Search Results (16)

Radiative cooling is a passive cooling strategy that dissipates heat externally through the atmospheric window (8–13 μm). This study presents a radiative cooling film with a simple and cost-effective fabrication process. The film was fabricated by mixing SiO₂ hollow microspheres with a UV-curable resin, employing a photopolymerization-induced phase separation method. The resulting gradient refractive index structure enhanced thermal radiation emissivity. At an optimal silica-to-resin mass ratio of 1:1.5 and a film thickness of 1.1 mm, the film achieved a solar reflectivity of 85% and an emissivity of 91% within the atmospheric window. Outdoor experiments conducted in both summer and winter demonstrated stable cooling performance. Under a solar irradiance of 796.9 W/m² (summer), the film reduced surface temperature by 10 °C compared to ambient air and 20 °C compared to an uncoated glass substrate, achieving a radiative cooling power of 76.7 W/m². In winter (solar irradiance of 588.8 W/m²), the film maintained a significant cooling effect, though with reduced efficiency due to lower solar exposure. Furthermore, long-term stability tests over six months showed that the film retained high solar reflectivity and infrared emissivity, indicating good durability. Overall, the developed radiative cooling films demonstrate excellent optical properties, structural stability, and cooling efficiency, making it a promising candidate for real-world radiative cooling applications. Further studies on environmental resilience and optimization under diverse climatic conditions are necessary for broader deployment. Full article

Silica (SiO₂) particles are widely used in various industries due to their chemical inertness, thermal stability, and wear resistance. The present study describes the preparation and potential use of porous hydrophobic and hydrophilic SiO₂ microcapsules (MCs) of a narrow size distribution. First, various layers of SiO₂ micro/nano-particles (M/NPs) were grafted onto monodispersed polystyrene (PS) microspheres of a narrow size distribution. Hydrophobic and hydrophilic sintered SiO₂ MCs were then prepared by removing the core PS from the PS/SiO₂ core–shell microspheres by burning off under normal atmospheric conditions or organic solvent dissolution, respectively. We examined how the size and quantity of the SiO₂ M/NPs influence the MC’s properties. Additionally, we utilized two forms of hollow SiO₂ MC for different applications; one form was incorporated into polymer films, and the other was free-floating. The hydrophobic microcapsules filled with 6% hydrogen peroxide were effective in killing the tomato brown rugose fruit virus (ToBRFV). The hydrophilic microcapsules filled with thymol and thin coated onto polypropylene films were successfully used to prevent mold formation for hay protection. Full article

Tetravalent Sn species, such as zeolite or oxide, possess Lewis acidic properties, and thus exhibit prominent catalytic performance in several reactions when they are incorporated into the silica framework. Unfortunately, the synthesis of Sn-based zeolite (Sn–Beta) usually suffers from several drawbacks, including a long crystallization time, limited framework Sn content and complex synthesis steps. Sn-based composite oxides are favored in the industry, due to their simple synthesis steps and easy control of their pore structure, morphology and Sn content. In this work, an aerosol-assisted method is used to prepare Sn–Si composite oxide microspheres, using CTAB as template. The method is based on the formation of aerosol from a solution of Sn, Si precursors and a template (CTAB). The introduction of CTAB causes the surface tension of the atomized droplets to decrease. During the fast drying of the droplets, the Sn–Si composite oxide microspheres with a concave hollow morphology were first formed. After calcination, calibrated mesopores of 2.3 nm were also formed, with a specific surface area of 1260 m²/g and a mesopores ratio of 0.84. Sn species are incorporated in the silica network, mainly in the form of single sites. The resulting material proved to exhibit high catalytic performances in the Baeyer–Villiger oxidation of 2-adamantanone by using H₂O₂ as green oxidant, which was mainly attributed to the enhancement of the access to the catalytic tin sites through both the continuous hollow and mesopore channels, which have a 52% conversion of 2-adamantanone after 3 h of reaction. This method is simple, convenient, cheap and can be continuously produced, meaning it has broad potential for industrial application. Full article

