Robust Amino-Functionalized Mesoporous Silica Hollow Spheres Templated by CO2 Bubbles

Hollow-structured mesoporous silica has wide applications in catalysis and drug delivery due to its high surface area, large hollow space, and short diffusion mesochannels. However, the synthesis of hollow structures usually requires sacrificial templates, leading to increased production costs and environmental problems. Here, for the first time, amino-functionalized mesoporous silica hollow spheres were synthesized by using CO₂ gaseous bubbles as templates. The assembly of anionic surfactants, co-structure directing agents, and inorganic silica precursors around CO₂ bubbles formed the mesoporous silica shells. The hollow silica spheres, 200–400 nm in size with 20–30 nm spherical shell thickness, had abundant amine groups on the surface of the mesopores, indicating excellent applications for CO₂ capture, Knoevenagel condensation reaction, and the controlled release of Drugs.     

Preparation of amino-functionalized mesoporous silica thin films with highly ordered large pore structures

Highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of triblock copolymer Pluronic P123 surfactant species under acidic conditions by sol-gel dip-coating. The effect of the sol aging on thin films organization is systematically studied, and the optimal sol aging time is obtained. The amino-functionalized mesoporous silica thin films exhibit a long-range ordering of 2D hexagonal (p6mm) mesostructure with a large pore size of 8.3 nm, a large Brunauer–Emmett–Teller (BET) specific surface area of 680 m² g⁻¹ and a large pore volume of 1.06 cm³ g⁻¹ following surfactant extraction as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM), and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for the amino-functionalized mesoporous silica thin films is calculated to be 3.2 amino-groups per nm². Moreover, the functionalized thin films display improved properties for immobilization of cytochrome c in comparison with pure-silica mesoporous thin films.     

A novel sol-gel-material prepared by a surface imprinting technique for the selective solid-phase extraction of bisphenol A

A novel and simple imprinted amino-functionalized silica gel material was synthesized by combining a surface molecular imprinting technique with a sol-gel process on the supporter of activated silica gel for solid-phase extraction-high performance liquid chromatography (SPE-HPLC) determination of bisphenol A (BPA). Non-imprinted silica sorbent was synthesized without the addition of BPA using the same procedure as that of BPA-imprinted silica sorbent. The BPA-imprinted silica sorbent and non-imprinted silica sorbent were characterized by FT-IR and the static adsorption experiments. The prepared BPA-imprinted silica sorbent showed high adsorption capacity, significant selectivity and good site accessibility for BPA. The maximum static adsorption capacity of the BPA-imprinted and non-imprinted silica sorbent for BPA was 68.9 and 34.0 mg g⁻¹, respectively. The relatively selective factor value of this BPA-imprinted silica sorbent was 4.5. Furthermore, the difference of the retention characteristics of BPA on the C₈ SPE column and BPA-imprinted silica SPE (MIP-SPE) was compared. The MIP-SPE-HPLC method showed higher selectivity to BPA than the traditional SPE-HPLC method. At last, the BPA-imprinted polymers were used as the sorbent in solid-phase extraction to determine BPA in water samples with satisfactory recovery higher than 99% (R.S.D. 3.7%).     

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.     

Synthesis and Polymerization Kinetics of Polystyrene Grafting using Azo-groups Bounded SiO2 as an Initiator

This work presents a new method for synthesis of inorganic/organic hybrid nanoparticles via the in-situ polymerization by the use of the azo-groups bounded silica nanoparticles as a radical initiator and styrene as a model vinyl-monomer. The synthesis and the structure of silica/polystyrene (SiO₂/PS), and the polymerization kinetics of the styrene initiated by the azo-groups bounded SiO₂ nanoparticles are studied with techniques such as FTIR, XPS, DSC, GPC, and TEM. Results show that the SiO₂-g-PS nanoparticles are synthesized successfully, and the resulting hybrid nanoparticles have a core-shell structure with SiO₂ in the core and the polystyrene on the outside layer. The percentage of the grafted PS on the SiO₂ surface increases with the progress of the polymerization before 6 h, and the largest amount of the grafted PS reaches 33% of the silica nanoparticles.

