Surface Of SiO2 Spheres Research Articles

Sandwich Ni-phyllosilicate@doped-ceria for moderate-temperature chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) enables the highly selective oxidation of CH4 and reduction of CO2. We designed sandwich and core-shell structured 5% Ni-SiO2@Ce0.8M0.2O2-δ (M = Fe, Co, Ni) catalysts for moderate-temperature CL-DRM. Highly dispersed nano Ni particles are anchored on the surface of SiO2 spheres, and then transition metal oxide-doped CeO2 is dispersed on the inner core to form a shell layer serving as the oxygen storage role. This trilayer structure provides abundant CeO2-Ni interfaces and catalytic sites. Doping of transition metal oxides helps to activate methane for synthesis gas generation at lower temperatures. In the chemical looping cycle, the available OSC (oxygen storage capacity) was enhanced by the introduction of transition metals into ceria and follows the order of Fe-doped (2.92 mmol g−1) > Ni-doped (1.69 mmol g−1) > Co-doped (0.86 mmol g−1) > undoped (0.58 mmol g−1) catalysts. The catalyst exhibits high coke resistance and redox reactivity in successive CL-DRM redox cycles at 620 °C. In situ Drifts and Raman of CH4/CO2 temperature programmed desorption over recycled/pre-reduced catalysts show that methane is activated into CHx over highly dispersed nickel nanoparticles at 400 °C and then converted into H2 and CO by lattice oxygen. Then, oxygen vacancies are refilled, reduced species (Fe0 and Fe2+) are re-oxidized using CO2 to produce CO, and deposited carbon from CH4 POx is also removed via CO2 gasification.

New vesicular carbon-based rhenium phosphides with all-pH range electrocatalytic hydrogen evolution activity

Considering the great application prospect of noble metal rhenium (Re) in the catalytic field derived from its intrinsic properties, exploring more novel and highly effective Re-based catalysts becomes an important topic. Herein, for the first time, we design a novel strategy for fabrication of Re2P and Re3P4 nanoparticles anchored in N, P doped vesicular carbon (NPVC) via pyrolyzing ammonium perrhenate (NH4ReO4), 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) and melamine on the surface of SiO2 spheres. Choosing hydrogen evolution as a probe reaction, Re3P4@NPVC heterostructure exhibits highly efficient catalytic activity compared with as-synthesized samples, which rivals the commercial Pt/C. Concretely, the Tafel slope is 38, 77 and 62 mV dec−1, and overpotential is 40, 70 and 61 mV at 10 mA cm−2 in 0.5 M H2SO4, 1 M phosphate buffer solution and 1 M KOH, respectively. Both experiment and DFT calculation unambiguously validate that Coupling metal Re and P is able to promote the HER pathway by tuning the ΔGH* value close to the optimum, balancing adsorption and desorption of hydrogen. Besides, the electronic coupling of NPVC layer and NPs synergistically enhances the proton adsorption and reduction kinetics.

Seed-mediated photodeposition route to Ag-decorated SiO2@TiO2 microspheres with ideal core-shell structure and enhanced photocatalytic activity

Ag-decorated SiO2@TiO2 microspheres (SiO2@TiO2-Ag) with ideal core-shell structure and enhanced photocatalytic activity were successfully fabricated by combining both coating anatase TiO2 on the surface of SiO2 spheres and subsequent depositing face-centered cubic Ag nanoparticles (NPs) on the coated TiO2 surface via novel sol-gel method and Ag-seed-mediated photodeposition (PD) route, respectively. The morphology, structure, composition and optical properties of the resulting composites were characterized in detail. The results reveal that the monodisperse SiO2 spheres of ∼260 nm were covered uniformly and perfectly by the TiO2 nanoparticle coating layer with the thickness of ca. 55 nm by the novel sol-gel method. Further, homogeneously and highly dispersed Ag NPs with an average size of 8 ± 1.5 nm were strongly anchored onto the TiO2 surface in SiO2@TiO2 core-shell spheres by the modified PD process (Ag-seed-mediated PD route), whereas polydispersed Ag aggregates and detached Ag NPs were irregularly deposited over the TiO2 surface in previous works, which is the inherent problem and has not been effectively solved for depositing noble metal NPs such as Au, Ag, Pt, Pd on TiO2 surface by conventional PD method. The formation mechanism of small and uniformly dispersed Ag NPs with narrow size distribution via the modified PD method is tentatively explained by both nucleation kinetics and growth kinetics. The key reason is that the pre-deposited seeds firmly tethered on SiO2@TiO2 spheres served as nucleation sites and anchoring points for the further nucleation and subsequent growth of Ag via photoreduction of Ag+.