With the development of the integrated circuit and chip industry, electronic products and their components are becoming increasingly miniaturized, high-frequency, and low-loss. These demand higher requirements for the dielectric properties and other aspects of epoxy resins to develop a novel epoxy resin system that meets the needs of current development. This paper employs ethyl phenylacetate cured dicyclopentadiene phenol (DCPD) epoxy resin as the matrix and incorporates KH550 coupling-agent-treated SiO₂ hollow glass microspheres to produce composite materials with low dielectric, high heat resistance, and high modulus. These materials are applied as insulation films for high density interconnect (HDI) and substrate-like printed circuit board (SLP) boards. The Fourier transform infrared spectroscopy (FTIR) technique was used to characterize the reaction between the coupling agent and HGM, as well as the curing reaction between the epoxy resin and ethyl phenylacetate. The curing process of the DCPD epoxy resin system was determined using differential scanning calorimetry (DSC). The various properties of the composite material with different HGM contents were tested, and the mechanism of the impact of HGM on the properties of the composite material was discussed. The results indicate that the prepared epoxy resin composite material exhibits good comprehensive performance when the HGM content is 10 wt.%. The dielectric constant at 10 MHz is 2.39, with a dielectric loss of 0.018. The thermal conductivity is 0.1872 Wm⁻¹ k⁻¹, the coefficient of thermal expansion is 64.31 ppm/K, the glass transition temperature is 172 °C, and the elastic modulus is 1221.13 MPa. Full article

Coal fly ash hollow aluminosilicate microspheres (cenospheres) of stabilized composition (glass phase—95.4; (SiO₂/Al₂O₃)_glass—3.1; (Si/Al)_at. = 2.6) were used to fabricate lutetium-176 encapsulated aluminosilicate microspheres as precursors of radiolabeled microspheres applied for selective irradiation of tumors. To incorporate Lu³⁺ ions into cenosphere’s aluminosilicate material, the following strategy was realized: (i) chemical modification of cenosphere globules by conversion of aluminosilicate glass into zeolites preserving a spherical form of cenospheres; (ii) loading of zeolitized microspheres with Lu³⁺ by means of ion exchange 3Na⁺ ↔ Lu³⁺; (iii) Lu³⁺ encapsulation in an aluminosilicate matrix by solid-phase transformation of the Lu³⁺ loaded microspheres under thermal treatment at 1273–1473 K. Two types of zeolitized products, such as NaX (FAU) and NaP1 (GIS) bearing microspheres having the specific surface area of 204 and 33 m²/g, accordingly, were prepared and their Lu³⁺ sorption abilities were studied. As revealed, the Lu³⁺ sorption capacities of the zeolitized products are about 130 and 70 mg/g Lu³⁺ for NaX and NaP1 microspheres, respectively. It was found that the long-time heating of the Lu³⁺-loaded zeolite precursors at 1273 K in a fixed bed resulted in the crystallization of monoclinic Lu₂Si₂O₇ in both zeolite systems, which is a major component of crystalline constituents of the calcined microspheres. The fast heating–cooling cycle at 1473 K in a moving bed resulted in the amorphization of zeolite components in both precursors and softening glass crystalline matter of the NaX-bearing precursor with preserving its spherical form and partial elimination of surface open pores. The NaX-bearing microspheres, compared to NaP1-based precursor, are characterized by uneven Lu distribution over the zeolite-derived layer. The precursor based on gismondin-type zeolite provides a near-uniform Lu distribution and acceptable Lu content (up to 15 mol.% Lu₂O₃) in the solid phase. Full article

In this paper, high-performance silica aerogel (SiO₂ aerogel) thermal insulation coatings were obtained and profited from the excellent thermal insulation capability of SiO₂ aerogel. The comprehensive properties and thermal insulation mechanism of the coatings were investigated via Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), contact angle, and temperature difference tests. Results showed that there was a contradiction between thermal insulation and mechanical property in this coating after the addition amount and proportion of silica aerogel, hollow glass microsphere, glass fibers, aqueous acrylic emulsion, and dispersing agents were optimized carefully. When the mass ratio of hollow glass to SiO₂ aerogel microspheres was 1:1, the overall performance of the coating was the best with thermal conductivity of 0.050 W/(m·K) and adhesive strength of 1024 kPa. Full article

In this study, hollow SiO₂ microspheres were synthesized by the hydrolysis of tetraethyl orthosilicate (TEOS) according to the Stober process, in which Pichia pastoris GS 115 cells were served as biological templates. The influence of the preprocessing method, the TEOS concentration, the ratio of water to ethanol, and the aging time on the morphology of microspheres was investigated and the optimal conditions were identified. Based on this, TiO₂-SiO₂ microspheres were prepared by the hydrothermal process. The structures and physicochemical properties of TiO₂-SiO₂ photocatalysts were systematically characterized and discussed. The photocatalytic activity for the degradation of methyl orange (MO) at room temperature under Xe arc lamp acting as simulated sunlight was explored. The result showed that the as-prepared TiO₂-SiO₂ microspheres exhibited a good photocatalytic performance. Full article

