Monodisperse Silica Nanospheres Research Articles

Synthesis of Monodisperse Silica Nanospheres and Titania Beads from Rotating Cylinder System

Economic raw materials such as low-grade ethanol and Tetraethyl Ortosilicate (TEOS) were adopted as reactants for the synthesis of monodisperse silica nanospheres using a Taylor Vortex flow reactor with a rotating cylinder system. Factors affecting the mean diameter and size distribution of the silica grains were investigated by changing the rotating speed of the inner cylinder and the composition of reactants. In the case of titania beads, grain diameter size was adjusted by changing the amount of precursor (titanium (IV) isopropoxide, TIP), hexadecylamine (HDA) or Potassium Chloride (KCl) and reaction temperature as well as the rotation speed of the cylinder. As a demonstrative application, titania beads could be used for the removal of organic dye as a model contaminant dissolved in an aqueous medium using a photocatalytic decomposition system.

Random lasing in composites of CdSe/CdZnS colloidal quantum wells and silica nanoparticles

Colloidal quantum wells (CQWs) are a new type of atomic flat semiconductor nanocrystals, which present excellent opportunities as optical gain materials owing to their ultranarrow emission linewidth, tunable emission wavelength, suppressed Auger effect, and large gain cross-section. Here we synthesized monodispersed silica nanospheres and CdSe(4ML)/CdZnS core/shell CQWs. We observed random lasing by optically pumping the composites of CdSe(4ML)/CdZnS core/shell CQWs and silica nanoparticle scattering layer. The random lasing ranges from 615 nm to 625 nm with a threshold of 0.55 mJ cm−2. Fourier analysis reveals that sufficient Rayleigh scattering is the primary reason for the low threshold in the spatial frequency spectrum of the random laser. Our findings suggest that CQWs can serve as an efficient optical gain medium for random lasing, enabling various applications such as speckle-free laser imaging, random number generation for secure communication, chemical and biological sensing, high brightness and energy-efficient lighting, and label-free bioimaging.

Inside Front Cover

An inorganic sub‐ambient radiative cooling coating that is synthesized with geopolymer (i.e., alkali‐activated aluminosilicate) as the matrix material and nano‐precipitated barium sulphate and monodispersed silica nanospheres as the functional fillers achieves a solar reflectance of 97.6% and an infrared emissivity of 0.9491. Such radiative cooling coating is expected to able to cool buildings without electricity. image

Hollow Silica Nano and Micro Spheres with Polystyrene Templating: A Mini-Review.

Synthesis of monodisperse hollow silica nanospheres, especially using a hard template route, has been shown to be successful, but a high yield is needed for this strategy to be used on an industrial scale. On the other hand, there is a research gap in the synthesis of hollow silica microspheres due to the popularity and easiness of the synthesis of silica nanospheres despite the larger spheres being beneficial in some fields. In this review, current trends in producing hollow silica nanospheres using hard templates, especially polystyrene, are briefly presented. Soft templates have also been used to make highly polydisperse hollow silica spheres, and complex designs have improved polydispersity. The effect of the main parameters on the coating is presented here to provide a basic understanding of the interactions between the silica and template surface in the absence or presence of surfactants. Surface charge, surface modification, parameters in the sol-gel method and interaction between the silica and templates need to be further improved to have a uniform coating and better control over the size, dispersity, wall thickness and porosity. As larger organic templates will have lower surface energy, the efficiency of the micro sphere synthesis needs to be improved. Control over the physical structure of hollow silica spheres will open up many opportunities for them to be extensively used in fields ranging from waste removal to energy storage.

Maximum Incorporation of Soft Microgel at Interfaces of Water in Oil Emulsion Droplets Stabilized by Solid Silica Spheres.

The incorporation of soft hydrophilic particles at the interface of water in non-polar oil emulsion droplets is crucial for several applications. However, the stabilization of water in non-polar oil emulsions with hydrophilic soft material alone is, besides certain exceptions, not possible. In our previous works, we showed that stabilizing the emulsions with well-characterized spherical hydrophobic silica nanospheres (SNs) and soft equally charged microgel particles (MGs) is a robust strategy to stabilize w/o emulsions while still incorporating a large amount of MGs at the interface. In the present study, we address the question of what the maximum amount of MGs at the interface in these kinds of emulsion droplets can be. By using well-characterized mono-disperse SNs, we are able to calculate the fraction of interface covered by the SNs and complementary that of the present MG. We found that it is not possible to decrease the SN coverage below 56% irrespective of MG softness and SN size. The findings elucidate new perspectives to the broader topic of soft/solid stabilized emulsions.

