Synthesis Of Microspheres Research Articles

Magnetic, monodisperse titania microspheres with bimodal pore size distribution by a new sol–gel templating method and their photocatalytic activity

A new sol gel templating method was developed for the synthesis of magnetic monodisperse-porous titania microspheres 5.5 µm in size. A bimodal pore size distribution including both mesoporous and macroporous regions was first reported for magnetic titania microspheres. The product obtained by developed method and its AuNP decorated forms were evaluated as photocatalyst for textile-dye degradation in batch fashion. Different from the photocatalytic degradations performed by titania nanoparticles (i.e. P25 or similar types), a decolorization process including two serial stages was observed with the magnetic-porous titania microspheres. In the first stage, the low intraparticular diffusion resistance originated from macropores and the high surface area originated from mesopores provided fast dye adsorption onto the magnetic photocatalyst and a sudden decrease in the dye concentration (i.e. fast decolorization) that was not observed with titania nanoparticles. In the second stage, a slower decolorization occurred due to the slower photochemical degradation of adsorbed dye molecules on the magnetic photocatalyst. Complete removal of dye was achieved at acidic pH, using magnetic titania microspheres. A marked enhancement in the decolorization rate was obtained by the decoration of magnetic titania microspheres with AuNPs synthesized by Martin method.

Hierarchical porous CoMn2O4 microspheres with sub-nanoparticles as advanced anode for high-performance lithium-ion batteries

To deal with the large volume change for lithium-ion batteries (LIBs), we illustrate the synthesis of CoMn2O4 microspheres with sub-nanoparticles by a hydrothermal method followed by thermal treatment. The size of microsphere is approximately 2.2 μm, and the sub-nanoparticle is about 17 nm. There is sufficient void space between CoMn2O4 microspheres with sub-nanoparticles for ensuring the well structural integrity. As advanced anode for LIBs, CoMn2O4 microspheres display stable specific capacity retention of 772 mAh g−1 over 500 cycles at a current density of 100 mA g−1. Such a kind of structure is beneficial for enhanced rate and cycling capabilities in LIBs applications, which could increase contact area between electrolyte and active materials, short path for lithium ions and electrons and accommodate the volume change with additional void space during cycling. It has a great application prospect for use as electrochemical energy storage because of the enhanced performance.

Rapid and Sensitive Detection of Cardiac Troponin I for Point-of-Care Tests Based on Red Fluorescent Microspheres.

A reliable lateral flow immunoassay (LFIA) based on a facile one-step synthesis of single microspheres in combining with immunochromatography technique was developed to establish a new point-of-care test (POCT) for the rapid and early detection of cardiac troponin I (cTnI), a kind of cardiac specific biomarker for acute myocardial infarction (AMI). The double layered microspheres with clear core-shell structures were produced using soap-free emulsion polymerization method with inexpensive compounds (styrene and acrylic acid). The synthetic process was simple, rapid and easy to control due to one-step synthesis without any complicated procedures. The microspheres are nanostructure with high surface area, which have numerous carboxyl groups on the out layer, resulting in high-efficiency coupling between the carrier and antibody via amide bond. Meanwhile, the red fluorescent dye, Nile-red (NR), was wrapped inside the microspheres to improve its stability, as well to reduce the background noise, because of its higher emission wavelength than interference from real plasma samples. The core-shell structures provided different functional areas to separate antibody and dyes, so the immunoassay has highly sensitive, wide working curves in the range of 0–40 ng/mL, low limits of detection (LOD) at 0.016 ng/mL, and limits of quantification (LOQ) at 0.087 ng/mL with coefficient of variations (CV) of 10%. This strategy suggested an outstanding platform for LFIA, with good reproducibility and stability to straightforwardly analyze the plasma samples without washing steps, thereby reducing the operating procedures for non-professionals and promoting detection efficiency. The whole detection process can be completed in less than 15 min. This novel immunoassay offers a reliable and favorable analytical result by detecting the real samples, indicating that it holds great potential as a new alternative for biomolecule detection in complex samples, for the early detection of cardiac specific biomarkers.

