Hollow Microspheres Research Articles

Fabrication of hollow Fe3O4 microspheres encapsulated by single-walled carbon nanohorns for high-performance microwave absorption

Fabrication of hollow Fe3O4 microspheres encapsulated by single-walled carbon nanohorns for high-performance microwave absorption

Hollow glass microsphere/polybutadiene composites with low dielectric constant and ultralow dielectric loss in high‐frequency

AbstractHigh‐frequency dielectric materials have been widely and rapidly applied in areas such as automotive radar, Internet of Things, artificial intelligence, and quantum computing. Currently, the challenge in high‐frequency dielectric materials lies in reducing the dielectric constant (Dk) and dielectric loss (Df) without sacrificing its mechanical properties. This study addresses this challenge by introducing air, as the most common “low dielectric factor,” into the polymer matrix in the form of hollow glass microspheres. Meanwhile, the reactive vinyl groups were also introduced onto the surface of the hollow glass microspheres, enabling an interfacial chemical reaction between the side vinyl groups of polybutadiene and its surface so that the organic–inorganic interface compatibility and interface peel strength are simultaneously improved. Consequently, the minimum Dk of 1.29 and Df of 0.0012 in 3–18 GHz are achieved, and the interface peel strength also reaches 0.65 N/mm. Molecular dynamics simulations, analysis of dielectric properties, and interface peel strength reveal the influence of hollow glass microspheres' morphology and chemical structure on their high‐frequency dielectric performance and adhesive strength. This paper provides effective strategies for the structural design and preparation of high‐frequency, low‐dielectric composites, contributing to the further development of next‐generation microwave communication devices towards higher frequencies and faster information transmission.

Ultrawhite and ultrablack asymmetric coatings for radiative cooling and solar heating

Passive daytime radiative cooling, a zero-energy and zero‑carbon cooling technology, has significant potential to substantially reduce reliance on compression-based cooling systems, combat the urban heat island effect, and mitigate global warming. However, current radiative cooling materials either exhibit low efficiency or are susceptible to overcooling, resulting in cooling penalties on winter days. In this work, we designed and fabricated the ultrawhite and ultrablack asymmetric coatings. The top-layer, designed for efficient radiative cooling, consists of a porous polymethyl methacrylate and hollow silica microspheres composite. The underlayer, tailored for solar heating, is composed of a carbon nanotubes and carbon black composite. The cooling side with an exceptional solar reflectivity of 0.98 and a mid-infrared emissivity of 0.97 achieves a comparable daytime subambient cooling of 7.6 °C, with a theoretical net cooling power of 98.8 W/m2. Conversely, the heating side with a solar absorptivity of 0.96, a ultra-high visible light absorptivity of 0.985, and a mid-infrared emissivity of 0.97, results in a daytime above-ambient heating of 12.8 °C, corresponding to a theoretical net heating power of 745 W/m2. Promisingly, our ultrawhite and ultrablack asymmetric coatings hold the promise of addressing the long-standing challenge of all-season temperature regulation, offering significant potential for electricity savings and CO2 emission reduction.

Emerging SiO2@ATO hierarchical submicron hollow microspheres with efficient photo-thermal shielding properties

Silicon dioxide/antimony doped tin oxide (SiO2@ATO) submicron hollow microspheres were prepared by hydrothermal method. The morphology and microstructure of the microspheres were characterized by XRD, SEM, EDS and HRTEM. The composite coatings were prepared by adding SiO2@ATO powders to acrylic matrix, and their photothermal shielding properties were investigated. In addition, the electronic structure and optical properties of SiO2@ATO heterojunction were calculated and analyzed using first principle. The results show that the interface binding energy of SiO2@ATO is ∼2.496 J/m2, which indicates that the interface can exist stably. The light transmittance of the acrylic matrix coating with 1.0 wt% submicron hollow SiO2@ATO microspheres can reach about 83 %. Moreover, it was found that the hollow double-shell SiO2@ATO/acrylic matrix coating lowered the indoor temperature of the homemade incubator by 11.5℃. In summary, the SiO2@ATO structure shows potential in the application of transparent thermal insulation coatings.

Sulfonate-Bonded Conjugated Microporous Polymer Hollowed-Out Spheres to Capture Fluoroquinolone Antibiotics and Cationic Dyes from Wastewater.