In an attempt to improve the photocatalytic activity of anatase TiO₂, we developed a composite photocatalyst composed of hollow TiO₂ microspheres (hTS) and graphene. The hTS were prepared through a two-step hydrothermal process, where SiO₂ microspheres with desirable diameters of 100–400 nm were used as sacrificial templates. Accordingly, the effect of the hTS cavity size on the activity of the catalyst in wet CO₂ photoreduction (CO₂PR) was studied. Furthermore, it was established that the hydrothermal pH value crucially influences the photocatalytic activity of the hTS photocatalyst, as well as its composition and microstructure. The hTS photocatalyst was also combined with graphene (0–90 wt%) to improve its photocatalytic activity. This study provides insight into the optimal microsphere diameter, hydrothermal pH value, and graphene/hTS_x ratio required for designing hollow microsphere-based photocatalysts with enhanced CO₂PR performances. Full article

This study shows the development of a combustion promoter for the oil-refining process called fluid catalytic cracking (FCC). The investigation of a catalyst prepared for the combustion of CO composed of 0.05 wt% Pt supported on SiO₂–Al₂O₃–0.5 wt% W microspheres with high mechanical resistance, promoted with tungsten oxides (WOx) that can inhibit the sintering of Pt, is reported. The addition of WOx in SiO₂–Al₂O₃ inhibited the decrease in the specific area when calcined from 550 °C to 950 °C. SiO₂–Al₂O₃ support in the form of calcined microspheres with average diameters between 70–105 µm were produced by spray drying, using two atomization discs with vanes of different geometry: a straight rectangular blade disc (DAR) and a curved rectangular vanes disc (DAC). The DAR disk produced whole microspheres, while the DAC had hollow and broken microspheres. The microspheres were characterized by XRD, SEM, optical microscopy, N₂ physisorption (BET area) and fracture resistance tests. The Pt catalysts were evaluated by TPR, H₂ chemisorption and CO combustion. The catalyst of 0.05 wt% Pt/SiO₂–Al₂O₃–0.5 wt% turned out to be the most stable. A thermal stabilization effect was observed at contents lower than 1 wt% W that allowed it to inhibit the sintering of the Pt catalyst. Full article

Co-processing of radioactive effluents with coal fly ash-derived materials is recognized as a resource-saving approach for efficient stabilization/solidification of radioactive components of wastewater. In this context, the paper is focused on the hydrothermal synthesis of Sr²⁺-bearing aluminosilicate/silicate phases as analogs of a mineral-like ⁹⁰Sr waste form using hollow glass-crystalline aluminosilicate microspheres from coal fly ash (cenospheres) as a glassy source of Si and Al (SiO₂-Al₂O₃)_glass) and Sr(NO₃)₂ solutions as ⁹⁰Sr simulant wastewater. The direct conversion of cenosphere glass in the Sr(NO₃)₂-NaOH-H₂O-(SiO₂-Al₂O₃)_glass system as well as Sr²⁺ sorption on cenosphere-derived analcime (ANA) in the Sr(NO₃)₂-H₂O-ANA system were studied at 150–200 °C and autogenous pressure. The solid and liquid reaction products were characterized by SEM-EDS, PXRD, AAS and STA. In the Sr(NO₃)₂-NaOH-H₂O-(SiO₂-Al₂O₃)_glass system, the hydrothermal processing at 150–200 °C removes 99.99% of the added Sr²⁺ from the solution by forming Sr-tobermorite and Sr-plagioclase phases. In the Sr(NO₃)₂-H₂O-ANA system, Sr²⁺ sorption on analcime results in the formation of solid solutions (Na_1−nSr_n/2)AlSi₂O₆·H₂O of the Na-analcime–Sr-wairakite series. The results can be considered as a basis for the development of environmentally sustainable technology for ⁹⁰Sr removal from wastewater and immobilization in a mineral-like form by co-processing waste from coal-fired and nuclear power plants. Full article

Spray pyrolysis of an aqueous solution of iron nitrate, proceeded with reduction of the product in hydrogen, gave iron powder with micron-sized hollow particles. Coating these iron particles with SiO₂ through tetraethyl orthosilicate hydrolysis prevented interparticle electrical contacts and suppressed DC percolation. This material shows a high ferromagnetic resonance frequency of 18 GHz, low permittivity, and weighs 20% less than common carbonyl iron. Potential microwave applications are for inductors and electromagnetic interference shielding designs. Full article

