Porous Structure Of Microspheres Research Articles

The superiority of TiO2 hollow microspheres over nanoparticles upon integration into a coating formulation for VOC removal

AbstractHeterogeneous photocatalysis is a promising technology for the abatement of pollutants in the air. Practical application of this technology requires the incorporation of the photocatalyst into a coating formulation. The coating can subsequently be applied on surfaces with a large geometric area, promoting various catalytic reactions. Photocatalysts, such as TiO2, appear to be most active in the form of nanoparticles. However, there is a rising concern regarding the adverse health effects of the nano‐sized particles. In this study, we investigate the photocatalytic oxidation of isopropanol, a common VOC, and demonstrate that a water‐based acrylic coating containing TiO2 micrometer‐sized hollow spheres can outperform a nanoparticle‐based coating by a factor of 10 in the rate of isopropanol removal. The porous shell structure of TiO2 hollow microspheres enables a three‐dimensional surface porosity within the coating film, thereby enhancing the access to the active catalytic surface. Our findings underscore the importance of the catalyst morphology for practical applications of photocatalytic materials when integrated into a coating formulation.

Co-adsorption of tetracycline and copper by the thiourea-modified porous sodium alginate microspheres

The gradual increase of antibiotics and heavy metals in aquatic environments poses a serious threat to human health and ecosystems, and finding effective methods for simultaneous removal of antibiotics and heavy metals has attracted increasing concern. In this study, a novel porous structure of thiourea-modified sodium alginate microspheres (UA-Ca) was synthesized by modification with thiourea, epichlorohydrin, and calcium chloride, and was applied for the simultaneous removal of tetracycline (TC) and Cu(II) from water. The results indicated that the UA-Ca material with 1:2 mass ratio of thiourea and sodium alginate showed the highest removal of TC and Cu(II) under the reaction condition of pH= 7. The removal process of both TC and Cu(II) follows the pseudo-second-order adsorption model and Langmuir isotherm model. UA-Ca had a high adsorption capacity toward TC and Cu(II) with the maximum value of 1.099 mmol/g and 2.793 mmol/g based on the Langmuir model at 298 K, respectively. Thermodynamical parameters revealed that TC and Cu(II) adsorption is spontaneous with endothermic nature. Competing ionic cations (Ca2+、Mg2+、NH4+) and organics (sulfamethoxazole, hygromycin) had a certain inhibitory effect on the removal of TC and Cu(II) by UA-Ca, whereas the anionic ions (CO32-、PO43-、SO42-) all had little effect on its removal. Fourier transform infrared spectra and X-ray photoelectron spectroscopy analyses showed that the removal of TC and Cu(II) by UA-Ca was mainly due to electrostatic adsorption and surface complexation. This work provides a promising UA-Ca material for the effective removal of TC and Cu(II) in contaminated water.

Insight into the Li-Storage Property of Surface-Modified Ti2Nb10O29 Anode Material for High-Rate Application.

Ti-based anode materials are considered to be an alternative to graphite anodes to accomplish high-rate application requirements. Ti2Nb10O29 (TNO15) has attracted much attention due to its high lithium storage capacity through the utilization of multiple redox couples and a suitable operating voltage window of 1.0 to 2.0 V vs Li/Li+. However, poor intrinsic electronic conductivity has limited the futuristic applicability of this material to the battery anode. In this work, we report the modification of TNO15 by introducing oxygen vacancies and using few-layered carbon and copper coatings on the surface to improve its Li+ storage property. With the support of the galvanostatic intermittent titration technique (GITT), we found that the diffusion coefficient of carbon/copper coated TNO15 is 2 orders of magnitude higher than that of the uncoated sample. Here, highly conductive copper metal on the surface of the carbon-coated oxygen-vacancy-incorporated TNO15 increases the overall electronic and ionic conductivity. The prepared TNO15-800-C-Cu-700 half-cell shows a significant rate capability of 92% when there is a 10-fold increase in the current density. In addition, the interconnected TNO15 nanoparticles create a porous microsphere structure, which enables better Li-ion transportation during charge/discharge process, and experiences an enhancement after the carbon and copper coating on the surface of the primary TNO15 nanocrystallites.

