SiO2 Hollow Spheres Research Articles

Highly dispersed spherical phosphors obtained by encapsulating silica hollow spheres with SnO2: Eu3+ layers for enhancing red light emission

Orange light (593 nm, 5D0→7F1) and red light (613 nm, 5D0→7F2) are the two most important emission lines belonging to Eu3+ ions in high and low symmetries, respectively, making them important indicators for judging the nanoenvironment around Eu3+ ions. Therefore, obtaining significant red light emission in Eu3+ doped SnO2 nanocrystals requires anchoring Eu3+ ions onto lattice sites with low symmetries, which can be achieved through maximizing surface doping. To achieve this goal, we coated very thin Eu3+ doped SnO2 nanocrystal (10–20 nm) coatings on extremely dispersed SiO2 hollow spheres (500 nm in diameter) to investigate doping dependent luminescent properties. A significant increase in red emission was observed in such a system, accompanied by a significant attenuation of orange light, and the intensity of red emission increases with increasing Eu3+ concentration. When the concentration of Eu3+ exceeds 3 at%, the intensity of red light emission sharply decreases due to the quenching effect. For the optimal doped hollow sphere sample (3 at%), the asymmetry ratio (red/orange light integration intensity ratio) under indirect excitation is 5.58, which further rises to 11.3 under direct excitation, while the asymmetry ratio of SnO2 nanopowder with the same doping concentration is less than 0.2 under both excitation modes, indicating that the current structural design plays a significant role in the modulation of Eu3+ ion luminescence. Our research not only demonstrates an effective method to enhance the red light emission of Eu3+ doped SnO2 nanocrystals, but also provides a method for manipulating the polychromatic luminescence of such systems.

Highly selective adsorption and biodegradation of emulsified oil by microorganisms embedded in SiO2 hollow sphere bioreactor

Highly efficient elimination and disposal of oils and organic contaminants from water is of great importance for the sustainable development of modern society. In this work, micron-sized “single pore” silica hollow spheres (SHMs) bioreactors were prepared using (W/O/W) ternary-phase microemulsion, and the size of pores was adjusted to the concept of “single-pore” composite microorganism bioreactor, preparation of single-pore silica hollow spheres with an average pore size of 8.572 μm, which enables the SHMs bioreactors to load microorganisms for oils biodegradation. The outer layer was sprayed with a layer of silica nanoparticles with a diameter of 500 nm produced by silane hydrolysis, which encapsulated the inner “single-pore” SHMs to form a core–shell structure (M/Microbe@SHMs). This micro-nano core–shell structure exhibits superhydrophobicity and superlipophilicity, which gives it excellent selective adsorption capacity. Interestingly, M/Microbe@SHMs have excellent emulsion-breaking effects in oil–water separation. In addition to the simultaneous oil/water separation ability, the adsorbed oil and grease can be subsequently degraded to CO2 and H2O by microorganisms' action in the inner layer of M/Microbe@SHMs. Based on this excellent selective adsorption and oil/water separation capacity, while one-step in-situ biodegradation, our microbial bioreactor may have a potential for a wide range of practical applications in wastewater treatment.

Ablation properties of SiC-reinforced PBI resin matrix composites under high-energy continuous laser ablation

In this work, poly-p-phenylene benzobisoxazole (PBO) fibers reinforced polybenzimidazole (PBI) resin-based laser ablation composites (thickness = 5 mm) with different SiC contents were prepared. SiC/PBI/PBO composites exhibited good mechanical properties, excellent thermal stability and laser ablation properties. The laser ablation properties and ablation mechanism of the composites were investigated using a high-energy continuous-wave laser (30 MW·m−2). Increasing the SiC content led to increase in composites density, while decreasing the bending performance of the composites. However, it improves the mass and linear ablation rates, resulting in an overall improvement in ablation properties. At a SiC content of 70 %, the composite exhibited a mass loss of 8.2 %, a mass ablation rate of 9.2 mg·s−1, and a linear ablation rate of 0.11 mm·s−1. The ablation process of SiC/PBI/PBO composites was delineated into pre-ablation and post-ablation stages, with the ablated composites divided into the ablation center, transition region, and outer region based on morphological characteristics. After ablation, numerous white hollow SiO2 spheres and SiO2 protective layers were formed in the ablation centers, the transition regions were deformed and cracked, while the outer region remained unscathed.