In this work, we report the design and synthesis of a series of heterostructured SnO₂-CuO hollow microspherical catalysts (H-SnO₂(x)-CuO, x is the weight ratio of Sn/Cu) for the Rochow reaction. The microspherical catalysts with nanosheets and nanoparticles as building blocks were prepared by a facile one-pot hydrothermal method coupled with calcination. When tested for the Rochow reaction, the prepared H-SnO₂(0.2)-CuO composite exhibited higher dimethyldichlorosilane selectivity (88.2%) and Si conversion (36.7%) than the solid CuO, hollow CuO and other H-SnO₂(x)-CuO microspherical samples, because in the former there is a stronger synergistic interaction between CuO and SnO₂. Full article

Thermoresponsive P(NIPAM-AA)/Fe₃O₄/SiO₂ microspheres with surface holes serving as carriers were prepared using p-Fe₃O₄/SiO₂ microspheres with a thermoresponsive copolymer. The p-Fe₃O₄/SiO₂ microspheres was obtained using a modified Pickering method and chemical etching. The surface pore size of p-Fe₃O₄/SiO₂ microspheres was in the range of 18.3 nm~37.2 nm and the cavity size was approximately 60 nm, which are suitable for loading and transporting biological macromolecules. P(NIPAM-AA) was synthesized inside and outside of the p-Fe₃O₄/SiO₂ microspheres via atom transfer radical polymerization of NIPAM, MBA and AA. The volume phase transition temperature (VPTT) of the specifically designed P(NIPAM-AA)/Fe₃O₄/SiO₂ microspheres was 42.5 °C. The saturation magnetization of P(NIPAM-AA)/Fe₃O₄/SiO₂ microspheres was 72.7 emu/g. The P(NIPAM-AA)/Fe₃O₄/SiO₂ microspheres were used as carriers to study the loading and release behavior of BSA. This microsphere system shows potential for the loading of proteins as a drug delivery platform. Full article

MoS₂/RGO composite hollow microspheres were hydrothermally synthesized by using SiO₂/GO microspheres as a template, which were obtained via the sonication-assisted interfacial self-assembly of tiny GO sheets on positively charged SiO₂ microspheres. The structure, morphology, phase, and chemical composition of MoS₂/RGO hollow microspheres were systematically investigated by a series of techniques such as FE-SEM, TEM, XRD, TGA, BET, and Raman characterizations, meanwhile, their electrochemical properties were carefully evaluated by CV, GCD, and EIS measurements. It was found that MoS₂/RGO hollow microspheres possessed unique porous hollow architecture with high-level hierarchy and large specific surface area up to 63.7 m²·g⁻¹. When used as supercapacitor electrode material, MoS₂/RGO hollow microspheres delivered a maximum specific capacitance of 218.1 F·g⁻¹ at the current density of 1 A·g⁻¹, which was much higher than that of contrastive bare MoS₂ microspheres developed in the present work and most of other reported MoS₂-based materials. The enhancement of supercapacitive behaviors of MoS₂/RGO hollow microspheres was likely due to the improved conductivity together with their distinct structure and morphology, which not only promoted the charge transport but also facilitated the electrolyte diffusion. Moreover, MoS₂/RGO hollow microsphere electrode displayed satisfactory long-term stability with 91.8% retention of the initial capacitance after 1000 charge/discharge cycles at the current density of 3 A·g⁻¹, showing excellent application potential. Full article

The effective activation and utilization of metakaolin as an alkali activated geopolymer precursor and its use in concrete surface protection is of great interest. In this paper, the formula of alkali activated metakaolin-based geopolymers was studied using an orthogonal experimental design. It was found that the optimal geopolymer was prepared with metakaolin, sodium hydroxide, sodium silicate and water, with the molar ratio of SiO₂:Al₂O₃:Na₂O:NaOH:H₂O being 3.4:1.1:0.5:1.0:11.8. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were adopted to investigate the influence of curing conditions on the mechanical properties and microstructures of the geopolymers. The best curing condition was 60 °C for 168 h, and this alkali activated metakaolin-based geopolymer showed the highest compression strength at 52.26 MPa. In addition, hollow micro-sphere glass beads were mixed with metakaolin particles to improve the thermal insulation properties of the alkali activated metakaolin-based geopolymer. These results suggest that a suitable volume ratio of metakaolin to hollow micro-sphere glass beads in alkali activated metakaolin-based geopolymers was 6:1, which achieved a thermal conductivity of 0.37 W/mK and compressive strength of 50 MPa. By adjusting to a milder curing condition, as-prepared alkali activated metakaolin-based geopolymers could find widespread applications in concrete thermal protection. Full article