Synthesis of penetrable macroporous silica spheres for high-performance liquid chromatography

Silica microspheres have been synthesized by phase separation and sol–gel transition coupled with emulsion method. The as-obtained material is characterized by scanning electron microscopy, nitrogen sorption, elemental analysis and particle size distribution measurements. The results demonstrated that the material featured with hierarchically porous structure, possessing both mesopores and penetrable macropores. The mesopores provide large surface area while the macropores traverse the silica particles, which may facilitate fast mass transfer as well as guarantee low backpressure when such materials are used for packed high-performance liquid chromatography (HPLC) column. Therefore, their preliminary applications as HPLC packings in fast separation and low-pressure separation have been attempted in the present study. Benzene, benzaldehyde and benzyl alcohol were separated within two minutes on the silica column at a flow rate of 7 mL min⁻¹. Vitamin E mixtures can also be baseline separated at a high flow rate of 8 mL min⁻¹. In addition, thirteen aromatic hydrocarbons were well separated on the octadecyl-bonded silica (ODS) column. In comparison with a commercial Kromasil ODS column, the pressure of the proposed column is much lower (<1/2) under the same chromatographic conditions, while comparable separation efficiency can be achieved.     

Impact of solvents and surfactants on the self-assembly of nanostructured amine functionalized silica spheres for CO_2 capture

Macroscopic SiO_2 spheres with a homogeneous amine distribution were synthesized by a one-step emulsion based synthesis approach in a flow column reactor. The CO_2 adsorption capacity of the nanostructured amine-functionalized silica spheres was studied in absence and presence of H_2O. The structural properties were adjusted by varying solvents and surfactants during the synthesis and, at constant amine loadings, were found to be the main factor for influencing the CO_2 sorption capacities. Under water-free conditions CO_2 is bound to the amino groups via the formation of carbamates, which require two neighboring amino groups to adsorb one CO_2 molecule. At constant amine concentrations sorbents with lower surface area allow to establish a higher amine density on the surface, which enhances the CO_2 uptake capacities under dry conditions. In presence of H_2O the CO_2 adsorption changes to 1:1 stoichiometry due to stabilization of carbamates by protonation of H_2O and formation of further species such as bicarbonates, which should in principle double the adsorption capacities. Low concentrations of physisorbed H2O(0.3 mmol/g) did not impair the adsorption capacity of the adsorbents for CO_2, while at higher water uptakes(0.6 and 1.1 mmol/g) the CO_2 uptake is reduced, which could be attributed to capillary condensation of H_2O or formation of bulky reaction products blocking inner pores and access to active sites.     

Formation of zein spheres by evaporation-induced self-assembly

Zein is an amphiphilic protein capable of self-assembly into microspheres. Zein microspheres may form by evaporation-induced self-assembly (EISA) of zein solutions in ethanol/water. The formation of microspheres is of particular interest for the development of delivery systems. Zein solutions in ethanol/water 75?% (v/v) were slowly evaporated to promote self-assembly of microspheres. The ethanol content of the solvent decreased during EISA changing solvent polarity which induced self-assembly of zein particles. The growth of zein spheres was modeled from the hydrophobic and hydrophilic contributions to the interfacial free energy (R ²?=?0.92). The good fit indicated that during EISA zein microspheres increased in size due to hydrophobic interactions between zein molecules. The model may allow the prediction of evaporation time and thus control over microsphere size.     

Formation of hollow silica spheres from molecular silica sols

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Graft polymerization of carbohydrates on the surface of a macroporous silica

Conclusions A graft polymerization of carbohydrates was carried out on the surface of a macro-porous glass in order to produce biocompatible materials based on macroporous silica.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2091–2094, September, 1987.     

Structural characterization of nanosized silica spheres

Silica nanospheres with wide applications on chemistry have been synthesized using the Stöber method and have been modified with several organic functional groups by post-synthesis reaction in anhydrous environments. The surface analysis of the silica nanosized spheres leads to low surface area values and large skeletal densities, pointing out to dense nanospheres. High-resolution transmission electron microscopy (HRTEM) and small-angle X-ray scattering (SAXS) prove the microstructure level of the surface porosity that is clearly affected by the organic functionalization.     

Sedimentation analysis of latex spheres and gold sols

Summary Analytical centrifugation was used for the analysis of latex spheres. It appeared that the latex spheres sedimented according to Stokes' law. Therefore the diameters calculated from the sedimentation coefficients deviated on average less than 5 % from the diameters observed with the electron microscope.Colloidal gold was also investigated and it was shown that the gold sol consisted of particles with discrete sizes. The masses of the particles expressed in the mass of the smallest particles formed the arithmetic series 1, 2, 3, 4...n. The fact that apparently colloidal gold particles cannot exist below a certain definite size was confirmed by gel filtration.It was concluded that analytical centrifugation can be safely used for the determination of the size distribution of relatively large particles, membrane vesicles included.

