006     

A study on the hydrolysis of bis(nitrophenyl)phosphate catalyzed by N‐methyldiethanolamine‐Ce(III) complex

The hydrolysis of bis(p‐nitrophenyl)phosphate (BNPP) catalyzed by N‐methyldiethanolamine‐Ce(III) complex in the presence and absence of cetyltrimethylammonium bromide (CTAB) and Brij35 surfactants at pH 7.20 and 303 K has been studied. The experimental results indicate that N‐methyldiethanolamine‐Ce(III) complex remarkably accelerates the hydrolysis of BNPP. The observed first‐order rate constant of the hydrolysis of BNPP catalyzed by N‐methyldiethanolamine‐Ce(III) complex at pH 7.20 and 303 K is 1.22 × 10^?2 s^?1, which is 1.09 × 10⁹ times of that of spontaneous hydrolysis of BNPP at pH 7. It is close to the activity of natural enzyme. A general quantitative treatment of the catalytic reaction involved a ternary complex as M_mL_lS has also been proposed in this paper. Applying this method to the catalytic hydrolysis of BNPP, we have obtained its thermodynamic and kinetic parameters. CTAB and Brij35 surfactant micelles obviously influence the rate constants of the catalytic hydrolysis of BNPP. Brij35 micelles promote the catalytic hydrolysis of BNPP, while CTAB micelles inhibit it. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 687–692, 2004     

Preparation of Mesoporous 1,4‐Phenylene‐silica Nanorings through a Dual‐templating Approach

Mesoporous 1,4‐phenylene‐silica nanorings were prepared using cetyltrimethylammonium bromide (CTAB) and (S)‐2‐methyl‐1‐butanol as a chiral dopant in concentrated aqueous NH₃ solutions. Transmission electron microscopy images of the samples indicated that the nanorings were formed by bending nanorods 360°. With increasing the stirring speed or the (S)‐2‐methyl‐1‐butanol/CTAB molar ratio, the morphologies of mesoporous 1,4‐phenylene‐silicas changed from helical nanofibers to nanorings, and then to nano‐saddles. Circular dichroism spectra of these hybrid silicas indicated that they were chiral.     

Simultaneous Determination of Mixtures of Nitrite and Nitrate by Reversed‐Phase Ion‐Pair Liquid Chromatography

To overcome the relatively low resolution in the separation and quantitative analysis of mixtures of nitrite and nitrate, a reversed‐phase ion‐pair liquid chromatographic method is developed with advantages of high accuracy, good selectivity, high efficiency, and low cost. By employing cetyltrimethylammonium bromide (CTAB) as the ion‐pair reagent, this method can work excellently in situations where one component in the mixture is highly in excess (e.g., molar ratio of n( NO₂⁻):n(NO₃⁻) ranging from 1:99 to 95:5). The operation parameters were optimized on a Shim‐pack VP‐ODS(150 L × 4.6) analytical column using a methanol/water ratio of 50:50 (v/v) mobile phase containing 7.0 mmol/L CTAB and 3.1 mmol/L potassium dihydrogen phosphate (KH₂PO₄).The column works at a temperature of 35 °C with a flow rate of 1.5 mL/min. Such a protocol can be applied to monitor the formation of trace nitrous acid during the oxidative decomposition of nitric acid.     

Effect of salts on synthesis of mesoporous materials with mixed cationic and anionic surfactants as templates

Mesoporous silica materials were synthesized using tetraеthoxysilane as precursor and liquid crystals formed in aqueous mixtures of cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) as templates, without and with the addition of NaBr or Na₂SO₄. For this purpose, the formation of liquid crystals as a function of the ratio of CTAB and SDS under different conditions was studied. It was found that liquid crystals formed in the mixed system of CTAB and SDS at certain mixing ratios are well-structured templates for the synthesis of mesoporous silicas. The synthesized silica materials were characterized by transmission electron microscope and nitrogen adsorption/desorption analysis. The pore size of mesoporous silicas could be controlled between 3 to 6 nm by simply changing the concentration of NaBr in solution. The mesoporous silicas exhibited lamellar structure and the order of structural arrangement was promoted with addition of NaBr. However, addition of Na₂SO₄ led to ink-bottle type pores of mesoporous silica with a narrow pore size distribution of around 2 nm and a higher specific surface area of 610 m² g^–1.     

