Porous Hollow Microspheres Research Articles

A triple-functional photoanode for light harvesting enhancement in dye sensitized solar cells

To improve the photoelectric performance of dye sensitized solar cells (DSSCs), graphene oxide (GO), upconversion luminescent material NaYbF4:Ho3+ (UC) and porous hollow titanium dioxide microspheres (PHTS) were synthesized to couple with the commercial P25 for improving the light-harvesting of DSSCs. In the composited nanostructure, the GO reduces the internal charge recombination, while the UC doping broadens the absorption spectral range, both of which were applied to the novel PHTS for improving the dye adsorption capacity and light utilization. The P25, P25/GO, P25/UC/GO, P25/UC/GO + PHTS photoanodes were fabricated and the morphology and photoelectric performance were analyzed respectively. Among them, DSSC using P25/UC/GO + PHTS photoanode showed the best performance with the power conversion efficiency (PCE) reaching as high as 9.41%.

Hollow porous BiOCl microspheres assembled with single layer of nanocrystals: spray solution combustion synthesis and the enhanced photocatalytic properties

The hollow porous microspheres assembled with BiOCl nanocrystals were successfully synthesized via a facile spray solution combustion synthesis method. The microstructure, morphology, absorbance, optical properties of the samples were investigated in detail. The results show that hollow porous BiOCl microspheres have narrow band gaps (2.66–2.71 eV), and the degradation rate of rhodamine B (RhB) can reach 98% under visible light irradiation for 60 min. Furthermore, the mechanism of the photocatalytic degradation of RhB was proposed through the experiment of trapping active species. This excellent photocatalytic property can be ascribed to the larger specific surface area and the special microstructure.

A facile strategy to synthesis graphene-wrapped nanoporous copper-cobalt-selenide hollow spheres as an efficient electrode for hybrid supercapacitors

Increasing demands from the electronics industries for fast energy storage devices motivate scientists to spend a tremendous time to design and optimize electrode materials. However, optimizing the full charge cycle requires a highly efficient electrochemical performance that depends on the smart morphological and structural design of the metal compounds and achieving the right chemical composition by taking into consideration the synergistic effect between different elements and the structure effect. Energy storage systems can benefit from the use of Ternary Transition Metal Selenide (TMSe) electrodes; however, the applicability and electrochemical efficiency of these electrodes are hampered by their low active surface area and conductivity. Constructing carbonate materials by introducing binary metal atoms, as well as designing a hollow structure at the nano- and microscales could efficiently overcome these limitations. In this study, we designed a facile self-template approach to preparing porous hollow copper-cobalt selenide microspheres wrapped on conductive networks of reduced graphene oxide (rGO-CCSe). The synthesized electrode is capable of providing considerable capacity retention of 91.5% after 6000 charge cycles through smart structural design and by taking advantage of the bimetallic synergy at the atomic level, with an extremely high specific capacitance of 724 C g−1 at 2 A g−1. Besides, we fabricated an asymmetric cell by using the rGO-CCSe hollow microsphere electrode to achieve very high values for energy densities (57.8 Wh kg−1). The graphene conductive support along with the battery-type CCSe cubics creates a synergistic effect, which accounts for such a remarkable electrochemical output from the rGO-CCSe electrode. In this study, we propose a novel approach to make highly efficient electrodes that can effectively enhance the performance of hybrid supercapacitors used in modern electronic devices.

Synthesis of hollow spherical nickel oxide and its gas-sensing properties

Semiconductor metal oxides have attracted wide attention in the area of gas sensor due to that they have unique advantages in the rapid and accurate detection of harmful gases. A simple strategy is to synthesize porous NiO hollow microspheres via a simple hydrothermal method with trisodium citrate as structure guide agent is presented in this paper, and the shell of the microsphere is composed of porous and lamellar assembly units. The cavity proportion can be adjusted by changing the amount of trisodium citrate. A reasonable mechanism was proposed to explain the formation of porous NiO hollow microspheres. As a gas-sensing material, porous NiO hollow microspheres show excellent gas selectivity and rapid response recovery time for n-butyl alcohol gas. When the content of trisodium citrate was 0.10 g, the synthesized hollow sphere NiO had the highest response value (25.6) to 100 × 10–6 of n-butyl alcohol at 300 °C and the response and recovery times were only 68 and 10 s.

