Uniform Silica Nanoparticles Research Articles

Structural, Optical, and Morphological Characterization of Silica Nanoparticles Prepared by Sol-Gel Process

In the current years, silica nanoparticles have become more favorable in various disciplines like medicine, nano-biotechnology, the food industry, and drug delivery due to their tunable physicochemical characteristics. In this paper, the silica nanoparticles were synthesized by hydrolysis and condensation of tetra-ethyl-ortho-silicate (TEOS) in an ethanolic medium using ammonia as a stimulator in the reaction. The chemical bond structures of silica nanoparticles were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) which confirmed the existence of the Si-O bonds according to the different absorption peaks of the samples. The amorphous structure of these nanoparticles was certified by finding the board peaks in the X-Ray Diffraction (XRD) patterns. The elemental chemical composition of silica nanoparticles was investigated by Energy Dispersive X-Ray Spectroscopy (EDX) where 61.48wt % of silicon and 23.48wt% of oxygen were found. Almost round-shaped spherical and uniform silica nanoparticles with smooth surfaces were investigated by Scanning Electron Microscopy (SEM) measurement. The different particle sizes of silica nanoparticles within the range of 95±5.59 to 280±7.8 nm were found by controlling the concentration of TEOS. The optical absorption spectra and band gap calculations were also analyzed by Ultraviolet-Visible (UV-Vis) spectrophotometry for the different concentrations of TEOS. The results revealed that with increasing the concentration of TEOS, the absorption spectra of silica nanoparticles increased and their optical bandgap decreased from 3.92 eV to 3.79 eV.

Poly(acrylic acid) Enabling the Synthesis of Highly Uniform Silica Nanoparticles of sub‐100 nm

AbstractRobust synthesis of small colloidal silica (SiO2) nanoparticles with narrow size distributions (<5%) is challenging because the possible involvement of continuous nucleation and growth of SiO2 in the widely used Stöber process usually results in silica nanoparticles with large sizes and broad size distributions. Promoting heterogeneous nucleation and growth of silica is promising to tackle the challenges by in‐situ forming transient colloidal seeds that provide nucleation surfaces for silica condensate. In this work, poly(acrylic acid) (PAA) is introduced to the Stöber synthesis solutions, which are usually composed of ethanol (containing a trace amount of water), tetraethyl orthosilicate (TEOS), and ammonia, to mediate the nucleation of TEOS hydrolysates and growth of SiO2 nanoparticles. PAA reacts with ammonia to form soft PAA‐NH3 complex colloids that serve as transient seeds to facilitate heterogeneous nucleation and growth of SiO2 nanoparticles after adding TEOS to the synthesis solution. The number of PAA‐NH3 complex colloidal particles, which strongly depends on the molar ratio of PAA and ammonia, determines the number of the resulting SiO2 nanoparticles and thus the size of the SiO2 nanoparticles correspondingly according to the supply of TEOS. Highly uniform SiO2 nanoparticles with finely tuned diameters in the sub‐100 region have been successfully synthesized, and the synthesis protocol is feasible to be scaled up while maintaining the high quality of SiO2 nanoparticles.

Highly uniform silica nanoparticles with finely controlled sizes for enhancement of electro-responsive smart fluids

Highly monodisperse silica nanoparticles with four different diameters (100, 150, 250 and 500 nm) are prepared by adjusting the reaction temperature. With increasing the reaction temperature, the nucleation is promoted, consequently reducing the particle size. As-prepared silica particles are adopted as dispersing materials for electro-responsive smart fluids. The influence of particle size on the electro-responsive characteristics is systematically studied and analyzed. The ER efficiency of the silica-based ER fluids is significantly enhanced from ca. 17 to 63 as the particle size increases from 100 to 500 nm at a shear rate of 1 s–1 under the electric field of 2.5 kV mm–1. Furthermore, the anti-sedimentation properties of the silica nanoparticles are investigated to achieve an in-depth insight into the effect of particle size on electrorheological performances. All silica-based ER fluids show excellent anti-settling property that maintains high sedimentation ratio over 0.987 even after 120 h.