A surfactant‐free synthesis of the silica nanosphere‐supported ultrafine silver nanoparticles and their antibacterial effects

In this study, a facile, efficient, and surfactant‐free method to synthesize silica nanosphere‐supported ultrafine silver nanoparticles (AgNPs) (~2.5 nm) was developed, and their antibacterial effects were investigated. In the synthesis process, the hydrolysis of 3‐mercaptopropyltrimethoxysilane was adopted to provide thiol groups and in situ reduce Ag⁺ to Ag⁰ for ultrafine AgNPs formation on the surface of the silica nanosphere. Electron microscopy characterization of the complex formed revealed that the ultrafine AgNPs were not agglomerated and grow without any surfactants because there were no excess electrons transported from the shell to reduce the silver ions to silver atoms. The antibacterial effects of the supported ultrafine AgNPs with the surfactant‐free surface were evaluated against the Escherichia coli even at very low dosage. After incubation with 20 μg/mL silica‐supported AgNPs up to 120 min, 99.7% of the E. coli were inactivated, according to the bacterial viability measured by flow cytometry.     

Temperature dependent synthesis of micro- and meso-porous silica employing the thermo-responsive polymer of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) as structure-directing agent

Temperature dependent synthesis of micro- and meso-porous silica employing the thermo-responsive homopolymer poly(N-isopropylacrylamide) or the random copolymer poly(N-isopropylacrylamide-co-acrylic acid) as structure-directing agent (SDA) and Na₂SiO₃ as silica source is proposed. The thermo-responsive character of the SDA provides the advantages including (1) temperature dependent synthesis of microporous silica, hierarchically micro-mesoporous silica, and mesoporous silica just by changing the aging temperature below or above the low critical solution temperature of the thermo-responsive SDA, and (2) elimination of the thermo-responsive SDA from silica matrix by water extraction. The synthesis mechanism is discussed, and the effect of the aging temperature and the weight radio of SDA/Na₂SiO₃ on the synthesis of micro- and meso-porous silica are studied. Microporous silica, hierarchically micro-mesoporous silica and mesoporous silica with the surface area at 3.5−9.0 × 10² m²/g and the pore volume at 0.28−1.13 cm³/g and the average pore size ranging from 1.1 to 9.0 nm are synthesized. The strategy affords a new and environmentally benign way to fabricate porous silica materials, and is believed to bridge the gap between the synthesis of microporous and mesoporous silica materials.     

Binding on strong polyelectrolytes of mixed ionic and nonionic surfactants below their critical micelle concentration observed by fluorescence

The binding of mixed surfactants of cationic cetyltrimethylammonium bromide (CTAB) and nonionic octaethylene glycol monododecyl ether (C ₁₂E ₈) on anionic polyelectrolyte poly[2-acrylamido-2-methylpropanesulfonic acid (PAMPS)] and fluorophore-labeled copolymers containing about 40 mol% of AMPS was investigated at different mole fractions, Y , of CTAB in the surfactant mixture. The excimer emission of the cationic probe 1-pyrenemethylamine hydrochloride (PyMeA·HCl), nonradiative energy transfer (NRET) between pyrene and naphthalene labels and I ₁/ I ₃ of the pyrene label were determined by varying the total surfactant concentration, c _Surf. The I _E/ I _M value of PyMeA·HCl firstly increases and then decreases to 0 with c _Surf, showing a maximum on every curve. The critical aggregation concentration of the mixed surfactants determined from the I _E/ I _M maximum decreased from 5×10 ^-5 to 1×10 ^-5 mol/l as Y increased from 0.1 to 0.50, and then leveled off as Y increased up to unity. And at least 5×10 ^-6 mol/l CTAB was required for the mixed surfactants to bind on the PAMPS cooperatively. Equimolar binding of CTAB on AMPS was formed at I _E/ I _M=0 when Y =0.25, while at Y =0.1 some CTAB molecules in the mixed micelle were directed to the water phase without binding with AMPS. Both the intramolecular and the intermolecular NRET increased and then decreased with c _Surf, having a maximum on each curve corresponding to the equimolar binding of CTAB and AMPS so long as Y >0, indicating the coiling of the chain and interchain aggregation upon bound surfactants. The I _Py/ I _Np value at the maximum decreased with decreasing Y because more nonionic surfactant C ₁₂E ₈ participated into the polyelectrolyte-mixed surfactant complexes together with bound CTAB.     

