Hollow Microsphere Composites Research Articles

A novel rGO-ZnFe2O4 hollow microsphere composite with excellent microwave absorption properties

In order to develop lightweight, efficient and broadband microwave absorbing materials, rGO-ZnFe2O4 hollow microsphere composites were prepared by the solution method in this paper. The effects of reduced graphene oxide (rGO) content on the microstructure of hollow microspheres and the microwave absorption properties of the material were studied. rGO micropowders and ZnFe2O4(ZFO) particles are uniformly distributed on the hollow microspheres. The rich porous hollow structure is conducive to the multiple reflection and scattering of electromagnetic microwaves. This structure and distribution state enable the composite material to have good impedance and form a synergistic effect of multiple absorption effects. The results show that the minimum reflection loss (RLmin) is −28.83 dB and the effective absorption bandwidth(EAB) is 5.92 GHz (11.04∼16.96 GHz) when the thickness is 2.00 mm and the rGO is 6.3 wt.%. The Radar scattering cross section(RCS) results show that the RCS values of the samples with the rGO is 6.3 wt.% are mostly below −20 dBm2 in the range of microwave incidence angle of −90°< Theta < 90°, which indicates the composites has wide-angle microwave absorption ability. This study provides a new approach to the design and preparation of efficient and lightweight electromagnetic microwave absorbing materials.

Fabrication of biodegradable hollow microsphere composites made of polybutylene adipate co-terephthalate/polyvinylpyrrolidone for drug delivery and sustained release.

Sustained drug release has attracted increasing interest in targeted drug therapy. However, existing methods of drug therapy suffer drug action time, large fluctuations in the effective concentration of the drug, and the risk of side effects. Here, a biodegradable composite of polybutylene adipate co-terephthalate/polyvinylpyrrolidone (PBAT/PVP) consisting of electrospun hollow microspheres as sustained-released drug carriers is presented. The as-prepared PBAT/PVP composites show faster degradation rate and drug (Erlotinib) release than that of PBAT. Furthermore, PBAT/PVP composites loaded with Erlotinib provide sustained release effect, thus achieving a better efficacy than that after the direct injection of erlotinib due to the fact that the composites allow a high drug concentration in the tumor for a longer period. Hence, this work provides a potential effective solution for clinical drug therapy and tissue engineering using drug microspheres with a sustained release.

In-situ construction of Bi2S3/Bi2MoO6 hollow microsphere with regulable oxygen vacancies for full-spectrum photocatalytic performance

Novel Bi2S3/Bi2MoO6 hollow microsphere composites with oxygen vacancies were successfully synthesized through in-situ anion exchange and hydrothermal method. After introducing sulfur into the Bi2MoO6 substrate with oxygen vacancies, Bi2S3 was close distributed on the surface of the Bi2MoO6 hollow microsphere to form Bi2S3/Bi2MoO6 heterojunctions and led to inducing the more oxygen vacancies. Compared to pristine Bi2MoO6 and Bi2S3, the Bi2S3/Bi2MoO6-0.03 exhibited higher photocatalytic efficiency toward Rhodamine B (RB) degradation under the full-spectrum (visible and near-infrared) light illumination. Meanwhile, it showed high near-infrared photocatalytic activity for antibiotics. The enhanced catalytic performance was attributed to the synergetic effect of heterojunction and the oxygen vacancies between Bi2MoO6 and Bi2S3. Meanwhile, the active species were carefully investigated by the active species capture tests and the electron spin resonance technique. Finally, the reasons for the improved photocatalytic performance and reaction mechanism were also uncovered in detail, and degradation products obtained by N-de-ethylation by the cleavage of CN of RB were demonstrated. The findings in this work provide insight into the potential applications in treating wastewater.