Synthesis and Li-storage property of flower-like SbPO4 microspheres

Hierarchical SbPO4 flower-like microspheres (SbPO4 FM) have been successfully prepared by a facile solvothermal method. The XRD, TEM, SEM and BET techniques were adopted to inspect the obtained SbPO4 products. Experimental results indicated that the as-prepared SbPO4 flower-like microspheres belonged to a monoclinic phase and were assembled by numerous nanoplates to form hierarchical porous architectures. A self-assembly mechanism accounted for the formation of the as-prepared SbPO4 flower-like microspheres. Besides, the electrochemical Li-storage property was also investigated as an anode for lithium-ion battery.

Synthesis and evaluation of porous polymethylsilsesquioxane microspheres as low silanol activity chromatographic stationary phase for basic compound separation

Polymethylsilsesquioxanes (PMSQ) are potentially useful materials for liquid chromatography owing to their unique chemical, electrical and mechanical properties. Surprisingly however, no systematic studies on the use of spherical PMSQ particles as chromatographic packing have been reported. Accordingly, we present a comprehensive study aimed to characterize the chromatographic properties of this material in high performance liquid chromatography (HPLC) and to compare them with those observed on methyl (C1) bonded silica phase under comparable conditions. Porous spherical particles were synthesized by a two-step hydrolysis and condensation procedure from methyltrimethoxysilane (MTMS) as a sole precursor. The as-synthesized microspheres possess spherical shape, narrow size distribution, mesoporous structure, high surface area (817 m2 g−1) and reasonable carbon load (16.6%). They can be used directly as the HPLC stationary phase without the need for size classification. The PMSQ phase exhibits typical reversed-phase chromatographic properties with higher methylene selectivity and low silanol activity compared with the C1 column. The retention mechanism for basic compounds was systematically evaluated by studying the effect of pH, ionic and solvent strength of the mobile phase. Basic compounds displayed lower retention factor and symmetric peak shape on the PMSQ column whereas longer retention and strong tailing peaks were observed on the C1 column. The difference in retention behavior between the two columns is explained in terms of different principal retention mechanisms. Because of the low silanol activity, retention of basic compounds on the PMSQ column is governed solely by a reversed-phase mechanism. By contrast, multiple interactions including reversed-phase, cation exchange and simultaneous reversed-phase/cationic exchange interaction contribute to the retention on the C1 column, as previously observed on other silica based reversed-phases. Furthermore, the PMSQ phase exhibited significantly enhanced stability under alkaline conditions compared with its silica-based counterpart. Taken together, the favorable morphology and pore structure combined with the benefits of low silanol activity, high pH stability and prolonged column lifetime make the newly developed PMSQ phase a promising and viable alternative to silica based reversed-phase packings for separation of basic compounds.

Fabrication of Silica Microspheres (HB/A@SI-MNS) for Hafnium and Zirconium Recovery from Zirconyl Leach Liquor

This work describes the synthesis of silica microspheres using sodium silicate obtained as a byproduct in the production of Egyptian Rosetta zircon concentrate. The obtained mesoporous silica microspheres were further modified with aminopropyltriethoxy silane and 2,4-Dihydroxybenzaldehyde to produce Schiff’s base silica sorbent (HB/A@Si-MNS). HB/A@Si-MNS was used for the selective extraction of hafnium from zircon mineral leach liqueur. The fabrication process and surface properties of HB/A@Si-MNS were confirmed by the means of X-ray Fluorescence (XRF), scanning electron microscop (SEM), energy depressive X-ray (EDX), Fourier-transform infrared spectroscopy (FT-IR), and elemental analysis. The uptake behavior of HB/A@Si-MNS towards Zr(IV) and Hf(IV) ions were studied under different experimental conditions. Adsorption curves indicate that the uptake of Zr(IV) and Hf(IV) on HB/A@Si-MNS is a spontaneous, endothermic monolayer system controlled by intraparticle diffusion. Elution efficiencies were found to be 94% and 98% for Zr(IV) and Hf(IV), respectively. The regenerated HB/A@SI-MNS showed uptake capacity comparable to that of fresh ones over 3 cycles. The results of the extraction of Hf(IV) than Zr(IV) from Rosetta zircon concentrate show that HB/A@SI-MNS has a preferential selectivity towards Hf(IV) than Zr(IV). Therefore, the studied material may be promising for the selective separation of Hf(IV) from Zr(IV).