Catalytic C–C bond formation over platinum nanoparticle catalyst on three-dimensional porous carbon

Three-dimensional porous carbon was prepared via a hard templating method using a colloidal crystal of monodispersed silica nanospheres (SNSs). Platinum nanoparticle catalyst on thus prepared porous carbon was prepared by a liquid-phase method using hydrogen hexachloroplatinate (IV) hexahydrate as Pt source in the presence of ethylene glycol. The prepared Pt catalyst on the carbon was characterized in detail and applied for the C-methylation reaction to elucidate the influence of the pore structure and morphology of the replicated porous carbon supports.

Continuous Synthesis of Monodisperse Spherical Silica Powder Using Tubular Reaction System

In the present study, monodisperse silica nanospheres were synthesized using a tubular reaction system in a continuous way. Screw-type blades were inserted inside a T-mixer for static mixing of the reactant streams which consisted of TEOS and NH4OH/H2O diluted with ethanol, for the continuous synthesis of the silica suspension. The diameter of the silica powder was monitored as a function of production time using dynamic light scattering to determine the optimum retention time and tube length, which were found to be 125 minutes and 7.5 m, respectively. The effects of reactant compositions on particle size were investigated by adjusting the amount of ammonia and water in the sol-gel reaction, which were then compared with the results from a batch reactor. Both the particle size and polydispersity index (PDI) of the silica suspension were measured to be comparable to nanospheres synthesized using a batch reactor. This implies that the tubular reaction system is more beneficial for potential industrial production applications in the size range from 115 to 310 nm, due to its continuous powder synthesis. The effect of the reaction medium was also studied, by replacing ethanol with methanol or propanol, indicating that the deviation in particle size with production time was not a serious issue in alcohols with lower molecular weight, such as methanol and ethanol.

Prediction of size, precursor ratio and monodispersity of silica nanospheres though adaptive neuro- fuzzy inference system

Highly monodisperse nanostructures are becoming the centre of focus in the field of material science towards the application of sensors, photocatalysis, gas sensing, antibacterial activity, drug delivery and energy applications. Monodisperse resembles uniform nanostructures towards better device performances and applications. In order to minimize the reaction time and characterization costs, an attempt has been made for development of a prediction model for the synthesis of monodisperse silica nanospheres using Adaptive Neuro-Fuzzy Inference System (ANFIS) software. Experimental parameters of the Stober method such as precursor's ratio (ethanol, water and ammonia), Tetraethyl Orthosilicate (TEOS) and sphere size were predicted in the model. The results from the prediction model were used for carrying out experimentation on thin films using vertical deposition technique. The prepared substrates were characterized by FE-SEM & XRD analysis. Obtained Experimental results shows that nanosphere with a size range of 200- 250 nm will form monodisperse layer. XRD analysis confirms the amorphous nature of SiO2 film. ANFIS has predicted best suitable size of silica nanospheres and optimized precursor's ratios for attaining highly monodisperse structure. The optimized parameters predicted from the ANFIS network matches well with the experimental results.

Broadband antireflection enhancement of c-Si solar cells by less 1/10 wavelength and subwavelength of silica nanosphere coatings

Monodisperse silica nanospheres with different diameters between 100 and 700 nm were fabricated using a slightly modified Stöber process. Silica nanosphere monolayers in a hexagonal array based on hydrophobically modification were well deposited on top of a bare crystalline silicon solar cell by a Langmuir-Blodgett method. The antireflection effect of various diameter silica nanospheres coatings was simulated using Comsol Multiphysics simulations. Silica nanosphere hexagonal array coatings with four kinds of diameters were fabricated based on results of simulations. The efficiency of solar cells covered by silica nanospheres has improved significantly with a maximum of 11.41% at 119 nm diameter while that of the planar solar cells was 10.17%, which is attributed to the improved photocurrents arising from the broadband antireflection and optical absorption. The antireflection effects produced by Rayleigh (<1/10 wavelength) and Mie scattering (subwavelength) of different diameters silica nanosphere structures were discussed in detail.