Synthesis and Study of the Composition of Hollow Microspheres of NiO and NiO/Ni Composition for Thermoelectrochemical Energy Converters of Low-Potential Temperature Gradients of Thermal Units Into Electricity

The article investigates the influence of the reduction modes of hollow nickel oxide microspheres synthesized by the pyrolysis of ultrasonic aerosols on the ratio of the oxide and metallic forms of nickel in their structure. The synthesis of microspheres from an aerosol of an aqueous solution of nickel nitrate was carried out; their composition and morphology were studied. The reduction of microspheres was carried out in a stream of hydrogen at different temperatures. The ratio of metallic nickel and oxide was determined by two different methods: according to the data of thermogravimetric analysis and by the Rietveld method based on the results of x-ray phase analysis. It is shown that the proportion of metallic nickel increases with an increase in the reduction temperature to approximately 375°C and then changes insignificantly. The fractional composition of microspheres was determined.

Synthesis and study of the composition of hollow microspheres of composition NiO and NiO / Ni for thermoelectrochemical energy converters of low-potential temperature gradients of thermal aggregates into electricity

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Degradation of acetaminophen by activated peroxymonosulfate using Co(OH)2 hollow microsphere supported titanate nanotubes: Insights into sulfate radical production pathway through CoOH+ activation

Pharmaceuticals and personal care products (PPCPs) are of great concern due to their increasing health effects, so advanced treatment technologies for PPCPs removal are urgently needed. In this study, titanate nanotubes decorated Co(OH)2 hollow microsphere (CoM/TNTs) composites were synthesized by a two-step solvothermal method, and used to activate peroxymonosulfate (PMS) through heterogenous catalysis for acetaminophen (ACE) degradation in water. The optimum material (CoM/TNTs0.5) activated PMS system exhibited high ACE removal efficiency and quick kinetic, as 93.0% ACE was degraded even within 10 min. The two components in CoM/TNTs showed a synergetic effect on PMS activation for radicals production: Co(OH)+ from CoM was the primary active species to active PMS, while TNTs could offer abundant –OH groups for Co(OH)+ formation. Density functional theory (DFT) calculation further interpreted the mechanism of Co(OH)+ for PMS activation by means of reaction potential energy surface (PES) analysis. Both the scavenger quenching tests and electron paramagnetic resonance analysis revealed that the sulfate radical (SO4-·) played a dominant role in ACE degradation. Moreover, DFT calculation also suggested that the ACE atoms with high Fukui index (f-) represented the active sites for electrophilic attack by SO4-·. The toxicity analysis based on quantitative structure-activity relationship (QSAR) verified the reduced toxicity of transformation products. Furthermore, CoM/TNTs also had good reusability and stability over five cycles. This work provides deep insights into the reaction mechanisms of radical production and organics attack in cobalt-based PMS activation system.

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.

Highly Active Zinc Sulfide Composite Microspheres: A Versatile Template for Synthesis of a Family of Hollow Nanostructures of Sulfides.

Hollow nanostructures of metal sulfides have gained tremendous attention in catalysis, biomedicine, and energy storage and conversion owing to their intriguing structural features and fascinating physicochemical properties. Here, we reported a hard template-engaged cation exchange method to fabricate a family of binary or ternary metal sulfide (CuS, Ag2S, Bi2S3, CuxBi1-xS, ZnxCo1-xS, ZnxCd1-xS, ZnxNi1-xS, and ZnxMn1-xS) hollow microspheres via adjusting the reaction kinetic parameters including solvent and temperature in the presence of unique ZnS composite microspheres. Particularly, the shell layer thickness of metal sulfide hollow microspheres could be modulated by manipulating the reaction temperature during the cation exchanging procedure. Meanwhile, the desired elementary composition of ternary metal sulfide hollow microspheres could be achieved by varying the mole ratio and species of the metal source. This synthetic strategy could be extended to rationally design and construct other metal sulfide hollow nanostructures and provide a deep insight into the nucleation and growth process of the metal sulfide hollow microspheres with well-controlled composition and microstructures.