Cell-loaded carboxymethylcellulose microspheres sustain viability and proliferation of ATDC5 cells

Cell-loaded carboxymethylcellulose (CMC) microspheres were generated via a flow focusing microfluidic device, with a final aim to obtain viable ATDC5 aggregates with sustained proliferation capacity. We synthesized various CMC with phenolic groups (CMC-Ph) and demonstrated that high CMC-Ph molecular weight, high CMC-Ph concentration (>0.8 g/ml) or long culturing period had obvious inhibition effect on ATDC5 proliferation, but low horseradish peroxidase concentration (HRP, <0.4 mg/ml) did not. CMC-Ph gels being obtained through HRP/H2O2 reaction showed an enhancing strength and decreasing break stain as the molecular weight of CMC-Ph increased, along with a decreasing gelation time. The microfluidics-based synthesis of cell-loaded microspheres with great design flexibilities was achieved using CMC-Ph with weight-average molecular weight of 1.0 × 105. ATDC5 cells were viable up to 41 days of culture and proliferated gradually with increasing culture time. High cell density in CMC-Ph solution and high fetal bovine serum concentration in culture medium were prone to forming cell aggregates. Isolated cells from the microspheres showed the typical spherical morphology of undifferentiated ATDC5. Therefore, CMC-Ph microspheres might be used as cell aggregates depots to study cell-cell or cell-biomaterials functions for tissue engineering applications.

Synthesis of hybrid microspheres from zirconium butoxide and an ionic–non-ionic copolymer

This work presents the synthesis and characterization of hybrid microspheres made of hydrated zirconium oxide and an organic copolymer. The synthesis was carried out in a two-stage procedure. First, the polymer microspheres were synthesized via the inverse emulsion polymerization of 4-vinyl benzyl trimethyl ammonium chloride (ClVBTA) and 2-hydroxy ethyl methacrylate (HEMA), and second, the copolymeric beads were impregnated with an inorganic precursor (Zr(ButO−)4) to form the hybrid through a sol-gel reaction. Several experimental variables were controlled in both stages of the synthesis, such as the formulation of the emulsion, concentration of the surfactant, molar ratio of the monomers, concentration of the inorganic precursor, and soak time. Well-defined microspheres with low polydispersity were obtained with a volume ratio of 0.2 and a low Span 80 surfactant concentration. While an increase in the ClVBTA/HEMA molar ratio enhanced the hydrophilicity of the particles, it did not necessarily increase the incorporation of oxide. Additionally, an increase in ClVBTA/HEMA decreased the resistance of the composite microspheres to the osmotic shock, resulting in rupturing of the beads. This polymer hybrid microspheres can be used in applications where surface processes are involved.

Synthesis of V2O5 microspheres by spray pyrolysis as cathode material for supercapacitors

Vanadium oxide (V2O5) microspheres have attracted considerable attention in the energy field due to their unique properties such as high stability and electrochemical activity. Here, massive V2O5 microspheres with smooth surface, hollow cavity and uniform particle sizes (0.4–1.5 μm), were synthesized by a facile spray pyrolysis process. Post-treatment at predefined temperatures effectively turned the microsphere shell into stacked nanorods with widths of 100 nm and lengths of 500 nm when processed at 500 °C for 3 h under nitrogen atmosphere, with enhanced crystallinity. When applied as cathode materials for supercapacitors, the post-treated V2O5 microspheres at 500 °C exhibited improved specific capacitance and longer discharge time. This is an effective method to manufacture massive V2O5 microspheres with tailored structure and potential applications in high-performance energy storage materials.