Dual Soft‐Template System Based on Colloidal Chemistry for the Synthesis of Hollow Mesoporous Silica Nanoparticles

A new dual soft‐template system comprising the asymmetric triblock copolymer poly(styrene‐b‐2‐vinyl pyridine‐b‐ethylene oxide) (PS‐b‐P2VP‐b‐PEO) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is used to synthesize hollow mesoporous silica (HMS) nanoparticles with a center void of around 17 nm. The stable PS‐b‐P2VP‐b‐PEO polymeric micelle serves as a template to form the hollow interior, while the CTAB surfactant serves as a template to form mesopores in the shells. The P2VP blocks on the polymeric micelles can interact with positively charged CTA⁺ ions via negatively charged hydrolyzed silica species. Thus, dual soft‐templates clearly have different roles for the preparation of the HMS nanoparticles. Interestingly, the thicknesses of the mesoporous shell are tunable by varying the amounts of TEOS and CTAB. This study provides new insight on the preparation of mesoporous materials based on colloidal chemistry.     

Nanoscale Control Over Interfacial Properties in Mixed Reverse Micelles Formulated by Using Sodium 1,4‐bis‐2‐ethylhexylsulfosuccinate and Tri‐n‐octyl Phosphine Oxide Surfactants

The interfacial properties of pure reverse micelles (RMs) are a consequence of the magnitude and nature of noncovalent interactions between confined water and the surfactant polar head. Addition of a second surfactant to form mixed RMs is expected to influence these interactions and thus affect these properties at the nanoscale level. Herein, pure and mixed RMs stabilized by sodium 1,4‐bis‐2‐ethylhexylsulfosuccinate and tri‐n‐octyl phosphine oxide (TOPO) surfactants in n‐heptane were formulated and studied by varying both the water content and the TOPO mole fraction. The microenvironment generated was sensed by following the solvatochromic behavior of the 1‐methyl‐8‐oxyquinolinium betaine probe and ³¹P NMR spectroscopy. The results reveal unique properties of mixed RMs and we give experimental evidence that free water can be detected in the polar core of the mixed RMs at very low water content. We anticipate that these findings will have an impact on the use of such media as nanoreactors for many types of chemical reactions, such as enzymatic reactions and nanoparticle synthesis.     

In Situ Small‐Angle X‐ray Scattering Investigation of the Formation of Dual‐Mesoporous Materials

The formation of a 2D‐hexagonal (p6m) silica‐based hybrid dual‐mesoporous material is investigated in situ by using synchrotron time‐resolved small‐angle X‐ray scattering (SAXS). The material is synthesized from a mixed micellar solution of a nonionic fluorinated surfactant, R^F₈(EO)₉ (EO=ethylene oxide) and a nonionic triblock copolymer, P123. Both mesoporous networks, with pore dimensions of 3.3 and 8.5 nm respectively, are observed by nitrogen sorption, transmission electron microscopy (TEM), and SAXS. The in situ SAXS experiments reveal that mesophase formation occurs in two steps. First the nucleation and growth of a primary 2D‐hexagonal network (N1), associated with mixed micelles containing P123, then subsequent formation of a second network (N2), associated with micelles of pure R^F₈(EO)₉. The data obtained from SAXS and TEM suggest that the N1 network is used as a nucleation center for the formation of the N2 network, which would result in the formation of a grain with two mesopore sizes. Understanding the mechanism of the formation of such materials is an important step towards the synthesis of more‐complex materials by fine tuning the porosity.     