Merging Mie solutions and the radiative transport equation to measure optical properties of scattering particles in optical phantoms.

We present a new method to calculate the complex refractive index of spherical scatterers in a novel optical phantom developed by using homemade monodisperse silica nanospheres embedded into a polyester resin matrix and an ethanol-water mixture for applications in diffuse imaging. The spherical geometry of these nanoparticles makes them suitable for direct comparison between the values of the absorption and reduced scattering coefficients (μa and μs', respectively) obtained by the diffusion approximation solution to the transport equation from scattering measurements and those obtained by the Mie solution to Maxwell's equations. The values of the optical properties can be obtained by measuring, using an ultrafast detector, the time-resolved intensity distribution profiles of diffuse light transmitted through a thick slab of the silica nanosphere phantom, and by fitting them to the time-dependent diffusion approximation solution to the transport equation. These values can also be obtained by Mie solutions for spherical particles when their physical properties and size are known. By using scanning electron microscopy, we measured the size of these nanospheres, and the numerical results of μa and μs' can then be inferred by calculating the absorption and scattering efficiencies. Then we propose a numerical interval for the imaginary part of the complex refractive index of SiO2 nanospheres, ns, which is estimated by fixing the fitted values of μa and μs', using the known value of the real part of ns, and finding the corresponding value of Im(ns) that matches the optical parameters obtained by both methods finding values close to those reported for silica glass. This opens the possibility of producing optical phantoms with scattering and absorption properties that can be predicted and designed from precise knowledge of the physical characteristics of their constituents from a microscopic point of view.

TEOS and Na2SiO3 as silica sources: study of synthesis and characterization of hollow silica nanospheres as nano thermal insulation materials

Hollow structured material (HSM) consisting of monodisperse hollow silica nanospheres (HSN) shows a promising potential for construction insulation due to its affordable cost and simple process. Yet the studies of high-yield and low-energy for the synthetic of HSN are still insufficient. This research reported the comparison of morphology and performance of synthesize HSN utilizing TEOS and Na2SiO3 as silica source. The average yield of Na2SiO3-based samples can reach 93.75%, which is about 10 times higher that of TEOS-based samples. Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) results revealed that the shell morphology of TEOS-based samples was raspberry-like or smooth structure, while the shell of the Na2SiO3-based samples was round honeycomb-like structure. Hot Disk thermal constant analyzer results demonstrated that the thermal conductivity of the Na2SiO3-based samples was lower than that of the TEOS-based samples with similar inner-diameter and shell thickness. Thereafter, the influence mechanism of the morphology on thermal insulation performance was also investigated. The prepared HSN as filler significantly enhanced the thermal insulation of acrylic coating. This research confirms that the synthesis route with Na2SiO3 was a greener method which can solve the low yield and high energy consumption caused using TEOS as a silica source. Excellent thermal insulation properties indicate HSN will have a broad application prospect in heat-insulating and energy-saving construction.

Long Chain Imidazolium Ionic Liquids as Templates in the Formation of Mesoporous Silica Nanospheres

Mesoporous silica material was first discovered by Mobil research group in 1990s. Its nanoscale form is favorable due to their properties such as high specific surface area, tunable sizes and easy surface functionalization. Mesoporous silica nanoparticles (MSNs) is commonly synthesize through condensation of silica source in the presence of templates. Two most commonly used templates are cetyltrimethylammonium bromide (CTAB) and polymer PF-127. However, in these recent years, new templates were discovered and one of it is ionic liquids (ILs). ILs are salt that has melting point below 100 °C and its core structure is similar to CTAB which consist of large organic cations and inorganic or organic anions. Therefore, it has the potential to serve as alternative template in formation of MSNs. This work reported usage of two long chain imidazolium ILs as template in the synthesis of monodispersed mesoporous silica nanospheres (MNSs). The effect of imidazolium ILs alkyl chain length on properties of MNSs were investigated. It was found that particle size of MNSs decreases with alkyl chain length of imidazolium ILs. The porosity of the MNSs were further analyzed through nitrogen sorption analysis where the surface areas were 570.61 and 598.71 m2 g-1 and pore volume up to 1.4 cm3 g-1.