Low Temperature Synthesis of Nest-Like Microsphere with Exposed (001) Facets and Its Enhanced Photocatalytic Performance by NaOH Alkalization

In this study, we completed a simple low-temperature synthesis of nest-like titanium oxide (TiO2) microspheres with exposed (001) facets. For the first time, the photocatalytic performance was enhanced by sodium hydroxide (NaOH) alkalization. The characterization of as-synthesized F-TiO2 and OH-TiO2 were analyzed by field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, fourier transform infrared spectroscopic analysis, ultraviolet-vis diffuse reflection spectra and Raman spectroscopy. The photocatalytic activity of the as-prepared catalyst was evaluated through the photocatalytic degradation of methylene blue (MB) and Rhodamine B (RhB) under simulated solar light. The results showed that modification using NaOH can lead to an increase in the percentage of (001) facets from 27.8% for F-TiO2 to 39.2% for OH-TiO2. OH-TiO2 showed superior catalytic photoactivity toward MB. The mechanism of NaOH on TiO2 is also discussed.

The synthesis and application of TiO2 microspheres as scattering layer in dye-sensitized solar cells

Mesoporous TiO2 microspheres have been synthesized via a simple one-plot hydrothermal method and were used as the light scattering layer on top of the P25 TiO2 compact layer to form a double-layer film based photoanode for the dye-sensitized solar cell (DSSC). Characteristics and light scattering properties were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen sorption analysis and ultraviolet–visible spectroscopy. Photovoltaic performance of the fabricated DSSC was also investigated. It showed that photoelectric conversion efficiency of the double-layer film based DSSC was increased to 5.61% compared with single P25 compact layer film based (2.67%) and single TiO2 microspheres layer film based (2.14%) DSSC. Improvement of DSSC performance can be attributed to excellent light scattering capability given by mesoporous TiO2 microspheres. Electrochemical impedance spectra analysis also proved that double-layered structure can result in prolonged exciton lifetime, improved charge collection efficiency and decreased charge recombination.

Scalable synthesis of NiMoO4 microspheres with numerous empty nanovoids as an advanced anode material for Li-ion batteries

Closely in line with advances in next-generation energy storage materials, anode materials for lithium-ion batteries (LIBs) with high capacity and long cycle life have been widely explored. As part of the current effort, nickel molybdate (NiMoO4) microspheres with empty nanovoids are synthesized via spray drying process and subsequent one-step calcination in air. Dextrin in the atomized droplet is phase segregated during the spray drying process and calcined in air atmosphere, resulting in numerous empty nanovoids well-distributed within a microsphere. The empty nanovoids alleviate volume expansion during cycling, shorten lithium-ion diffusion length, and facilitate contact between electrode and electrolyte materials. Along with the high discharge capacity of NiMoO4 material, as high as 1240 mA h g−1 for the 2nd cycle at a high current density of 1 A g−1, uniquity of the structure enables longer cycle life and higher quality performances. The discharge capacity corresponding to the 500th cycle is 1020 mA h g−1 and the capacity retention calculated from the 2nd cycle is 82%. In addition, a discharge capacity of 413 mA g−1 is obtained at an extremely high current density of 10 A g−1.