The structural coloration of textile materials using self-assembled silica nanoparticles

The work presented investigates how to produce structural colours on textile materials by applying a surface coating of silica nanoparticles (SNPs). Uniform SNPs with particle diameters in a controlled micron size range (207–350 nm) were synthesized using a Stöber-based solvent varying (SV) method which has been reported previously. Photonic crystals (PCs) were formed on the surface of a piece of textile fabric through a process of natural sedimentation self-assembly of the colloidal suspension containing uniform SNPs. Due to the uniformity and a particular diameter range of the prepared SNPs, structural colours were observed from the fabric surface due to the Bragg diffraction of white light with the ordered structure of the silica PCs. By varying the mean particle diameter, a wide range of spectral colours from red to blue were obtained. The comparison of structural colours on fabrics and on glasses suggests that a smooth substrate is critical when producing materials with high colour intensity and spatial uniformity. This work suggested a promising approach to colour textile materials without the need for traditional dyes and/or pigments.Graphical abstract

Facile control of silica nanoparticles using a novel solvent varying method for the fabrication of artificial opal photonic crystals.

In this work, the Stöber process was applied to produce uniform silica nanoparticles (SNPs) in the meso-scale size range. The novel aspect of this work was to control the produced silica particle size by only varying the volume of the solvent ethanol used, whilst fixing the other reaction conditions. Using this one-step Stöber-based solvent varying (SV) method, seven batches of SNPs with target diameters ranging from 70 to 400 nm were repeatedly reproduced, and the size distribution in terms of the polydispersity index (PDI) was well maintained (within 0.1). An exponential equation was used to fit the relationship between the particle diameter and ethanol volume. This equation allows the prediction of the amount of ethanol required in order to produce particles of any target diameter within this size range. In addition, it was found that the reaction was completed in approximately 2 h for all batches regardless of the volume of ethanol. Structurally coloured artificial opal photonic crystals (PCs) were fabricated from the prepared SNPs by self-assembly under gravity sedimentation. Figureᅟ Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-016-3691-8) contains supplementary material, which is available to authorized users.

Self-assembly of silica colloidal crystal thin films with tuneable structural colours over a wide visible spectrum

Colloidal crystal (CC) thin films that produce structural colours over a wide visible spectrum have been self-assembled from silica nanoparticles (SNPs) using a natural sedimentation method. A series of colloidal suspensions containing uniform SNPs (207–350nm) were prepared using the Stöber method. The prepared silica suspensions were directly subjected to natural sedimentation at an elevated temperature. The SNPs were deposited under the force of gravity and self-assembled into an ordered array. The solid CC thin films produced structural colours over a wide visible spectrum from red to violet. Visual inspection and colorimetric measurements indicated that the structural colour of the CC thin film is tuneable by varying the SNPs diameters and the viewing angles. The closely packed face-centred cubic (fcc) structure of the CC thin film was confirmed using SEM imaging and was in agreement with the intense colour observed from the film surface.

The Critical Effect of Niobium Doping on the Formation of Mesostructured TiO2 : Single-Crystalline Ordered Mesoporous Nb-TiO2 and Plate-like Nb-TiO2 with Ordered Mesoscale Dimples.

Highly ordered mesoporous niobium-doped TiO2 with a single-crystalline framework was prepared by using silica colloidal crystals with ca. 30 nm in diameter as templates. The preparation of colloidal crystals composed of uniform silica nanoparticles is a key to obtain highly ordered mesoporous Nb-doped TiO2 . The XPS measurements of Nb-doped TiO2 showed the presence of Nb(5+) and correspondingly Ti(3+) . With the increase in the amount of doped Nb, the crystalline phase of the product was converted from rutile into anatase, and the lattice spacings of both rutile and anatase phases increased. Surprisingly, the increase in the amount of Nb led to the formation of plate-like TiO2 with dimpled surfaces on one side, which was directly replicated from the surfaces of the colloidal silica crystals.

Synthesis and characterization of uniform silica nanoparticles on nickel substrate by spin coating and sol–gel method

Spin coating and sol–gel methods are proposed for the preparation of silica nanoparticles on a nickel substrate using silicon tetrachloride, 2-methoxyethanol, and four different types of alkaline solutions. The effects of the type of alkaline solution, concentration of silica solution, and speed of spin coating on the properties of silica nanoparticles are investigated systematically. Uniform spherical shape of silica nanoparticles on Ni with the smallest size are obtained with sodium carbonate among the alkaline solutions after stirring at 70°C for 6h and spin-coating at 7000rpm. Physical and electrochemical properties of the silica particles are investigated.

