Hollow Submicrospheres Research Articles

Catalytic combustion of lean methane over different Co3O4 nanoparticle catalysts

Three types of Co3O4 catalyst, namely Co3O4 nanoparticles (denoted as Co3O4-NPs, ∼12 nm in diameter), Co3O4 nanoparticles encapsulated in mesoporou s SiO2 (denoted as Co3O4@SiO2), and Co3O4 nanoparticles inside microporous SiO2 hollow sub-microspheres (denoted as Co3O4-in-SiO2), were explored to catalyze the combustion of lean methane. It was found that the methane conversion over the three catalysts has the order of Co3O4-NPs ≈ Co3O4@SiO2 > Co3O4-in-SiO2 due to the different catalyst structure. The comparison experiments at high temperatures indicate the Co3O4@SiO2 has a significantly improved anti-sintering performance. Combined with the TEM and BET measurements, the results prove that the presence of the mesoporous SiO2 layer can maintain the catalytical activity and significantly improve the anti-sintering performance of Co3O4@SiO2. In contrast, the microporous SiO2 layer reduces the catalytical activity of Co3O4-in-SiO2 possibly due to its less effective diffusion path of combustion product. Thus, the paper demonstrates the pore size of SiO2 layer and catalyst structure are both crucial for the catalytical activity and stability.

Mechanistic study for enhanced photocatalytic degradation of acetaminophen by Fe(III) doped TiO2 hollow submicrospheres

The Fe (III) ions incorporated into TiO2 hollow submicrospheres are an excellent photocatalyst that could improve the catalyst activity by varying experimental parameters like controlling the flow rate, rotation speed, and contaminant concentration. Fe-TiO2 hollow submicrospheres with different Fe wt% in TiO2 were prepared. Our studies revealed that 2.5 wt% Fe-TiO2 has the best photocatalyst activity to generate strong oxidizing hydroxyl radicals during the photocatalytic degradation reaction. Ex-situ L and K-edge of Ti and Fe X-ray absorption near edge structure (XANES) spectra showed that Fe3+ ions in the 2.5 wt% sample produced more structural distortions in the TiO6 octahedral symmetry. Further, in-situ XANES Ti and Fe 3d spectral changes above the Fermi level (EF) revealed an increased electron charge transfer attributed to the Fe 3dz2- O 2pz orbital hybridization. Fe(III) doping not only increases the interaction between transition metal (Fe and Ti) 3d orbitals in TiO2, but also promotes the Fe(III)/Fe(II) redox kinetics and the associated photo-Fenton degradation of acetaminophen. Taking advantage of the magnetic property of the catalyst, the samples can be effectively recycled by applying a magnetic field.

Fabrication of Pt–Ag–Au heterogeneous truncated hollow sub-microspheres for chemically self-propelled colloidal motors

Colloidal motors with cavity structure, which have advantages over solid motors in catalytic efficiency, cargo capacity and biocompatibility, are still expected. Here, we design and fabricate a type of truncated hollow sub-microsphere via organic colloidal template etching/heating and layer-by-layer isotropic deposition. The as-prepared truncated hollow sphere is of one circular open pore through the shell layer and built of Pt, Ag and Au shell layers from inside to outside. They are controllable in sphere diameter, circular open pore size and shell thickness, which depend on the template and deposition conditions. Further experiments have shown that the Ag sandwich layer and post-deposition ageing process are crucial to obtaining strong and complete truncated hollow sub-microspheres. Their formation is attributed to the template geometry and nearly isotropic deposition. Due to the catalytic Pt layer on the inner surface and the truncated hollow spherical structure, such Pt–Ag–Au hollow spheres are demonstrated to be chemically propelled colloidal motors, which can directionally move in H2O2-containing solutions. This study presents a controllable route for mass-fabricating heterogeneous multi-layer truncated hollow sub-microspheres, and provides a new type of chemically self-propelled colloidal motor.

Donor–acceptor covalent organic framework hollow submicrospheres with a hierarchical pore structure for visible-light-driven H2 evolution

A novel donor–acceptor covalent organic framework PETZ–COF with hierarchical pore structure was synthesized, and showed a high photocatalytic H2 evolution performance. The structure–function relationship was proved by experiments and calculations.

Hollow submicrospheres of trimetallic selenides for high-capacity lithium and sodium ion batteries

Highly conductive metal selenides have drawn increasing attention in the field of energy storage. Unfortunately, their application is severely limited by the inferior capacity contribution as well as unsatisfactory cycling stability. Here, we propose a simple and practical way to prepare hollow nickel–cobalt–manganese selenides (NCMSe) submicrospheres. The NCMSe submicrospheres exhibit rich redox reactions during the reaction process into which much more alkali metal ions can be inserted, leading to high reversible capacity and their hollow structure facilitates the contact between the active material and electrolyte to accelerate the redox kinetics. Benefiting from these features, the hollow NCMSe submicrospheres show superior Li–storage capacity (1600 mAh g−1 after 1000 cycles at 2 A g−1) and Na–storage capacity (695 mAh g−1 after 200 cycles at 0.1 A g−1). This work offers a novel insight to the remarkable electrochemical performance anode materials for both lithium and sodium ion batteries.

Facile Solvothermal Synthesis of Hollow BiOBr Submicrospheres with Enhanced Visible-Light-Responsive Photocatalytic Performance.

