Monodisperse Microspheres Research Articles

Three-dimensional monodispersed TiO2 microsphere network formed by a sub-zero sol-gel method

The monodispersed TiO2 microspheres were synthesized by a sub-zero sol-gel method followed by calcination. The precursor was prepared by hydrolysis of tetrabutyl titanate at −10 °C. The influence of the post-calcination temperature on the particle morphology and the crystal properties was investigated. The microspheres have possessed excellent thermal stability without anatase-to-rutile transformation even at 900 °C, probably due to the stabilized microstructure of a honeycomb mesh. The photocatalytic activity for oxidative decomposition of methyl orange depends on the morphology and the crystalline properties, being the highest for highly crystallized and mesoporous sample, prepared at 700 °C calcination.

Synthesis of Diatomite-Based Mesoporous Wool-Ball-Like Microspheres and Their Application for Toluene Total Oxidation Reaction.

Diatomite (DE) has attracted considerable attention owing to its abundance, low cost, and potential for a wide variety of applications. This work reports the development of mesoporous wool-ball-like (WBL) microspheres from natural DE through a simple hydrothermal treatment. We discovered that the presence of cetyltrimethylammonium bromide is a prerequisite for generating monodispersed WBL microspheres. The mechanism for the transformation of pristine DE into mesoporous microspheres through dissolution–recrystallization was clearly investigated. Interestingly, the microspheres exhibited a specific surface area 25–60 times larger than that of the pristine DE. The application of WBL microsphere DE as an effective support for metallic catalysts in the toluene total oxidation reaction was demonstrated.

Dye-Doped ZnO Microcapsules for High Throughput and Sensitive Optofluidic Micro-Thermometry.

The main objective of this work is to show the proof of concept of a new optofluidic method for high throughput fluorescence-based thermometry, which enables the measure of temperature inside optofluidic microsystems at the millisecond (ms) time scale (high throughput). We used droplet microfluidics to produce highly monodisperse microspheres from dispersed zinc oxide (ZnO) nanocrystals and doped them with rhodamine B (RhB) or/and rhodamine 6G (Rh6G). The fluorescence intensities of these two dyes are known to depend linearly on temperature but in two opposite manner. Their mixture enables for the construction of reference probe whose fluorescence does not depend practically on temperature. The use of zinc oxide microparticles as temperature probes in microfluidic channels has two main advantages: (i) avoid the diffusion and the adsorption of the dyes inside the walls of the microfluidic channels and (ii) enhance dissipation of the heat generated by the focused incident laser beam thanks to the high thermal conductivity of this material. Our results show that the fluorescence intensity of RhB decreases linearly with increasing temperature at a rate of about −2.2%/°C, in a very good agreement with the literature. In contrast, we observed for the first time a nonlinear change of the fluorescence intensity of Rh6G in ZnO microparticles with a minimum intensity at a temperature equal to 40 °C. This behaviour is reproducible and was observed only with ZnO microparticles doped with Rh6G.

Spray-coated monodispersed SnO2 microsphere films as scaffold layers for efficient mesoscopic perovskite solar cells

Mesoporous SnO2 microspheres are a class of promising electron transport materials for mesoscopic perovskite solar cells, but a smooth and dense film as requested by electron transport layer is difficult to realize using the microspheres. Here, a series of monodispersed SnO2 microspheres with high specific surface area and good crystallinity are synthesized via a surfactant-free solvothermal method. These SnO2 microspheres showing small diameters of about 75, 110 and 200 nm with narrow size distribution are achieved by precisely controlling the crystal growth process. They are suitable for constructing the electron transport layers whose thickness is only about hundreds nanometers. Besides, as the microspheres easily slip off from the substrate during the conventional spin coating process, the spray coating method is exploited to prepare high quality electron transport layers. As a result, a power conversion efficiency of 16.85% is yielded by using the 75 nm sized SnO2 microspheres as the electron transport layers. This high power conversion efficiency is attributed to the fast electron transport and inhibited charge recombination. To further improve the charge transfer between the electron transport layer and perovskite layer, graphene quantum dots are added into the SnO2 microspheres, and a best efficiency of 17.08% is obtained.

