Pore Structure Control of Silica Gels Based on Phase Separation

In the alkoxy-derived sol-gel system, various macroporous morphologies can be obtained by inducing the phase separation parallel to the sol-gel transition. This principle of macroporous morphology control can be best applied to pure silica and silica-based multicomponent oxide systems. The earlier the phase separation takes place than the sol-gel transition, the larger the characteristic sizes of pores and gel skeletons become. The time resolved light scattering measurements revealed that the morphology formation process exhibits the features of spinodal decomposition and that the final gel morphology is determined by the competitive kinetics between the domain coarsening and the structure freezing by sol-gel transition. The mesopore structure of such macroporous gel skeletons could be easily tailored by the solvent exchange procedures. Silica gels with controlled macropores and mesopores were successfully applied as a material for the continuous rod type column for high performance liquid chromatography.     

Structure Characterization of Surfactant Assisted Polymer Thickeners by Silica Nanocasting

The aggregation behavior of the hydrophobically modified polyelectrolytes which act in the interplay with special surfactant mixtures as a thickener is examined by replication of the different soft matter nanostructures into silica gels. The inorganic solidified replicas can be easily microtomed and analyzed by gas sorption measurements, quantitative small angle X‐ray scattering and transmission electron microscopy. The bare hydrophobically modified polyelectrolytes show a very homogeneous structure, free of larger aggregated moieties. In addition, a transition between a weakly‐ or unaggregated structure and an aggregated structure of the bare copolymer with hydrophobic moieties of ca. 3 nm diameter was found which depends on the degree of hydrophobic substitution, the concentration, and the salt content. The simultaneous presence of surfactant in the polymer solution leads to nanocasting of both spherical (ionic surfactant) and worm‐like (zwitterionic surfactant) micelles, which are essentially unperturbed by the incorporate the hydrophobic moieties of the polymer. Optimal thickening efficiency is obtained when each of those micelles is coupled to at least two of the polymers. The resulting sterical demands are best met by the presence of worm‐like surfactant micelles.     

Quantitative Electron Microscopic Investigation of the Pore Structure in 10:90 Colloidal Silica/Potassium Silicate Sol-Gels

Transmission electron microscopy (TEM), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and nitrogen sorption technique (BET) were utilized to characterize the microstructure of a 10:90 wt% colloidal silica/potassium silicate gel as first described by Shoup. Gels in the unsintered state (15% theoretical density) were prepared for microscopy by the techniques of ultramicrotomy, Pt/C replication, and pore casting. Electron microscopic images of the ultramicrotomed thin sections (70 nm) show that the unfired gel possesses three distinct species of pores which are referred to as the micropores, mesopores, and macropores. The average micropore diameter was found to be 4 nm as determined by nitrogen desorption. Quantitative stereological analysis of the ultramicrotomed sections indicated that the average circular and lengthwise dimensions of the cylindrical mesopores were 0.15 and 0.39 μm, respectively. Similarly, this same analysis determined the average spherical macropore diameter to be 0.83 μm. In contrast, MIP results suggested that these gels possessed a unimodal pore size distribution centered around the 0.2-μm pore size. The discrepancy between MIP and microscopy can be explained by viewing the void space as a pore-throat network. Experimental evidence for this type of pore geometry was obtained from stereo pairs of Pt/C replicas and thick microtomed sections (0.5 μm) which gave information about particle connectivity and pore casts which depicted the pore connectivity in three dimensions.     

共聚物为模板制备草莓状二氧化硅空心球

成功地通过三嵌段共聚物聚乙二醇-聚丙二醇-聚乙二醇(PEG-PPG-PEG)为模板,正辛烷为壳材料来制备介孔外壳的草莓状二氧化硅空心球。其中正硅酸乙酯(TEOS)作为二氧化硅的前驱体。通过改变反应参数,我们发现当将反应最终溶液先室温下静置24h然后加热到较高温度12h可以获得草莓状结构。产物的表面形貌通过扫描电子显微镜(SEM)来分析;透射电子显微镜(TEM)表明空心球的平均直径为800nm,外壳为20nm;多孔性分析通过氮气吸附-解附法来测量,同时用Brunauer-Emmett-Tell-er(BET)的方法来测孔径大小。另外我们提出了二氧化硅的形成机理。     

Separation and Recovery of Tetramethyl Ammonium Hydroxide with Mesoporous Silica Having a Hexagonal Structure (MCM-41)

