Microporous Silica Hollow Nanospheres Templated by Anionic Polypeptide

Anionic polypeptide, the poly(sodium L-glutamate), was applied to fabricate microporous silica hollow nanospheres templated by the secondary structures of the polypeptide as porogens. In the synthesis, 3-aminopropyltrimethoxysilane (APMS) and tetraethyl orthosilicate (TEOS) were used as the silica sources, and the coassembly followed the mechanism of the anionic surfactant-templated mesoporous silica (AMS) through a S_-N₊-I_- pathway, where S indicates the anionic polypeptide, I indicates inorganic precursors (TEOS), and N indicates costructure-directing agent (APMS), which interacted with the negatively charged anionic polypeptide secondary structures electrostatically and cocondensed with silica source to form the silica framework. The product was subjected to characterizations of X-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimetric (TG) analysis, scanning electron microscopy (SEM), transmitted electron microscopy (TEM), and nitrogen adsorption-desorption measurement. It was found that the pH value of the synthesis solution was an important factor to the morphological control of the silica products. Besides the microporous hollow nanospheres, microporous submicron silica solid and hollow spheres were also obtained facilely by changing the synthesis parameters. Our study further implied that anionic polypeptides, which were able to control mineralization of calcium carbonate and calcium phosphate, could also induce silica condensation in the presence of proper silica precursors. It was also expected that functional calcium carbonate (phosphate)/silica-nanocomposite materials would be fabricated under the control of the anionic polypeptide.     

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.     

Preparation of core-shell microporous organic polymer-coated silica microspheres for chromatographic separation and N-glycopeptides enrichment

Through a “one-pot” strategy, a layer of microporous organic polymer was coated onto the surface of monodisperse amino-functionalized silica microsphere via amino-aldehyde condensation reaction with core-shell structure. The change in chemical structure of material before and after modification was determined by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Due to existence of a large number of amino and aldehyde groups in microporous organic polymer shell, the water contact angle decreased from 56.8° (silica microspheres) to 34.7° (microporous organic polymer-coated silica microspheres). Based on these properties, microporous organic polymer-coated silica microspheres were employed as the stationary phase for capillary liquid chromatography and successfully offered baseline separation of polar small molecules. Additionally, the material could also be served as the sorbent of hydrophilic interaction chromatography to enrich glycopeptides from human serum digest. A total of 470 unique N-glycopeptides and 342 N-glycosylation sites mapped to 112 N-glycosylated proteins were unambiguously identified from 2 μL of human serum, exhibiting a promising application prospect of microporous organic polymer-coated silica microspheres in the pretreatment of proteomics samples.     

Active Salt/Silica‐Templated 2D Mesoporous FeCo‐Nx‐Carbon as Bifunctional Oxygen Electrodes for Zinc–Air Batteries

Two types of templates, an active metal salt and silica nanoparticles, are used concurrently to achieve the facile synthesis of hierarchical meso/microporous FeCo‐N_x‐carbon nanosheets (meso/micro‐FeCo‐N_x‐CN) with highly dispersed metal sites. The resulting meso/micro‐FeCo‐N_x‐CN shows high and reversible oxygen electrocatalytic performances for both ORR and OER, thus having potential for applications in rechargeable Zn–air battery. Our approach creates a new pathway to fabricate 2D meso/microporous structured carbon architectures for bifunctional oxygen electrodes in rechargeable Zn–air battery as well as opens avenues to the scale‐up production of rationally designed heteroatom‐doped catalytic materials for a broad range of applications.     

Synthesis of hollow spherical silica with MCM-41 mesoporous structure

Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm^–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N₂ gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N₂ adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased     

Amino‐functionalized hollow microporous organic nanospheres for pd supported catalysis and I2 uptake

Amino‐functionalized hollow microporous organic nanospheres (NH₂‐HMONs) were successfully synthesized by a combination of hyper‐crosslinking mediated self‐assembly process and a post‐modification strategy. Benefiting from amino groups and hollow microporous structure, the resultant NH₂‐HMONs can be used to immobilize Pd nanoparticles (Pd@NH₂‐HMONs) and enhance the adsorption capacity for iodine. The obtained Pd@NH₂‐HMONs exhibited outstanding catalytic activity for hydrogenation of nitroarenes to aniline analogues. This strategy represents a new method for the preparation of porous organic polymers with special morphologies and functionalizations for potential applications including adsorption, separation, and catalysis. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2045–2052     

Effect of non-ionic surface active agents on TEOS-derived sols,gels and materials

