Fluorescent monodisperse spherical particles based on mesoporous silica containing rhodamine 6G

Fluorescent monodisperse spherical silica (SiO₂) particles with a regular mesoporous structure containing encapsulated Rhodamine 6G (R6G) dye have been synthesized. The as-synthesized particles have been coated with SiO₂ and SiO₂-CTAB (cetyltrimethylammonium bromide, C₁₆H₃₃N(CH₃)₃Br) shells in order to prevent uncontrolled release of the dye from pores. The kinetics of R6G release from the pores of silica particles has been studied. It has been found that the particles synthesized by adding CTAB and R6G to the reaction mixture, as well as the particles coated with the SiO₂-CTAB shell, are characterized by the maximum duration of dye release from the pores, which is probably associated with the formation of chemical bonds between R6G and CTAB molecules.     

Controllable fabrication and characterization of biocompatible core-shell particles and hollow capsules as drug carrier

SiO₂@CdSe core-shell particles were fabricated by controllable deposition CdSe nanoparticles on silica colloidal spheres. Step-wise coating process was tracked by the TEM and XRD measurements. In addition, SiO₂@CdSe/polypyrrole(PPy) multi-composite particles were synthesized based on the as-prepared SiO₂@CdSe particles by cationic polymerization. The direct electrochemistry of myoglobin (Mb) could be performed by immobilizing Mb on the surface of SiO₂@CdSe particles. Immobilized with Mb, SiO₂@CdSe/PPy-Mb also displayed good bioelectrochemical activity. It confirmed the good biocompatible property of the materials with protein. CdSe hollow capsules were further obtained as the removal of the cores of SiO₂@CdSe spheres. Hollow and porous character of CdSe sub-meter size capsules made them becoming hopeful candidates as drug carriers. Doxorubicin, a typical an antineoplastic drug, was introduced into the capsules. A good sustained drug release behavior of the loading capsules was discovered via performing a release test in the PBS buffer (pH 7.4) solution at 310 k. Furthermore, SiO₂@CdSe/PPy could be converted to various smart hollow capsules via selectively removal of their relevant components.     

Rapid synthesis of SiO<Subscript>2</Subscript> by ultrasonic-assisted Stober method as controlled and pH-sensitive drug delivery

In this paper, the monodisperse silica nanoparticles were prepared by ultrasonic-assisted Stober method, and it explained that the ultrasonic cavitation effect shortened the reaction time from the original hours to f5 min. The effects of ultrasonic time, ultrasonic power, and stirring speed on the morphology, composition, and specific surface area of silica nanoparticles were investigated by field emission electron microscopy (FE-SEM). The results showed that nanoparticles with the best dispersity and the most uniform morphology were obtained under the optimized conditions (ultrasonic time is 5 min, ultrasonic power is 160 W, and the magnetic stirring speed is 999 rpm). The phase composition of SiO₂ was characterized by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), nano-size/zeta potential analyzer, and Fourier transform infrared spectroscopy (FT-IR). It showed that all typical peaks of samples are in line with the SiO₂ spectrum, the particle size distribution and zeta potential value of the silica is 615?±?35.6 nm and 59.87?±?0.91 mv, respectively, which further verified that the spherical silica nanoparticles with good dispersity can be synthesized in a very short time. Hemolysis test showed that nano-SiO₂ had high blood compatibility and biocompatibility when its concentration was less than 1 mg/mL. Doxorubicin (DOX·HCl) was regarded as a drug model to investigate the drug loading capacity of synthesized SiO₂; the results showed that the drug loading capacity and encapsulation efficiency reached 42.6?±?1.2 and 85.2?±?2.5%, respectively. Furthermore, the drug release experiments fitted well with the Higuichi equation with correlation coefficient (R²) of 0.9984, which further confirmed that the SiO₂/DOX drug delivery system has the controlled release property, and it also displayed pH-responsive behavior (at 96 h, the cumulative release of SiO₂/DOX in PBS solution with pH 7.4, 6.5, and 5.0 was 48.33, 62.31, and 94.86%, respectively). Therefore, this paper provides the possibility for developing more effective, safer, and more targeted controlled drug carriers.     