Developing adsorbent materials for the efficient removal of multiple organic pollutants in water is of importance technological significance. In the present work, a kind of conjugated microporous polymer (CMP) with a hollow sphere structure was constructed by applying SiO2 nanoparticles as a template and 1,3,5-triethynylbenzene (TEB) and 2,7-dibromocarbazole (27-DBCZ) as building blocks via the Sonogashira-Hagihara cross-coupling reaction. In order to further improve the dispersibility of the as-resulting CMPs in water, hydrophilic CMPs (H-S-CMPs) were obtained by a sulfonation modification. The adsorption performance of H-S-CMPs on dyes and antibiotics was investigated, which was based on different experimental parameters such as the initial concentration, contact time, temperature, pH, and adsorbent dose. The adsorption isotherm, kinetics, and thermodynamics were also studied, and the possible adsorption mechanism of H-S-CMPs was discussed. The experimental results illustrated that the adsorption process of H-S-CMPs on dyes and antibiotics is more consistent with the Langmuir isotherm model and the pseudo-second-order kinetic model. The maximum adsorption capacities of H-S-CMPs for rhodamine B (RhB), methylene blue (MB), ciprofloxacin, and norfloxacin were 206.2, 324.7, 222.2, and 216.9 mg/g, respectively, which were determined according to the Langmuir isothern model. In addition, the adsorption mechanism of H-S-CMPs may be attributed to the synergistic effects of hydrogen bonding, electrostatic attraction, π-π stacking, and pore filling. After 5 cycles, H-S-CMPs still maintained good stability, and their removal rate of dyes could reach more than 70%. Notably, this polymeric hollow microsphere has been less extensively investigated as an adsorbent for the removal of dyes and antibiotics. As a result, based on the designable flexibility of CMPs and the unique structure of hollow microspheres, the material holds great promise for wastewater treatment in the presence of multiple pollutants.

Synthesis of chiral hollow polymer microspheres and their applications in the spectroscopic chiral discrimination of tryptophan isomers

Hollow polymer microspheres (HPMs) were synthesized, which were then hydrolyzed in aqueous ammonia to produce carboxyl (–COOH) groups on their surface. L-phenylalanine (L-Phe) was grafted to the hydrolyzed HPMs (H-HPMs) through amidation reactions, endowing the H-HPMs with chirality. The resultant chiral HPMs (C-HPMs) were used for the chiral discrimination of tryptophan (Trp) isomers. Due to the same rotatorydirection of L-Phe and L-Trp, the C-HPMs showed greatly higher selectivity toward L-Trp than its isomer. After being adsorbed by the C-HPMs, the absorbance of the residual L-Trp is significantly lower than that of the residual D-Trp, and thus spectroscopic chiral discrimination of the Trp isomers was successfully achieved. The Trp isomers were also discriminated by the chiral solid polymer microspheres (C-SPMs), while the difference in the absorbance of the residual L-Trp and D-Trp is remarkably smaller than that obtained by the C-HPMs. The outstanding discrimination capability of the C-HPMs might be ascribed to their high surface permeability resulted from their unique hollow structure.

Regulating the Electronic Structure of Cu Single-Atom Catalysts toward Enhanced Electro-Fenton Degradation of Organic Contaminants via 1O2 and •OH.

Heterogeneous electro-Fenton degradation with 1O2 and •OH generated from O2 reduction is cost-effective for the removal of refractory organic pollutants from wastewater. As 1O2 is more tolerant to background constituents such as salt ions and a high pH value than •OH, tuning the production of 1O2 and •OH is important for efficient electro-Fenton degradation. However, it remains a great challenge to selectively produce 1O2 and improve the species yield. Herein, the electronic structure of atomically dispersed Cu-N4 sites was regulated by doping electron-deficient B into porous hollow carbon microspheres (CuBN-HCMs), which improved *O2 adsorption and significantly enhanced 1O2 selectivity in electro-Fenton degradation. Its 1O2 yield was 2.3 times higher than that of a Cu single-atom catalyst without B doping. Meanwhile, •OH was simultaneously generated as a minor species. The CuBN-HCMs were efficient for the electro-Fenton degradation of phenol, sulfamethoxazole, and bisphenol A with a high mineralization efficiency. Its kinetic constants showed insignificant changes under various anions and a wide pH range of 1-9. More importantly, it was energy-efficient for treating actual coking wastewater with a low energy consumption of 19.0 kWh kgCOD-1. The superior performance of the CuBN-HCMs was contributed from 1O2 and •OH and its high 1O2 selectivity.