Asymmetric Morphology Transformation of Azo Molecular Glass Microspheres Induced by Polarized Light.

In this work, photoinduced asymmetric morphology transformation of a type of azo molecular glass microspheres was thoroughly investigated to understand the effects of controlling factors on the process, related mechanism and unique functions. The monodispersed microspheres with their sizes over ten microns were fabricated from an isosorbide-based azo compound (IAC-4) by microfluidics. Under irradiation with linearly polarized light, the ten-micron-scale microspheres were transformed into three-dimensional (3D) asymmetric particles through directional mass transfer. Microscopic observations and optics simulation were employed to investigate the morphology transformations. The results show that the penetration depth of light at different wavelengths plays an extremely important role to affect the asymmetric deformation behavior of the IAC-4 microspheres, which determines deformation region, deformation degree and final shapes of the particles. The light intensity (50-200 mW/cm2) is a less important factor, while the deformation rate of the light-penetrated part linearly increases with the intensity. When the light intensity varies in this range, the deformation degree and the final asymmetric morphology are determined by exposure energy (light intensity × irradiation time). The IAC-4 microspheres with different sizes show distinct morphology transformation behavior and the deformed particles possess different shapes, caused by the variation of volume fraction of the light-penetrated part in the microspheres. The increase in the ratio of the light-penetrated part to the total volume of the microspheres results in larger scale deformations. Based on the above understanding, asymmetric particles with various morphologies can be fabricated through a precisely controllable way. The asymmetric particles loaded on various surfaces show ability to render remarkable wetting anisotropy of water droplets on the substrates.

A facile route to preparation of immobilized cellulase on polyurea microspheres for improving catalytic activity and stability

Abstract The input-output ratio of the immobilization process is crucial to determining whether the immobilized cellulase can truly participate in industrial production. This study reports a simple, efficient and environmentally friendly method for covalent immobilization of cellulase on uniform, monodisperse polyurea microspheres. The reported method offers several benefits including (i) polyurea microspheres can be obtained after one step reaction without any shaking or stirring at room temperature, (ii) Without any modification, the surface of polyurea microspheres contains abundant amine groups for immobilized cellulase, (iii) Compared with porous materials, cellulase was immobilized on the surface of the support, leading to less mass transfer resistance during immobilization and catalytic reaction. The support and immobilized cellulase were characterized by SEM, TEM, AFM, FT-IR, TGA. The immobilized cellulase demonstrated a high recovery of activity (77.9%) and showed improved thermostability, pH tolerance, reusability and lifetime. Notably, the immobilized cellulase exhibited a superior performance after 36 h in the continuous process. More interestingly, trace amounts of dimethyl sulfoxide was found to promote cellulase activity. This work provides a simple and practically method for promising applications as biocatalyst in cellulose hydrolysis and an effective strategy for the immobilization of other enzymes in green chemical industry.

Simple method to generate calibrated synthetic smoke-like atmospheres at microscopic scale.

Artificial smokes focusing on macroscopic or fluid properties of smoke have been available for a long time. This paper presents a simple method to generate fully customizable smoke-like atmospheres at microscopic scale (i.e. considering their constituent particles as discrete elements) using a different approach. Synthetic, reproducible media can be generated combining monodisperse microspheres with known geometrical and optical properties conveniently parameterized. The method is presented as a proof-of-concept, highlighting the design decisions along with their implications. Practical issues such as aerosol nebulization, particle carrier selection or the features of the medium chamber where the smoke-like atmosphere is to be tested are analyzed. A comparison between methanol and ethanol as carriers for polystyrene microsphere nebulization is also made. The method could be the seed for the obtention of standard reference media for calibration or standardized characterization of not only smoke detectors and exhaust smoke sensors but also other instruments relying on optical properties of dispersive media (dust in PV panels, public lighting, etc.).