Embedment of hollow SiO2 spheres into flower-like Ti3C2Tx MXene framework with decoration of carbon for efficient microwave absorption

With the advancement of modern microwave communication technologies, the development of lightweight absorption materials with high capacity and a wide absorption bandwidth has aroused great interest. Despite its low density, strong temperature resistance, high strength, and great electromagnetic energy storage capacity, SiO2 still has a long way to go in terms of efficiently dissipating microwaves due to its low polarization loss and conductive loss. Herein, the 3D sandwich-like M-Ti3C2Tx @SiO2 @C hybrids are synthesized by inserting SiO2 hollow spheres into the flower-like Ti3C2Tx MXene framework and decorating with carbon. SiO2 hollow spheres securely attached on monolayer Ti3C2Tx MXene nanosheets provide large electromagnetic energy storage capacity as well as additional interfacial polarization. The 3D flower-like Ti3C2Tx MXene framework and carbon coating ensure high conductive loss. The 3D sandwich-like M-Ti3C2Tx @SiO2 @C hybrids shows excellent microwave absorption performance. Under 40 wt% filler loadings, the 3D sandwich-like M-Ti3C2Tx @SiO2 @C hybrids deliver minimum reflection loss of − 43.97 dB at 4.5 mm thickness. At 1.5 mm thickness, their effective absorption band expands to 4.12 GHz. The facile and scalable synthesis strategy offers a novel design concept for the commercialization of high-performance microwave absorbers.

Hybrid emitters with raspberry-like hollow SiO2 spheres for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) has been vigorously investigated in recent years because it does not require electrical energy, reducing greenhouse gas emissions for a more sustainable society. Representative approaches to improve radiative cooling performance are the design of metamaterials with a long-wave infrared (LWIR) emissivity and porous polymer structures with a high-solar reflectivity. Furthermore, coating materials for a simple process should be researched to improve the applicability of radiative cooling. In this study, we investigate a daytime radiative cooling coating using raspberry-like hollow SiO2 spheres (RHSs) to achieve effective radiative cooling performance and a simple coating process. The raspberry-like morphologies of the synthesized hollow SiO2 spheres contribute to multiple scattering of sunlight, resulting in enhanced performance of the radiative cooling coating. Moreover, the results of an outdoor experiment and energy-saving demonstration suggest that the RHS coating is suitable for effective heat management of the buildings. The RHS coating achieves a cooling temperature of 9.7 °C under solar irradiance of 800 W m−2. The inner temperature of a house coated with PDRC is 6.6 °C lower than that of a bare house under direct sunlight.

Revealing bulk reaction kinetics of battery-like electrode for pseudocapacitor with ultra-high rate performance

Battery-like electrode materials have a high theoretical capacity but suffer from low electrical conductivity and poor structural stability, which are expected to be solved by revealing bulk reaction kinetics of crystal structure to improve the electrochemical performance. Herein, we grow NiCo-LDH single-crystal nanowires along the [003] crystal plane on the surface of amorphous SiO2 hollow spheres. This heterostructured architecture provides a synergistic effect among different components and enlarges the interlayer spacing of the grown NiCo-LDH single-crystal, offering more reactive sites and improving electrical conductivity. The prepared NiCo-LDH@SiO2/C electrode demonstrates ultra-high rate capability with 78.1 % capacitance retention even after a 40-fold increase in the current density. The asymmetric supercapacitors with NiCo-LDH@SiO2/C cathode and active carbon anode could deliver a maximum energy density of 47.6 Wh/g at 1383 W/kg. This work presents a new method to guide the design of NiCo-LDH electrode materials and opens up a new opportunity to develop high-performance battery-type electrode materials for pseudocapacitors.

High specific capacity of carbon coating lemon-like SiO2 hollow spheres for lithium-ion batteries

Hollow structure is a kind of special structure that can effectively relieve the volume expansion of anode material, but the large space in hollow structure also sacrifices the specific capacity of the material to some extent. In this paper, lemon-like hollow SiO2 spheres were prepared by soft template method as anode material for lithium-ion batteries. The advantages of the anode material are: (1) There is a certain space inside the hollow sphere to relieve the volume expansion, which can improve the cyclic stability of the material; (2) There are many SiO2/SiOx nanoparticles wrapped inside the hollow sphere, which can improve the specific capacity of the material in the cycle; (3) There is a certain gap between the SiO2/SiOx nanoparticles inside the hollow sphere. This provides a channel for the migration of Li+ in the cycle, which is conducive to the migration of Li+ and improves the rate performance of lithium-ion battery. (4) The lemon-like hollow SiO2 spheres can be prepared by one-step method, and the preparation process is simple. The discharge mass specific capacity of composite materials is 786 mA h g−1 at current density of 1.0 A g−1 after 500 cycles. The discharge specific capacity at current densities of 0.2, 0.5, 1.0, 2.0 and 5.0 A g−1 are 900, 854, 787, 681, 492 mA h g−1, respectively. The composite materials show certain potential as anode materials for high performance lithium-ion batteries.