Poly (hydroquinone-oxovanadium (IV)) porous hollow microspheres for voltammetric detection of phenol

This study describes the synthesis of poly (hydroquinone-oxovanadium (IV)) porous hollow microspheres (poly HQVHMs) and their implementation as new modifier for voltammetric sensing of phenol (Ph). Poly HQVHMs present interesting electrocatalytic activity toward eletrooxidation of Ph in phosphate buffer solution (0.1 M, pH 2) to a well-defined oxidation peak at 0.88 V (vs. Ag/AgCl). The modified carbon paste electrode with poly HQVHMs (CPE/poly HQVHMs) displays a low detection limit of 30 nM and good linearity in the range of 0.5–150 µM. The applicability of CPE/poly HQVHMs for real sample analysis was further confirmed by the obtained recoveries in the range of 95.3 to 102.0%. Moreover, the results obtained by applying the proposed method were statistically compared with the results obtained by applying standard HPLC method. Calculated t-value showed no significant difference between our proposed method and standard HPLC method (t obtained = 0.34 < t critical = 2.57 for α = 0.05).

Macroporous microspheres consisting of thickness-controlled bamboo-like CNTs and flower-like Co3O4 nanoparticles as highly efficient bifunctional oxygen electrocatalysts for Zn–air batteries

Co3O4 nanoparticle-decorated porous hollow microspheres composed of N-doped CNTs are synthesized by spray pyrolysis. When tested as electrocatalysts for a Zn–air battery cathode, they exhibit superior bifunctional oxygen catalytic activities.

Solid dispersion improves release of curcumin from nanoparticles: Potential benefit for intestinal absorption

Curcumin-loaded nanocarriers clustered into hollow porous microspheres composed of arabic gum (AG) and xanthan gum (XG) form a solid dispersion, so-called nanoencapsulated curcumin (NEC), were investigated. In vitro study shows little or no release of curcumin from NEC into a buffer at pH 1.2, whereas a release rate of 1.4 %/h was obtained from that at pH 6.8 after 6 h, indicating intestinal absorption. In vivo evaluation in hamsters presented a peak plasma curcumin level of 400 ng/mL at 24 h after oral administration indicated an extended release of curcumin. Mucoadhesive NEC was rarely observed in stomach tissues but mostly in intestine after 72 h consumption, resulting in curcumin was detectable in plasma up to 3 days. NEC was not cytotoxic to normal fibroblasts but cytotoxic to cholangiocarcinoma cell line, suggesting anti-cholangiocarcinoma potentials. Under normal storage conditions for 3 years, up to 97 % of curcumin could be found in NEC, suggesting long-term stability. Therefore, NEC, a solid dispersion of curcumin-loaded nanocarriers in AG/XG gums, prolonged release with mucoadhesion providing enhanced intestinal absorption of curcumin and indicating cholangiocarcinoma potentials.

Biomineralization synthesis of hollow microspheres of hydroxyapatite using tea saponin as a template

ABSTRACT Porous hollow hydroxyapatite (HA) microspheres were synthesized by biomineralization using Ca(NO3)2 · 4H2O and (NH4)3PO4 · 3H2O as starting materials and tea saponin as a template. With increasing amounts of tea saponin, the HA morphology exhibited a variation from irregular floccules to rod-like, which formed a spherical prototype, and then grew into porous hollow microspheres. With further increase in the tea saponin concentration, the rods became sheet-like and then formed cross-flakes. A possible mechanism for this morphology change was also discussed.

