Sol–gel encapsulation of bromothymol blue pH indicator in presence of Gemini 12-2-12 surfactant

A sol–gel approach was used to encapsulate bromothymol blue (BTB) C₂₇H₂₈Br₂O₅S pH indicator into mesoporous silica material, in presence of ethanediyl-1,2-bis(dimethyldodecylammonium chloride) (Gemini 12-2-12) surfactant. An ordered mesoporous inorganic matrix including Gemini 12-2-12 and BTB was obtained. It is found that encapsulated BTB/Gemini 12-2-12 exhibit same behavior for pH change as that of the free BTB, which indicate that only physical interaction between BTB molecules and host mesoporous silica network are obtained. The addition of Gemini 12-2-12 surfactant has increased the porosity of the host silica material and increased its sensing capability. The presence of Gemini 12-2-12 surfactant has shifted pKa values of the system to more acidic in comparison with that of free BTB, BTB entrapped silica and BTB/CTAB entrapped silica.     

Preparation of mesoporous submicrometer silica capsules via an interfacial sol-gel process in inverse miniemulsion

Mesoporous silica capsules with submicrometer sizes were successfully prepared via the interfacial hydrolysis and condensation reactions of tetraethoxysilane (TEOS) in inverse miniemulsion by using hydrophilic liquid droplets as template. The inverse miniemulsions containing pH-controlled hydrophilic droplets were first prepared via sonication by using poly(ethylene-co-butylene)-b-poly(ethylene oxide) (P(E/B)-PEO) or SPAN 80 as surfactant. TEOS was directly introduced to the continuous phase of an inverse miniemulsion. The silica shell was formed by the deposition of silica on the surface of droplets. The formation of capsule morphology was confirmed by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The mesoporous structure was verified by nitrogen sorption measurements. The specific surface area could be tuned by the variation of the amount of cetyltrimethylammonium bromide (CTAB) and TEOS, and the pore size by the amount of CTAB. The influences of synthetic parameters on the particle size and morphology were investigated in terms of the amount of CTAB, pH value in the droplets, TEOS amount, surfactant amount, and type of solvent with low polarity. A formation mechanism of silica capsules was proposed.     

乙二亚甲基-双（十六烷基二甲基溴化铵）稀水溶液的特性

合成并表征了阳离子Gemini表面活性剂乙二亚甲基-α,β-双（十六烷基二甲基溴化铵）（16-2-16）.用表面张力和粘度法确定了其cmc，通过表面张力曲线计算了16-2-16的表面吸附量、吸附分子面积和胶束形成自由能；并用悬滴法测定了16-2-16在空气表面和十二烷界面的动态表（界）面张力.用改进的Washburn方法测定16-2-16水溶液在硅胶粉末表面的接触角，并进一步讨论了16-2-16在硅胶表面的吸附引起的润湿性变化. 探讨润湿性变化与动态张力的关系. 将16-2-16 与溴代十六烷基三甲胺(CTAB)做比较:两种物质在含油硅胶粉末上引起的最高脱油率（实验室模拟驱油）均发生在cmc附近,但16-2-16的最高脱油率是68％， CTAB的是63％.而所用CTAB的cmc比16-2-16的约大50倍,也就是说用16-2-16可以获得更高的脱油率.     

嵌段共聚物与阳离子表面活性剂混合模板合成介孔SiO_2

利用三嵌段共聚物EO_(20)PO_(70)EO_(20)与阳离子表面活性剂CTAB作为混合 模板合成了内部孔结构与外观形貌同时受到调控的介孔氧化硅。与使用单一共聚物 模板制备的介孔氧化硅相比，在混合模板作用下得到的介孔氧化硅的孔结构有序度 降低，而孔径则随混合模板中共聚物的质量分数的降低而减小。在EO_(20)PO_(70) EO_(20)与CTAB质量比为1:1时可得到形貌完好、表面光滑的介孔氧化硅微米球，其 平均孔径为3.2nm，比表面积为972m~2/g。     