Design of Co3O4@SiO2 Nanorattles for Catalytic Toluene Combustion Based on Bottom-Up Strategy Involving Spherical Poly(styrene-co-acrylic Acid) Template

Bearing in mind the need to develop optimal transition metal oxide-based catalysts for the combustion of volatile organic compounds (VOCs), yolk-shell materials were proposed. The constructed composites contained catalytically active Co3O4 nanoparticles, protected against aggregation and highly dispersed in a shell made of porous SiO2, forming a specific type of nanoreactor. The bottom-up synthesis started with obtaining spherical poly(styrene-co-acrylic acid) copolymer (PS30) cores, which were then covered with the SiO2 layer. The Co3O4 active phase was deposited by impregnation using the PS30@SiO2 composite as well as hollow SiO2 spheres with the removed copolymer core. Structure (XRD), morphology (SEM), chemical composition (XRF), state of the active phase (UV-Vis-DR and XPS) and reducibility (H2-TPR) of the obtained catalysts were studied. It was proven that the introduction of Co3O4 nanoparticles into the empty SiO2 spheres resulted in their loose distribution, which facilitated the access of reagents to active sites and, on the other hand, promoted the involvement of lattice oxygen in the catalytic process. As a result, the catalysts obtained in this way showed a very high activity in the combustion of toluene, which significantly exceeded that achieved over a standard silica gel supported Co3O4 catalyst.

Bimetallic Ag/Cu supported hollow SiO2 sphere drives the efficient hydrogenation of nitroarenes

Constructing a low-cost and efficient catalyst is of high importance toward the hydrogenation of nitroarenes. In this work, we design an Ag/Cu bimetallic catalyst by supporting Ag/Cu nanoparticles on the surface of hollow SiO2 sphere (HS–Ag/Cu), in which SiO2 acts as a support to disperse silver and copper nanoparticles due to its hydrophilic surface and chemical inertness, making it easier to decrease the aggregation of metal nanoparticles. Notably, the hollow/porous structure of SiO2 considerably drives the diffusion of reactants/products by decreasing diffusion limitation, leading to an enhanced catalytic activity toward the hydrogenation of nitroarenes than monometallic catalyst. Furthermore, corresponding aniline is almost quantitatively produced, indicating a significantly practical potential.

High photocatalytic activity of Cu2O embedded in hierarchically hollow SiO2 for efficient chemoselective hydrogenation of nitroarenes

Photocatalytic organic conversion is a crucial process in the hydrogenation of nitroarenes, but harsh reaction conditions such as long reaction time, high hydrogen pressure, and organic medium still need to be considerably overcome under visible-light irradiation. Here, we have constructed a transition metal oxide photocatalyst by embedding low-cost Cu2O with strong visible-light absorption into hierarchically hollow SiO2 sphere (SiO2-Cu2O@SiO2) that can suppress the escape of photogenerated atomic hydrogen and promote the contact probability between hydrogen atom and nitroarene molecules due to confinement effect. Remarkably, the SiO2-Cu2O@SiO2 photocatalyst can exhibit efficient chemoselectivity toward the hydrogenation of various nitroarenes in an aqueous system at ambient conditions, successfully working out the requirement of strict hydrogenation conditions, especially for organic medium over almost all of the reported photocatalysts. Notably, quantitative aniline can be produced for the visible-light catalytic reduction of nitroarenes, suggesting a considerable potential for industrial applications.

Designing Re-Entrant Geometry: Construction of a Superamphiphobic Surface with Large-Sized Particles.