Preparation of remarkably tough polyHIPE materials via polymerization of oil‐in‐water HIPEs involving 1‐vinyl‐5‐aminotetrazole

Interconnected microcellular polymeric monoliths having unexpected high mechanical strength have been prepared using the high internal phase emulsion (HIPE) methodology. Oil‐in water concentrated emulsions of aqueous 1‐vinyl‐5‐amino [1,2,3,4]tetrazole (1‐VAT) mixed with a low molar ratio (7%) of N,N′‐methylenebisacrylamide as crosslinking agent were prepared using dodecane as dispersed phase and a mixture of hydrophilic surfactants. “Reverse” polyHIPE materials were obtained after radical copolymerization, solvent extraction, and drying. Their morphology, chemical composition, and physicochemical behavior are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2942–2947, 2010     

Effect of dicationic gemini surfactants 16–s‐16 (s = 4, 5, 6) on the ninhydrin‐dipeptide (glycyl‐tyrosine) reaction

The effect of dicationic gemini surfactants H₃₃C₁₆(CH₃)₂N⁺‐(CH₂)_s‐N⁺(CH₃)₂ C₁₆H₃₃, 2Br^? (s= 4, 5, 6) on the reaction of a dipeptide glycyl–tyrosine (Gly–Tyr) with ninhydrin has been studied spectrophotometrically at 70°C and pH 5.0. The reaction follows first‐ and fractional‐order kinetics, respectively, in [Gly–Tyr] and [ninhydrin]. The gemini surfactant micellar media are comparatively more effective than their single chain–single head counterpart cetyltrimethylammonium bromide (CTAB) micelles. Whereas typical rate constant (k_Ψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produces a third region of increasing k_Ψ at higher concentrations. This subsequent increase is ascribed to the change in the micellar morphology of the geminis. The pseudophase model of micelles was used to quantitatively analyze the k_Ψ ? [gemini] data, wherein the micellar‐binding constants K_S for [Gly–Tyr] and K_N for ninhydrin were evaluated. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 800–809, 2012     

表面活性剂辅助合成LiNi0.8Co0.1Mn0.1O2正极材料

通过添加烷基季铵盐类表面活性剂来调控材料形貌和粒径的改性方法,在LiNi_0.8Co_0.1Mn_0.1O₂前驱体合成过程中添加表面活性剂十二烷基三甲基溴化铵(DTAB)和十六烷基三甲基溴化铵(CTAB),利用尿素作为配合剂和沉淀剂,采用溶剂热法合成LiNi_0.8Co_0.1Mn_0.1O₂前驱体。最后,高温混锂煅烧合成椭球形的空心多孔材料。相比于不添加表面活性剂的样本,改性的材料有着更小的粒径和更加规整的形貌。电化学测试表明,添加DTAB和CTAB之后,首次充电容量分别达到223与251 mAh·g^-1(0.1C)。其中,添加CTAB的样品首次放电容量达到216 mAh·g^-1(0.1C),100次循环后容量保持率为85.1%,高于LiNi_0.8Co_0.1Mn_0.1O₂的81.7%(0.1C)。表面活性剂的改性显著提高了材料的电化学性能,为高镍三元正极材料的改性提供了一种新的思路。     

Influence of Amine‐Based Cationic Gemini Surfactants on Catalytic Activity of α‐Chymotrypsin

The α‐chymotrypsin activity was tested in aqueous media with the presence of novel cationic amine–based gemini surfactant, with different spacer chain lengths and head group size, and also compared with the cationic cetyltrimethylammonium bromide (CTAB) and cetyltriphenylphosphonium bromide (CTPB) surfactants and aqueous buffer only. The p‐nitrophenyl acetate (PNPA) hydrolysis rate was monitored in the presence of the surfactant concentration at 30°C. Most of these gemini surfactants gave higher catalytic activity as compared to cationic CTAB and CTPB. The highest superactivity was measured in the presence of gemini 16‐12‐16, [dodecanediyl‐1,12‐bis(cetyldimethylammonium bromide)] surfactant at pH 7.5. The catalytic reaction follows the Michaelis–Menten mechanism. The catalytic rate constants, k_cat, show the same profile that the catalytic affinity; K_M being enhanced with increasing space chain length. The results are favorable for considering that the amine‐based gemini surfactant influences more than both the aqueous and cationic micellar media.     