Template Synthesis of Ag@Fe-N-Doped Carbon Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media

With the development of fuel cells, it is critical to find suitable oxygen reduction reaction (ORR) catalyst materials to replace current commercial Pt/C catalysts. On the one hand, atomically dispersed Fe-N-C with highly active Fe-Nx centers has been proved to be one of the best ORR catalysts comparable to the Pt/C. In addition, structural effects and strong metal-carrier interactions greatly improve performance. Therefore, various templates have been used for controlling the structure of Fe-N-C catalysts. For instance, polypyrrole is widely utilized as a nitrogen-rich carbon precursor, and hollow porous Fe3O4 microspheres with polypyrrole (PPy) encapsulated on the surface were pyrolyzed to obtain Fe-N-doped double-shell hollow carbon microspheres. Also, silica balls were applied as templates to fabricate hollow Fe-N-C carbon using a nano-casting method. These hollow structural Fe-N-C materials showed efficient ORR catalytic activities. On the other hand, Ag-based catalysts are also considered as possible candidates for ORR in alkaline medium due to their comparatively low cost and good CO tolerance capability. For example, Janus nanostructured Ag@N-C synthesized by pyrolyzing core-shell Ag@PPy demonstrated comparable ORR activity to the Pt/C, which was largely attributed to the synergistic effect between Ag nanoparticles and carbonized PPy shell. Therefore, rational design of porous Fe-N-C structure with Ag nanoparticles would achieve excellent ORR electrocatalysts. Herein, Ag@Fe3O4 nanoparticles were synthesized by a solvothermal method and utilized as templates, and PPy enveloped on the template surface functioned as nitrogen and carbon sources. After pyrolysis, hollow porous Fe-N-C was decorated with Ag nanoparticles, which demonstrated excellent ORR catalytic activity and durability in alkaline medium. Therefore, this study provides a new simple method for preparing Ag@Fe-N-C hybrid catalysts.

Take a cue from nature: Promoting electrocatalytic watersplitting with a helping hand of hemoglobin

Electrocatalytic water splitting is a promising approach to generating hydrogen from water. In order to enhance water splitting efficiency, it is essential to promote gas revolution from catalysts surface, reduce the over-potential of oxygen evolution (OER), and inhibit the production of the hydrogen peroxide by-product. To realize them, in this work, we take a cue from nature to promote water splitting activity of hollow porous Fe3O4 microspheres (M−Fe3O4) with the aids of hemoglobin. Hemoglobin monolayer was self-assembled on the surface of M−Fe3O4 catalysts. It transported newly-generated oxygen molecules away from catalysts surface and exhibited chiral-induced spin selectivity (CISS) effect during OER reaction. Owing to the “helping hand” of hemoglobin, the OER onset potential of hollow porous Fe3O4 microspheres reduced by 100 mV and the current density was enhanced 2 folds. The results indicate a new strategy for designing earth-abundant catalysts which combine the merits of oxygen transferring and CISS effect for electrocatalytic water splitting.

An elaborate insight of lithiation behavior of V2O5 anode

Abstract Vanadium pentoxide (V2O5) has been a promising insert-type cathode material and/or a potential high energy anode material for rechargeable lithium ion batteries (LIBs). However, the lithiation behavior of V2O5 anode has been a long-standing challenge. In this study, we design nanoflake-assembled three-dimensional hollow porous V2O5 microspheres via a one-step template-free solvothermal-based method to enhance its structural stability as well as electrochemical activity. Commendably, this original product evaluated as anode electrodes for LIBs exhibits outstanding cycling stability and rate capability. It delivers a high reversible capacity of 527 mAh g-1 after 100 cycles at 0.1 A g-1, and a stable capacity of 318 mAh g-1 at 3.0 A g-1 in the potential range of 0.01 V and 3.0 V (vs. Li/Li+). Furthermore, electrode kinetics and performance evolution was studied by use of electrochemical impedance spectroscopy (EIS). Following these efforts, a definite and tenable lithiation mechanism of V2O5 anode is presented based on redox behaviors, X-ray powder diffraction (XRD) results, and other convincing proofs, providing valuable revelation for the understanding of conversion reaction and reaction mechanism toward other vanadium oxide anode materials in lithium/sodium ions storage. Meanwhile, the research perspective and strategy presented herein can be extended to other active materials in LIBs and/or sodium ion batteries.

