Hollow SiO2 Research Articles

Preparation of Hollow SiO₂@BiOI Nanocomposites and Their Photocatalytic Performance in Ammonia Nitrogen Degradation.

Hollow SiO₂ microsphere-supported bismuth oxyiodide (BiOI) nanocomposites were prepared using Bi(NO₃)₃ · 5H₂O and KI as the precursors of BiOI at 80 °C in an aqueous solution by the liquid chemical deposition method. The BiOI nanosheets with the thicknesses of 25-40 nm and the widths of 1-2 μm were deposited on the hollow SiO₂ microsphere surfaces. There were interactions between the BiOI nanosheets and hollow SiO₂ microspheres, which enlarged the ban gap of the BiOI nanosheet as compared with the pure BiOI. The band gap energy increased with the increase in SiO₂/BiOI weight ratios. The hollow SiO₂@BiOI nanocomposites showed high photocatalytic activity in ammonia nitrogen degradation when the photocatalytic degradation reaction was performed in aqueous solution under visible light irradiation. The degradation extent of ammonia nitrogen was upto 81% when the ammonia nitrogen degradation reaction was photocatalyzed by the hollow SiO₂@BiOI(100:10) nanocomposite at an initial concentration of ammonia nitrogen of 10 mg L-1 and 25 °C for 4 h. The reaction kinetics of ammonia nitrogen degradation was well simulated by the first-order reaction model.

Molecular dynamics simulations of stability and fluidity of porous liquids

Due to the limitation of experimental methods at the atomic level, research on the stability and fluidity of porous liquid was quite rare. Porous liquids composed of hollow SiO2 molecules, which were functionalized with polymer chains containing corona and canopy to make them liquid at accessible temperatures, were quite different from pure SiO2 nanoparticles or SiO2 nanofluids. In order to study the kinetic process and the microscopic mechanism of porous liquid more clearly, distance between nanoparticle surfaces, interface interaction energy, hydrogen bond, entanglement depth and steric effect were studied here. Simulation results demonstrated that hollow SiO2 nanoparticles were easy to aggregate without solvents. Addition of water could delay the aggregation of nanoparticles, but it was not enough to form stable porous liquid. Polymer chains of porous liquid increased the interface distance, which could disperse the nanoparticles and have better stability.

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.

Reflectivity of solid and hollow microsphere composites and the effects of uniform and varying diameters

While solid and hollow microsphere composites have received significant attention as solar reflectors or selective emitters, the driving mechanisms for their optical properties remain relatively unclear. Here, we study the solar reflectivity in the 0.4–2.4 μm wavelength range of solid and hollow microspheres with the diameter varying from 0.125 μm to 8 μm. SiO2 and TiO2 are considered as low- and high-refractive-index microsphere materials, respectively, and polydimethylsiloxane is considered as a polymer matrix. Based on the Mie theory and finite-difference time-domain simulations, our analysis shows that hollow microspheres with a thinner shell are more effective in scattering the light, compared to solid microspheres, and lead to a higher solar reflectivity. The high scattering efficiency, owing to the refractive-index contrast and large interface density, in hollow microspheres allows low-refractive-index materials to have a high solar reflectivity. When the diameter is uniform, 0.75 μm SiO2 hollow microspheres provide the largest solar reflectivity of 0.81. When the diameter is varying, the randomly distributed 0.5–1 μm SiO2 hollow microspheres provide the largest solar reflectivity of 0.84. The effect of varying diameter is characterized by strong backscattering in the electric field. These findings will guide optimal designs of microsphere composites and hierarchical materials for optical and thermal management systems.

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.