Use of glass granules to produce effective gypsum composites

The possibility of using glass hollow microspheres in self-reinforced gypsum composites in the work is investigated. The need to use microspheres for gypsum products is dictated by modern high requirements for safety and environmental protection to construction sites and the building materials industry. The dispersion characteristics and grain composition of Russian production glass hollow microspheres, as well as the main component, a gypsum binder, were studied. It was established that all compositions contain particles of micro- and nanometer size. It is shown that glass microspheres provide the structure of a composite with a hardened matrix a low density while maintaining the necessary strength without the introduction of expensive and environmentally unsafe chemical additives.

Mechanical property modifications of microsphere glass induced by Ar ion irradiation

In order to study the mechanical properties of ion irradiated hollow glass microspheres, the glass sample with the same composition of the hollow glass microspheres was irradiated by Ar ions. Combining with the annealing treatment, the mechanical properties of microsphere glass were studied by means of nanoindentation. The results show that the hardness and modulus of the microsphere glass are decreased after ion irradiation, and the recovery resistance is obviously increased. After annealing, the hardness and modulus of unirradiated samples showed an upward trend, and the recovery resistance did not change within the error range; the hardness of the irradiated microsphere glass is increased, while the modulus and the recovery resistance are significantly decreased. After annealing at around 300 ℃, the recovery resistance of the irradiated sample is the same as the unirradiated sample within the error range.

Construction of Layered Double Hydroxides/Hollow Carbon Microsphere Composites and Its Applications for Mutual Removal of Pb(II) and Humic Acid from Aqueous Solutions

Development of a highly efficient material with large specific area was scientifically and technologically important for simultaneous elimination of inorganic and organic pollutants from wastewater. In this work, layered-double-hydroxides-coated (LDHs-coated) hollow carbon microsphere composites (HCMSs; LDHs/HCMSs) were fabricated using carbon spheres as templates via a hydrothermal method and were then applied for mutual removal of Pb(II) and humic acid (HA) under various experimental conditions, i.e., pH, ionic strength, contact time, addition sequences, and coexisting ions. The results indicated that the copresence of Pb(II) and HA facilitated single target pollutant [Pb(II) or HA] adsorption at pH < 8.0. The adsorbed HA was responsible for the improvement of Pb(II) adsorption, primarily as a result of the formation of HA-Pb-LDHs/HCMSs ternary complexes. Competitive adsorption of Cu(II), Co(II), Pb(II), and Ni(II) ions on LDHs/HCMSs was also investigated, and the LDHs/HCMSs had the affinity in the orde...

Magnetically separable and recyclable Fe3O4–polydopamine hybrid hollow microsphere for highly efficient peroxidase mimetic catalysts

Magnetic Fe3O4–polydopamine (PDA) hybrid hollow microspheres, in which Fe3O4 nanoparticles were firmly incorporated in the cross-linked PDA shell, have been prepared through the formation of core/shell PS/Fe3O4–PDA composites based on template-induced covalent assembly method, followed by core removal in a tetrahydrofuran solution. The morphology, composition, thermal property and magnetic property of the magnetic hybrid hollow microspheres were characterized by SEM, TEM, FT-IR, XRD, TGA, and vibrating sample magnetometer, respectively. Results revealed that the magnetic hybrid hollow microspheres had about 380nm of inner diameter and about 30nm of shell thickness, and 13.6emug−1 of magnetization saturation. More importantly, the Fe3O4–PDA hybrid hollow microspheres exhibited intrinsic peroxidase-like activity, as they could quickly catalyze the oxidation of typical substrates 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide. Compared with PDA/Fe3O4 composites where Fe3O4 nanoparticles were loaded on the surface of PDA microspheres, the stability of Fe3O4–PDA hybrid hollow microspheres was greatly improved. As-prepared magnetic hollow microspheres might open up a new application field in biodetection, biocatalysis, and environmental monitoring.