Tailoring structure of Ni-rich layered cathode enable robust calendar life and ultrahigh rate capability for lithium-ion batteries

Tailoring the structure of Ni-rich ternary layered cathode is considered as an effective way to solve its poor cycling and rate capability. Herein, a special structure of Ni0.6Co0.2Mn0.2(OH)2 precursor, in which strips composed of lamellar primary particles are vertically inserted, is rationally designed through feasible industrialized co-precipitation process. Particularly, precursor possesses a loose interior and dense exterior structure by observation of cross section. After sintering, LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode shows monodispersed microspheres whose external surface is tightly wrapped rod-like primary particles. Moreover, NCM622 microspheres inherits the properties of Ni0.6Co0.2Mn0.2(OH)2 precursor, displaying hollow structure and aligned primary particles along the radial direction. NCM622 cathode shows optimal electrochemical properties in the voltage window of 2.8–4.4 V. It displays a revisable capacity of 142.4 mAh g−1 (79.3% for capacity retention ratio) after 300 cycles under current density of 1 C. A reversible capacity of 110.3 mAh g−1 can be obtained after 500 cycles even at current density of 3 C, and corresponding capacity decay rate is only 0.068% for each cycle. The tailored cathode has great potential applications in batteries of high-power and long calendar life as well as provides an idea for structural design of high nickel cathode.

A Novel Method for Rapid Fabrication of Colloidal Clusters.

In this work, a novel method was proposed to prepare two kinds of colloidal clusters. One was unitary cluster composed of monodisperse microspheres, the other was binary cluster consisting of bidisperse particles (large microsphere and small nanosphere). Each unitary cluster with fixed number (n) of monodisperse microspheres had its own unique configuration. Most unitary clusters had the configurations identical with the theoretical geometries, while some clusters were not the theoretical clusters. For binary clusters, a fascinating phenomenon was that the presence of nanospheres could not change the configuration of large microspheres, but just could affect their morphologies.

Preparation of monodisperse ZrO2 ceramic microspheres (>200 μm) by co-axial capillary microfluidic device assisted internal gelation process

Abstract The internal gelation process was combined with a co-axial capillary microfluidic device to prepare monodisperse ZrO2 ceramic microspheres. Large sized gel microspheres in the range of hundreds of micrometers could be produced with the capillary microfluidic device with co-axial flow structure and the large sized outlet tubing. After drying and sintering, large sized ZrO2 ceramic microspheres (>200 μm) which had good sphericity and narrow size distribution were prepared.

Capillary-Based Microfluidic Fabrication of Liquid Metal Microspheres toward Functional Microelectrodes and Photothermal Medium

Liquid metals (LMs) possess tremendous potential applications in flexible electronic devices, heat flow management, and smart actuators. Splitting the bulk LMs into microspheres is of great significance to fabricate free-standing and microscale LM-based functional materials and devices. However, it is difficult to disperse the bulk LMs into microspheres because of their large surface tension and high density. In this work, the capillary-based microfluidic chip is employed to continuously and automatically generate LM microspheres in a large scale. The capillary-based microfluidic fabrication is universally applicable in ionic aqueous solution, hydrophobic solution, and the polymeric aqueous solution. The precise size control of LM microspheres can be easily realized by the co-flowing configuration in the microchannels. The coefficient of size variation of monodispersed LM microspheres can be controlled to as low as 0.47%. The free-standing LM microspheres can be used as functional microelectrodes within a wide temperature range from -19.8 to 20 °C and to fabricate tunable integrated circuits with different output powers. Most importantly, the LM microspheres exhibit photothermal property, which is used to make the optical sensor with linear response and to conduct the solar energy harvesting. The capillary-based microfluidic fabrication of LM microspheres provides a facile and templated methodology for processing bulk LMs into microscale units. The LM microspheres with excellent electrical conductivity and photothermal property hold great promise for the development of miniature soft electronics, light-driven actuators, and energy conversion medium.