The role of electro-sprayed silica-coated zinc oxide nanoparticles to hollow silica nanoparticles for optical devices material and their characterization

Studies of the synthesis of composite zinc oxide-silica (ZnO@SiO2) particles remain a great challenge in terms of obtaining a more precise design and suppress the agglomeration of pure ZnO. However, recent methods encounter problems in production, such as time consumption, multistep processes, and agglomeration of the final product. To this end, a one-step process for the production of composite ZnO@SiO2 particles which has good potential as UV-attenuating materials was proposed via the electrospray method for the first time. The results from this study offer, for the first time, new insights into the design of ZnO@SiO2 as a core-shell particles morphology in which ZnO was coated with SiO2 by using the electrospray method with good control of particle agglomeration. A possible core-shell formation mechanism is proposed to offer an in-depth understanding. When tested as ultraviolet (UV) attenuation materials, the obtained core-shell particles exhibited an activation transmission near 30 % in the wavelength range of 280−400 nm under UV A and B light. This activation transmission is better than that of the same composite without a core-shell structure. Another particle with different characteristics (e.g., hollow SiO2) was obtained after the removal of ZnO from the core-shell composite structure. The activation transmission of hollow silica reached approximately 80 % under UV–vis light, indicating that hollow SiO2 has potential applications in future transparent devices.

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.

3D printing of porous SiC ceramics added with SiO2 hollow microspheres

Porous SiC ceramics were fabricated by 3D printing through selective laser sintering (SLS) and adding hollow spheres (AHS). The process was based on the mullitization of Al2O3 and kaolin, and the SiC particles were bonded by the mullite and melted SiO2. The pores were produced by the stacking of SiC particles, debonding of epoxy, and adding of SiO2 hollow microspheres. The phase composition, microstructure, porosity, and flexural strength of the porous SiC ceramics with and without SiO2 hollow microspheres were compared. Additionally, the effect of the sintering temperature, size, and mass fraction of the SiO2 hollow microspheres on the porous SiC ceramics was investigated. After the addition of the SiO2 hollow microspheres, an open porosity of 62.51% and flexural strength of 40.93 MPa were obtained for the porous SiC ceramics. Using the results, three types of hierarchically porous SiC structures with porosities ranging from 92–97% were manufactured by SLS combined with AHS.

Preparation and tribological properties of solid-liquid synergetic self-lubricating PTFE/SiO2/PAO6 composites

Herein, 25 kinds of polytetrafluoroethylene (PTFE) composites with solid-liquid synergetic self-lubricating property were prepared by filling PTFE matrix with hollow SiO2 particles and lubricating oil (PAO6). Hollow SiO2 particles containing PAO6 acting as lubricating fillers were applied to enhance the tribological performances of PTFE matrix. The generated PTFE composites displayed solid-liquid synergetic self-lubricating property and could achieve ultralow friction. Factors such as the cold-pressed pressure and the SiO2 content that affect the tribological performance of the composites were investigated in detail. The compactness of the composites was enhanced when the cold-pressed pressure increased. The porosity of the composite with 25 wt% SiO2 decreased from 38.2% to 14.3% when the cold-pressed pressure was increased from 10 MPa to 50 MPa. As the cold-pressed pressure was increased, the antiwear performance of the composites was enhanced but their antifriction performance become worse. The composites containing PAO6 achieved lower coefficient of friction (COF) and smaller wear rates than composites without PAO6. The COF value decreased from 0.143 (pure PTFE) to an ultralow value of 0.037 (composite 5%-10 MPa-oil). The enhanced antifriction performance of the composite was associated with the synergistic lubricating effect of the liquid lubricant of PAO6 and the lubrication of the PTFE matrix. All the prepared PTFE/SiO2/PAO6 composites exhibited excellent antifriction performance and improved antiwear property and thus can be used to fabricate a new kind of self-lubricating materials.

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.

Template-assisted synthesis of LiNi0.8Co0.15Al0.05O2 hollow nanospheres as cathode material for lithium ion batteries

Based on hydrothermal synthesis and solid-phase thermal reaction, LiNi0.8Co0.15Al0.05O2 hollow nanospheres (LNCA HNSs) were synthesized by using SiO2 hollow nanospheres as hard template. Firstly, the SiO2 HNSs were prepared. Then, (Ni0.8Co0.15Al0.05)CO3 nanosheets grew on the surface of SiO2 HNSs to form SiO2@(Ni0.8Co0.15Al0.05)CO3 hollow nanospheres with double shells by hydrothermal method. Finally, the above precursors and lithium source were calcined at high temperature, and then SiO2 template was etched to obtain hollow LNCA HNSs. The characterization results showed that the LNCA HNSs are hollow spheres with a diameter of about 1.8 μm. The shell thickness of LNCA HNSs is about 300 nm. Compared with LNCA nanoparticles and LNCA microparticles, LNCA HNSs showed excellent stability, high capacity, and good rate performance as cathode materials for lithium ion batteries. The LNCA HNSs exhibited a reversible capacity of 202.4 mA h g−1 at 0.1 C and good stability of 179.1 mA h g−1 at 1 C after 80 cycles.