Sol–gel encapsulation of cresol red in presence of surfactants

Cresol Red (CR) pH indicator was encapsulated into silica network using the sol–gel process. Transparent monolithic disks of entrapped CR were obtained in the presence of cetyl trimethyl ammonium bromide (CTAB) or dodecyl dimethyl amino oxide (Genaminox LA,GLA) alkyl hydroxyethyl dimethyl ammonium chloride (HY, R = 12–14) and TX-100 surfactants. UV/VIS spectra showed that the encapsulated CR retains its structure in terms of its response to pH. At the neutral conditions it is found that the HY surfactant is considered as proton donor as favor the cationic form of the indicator, while CTAB surfactant favor the neutral, however GLA surfactant, the anionic form of CR is more favored because GLA has a zwitterionic head. The surfactant GLA with TEOS has shifted the equilibrium to the ionized form of CR due to the electrostatic interaction between the surfactant and the CR anion. Therefore their pH range is dependent on the nature of a surfactant used. It is found that the HY surfactant is more efficient as far as loading of CR is concern and it widened the working pH range.     

包覆铕配合物Eu(DBM)3phen的硅胶纳米荧光检测材料的制备

以十六烷基三甲基溴化铵(CTAB)和一种短链氟碳阴离子表面活性剂(Capstone FS-66)作为双模板,通过四乙氧基硅烷(TEOS)和含氯官能团的硅烷偶联剂制备了含氯官能团的大孔径树枝状介孔二氧化硅纳米球(MSNs);利用EuCl3·6H2O、1,10-邻菲啰啉盐酸盐和二苯甲酰甲烷合成铕的配合物Eu(DBM)3phen,然后以MSNs为基质填充Eu(DBM)3phen。为了更好地将Eu(DBM)3phen嵌入到纳米球孔道内,对所制备的介孔纳米球的孔道表面进行聚乙烯亚胺(PEI)修饰;同时为了解决荧光配合物从孔道泄露的问题,在纳米球表面层层自组装吸附多层聚合物,然后包覆一层二氧化硅膜形成核-壳结构。最后将所制备的荧光纳米球与3-氨丙基三乙氧基硅烷反应,使其表面带有氨基,用来嫁接生物分子如抗体等。通过透射电子显微镜(TEM)、荧光光度计和傅里叶红外光谱仪(FTIR)等多种方法对最终合成的纳米球的结构和性能进行了表征。结果表明:本制备的荧光纳米球粒径约为230μm、荧光强度约为2800a.u,1543cm^-1处出现了氨基的弯曲振动峰。     

Encapsulation of Bromothymol Blue into a Polysiloxane Network Matrix in Presence of Surfactants

Bromothymol blue (BTB) pH indicator was encapsulated into polysiloxane network using the sol-gel process. Transparent monolithic disks of entrapped BTB were obtained in the presence of cetyl trimethyl ammonium bromide (CTAB) or dodecyl dimethyl amino oxide (Genaminox LA, GLA) surfactant. Ultraviolet visible spectra showed that the encapsulated BTB retains its structure in terms of its response to pH. The kinetic studies reveal that there was a faster response to pH in the case of GLA surfactant than in the case of CTAB. It is found that the co-entrapment of cationic surfactant CTAB or zwitterionic surfactant GLA with TEOS has shifted the equilibrium of the BTB to the ionized form due to the electrostatic interaction between the surfactant and the BTB anion and therefore the base form becomes more pronounced (e.g., shift from yellow to red) than that of sol-gel matrix without surfactant.     

Surfactant mediated synthesis of spherical binary oxides photocatalytic with enhanced activity in visible light

Spherical silica and zirconia mixed titania and pure titania samples were prepared in presence of cetyltrimethylammonium bromide (CTAB) through controlled hydrolysis of corresponding metal alcoxides. Effect of surfactant amount and calcinations temperature on morphology, surface area and photocatalytic activity is studied using PXRD, SEM, FTIR, Solid state UV-vis spectroscopy and BET surface area. It is well observed that in presence of 2 mol% CTAB, uniform sized spherical oxide particles can be synthesized. However, increasing or decreasing the surfactant amount does not favor the spherical particle formation. Material synthesis in presence of CTAB not only helps in the spherical particle formation but also increases the surface area and visible light absorption. Studies on photocatalytic lead removal with respect to calcination temperature indicate that the calcination at 500 degrees C is most suitable for the best photocatalytic activity. Mixing of zirconia and silica helps in anatase phase stabilization even at 900 degrees C calcination. Accordingly low decrease in surface area even at 900 degrees C calcination is observed. Due to the phase stabilization and higher surface area binary oxide materials showed comparatively better photocatalytic activity even after calcination at 900 degrees C. So it can be concluded that present synthesis approach can produce uniform sized spherical binary oxide materials with better photocatalytic activity in visible light.     