Surface modification of HMS material with silica sol leading to a remarkable enhanced catalytic performance of Cu/SiO2

Cu/SiO₂ catalysts with different bimodal pore structures adjusted by the ratio of HMS and silica sol were prepared via modified impregnation method. Structure evolutions of the catalyst were systematically characterized by N₂-physisorption, X-ray diffraction, H₂ temperature-programmed reduction, N₂O titration and X-ray photoelectron spectroscopy. The results show that the composite silica supported copper catalysts showed remarkably enhanced catalytic performance in the selective hydrogenation of dimethyl oxalate to ethylene glycol compared to the individual silica supported ones obtained by the same method. The dimethyl oxalate conversion and the ethylene glycol selectivity can reach 100% and 98% at 473 K with 2.5 MPa H₂ pressure and 1.5 h⁻¹ liquid hour space velocity of dimethyl oxalate over the optimized Cu/SiO₂ catalyst. The remarkably enhanced catalytic performance of Cu/SiO₂ catalysts might be attributed to the homogeneous dispersion and uniformity of the active copper species and to the larger copper surface areas attained on the HMS supports with large pore diameters and surface areas.     

Properties of Natural Rubber Vulcanizates/Nanosilica Composites Prepared Based on the Method of In-situ Generation and Coagulation

Using the characteristics of silica sol dispersing well in water and easy formation of silica gel when the silica sol is heated, by mixing a system of concentrated natural rubber latex and silica sol, the silica sol can in-situ generate SiO₂ particles when heated. After coagulation of the mixed system, natural rubber/nanosilica composites C(NR/nSiO₂) were obtained. The composites C(NR/nSiO₂) and their vulcanizates were studied using a rubber processing analyzer (RPA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The influence of silica contents on the C(NR/nSiO₂) vulcanizates mechanical properties, cross-linking degree, Payne effect, dissipation factor (tanδ), and the particle size and dispersion of SiO₂ in NR were investigated. The results obtained were compared with the NR/SiO₂ composites based on traditional dry mixing of bale natural rubber and precipitated silica (white carbon black). The results showed that when using a sulfur curing system with a silica coupling agent (Si69) in C(NR/nSiO₂), the vulcanizate had better mechanical properties, higher wet resistance, and lower rolling resistance than those without Si69. In the composites C(NR/nSiO₂) and their vulcanizates, the SiO₂ particles’ average grain diameter was 60 nm, and the good-dispersion of the in-situ generated SiO₂ in the rubber matrix were a significant contribution to the satisfactory properties of C(NR/nSiO₂) composites and their vulcanizates.     

Multiple Emulsion Templating of Hybrid Ag/SiO2 Capsules for Antibacterial Applications

Silver nanoparticles (NPs) encapsulated in amorphous silica shells are synthesized and evaluated for their antibacterial action using the Gram‐negative Escherichia coli bacterium. These inorganic capsules are synthesized using a new approach that comprises the use of oil‐in‐water‐in‐oil (O/W/O) multiple emulsions to fabricate SiO₂ capsules incorporating organically capped Ag NPs. This strategy is explored as a mean to promote the bioadhesion of the microorganisms to the silica rough surfaces while still keeping the system with a high surface area for the active metal. The results have shown that the hybrid capsules enable a slow release of cationic silver from the interior of the silica microsphere to the external medium probably through the pore channels in the shell. The antibacterial activity against E. coli is mainly determined by the Ag⁺ ion release rate, suggesting that these particulates can be employed as a robust system for prolonged used as an antimicrobial material.     

Synthesis and characteristics of nano-size sandwich structure (Y,Gd)BO3: Eu3+ phosphors

The sandwich structure core–shell–shell nanospheres SiO₂@(Y,Gd)BO₃:Eu³⁺@SiO₂ (SiO₂@YGB@SiO₂) have been synthesized by depositing YGB nanoparticles on silica core surface through the precipitation method, followed by sol–gel processing of tetraethoxysilane (TEOS) to form smooth silica shell over the surface of YGB. The phosphors were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electronic microscope (TEM) and photoluminescence spectra. The results showed that the phosphors with spherical morphology can be produced easily by assembling the core–shell or core–shell–shell structure, and the XRD patterns indicated that the crystallinity of YGB is weakened due to the core–shell structure, which resulting from the local site symmetry of Eu³⁺ was decreased. The photoluminescence properties of the product are compared with those of the pure YGB, the core–shell structure SiO₂@YGB and YGB@SiO₂. The emission intensity, relative luminous efficiency and Red/Orange values of phosphors are increased in the order SiO₂@YGB@SiO₂>SiO₂@YGB>YGB@SiO₂>YGB; and the chromaticity coordinates of the phosphors are shifted from orange of pure YGB to red of SiO₂@YGB@SiO₂.     