Nanoseeded Catalytic Terpolymerization of CO, Ethylene, and Propylene by Size-Controlled SiO2@Sulfonated Microporous Organic Polymer

Nanoseeds with silica@sulfonated microporous organic polymer (SiO2@S-MOP) structure were prepared by the formation of MOP layers on the surface of SiO2 spheres and the successive sulfonation of the MOPs. Using the SiO2@S-MOPs as seed materials, catalytic terpolymerization of CO, ethylene, and propylene was studied. The designed SiO2@S-MOP nanoseeds not only activated catalyst precursors but also controlled the catalytic formation of polyketones. While the homogeneous system showed a severe reactor fouling and a wide molecular weight distribution of terpolymer, the SiO2-190@S-MOP system resulted in the narrow molecular weight distribution of terpolymers without a reactor fouling. The size of nanoseeds was critical to obtaining the granular terpolymers. Moreover, the SiO2-190@S-MOP system showed a good activity of 17.2 kg of polymer/g of Pd, comparable to the homogeneous system with 19.6 kg of polymer/g of Pd. We believe that more various nanoseeded catalytic polymerizations can be developed using new nanos...

Photoluminescence and Confinement of Excitons in Disordered Porous Films

The exciton confinement effect in quantum dots at the surface of SiO2 spheres and the percolation phase transition in films based on a mixture of pure SiO2 spheres and spheres covered by CdS quantum dots (SiO2/CdS nanoparticles) are studied. It is found that, due to the high surface energy of spheres, the quantum dots deposited onto their surface are distorted, which modifies the exciton confinement effect: the effect is retained only in one direction, the direction normal to the surface of the spheres. As a result, the energy of the exciton ground state exhibits a complex dependence on both the quantum-dot radius and sphere size. In the optical spectra of films based on this mixture, the clustering of small-sized nanoparticles and then, at a critical concentration of nanoparticles of ~60%, the formation of a percolation cluster are detected for the first time. The critical concentration is twice higher than the corresponding quantity given by the model of geometrical “colored percolation”, which is a consequence of interaction between submicrometer nanoparticles. The relation between the basic parameters of the percolation transition, such as the film porosity, coordination number, and the quantity defining the number of particles in the percolation cluster, is obtained and analyzed.

Self-assembly preparation of SiO2@Ni-Al layered double hydroxide composites and their enhanced electrorheological characteristics.

The core-shell structured SiO2@Ni-Al layered double hydroxide (LDH) composites were prepared via self-assembly of Ni-Al LDH on the surface of SiO2 spheres. Only coating a layer of ultrathin Ni-Al LDH sheet, the resulting SiO2@Ni-Al LDH composites exhibit significantly enhanced electrorheological (ER) characteristics compared to conventional bare SiO2 spheres. The monodispersed SiO2 spheres with average diameters of 260 nm were synthesized by the hydrolysis of tetraethyl orthosilicate (TEOS), while the shell part, Ni-Al LDH sheet was prepared by the hydrothermal procedure. The morphology of the samples was investigated via scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure of the samples was characterized by X-ray diffraction (XRD). The species and distribution of elements in samples were confirmed by X-ray photoelectron spectroscopy (XPS), Energy dispersive analysis of X-ray (EDX) and elemental mapping in STEM. Subsequently, the ER characteristics of the composites dispersed in insulating oil were characterized by a rotational rheometer. The electric field-stimulated rheological performances (yield stress, viscosity, modulus, etc.) were observed under an external electric field, which is different from the Newtonian state in the free electric field.

One-step preparation and characterization of core-shell SiO2/Ag composite spheres by pulse plating

Abstract A simple method of one-step pulse plating was used in the fabrication of core-shell SiO2/Ag composite spheres. Structural characteristics and morphologies of the prepared SiO2/Ag composite spheres are characterized by means of X-ray diffraction, scanning electron microscope, and transmission electron microscopy. The Ag shell is uniformly coated on the surface of SiO2 spheres with the thickness of about 20 nm. Photoluminescence (PL) spectrum has revealed that PL of the core-shell samples is much stronger than that of bare SiO2 spheres. Raman spectrometer measurements show that the SiO2/Ag composite spheres have excellent surface-enhanced Raman scattering performance. In addition, the current-voltage characteristic of SiO2/Ag composite spheres has improved at the same time.