Magnetic properties and dye adsorption capacities of silica–hematite nanocomposites with well-defined structures prepared in surfactant solutions

Silica–hematite (α-Fe₂O₃) nanocomposites were synthesized by addition of aqueous solution containing ferrous ions (Fe²⁺), cetyltrimethylammonium bromide (CTAB) as a surfactant and tert-butanol (t-butanol) as a cosurfactant into colloidal silica solution. At alkaline atmosphere, silica surface with negative charges electrostatically attracts positively-charged iron hydroxide nuclei or particles which are stabilized by cationic CTAB molecules, and then silica–iron compound composites could be formed. Finally, the silica–hematite composite particles were obtained after calcination at 800 °C for 4 h. Through these processes, two types of composites having “core–shell type” or “decorated type” could be achieved. Morphology, BET surface area, crystallinity and magnetic properties of samples were analyzed by using TEM, BET, XRD and VSM, respectively. The “decorated type” composites had larger BET surface area and better magnetization. Also, to estimate the application in water treatment, adsorption properties of composites were studied through methylene blue (MB) adsorption which was characterized by UV–vis spectroscopy, involving collection of composites with neodymium magnet.     

Templated surfactant readsorption on polyelectrolyte-induced depleted surfactant surfaces

Changes in the structure of a surfactant adsorbed on oxidized silicon arising from interaction with a polyelectrolyte have been studied using polarized infrared attenuated total reflection spectroscopy. Specifically, the cationic surfactant cetyltrimethylammonium bromide (CTAB) was found to form a highly ordered layer on oxidized silicon at a concentration of 5.5 x 10(-5) M and a pH of 9.6. Addition of a solution of the anionic polyelectrolyte poly(styrenesulfonate) to the ordered CTAB layer resulted in a rapid and dramatic decrease in the surface excess of CTAB. Interestingly however, the interfacial order of the residual surfactant was retained for a time period greater than 1 h, before decreasing. Reintroduction of a surfactant solution prior to destabilization of the residual interfacial CTAB resulted in the readsorption of the surfactant, the recovery of the initial equilibrium coverage, and the maintenance of an ordered CTAB conformation. This desorption/readsorption process may be subsequently repeated without destroying the order of the CTAB on the surface. If however sufficient time is allowed for the residual interfacial surfactant to destabilize prior to readdition of CTAB, the degree of surfactant order remains low, despite the rapid reobtainment of a surface excess equal to or greater than that initially measured. These results are interpreted in terms of polymer/surfactant interfacial complexation and the removal of adsorbed surfactant into solution. The ordering behavior of the residual surfactant suggests that CTAB is left on the surface in isolated patches of highly ordered species that maintain their order until two-dimensional diffusion leads to a more homogeneous surfactant surface distribution and hence the loss of conformational order. The degree of orientation order assumed by surfactant readsorbing on a depleted surface appears to be templated by the order of the residual interfacial surfactant, suggestive of a two-dimensional epitaxial growth mechanism for CTAB readsorption.     

Biomolecular materials based on sol-gel encapsulated proteins

The proteins copper-zinc superoxide dismutase (CuZnSOD), cytochrome c, myoglobin, hemoglobin, and bacterio-rhodopsin are encapsulated in stable, optically transparent, porous, silica glass matrices prepared by the sol-gel method such that the biomolecules retain their characteristic reactivities and spectroscopic properties. The resulting glasses allow transport of small molecules into and out of the glasses at reasonable rates but retain the protein molecules within their pores. The transparency of the glasses enables the chemical reactions of the immobilized proteins to be monitored by means of changes in their visible absorption spectra. Silica glasses containing the immobilized proteins have similar reactivities and spectroscopic properties to those found for the proteins in solution. The enzymes glucose oxidase and peroxidase were also encapsulated in transparent silica glass matrices. Upon exposure to glucose solutions, a colored glass is formed that can be used as the active element in a solid state optically based glucose sensor.     