Dispersion of TiO2 on high‐surface‐area mesoporous silica: functionalization with tungstophosphoric acid and application in solvent‐free,aerobic oxidation of n‐hexadecane

Imidazole type ionic liquid, 1‐hexadecyl‐3‐methylimidazolium chloride, was used to template the synthesis of high‐surface‐area mesoporous silica under acidic conditions and crystalline titanium dioxide (TiO₂) nanoparticles of anatase phase were inserted utilizing a solvent evaporation‐induced method. The surface area of more than 700 m² g^?1 was obtained after TiO₂ impregnation. Further, the polyoxometalate, 12‐tungstophosphoric acid (PW₁₂) was dispersed on the surface of TiO₂ to form PW₁₂–TiO₂–silica hybrid catalytic materials. The catalytic activity of this hybrid material was tested for solvent‐free, aerobic oxidation of n‐hexadecane. The experimental investigation shows that PW₁₂–TiO₂ nanocrystals did not block the pore channels and gave good conversion. Copyright © 2012 John Wiley & Sons, Ltd.     

Syntheses and structures of four new mixed‐amide phosphoric triamides

Phosphoric triamides have extensive applications in biochemistry and are also used as O‐donor ligands. Four new mixed‐amide phosphoric triamide structures, namely rac‐N‐tert‐butyl‐N′,N′′‐dicyclohexyl‐N′′‐methylphosphoric triamide, C₁₇H₃₆N₃OP, (I), rac‐N,N′‐dicyclohexyl‐N′‐methyl‐N′′‐(p‐tolyl)phosphoric triamide, C₂₀H₃₄N₃OP, (II), N,N′,N′′‐tricyclohexyl‐N′′‐methylphosphoric triamide, C₁₉H₃₈N₃OP, (III), and 2‐[cyclohexyl(methyl)amino]‐5,5‐dimethyl‐1,3,2λ⁵‐diazaphosphinan‐2‐one, C₁₂H₂₆N₃OP, (IV), have been synthesized and studied by X‐ray diffraction and spectroscopic methods. Structures (I) and (II) are the first diffraction studies of acyclic racemic mixed‐amide phosphoric triamides. The P—N bonds resulting from the different substituent –N(CH₃)(C₆H₁₁), (C₆H₁₁)NH–, 4‐CH₃‐C₆H₄NH–, (tert‐C₄H₉)NH– and –NHCH₂C(CH₃)₂CH₂NH– groups are compared, along with the different molecular volumes and electron‐donor strengths. In all four structures, the molecules form extended chains through N—H…O hydrogen bonds.     

Synthesis of Mesoporous Lithium Titanate Thin Films and Monoliths as an Anode Material for High‐Rate Lithium‐Ion Batteries

Mesoporous Li₄Ti₅O₁₂ (LTO) thin film is an important anode material for lithium‐ion batteries (LIBs). Mesoporous films could be prepared by self‐assembly processes. A molten‐salt‐assisted self‐assembly (MASA) process is used to prepare mesoporous thin films of LTOs. Clear solutions of CTAB, P123, LiNO₃, HNO₃, and Ti(OC₄H₉)₄ in ethanol form gel‐like meso‐ordered films upon either spin or spray coating. In the assembly process, the CTAB/P123 molar ratio of 14 is required to accommodate enough salt species in the mesophase, in which the Li^I/P123 ratio can be varied between molar ratios of 28 and 72. Calcination of the meso‐ordered films produces transparent mesoporous spinel LTO films that are abbreviated as Cxx‐yyy‐zzz or CAxx‐yyy‐zzz (C=calcined, CA=calcined–annealed, xx=Li^I/P123 molar ratio, and yyy=calcination and zzz=annealing temperatures in Celsius) herein. All samples were characterized by using XRD, TEM, N₂‐sorption, and Raman techniques and it was found that, at all compositions, the LTO spinel phase formed with or without an anatase phase as an impurity. Electrochemical characterization of the films shows excellent performance at different current rates. The CA40‐350‐450 sample performs best among all samples tested, yielding an average discharge capacity of (176±1) mA h g^?1 at C/2 and (139±4) mA h g^?1 at 50 C and keeping 92 % of its initial discharge capacity upon 50 cycles at C/2.