Cu2O nanoparticles supported hydrothermal carbon microspheres as catalyst for propargylamine synthesis

Cu2O nanoparticles supported on hydrothermal carbon microsphere (HTC) have been synthesized by hydrothermal synthesis followed by chemical reduction method. The prepared catalyst was used for propargylamine synthesis from the coupling of phenyl acetylene with benzaldehyde and piperidine. In this protocol, biomass derived D-glucose was used as carbon source for the synthesis of carbon microspheres by hydrothermal treatment and CuCl2·6H2O as a copper precursor. The activity of Cu2O@HTC was compared with different catalysts such as CuFe2O4, CuCl2·2H2O, commercial CuO, and Cu2O. Among them Cu2O@HTC exhibited the best activity and selectivity for propargylamine synthesis. The catalyst was well characterized by several analytical techniques such as SEM, XRD, FTIR, TEM, ICP-AES, and XPS analysis before and after 5th reuse. The effect of various parameters was studied including solvent, catalyst loading, mole ratio and temperature of the reaction to achieve the best yield at 60 °C and 1.5 × 10−3 g/cm3 catalyst loading. Notably, Cu2O@HTC was recycled five times and found to be robust.

Scalable and sustainable synthesis of carbon microspheres via a purification-free strategy for sodium-ion capacitors

Sodium-based energy storage receives a great deal of interest due to the virtually inexhaustible sodium reserve, while the scalable and sustainable strategies to synthesize carbon-based materials with suitable interlayer spaces and large sodium storage capacities are yet to be fully investigated. Carbon microspheres, with regular geometry, non-graphitic characteristic, and stable nature are promising candidates, yet the synthetic methods are usually complex and energy consuming. In this regard, we report a scalable purification-free strategy to synthesize carbon microspheres directly from 5 species of fresh juice. As-synthesized carbon microspheres exhibit dilated interlayer distance of 0.375 nm and facilitate Na+ uptake and release. For example, such carbon microsphere anodes have a specific capacity of 183.9 mAh g−1 at 50 mA g−1 and exhibit ultra-stability (99.0% capacity retention) after 10000 cycles. Moreover, via facile activation, highly porous carbon microsphere cathodes are fabricated and show much higher energy density at high rate than commercial activated carbon. Coupling the compelling anodes and cathodes above, novel sodium-ion capacitors show the high working potential up to 4.0 V, deliver a maximum energy density of 52.2 Wh kg−1, and exhibit an acceptable capacity retention of 85.7% after 2000 cycles.

On-Chip Facile Preparation of Monodisperse Resorcinol Formaldehyde (RF) Resin Microspheres.

Monodisperse resorcinol formaldehyde resin (RF) microspheres are an important polymeric material because of their rich surface functional group and uniform structural characteristics and have been increasingly applied as an electrode material, catalyst support, absorbent, and carbon microsphere precursor. The polymerization conditions, such as the gelation/solidification temperature and the residence time, can largely influence the physical properties and the formation of the 3D polymeric network of the RF microspheres as well as the carbon microspheres. However, few studies have reported on the complexity of the gelation and solidification processes of resol. In this work, we developed a new RF microsphere preparation device that contains three units: a droplet generation unit, a curing unit, and a collection unit. In this system, we controlled the gelation and solidification processes of the resol and observed its curing behavior, which helped us to uncover the curing mechanism of resol. Finally, we obtained the optimized polymerization parameters, obtaining uniform RF microspheres with a variation coefficient of 4.94%. The prepared porous RF microspheres presented a high absorption ability, reaching ~90% at 10 min. Thus, our method demonstrated the practicality of on-chip monodisperse microspheres synthesis. The product was useful in drug delivery and adsorbing large poisonous molecules.

Prussian blue-derived synthesis of uniform nanoflakes-assembled NiS2 hierarchical microspheres as highly efficient electrocatalysts in dye-sensitized solar cells.