Gold-doped ceria–lanthana solid solution: surfactant assisted preparation,nanostructural and catalytic properties

The effect of preparation methods on the formation of gold doped ceria–lanthana solid solution (Au-CLSS) nanoparticles (NPs) was studied. The nanoparticles were prepared by surfactant assisted precipitation methods viz., co-precipitation (CP) and deposition precipitation (DP) in the presence of cetyltrimethylammonium bromide (CTAB). The as prepared nanoparticles were characterized using BET, FESEM, EDS, Raman, TEM, XRD and UV–Vis. spectroscopic techniques to investigate the preferred method for the preparation of nanoparticles for catalytic applications. The cubic fluorite phase formation of nanoparticles was confirmed by XRD analysis and the average crystallite size was calculated to be around 7–10 nm. Surface area studies revealed that the NPs formed by CTAB assisted method have higher surface area. The morphology of NPs formed by both methods was flaky. Raman studies confirmed that the samples prepared by DP method generated increased oxygen vacancies than those prepared by CP method. In the present work, catalytic oxidation efficiency of the catalysts studied with toluene vapours showed maximum efficiency for Au-CLSS at low temperatures (450 K) as compared to undoped CLSS.     

Interactions between bromophenol blue and cetyl- trimethylammonium bromide in aqueous solutions and microemulsions

The UV-Vis light absorption spectroscopy of bromophenol blue (BPB) in a series of cetyltrimethylammonium bromide (CTAB) aqueous solutions and microemulsions has been determined. There exist association interactions between the BPB and cationic surfactant CTAB. By establishing the appropriate association models and measuring the absorbance in different concentrations of BPB aqueous solutions and microemulsions that have different R values, the association constants K were obtained and the values of thermodynamics functions of association Δ_rG_m were calculated. It shows that the formation of microemulsion has inhibitory effects on the association reaction.     

Formation of Lamellar Mesostructured Crystalline Silica by Self-assembly of CTAB

Controlling organic-inorganic liquid crystal structures to form lamellar mesostructured crystalline silica nanosheets(LCS) was achieved by using the simple cationic surfactant cetyl trimethyl ammonium bromide(CTAB). The organic-inorganic interaction under the condtions of a high surfactant concentration and suitable synthesis temperature played an important role in the construction of mesostructured crystalline silica.     

All‐Silica Submicrometer Colloidosomes for Cargo Protection and Tunable Release

Colloidosomes have received considerable attention for the controlled delivery of active ingredients in medicine, agrochemicals, and cosmetics. However, most reported colloidosomes are highly permeable and size is larger than 1 μm. All silica colloidosomes have now been prepared with adjustable size, compact shell and low permeability. Our approach is based on the formation of inverse water‐in‐oil (w/o) emulsions stabilized solely by hydrophobic silica nanoparticles and subsequent locking of the particle at the oil–water interface by a simple sol–gel reaction of silica precursor at room temperature. The colloidosomes obtained display a robust and closed shell, ensuring a long‐term retention of small hydrophilic molecules such as Methylene Blue. Remarkably, unlike all other reported silica colloidosomes, a timely and stepwise release of the encapsulated cargo can be triggered by adding ethanol or surfactant without destroying the capsule shell.     

Solid-state NMR study of MCM-41-type mesoporous silica nanoparticles

A systematic study of the surface of MCM-41-type mesoporous silica nanoparticles prepared under low surfactant concentration was carried out using high-resolution solid-state nuclear magnetic resonance spectroscopy. The structures and concentrations of various species present during dehydration and rehydration of mesoporous silicas between -25 and 500 degrees C were detailed by employing one-dimensional and two-dimensional (1)H, (13)C, and (29)Si NMR, including (1)H signal intensity measurements, (1)H-(1)H homonuclear correlation experiments (double quantum, exchange, and RFDR), and (1)H-(29)Si heteronuclear correlation NMR. These experiments employed high MAS rates of up to 45 kHz. The study shows that the surfactant (CTAB) was almost completely removed by acid extraction. The residual molecules assumed prone positions along the pores, with the tailgroup being most mobile. The weakly adsorbed water was hydrogen bonded to the silanol groups, all of which were involved in such bonds under ambient humidity. Specific structures involving water and silanol groups were proposed for various stages of thermal treatment, which included dehydration, dehydroxylation, and subsequent rehydration.     