Hollow Fe3O4 microspheres/graphene composites with adjustable electromagnetic absorption properties

Fe3O4@rGO composites, consisting of monodisperse hollow Fe3O4 microspheres with an average particle size of 320 nm and reduced graphene oxide, were prepared by using a facile and efficient two-step solvothermal method. Compositions, microstructure and electromagnetic properties of the Fe3O4@rGO composites were systematically studied by using various analytical techniques. Compared with the hollow Fe3O4 and bare rGO, the Fe3O4@rGO composites have significantly higher electromagnetic absorption performances. A maximum reflection loss (RL) of −49.8 dB was achieved at 8.48 GHz, with a wide bandwidth of 3.3 GHz from 6.6 GHz to 9.9 GHz, when the Fe3O4@rGO composites with a Fe3O4 to rGO mass ratio of 2:1 were synthesized at 200 °C for 7 h by using ethylene glycol as the hydrothermal solvent. The absorption covered the mid-low frequency X-band, while the optimum match thickness was 3.0 mm. The peak position of the minimum reflectance of the Fe3O4@rGO composites shifted to lower frequencies with increasing content of Fe3O4. The electromagnetic absorption properties of the Fe3O4@rGO composites could be adjusted by controlling the mass ratio of the two components, reaction time and the sample thickness. SuchhHollow Fe3O4 microspheres/graphene composites could be used as light-weight microwave absorption materials at the mid-low frequency bands.

Preparation and characterization of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) microspheres for controlled release of buprofezin.

Extensive application of pesticides has caused a lot of environmental pollution and health problems, prompting the development of highly efficient and lowly toxic pesticide formulations. Here, buprofezin (BPF)-loaded poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-HH)) microspheres were prepared by O/W emulsion/solvent evaporation method. Under optimal conditions (P(HB-HH) 7.07% (w/v) and PVA 1.84% (w/v)), the spherical and monodispersed microspheres were obtained. The average particle size, pesticide loading (PL), and encapsulation efficiency (EE) of the optimized microspheres were 1.2μm, 15.68%, and 78%, respectively. Release of 80% BPF from the microspheres in pH 5 (192h) was faster than that in pH 7 (228h) and 8 (204h). Moreover, kinetic analysis indicated that BPF release behaved in a non-Fickian diffusion manner (0.43 <n< 0.85) and the release mechanism was the combined effects of pesticide diffusion and hydrolysis of polymer. The bioassay and toxicity results showed that encapsulation of BPF could exhibit high efficacy on the target organism and low toxicity to the non-target organism. Therefore, these results demonstrated that BPF-loaded P(HB-HH) microspheres with good stability were prepared successfully, and they could be further explored for constructing other highly efficient and lowly toxic pesticide formulations.

One-pot solvothermal synthesis of magnetically separable rGO/MnFe2O4 hybrids as efficient photocatalysts for degradation of MB under visible light

Efficient and easily separable photocatalysts with visible light response are of great importance for the degradation of organic pollutants in wastewater treatment. In this work, magnetically separable reduced graphene oxide (rGO) supported MnFe2O4 hybrids were prepared using graphene oxide and metal ions (Fe3+ and Mn2+) as starting materials via a one-pot solvothermal synthesis method. The hybrids were characterized by X-ray powder diffraction, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, Fourier Transform Infrared Spectroscopy, Ultraviolet–visible spectroscopy, and vibrating sample magnetometer. The influence of the rGO content on the morphology and catalytic performance was investigated. It was shown that monodispersed MnFe2O4 microspheres with uniform size were successfully embedded in the rGO nanosheets. The photocatalytic activity has been evaluated by photocatalytic degradation of methylene blue under visible light irradiation. Among the hybrids with various rGO contents, the hybrid (10% rGO/MnFe2O4) prepared with 10 wt% GO showed the best performance with reaction rate of 0.01443 min−1, around 6 times higher than that of MnFe2O4 (0.00248 min−1), demonstrating the important role of rGO for the photocatalytic activity. Benefiting from their considerable saturation magnetization, lower remanence and coercivity, the hybrids can be easily separated and recycled from the solution by an external magnet. This research would provide a strategy for designing efficient and magnetically recycled photocatalysts for wastewater decontamination under visible light.