Cross-Linked Monolithic Xerogels Based on Silica Nanoparticles

Low density silica xerogels were obtained by reducing the capillary forces and thus the shrinkage upon ambient pressure drying. This was achieved by increasing the particle and thus also the pore size at a given target density. To increase the particle size beyond the values characteristic for classical silica aerogels, particle growth and formation of the interconnected network were decoupled. Uniform silica nanoparticles of 20 to 30 nm in diameter synthesized by a Stober process were subsequently cross-linked. To strengthen the gel network additional treatments were applied including an organic coating of the gel structure. For that purpose 3-Aminopropyltriethoxysilane (APTES) was used as a linker between the inner surface of the silica backbone and the organic component. Simultaneously, APTES serves as a catalyst for the gelation. Since the components for the organic coating of the silica backbone do not interfere with the network formation, a one-pot synthesis is feasible. Several bifunctional epoxide...

Covalent conjugation of avidin with dye-doped silica nanopaticles and preparation of high density avidin nanoparticles as photostable bioprobes

Progress in biomedical imaging depends on the development of bioprobes with a high sensitivity and stability. Fluorescent silica nanoparticles (NPs) covalent conjugation of avidin has been proposed for cancer cells imaging by fluorescence microscopy. Uniform silica NPs were prepared using water-in-oil (W/O) microemulsion methods and primary amine groups were introduced onto the surface of the NPs by condensation of tetraethyl orthosilicate (TEOS). Optically stable organic dyes, tris(2,2'-bipyridyl) dichlororuthenium(II) hexahydrate (Rubpy), were doped inside the silica NPs. The amine functions were transferred to carboxyl groups coupled with a linker elongation. Avidin was immobilized at the surface of the NPs by covalent binding to the carboxyl linkers. The binding capacity of the avidin-covered NPs for ligand biotin was quantified by titration with biotin(5-fluorescein) conjugate to 1.25 biotin binding sites/100nm2. We used biotinylated antibody and cell recognition by fluorescence microscopy imaging technique. The lung carcinoma cells were identified easily with high efficiency using these antibody-coated NPs. By comparison with fluorescein isothiocyanate (FITC), dye-doped silica NPs display dramatically increased stability of fluorescence as well as photostability, as compared to the common organic dye, when under continuous irradiation.

Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex

A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 ± 3 nm) or on mesoporous silica particles. The covalent bonding of Eu(TTA-Si)3 inside the core of uniform silica nanoparticles (40 ± 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen.

聚电解质包覆的铕(Ⅲ)配合物@SiO2荧光纳米粒的合成与性质

Uniform silica nanoparticles were synthesized via St(o|¨)ber method,and fluorescent europium complex with three chelate ligands(i.e.dibenzoylmethane,phenanthroline and acrylic acid)has been prepared.The hydrosoluble silica nanoparticles adsorbed liposoluble europium chelate with strong fluorescence in the aid of ultrasonication and phase-transfer solvent,and then were coated by cationic polyelectrolyte polydi-allyldimethylammonium chloride and anionic polyelectrolyte poly(acrylic acid)(PAA)one layer by one layer. The obtained fluorescent nanoparticles were charactered by transmission electron microscopy,ultraviolet spectrophotometer, infrared spectrophotometer,fluorescence spectrophotometer and Zeta potential.These nanoparticles have the advantages of uniform size,strong fluorescence,good photostability and leakage free. Futhermore,the nanoparticles with rich carboxy groups resulting from PAA coated on their surfaces made the surface modification and bioconjugation easier.These properties suggest their great potential in the application field of biology and medicine.

Scalable fabrication of superhydrophobic hierarchical colloidal arrays

Here we report a scalable bottom-up technology for assembling hierarchical colloidal arrays with superhydrophobic surface. Non-close-packed (NCP) colloidal multilayers, which facilitate the formation of more hydrophobic surface than close-packed arrays due to a higher fraction of entrapped air in between colloidal particles, are first fabricated by a simple spin-coating technology. Uniform silica nanoparticles are then assembled on the NCP microsphere arrays by a second spin-coating process. After surface functionalization of silica particles with fluorosilane, the resulting hierarchical colloidal arrays exhibit superhydrophobic surface with high apparent water contact angle (159°) and low contact angle hysteresis (4.7°). The experimental results on both the wettability and contact angle hysteresis can be qualitatively explained by adapting the Cassie's model. This spin-coating-based colloidal self-assembly technology is compatible with standard microfabrication and enables large-scale production of superhydrophobic coatings that could find important technological applications ranging from self-cleaning diffractive optics to microfluidic devices.