Consequently, the size of the nanoparticles increases ca. 20 nm upon the polystyrene grafting. The molecular weight of the grafted PS increases with the polymerization, and it has reached a much large value in the first several polymerization hours while it keeps a constant value approximately in the following polymerization process. Meanwhile, the polydispersity index of the grafted PS gradually increases with the progress of the polymerization. These phenomena agree with the theory of the traditional free radical polymerization very well.     

Preparation of a Novel Amino-Phosphate Zwitterionic Stationary Phase for Hydrophilic Interaction Chromatography

A new stationary phase which contains both negatively charged phosphate groups and positively charged amino groups was successfully synthesized by modification of amino-functionalized silica particles with trichlorophosphine oxide (POCl₃) for hydrophilic interaction chromatography (HILIC). The composition of the surface grafts was determined by Fourier transform infrared spectroscopy and elemental analysis. Various parameters, such as column temperature, water content, pH values and ionic strength of the mobile phase were investigated to study the retention mechanism. The results demonstrated that the stationary phase involved a complex retention process including surface adsorption, partitioning and electrostatic interactions. Under optimized conditions, the separation of nucleobases and nucleosides, water-soluble vitamins, organic acids on the novel stationary phase could be achieved in the HILIC mode.

     

Preparation and Evaluation of Uniform-Sized Sol–Gel Theophylline Imprinted Microspheres as Solid Phase Extraction Sorbent

A highly selective imprinted amino-functionalized silica gel microsphere was prepared by a simple molecular imprinting technique with a sol–gel process. Theophylline was used as template; 3-aminopropyltrimethoxysilane (APTMS) as functional monomer and tetraethylorthosilicate (TEOS) as reticulating agent. These theophylline imprinted silica microspheres were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron micrographs (SEM), thermogravimetric analysis (TGA), and high performance liquid chromatography (HPLC) in detail. The results showed that monodispersive APTMS-silica imprinted microspheres with size of 250 nm were synthesized successfully. Two kind of binding sites exist between the sol–gel imprinted microspheres and theophylline with K _D and Q _max for the higher affinity binding parameters was 1.89 μg/mL and 7.47 μg/mg dry polymers, and for the lower affinity binding sites were found to be 0.18 μg/mL and 3.47 μg/mg dry polymers, respectively. Packed in column, the imprinted microspheres were employed to extract theophylline from green tea successfully.     

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.     

A Fluorescent Blue Phosphazene Dye: Synthesis,Structure and Optical Properties of 1,6‐Bis(Dimethylamino)‐2,5,7,10‐Tetraazo‐1,6λ5‐Diphosphapyrene

Herein we report on the synthesis, structure, and optical properties of the fluorescent blue phosphazene dye 1,6‐bis(dimethylamino)‐2,5,7,10‐tetraazo‐1,6λ⁵‐diphosphapyrene, which was isolated as the unexpected product of the reaction between 1,4,5,8‐(tetraamino)naphthalene and [P(NMe₂)₃Br]Br. This dye, which turned out to be soluble in water and a range of organic solvents (including hexane, tetrahydrofuran / petroleum ether, acetonitrile, and ethanol), was structurally characterized by XRD. Its absorption as well as emission spectra and their sensitivity to pH variations were analyzed. The experimental work is complemented by quantum chemical calculations on the possible intermediate on the way to the isolated product and on its pK_a value.     