Re-entrant geometries can effectively trap air pockets beneath coating surfaces, prevent the penetration of low surface tension organic liquids, and achieve superamphiphobic performance. However, the creation of re-entrant geometries through particle-based spray coating remains a challenge. In the past decade, various studies have focused on the preparation of superamphiphobic coatings using ultrafine nanoparticles (10-15 nm) using conventional spray-coating methods. In this work, we aim to fabricate a spray-coated superamphiphobic surface using large particles with a hierarchical structure. The study systematically investigated the wetting behaviors of liquids with different topographies obtained using large particles (i.e., smooth, micro, nano, and micro/nanostructures) by different coating methods. The findings suggested that compared with the typical colloid template method, the surface obtained using the spray-coating method showed much greater roughness, which greatly enhanced the oleophobicity of the coating. Furthermore, only hierarchically monodisperse hollow SiO2 spheres (MDH-SiO2) showed excellent superamphiphobicity, which was independent of the hollow sphere size. While maintaining the coating roughness, by applying solid C@SiO2 as a reference sample, the important role of the hollow structure of MDH-SiO2 at the solid-liquid-air interface was confirmed. Nanosphere-surrounded hollow structures were shown to serve as a re-entrant type structure, preventing the imbibition of the liquid, finally leading to a stable Cassie state. This design strategy may provide useful guidelines for the fabrication of large particle-based spray-coated superamphiphobic surfaces.

FeS2/SiO2 mesoporous hollow spheres formation and catalytic properties in the Fenton reaction

Transition metal sulfides (TMSs) show excellent catalytic activity in the Fenton reaction. However, the metal ion in TMSs always leached in solution during the reaction, which induced the second pollution. At present, mesoporous hollow spherical FeS2/SiO2 composite was synthesized, which the FeS2 particles were deposited at the inner wall of SiO2 hollow spheres. The composite exhibited higher adsorption capacity and catalytic activity for rhodamine B (RhB) degradation in the Fenton reaction than FeS2. The Fe ionic concentration leashed from the composite is smaller about 24-fold than the FeS2. This method provides a possible solution for the stable TMSs formation as catalysts in the Fenton reaction.

Core–Shell Encapsulation of Salt Hydrates into Mesoporous Silica Shells for Thermochemical Energy Storage

The advent of thermochemical energy storage (TcES), that is, storage of thermal energy by means of reversible chemical reactions, incites finding pathways of stabilization of thermochemical materials for thermal batteries of the future. Currently, hydrates such as LiCl·H2O, CaCl2·6H2O, and SrBr2·6H2O are being actively studied for TcES in buildings due to both high energy storage density (1-2.5 GJ/m3) and high storage duration. In this work, we report the core-shell composites salt in hollow SiO2 spheres with mesopores(salt = LiCl·H2O, CaCl2·6H2O, SrBr2·6H2O) for domestic TcES. The hydrates were encapsulated into submicrometer-sized hollow SiO2 (HS) capsules as confirmed by transmission electron microscopy (TEM) and N2 sorption analyses. High sorption/desorption rates due to mesopores of the shells were shown by thermogravimetric analysis (TGA). The sorption equilibrium for salt@HS was reported, and the applicability of the materials for domestic heat batteries was analyzed. As a result of almost the densest packing of salt@HS, the composites were shown to provide a state-of-the-art energy storage density up to 0.86 GJ/m3 on the bed level for the high-temperature lift of 32-47 °C, showing high energy storage capacity. The stability in at least 50 charging/discharging cycles was confirmed by TGA and TEM.

Hierarchical Flower-Like Hollow SiO2@TiO2 Spheres with Enhanced Thermal Insulation and Ultraviolet Resistance Performances for Building Coating.

In this paper, a novel 3D hierarchical flower-like hollow SiO2@TiO2 sphere (FHST) with a large number of irregular nanosheets was successfully prepared by a solvothermal method and subsequent calcination process, in which multiple different functional components were perfectly integrated into a single nanostructure. The morphology and structure of FHSTs were characterized by SEM, TEM, XRD, XPS, and BET. The growth mechanism of the 3D flower-like structure was obtained through a series of single-factor experiments, of which hexamethylenetetramine acted in a vital role. Moreover, it was also used as a filler for polyacrylate substrate to improve the thermal insulation and ultraviolet resistance properties of architectural coatings. The results showed that the composite film with FHSTs had lower thermal conductivity and higher light reflection performance compared to those with hollow SiO2 spheres, hollow TiO2 spheres, and hollow SiO2@TiO2 spheres. More significantly, its transmittance at the full wavelength of ultraviolet light was almost zero, exhibiting a prominent inhibitory effect on UVA. In addition, compared with commercially available hollow glass microspheres, FHSTs had more excellent thermal insulation performance in practical applications.