In-situ growth of core-shell ZnFe2O4 @ porous hollow carbon microspheres as an efficient microwave absorber

The special structure and composition are the important factors that determine the microwave absorption properties. In this study, the porous hollow carbon microsphere (PHCMS) is synthesized by the self-assembly technology, and ZnFe2O4 particles are synthesized inside the carbon sphere by in-situ preparation with taking advantage of the porous and hollow characteristics of the carbon sphere, which prepares ZnFe2O4@PHCMS composite material. The composite shows good performance in terms of minimum reflection loss and absorption bandwidth. The results show that the maximum adsorption capacity of the composite is −51.43 dB at 7.2 GHz. When the thickness is 4.8 mm, the effective absorption bandwidth of RL ≤ 10 dB electromagnetic wave is 3.52 GHz. Such enhanced electromagnetic wave absorption properties of ZnFe2O4@PHCMS are ascribed to the suitable impedance characteristic, the dipole polarization and interfacial polarization, the multiple Debye relaxation process and strong natural resonance, multiple reflection and scattering. This work provides an approach to design effective microwave absorbers having a unique structure to enhance the microwave absorption properties.

Controlled Synthesis of EDTA-Modified Porous Hollow Copper Microspheres for High-Efficiency Conversion of CO2 to Multicarbon Products.

Electrochemical reduction of CO2 into value-added products is an effective approach to relieve environmental and energetic issues. Herein, EDTA anion-modified porous hollow copper microspheres (H-Cu MPs) were constructed by EDTA-2Na-assisted electrodeposition. The faradic efficiency (FE) of ethylene doubled from 23.3% to 50.1% at -0.82 V vs RHE in nearly neutral 0.1 M KHCO3 solution, one of the highest values among copper-based electrodeposited catalysts. Apart from the favorable influence from morphology regulated by EDTA-2Na, theoretical calculations revealed that the adsorbed EDTA anions were able to create a local charged copper surface to stabilize the transition state and dimer and to assist in the stabilization by interacting with OCCO adsorbate synergistically, which contributed to the outstanding catalytic performance together.

The Gas Sensor Based on Novel Hierarchical Ni0.7Zn0.3o Hollow Porous Microspheres for VOCs Detection

Bimetallic oxides have attracted substantial interest for gas sensing since their high compositional flexibility allows for tunable properties. In this work, we design and constructed a rocksalt solid solution Ni0.7Zn0.3O with hierarchical and hollow porous microspheres by deriving from bimetallic Zn/Ni-based metal-organic frameworks for the first time. This hollow spheres are constructed with a thin shell (100 nm) that assembled with smaller nanoparticles (15~30 nm). This unique morphology would provide a high special surface area that is very advantageous for gas sensing. The gas sensing performance of this rocksalt solid solution were investigated for the first time. The gas sensor based on these Ni0.7Zn0.3O microspheres exhibits a highly sensitivity toward to low concentration about 500 parts per billion (ppb) of acetone (S=1.21), aniline (S=1.44) and TEA (S=1.34) at 350 ℃, the response/recovery speed is extremely fast (less than 15 s) and selectivity is good (its responses to 5 ppm of other VOCs, such as ethanol, benzene, xylene, formaldehyde, ammonia, methylbenzene, formamide and ethanamide are less than 1.05). Even at low temperature (~200 ℃), the sensor still shows a good gas sensing performance. Moreover, a special response mode has been found in this work. This hierarchical nanostructured rocksalt Ni0.7Zn0.3O solid solution proposes a novel gas sensing material for achieving highly selective and sensitive gas sensing performance. Figure 1

Polypyrrole encapsulation-protected porous multishelled Co3O4 hollow microspheres for advanced all-solid-state asymmetric supercapacitors with boosted reaction kinetics and stability