Lightweight and self‐healing thermally expandable microsphere/silver composites with segregated conductive network for high‐efficiency electromagnetic interference shielding

AbstractPolymer‐based electromagnetic interference (EMI) shielding materials with lightweight, self‐healing and high shielding performance show a wide application in electronics, medicine, national defense, aerospace and other fields. However, the conflict between a good conductive network structure and obtaining low density and excellent self‐healing property brings about tremendous challenges for fabricating these polymer‐based materials. Herein, a lightweight and self‐healing thermally expandable microsphere / silver (TEM/Ag) EMI shielding composites were prepared through a thermal foaming process. Due to the segregated Ag conductive network and expanded porous microsphere structure, the TEM/Ag composites possessed low density (0.095 g/cm3) and super‐high EMI specific shielding effectiveness (2816.3 dB cm2/g). In addition, benefiting from this unique structure, the composites exhibited excellent EMI shielding durability that can withstand ultrasonic washing 6 h (100 W), ethanol (99.5% purity), strong acid (pH 2.0), strong base (pH 12.0), NaCl solution soaking and long‐term air exposure (180 days). Furthermore, the inherent long‐chain entanglement imparts the composites a self‐healing feature, and 86% of the EMI shielding effectiveness can be maintained after self‐healing procedure.

The synergistic effect of carbon and polypyrrole co-coating enhances the electrochemical performance of TiO2 microspheres for high-performance supercapacitors

Carbon and polypyrrole co-coated TiO2 microspheres (TiO2@NC@PPy) electrodes were synthesized by hydrothermal, coating and potentiostatic deposition. The carbon coating layer and polypyrrole layer can significantly improve the conductivity of the electrode, and the unique hierarchical porous microsphere structure can adsorb PPy, preventing its structural decomposition and volume expansion while enhancing the cycle stability. Therefore, the areal capacitance was increased from 2.26 mF/cm2 to 389.76 mF/cm2 at a current density of 2 mA/cm2, retaining 73.34% capacity after 2000 cycles.

Synergetic effect of 3D porous microsphere structure and activation of adenosine A2B receptor signal on promoting osteogenic differentiation of BMSCs

Biodegradable microspheres offer great potential as functional building blocks for bottom-up bone tissue engineering. However, it remains challenging to understand and regulate cell behaviors in fabrication of injectable bone microtissues using microspheres. The study aims to develop an adenosine functionalized poly (lactide-co-glycolide) (PLGA) microsphere to enhance cell loading efficiency and inductive osteogenesis potential, and subsequently to investigate adenosine signaling-mediated osteogenic differentiation in cells grown on three-dimensional (3D) microspheres and flat control. Adenosine was loaded on PLGA porous microspheres via polydopamine coating, and the cell adhesion and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) were improved on these microspheres. It was found that adenosine A2B receptor (A2BR) was further activated by adenosine treatment, which consequently enhanced osteogenic differentiation of BMSCs. This effect was more obvious on 3D microspheres compared to 2D flats. However, the promotion of osteogenesis on the 3D microspheres was not eliminated by blocking the A2BR with antagonist. Finally, adenosine functionalized microspheres could fabricate injectable microtissues in vitro, and improve cell delivery and osteogenic differentiation after injection in vivo. Therefore, it is considered that adenosine loaded PLGA porous microspheres will be of good value in minimally invasive injection surgery and bone tissue repair.

Hydrophilic polyelectrolyte microspheres as a template for poly(3,4-ethylenedioxythiophene) synthesis.