Antireflective Optical Properties of Colloidal Subwavelength Nanostructured Surfaces

AbstractColloidal subwavelength nanostructured surfaces were fabricated by the deposition of uniform silica nanoparticles on a glass substrate by means of electrostatic attraction between charged colloidal particles and charged polyelectrolyte multilayers. The effects of surface morphology via the variation of nanoparticles on the antireflective properties of the nanostructured surfaces were investigated by the analysis of the reflection spectra and the SEM images. The Maxwell's equations were solved by a rigorous coupled-wave analysis (RCWA) to evaluate the experimental results. It was found that the reflective properties revealed by the simulation analysis were similar to the experimental results. The nanostructured surfaces with particles of ~120 nm in diameter yielded the most suitable performance for antireflection with respect to the visible-light region. In addition, the nanostructured surfaces showed the good anti-scratch when the nanoparticles were bound by polyethoxysiloxane.

Study on Controllable Preparation of Silica Nanoparticles with Multi-sizes and Their Size-dependent Cytotoxicity in Pheochromocytoma Cells and Human Embryonic Kidney Cells

High-tech products made by nano-materials are tightly connected to people's life. However environmental impacts and health effects of nanoparticles are widely getting attention. In this paper, we focused on the potential size-dependent cytotoxicity of nanomaterials. Silica (SiO2) nanoparticles were used as model material. The ion exchange method and modified StÖber method were used to controllably prepare monodisperse uniform silica nanoparticles with six types of size (20, 50, 80, 140, 280 and 760 nm). And the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cellular morphology were introduced to evaluate the effect of the six sizes SiO2 nanoparticles on pheochromocytoma (PC12) and human embryonic kidney (HEK293) cells viability. The results indicated that nanosized-SiO2 (20, 50 and 80 nm) caused more cell damage when compared with microsized-SiO2 (140, 280 and 800 nm). IC50 of 24 hr exposure in PC12 cells were 118.2±7.3, 320.4±9.8, and 380.7±10.5 μg/ml, and in HEK293 cells were 80.2±6.4, 140.3±9.6 and 309.2±11.3 μg/ml for 20, 50- and 80-nm SiO2 particles, respectively. Additionally, the SiO2 particles of the other three sizes over 80-nm had little influence on the cell viability at the concentrations below 2000 μg/ml for two cultured cells. The results suggested that the exposure of SiO2 nanoparticles with different sizes leaded to cellular morphological modifications and apoptosis in a size-dependent manner. Further studies on the molecular mechanisms of apoptosis and the toxicity in vivo are necessary.

Uniform silica nanoparticles encapsulating two-photon absorbing fluorescent dye

We have prepared uniform silica nanoparticles (NPs) doped with a two-photon absorbing zwitterionic hemicyanine dye by reverse microemulsion method. Obvious solvatochromism on the absorption spectra of dye-doped NPs indicates that solvents can partly penetrate into the silica matrix and then affect the ground and excited state of dye molecules. For dye-doped NP suspensions, both one-photon and two-photon excited fluorescence are much stronger and recorded at shorter wavelength compared to those of free dye solutions with comparative overall dye concentration. This behavior is possibly attributed to the restricted twisted intramolecular charge transfer (TICT), which reduces fluorescence quenching when dye molecules are trapped in the silica matrix. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells with low cytotoxicity.