The sol-gel process, starting from tetraethylorthosilicate precursor, is a suitable technique for the preparation of silica thin films. The use of specific organic additives, like non ionic surface-active agents, drastically modifies the gelation process and allows the preparation of microporous materials with a high microporous volume. The effects of additives on the sol, gel and material characteristics have been investigated by several methods such as ²⁹Si NMR, QELS, SAXS (for sols and gels), and N₂ adsorption, FESEM (for fired materials). It appears that the interactions of surface active agents with TEOS derived species limit condensation reactions and particle growing. A brittle gel structure is generated which leads to highly porous microporous silica after the elimination of organic chains by thermal treatment at 450°C. The material porous texture (specific surface area, pore size distribution and porous volume) can be varied especially by varying the surface active agent chain length and quantity. This kind of sol-gel system is suitable to prepare microporous silica membranes candidate for gas separation or catalytic reactor applications.     

Methods to Analyse the Texture of Alginate Aerogel Microspheres

Nitrogen adsorption at 77 K has been applied to the study of the texture of alginate aerogel microspheres obtained by CO₂ supercritical drying of alcogels. The limited volume shrinkage suggests that the aerogels preserve the texture of the hydrogels. Alginate aerogels presents a N₂ adsorption at small pressure higher than reference non-porous silica, to be attributed to the polarity of the surface or to a small microporous volume. The aggregated nanobead strings of the guluronic-rich gels accounts for a significant mesoporosity. The N₂ adsorption results correspond to electron microscopy observations for features smaller than 50 nm.     

Anodic alumina supported dual-layer microporous silica membranes

We present a new processing scheme for the deposition of microporous, sol–gel derived silica membranes on inexpensive, commercially available anodic alumina (Anodisk™) supports. In a first step, a surfactant-templated mesoporous silica sublayer (pore size 2–6 nm) is deposited on the Anodisk support by dip-coating, in order to provide a smooth transition from the pore size of the support (20 or 100 nm) to that of the membrane (3–4 Å). Subsequently, the microporous gas separation membrane layer is deposited by spin-coating, resulting in a defect-free dual-layer micro-/mesoporous silica membrane exhibiting high permeance and high selectivity for size selective gas separations. For example, in the case of CO₂:N₂ separation, the CO₂ permeance reached 3.0 MPU (1 MPU = 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹) coupled with a CO₂:N₂ separation factor in excess of 80 at 25 °C. This processing scheme can be utilized for laboratory-scale development of other types of microporous or dense inorganic membranes, taking advantage of the availability, low cost and low permeation resistance of anodic alumina (or other metal oxide) meso- and macroporous supports.     

General routes to porous metal oxides via inorganic and organic templates

The generation of porous metal oxides by removal of template molecules from inorganic polymers formed by sol-gel type hydrolysis and condensation of metal alkoxides is described. The template molecules include organic polymers, copper (II) ions in hybrid copper oxide/silica sols and copper (II) bis(hexafluorocetylacetonate) (hfac). Neutron scattering experiments on the system in which polyacrylic acid (Mw=2,000 Daltons) is used as an organic template to generate microporous tin oxide show that removal of the template generates skeletal voids. In a second series of experiments, mixed copper/silicon oxide xerogels were prepared by hydrolysis of mixtures of Si(OEt)₄ and Cu(OCH₂CH(CH₃)N(CH₃)H)₂ in the ratios of Si:Cu=2:1, 4:1, 9:1. Selective removal (etching) of the copper component generates porous silica. Neutron scattering data and BET surface area measurements are consistent with the creation of pores with molecular dimensions (micropores, 10 Å or less). In the third strategy, Si(OEt)₄ is hydrolyzed in the presence of Cu(hfac)₂, a volatile, inert inorganic template, in a 4 to 1 molar ratio. Removal of the template from the xerogel at 100°C in vacuo affords microporous silica.     

Solvent‐Dependent Synthesis from Layer to Microporous Pillared‐Layer Framework for Selective Sorption of Gas Light Hydrocarbons

Three metal‐organic frameworks, [Zn₃(bdc)₃(DMA)₂] ( 1 ) (H₂bdc = terephthalic acid; DMA = N,N‐dimethylacetamide), [Zn₃(bdc)₃(DMA)(DMPU)] ( 2 ) (DMPU = 1,3‐dimethylpropyleneurea), and [Zn₃(bdc)₄(Hdma)₂] ( 3 ) [Hdma = protonated dimethylamine (Me₂NH₂)] were synthesized by using different solvents. The solvents determine the framework architectures range from layer to microporous pillared‐layer framework. The microporous framework has 8‐connected bcg topology and shows selective sorption ability for gas light hydrocarbons.     