It's urgent and challenging to explore cost-effective and robust electrocatalyst in the development of large-scaled dye-sensitized solar cells (DSSCs). In this work, we develop a novel strategy to prepare 3D hierarchical NiS2 microspheres constructed by nanoflakes through a facile chemical etching/anion exchange reaction. Nickel–cobalt Prussian blue analogous (PBA) nanocubes and (NH4)2S are employed to initially produce uniform γ-NiOOH/NiSx hierarchical microspheres, which were then converted to uniform 3D hierarchical NiS2 microspheres by a controlled annealing treatment. Due to their favorable structural features, the as-obtained NiS2 hierarchical microspheres possess large surface areas, high structural void porosity and accessible inner surface. All of these advantages facilitate the mass diffusion and charge transport between electrolyte and counter electrode material. As a result, the titled NiS2 hierarchical microspheres exhibit excellent electrocatalytic activity toward the reduction of I3− ions in DSSCs. A typical DSSC with NiS2 achieves an impressive power conversion efficiency of 8.46% under AM1.5G illumination (100 mW cm−2), higher than that of pyrolysis Pt electrodes (8.04%). Moreover, the fast activity onset and relatively long stability further demonstrate that the NiS2 hierarchical microspheres are promising alternatives to Pt in DSSCs.

Synthesis and sensitivity of ZnO and Au-ZnO hollow microspheres

Synthesis and sensitivity of ZnO and Au-ZnO hollow microspheres

Size-controllable synthesis of NiCoSe2 microspheres as a counter electrode for dye-sensitized solar cells.

NiCoSe2 microspheres have been successfully synthesized by a facile one-step hydrothermal method at different hydrothermal temperatures. The prepared samples are divided according to their reaction temperatures (90, 120, 150 and 180 °C) and named NiCoSe2-90, NiCoSe2-120, NiCoSe2-150 and NiCoSe2-180, respectively. The diameters of the NiCoSe2 microspheres strongly depend on the different hydrothermal temperatures. When the temperature is increased to 150 °C, the size of the resultant NiCoSe2 microspheres changes from 200 to 800 nm, and the interior of NiCoSe2-150 possesses a flocculent structure. However, NiCoSe2-180 displays a cauliflower-like aggregated structure. The prepared NiCoSe2 alloys are used as high-performance Pt-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Cyclic voltammogram measurement indicates that NiCoSe2-150 CE has larger current density than Pt CE. Electrochemical impedance spectroscopy shows that NiCoSe2-150 CE has a low charge-transfer resistance of 1.8 Ω cm2. Due to their unique morphologies and well-defined interior and exterior structures, DSSCs based on NiCoSe2-120 and NiCoSe2-150 CEs achieve high power conversion efficiencies of 8.48% and 8.76%, respectively, which are higher than that of the solar cell based on Pt CE (8.31%).

Hydrothermal synthesis of flower-like molybdenum disulfide microspheres and their application in electrochemical supercapacitors.

Three-dimensional flower-like molybdenum disulfide microspheres composed of nanosheets were prepared by a hydrothermal method using ammonium molybdate as the molybdenum source and thiourea as the sulfur source. Structural and morphological characterizations were performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of MoS2 electrode were studied by performing cyclic voltammetry (CV), galvanostatic charge–discharge analysis and electrochemical impedance spectroscopy (EIS). When used as an electrode material for supercapacitor, the hybrid MoS2 showed a high specific capacity of 518.7 F g−1 at a current density of 1 A g−1 and 275 F g−1 at a high discharge current density of 10 A g−1. In addition, a symmetric supercapacitor composed of MoS2 as positive and negative electrodes was prepared, which exhibited a high energy density of 12.46 W h kg−1 at a power density of 70 W kg−1 and still maintains an impressive energy density of 6.42 W h kg−1 at a large power density of 7000 W kg−1. The outstanding performance of the MoS2 electrode material indicates its great potential for applications in high-performance energy storage systems.

Towards active macro–mesoporous hydrotreating catalysts: synthesis and assembly of mesoporous alumina microspheres

Stable macro–mesoporous alumina formed via a pore-directing-agent-free molding process shows promise for the hydrotreatment of heavy oils.