Synthesis and characterization of double –SO3H functionalized Brönsted acidic hydrogensulfate ionic liquid confined with silica through sol-gel method

Imidazolium-based metal and halogen-free Brönsted acidic ionic liquid (BAIL) (3,3′-(hexane-1,6-diyl)bis(2-methyl-1-(3-sulfopropyl)-1H-benzimidazolium) hydrogensulfate [HbMBIM-PS][HSO₄] was synthesized. The physicochemical properties of this BAIL were investigated using a variety of different analytical and spectroscopic techniques such as ¹H and¹³C-NMR, FT-IR, mass, UV–vis and TGA spectra. A porous silica matrix has been synthesized using BAIL and tetraethoxysilane (TEOS) as silica source by nonhydrolytic sol–gel method. The properties of IL confined silica gel matrix have been studied using FTIR, TGA, SEM, N₂-sorption measurement (BET characterization for determining pore parameters), and NH₃-TPD techniques. From the N₂-sorption measurement, it has been found that BET surface area decreased while pore volume, average pore size and porosity decreased. The thermal stability of the IL has been found to increase upon confinement in silica gel matrix. The results suggested that IL had been successfully confined on silica gel. This IL confined silica gel catalyst is environment friendly and useful for alkane isomerization and esterification reactions.     

Highly selective fluorescent chemosensor for detecting Hg(II) in water based on pyrene functionalized core–shell structured mesoporous silica

Novel pyrene functionalized mesoporous core–shell structured silica (denoted as SiO₂@mSiO₂/Py-Si) was designed and synthesized as a highly selective fluorescent chemosensor for detecting Hg²⁺ in water. The core–shell structured silica was prepared by a simple sol–gel process through coating SiO₂ nanospheres with a layer of ordered mesoporous silica. The surface of outer mesoporous silica shell was then further functionalized by the fluorescent chromophore alkoxysilane modified pyrene (Py-Si). XRD data confirmed that the hexagonal ordered mesoporous structure was preserved after functionalization. The chemosensing material successfully exhibited a remarkable “turn on” response toward Hg²⁺ over miscellaneous metal ions. A good linear response towards Hg²⁺ in the concentration range of 10^?8–10^?4 M was constructed with R²=0.9913. Most importantly, a satisfactory detection limit of 3.4×10^?9 g mL^?1 (down to ppb level) was obtained, which is 100 times lower than our previous report of covalently grafted Py-OH to the bulk mesoporous silica SBA-15. These results indicated that SiO₂@mSiO₂/Py-Si can be used as a highly selective and sensitive fluorescence sensor for Hg²⁺.     

Development of porous silica production by hydrothermal method

Abstract

A new process for porous silica production has been developed using a hydrothermal method. Hydrothermally synthesized calcium silicate was used as the starting material in this study, which was produced from a mixture of Ca(OH)₂ and amorphous silica (white carbon) under hydrothermal conditions of 140°C and 0.4 MPa, for 8 hours. The calcium silicate was subsequently treated with an acid solution, facilitating the leaching of Ca ions. After washing with pure water, the multant Ca²⁺ -free silica powder was allowed to dry. The Ca²⁺ -free silica powder was found to have an amorphous structure, with 0.9 ml/g pore volume, up to 610m²/g BET specific surface area, and an average 5 ～ 8 nm pore size. Our hydrothermal process is simple and low cost, and is anticipated to have numerous applications to the petrochemical industry.     

Magnetic Core/Shell Nanocomposites MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> for Biomedical Application: Synthesis and Properties

Magnetic core/shell (CS) nanocomposites (MNCs) are synthesized using a simple method, in which a magnesium ferrite nanoparticle (MgFe₂O₄) is a core, and an amorphous silicon dioxide (silica SiO₂) layer is a shell. The composition, morphology, and structure of synthesized particles are studied using X-ray diffraction, field emission electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), scattering electrophoretic photometer, thermogravimetric analysis (TGA), and Mössbauer spectroscopy. It is found that the MgFe₂O₄/SiO₂ MNC has the core/shell structure formed by the Fe?O–Si chemical bond. After coating with silica, the MgFe₂O₄/SiO₂ MNC saturation magnetization significantly decreases in comparison with MgFe₂O₄ particles without a SiO₂ shell. Spherical particles agglomerated from MgFe₂O₄ nanocrystallites ～9.6 and ～11.5 nm in size function as cores coated with SiO₂ shells ～30 and ～50 nm thick, respectively. The total size of obtained CS MNCs is ～200 and 300 nm, respectively. Synthesized CS MgFe₂O₄/SiO₂ MNCs are very promising for biomedical applications, due to the biological compatibility of silicon dioxide, its sizes, and the fact that the Curie temperature is in the region required for hyperthermal therapy, 320 K.     