Conducting polymer polyelectrolyte microspheres are typically composed of a cationic conducting polymer and an anionic polymer. The polymer chains inside these microspheres are physically or chemically cross-linked, creating a network that enables high water retention. Poly(3,4-ethylenedioxythiophene) (PEDOT) being an electrically conductive polymer exhibits a high conductivity and has great biotechnological applications. The unique combination of properties of PEDOT containing polyelectrolyte microspheres makes them widely investigated materials for electroresponsive cells, tissue engineering, and bio-sensors. The demand to produce PEDOT with varied properties depending the specific application requires the understanding of the basic principles of template formation. In the present work, we studied the inverse suspension polymerization of p-styrenesulfonic acid in the presence of a cross-linking agent as a synthetic way for the formation of porous polyelectrolyte microspheres. We traced how the nature of the emulsifier affected both the structure of the surface layer of the microspheres and the degree of their cross-linking. The porous structure of polyelectrolyte microspheres obtained is found to promote the polymerization of EDOT in their presence throughout the entire microsphere volume. The structural characteristics of the polyelectrolyte/PEDOT complexes in relation to their electrochemical properties have been studied.

Fabrication of alginate-based microspheres with cellular structure for tuning ammonium dinitramide performance

Recently, an emerging category green of energetic material ammonium dinitramide (ADN) has exhibited promising application in propellants due to its outstanding merits in energy release and environmental friendliness. It can be considered to substitute traditional oxidizer of ammonium perchlorate (AP) in military systems and aerospace. In this paper, a novel spherical energetic composite ADN/copper alginate (CA) with a microporous structure was designed and prepared by the W/O gel emulsion method, and a desirable porous microsphere structure was obtained. Multiple characterization techniques were used to investigate the structure and properties of ADN/CA composites. The results showed that ADN crystals were homogeneously encapsulated in an alginate-gel matrix. Thermal decomposition temperature was reduced to 151.7 °C compared to ADN, while the activation energy of them was reduced from 129.73 kJ/mol (ADN) to 107.50 kJ/mol (ADN/CA-4). In addition, as-prepared samples had lower impact and frictional sensitivity than ADN. The mechanism of sensitivity reduction and decomposition are also discussed. Constant-volume combustion tests show that peak pressure of the ADN/CA-4 achieves 253.4 kPa and pressurization rate of 2750.4 kPa/s. Hence, this has a promising application in improving the combustion performance and safety performance of solid propellants.

Development of high reusability trifunctional polyethersulfones microspheres for the removal of methyl orange

This study focused on the synthesis of trifunctional microspheres with adsorption, degradation, and magnetic responsive properties. Firstly, polyethersulfones (PES) encapsulated poly(diallyldimethyl ammonia) chloride (PDDA) functionalized iron oxide (Fe3O4) microspheres were produced via phase inversion method. The PDDA/Fe3O4-PES microspheres were further coated with Fe3O4 nanoparticles (NPs) on the surface to provide the degradation ability to the formed c-PDDA/Fe3O4-PES microspheres. Characterization results such as FTIR analysis confirmed the coating of PDDA on Fe3O4 NPs, while the TGA analysis proved the excellent thermal stability of microspheres after the incorporation of PDDA/Fe3O4 NPs. BET specific surface area of microspheres was measured at 13.90 m2/g. Besides, the pH drift method confirmed the presence of positive charge on microspheres surface, which is important for the removal of anionic pollutants. Moreover, porous structure of microspheres was also observed under SEM. Formulation study was also carried out to investigate the suitable concentration for the synthesis of microspheres, including the concentration of PES polymer (1–20 wt%), the loading of PDDA/Fe3O4 NPs (1–5 wt%), and the concentration of polyethylene glycol (PEG) (1–20 wt%). The microspheres synthesized from different formulations were subjected to the batch removal of methyl orange (MO). Results showed that a 72.53 % removal of MO can be obtained under the following microspheres synthesis formulations: 10wt% of PES polymer, 2 wt% of PDDA/Fe3O4 NPs, and 5 wt% of PEG polymer. Lastly, the c-PDDA/Fe3O4-PES microspheres also demonstrated an excellent reusability as compared to pure PES microspheres. The c-PDDA/Fe3O4-PES microspheres could be reused up to 5 cycles without the need of regeneration while still maintaining high MO removal efficiency.