Waterborne novolac epoxy‐based thermal resistant and fire‐retardant thermal insulation coatings

AbstractWaterborne novolac epoxy based thermal resistant and fire‐retardant thermal insulation coatings were developed in this work. Novolac (phenolic) epoxy emulsion (PEE) was prepared by the phase inversion method based on formulation optimization by orthogonal array testing. The prepared emulsions have similar particle size, viscosity, and stability to commercial bisphenol a glycidyl ether epoxy emulsion (PZ). DSC results showed that the varnish film based on PEE had a higher glass transition temperature and initial thermal decomposition temperature compared with PZ cured by the same curing agent. Waterborne thermal insulation coating with PEE and PZ as binders and hollow glass microspheres (HGMs) as thermal insulation fillers were studied. The results indicated that the thermal conductivity of the coating decreased with an increase in HGMs content. Specifically, the thermal conductivity of the PEE coating containing 20 wt% HGMs is as low as 0.093 W/(m·K). It reduces the exterior temperature of the hot tank from approximately 200 °C to approximately 106 °C. Furthermore, the HGMs/PEE waterborne thermal insulation coating exhibits good thermal stability and flame retardance.

A multifunctional platform based on ZIF-67 templated NiCo-LDH and Fe3O4 hollow spheres for photocatalytic CO2 conversion and supercapacitors

This work presented a series of hybrid materials F@P-LDHs exhibiting the core-shell structure with PPy as the interface modifier, explored as dual-functional materials for studying photocatalytic reduction of CO2 and electrochemical behaviors. F@P-LDHs served as photocatalysts, effectively convert CO2 into CO without using any sacrificial agents and photosensitizers via the gas-solid mode under the visible light irradiation. The generation rate of CO was as high as 10.32 μmol g−1h−1, which was 5.4 and 6.4 times higher than the original Fe3O4@PPy and NiCo-LDH. The well performance might be ascribed to the generation of type Z heterojunction with the interface modifier PPy, jointly accelerating the separation and migration of photo-generated charge carriers between Fe3O4@PPy and NiCo-LDH. Besides, F@P-LDHs were also developed as supercapacitors, and their electrochemical behaviors were investigated. Their good electrochemical performances were attributed to the synergistic effect among hollow Fe3O4 microspheres, polypyrrole and NiCo-LDH. Therefore, as dual-functional materials, the hybrid materials have great potential in the field of CO2 conversion and supercapacitors.

Template-synthesized CdWO4/Cd0.5Zn0.5S hollow microsphere photocatalyst for high-efficient hydrogen evolution under visible light

Photocatalytic water splitting for hydrogen production is a promising strategy for renewable energy. While Cd1-XZnXS catalysts display high photocatalytic hydrogen evolution efficiency in pure water, they are limited by severe photocorrosion and rapid recombination of electron–hole pairs. In this study, HGM (hollow glass microspheres) was used as the support template, Cd0.5Zn0.5S and CdWO4 were successively coated on the template by hydrothermal method. The tightly packed heterojunction interface between the coatings ensures efficient electron transport and suppresses the recombination of electron-hole pairs. Under visible light irradiation, when the theoretical mass ratio of Cd0.5Zn0.5S to CdWO4 is 4:1, the Cd0.5Zn0.5S/CdWO4-25% hollow microsphere photocatalyst exhibits the highest hydrogen evolution rate, reaching 41.40 mmol g−1 h−1, which is approximately 3.4 times higher than the hydrogen evolution rate of pure Cd0.5Zn0.5S (12.31 mmol g−1 h−1). This research provides a novel approach for the design and synthesis of efficient and stable photocatalysts.