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Zusammenfassung Die Brauchbarkeit der analytischen Zentrifugation zur Bestimmung der Größenverteilung von relativ großen Partikeln wurde untersucht. Latexkügelchen sedimentierten entsprechend dem Stokes'schen Gesetz. Dementsprechend stimmten die aus den Sedimentationskoeffizienten berechneten Durchmesser binnen 5 % mit den elektronenphonetisch ermittelten Durchmessern überein.Kolloidales Gold ergab eine diskrete Größenverteilung der im Kolloid enthaltenen Goldpartikel. Die Massen der Partikel waren ganzzahlige Vielfache (1, 2, 3, 4...n) der Masse der kleinsten Partikel. Durch Gelfiltration wurde bestätigt, daß die Partikel eines Goldkolloids nicht unter einer bestimmten Mindestgröße vorkommen.Aus den beschriebenen Versuchen wurde abgeleitet, daß die analytische Zentrifugation eine sichere Methode zur Bestimmung der Größenverteilung relativ großer Partikel - Membranbläschen inbegriffen - darstellt.

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With 3 figures and 2 tables     

Catalytic properties of silver nanoparticles supported on silica spheres

In this work, we investigate the catalytic properties of silver nanoparticles supported on silica spheres. The technique to support silver particles on silica spheres effectively avoids flocculation of nanosized colloidal metal particles during a catalytic process in the solution, which allows one to carry out the successful catalytic reduction of dyes. The effects of electrolytes and surfactants on the catalytic properties of silver particles on silica have been investigated. It is found that the presence of surfactants depresses the catalytic activity of the silver particles to some extent by inhibiting the adsorption of reactants onto the surface of the particles. Electrolytes either increase the migration rate of reactants in the solution resulting in an increase in the catalytic reaction rate or inhibit the adsorption of reactants onto the surface of the silver particles leading to a loss in the activity of the metal particles.     

Liposome induced self-assembly of gold nanoparticles into hollow spheres

Gold nanoparticles were prepared by the reduction of [(C7H15)4N]+ [AuCl4]- with 3,4-ethylenedioxythiophene (EDOT) as reductant in toluene solution. The employed stabilizers include 3,3'-thiodipropionic acid (TDPA), 1-dodecanethiol (DDT), (+/-)-10-camphorsulfonic acid (CSA), and 11-mercaptoundecanoic acid (MUA). The reaction processes were tracked by UV-vis and FT-IR spectroscopy, and the as-prepared gold nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy measurements. When TDPA and MUA, which possess both -S- and -COOH groups, were used as the stabilizer in the preparation, the as-prepared nanoparticles could self-assemble into hollow spheres. While when DDT with a -SH group or CSA with a -SO3H group was used as the protecting agents, only discrete gold nanoparticles were observed. The results show that the groups of both -S- and -COOH in the stabilizer play an important role in forming the hollow nanospheres. It is proposed that the formation mechanism of the hollow spheres is a liposome that formed between -COO- and [(C7H15)4 N]+ could act as a template to induce the self-assembly of the gold nanoparticles into the hollow spheres.     

Using hierarchical self-assembly to form three-dimensional lattices of spheres

This paper describes an approach to the fabrication of three-dimensional (3-D) structures of millimeter-scale spherical beads having a range of lattices-tetragonal, cubic, and hexagonal-using hierarchical self-assembly. The process has five steps: (i) metal-coated beads are packed in a rod-shaped cavity in an elastomeric polymer (poly(dimethylsiloxane), PDMS); (ii) the beads are embedded in a second polymer (PDMS or polyurethane, PU) using a procedure that leaves the parts of the beads in contact with the PDMS exposed; (iii) the exposed areas of the beads are coated with a solder having a low melting point; (iv) the polymer rods-with embedded beads and exposed solder drops-are suspended in an approximately isodense medium (an aqueous solution of KBr) and allowed to self-assemble by capillary interactions between the drops of molten solder; and (v) the assembly is finished by several procedures, including removing the beads from the polymer matrix by dissolution, filling the voids left with another material, and dissolving the matrix. The confinement of the beads in regular structures in polymer rods makes it possible to generate self-assembled structures with a variety of 3-D lattices; the type of the lattice formed can be controlled by varying the size of the beads, and the size and shape of the cross-section of the rods.     