Aluminum as a bi-functional reducing agent for the fabrication of graphene encapsulated silicon microspheres as anodes for high-performance lithium-ion batteries

The composites of reduced graphene oxide (rGO) encapsulated porous silicon (P-Si) microspheres are constructed using metallic aluminum as a bi-functional reducing agent at low temperatures. The preparation process of P-Si is carried out in a special reactor at 300 °C. For the reaction, SiO2 is used as the silicon source and AlCl3 is added to maintain the smooth progress of the thermite reduction reaction. Subsequently, graphene oxide is reduced by aluminum powder in an acidic liquid phase system and then the P-Si/rGO composite material is constructed by freeze-drying technique. As a kind of promising anode for lithium-ion batteries (LIBs), the porous structure of silicon microspheres can relieve the internal stress caused by volume expansion and shorten the diffusion path of lithium ions during charge/discharge processses. The flexible graphene layers can adapt the volume effect of the P-Si microspheres and therefore maintain the structural stability of the composites and enhance the electrical conductivity. The obtained P-Si/rGO composite material exhibits excellent electrochemical performance, which can maintain a superior capacity of 837 mAh g−1 upon 500 cycles under a current density of 0.5 A g−1 and exhibit satisfied cycling stability with a capacity of 704 mAh g−1 after 1000 cycles at a 1 A g−1 current density.

Synthesis of porous Mn-based spinel microspheres with enhanced lithium storage properties

Mn-based spinel materials MgMn2O4 with porous structure were synthesized by reverse coprecipitation method at annealing temperature of 700–900 °C. The as-synthesized samples were compared with those prepared by solid-state reaction method. The phase, micro-morphology and cation distribution of spinel materials were studied by using X-ray powder diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The results show that the MgMn2O4 samples obtained by reverse coprecipitation method are porous microspheres, and the particle size of the samples grows with the increase of annealing temperature. The material annealed at 700 °C has the most regular morphology, and the microspheres with a diameter of about 2 µm are assembled from uniform nanoparticles (50–60 nm). X-ray photoelectron spectroscopy analysis show that all samples are mixed spinel, Mn exists in multivalent state, Mn2+ ions occupy tetrahedral sites and Mn3+ / Mn4+ ions occupy octahedral sites of spinel structure. The effects of synthesis conditions on the inversion degree (ν) of MgMn2O4 spinel were discussed. As the anode material of Li-ion batteries, the sample annealed at 700 °C shows the best electrochemical performance, and the lithium storage capacity in the first cycle is 1037.8 mAhg−1. The enhanced lithium storage properties of the anode material are due to its regular porous microsphere structure, which is conductive to contact between the electrode materials and electrolyte and improves the migration of lithium ions. In addition, the relationship between cation distribution in spinel structure and electrochemical properties was also discussed.

Generating porous polymer microspheres with cellular surface via a gas-diffusion confined scCO2 foaming technology to endow the super-hydrophobic coating with hierarchical roughness

Porous polymer microspheres have been applied in various fields due to their hierarchical morphology and extensive surface area. However, it is difficult to create porous microspheres, especially porous microspheres without solid skin layer, via conventional supercritical carbon dioxide (scCO2) foaming technology due to the fast diffusion of gas. In order to prevent gas diffusing from microspheres, a continuous polymethyl methacrylate (PMMA) phase is employed as a gas-diffusion confinement in this work. When pressure quenched, CO2 is retained in/on the polystyrene (PS) microspheres for the cell nucleation and development. Therefore, a porous PS microsphere is fabricated by a diffusion-confined scCO2 foaming technology for the first time. The prepared microsphere displays an open cellular surface and a closed cellular core. The cell structure of porous microspheres is tunable depending on the foaming parameters. This method with the advantages of simple, versatile and controllable provides a novel perspective for fabrication of porous polymer microspheres. Furthermore, a super-hydrophobic coating is constructed using polymer microspheres as fillers and beeswax as a hydrophobic agent. Compared to the arrays composed of solid microspheres, the arrays composed of porous polymer microspheres show a super-hydrophobicity, low water-adhesion, outstanding antifouling and self-cleaning property.