Nano-designing of Mg doped phosphate tungsten bronzes and SiO2 composite obtained by ultrasonic spray pyrolysis method

In this study, the structure and substructure of SiO₂–Mg phosphate tungsten bronzes, MgPTB, (MgHPW₁₂O₄₀ · 29H₂O) obtained by ultrasonic spray pyrolysis method from a silica sol, and a MgPTB solution, obtained by the ion exchange method, as precursors were investigated.The mechanism of the formation of aerosol droplets is discussed. Phase composition, structure and substructure of SiO₂–MgPTB particles were investigated by X-ray powder diffraction (XRPD) analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM).Good agreement between the theoretically predicted values for the mean diameters of particles and subparticles (1.27 μm and 75.4 nm, respectively) and the experimentally obtained ones (1.17 μm and 65–90 nm) was found.This agreement confirms the applicability of the model to get a satisfactory prediction of the most important data related to the nano-structural design of SiO₂–MgPTB powders.     

Emulsion Combustion and Flame Spray Synthesis of Zinc Oxide/Silica Particles

Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO₂ and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO₂ sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO₂ sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 m). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO₂ occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO₂ sol and ZA, creating a ZnO and SiO₂ mixture. The reaction of ZnO with SiO₂ was likely to be enhanced by ECM of the SiO₂ sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, -willemite and Zn_1.7SiO₄ mixed phase.     

SiO2 stabilized Pt/C cathode catalyst for proton exchange membrane fuel cells

This paper describes the preparation of SiO₂ stabilized Pt/C catalyst (SiO₂/Pt/C) by the hydrolysis of alkoxysilane, and examines the possibility that the SiO₂/Pt/C is used as a durable cathode catalyst for proton exchange membrane fuel cells (PEMFCs). TEM and XRD results revealed that the hydrolysis of alkoxysilane did not significantly change the morphology and crystalline structure of Pt particles. The SiO₂/Pt/C catalyst exhibited higher durability than the Pt/C one, due to the facts that the silica layers covered were beneficial for reducing the Pt aggregation and dissolution as well as increasing the corrosion resistance of supports, although the benefit of silica covering was lower than the case of Pt/CNT catalyst. Also, it was observed that the activity of the SiO₂/Pt/C catalyst for the oxygen reduction reaction was somewhat reduced compared to the Pt/C one after the silica covering. This reduction was partially due to the low oxygen kinetics as revealed by the rotating-disk-electrode measurement. Silica covering by hydrolysis of only 3-aminopropyl trimethoxysilane is able to achieve a good balance between the durability and activity, leading to SiO₂/Pt/C as a promising cathode catalyst for PEMFCs.     

Preparation of mesoporous poly (acrylic acid)/SiO2 composite nanofiber membranes having adsorption capacity for indigo carmine dye

Mesoporous poly (acrylic acid)/SiO₂ (PAA/SiO₂) composite nanofiber membranes functionalized with mercapto groups were fabricated by a sol-gel electrospinning method, and their adsorption capacity for indigo carmine was investigated. The membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray powder diffraction (XRD), and nitrogen adsorption–desorption measurement. SEM and TEM observation results showed that the PAA/SiO₂ fibers had diameters between 400–800 nm and mesopores with an average pore size of 3.88 nm. The specific surface area of the mesoporous nanofiber membranes was 514.89 m²/g. The characteristic peaks for mercapto group vibration in FTIR and Raman spectra demonstrated that the mercapto groups have been incorporated into the silica skeleton. The adsorption isotherm data of indigo carmine on the membranes fit well with Redlich–Peterson model, and the maximum adsorption capacity calculated was 523.11 mg/g. It was found that the removal rate of indigo carmine by the membranes reached a maximum of 98% in 90 min and the adsorption kinetics followed a pseudo-second-order model. The high adsorption capacity of PAA/SiO₂ nanofiber membrane makes it a promising adsorbent for indigo carmine removal from the wastewater.     

Production and characterization of spodumene dosimetric pellets by prepared by pechini and proteic sol–gel route

Spodumene is an aluminosilicate that has proven suitable for high-dose TL dosimetry of beta or gamma rays. Due to the presence of lithium in its chemical composition (LiAlSi₂O₆ – β-LAS), it has potential as neutron dosimeter as well. This silicate may be obtained naturally or synthetically. The synthetic LAS has been produced by solid state reaction and conventional sol–gel, whose difficulty arises from the need to employ high temperatures and high cost reagents, respectively. Alternative routes like Pechini and proteic sol–gel methods are promising, because they can reduce production costs and the possibility of environmental pollution. This work aimed at producing spodumene with the proteic sol–gel method using edible unflavored gelatin as a precursor and also with the Pechini method. The products were characterized physically and morphologically, and their applicability as TL dosimeter was investigated, comparing the sensitivity of samples produced by different methods. Two sets of samples were produced using different sources of silicon, tetraethyl orthosilicate (TEOS, Si(C₂H₅O)₄) and silica (SiO₂). The materials produced were characterized by X-ray diffraction and by thermal analysis in order to evaluate their structural properties, as well as possible temperature-dependent changes in physical or chemical properties. The syntherized pellets produced with these crystals were irradiated with a ⁹⁰Sr–⁹⁰Y source and their TL glow curves were evaluated. The production of β-LAS was successful by both methods, either using silica or TEOS as a silicon source. The crystals were obtained using much lower temperatures than by methods described in literature. We observed that the method of powder production was critical to develop a radiation detector: the best TL material was the powder produced using silica and the Pechini Method.     