Interfacial properties of cetyltrimethylammonium-coated SiO 2 nanoparticles in aqueous media as studied by using different indicator dyes

In this paper, we compare the properties of SiO 2/water interface modified by cetyltrimethylammonium bromide (CTAB) with those of CTAB spherical micelles. The suspension of uniform silica nanoparticles coated with CTAB adlayer was investigated by using a set of acid–base indicators. The study of the colloidal system has been provided using electron microscopy and dynamic light scattering methods; the diameter of the initial SiO 2 particles in dried state was ca. 40 nm. The increase in the ζ-potential value of nanoparticles from −34 to +(37–54) mV on going from pure silica suspension to the CTAB-containing system points on the silica surface recharging and formation of surfactant bilayer (or multilayer) on the silica/water interface. To obtain further information about the interfacial surfactant adlayer, the behavior of different indicator dyes has been studied in CTAB-modified SiO 2 suspension. Comparison of the indices of apparent ionization constants, i.e., p K a a values of phenol red, bromothymol blue, and fluorescein with those determined in CTAB micellar solutions have confirmed the supposition about certain similarity between CTAB-covered silica nanoparticles and common spherical surfactant micelles. However, the experiments on kinetics of bromophenol blue fading, as well as the spectral properties of methyl orange and solvatochromic Reichardt's indicator and some other data revealed the specificity of surfactant-coated silica nanoparticles, presumably, originating from their surface morphology.

Silica nanoparticles-walled microcapsules

Colloidosomes are microcapsules with shells consisting of coagulated or partially fused colloid particles [1]. Since Dinsmore and collaborators [2] proposed the first concept of colloidosomes, many types of colloidosome structures have been proposed and discussed, and the research related to colloidosomes had become an attractive subject of many research groups. For example, Paunov et al. [3] reported the fabrication of ‘‘hairy’’ colloidosomes with shells of polymeric microrods. Wang et al. [4] produced the magnetic colloidosomes using a nanoparticle interfacial selfassembly method. Using the principles of colloidosomes, Binks and collaborators [5] investigated the temperatureinduced inversion of nanoparticle-stabilized emulsions. Due to its novel microstructures, colloidosomes are expected to have potential applications in many areas of science and technologies [6]. It has been recognized that the colloidosome membranes offer a great potential in controlling the release rate of entrapped species. Their major advantage is that the membrane pores size can be varied by varying the size of the particles and by controlling their degree of fusion. The fabrication of colloidosomes not only provides a way to construct novel microstructures with nanosized building-blocks, but also gives a new way to generate microcapsules with controllable permeability. Currently, the fabrication processes of colloidosomes are mainly based on the assembly of nanoparticles at the oil–water interfaces. In those processes, solid fine particles are first prepared and then these solid particles are assembled at the oil–water interface to produce the colloidosome structures. In this letter, we demonstrate the direct fabrication of silica colloidosome via a simple sol–gel process. The resultant silica colloidosomes are hollow, silica nanoparticles-walled microcapsules. Microcapsules are novel structures which are designed for the protection, transmission and controlled releasing of active ingredients such drugs, proteins, vitamins, flavors, gas bubbles, or even living cells. Versatile core materials are encapsulated for several reasons, such as improvement of long-time efficiency, stabilization against environmental degradation, easy handling through solidification of liquid core, and maintenance of non-toxicity of degradation products [7]. In a microcapsule system, the controlling behavior of the microcapsule is greatly determined by the structure and properties of the shell material used. Currently, the commonly used wall materials are urea formaldehyde and melamine formaldehyde (MF) resins. With the expanding applications of microcapsules, in some case, these microcapsules will be used in more rigorous conditions, e.g., at high temperatures. The commonly used wall materials cited above cannot meet these challenges. In addition, how to well construct the microstructures of the walls is still a challenge to researchers. Herein, we demonstrate the fabrication of a new type of silica nanoparticles-walled microcapsule. The schematic microstructure of the silica nanoparticleswalled microcapsule is shown in Fig. 1. This silica nanoparticles-walled microcapsule can be well constructed by using a two-step sol–gel process shown in Fig. 2. The principle for the formation of uniform silica nanoparticles is based on a two-step sol-gel process which is found in a literature method [8]. Using this two-step sol–gel method, uniform silica nanoparticles can be prepared. In this two-step sol–gel method, silica precursors were firstly hydrolyzed in aqueous media under the catalysis of diluted acid, and then ammonia was introduced for the Y. Liu (&) AE X. Chen AE J. H. Xin Nanotechnology Center, Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hong Kong, P. R. China e-mail: tcliuyy@inet.polyu.edu.hk J Mater Sci (2006) 41:5399–5401 DOI 10.1007/s10853-006-0248-8