Lower methane combustion temperature on palladium nanoparticles anchored on TiOx subnano-islets in stellate mesoporous silica nanospheres

Highly accessible and active palladium nanoparticles stabilized on TiOx subnano-islets in monodispersed mesoporous silica nanospheres for methane combustion at low temperature.

Triamino-anchored KCC-1: A novel and promising adsorbent for fast and highly effective aqueous CrVI removal

Triamino-anchored monodispersed fibrous silica nanospheres (Triamino-KCC-1) was successfully fabricated, for the first time, via anchoring 3-[2-(2 Aminoethylamino) ethylamino] propyltrimethoxysilane by a facile and effective post-grafting approach. Triamino-KCC-1 with fibrous silica nanosphere morphology showed large pore volume (1.15 m3 g–1) and surface area (∼536 m2 g−1) containing the micro-mesostructured silica fibers. The adsorption behaviors of hexavalent chromium (CrVI) from aqueous media on the Triamino-KCC-1 adsorbent were monitored as a function of initial pH solution, adsorbent dose, initial CrVI concentration, and contact time. The Triamino-KCC-1, as a novel functionalized fibrous silica adsorbent, had high adsorption efficiency at acidic pH and the adsorption rate was fast. The adsorption data for Triamino-KCC-1 was consistent with the Langmuir isotherm model with a calculated maximum uptake capacity of ∼316 mg g−1, which was in reasonable agreement with experimental adsorption capacity (∼317 mg g−1). According to the results obtained by applying isotherm and kinetic parameters, we can conclude that the most active sites of Triamino-KCC-1 are easily accessible. The results obtained in the present study indicate that it is of great practical and research interest to develop functionalized fibrous silica-based adsorbents for effective heavy metals removal.

Preparation of colloidal crystal template for inverse opal hydrogels

Colloidal crystal template for inverse opal hydrogel is constructed by vertical deposition method using monodispersed silica nanospheres. By adjusting the concentration of monodispersed silica nanospheres, it is found that well-structured silica template with more than 20 layers is formed when the concentration of the silica is 3.5 wt%. To enhance its strength, the prepared template is put in an oven at 500 °C for 2 h. The surface of the template is divided into many blocks by cracks formed in the process of heat treatment. The number of blocks varies with the rising time of the temperature from 25 to 500 °C. Under the same magnification, blocks formed with the rising time of 150 min can be nearly 4 times more than the blocks with a rising time of 300 min or 500 min, which means the slow rising velocity of the temperature can lead to a better colloidal crystal template with fewer blocks.

The structure evolution of colloidal aggregates composed of monodisperse silica nanospheres

In this work, colloidal aggregates, such as higher-order clusters with polyhedral geometry, supraparticles with intermediate packing ordering, different inner structured supraballs with face-centered cubic ordering were produced through self-assembly of different quantities of monodisperse silica nanospheres in water-in-oil emulsion droplets which were formed by ultrasonic dispersion of silica nanospheres suspension into different solvents. The structure evolution of colloidal aggregates as a function of the number of constituent silica nanospheres was studied in this article. It was found that the inner structures of colloidal aggregates would be changed with increasing of the number of constituent silica nanospheres in different solvents. In the case of n-octanol being as solvent, the supraparticles were the transition structure for higher-order clusters into supraballs with hollow structure, while in silicone oil, the supraparticles were the transition structure for higher-order clusters into solid structured supraballs.

Dispersed Vanadium in Three-Dimensional Dendritic Mesoporous Silica Nanospheres: Active and Stable Catalysts for the Oxidative Dehydrogenation of Propane in the Presence of CO2.