Experimental study on the improvement of bamboo properties using amide polymer repair material based on the principle of self-energy dissipation

Traditional bamboo and wood components have different holes due to their own and external factors, and the appropriate hole repair technology is the key to improve the component's energy dissipation capacity. In this paper, based on the principle of in-situ free radical polymerization and hollow glass microsphere (HGM) reinforced polymer, PAM hydrogel (PAMHG) with better deformation recovery ability and PAM/HGM amide polymer (AP) with better mechanical properties were prepared. Based on the principle of self-energy dissipation of components, AP is used to improve the deformation capacity of hollow bamboo. The ratio of PAMHG and AP was optimized by single factor test and orthogonal test. The performance of AP was verified by bending test, SEM, energy consumption analysis，durability test and statistical analysis of small diameter round bamboo. The size of the bamboo sample is 250 mm (L)×15 mm (D)×2.5 mm (t), in accordance with LY/T 3347–2023 " Testing methods for physical and mechanical properties of small diameter round bamboo " (China). The results showed that an appropriate amount of glycerol could effectively improve the volume stability of the hydrogel. HGM effectively improved the strength of the polymer, and when the mass ratio of HGM/PAM was 0.48, the maximum compressive strength was 0.8 MPa, which was 2.4 times higher than that of the undoped HGM, and at this time, the optimal polymer ratios were 25 g of AM, 1 g of MBA, 0.01 g of APS, 2 g of TEA, 2 g of Carbomer SF-1, a volume ratio of 1:1 of glycerol/deionized water that the dispersion medium was 70 ml, and HGM was 12 g. The average energy dissipation of grouted bamboo at ultimate load was 2.02 times that of the control group, and the highest bending strength and elastic modulus were 128.01 MPa and 11.24 GPa, which were 41.39 % and 39.75 % higher than that of the control group, respectively. The SEM results revealed that the AP partially prepolymerized solution could infiltrate into the cells and pores of the bamboo material to achieve filling, bonding, as well as reinforcing the bamboo tissue. In addition, the durability test shows that AP has good resistance to environmental pressure. The results of this paper can provide a reference for the restoration materials of bamboo and wood components.

Lightweight composite from graphene-coated hollow glass microspheres for microwave absorption

In developing the effective and lightweight materials for microwave absorption, graphene holds a bright promise because of its excellent electrical properties and low density, but it suffers from poor impedance matching; while the hollow glass microspheres on the other hand have extremely low density and are dielectric. Their synergistic combination could achieve a perfect impedance matching and thus create a novel lightweight absorption composite. The metamaterial structure absorber can efficiently absorb electromagnetic waves over a wide frequency range. This study employs a hydrothermal method to deposit graphene onto the surfaces of hollow glass microspheres, followed by the design of a metamaterial absorber. Upon coating with graphene flakes, the composite material effectively dissipates electromagnetic wave energy through mechanisms such as interfacial polarization, dielectric loss, and the multiple scattering effects of hollow glass microspheres and graphene flakes. The composite exhibits an effective absorption bandwidth up to 4.02 GHz under a graphene flakes mass fraction of 30 %. More importantly, the incorporation of the metamaterial absorber design further significantly enhances the absorption bandwidth to 7.7 GHz. This material demonstrates significant advantages in terms of lightweight and broadband absorption performance, providing new insights for the research of high-performance lightweight and wideband absorbing materials in the future. However, further investigation is required to examine its long-term stability and performance in complex environments.

Design, fabrication, and characterization of 1–3 piezoelectric composite air-coupled ultrasonic transducers with micro-membrane filter matching layer

Air-coupled ultrasonic transducers are widely used in various fields of nondestructive material characterization. This paper presents the fabrication and performance characterization of 1–3 piezoelectric composite air-coupled ultrasonic transducers operating at frequencies ranging from 400 kHz to 600 kHz. The transducers are fabricated using a dice-and-fill method with PZT-5 as the active material. A double-layer matching strategy is employed, utilizing hollow glass microsphere filled epoxy resin as the first matching and bonding layer. Additionally, micro-membrane filters with different pore sizes are used as the second matching layer. Thermoplastic adhesive TPU is utilized to bind the micro-membrane filter and the first matching layer. Due to the low acoustic impedance of the hollow glass microsphere filled epoxy resin and micro-membrane filter, acoustic impedance mismatch is reduced. Finite element simulation is used to determine the optimal ceramic volume fraction and ceramic pillar height of the 1–3 piezoelectric composites. When the pore size of the micro-membrane filter is 0.8 μm, the transducer achieves the lowest two-way insertion loss of −56.86 dB and the highest −6 dB bandwidth of 15.6 %, making it feasible for through mode applications.