Preparation and Structure of Microporous Silica Membranes

Silica sols have been prepared in an alcoholic solution by hydrolysis and condensation of TEOS (tetra-ethyl-ortho-silicate) molecules as a function of water and nitric acid concentration. The polymers are intended as precursors for ceramic, gas separation membranes. These molecules show fractal behavior as determined by SAXS (Small Angle X-ray Scattering). Microporosity of dried and calcined silica polymers is determined by N₂-adsorption at 77 K. Fractal dimension and porosity increase with increasing acid concentration. Both the sol structure and the drying kinetics determine the porosity values. N₂-adsorption isotherms are not very suitable for the determination of pore size distributions of microporous silica.     

Gemini Surfactants Templated Mesoporous Silica Microparticles: from Solid to Hollow Mesoporous Spheres

We synthesized a series of mesoporous silica microparticles (MSs) using cationic gemini surfactants C_14–2‐n (n = 2, 6, 10, 14) as templates. The porous structures and pore size of these MSs can be tuned by varying the length of alkyl chain in gemini surfactant templates. These MSs showed effective doxorubicin (DOX) loading and a pH‐responsive drug release characteristics. These results indicate that the MSs, especially the hollow mesoporous silica nanoparticles, have great potential for biomedical applications.     

Hollow fiber stir bar sorptive extraction for determination of phthalic acid esters in environmental and biological matrices

The purpose of this paper is to introduce a novel hollow fiber stir bar sorptive extraction for collecting and determining of phthalic acid esters in environmental and biological matrices. Shell–core ZrO₂/SiO₂ composite microspheres and porous C₁₈ silica microspheres were compared as the sorbents, which were loaded in the lumen of a microporous hollow fiber membrane. A thin stainless‐steel wire was also inside of the hollow fiber membrane acting as the magnetic stirrer, thus affording the procedures like stir bar sorptive extraction to perform the active trapping of the analytes. Variables affecting the extraction (salt addition and pH of samples, extraction temperature, and time) and desorption (microwave time and eluted solvents) have been optimized. Under the optimal conditions, good linearity (r > 0.9968) of all calibration curves was obtained in validation experiments. And the limits of quantification ranged from 0.01 to 1000 ng/mL. The recoveries in different matrices were in the range of 64.90–112.60% with relative standard deviations less than 8.60%. The present work demonstrated the applicability of the developed method for the determination of phthalic acid esters in environmental and biological sample, allowing the selective extraction of phthalate esters in complex samples with low consumption of organic solvents and no sample clean‐up.     

Synthesis and characterization of new silica–titania mixed oxide in the presence of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide by sol–gel technique

Silica–titania mixed oxide were prepared by sol–gel method from tetraethylorthosilicate and titanium (IV) isopropoxide as precursors in the presence of room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [C₄MIm][NTf₂]. The effects of [C₄MIm][NTf₂] on the structural and textural characteristics of silica–titania matrix are investigated in this paper. The materials obtained were well characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis X-ray powder diffraction (XRPD), field emission scanning electron microscope (FESEM) and N₂ adsorption–desorption analysis. It is believed that the [C₄MIm][NTf₂] plays an important role as a template and the high surface area of the samples is thought to mainly attribute to the formation of microporous in the reaction. The synthesized materials showed the presence of C–N groups in the FTIR spectrum which indicates the presence of RTIL in the silica–titania matrix. XRPD, FESEM and N₂ adsorption–desorption analysis results indicated that the composite materials possessed good microporous character. The subsequent material displayed average pore diameter of 1.70–2.12 nm, pore volume of 0.08–0.19 cm³/g and BET surface area of 191–386 m²/g. Increasing the content of RTIL resulted in an increase of the average pore diameter of the silica–titania gel.     

Chirally Functionalized Hollow Nanospheres Containing L‐Prolinamide: Synthesis and Asymmetric Catalysis

Chirally functionalized hollow nanospheres with different surface properties were successfully synthesized by co‐condensation of (2S,1′R,2′R)‐N‐tert‐butyloxycarbonylpyrrolidine‐2‐carboxylic acid [2′‐(4‐trimethoxysilylbenzylamide)cyclohexyl] amide with 1,2‐bis(trimethoxysilyl)ethane or tetramethoxysilane using F127 (EO₁₀₆PO₇₀EO₁₀₆) as surfactant in water. The TEM and N₂ sorption characterizations show that the particle size of the hollow nanosphere is 15–21 nm with a core diameter of 10–16 nm. These L ‐prolinamide‐functionalized hollow nanospheres are highly efficient solid catalysts for the direct asymmetric aldol reaction between cyclohexanone and aromatic aldehydes. It was found that the addition of water in the reaction system not only enhanced the catalytic activity but also increased the enantioselectivity, which is probably due to the enhanced hydrogen bond between the amide oxygen atom and the hydroxyl group of water. Moreover, the catalytic activity increases sharply as the surface hydrophobicity of the hollow nanospheres increases. These hollow nanospheres are quite stable and can be reused with almost the same enantioselectivity and only a slight decrease in catalytic activity.     