Protoporphyrin IX‐Functionalized AgSiO2 Core–Shell Nanoparticles: Plasmonic Enhancement of Fluorescence and Singlet Oxygen Production

Metal‐enhanced processes arising from the coupling of a dye with metallic nanoparticles (NPs) have been widely reported. However, few studies have simultaneously investigated these mechanisms from the viewpoint of dye fluorescence and photoactivity. Herein, protoporphyrin IX (PpIX) is grafted onto the surface of silver core silica shell NPs in order to investigate the effect of silver (Ag) localized surface plasmon resonance (LSPR) on PpIX fluorescence and PpIX singlet oxygen (¹O₂) production. Using two Ag core sizes, we report a systematic study of these photophysical processes as a function of silica (SiO₂) spacer thickness, LSPR band position and excitation wavelength. The excitation of Ag NP LSPR, which overlaps the PpIX absorption band, leads to the concomitant enhancement of PpIX fluorescence and ¹O₂ production independently of the Ag core size, but in a more pronounced way for larger Ag cores. These enhancements result from the increase in the PpIX excitation rate through the LSPR excitation and decrease when the distance between PpIX and Ag NPs increases. A maximum fluorescence enhancement of up to 14‐fold, together with an increase in photogenerated ¹O₂ production of up to five times are obtained using 100 nm Ag cores coated with a 5 nm thick silica coating.     

介孔SiO2的改性及对诺维信漆酶的交联固定化

采用十六烷基三甲基溴化铵(CTAB)为模板剂,四乙氧基硅烷(正硅酸乙酯,TEOS)为硅源,硝酸为催化剂来制备介孔SiO2,并采用后嫁接法对介孔SiO2进行氨基化改性。利用红外光谱(IR),X射线粉末衍射(XRD),差热-热重分析(DTA-TG),扫描电镜(SEM),元素分析,微电泳法及N2吸附-脱附方法对改性前后的产物进行表征。结果表明氨基已成功嫁接到介孔SiO2孔道中,改性后的介孔SiO2有序度有所下降,但仍为介孔材料;改性之后介孔材料的孔径、比表面积、孔体积均变小。等电点由原来的2.74变为4.75。本文还以氨基修饰的介孔SiO2为载体,通过交联剂戊二醛固定诺维信(Novozymes)工业级漆酶,并采用正交设计法对固定化条件进行了优化。研究表明漆酶经固定化后,其操作稳定性比游离酶高。     

Modified generalized kinetic model and degradation mechanistic pathways for catalytic oxidation of NBS dye in Fenton-like oxidation process

Rice husk was utilized as a silica source for the synthesis of mesoporous silica (MS), which was further used for the surface modification of iron oxide nanoparticles (IO-NPs) to form mesoporous silica-modified iron oxide nanoparticles (MSIO-NPs). IO-NPs and MSIO-NPs were characterized using FT-IR, XRD, X-ray photoelectron spectroscopy, vibrating sample magnetometry, nitrogen adsorption–desorption, TEM and dynamic light scattering analysis. The catalytic activity of MSIO-NPs was tested for degradation and mineralization of Nile blue sulphate dye (NBS) in Fenton-like oxidation process. The degradation efficiency and total organic carbon (TOC) removal of NBS dye onto MSIO-NPs was found to be 92.46 and 66.58%, respectively, after 20 min of reaction time using 5 mM of H₂O₂ concentration. Modified generalized kinetic model was developed for TOC removal of dye degradation onto MSIO-NPs, to account for oxidizable compounds, non-oxidizable compounds, and intermediate organic compounds. The intermediate products formed during degradation of NBS dye were detected by LC–MS experiment and ten fragments were identified based on mass to charge ratio (m/z). The mechanistic pathway for degradation of NBS dye onto MSIO-NPs has been proposed.     

Preparation of a Novel Amino-Phosphate Zwitterionic Stationary Phase for Hydrophilic Interaction Chromatography

A new stationary phase which contains both negatively charged phosphate groups and positively charged amino groups was successfully synthesized by modification of amino-functionalized silica particles with trichlorophosphine oxide (POCl₃) for hydrophilic interaction chromatography (HILIC). The composition of the surface grafts was determined by Fourier transform infrared spectroscopy and elemental analysis. Various parameters, such as column temperature, water content, pH values and ionic strength of the mobile phase were investigated to study the retention mechanism. The results demonstrated that the stationary phase involved a complex retention process including surface adsorption, partitioning and electrostatic interactions. Under optimized conditions, the separation of nucleobases and nucleosides, water-soluble vitamins, organic acids on the novel stationary phase could be achieved in the HILIC mode.     