The adsorption of cesium by sulfonic acid functionalized hollow mesoporous silica microspheres

With the development of nuclear industry, radioactive elements such as 137Cs put a threat on the water environment. It is a challenging task to remove the Cs+ in the nuclear wastewater. In the current study, we prepared a new Cs+-adsorbing material by introducing sulfhydryl group onto the surface of hollow mesoporous silica microspheres, then oxidizing the sulfhydryl group to sulfonic acid group. The obtained HMSS-SO3H material had an excellent adsorption capacity for Cs+ in the aqueous solution, with an adsorption capacity of 51.53 mg g−1 in 30 min. Characterization approaches, such as FT-IR and EDS, were used to confirm the result of modification. Adsorption experiments were carried out under. The influence of various parameters on the adsorption process was investigated under the conditions of changing pH, temperature, and time. The effect of competitive ions was also explored. The results indicated that the adsorption process followed the pseudo-second-order model and the main adsorption mechanisms are electrostatic interaction and coordination. The material had a best adsorption performance at a neutral pH. The adsorption process could well-fit the Langmuir's model, with a theoretical maximum adsorption capacity of 81.31 mg g−1. And the adsorption capacity was slightly affected by competing ions such as Mg2+ and Ca2+. The results indicate that the HMSS-SO3H prepared in this study is a promising adsorbent for Cs+, with the advantages of high adsorption capacity, fast adsorption rate and high selectivity.

Porous TiO2 microspheres containing MgO nanoparticles/epoxy composite with superior thermal conductivity, EMI shielding, and electrical insulation

With the continuous advancement of electronic devices, the amounts of heat as well as electromagnetic (EM) waves generated have increased. Materials with high thermal conductivity and excellent EM interference shielding effectiveness (EMI SE) can be utilized to address this issue. In this work, we synthesized hollow anatase TiO2 microspheres. Through a reaction, MgO nanoparticles were incorporated into the interior of TiO2 microspheres. (H-TiO2/MgO). The heterostructure of the fillers contributed to performance enhancement. TiO2 and MgO particles formed a dual thermal-conduction pathway. H-TiO2/MgO effectively weakened the energy of EM waves upon contact. Additionally, TiO2, MgO, and epoxy all exhibited hydrophilicity. Consequently, the interfacial compatibility between H-TiO2/MgO and epoxy was excellent. They formed strong interfacial interactions by hydrogen bonding. Because of the excellent electrical insulation properties of H-TiO2 and MgO, the composites exhibited superior insulation performance (over 1010 Ω·cm). Our H-TiO2/MgO/Epoxy composites exhibited a maximum thermal conductivity of 7.52 W/m·K, an EMI SE of 64.92 dB, and a tensile strength of 79.10 MPa. Our composites are expected to effectively manage heat and EM waves generated by electronic devices

High-performance trimethylamine gas sensor based on Sn-W co-doped MOF-derived hollow flower-like nickel oxide

In this study, a simple hydrothermal method was used to synthesize metal-organic framework-derived Sn/W co-doped NiO hollow flower-like spherical structure. The prepared NiO composites were utilized to prepare gas sensors to explore the response characteristics to different gases. The results showed that the response of the bimetal-doped NiO hollow microspheres to trimethylamine was 95 at 100 ppm, which was 63 times that of the pristine NiO nanoflowers. In addition, the sensor has a ppb-level detection limit for trimethylamine (0.1 ppm, 1.5). These good sensing performance of the Sn/W co-doped NiO sensor are not only affected by the initial resistance(Ra), but are also closely related to the rich oxygen vacancies, special hollow flower-like spherical structure and high Ni3+/Ni2+ ratio in the composite nanomaterials. This study provides an elegant co-doping method to improve the gas sensing performance of P-type MOS.

Template-free synthesis of hollow microsphere CdS/ZnO heterojunction photocatalysts for photocatalytic hydrogen production

Template-free synthesis of hollow microsphere CdS/ZnO heterojunction photocatalysts for photocatalytic hydrogen production

Self-Templating Engineering of Hollow N-Doped Carbon Microspheres Anchored with Ternary FeCoNi Alloys for Low-Frequency Microwave Absorption.