Separation and recovery of tetramethyl ammonium hydroxide (TMAH) was investigated using several types of MCM-41 (mesoporous silica having hexagonal structure) adsorbents. The MCM-41s were prepared by hydrothermal synthesis with structure-directing agents with different alkyl chains. The prepared MCM-41s were characterized with X-ray diffraction, transmission electron microscope, nitrogen gas adsorption, and zeta potential, and then used for adsorption of TMAH. The adsorption of TMAH with MCM-41s increased with pH up to pH ≈ 10 and then decreased as the MCM-41 dissolved. The adsorption of TMAH progressed via the Langmuir mechanism. The maximum adsorption corresponded to the pore diameter and the pore volume of the MCM-41s. MCM-41 also possesses selectivity for TMAH against phenol. The chromatographic operation was conducted using granulated MCM-41 to avoid excessive pressure-drop through the packed column and quantitative adsorption-elution processing of TMAH could be achieved.     

非离子表面活性剂在苦参碱提取中的应用

将0．2％的吐温20或吐温80非离子型表面活性剂加入到苦参药材提取溶剂中，来降低药材与溶剂之间的表面张力，增加湿润性。增溶提取出的游离苦参碱，同时施以机械振荡外力，能显著增加苦参碱的提出率，缩短提取时间，降低成本，提高经济效益。     

Adsorption of Noble Metals Using Silica Gel Modified with Surfactant Molecular Assembly Containing an Extractant

Silica gel modified with a surfactant, Triton X-100 molecular assembly containing an extractant, 1-(2-pyridylazo)-2-naphthol, was prepared as an adsorbent to adsorb palladium, platinum, and gold. In this study, methods of metal recovery and mutual separation from the metal coexisting solution were studied by using the modified silica gel (PT100S). The effects of pH, chloride-ion, and metal-ion concentrations on the metal adsorption rate were evaluated through batch experiment. Pd(II) and Au(III) were adsorbed on PT100S, while Pt(IV) was not adsorbed. Furthermore, it was found that Pd(II) reacted with an adsorption site on PT100S, and that Au(III) reacted with a different adsorption site from Pd(II). These results enabled to separate the metals using a column packed with PT100S.     

Application of Counter-Current Solvent Extraction to the Separation of Naphthalene and Nonionic Surfactants

This study conducted counter-current solvent extraction to investigate the influence of solvent/solution volumetric ratio, solvent flow rate, and surfactant concentration on extraction efficiency. Fitting formulas for predicting the partition coefficients of the contaminant and surfactant between the aqueous and solvent phases were developed to optimize the counter-current solvent extraction. It is found that the solvent/solution volumetric ratio and the surfactant concentration had greater impact than the solvent flow rate on the extraction efficiency. The relationship between the partition coefficient K and the solvent/solution volumetric ratio or surfactant concentration was closely related to power function. Besides, the accuracy of the fitting formulas was consistent with the experimental results.     

利用简单模板制备多孔二氧化硅

以简单有机模板为致孔剂、正硅酸乙酯(TEOS)为硅源制备了多孔SiO2,考察了模板剂加入量对样品比表面和孔容的影响,测定了样品的比表面和孔结构,提出了简单有机模板对多孔SiO2的致孔机理,并与以碱性硅溶胶为硅源对比,验证了该机理. 结果表明,简单有机模板添加量为模板剂/TOES=0.3 mg/mL时,样品比表面积可提高至650 m2/g以上,孔容大于1.0 mL/g,孔道为无规则结构. 该多孔结构的产生很可能是因为简单有机模板和TEOS的聚合物发生分子级混合,从而在凝胶和煅烧过程中使样品中产生了丰富的孔道.     

Hexagonal Mesoporous Silica with Noodle-Like Shape

Hexagonal mesoporous silica (HMS) was prepared at ambient temperature by using dodecylamine (DDA) as the surfactant and tetraethyl orthosilicate (TEOS) as the silica precursor. The HMS materials were characterized by X-ray powder diffraction, N₂ adsorption/desorption, scanning electron microscopy and transmission electron microscopy. The samples prepared at various addition rates of TEOS and various alcohol/water (R/H) ratios were investigated. As the addition rate of TEOS decreased, the size of HMS particles increased and the textural porosity decreased. Non-alcoholic solution was required to prepare non-spherical particles. The HMS with noodle-like structures was prepared in the absence of alcoholic solvent. These noodle-like particles were about 0.1m in diameter and about submicrometer to several micrometers in length.     