The uniform monodispersed vanadium-doped three-dimensional dendritic mesoporous silica nanospheres (nV-MSNSs) were successfully synthesized in a heterogeneous oil-water biphase stratification reaction system and characterized by several state-of-the-art methods. The synthesized nV-MSNSs were applied to the oxidative dehydrogenation of the propane (ODHP) reaction with the presence of CO2 and exhibited excellent catalytic performances. The results show that the vanadium loading (1.3-8.0 wt %) evidently influences the textural properties, oxidation state, and polymerization degree of vanadium species of nV-MSNSs. The specific surface area (SBET), pore diameter (Dp), and pore volume (Vp) of nV-MSNSs decrease with the loading of vanadium species. The excessively high vanadium loading leads to the slight connection of nanospheres, but does not affect the assembly and growth of the three-dimensional (3D) dendritic channels. The percentage of highly dispersed vanadium VV species gradually increases and attains the maximum value for 5.2V-MSNSs with the loading of vanadium and then decreases with further vanadium addition. The higher-polymerized VOx species gradually generates above 5.2 wt % vanadium content for nV-MSNSs. The lower-polymerized VOx species appear to be more active than the higher-polymerized VOx species. Markedly, the 5.2V-MSNSs exhibit the highest catalytic activity with the initial propane conversion of 58% for the ODHP. The excellent catalytic performance can be maintained after eight reaction-regeneration cycles. The silica mesoporous frameworks can be well preserved in the reaction-regeneration cycles; meanwhile, the highly dispersed vanadium oxide also can be fully recovered after in situ regeneration. Hence, nV-MSNS catalysts exhibit outstanding activity and stability, and it would have a promising application in the DH of alkanes.

Synthesis of 3D silicon with tailored nanostructure: Influence of morphology on the electrochemical properties

Within this work, monodisperse porous silicon nanospheres have been derived from monodisperse silica nanospheres via two different magnesiothermic reduction routes, namely (i) magnesiothermic reduction using a two-chamber set-up, and (ii) magnesiothermic reduction using NaCl as heat scavenger. Both methods allow a size- and shape-preserving preparation of mesoporous silicon. Crystalline silicon with a particle size of 56nm and a specific surface area of 198m2g−1 and amorphous silicon with a particle size of 35nm and a specific surface area of 623m2g−1 are synthesized using the two chamber and salt assisted routes, respectively. TEM micrographs confirm enhanced porous character of silicon from NaCl assisted route. An unstable electrochemical performance of the crystalline silicon is found, whereas the amorphous Si presents a stable electrochemical behavior.

Synthesis of Monodisperse Silica Particles using Rotating Cylinder Systems

Monodisperse silica nanospheres were synthesized by Stober method using rotating cylinder systems with batch or continuous manner. The particle size could be controlled by adjusting the reactant compositions such as the amount of monomer, catalyst, and water in the reaction mixture. The size and monodispersity of the ceramic particles could be controlled by changing the reaction medium with different alcohols other than ethanol or changing the reaction temperature. The effect of Taylor number (Ta) on the average diameter and standard deviation of silica particles were also studied by adjusting the rotation speed of inner cylinder, and the maximum diameter of particles was observed at Ta ? 3,000.

Optical properties of gold nanoshells on monodisperse silica cores: Experiment and simulations

Gold nanoshells (GNSs) on silica cores are widely used in various biomedical applications that need the spectral tunability and controlled absorption/scattering ratio. However, the plasmonic quality of experimental extinction spectra of GNS colloids differs from that predicted by Mie theory. In this work, we fabricated highly monodisperse silica nanospheres to use them further as cores for synthesis of silica/gold nanoshells. Four GNS samples with 116-nm core and gold shell thickness ranging from 16 to 34nm (116/16, 18, 25, 34) were additionally separated in glycerol gradient solutions to obtain fractions with dominant percentage of single particles or aggregates of various sizes. The separated samples demonstrated extinction spectra with a high extinction maximum to minimum ratio about 3. Optical properties of GNS monomers and aggregates with fixed and random orientations were calculated by Mie theory for polydisperse GNSs, by a generalized multiparticle Mie (GMM) theory for aggregates of separated GNSs, and by the finite-difference time-domain (FDTD) method for aggregates of overlapped GNSs. The extinction spectra of upper fractions from 116/25 and 116/34 samples are shown to be well described by Mie theory for GNSs with polydisperse shell thickness. However, for as prepared 116/16 sample this approach fails because of strong near infrared (NIR) contribution from GNS dimers and trimers. The formation of such aggregates is due to coupling of silica cores at early stages of nanoshell synthesis, thus leading to peanut structures with overlapped gold shells. We suggested TEM-based ensemble model with single particles and small dimer and trimer aggregates, which gives satisfactory agreement between measured and FDTD simulated spectra in the vis-NIR region. Thus, the proposed synthetic technology produces high quality gold nanoshells, which remarkable optical properties are in good agreement with electromagnetic simulations based on TEM data.