Microporous Silica Xerogel Membrane with High Selectivity and High Permeance for Carbon Dioxide Separation

The asymmetric microporous silica xerogel membrane was prepared by sol-gel method. A multi-layer (asymmetric) structure was obtained by silica xerogel layer on top of mesoporous silica layer (mean pore diameter of 4 nm), supported by porous alumina tube (mean pore diameter of 0.1 m). The ratio of the permeances, CO₂/N₂ for this membrane attained more than 60 at 298 K. This value is considerably higher than the theoretical Knudsen value (CO₂/N₂ = 0.8). The gas permeances of this membrane were about 5–10 times higher than the previous membrane. Application of the membrane to an enrichment of CO₂ from air was also investigated. CO₂ in the air (about 300 ppm) was concentrated to more than 1000 ppm by using the membrane at 298 K.     

Solubility‐Parameter‐Guided Solvent Selection to Initiate Ostwald Ripening for Interior Space‐Tunable Structures with Architecture‐Dependent Electrochemical Performance

Despite significant advancement in preparing various hollow structures by Ostwald ripening, one common problem is the intractable uncontrollability of initiating Ostwald ripening due to the complexity of the reaction processes. Here, a new strategy on Hansen solubility parameter (HSP)‐guided solvent selection to initiate Ostwald ripening is proposed. Based on this comprehensive principle for solvent optimization, N,N‐dimethylformamide (DMF) was screened out, achieving accurate synthesis of interior space‐tunable MoSe₂ spherical structures (solid, core–shell, yolk‐shell and hollow spheres). The resultant MoSe₂ structures exhibit architecture‐dependent electrochemical performances towards hydrogen evolution reaction and sodium‐ion batteries. This pre‐solvent selection strategy can effectively provide researchers great possibility in efficiently synthesizing various hollow structures. This work paves a new pathway for deeply understanding Ostwald ripening.     

Synthesis and characteristics of poly(N‐isopropylacrylamide‐co‐methacrylic acid)/Fe3O4 thermosensitive magnetic composite hollow latex particles

In this study, the poly(NIPAAm–MAA)/Fe₃O₄ hollow latex particles were synthesized by three steps. The first step was to synthesize the poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles by the method of soapless emulsion polymerization. Following the first step, the second step was to polymerize N‐isopropylacrylamide (NIPAAm), MAA, and crosslinking agent (N,N'‐methylene‐bisacrylamide (MBA)) in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly (NIPAAm‐MAA) core‐shell latex particles. After the previous processes, the core‐shell latex particles were heated in the presence of NH₄OH to dissolve the linear poly(MMA‐MAA) core in order to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, Fe²⁺ and Fe³⁺ ions were introduced to bond with the ? COOH groups of MAA segments in the poly(NIPAAm‐MAA) hollow polymer latex particles. Further by a reaction with NH₄OH and then Fe₃O₄ nanoparticles were generated in situ and the poly(NIPAAm‐MAA)/Fe₃O₄ magnetic composite hollow latex particles were formed. The concentrations of MAA, crosslinking agent (N,N'‐methylene bisacrylamide), and Fe₃O₄ nanoparticles were important factors to influence the morphology of hollow latex particles and lower critical solution temperature of poly(NIPAAm–MAA)/Fe₃O₄ magnetic composite hollow latex particles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Characterization and Transport Properties of Surfactant-Templated Silica Layers for Membrane Applications

An intermediate surfactant-templated silica (STS) layer is applied between the supporting mesoporous γ-Al₂O₃ and the amorphous microporous silica overlayer resulting in dual-layered microporous silica membranes for gas separation applications that show improved values for both hydrogen flux and selectivity. Determination of thickness and porosity of as-deposited membrane layers by spectroscopic ellipsometry reveals that the STS layer is present as a distinctive layer of ～20 nm thickness, with penetration up to a depth of ～70 nm into the underlying γ-Al₂O₃support layer, whose thickness and porosity are determined to be 1.3 μm and 50%, respectively.