Controlled growth of CuO/Cu2O hollow microsphere composites as efficient visible-light-active photocatalysts

Copper oxide composites with tunable composition and morphology were hydrothermally synthesized and used as highly efficient photocatalysts towards the degradation of dye pollutants under visible light irradiation. Effects of key synthesis reaction parameters, i.e., soft template (P123), pH of precursor solution, hydrothermal reaction temperature, the durations on the resultant copper oxide structures have been systematically investigated and a tentative mechanism was proposed for the formation of the copper oxide composites with different synthesis reaction parameters. Furthermore, the photocatalytic activities of resultant copper oxide materials towards the degradation of dye (methyl orange) demonstrated strong dependence on the compositional and morphological properties of the photocatalysts. CuO/Cu2O hollow microsphere composites exhibited the highest visible light photocatalytic activity that can be attributed to their unique hollow structure and CuO/Cu2O heterostructure. The demonstrated controlled growth of metal oxide composite hollow structure provides enlightenments in fabrication of highly efficient heterostructured photocatalysts for environmental remediation.

Characterization of maxillofacial silicone elastomer reinforced with different hollow microspheres

The composition and properties of silicone–hollow microsphere composites were studied in view of establishing a new type of maxillofacial prosthesis material. Two types of microspheres were used in different concentrations and were well dispersed in the silicone matrix. The mechanical properties of the composites were evaluated. Expancel hollow microspheres improve the density, Shore A hardness, and breaking elongation of the materials but degrade their tensile strength, tear strength, and dynamic mechanical properties, while opposite trends were observed with hollow SiO2 microspheres. Ideal properties for maxillofacial prosthetic applications can thereby be obtained by blending the two types of hollow microspheres in specific proportions.

Enhanced visible light photocatalytic degradation of Rhodamine B by Bi/Bi2MoO6 hollow microsphere composites

Bi/Bi2MoO6 hollow microsphere (BMO-HMS) composites were successfully synthesized via a microwave-assisted reaction of a Bi2MoO6 precursor in an ethylene glycol solution using a microwave synthesis system and subsequent annealing in a nitrogen atmosphere. The morphology, structure and photocatalytic performance of the composites in the degradation of Rhodamine B (RhB) were characterized by scanning electron microscopy, X-ray diffraction, electrochemical impedance spectra, UV-vis absorption spectroscopy, Raman spectroscopy and nitrogen adsorption–desorption, respectively. The results show that the BMO-HMS composites exhibit enhanced photocatalytic performance in the degradation of RhB with a maximum degradation rate of 91% under visible light irradiation compared with the pure Bi2MoO6. The improved photocatalytic performance is ascribed to the enhanced light absorption and the reduced electron–hole pair recombination with the presence of Bi in the composites.

Template-induced covalent assembly of hybrid particles for the facile fabrication of magnetic Fe3O4–polymer hybrid hollow microspheres

Magnetic Fe3O4–poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) hybrid hollow microspheres, in which Fe3O4 nanoparticles were firmly incorporated in the cross-linked PZS shell, have been fabricated through the formation of core/shell PS/Fe3O4–PZS composites based on template-induced covalent assembly method, followed by core removal in a tetrahydrofuran solution. The morphology, composition, thermal property, and magnetic property of the magnetic hollow microspheres were characterized by scanning electron microscope, transmission electron microscope, Fourier transform infrared spectra, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometer respectively. Results indicated that the typical hollow microspheres had about 950 nm of inner diameter and about 210 nm of shell thickness, 440 °C of initial decomposition temperature under nitrogen atmosphere, and 13.3 emu g−1 of magnetization saturation. Furthermore, the shell thickness of magnetic hollow microspheres could be easily controlled by tuning the mass ratio of PS to comonomers. As-fabricated hybrid hollow microspheres exhibit great potential as good catalyst supports.