Dual-Mode of Fluorescence Turn-On and Wavelength-Shift for Methylamine Gas Sensing Based on Space-Confined Growth of Methylammonium Lead Tribromide Perovskite Nanocrystals.

The defect-tolerant nature of lead halide perovskites renders outstanding luminescence by simple space-confined growth in nanopores. The fluorescence turn-on and wavelength-shift phenomena could be found in the formation of methylammonium lead tribromide (MAPbBr3) nanocrystals in hollow SiO2 nanospheres triggered by the reaction between methylamine (MA) gas and HPbBr3/PbBr2@SiO2 nanospheres. The enhanced fluorescence intensity is linear with the MA concentration in the range of 1.0-95 ppm with a limit of detection (LOD) of 70 ppb (S/N = 3). In addition, the maximum emission wavelength is consistently red-shifted from 478.7 to 510.6 nm as the MA concentration increases from 1.0 to 95 ppm, imparting the potential for colorimetric sensing. By combining the fluorescence turn-on and colorimetric sensing modes, the flexible method meets the demands for visual discrimination and point-of-care determination with portable devices.

Preparation of monodisperse SiO2 nanorods with hollow structure and parameters affecting the length-diameter ratio

Monodisperse SiO2 nanorods with hollow structure were prepared using FeOOH as a template. Powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption isotherms were utilized to characterize the products. With a FeCl3 concentration of 0.1 M, the average length and width of the prepared hollow SiO2 nanorods were 397 nm and 116 nm, respectively, and the average length-diameter ratio was calculated as 3.4. The average size of the nanopores of the amorphous SiO2 shell were measured as 2.5 nm. Furthermore, increasing the concentration of Cl− ions improved length-diameter ratios of the FeOOH nanorod template and hollow SiO2 nanorods.

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 SiO2 microspheres with thiol-rich surfaces: The scalable templated fabrication and their application for toxic metal ions adsorption

In this study, the templated fabrication of hollow SiO2 microspheres with thiol-rich surfaces and their application as adsorbents for toxic metal ions were demonstrated. (Cyclohexane + TEOS)-in-water Pickering emulsion was first prepared employing detachable polyurethane-g-poly (N,N-dimethyl acrylamide) (PU-g-PDMA) copolymer micelles as emulsifiers. The subsequent Pickering emulsion interface directing sol-gel reaction of TEOS led to the formation of SiO2 microspheres. Hydrophobic PU cores of PU-g-PDMA copolymer emulsifier micelles were in-situ entrapped in the formed SiO2 layers, while hydrophilic PDMA shells were completely exposed on the surfaces of the SiO2 shells, forming polymer brush-like structure. The subsequent removal of PDMA shells through the cleavage of the reversible disulfide linkages between PU core and PDMA shells left a large number of thiol groups on the surfaces of hollow SiO2 microspheres. The resulting hollow SiO2 microspheres with thiol-rich surfaces, described as SiO2@SH in the text, demonstrated a promising recyclable adsorption for toxic metal ions. ~88% of adsorption capacity for Pb2+ has been maintained after four cycles of adsorption-desorption. The structure of hollow SiO2@SH microspheres was carefully characterized with scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy, respectively.