气-液界面有序介孔SiO2无机膜的仿生合成

早在几百万年以前,自然界就通过生物矿化过程形成了结构高度有序的有机/无机复合材料,如哺乳动物的牙床、骨骼以及贝壳珍珠层等[1]。随着对天然生物材料生物矿化过程研究的逐渐深入,材料研究者从中得到极为重要的启示:先形成有机物自组装体,无机先驱物在自组装聚集体与溶液相的界面处发生化学反应,在有机自组装体的模板作用下,形成有机/无机复合体,再将有机模板去除即可得到具有一定形状与组织结构的无机材料。这种模仿生物矿化中无机物在有机物调制下形成过程的材料合成,称为仿生合成(biomimetic synthesis)[2]。仿生合成过程中,通过选择有…     

Use of the ternary phase diagram of a mixed cationic/glucopyranoside surfactant system to predict mesostructured silica synthesis

Mixed surfactant systems have the potential to impart controlled combinations of functionality and pore structure to mesoporous metal oxides. Here, we combine a functional glucopyranoside surfactant with a cationic surfactant that readily forms liquid crystalline mesophases. The phase diagram for the ternary system CTAB/H(2)O/n-octyl-beta-D-glucopyranoside (C(8)G(1)) at 50 degrees C is measured using polarized optical microscopy. At this temperature, the binary C(8)G(1)/H(2)O system forms disordered micellar solutions up to 72 wt% C(8)G(1), and there is no hexagonal phase. With the addition of CTAB, we identify a large area of hexagonal phase, as well as cubic, lamellar and solid surfactant phases. The ternary phase diagram is used to predict the synthesis of thick mesoporous silica films via a direct liquid crystal templating technique. By changing the relative concentration of mixed surfactants as well as inorganic precursor species, surfactant/silica mesostructured thick films can be synthesized with variable glucopyranoside content, and with 2D hexagonal, cubic and lamellar structures. The domains over which different mesophases are prepared correspond well with those of the ternary phase diagram if the hydrophilic inorganic species is assumed to act as an equivalent volume of water.     

Binding of oppositely charged surfactants to spherical polyelectrolyte brushes: a study by cryogenic transmission electron microscopy

The formation of a complex between an anionic spherical polyelectrolyte brush (SPB) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is investigated. The SPB consists of long chains of the strong polyelectrolyte poly(styrene sulfonate) (PSS), which are bound chemically to a solid poly(styrene) core of 56 nm in radius. The SPB are dispersed in water, and the ionic strength is adjusted by addition of NaBr. The resulting complexes are investigated in dilute solution by dynamic light scattering, by electrophoretic light scattering, and by cryogenic transmission electron microscopy (cryo-TEM). The formation of the complex between the SPB and the surfactant can be monitored by a strong shrinking of the surface layer when adding CTAB to dilute suspensions (0.01 wt %) and by a decrease of the effective charge of the complexes. Complex formation starts at CTAB concentrations lower than the critical micelle concentration of this surfactant. If the ratio r of the charges on the SPB to the charge of the added surfactant is exceeding unity, the particles start to flocculate. Cryo-TEM images of the complexes at r = 0.6 measured in salt-free solution show that the surface layer composed of the PSS chains and the adsorbed CTAB molecules is partially collapsed: A part of the chains form a dense surface layer while another part of the chains or aggregates thereof are still sticking out. This can be deduced from the cryo-TEM micrographs as well as from the hydrodynamic radius, which is still of appreciable magnitude. The 1:1 complex (r = 1.0) exhibits a fully collapsed layer formed by the PSS chains and CTAB. If the complex is formed in the presence of 0.05 M NaBr, r = 0.6 leads to globular structures directly attached to the surface of the core particles. All structures seen in the cryo-TEM images can be explained by a collapse transition of the surface layer brought about by the hydrophobic attraction between the polyelectrolyte chains that became partially hydrophobic through adsorption of CTAB.     

Mesoporous Silica Materials Synthesized via Sol-Gel Methods Modified with Ionic Liquid and Surfactant Molecules

Mesoporous silica materials were synthesized via a sol-gel method employing a room temperature ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4) as a new solvent medium and further modified with surfactant (hexadecyl-trimethyl-ammonium bromide, CTAB) as a pore templating material. The synthesized samples were characterized by the transmission electron microscopy, X-ray diffraction, and N2 adsorption-desorption techniques. The results indicated that the mesoporous silica synthesized by using bmimBF4 and CTAB as mixed templates showed better mesostructural order and smaller pore size, compared with mesoporous silica materials synthesized by using single bmimBF4 as template under the same conditions. This indicates that the presence of surfactant can affect the microstructures of silica prepared by the present synthesis method.