Synthesis and enhanced electrochemical performance of LiNi0.5Mn1.5O4 materials with porous hierarchical microsphere structure by a surfactant-assisted method

Synthesis and enhanced electrochemical performance of LiNi0.5Mn1.5O4 materials with porous hierarchical microsphere structure by a surfactant-assisted method

A Study on the Effects of Surfactant Concentration and Particle Size on Ethylcellulose Microspheres Containing Indinavir Sulphate

Microspheres containing indinavir sulfate were prepared by the emulsion solvent evaporation technique using surfactant sorbitan monooleate 80. The evaluation reports for Fourier-transform infrared spectroscopy and X-ray diffraction spectroscopy were taken to see whether the surfactant altered the physicochemical features of the produced microspheres. Scanning electron microscopy was used to observe the surface topography of the microspheres. When sorbitan monooleate 80 was employed at dissimilar concentrations, the sorbitan monooleate 80 microspheres had higher concentrations that resulted in smaller particle size as compared to the lower concentrations of sorbitan monooleate 80 microspheres, therefore, the faster release rate was observed by utilizing a higher concentration of sorbitan monooleate 80. The microspheres entrapped 71 % to 96 % of the drug and released it for up to 7 h. X-ray diffraction revealed a decrease in the crystallinity of the drug. Scanning electron microscopy analysis revealed the spherical and after dissolution detected porous structure of microspheres. The excellent fit release kinetics is accomplished with the zero-order, Higuchi plot followed by first-order, Hixson-Crowell and Korsmeyer-Peppas equations. As a result, the drug indinavir sulfate release rate was influenced by surfactant concentrations, drug-polymer ratio, particle size and the diffusion release mechanism.

Photo/electrochemical synthesis of Si@Sn microsphere composites with excellent electrochemical lithium storage

Silicon-based anode materials with significantly improved lithium storage would play an important role in the next generation high-performance lithium-ion batteries (LIBs). Herein, a simple photo/electrochemical deposition strategy is applied to synthesize a new type of porous Si@Sn composite, using the low-cost SiAl alloy microspheres as precursor. In the dark, the galvanic replacement reaction between Si and Sn2+ induces the in-situ deposition of Sn onto the porous Si microspheres. Under light illumination, both the photogenerated electrons and the electrons from the dissolution of Si lead to the reduction from Sn2+ to Sn. The porous Si@Sn microsphere composite synthesized under the conditions of light irradiation and the optimized pH (8.0) shows excellent lithium storage performance, with a reversible capacity of 1184.4 mAh g−1 after 500 cycles at 1 A g−1 and the first coulombic efficiency of 85.19%. This may be ascribed to the integral 3D porous Si microsphere structure with the embedding of more Sn nanoparticles. This work provides an easy and efficient strategy to design and synthesize the high-performance Si-based anode materials for LIBs.

Enhanced electromagnetic wave absorption properties integrating diverse loss mechanism of 3D porous Ni/NiO microspheres

The research and development of electromagnetic wave absorbing materials with light weight, thin thickness, powerful absorption, and wide frequency bandwidth is a long-term pursuing. Here, Ni/NiO microspheres were synthesized through hydrothermal reaction followed by thermal reduction process. The experimental results indicated that the electromagnetic parameters and electromagnetic wave absorption performance were seriously affected by the morphology, composition and loading of Ni/NiO microspheres. When the reduction temperature rose to 550 °C, Ni/NiO550 showed a special porous-microsphere structure which assembled by irregular Ni/NiO core-shell nanorods. The micro-size combination of porous and core-shell structures, the affluent surface area, sufficient NiO-Ni interface, high-concentration active sites were conducive to the impedance matching and diverse loss mechanism including conductive loss, interfacial polarization, dipole polarization, natural/exchange resonance and multiple scattering. Finally, 45 wt% porous Ni/NiO/paraffin composite exhibited high reflection loss (− 52.15 dB) and broad effective frequency bandwidth (3.22 GHz) at a thickness of 2.17 mm.