Formation of octahedron-shaped ZnFe2O4/SiO2 with yolk–shell structure

In this study, octahedron-shaped ZnFe2O4/SiO2 was fabricated using a facile solvothermal method by adding hollow SiO2 spheres to the reaction system. The experimental results indicated that the octahedron-shaped ZnFe2O4/SiO2 with a yolk–shell structure was only synthesized at a high heating rate (2.0 °C/min). A sample fabricated at a low heating rate (0.25 °C/min) did not form a yolk–shell structure. Calorimetry was conducted to investigate the mechanism associated with the formation of the yolk–shell structure. Several intermediates were obtained based on the as-measured calorimetric curve, which were characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, Fourier transform-infrared spectroscopy, and X-ray photoelectron spectroscopy. The results indicated that Fe3+ and Zn2+ first entered the hollow core of the SiO2 spheres through the mesoporous shell, before α-(Fe,Zn)OOH and α-Fe2O3 were formed in the core and outer surfaces of the hollow SiO2 spheres at a heating rate of 2.0 °C/min α-Fe2O3 had an octahedral shape. Finally, α-Fe2O3 was converted into the octahedron-shaped ZnFe2O4. The hollow SiO2 spheres were simultaneously changed into nanosheets, which induced the formation of the yolk–shell structure.

Super-low thermal conductivity fibrous nanocomposite membrane of hollow silica/polyacrylonitrile

Global warming aggravates mainly due to human activities, such as the massive use of fossil energy and excessive deforestation. Thus, reducing energy waste becomes has gained more importance. Thermal insulation materials with superlow thermal conductivity show notable potential in energy saving. Herein, an adiabatic hollow silica/polyacrylonitrile (SiO2-PAN) fibrous nanocomposite membrane was prepared via electrospinning. Hollow SiO2 spheres were prepared by using tetraethyl orthosilicate as a silica source and hydrothermal carbon spheres as the template. The thermal insulation property of PAN fibrous nanocomposite membrane can be enhanced by appending hollow SiO2 spheres. The solid conduction of the fibrous nanocomposite membrane was reduced by the addition of hollow SiO2 spheres. The composite fibrous nanocomposite membrane is flexible and achieves an optimal thermal conductivity of 16 mW/(m·K). The fibrous nanocomposite membrane can maintain its thermal insulation property and becomes hydrophobic after treatment with silicone oil. The developed membrane provides a new idea for the future development of thermal insulation materials.

Hollow spherical SiO2 micro-container encapsulation of LiCl for high-performance simultaneous heat reallocation and seawater desalination

Micro hollow SiO2 spheres with LiCl encapsulated inside for high-performance simultaneous heat reallocation and seawater desalination.

Catalysis of silica-based anode (de-)lithiation: compositional design within a hollow structure for accelerated conversion reaction kinetics

New hierarchical hollow SiO2 spheres decorated with metal nanoparticles were designed by using an in situ self-assembly approach for lithium-ion battery applications.

Preparation of corundum-mullite refractories with lightweight, high strength and high thermal shock resistance

The influences of PMMA sphere, hollow SiO2 sphere, hollow corundum sphere and AlF3·3H2O on properties of corundum-mullite refractories have been investigated. The finite-element analysis was used to simulate thermal stress of the samples in the process of thermal shock. The PMMA, hollow SiO2 and hollow corundum were used to form different pore structures. The AlF3·3H2O was used as a reaction medium to promote the mullite whiskers formation. F2 was formed by oxidation reaction between AlF3 and O2 which could react with edges of fused mullite aggregate besides corundum and silica. SEM results showed that much mullite whiskers formed in the contact area of matrix powder and fused mullite aggregate. Bridging mullite whiskers of in-situ formation between matrix and aggregates strongly improved strength performance and thermal shock resistance of corundum-mullite materials. The closed pores from hollow corundum sphere were beneficial to thermal shock resistance. The high open porosity after PMMA burning out is adverse to in-situ formation of mullite whisker. Hollow corundum sphere, AlF3·3H2O and suitable grain composition worked together providing corundum-mullite refractories of lightweight, high strength and high thermal shock resistance.

Octahedral yolk-shell-structured ZnFe2O4/SiO2 formation and Fenton performance

Octahedron-shaped ZnFe2O4 was fabricated through a facile process, where the ZnFe2O4 showed yolk-shell-structured. Hollow mesoporous SiO2 spheres were used as template in the process. The SiO2 spheres changed to nanosheets assembled at the surface of the as-formed octahedron-shaped ZnFe2O4. The ZnFe2O4/SiO2 composite exhibits higher surface area (154.03[Formula: see text]m2/g) than those reported. The composite showed excellent catalytic activity in Fenton and photo-Fenton processes, for which the rate constants reached 0.034 and 0.063[Formula: see text][Formula: see text], respectively. And the composite exhibited stable catalytic activity for three cycles. These results demonstrate that the composite shows potential applications in environmental treatment.