Cloud Point Extraction (CPE) of Parabens using Nonionic Surfactant Phase Separation

A cloud point extraction (CPE) method was developed using silicone-ethylene oxide surfactant, DC193C, to study the equilibrium phase separation of parabens in environmental water samples. The volume of the surfactant rich phase (V_s), aqueous phase (V_w), preconcentration factor (C_F), distribution coefficient (K_d), and percentage of recovery (%R) were evaluated to obtain the optimum condition for phase separation of parabens. Satisfactory results were obtained whereby the preconcentration factor for methylparaben, ethylparaben, propylparaben, and benzylparaben were close to 65, 60, 80, and 45, respectively, at 0.5% weight of surfactant. The presence of DC193C gave a low phase volume ratio but insignificant result was observed with the increased of surfactant concentration. The parabens were well separated on a reverse-phase Chromolith C₁₈ column (100 mm × 4.6 mm) with a gradient elution (acetonitrile: water; 30:70 v/v) and detected at 254 nm. The proposed method was successfully applied to environmental samples such as river water, treated wastewater, sea water, and tap water with satisfactory results. The method detection limit was 0.1–0.2 ppb and the recoveries were 71.2–97.7% with the relative standard deviations of 0.3–2.1%.     

Polyethylene–Silica Nanocomposites with the Structure of Semi‐Interpenetrating Networks

Organic–inorganic nanocomposites with the structure of interpenetrating or semi‐interpenetrating networks are considered as advanced materials, since they have improved thermal and mechanical properties. An alternative approach to the preparation of such hybrid systems is proposed. It is based on the synthesis of silica from the precursor of hyperbranched polyethoxysiloxane by the hydrolytic condensation reaction in the volume of pores of a polymer matrix (bulk porosity is 40 vol%) stretched via the environmental crazing mechanism. Polyethylene–silica nanocomposites with the structure of semi‐interpenetrating networks when the content of silica is not less than 20–25 wt% are obtained. These composites can undergo an additional phase separation at a temperature of 160 °C (above the melting point of polyethylene), which is accompanied by an increase in the size of the polymer phase with the formation of macrophases. At the same time, the environment (orthophosphoric acid), in which the composite is heated, fills the pores that have appeared. As a result, the content of the third component with the new functionality increases up to 50 wt%, which allowed us to impart proton‐conducting properties to the composite material and preserve its shape stability.     

制备条件对钴掺杂二氧化硅溶胶胶粒粒径和膜孔结构的影响

以正硅酸乙酯(TEOS)为前驱体,六水合硝酸钴(Co(NO_3)_3·6H_2O)为钴源,十六烷基三甲基溴化铵(CTAB)为模板剂,通过溶胶-凝胶-模板技术制备了不同条件下的微孔钴掺杂二氧化硅膜。研究了酸量、水量、钴掺杂量、焙烧温度对溶胶胶粒粒径及膜材料孔结构的影响。结果表明:酸和水添加量以及焙烧温度相对于钴掺杂量是主要的影响因素。溶胶胶粒粒径随着酸量的增多先减小后增大,在HNO_3/TEOS摩尔比为0.055时溶胶胶粒粒径达到最小值;随着水量的增大而粒径增大,且粒径分布变宽,在H_2O/TEOS摩尔比为10时最明显;随着酸量和焙烧温度的增大,膜材料的比表面积和微孔孔容先增大后降低,在HNO_3/TEOS摩尔比为0.085时,450℃焙烧的膜材料的比表面积和微孔孔容达到最大值。     

低质量分数表面活性剂作模板合成 MCM-41中孔分子筛

以硅酸钠为硅源,表面活性剂十六烷基三甲基溴化铵(CTMABr)为结构模板剂,用水热晶化法在w(CTMABr)=1%～3%下制备全硅MCM-41中孔分子筛。采用染料吸附脱色实验比较了原料配比、反应体系pH值、晶化时间、晶化温度、脱模温度对MCM-41合成的影响。结果表明,合成MCM-41中孔分子筛时表面活性剂CTMABr质量分数必须达到1%以上;pH=10～12;晶化温度以125℃左右为好;前驱体脱模温度控制在600～800℃。在较优的工艺条件w(CTMABr)=1 5%、pH=11、晶化温度125℃、晶化时间24h、脱模温度640℃下得到了具有完美晶型结构、BET比表面积=1370m2/g、平均孔径3 28nm的全硅MCM-41中孔分子筛。     