In Situ Electrochemical Route to Bromide Anion-Adsorbed Coral-like Porous Silver Microspheres Achieving Highly Selective Electroreduction of CO2 to CO over a Wide Potential Range

Silver catalysts play an irreplaceable role in the electroreduction of CO2 to CO. Here, we report the structure of bromide anion-adsorbed coral-like porous microspheres of silver (Ag BACPSs). They ...

Studies on Preparation, Characterization and Application of Porous Functionalized Glycidyl Methacrylate-Based Microspheres.

A one-step swelling and polymerization technique was used in the synthesis of porous glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA) monodisperse polymeric microspheres. The polystyrene (PS) seed obtained in the dispersion polymerization was used as a shape template. The presence of epoxide rings in the chemical structure of microspheres enables their post-polymerization chemical modifications involving: the Diels-Alder reaction with sodium cyclopentadienide and maleic anhydride, the reaction with 4,4′-(bismaleimido)diphenylmethane, and the thiol-Michael reaction with methacryloyl chloride and 2-mercaptopropionic acid. Changing the reaction mixture composition—the amounts of crosslinking monomer and PS seed as well as the type and concentration of porogen porous microspheres of different porous structures were obtained. Their porous structures were characterized in the dry and swollen states. The copolymers obtained from the equimolar monomers mixture modified in the above way were applied as the column packing materials and tested in the reverse-phase HPLC (High-Performance Liquid Chromatography). A few factors influencing morphology and porous structure of microspheres were studied.

Toward high-performance Li storage anodes: design and construction of spherical carbon-coated CoNiO2 materials

CoNiO2 nanosheets were prepared by a simple hydrothermal process, and then the spherical CoNiO2@C micro-nano structures composed of nanoparticles were designed by morphology reshaping for the first time. The results show that the carbon coating changes the morphology of CoNiO2, and the CoNiO2@C composite shows porous microsphere structure consisted of nanoparticles. The porous structure combined with highly conductive carbon shell indicates an improved electronic conductivity and charge transfer. The carbon shell decreases the charge-transfer resistance of CoNiO2, and thus enhances the kinetic performances. The pristine CoNiO2 and CoNiO2@C (3, 5, and 10 wt%) composites deliver charge/discharge capacities of 511.7/526.9, 811.3/826.3, 997.1/1013.1, and 1216.1/1241.8 mAh g−1 at 500 mA g−1 after 200 cycles, respectively. The carbon coating improves the reversible capacity, rate capability, and cycle performance of CoNiO2, especially at high rates. The improved rate performance, excellent cycle performance, and high kinetic performances are ascribed to the elaborate design of architecture and composition. Hence, such porous CoNiO2@C microsphere consisted of nanoparticles can be regarded as promising candidates as anode materials for lithium-ion battery.

Novel porous Si–Cu3Si–Cu microsphere composites with excellent electrochemical lithium storage

Si based alloy anode materials with remarkably enhanced electrochemical lithium storage are crucial forthe next generation high-performance lithium-ion batteries (LIBs). Herein, novel porous Si–Cu3Si–Cu microsphere composites are prepared from commercially available low-cost SiAl alloy microsphere precursor by a facile chemical reduction/etching strategy. The formation mechanism and unique microstructure of the porous Si–Cu3Si–Cu microsphere composites are elucidated, based on the physical characterizations of different intermediates and final products as well as the precursor. The final product Si–Cu3Si–Cu composite shows a porous microsphere structure, with Cu/Cu3Si nanoparticles anchoring on the Si surface and embedding in the 3D porous silicon networks. This improves the electronic conductivity of the composite and enhances the structure stability of porous Si microspheres. The as-prepared porous Si–Cu3Si–Cu microsphere composite displays an excellent electrochemical lithium storage performance, with a reversible capacity of 1401.2 mAh g−1 after 200 cycles at a relatively high rate of 1 A g−1. Based on the unique microstructures and the electrochemical experimental results, the enhanced lithium storage performance of the porous Si–Cu3Si–Cu microsphere composites is clarified.