Controlled synthesis of uniform hollow polypyrrole microcapsules by a cosolvent approach

A simple and effective synthetic approach is demonstrated for the formation of uniform hollow polypyrrole (PPy) microcapsules. This process entails the preparation of homogeneous polystyrene@polypyrrole (PS@PPy; core@shell) microspheres, followed by chemical extraction of the PS cores. By proper dispersion of monodispersive PS microspheres and pyrrole molecules in a water/ethanol cosolvent to minimize the diffusion of pyrrole molecules to the PS microspheres, we are able to prepare uniform PS@PPy microspheres with significantly reduced size variation, deformation, and aggregation. The PS microspheres, in diameter of 490 nm, carry negative surface charges, and after the deposition of PPy, reveal a transition from positive to negative surface charges with increasing pH values. The hollow PPy microcapsules, in diameter of 527 nm and shell thickness of 20 nm, are fabricated after selective removal of PS cores from the PS@PPy microspheres in tetrahydrofuran. Analysis tools including Fourier transform infrared spectroscopy, thermogravimetric analyzer, and zeta potential, as well as scanning and transmission electron microscopes are employed for material characterization.

Poly(glycidyl methacrylate-co-1,4-dimethacryloyloxybenzene) monodisperse microspheres - synthesis, characterization and application as chromatographic packings in RP-HPLC

The study describes the synthesis of porous microspheres with glycidyl methacrylate (GMA) and 1,4-dimethacryloyloxybenzene (DMB) using the seed swelling polymerization. As a shape template the polystyrene (PS) seed obtained via the dispersion polymerization was used. Oxirane, esters and aromatic groups are present in the structure of copolymers. Changing the reaction mixture composition – the amounts of crosslinking monomer and PS seed, almost monosized poly(GMA-co-DMB) microspheres of the diameters in the range of 8.20 μm to 11.61 μm and highly developed porous structure with specific surface area (SBET) up to 353 m2/g were obtained. The pore size distribution and the volume of pores measured for the copolymer in the dry and the swollen states differ. In the dry state in the internal copolymer structure mesopores were observed whereas in the swollen state additionally micro- and macropores appeared. The copolymer obtained with the equimolar mixture of monomers was applied as the column packing material and tested in the reverse-phase HPLC. The isocratic separation of alkylbenzenes was achieved with satisfactory resolution using the 100 × 4.6 mm i.d. column with the acetonitrile/phosphate buffer mobile phase. The theoretical plate numbers up to 12,000 were obtained for benzene as the analyte. Using the retention indices for the test compounds it was found that the retention mechanism on the studied copolymer is the sum of π-π hydrophobic interactions, dipole interactions and to a smaller extent of hydrogen acceptance interactions rather than hydrogen donation interactions.

A biomimetic hybrid material consisting of CaCO3 mesoporous microspheres and an alternating copolymer for reversed-phase HPLC.

We developed a biomineral-inspired hybrid material composed of CaCO3 and an organic polymer as a column packing material for HPLC. This material combines a hierarchical mesoporous structure and the functionality of the polymer. The surface of monodispersed mesoporous CaCO3 microspheres was modified with poly(maleic acid-alt-1-octadecene) (PMAcO) comprising hydrophobic alkyl chains and anionic carboxylate groups. PMAcO adsorbed onto the surface of CaCO3 through electrostatic interaction between Ca2+ sites and carboxylate groups, resulting in an octadecene coated microsphere interface. These microspheres were applied as a HPLC column and exhibited reversed-phase retention behavior in the separation of alkylbenzenes. This column showed high alkaline mobile phase resistance compared with the conventionally applied ODS column packing material. Quantitative analysis of the basic antidepressants clomipramine and imipramine spiked into whole blood was achieved with an alkaline mobile phase, demonstrating the potential of the biomineral-inspired material as a HPLC stationary phase for practical applications in routine analyses of basic drugs requiring alkaline mobile phases.