Design and Verification of a Deep Rock Corer with Retaining the In Situ Temperature

Deep rock is always under high‐temperature conditions. However, traditional coring methods generally have no thermal insulation design, which introduces large deviations in the guidance required for resource mining. Thus, a thermal insulation design that utilizes active and passive thermal insulation was proposed for deep rock corers. The rationale behind the active thermal insulation scheme was to maintain the in situ core temperature through electric heating that was controlled by using a proportional‐integral‐derivative (PID) chip. Graphene heating material could be used as a heating material for active thermal insulation through testing. In regard to the passive thermal insulation scheme, we conducted insulation and microscopic and insulation effectiveness tests for hollow glass microsphere (HGM) composites and SiO2 aerogels. Results showed that the #1 HGM composite (C1) had an excellent thermal insulation performance (3 mm thick C1 can insulate to 82.6°C), high reflectivity (90.02%), and wide applicability. Therefore, C1 could be used as a passive insulation material in deep rock corers. Moreover, a heat transfer model that considered multiple heat dissipation surfaces was established, which can provide theoretical guidance for engineering applications. Finally, a verification test of the integrated active and passive thermal insulation system (graphene heating material and C1) was carried out. Results showed that the insulating effect could be increased by 13.3%; thus, the feasibility of the integrated thermal insulation system was verified. The abovementioned design scheme and test results provide research basis and guidance for the development of thermally insulated deep rock coring equipment.

Polyoxometalates encapsulated into hollow double-shelled nanospheres as amphiphilic nanoreactors for an effective oxidative desulfurization.

Although some catalytic hollow nanoreactors have been fabricated in the past, the encapsulated active species focus on metal nanoparticles, and a method for polyoxometalate (POM)-containing hollow nanoreactors has seldom been developed. Herein, we report a synthetic strategy towards POM-based amphiphilic nanoreactors, where the hollow mesoporous double-shelled SiO2@C nanospheres were used to encapsulate Keggin-type H3PMo12O40 (PMo12). The outer hydrophobic carbon shell was beneficial for the enrichment of the organic substrate around the nanoreactor and simultaneously prevented the deposition of POMs on the outer surface of the nanoreactor. The inner hydrophilic silica cavity was modified by two types of organosilanes, which not only created an amphiphilic cavity environment but also acted as an anchor to mobilize PMo12. As the POM nanoreactor had the hydrophilic@hydrophobic SiO2@C shell and an amphiphilic cavity, both dibenzothiophene (DBT) and H2O2 could smoothly diffuse into the nanosized cavity, where the DBT was effectively oxidized (conversion: >99%) by the immobilized PMo12 under mild conditions. Importantly, the control experiments indicated that the confined effect of nanoreactor, amphiphilic SiO2@C double-shell, unique cavity environment, and mesoporous channels accounted for an excellent catalytic performance. Moreover, the nanoreactor was robust and could be reused for five cycles without loss of activity.

Reactive amphiphilic hollow SiO2 Janus nanoparticles for durable superhydrophobic coating.

Durable superhydrophobic coating is attractive due to its long-term superhydrophobicity, anti-fouling and self-cleaning properties. However, the fabrication of durable superhydrophobic coatings on a fragile surface, including leather and paper, is still a challenge due to its bad resistance to harsh environments such as high temperature, high pressure and strong acid or strong base. Herein, we developed a universal way to fabricate long-lasting superhydrophobic coating on leather via amphiphilic Janus particles, which have one of the semispheres functionalized with hydrophobic 1-dodecanethiol and the other semisphere functionalized with hydrophilic β-mercaptoethylamine. Polyurethane with isocyanate end groups was sprayed on the leather surface as an intermediate layer to strongly link Janus particles with leather via cross-linking. Moreover, amphiphilic Janus particles were fabricated from hollow SiO2 particles via a thiol-ene click reaction due to its low density. The superhydrophobic coating on leather possessed a high water contact angle of 162.2°. Furthermore, it still retained excellent hydrophobicity with a water contact angle of 154° after 140 cycles of abrasion using sandpaper. This study not only provides a novel method for the fabrication of amphiphilic hollow SiO2 Janus nanoparticles, but also resolves the difficulties in constructing long-lived superhydrophobic coatings on fragile surfaces by existing methods. Meanwhile, the present study also suggests a potential way to translocate functional Janus microcapsules, which may give some significant suggestions on the future nanoparticle design for drug delivery and energy storage.

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.