Large Scale Synthesis of Highly Stable Fluorescent Carbon Dots Using Silica Spheres as Carriers for Targeted Bioimaging of Cancer Cells

In this paper, fluorescent carbon dots (CDs) loaded on silica (SiO2) spheres are synthesized by the one‐pot hydrothermal route, and then folic acids (FA) are covalently conjugated on the surface of SiO2 spheres. The formed SiO2@CDs‐FA composites can target specific tissues, e.g., cancer. The key of this method is the employment of (3‐aminopropyl)trimethoxysilane as bridge joint, which not only serves as surface passivation agents allowing the large scale synthesis of CDs with high quantum yield, but also enables SiO2@CDs composites further covalent conjugation of FA. The resultant SiO2@CDs composites have many advantages such as easy separation and purification, highly stable, well water‐soluble, and biocompatible. Moreover, the SiO2@CDs‐FA could be used as fluorescent probes for biological imaging in vitro. The uptake of the SiO2@CDs‐FA into HeLa cells is receptor‐mediated endocytosis, which is confirmed by a comparative study using FR‐negative 293T cells. Findings from this study suggest that the SiO2@CDs‐FA composites could be used as a platform for cancer diagnosis studies in various biological systems.

Controlled growth of Ag nanoparticles decorated onto the surface of SiO2 spheres: a nanohybrid system with combined SERS and catalytic properties

A versatile water-method for the controlled growth of Ag nanoparticles deposited onto the surface of SiO2 spheres is developed. The nanohybrid systems exhibited exceptional SERS and catalytic properties.

Metal Fe3+ ions assisted synthesis of highly monodisperse Ag/SiO2 nanohybrids and their antibacterial activity

Highly monodispersed Ag/SiO2 nanohybrids with excellent antibacterial property were synthesized by using DMF as a reducing agent and employing an additional redox potential of metal Fe3+ ion as a catalytic agent. The obtained Ag/SiO2-2 nanohybrids of about 240nm were highly monodispersity and uniformity by adding trace Fe3+ ions into the reaction which Ag+ reacted with N,N-dimethyl formamide (DMF) at 70°C. Compared to the conventional techniques, which need long time and high temperature for silica coating of Ag nanoparticles, this new method was capable of synthesizing monodispersed, uniform, high yield Ag/SiO2 nanohybrids. The electron was transferred from the Fe2+ ion to the Ag+ ion to accelerate the nucleation of silver nanoparticles. The chemical structures, morphologies and properties of the Ag/SiO2 nanohybrids were characterized by X-ray diffraction (XRD), (High-resolution, Scanning transmission) transmission electron microscopy (TEM, HRTEM and STEM), and X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy (UV–vis) and test of antibacterial. The results demonstrated that the silver nanoparticles supported on the surface of SiO2 spheres in Ag/SiO2-2 nanohybrids structure, the Ag nanoparticles were homogeneous and monodispersed. The results also indicated that the Ag/SiO2-2 nanohybrid had excellent antibacterial.

Preparation and characterization of Au–ZrO2–SiO2 nanocomposite spheres and their application in enrichment and detection of organophosphorus agents

Au–ZrO2–SiO2 nanocomposite spheres were synthesized and used as selective sorbents for the solid-phase extraction (SPE) of organophosphorous agents. A non-enzymatic electrochemical sensor based on a Au–ZrO2–SiO2 modified electrode was developed for the selective detection of organophosphorous pesticides (OPs). The Au–ZrO2–SiO2 nanocomposite spheres were synthesized by the hydrolysis and condensation of zirconium n-butoxide (TBOZ) on the surface of SiO2 spheres and then the introduction of gold nanoparticles on the surface. Transmission electron microscopy and X-ray photoelectron spectroscopy were performed to characterize the formation of the nanocomposite spheres. Fast extraction of OP was achieved by the Au–ZrO2–SiO2 modified electrode within 5 min via the specific affinity between zirconia and the phosphoric group. The assay yields a broad concentration range of paraoxon-ethyl from 1.0 to 500 ng mL−1 with a detection limit of 0.5 ng mL−1. This selective and sensitive method holds great promise for the enrichment and detection of OPs.