第三次纳米自组装制备大孔主客体催化材料

本文提出了第三次纳米自组装的正向胶束、反向胶束法,并利用其制备了一种大孔主客体催化材料．以二次纳米自组装Al2O3为主体,根据压汞法,正向胶束法制备的催化材料孔容为0．62～0．80cm^3／g、比表面积为123～137mZ／g、平均孔径为20～23．3nm,孔径分布大于30nm范围的可达58．69％,堆积密度为0．43—0．55g／cm^3,活性金属负载量可达36．99％;由氮气吸附法,反向胶柬法制备的催化材料具有0．74cm^3／g的孔容、262m2／g的比表面积、11．8nm的平均孔径．结果显示,活性金属以球形或棒状的结晶态存在于主体表面,其中,正向胶束法中为直径2-3nm的微晶态纳米粒子,反向胶束法中为直径0．1μm、长1-2．5μm的棒状体．采用催化裂化柴油和催化裂化重循环油（1：2,体积比）混合而得油品对FA．Z20进行50h加氢评价实验,其单位体积活性金属的脱硫率、脱氮率、脱芳烃率（四环、五环）分别为参比剂的4．6、2．1和4．7倍,初活性良好,具有较强的抗结焦性能．     

Transport of nanoscale latex spheres in a temperature gradient

We use a micrometer-scale optical beam deflection technique to measure the thermodiffusion coefficient D(T) at room temperature (approximately 24 degrees C) of dilute aqueous suspensions of charged polystyrene spheres with different surface functionalities. In solutions with large concentrations of monovalent salts, < or approximately = 100 mM, the thermodiffusion coefficients for 26 nm spheres with carboxyl functionality can be varied within the range -0.9 x 10(-7) cm2 s(-1) K(-1) < D(T) < 1.5 x 10(-7) cm2 s(-1) K(-1) by changing the ionic species in solution; in this case, D(T) is the product of the electrophoretic mobility mu(E) and the Seebeck coefficient of the electrolyte, S(e) = (Q(C)* - Q(A)*)/2eT, D(T) = -S(e) mu(E), where and are the single ion heats of transport of the cationic and anionic species, respectively. In low ionic strength solutions of LiCl, < or approximately = 5 mM, and particle concentrations < or approximately = 2 wt %, D(T) is negative, independent of particle concentration and independent of the Debye length; D(T) = -0.73 +/- 0.05 x 10(-7) cm2 s(-1) K(-1).     

Probing the conformation of polyelectrolytes in mesoporous silica spheres

We report a fluorescence-based approach to probing the conformation of a macromolecule, poly(allylamine hydrochloride) (PAH), in bimodal mesoporous silica (BMS) particles. The method involves monitoring the fluorescent properties of the probe, 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (4-PSA), upon electrostatic binding to PAH molecules adsorbed in the nanopores of the BMS particles. PAH infiltration into the BMS particles, quantified by thermogravimetric analysis and visualized by confocal laser scanning microscopy, was examined as a function of PAH adsorption time, PAH molecular weight, and the sodium chloride (NaCl) concentration and pH of the PAH adsorption solution. The conformation of PAH molecules in the nanopores was investigated by incubating the PAH-loaded BMS particles in 4-PSA and using the ratio of the excimer to monomer emission intensity to discern differences in the PAH conformation in the nanopores. Control experiments involving nonporous silica (NS) particles were also conducted to determine the extent to which the nanopores within the BMS particles influence the degree of PAH adsorption and the conformation of the adsorbed PAH molecules. The data indicate that PAH molecules adsorbed in the nanopores adopt a more coiled conformation than PAH molecules adsorbed on NS particles over a wide range of conditions. Further, the conformation of PAH molecules in the nanopores can be tuned by adjusting the NaCl concentration and/or pH of the PAH adsorption solution. 4-PSA titration experiments revealed that at saturation binding there are ca. 3.8 PAH monomer units per 4-PSA molecule. This study provides insights into macromolecule infiltration and conformation in nanopores, which are important for the application of mesoporous materials in the fields of adsorption/immobilization, catalysis, delivery, sensing, separations, and synthesis.     

Preparation and self-assembly of carboxylic acid-functionalized silica

A simple method for the fabrication of silica nanoparticle film based on the covalent-bonding interaction between carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) and amino-terminated silicon wafer was developed. Prior to assembly, silica nanoparticles with an average diameter 80 nm were prepared using the St?ber method, amino-functionalized silica nanoparticles (SiO(2)-NH(2)) were prepared by a silanization with 3-aminopropyltriethoxysilane (APTES), while carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) were prepared by a ring opening linker elongation reaction of the amine functions with succinic anhydride, at the same time, amino-terminated silicon wafer (Si-NH(2)) was obtained by self-assembling 3-aminopropyltriethoxysilane, then one layer relative close-packed carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) was arranged on silicon wafer through amidation reaction under DCC coupling agent.     

One-step synthesis of highly dispersed gold nanocrystals on silica spheres

Highly dispersed gold nanocrystals decorating silica spheres were prepared from HAuCl4 and NaOH via a deposition-precipitation (DP) process, in which the isoelectric point (IEP) of the substrate was adjusted during sphere synthesis by interaction of the surface with ammonia molecules. Through the systematic variation of pH (4-8), reaction temperature (65-96 degrees C), and time (10-30 min), a superior product with small (2-5 nm), homogeneously distributed gold crystals was obtained at pH 7 and a reaction temperature of 96 degrees C. These materials will offer enhanced performance as catalysts and contrast enhancers in biomedical imaging.