介孔二氧化硅微球的扩孔及组装磁性纳米铁粒子

以十六胺为模板剂、正硅酸乙酯(TEOS)为硅源合成孔径约3 nm的多孔球形结构介孔二氧化硅(MS)材料. 为满足组装磁性纳米粒子所需的孔径要求,提出了一种可较大程度扩大孔径的方法?复盐浸渍法,用多组分盐溶液(NaC1:LiCl:KNO3=4:1:1, w)浸渍MS微球,然后在300℃加热2 h,扩大MS孔径,扩孔后的MS微球孔径在10 nm左右. 采用电化学方法在MS介孔内合成Fe纳米粒子,并在H2气氛下加热还原得到Fe/SiO2磁性复合微球,制备出的磁性复合微球孔道内均匀地分布着Fe粒子.     

Surface Modification of Silica Aerogels Dried with 2-Methyl-1-Propanol in the Sub-Critical Pressure

Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by drying under sub-critical pressure with iso-butanol. The shrinkage (linear), specific surface area, S_BET, SEM, TEM and the pore size distribution of the silica aerogels were investigated. The results show that the shrinkage (linear) is below 5%, diameter of the silica particles is about 6 nm and the pore size of the silica aerogels is 10 nm. The specific surface area of the silica aerogel is 559.2 m²/g. IR and NMR techniques were used to determine the organic groups on the silica matrix, GC/MS was also introduced to analyse the composition of the recycled iso-butanol. The surface modification and the reactions of iso-butanol to the silica aerogel are also discussed.     

Solvent Extraction of DNA with a Hydrolysable Double-chain Surfactant

Abstract

A cationic lipophilic surfactant with two hydrolysable groups, di(1-octadecyloxycarbonylmethyl)dimethylammonium chloride, was synthesized and solvent extraction of deoxyribonucleotide (DNA) into organic solution (isooctane/1-octanol) with it as an extractant was examined. Not only a forward extraction of DNA into the organic phase but also back extraction into the aqueous phase (pH > 9) at room temperature proceeded efficiently. The forward extraction is promoted by electrostatic interactions of the surfactant and DNA and the back extraction is exclusively caused by hydrolysis of the surfactant to a non-surfactant.     

Adsorption of Tetraalkyl Ammonium Hydroxide with Mesoporous Silica

Adsorption of tetraalkyl ammonium hydroxide (TAAH) with mesoporous silica such as MCM-41 and MCM-48 has been investigated. The adsorption of TAAH with the mesoporous silica increases with increase in pH of the aqueous solution. The maximum adsorption amounts of TAAH with the mesoporous silica, determined by Langmuir isotherms, correspond to the relationship between the pore diameter of the mesoporous silica and the molecular size of TAAH, while no significant relationship is observed with both the specific surface area and the amount of silanol group of the mesoporous silica. Mesoporous silica having large pore diameter is applicable to the adsorptive separation of TAAH from the effluent solution.     

非离子表面活性剂在液体染料制备中的稳定及增溶作用

对加入聚氧乙烯醚非离子表面活性剂的液体C·I·碱性橙2的紫外可见吸收光谱进行了研究,结果表明,随着表面活性剂浓度的变化,碱性橙在最大吸收波长处的吸光度值先增大后减小,出现最大值时所对应的表面活性剂浓度对液体染料碱性橙的增溶效果最好。     

Effect of Nonionic Surfactant on the Micro‐Emulsifying Water in Silicone Media

Reverse micro‐emulsion dyeing technology shows a high dye uptake and fixation rate, and effectively decreases the amount of waste water in the textile industry. However, the influence of surfactants and co‐surfactants on micro‐emulsifying water in reverse micro‐emulsions has not been investigated. In this study, the micro‐emulsifying mechanism in silicone media and the influence of nonionic surfactants and co‐surfactants on micro‐emulsifying water have been investigated. The results show that a large amount of water can be emulsified using alcohol‐polyoxyethylene ethers, especially under 3–5 ethylene oxide groups in molecular structure. As co‐surfactant, alcohol which contains 4–9 carbon chains could spontaneously form reverse micro‐emulsions in silicone media. The effects of solution pH and ionic strength on the amount of emulsified water were also evaluated. The results show that a large amount of water could be emulsified in silicone media at solution pH 2–9. Meanwhile, the amount of emulsified water decreased with increasing ionic strength. Thus, the optimum conditions for water emulsification are low ionic strength and pH between 2 and 9.