Microstructure evolution in Stöber-type silica nanoparticles and their in vitro apatite deposition

Prepared via Stöber-type sol–gel routes were three types of silica particles of <1 μm in size: pure silica, Ca-involving silica, and chitosan/alginate-coated silica with a polymershell-silica core structure. Calcium ions were impregnated in the organic layers of the polymer-coated silica particle. The sol–gel procedure was applied to tetraethoxysilane dissolved in an ethanol/water mixture, while Ca–silica was derived from CaCl₂-containing ethanol/water solutions. Scanning and transmission electron micrograph analyses indicated that those silica particles consisted of ~10 nm primary particles, the Ca–silica particles (~500 nm) were larger than the Ca-free ones (~200 nm) and that their size increased with the Ca concentration in the precursor solutions. From ¹H- and ²⁹Si- magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra and ²⁹Si cross-polarization NMR spectra, the mechanism of primary particle agglomeration and degradation of the secondary particles in saline were discussed in terms of the content of H₂O molecules and >Si–OH as well as hydrogen bonding interactions among them. In addition, the Ca–silica and core-shell silica deposited apatite in Kokubo’s simulated body fluid. Thus, the present Ca–silica and polymer-coated silica particles were suggested to be applicable to injectable bone fillers for bone generation.     

Raspberry-like polymer/silica core-corona composite by self-assemble heterocoagulation based on a hydrogen-bonding interaction

Raspberry-like poly(ethyleneglycol dimethacrylate-co-4-vinylpyridine)/silica (poly(EGDMA-co-VPy)/SiO₂) core-corona composite was prepared by a self-assemble heterocoagulation based on a hydrogen-bonding interaction between the pyridyl group of poly(EGDMA-co-VPy) core and the active hydroxyl group of silica corona. The raspberry-like composite was stable near the neutral environment with pH ranging from 5.0 to 8.0. The effects of the solvent and the mass ratio of silica to polymer microsphere on the coverage of the silica corona on poly(EGDMA-co-VPy) core were investigated in detail. The resultant core-corona heterocoagulates were characterized with scanning electron microscope and the nature of the interaction between the polymer core particle and silica corona particle was identified as hydrogen bonding with Fourier Transform Infrared spectroscopy.     

Solid-Phase Reagent for Analgin and Ascorbic Acid on the Basis of a Copper(II) Complex with Tetrabenzotetraazacyclohexadecine Immobilized by Adsorption on Silica Gel

The reactions of a number of natural organic reducing agents with a copper(II) complex with tetrabenzo[b, f, j, n][1, 5, 9, 13]tetraazacyclohexadecine adsorbed on silica were examined. A solid-phase reagent was proposed for the sorption–spectrophotometric determination of Analgin and ascorbic acid (c _min= 0.91 and 0.06 mg/L, respectively) and for the visual test determination of the above compounds (c _min= 0.50 and 0.025 mg/sample, respectively).     

Separation behavior of basic compounds on unbonded silicon oxynitride and silica high‐performance liquid chromatography stationary phases with reversed‐phase eluents

Unbonded silicon oxynitride and silica high‐performance liquid chromatography stationary phases have been evaluated and compared for the separation of basic compounds of differing molecular weight, pK_a, and log D using aqueous/organic mobile phases. The influences of percentage of organic modifier, buffer pH, and concentration in the mobile phase on base retention were investigated on unbonded silicon oxynitride and silica phases. The results confirmed that unbonded silicon oxynitride and silica phases demonstrated excellent separation performance for model basic compounds and both the unbonded phases examined possessed a hydrophobic/adsorption and ion‐exchange character. The silicon oxynitride stationary phase exhibited high hydrophilicity compared with silica with a reversed‐phase mobile phase. An ion‐exclusion‐type mechanism becomes predominant for the separation of three aimed bases on the silicon oxynitride column at pH 2.8. Different from silicon oxynitride stationary phase, no obvious change for the retention time of three model bases on silica stationary phase at pH 2.8 can be observed.     