Effect of hybrid phenolic hollow microsphere and silica-filled vinyl ester composites

Study on phenolic hollow microspheres (PHMS)-filled vinyl ester (VE) composites has been carried out. Effect of adding PHMS fillers at different filler loading on flexural, impact, and thermal properties were studied. The impact strength increased with the addition of PHMS fillers but at the expense of flexural strength, flexural modulus, and thermal stability of the composites. The second stage of this article aims to study the effect of adding silica as second filler in PHMS-filled VE composite system, and the influence of silane treatment on the mechanical properties of silica/PHMS/VE hybrid composites. PHMS/VE composites filled with silane-treated silica were found to show an increase in flexural modulus with increasing filler content. On contrary, the untreated silica fillers were observed to provide reinforcing effect in PHMS/VE composites at rather low filler concentration. The flexural strengths of silica/PHMS/VE hybrid composites were found to decrease with addition of silica content in the composites, and further decreased with increasing in silica content for both untreated and treated silica/PHMS-filled VE composites. Addition of silane-treated silica in the composites also provided an increase in the impact resistance of the PHMS/VE composites. Interestingly, the addition of silica and PHMS fillers in VE matrix has resulting in low density composites with improved flexural modulus and impact resistance.

Preparation and characterisation of ZnO nanorod array-coated hollow glass microsphere composites

Uniform and oriented ZnO nanorod arrays on the surface of hollow glass microspheres (HGMs) were fabricated by using a seed growth process in aqueous solution of zinc nitrate and hexamethylenetetramine at low temperature. The structure and morphology of as-obtained ZnO nanorod array-coated hollow glass microsphere (HGM/ZnO) composites were analysed by using X-ray diffraction and scanning electron microscopy. The results showed that all the HGMs were coated with a well-aligned layer of ZnO nanorod arrays and the ZnO nanorods possessed relatively uniform hexagonal rod structures and stood perpendicular. Moreover, the ZnO nanorod arrays were affected by a variety of growth conditions such as the growth solution concentration and the solution temperature.

Preparation and characterization of WO3/TiO2 hollow microsphere composites with catalytic activity in dark

The WO3/TiO2 hollow microsphere composites with the diameter of 3–5μm were prepared by an alcohothermal method. The obtained composites were characterized by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen sorption isotherms and ultraviolet–vision spectroscopy (UV–vis). After light irradiation, the catalytic activity of the pure TiO2 hollow microspheres and the WO3/TiO2 composites in dark was evaluated by the degradation of methyl orange (MO) in aqueous solution. The results indicated that the presence of WO3 may be responsible for more preferable properties and the catalytic activity in dark of the composites. Compared with the pure TiO2, the WO3/TiO2 hollow microsphere composites provided the higher specific surface area and the wider absorption wavelength range. In particular, the maximum degradation efficiency in dark reached 22% as the WO3 content of the hollow microsphere composites was 15mol%.

Hollow polyaniline/Fe 3O 4 microsphere composites: Preparation, characterization, and applications in microwave absorption

Hollow polyaniline/Fe 3O 4 microsphere composites with electromagnetic properties were successfully prepared by decorating the surface of hollow polyaniline/sulfonated polystyrene microspheres with various amounts of Fe 3O 4 magnetic nanoparticles using sulfonated polystyrene (SPS) as hard templates and then removing the templates with tetrahydrofuran (THF). The synthesized hollow microsphere composites were characterized by FT-IR, UV/Vis spectrophotometry, SEM, XRD, elemental analysis, TGA, and measurement of their magnetic parameters. Experimental results indicated that the microspheres were well-defined in size (1.50–1.80 μm) and shape, and that they were superparamagnetic with maximum saturation magnetization values of 3.88 emu/g with a 12.37 wt% content of Fe 3O 4 magnetic nanoparticles. Measurements of the electromagnetic parameters of the samples showed that the maximum bandwidth was 8.0 GHz over −10 dB of reflection loss in the 2–18 GHz range when the Fe 3O 4 content in the hollow polyaniline/Fe 3O 4 microsphere composites was 7.33 wt%.