Hypercrosslinked strong anion-exchange polymers for selective extraction of fluoroquinolones in milk samples

In this work, hypercrosslinked strong anion-exchange polymer resins (HXLPP-SAX) were synthesized and evaluated as solid-phase extraction (SPE) sorbents for extracting fluoroquinolones (FQs) in milk samples. These particles were prepared using a protocol that was facile and cost-effective by combining hypercrosslinking reactions and quaternisation reactions in one step. After the synthesis, the morphological properties and anion-exchange, adsorption, and selectivity performances of the HXLPP-SAX resins were characterized and evaluated. It was shown that the polymers were monodisperse microspheres, with the mean diameters of 2–4 μm, ion-exchange capacity (IEC) of 0.311 meq/g, and specific surface area more than 1000 m2/g. The resins applied as SPE sorbents possessed high selectivity in the extraction of amphoteric compounds (enoxacin and enrofloxacin as the representatives) followed by HPLC-UV analysis, as compared to commercially available strong anion-exchange sorbents (Oasis MAX). The SPE-HPLC-UV method was fully validated and exhibited good linearity (10–2000 ng/g, R2 ≥ 0.997), low limits of detection (2.8–5.1 ng/g), good recoveries (85.8%–117.9%, RSDs ≤ 7.1%) and precisions (intra-day RSDs ≤ 7.7% and inter-day RSDs ≤ 9.4%). Then the method was performed the selective enrichment of six FQs (enoxacin, norfloxacin, ciprofloxacin, lomefloxacin, enrofloxacin, and sparfloxacin) in milk samples. The present results demonstrated that the proposed resins exhibited a promising potential for the enrichment and determination of FQ residues in milk samples as well as in other samples with complex matrices.

Immobilization of Myceliophthora thermophila laccase on poly(glycidyl methacrylate) microspheres enhances the degradation of azinphos‐methyl

ABSTRACTLaccase enzymes are multicopper oxidases capable of oxidizing different compounds. However, to be able to use this biocatalyst for industrial applications, their immobilization is needed. The present work investigates the immobilization of Myceliophthora thermophila laccase (MtL) on monodisperse microspheres of poly(glycidyl methacrylate) (PGMA) to be used in azinphos‐methyl degradation. The immobilization was optimized to achieve the highest activity of the immobilized enzyme. As result, the protein load obtained was 2.5 mg protein g−1 carrier (35 U g−1 of carrier). The immobilized enzymes showed a broadened pH and temperature range of optimum activity and significantly improved the storage and operational stability. Finally, the complete degradation of azinphos‐methyl using immobilized laccase was achieved after 1 h of reaction. The collected data indicate that the immobilization of MtL on PGMA microspheres is an excellent alternative to improve biochemical properties in the enzyme and to allow their efficient use in pesticides degradation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47417.

Shell-in-shell monodispersed triamine-functionalized SiO2 hollow microspheres with micro-mesostructured shells for highly efficient removal of heavy metals from aqueous solutions

For the first time, triamine-functionalized SiO2 hollow microspheres (TAS-HMSs) with shell-in-shell morphology and micro-mesoporous walls were utilized to remove some heavy metal cations namely Pb(II), Cu(II), Cd(II), and Cr(III) from aqueous solution. Moreover, a facile one-pot co-condensation methodology was applied for preparing the TAS-HMSs. Adsorption kinetics fitted by both pseudo-first-order and pseudo-second-order models (their nonlinear regressions ∼ 0.98). The equilibrium data fitted better with the Langmuir model for TAS-HMSs and the sequence of maximum adsorption capacities under optimal conditions (pH: 5.0; adsorbent dose: 5.0 mg; contact time: 120 min) was as follows: Pb(II) (295.36/mg g–1), Cu(II) (275.88/mg g–1), Cd(II) (251.67/mg g–1), and Cr(III) (192.87/mg g–1). Thermodynamic parameters, i.e. ΔG°, ΔS°, and ΔH° suggested that heavy metals adsorption onto TAS-HMSs is a spontaneous, endothermic, and physicochemical adsorption process. These findings highlight the potential usefulness of TAS-HMSs as a high efficient adsorbent for heavy metals removal.