Fabrication and performance of nanoporous TiO2/SnO2 electrodes with a half hollow sphere structure for dye sensitized solar cells

The incorporation of nano-crystalline semiconductors with novel kinds of ordered microstructure is a very important area of research in the field of dye sensitized solar cells. A sol–gel method involving hydrolysis of titanium isopropoxide was used to form TiO2 nanoparticles on the surface of SiO2 spheres. In this process, 1, 5, or 10 wt% of SnCl2.2H2O was added to the sol–gel solution. To prepare TiO2/SnO2 nanoparticles with a half hollow sphere structure, SiO2 was removed with NaOH solution. The crystal phase, crystal shape, and surface properties of the metal oxide nanocrystals were studied by x-ray diffraction and scanning electron microscopy. The photovoltaic performance of the TiO2/SnO2 nanoparticles with half hollow sphere structures was measured. The dye sensitized solar cell using nanoporous TiO2 as electrode materials exhibits an overall conversion efficiency of 7.36% with a light intensity of 100 mW/cm2. The short circuit photocurrent (Isc), open circuit photovoltage (Voc), and conversion efficiency (η) of these solar cells were improved over conventional materials.

Amphibious polymer-functionalized CdTe quantum dots: Synthesis, thermo-responsive self-assembly, and photoluminescent properties

A straightforward strategy is presented to functionalize aqueous-phase synthesized CdTe quantum dots (QDs) with thermo-sensitive poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) via direct surface-initiated oxyanionic vinyl polymerization. The polymer grafting quantity can be facilely controlled in a wide range up to 95.2wt% by adjusting the weight feed ratio of monomer to pristine QDs. The polymer-grafted QDs still retain good fluorescence properties in solution, solid polymer matrix, and on surfaces of silica (SiO2) sphere. The resulting QD@PDMAEMAs show excellent solubility both in water and organic solvents (e.g., chloroform, dichloromethane, dioxane, ethyl acetate, acetone, methanol, and N, N-dimethylformamide). We have called them amphibious QDs. The thermo-sensitive PDMAEMAs make QDs accessible to self-assemble reversibly by adjusting temperature when the grafted polymer content is over a certain value. The self-assembly process and resulting structure were demonstrated by TEM, variable temperature dynamic light scattering (DLS) and UV-vis spectrometer. Because PDMAEMA is a kind of positive polyelectrolyte, QD@PDMAEMAs were used as building blocks in the layer-by-layer self-assembly process on the surface of SiO2 spheres, affording fluorescent SiO2 spheres.

Facile preparation of anatase/SiO2 spherical nanocomposites and their application in self-cleaning textiles

Anatase TiO2/SiO2 nanocomposites were prepared by a sol–gel process at a low temperature. The structural properties of these as-prepared nanocomposites were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD), showing that TiO2 nanoparticles were deposited on the surface of SiO2 spheres. The spherical TiO2/SiO2 nanocomposites were coated onto cotton fabrics by a simple dip-pad–dry-cure process. The treated cotton fabrics demonstrated higher photocatalytic activity in comparison to pure TiO2 treated cotton fabrics in a typical photocatalytic test using a model compound of Neolan Blue 2G dye. Our results demonstrate that this composite material is a step towards better self-cleaning performance of textile materials.

Preparation of movable 3D periodic structures of silica spheres

Monodispersed silica spheres were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of water and ammonia in ethanol medium. The net negative charge on the surface of SiO2 spheres was enhanced after ageing silica spheres under suitable condition. Thus, a novel viscous liquid composed of mono-dispersed silica spheres was obtained. Due to the ex- isting net repulsive forces between particles, the viscous liquid can quickly form a movable 3D periodic ordered structure with vivid color, indicating a high degree of ordering of the particles.

Preparation of uniform CdSe/polyelectrolyte multilayers on the surface ofSiO2 spheres

CdSe/PE2 (PE means polyelectrolyte) multilayers have been successfully synthesized on the surface ofSiO2 spheres by using a layer-by-layer technique. The layer structure can be distinguished clearlyand the layer thickness can be tailored easily.