Physicochemical and photocatalytic properties of nanosized titanium dioxide deposited on silicon dioxide microspheres

The synthesis of SiO₂ core-TiO₂ shell composites from a titanium dioxide sol and a suspension of microspherical silicon dioxide is described. The main factors ensuring the formation of a composite with a preset morphology are the size and charge of the TiO₂ sol particles (10–45 nm) and silicon dioxide core particles (300–700 nm), the pH values of the suspensions of the starting components and the resulting composite, and the proportions and way of mixing of the siliconand titanium-containing components. The SiO₂ core-TiO₂ shell composites show high photocatalytic activity in the degradation of Rhodamine FL-BM dye (rate constant of k = 0.0813 min⁻¹) and are much more active than precipitated TiO₂ powder (k = 0.0022 min⁻¹). The activity of the composite is determined by the calcination temperature (700–800°C), by the proportion and accessibility of the active component (TiO₂), and by the presence of a dopant (P₂O₅).     

Template synthesis of imine-based covalent organic framework core-shell structure and hollow sphere: a case of COF<Subscript>TTA-DHTA</Subscript>

Controllably synthesizing well-dispersed covalent organic frameworks (COFs) with uniform both morphology and size is still a challenge. Herein, we report the template-directed synthesis of COF_TTA-DHTA-based core-shell hybrids under solvothermal conditions by using amino-functionalized SiO₂ microspheres as templates coupled with stepwise addition of initial monomer molecules. The modified amino groups on the surfaces of SiO₂ templates play an important role in the formation of well-defined NH₂-f-SiO₂@COF_TTA-DHTA core-shell hybrids. COF_TTA-DHTA hollow spheres can be obtained by etching SiO₂ cores of NH₂-f-SiO₂@COF_TTA-DHTA. Both the NH₂-f-SiO₂@COF_TTA-DHTA and COF_TTA-DHTA hollow spheres possess the well-defined morphology, high crystallinity and porosity, excellent dispersion property and high chemical stability. The template synthesis method demonstrated in this work provides a general method for the shape-controlled synthesis of COF-based materials, which is important for the further applications in the fields such as energy storage, drug delivery and catalysis.     

Adsorption of Remazol Red 3BS from aqueous solutions using APTES- and cyclodextrin-modified HMS-type mesoporous silicas

The removal of Remazol Red 3BS (C.I. 239) dye by HMS ordered mesoporous silica, aminopropyl-modified HMS (HMS-NH₂) and β-cyclodextrin-modified HMS (HMS-CD) materials was studied in the present work. The modified materials were functionalized in situ by adding the organic modifiers (3-aminopropyltriethoxysilane and a silylated derivative of MCT-β-CD) in the synthesis mixture and using dodecylamine as the mesopore structure directing agent. The successful incorporation of aminopropyl groups in HMS-NH₂ and of cyclodextrin moieties in HMS-CD was verified by means of FT-IR spectroscopy, elemental analysis and N₂ porosimetry. The HMS-CD material exhibited significantly higher adsorption capacity compared to that of the HMS-NH₂ material, while the parent HMS mesoporous silica showed negligible adsorption capability. The maximum adsorption capacities obtained (at the optimum pH 2) on the basis of the Langmuir analysis were 0.28 mmol/g for HMS-CD and 0.14 mmol/g for HMS-NH₂. It was shown that the HMS-CD sorbent can be effectively regenerated by the surfactant-enhanced regeneration method using SDS and that can be reused without significant loss of its adsorption capabilities.