Transition metal oxides (TMOs) have shown great potential in high-performance supercapacitors (SCs) because of their high theoretical capacities, low cost and simple preparation process. However, considerable challenges still remain in simultaneously improving their electrical conductivity, reaction kinetics and stability. Herein, we deliberately designed a polypyrrole encapsulation-protected porous multishelled Co3O4 hollow microspheres (pMS-Co3O4/PPy) composite via a modified carbon self-templating method and in situ oxidative polymerization route. The unique porous multishelled structure of the pMS-Co3O4 hollow microspheres assembled by interconnected Co3O4 nanoparticles can provide sufficient active sites, shorted ion diffusion paths and efficiently alleviate the structural strain. Meanwhile, the PPy encapsulation-protected nanolayers significantly improve their electrical conductivity, contribute pseudocapacitance and protect Co3O4 nanoparticles from structural pulverization-chemical dissolution into electrolyte. The prepared pMS-Co3O4/PPy electrodes exhibited a high specific capacitance (1292.2 F g−1 at 1 A g−1), excellent rate capability (1205.8 F g−1 at 10 A g−1) and cycle stability (ultrahigh capacitance retention of 91.5% for 5000 cycles), which has rarely been achieved in previously reported Co3O4-based electrodes. Furthermore, the assembled all-solid-state asymmetric supercapacitors (pMS-Co3O4/PPy//AC) delivered a high energy density of 40.2 Wh kg−1 at a power density of 761.7 W kg−1 and superior stability with a capacitance retention of 90.6% for 5000 cycles. This study offers an effective nanostructure design strategy to solve the issues of TMOs and develop high-performance energy storage systems.

Application of NiO-modified NiCo2O4 hollow spheres for high performance lithium ion batteries and supercapacitors

Abstract In this report, we synthesize a series of metal oxide hollow microspheres by adjusting the ratio of reactants, through a facial one-step hydrothermal treatment followed by annealing. The properties of as-prepared hollow microspheres are investigated to be applied as electrode for both lithium ion batteries (LIBs) and supercapacitors (SCs). The obtained NiCo2O4/NiO composite, with mesopores at the surface of hollow spheres, shows excellent electrochemical performances according to the cyclic voltammetry and impedance measurements. At a current density of 100 mA g−1, a large reversible capacity of 659 mAh g−1 was achieved for NiCo2O4/NiO after 100 cycles as the anode material of LIBs. As an electrode for SCs, NiCo2O4/NiO exhibits high electrochemical performances with a capacitance of 708.4 F g−1 at a current density of 1 A g−1 and a high retention about 94.3% after 10,000 cycles at 10 mA g−1. It was estimated to deliver a high energy density of 25.06 Wh kg−1 at a power density of 250 W kg−1. The outstanding electrochemical properties can be attributed to the synergistic effect of different metal oxides, and the special morphology of porous hollow microspheres, which has a high specific surface area to facilitate the soaking of electrolyte and fast Li+ diffusion, as well as offer accommodation for the volume change.

Effect of Heat Treatment Temperature and Time on Preparation of Porous Walled Hollow Glass Microspheres (PWHGMs)

The development of hollow glass microspheres (HGMs) with porous walls provides a unique system in which filling agents can be incorporated into the porous walled hollow glass microspheres (PWHGMs). Applications of these have been increased due to the many proposed uses for such a material. They are widely used in various fields of science and technology because of their unique properties, such as catalyst supports, photo catalysts, sorbents, gas sensors, molecular sieves, drug and bioactive delivery systems as well as chemical and biological indicators, etc. PWHGMs with their interior hollow volume and porous walls offer greater storage capacity and pathways for retaining and releasing of stored material. PWHGMs as additives can be used to increase porosity in the electrodes for more electrolyte storage in lead acid batteries and enhance the energy performance of the battery. Further, PWHGMs have potential applications in sensor materials, fuel cells, solar cell, chromatograph column fillers and as micro reactors to encapsulate Pd for catalytic hydrodechlorination of chlorophenols in water. In this research, efforts have been made to prepare PWHGMs from readily available borosilicate glass frits in the laboratory using flame spheroidisation method. The effect of heat treatment temperature and time on preparation of porous walled hollow glass microspheres was investigated. Hollow glass microspheres with wall thickness of 0.5–2 μm were fabricated from borosilicate glass frits in air-acetylene flame. The prepared microspheres were heat-treated and acid leached to produce porous walled hollow glass microspheres. According to results, suggest that heat treatment times used in this research are not as effective as the heat treatment temperatures in changing the porosity (or phase separation) in HGMs and the resulting PWHGMs.