Structural and optical tunability of metallodielectric composites with gradual shell growth

Metallodielectric (gold@silica) composites were prepared by seed and grow method. The dielectric microspheres (core material) of an average size of 400 nm were synthesized by sol–gel method and gold nanoparticles (AuNPs) were prepared by reducing the chloroauric solution. Shell growth around silica (SiO₂) microspheres was carried out in a multistep layer-by-layer process. The synthesized composites were characterized using techniques such as field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and UV–Visible (UV–Vis) spectroscopy. FE-SEM and FTIR analyses have confirmed the functionalization of SiO₂ surfaces with the amine terminal group along with the gold shell growth. XRD analysis has given an average crystallite size of 12.3 nm for metallodielectric composites. Absorption spectra have demonstrated the dependence of surface plasmon resonance (SPR) peak on the successive shell growth by exhibiting a red shift.     

Bactericidal effects of Ag nanoparticles immobilized on surface of SiO2 thin film with high concentration

Bactericidal activity of high concentration Ag nanoparticles immobilized on surface of an aqueous sol–gel silica thin film was investigated against Escherichia coli and Staphylococcus aureus bacteria. Size of the surface nanoparticles was estimated in the range of 35–80 nm by using atomic force microscopy. Due to accumulation of the silver nanoparticles at near the surface (at depth of 6 nm and about 40 times greater than the silver concentration in the sol), the synthesized Ag–SiO₂ thin film (with area of 10 mm²) presented strong antibacterial activities against E. coli and S. aureus bacteria with relative rate of reduction of the viable bacteria of 1.05 and 0.73 h⁻¹ for initial concentration of about 10⁵ cfu/ml, respectively. In addition, the dominant mechanism of silver release in long times was determined based on water diffusion in surface pores of the silica film, unlike the usual diffusion of water on the surface of silver-based bulk materials. Therefore, the Ag nanoparticles embedded near the surface of the SiO₂ thin film can be utilized in various antibacterial applications with a strong and long life activity.     

Synthesis and characterization of mono-dispersed Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Er<Superscript>3+</Superscript>-coated SiO<Subscript>2</Subscript> nanoparticles by co-precipitation process

In this paper, a facile co-precipitation process for preparing mono-dispersed core–shell structure nanoparticles is reported. The 110 nm SiO₂ cores coated with an yttrium aluminum garnet (Y₃Al₅O₁₂) layer doped with Er³⁺ were synthesized and the influence of the concentration ratio of [urea]/[metal ions] on the final product was investigated. The structure and morphology of samples were characterized by the X-ray powder diffraction, Fourier transform IR spectroscopy and transmission electron microscopy, respectively. The results indicate that a layer of well-crystallized garnet Y₃Al₅O₁₂:Er³⁺ were successfully coated on the silica particles with the thickness of 20 nm. The near infrared and upconversion luminescent spectra of the SiO₂@Y₃Al₅O₁₂:Er³⁺ powders further confirm that a Y₃Al₅O₁₂:Er³⁺ coating layer has formed on the surface of silica spherical particles.     

Preparation and characterization of SiO2/ZrO2/Ag multicoated microspheres

A new type of multicoated silica/zirconia/silver (SiO₂/ZrO₂/Ag) core-shell composite microspheres is synthesized in this paper. In the process, ZrO₂-decorated silica (SiO₂/ZrO₂) core-shell composites were firstly fabricated by the modification of zirconia on silica microspheres through the hydrolysis of zirconium precursor. Subsequently, on SiO₂/ZrO₂ composite cores, silver nanoparticles were introduced via ultrasonic irradiation and acted as “Ag seeds” for the formation of integrate silver shell by further reduction of silver ions using formaldehyde as reducer. The resulting samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared, energy-dispersive X-ray, and UV-vis spectroscopy, indicating that zirconia and silver layers were successfully coated on the surfaces of silica microspheres.