Rational design and precision fabrication of magnetic-dielectric composites have significant application potential for microwave absorption in the low-frequency range of 2-8GHz. However, the composition and structure engineering of these composites in regulating their magnetic-dielectric balance to achieve high-performance low-frequency microwave absorption remains challenging. Herein, a self-templating engineering strategy is proposed to fabricate hollow N-doped carbon microspheres anchored with ternary FeCoNi alloys. The high-temperature pyrolysis of FeCoNi alloy precursors creates core-shell FeCoNi alloy-graphitic carbon nano-units that are confined in carbon shells. Moreover, the anchored FeCoNi alloys play a critical role in maintaining hollow structural stability. In conjunction with the additional contribution of multiple heterogeneous interfaces, graphitization, and N doping to the regulation of electromagnetic parameters, hollow FeCoNi@NCMs exhibit a minimum reflection loss (RLmin) of -53.5dB and an effective absorption bandwidth (EAB) of 2.48GHz in the low-frequency range of 2-8GHz. Furthermore, a filler loading of 20wt% can also be used to achieve a broader EAB of 5.34GHz with a matching thickness of 1.7mm. In brief, this work opens up new avenues for the self-templating engineering of magnetic-dielectric composites for low-frequency microwave absorption.

In-situ photoelectrochemical surface-enhanced Raman scattering based on Au@Ag/WO3 hollow microsphere for dual-mode sensing of microcystin-LR

Developing an accurate assay for early warning of microcystin-LR (MC-LR) is of great importance for environmental protection and agricultural production. Herein, this paper reported an in-situ photoelectrochemical surface-enhanced Raman scattering (PEC-SERS) strategy for dual-mode detection of MC-LR. The Au@Ag core-cell nanoparticles loaded hollow WO3 microsphere (Au@Ag/H-WO3) acted as in-situ PEC-SERS substrate to take advantage of the synergy between electromagnetic and chemical enhancement, while methylene blue (MB) was chosen as a bifunctional probe to produce photocurrent and SERS signal. For this strategy, double signals from MB were simultaneously induced by a 532 nm laser that the SERS signal and photocurrent offered a 57.9-fold and a 4.7-fold amplification, respectively, in the presence of Au@Ag/H-WO3. For analysis, the binding of MC-LR to aptamer led to the stripping of MB from the substrate and further decreased signals. Such a strategy offered linear ranges of 0.3–50 ng/mL in PEC mode while 1–100 ng/mL in SERS mode for MC-LR detection with high accuracy and applicability for real sample analysis. This in-situ PEC-SERS strategy offered an efficient way to monitor hazardous materials in the environment and agriculture.

Research on the properties of brucite-based magnesium phosphate cement fire resistive coating for steel structures

Magnesium Phosphate Cement (MPC) exhibits high strength, exceptional high-temperature resistance, and outstanding adhesion properties at the steel interface, rendering it an ideal material for fire resistive coatings on steel structures. In this study, natural brucite powder was employed as the magnesium source, while hollow glass microspheres (HGM) were utilized as functional modifiers to formulate brucite-based MPC fire resistive coatings for steel structures. This research explored the influence of the mass ratio of brucite powder to ammonium dihydrogen phosphate (M/P), the brucite particle size, and the addition of HGM on the physical, mechanical, and fire-retardant properties of the coatings. The microstructure of the brucite-based MPC before and after fire testing was examined using SEM, XRD, TG-DTG, and X-CT. The results indicated that with an M/P ratio of 2.5:1 and a brucite particle size of 75–150 μm, the material exhibited optimal overall performance and was suitable as a matrix material for MPC. The incorporation of an appropriate amount of HGM increased the compressive strength of brucite-based MPC by 33.4 %, reduced the dry density by 20.5 %, extended the fire resistance of the structure, and decreased the thermal conductivity by 48.2 %. This can be attributed to: (i) HGM filling the pores in brucite-based MPC, creating a denser microstructure; (ii) HGM forming a closed porous structure with the MPC matrix, reducing thermal conductivity and increasing thermal resistance; (iii) The low thermal diffusivity of HGM/MPC impeded heat transfer, thereby decelerating thermal decomposition and flame propagation.