Electrophoretic Deposition and Characterization of an Al/CuO Energetic Film with a Porous Hollow Microsphere Structure

In this work, an Al/CuO energetic film with a porous hollow structure was obtained by electrophoretic deposition (EPD) from an aqueous solution at low field strengths of 20 V cm−2 instead of from organic solvents. CuO porous hollow microspheres (PHMSs) were prepared by a one-step hydrothermal method. The shape of the CuO PHMSs was very uniform at the macroscale with a size of 5 μm. To codeposit the species during the EPD process, the nano-Al particles and CuO PHMSs were modified with acrylic acid and citric acid, respectively. The nano-Al particles were deposited on the surface or in the interior of the CuO PHMSs by an electrical field and formed Al/CuO PHMS composites. The chemical composition, morphology, heat release and combustion of the as-prepared composite coating films were analyzed by XRD, FESEM, FT-IR, EDS, TG-DSC and with a high-speed camera. The heat release of the Al/CuO porous thermite reached 3804 J/g with excellent combustion performance due to the novel microstructure and appropriate modifications.

Fabrication of porous polyimide hollow microspheres through O/W/O multiple emulsion

Herein, we demonstrate a novel strategy for the fabrication of porous polyimide hollow microspheres through building oil-in-water-in-oil (O/W/O) multiple emulsion using poly(amic acid) salt (PAAS) water solution as W phase, liquid paraffin (Lp) as O phase, and Op-10, Span-80 as emulsifiers, respectively. After the addition of the chemical imidization reagent, hollow polyimide microspheres with a porous structure were successfully prepared. The morphology and forming process of obtained hollow PI microspheres were well characterized by OM, SEM, FTIR. The results show that size and morphology control of the polyimide hollow spheres was examined by tuning different contents of PAAS, Op-10 and Span-80. Less adhesion and collapse spheres were achieved with PAAS increased up to 3.5wt%. The number of holes on surface of the spheres increases with the decreasing of op-10 content, while the size of the spheres decreases as the span-80 content increases. A phenomenological elucidation of the mechanism for growth of the hollow polyimide architectures has been proposed. This simple method could fabricate different PI hollow spheres, and also used for fabricating the corresponding carbon hollow spheres. Because of the excellent properties of PIs, their porous hollow structure microspheres may be used for coatings, inks, catalyst loading, nanoparticle dispersion, and so forth.

N-doped porous carbon hollow microspheres encapsulated with iron-based nanocomposites as advanced bifunctional catalysts for rechargeable Zn-air battery

The design and development of low-cost, efficient, and stable bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are desirable for rechargeable metal-air batteries. In this work, N-doped porous hollow carbon spheres encapsulated with ultrafine Fe/Fe 3 O 4 nanoparticles (FeO x @N-PHCS) were fabricated by impregnation and subsequent pyrolysis, using melamine-formaldehyde resin spheres as self-sacrifice templates and polydopamine as N and C sources. The sufficient adsorption of Fe 3+ on the polydopamine endowed the formation of Fe-N x species upon high-temperature carbonization. The prepared FeO x @N-PHCS has advanced features of large specific surface area, porous hollow structure, high content of N dopants, sufficient Fe-N x species and ultrafine FeO x nanoparticles. These features endow FeO x @N-PHCS with enhanced mass transfer and considerable active sites, leading to high activity and stability in catalyzing ORR and OER in alkaline electrolyte. Furthermore, the rechargeable Zn-air battery with FeO x @N-PHCS as air cathode catalyst exhibits a large peak power density, narrow charge-discharge potential gap and robust cycling stability, demonstrating the potential of the fabricated FeO x @N-PHCS as a promising electrode material for metal-air batteries. This new finding may open an avenue for rational design of bifunctional catalysts by integrating different active components within all-in-one catalyst for different electrochemical reactions. N-doped porous hollow microspheres with encapsulated Fe-based nanocomposite show impressive activity and stability for ORR and OER, capable of serving as efficient cathode catalysts for the rechargeable Zn-air batteries.