In this work, hierarchical hollow BiOBr submicrospheres (HBSMs) were successfully prepared via a facile yet efficient solvothermal strategy. Remarkable effects of solvents upon the crystallinities, morphologies, and microstructures of the BiOBr products were systematically investigated, which revealed that the glycerol/isopropanol volumetric ratio played a significant role in the formation of hollow architecture. Accordingly, the underlying formation mechanism of the hollow submicrospheres was tentatively put forward here. Furthermore, the photocatalytic activities of the resulting HBSMs were evaluated in detail with photocatalytic degradation of the organic methyl orange under visible light irradiation. Encouragingly, the as-obtained HBSMs with striking recyclability demonstrated excellent visible-light-responsive photocatalytic performance, which benefits from their large surface area, effective visible light absorption, and unique hollow feature, highlighting their promising commercial application in waste water treatment.

Multifunctional Gadolinium-Based Coordination Polymer Hollow Submicrospheres: Synthesis, Characterization and Properties

In this work, we have developed a general, simple and template-free solvothermal strategy to prepare Yb3+ and Er3+ codoped Gd-based coordination polymer (GdCP) hollow spheres with glycylglycine as a ligand. Scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, energy dispersive X-ray spectroscopy, infrared and thermogravimetric analysis were used to characterize the hollow spheres. The GdCP hollow spheres are with a size of about 200 nm and the thickness of the shell was about 30 nm. Upconversion emission with 832 nm being the strongest was realized in the hollow spheres when excited with 980 nm laser. Magnetic measurement reveals that the GdCP hollow sphere is paramagnetic. The relaxation information was measured and the product is subjected to T1 weighted imaging. These prepared GdCP hollow spheres may be applied to multimodal imaging.

High energy K-ion batteries based on P3-Type K0·5MnO2 hollow submicrosphere cathode

Potassium-ion batteries are attracting intense attention as a promising energy storage system for grid-level applications due to their much lower cost compared with that of lithium-ion batteries. However, the lack of appropriate cathode materials becomes the most challenging issue caused by the contradiction between the higher difficulty on the controlled synthesis of K-based cathode candidates and the more rigorous requirement on the size, morphology and structure modulation in order to resist the drastic variation during the K insertion/extraction. In this work, we develop a scalable two-step self-templating strategy to synthesize P3–K0.5MnO2 hollow submicrospheres, in which largely optimized K-ion storage performance with superior cycling stability can be achieved benefitting from the synergistic effect of size, morphology and hollow interior. More importantly, the feasibility of the practical applications is further demonstrated via assembling the P3–K0.5MnO2 hollow submicrospheres cathode//graphite anode potassium-ion full cell and a high energy density of 100.7 Wh kg−1 is acquired based on the mass of cathode and anode, which highly strengthens the confidence on the future development of potassium-ion battery technology.

MOF-Derived Hybrid Hollow Submicrospheres of Nitrogen-Doped Carbon-Encapsulated Bimetallic Ni-Co-S Nanoparticles for Supercapacitors and Lithium Ion Batteries.

The development of bimetallic transition-metal sulfide and nitrogen-doped carbon composites with unique hollow structure is highly desirable for energy storage applications but is also challenging. In the present work, we demonstrate a facile metal-organic framework engaged strategy for synthesizing bimetallic nickel cobalt sulfide and nitrogen-doped carbon composites with hollow spherical structure (denoted as hollow Ni-Co-S- n/NC composites) and a Ni/Co molar ratio ( n value) that can be easily controlled. When evaluated as electrode materials for both supercapacitors and lithium ion batteries, it is found that the hollow Ni-Co-S-0.5/NC composite with a Ni/Co molar ratio of 0.5 exhibits optimal electrochemical performance. The hollow Ni-Co-S-0.5/NC composite exhibits a high specific capacity of 543.9 C g-1 at 1 A g-1 and maintains a capacity retention of 67.3% when the current density is increased to 20 A g-1. An asymmetric supercapacitor based on the hollow Ni-Co-S-0.5/NC composite is fabricated, which shows good electrochemical performance with a high energy density of 39.6 W h kg-1 at a power density of 808 W kg-1. For lithium storage, the hollow Ni-Co-S-0.5/NC composite manifests a high reversible discharge capacity of 755.0 mA h g-1 at 200 mA g-1 for 200 cycles as well as good rate capability. The excellent electrochemical performance could be attributed to the desirable structural, compositional, and component advantages. This work could offer new insight into the rational design and synthesis of highly efficient electrode materials for both supercapacitors and lithium ion batteries.

Multifunctional Gd-Based Coordination Polymer Hollow Sub-Microspheres: Synthesis, Upconversion Emission and Magnetic Resonance Imaging Evaluation

Multifunctional Gd-Based Coordination Polymer Hollow Sub-Microspheres: Synthesis, Upconversion Emission and Magnetic Resonance Imaging Evaluation

One-step controlled synthesis of hierarchical hollow Ni3S2/NiS@Ni3S4 core/shell submicrospheres for high-performance supercapacitors

Composition and microstructure are two main factors for enhancing the specific capacity, rate capability, and cycling life of electrode materials in electrochemical energy storage devices. Here, size-tunable hierarchical hollow core/shell submicrospheres based on nickel sulfide are for the first time rationally designed and synthesized through a one-step hydrothermal route, in which Ni3S2/NiS hollow submicrosphere works as a core and Ni3S4 nanoflakes as shells. The diameter of the hierarchical sphere can be controlled by cetyltrimethyl ammonium bromide. The formation mechanism of this unique structure is systematically investigated, which can be attributed to the combined action of cage effect, Kirkendall effects and Ostwald ripening mechanism. Due to the synergistic effects of various phase nickel sulfide, such hybrids exhibit superior electrochemical performance. When served as electrodes for supercapacitors, the hybrids show a high specific capacity of 1031.3 C g−1 at a current density of 2 A g−1. Even as the current density increases to 40 A g−1, the hierarchical core-shell nanosphere still reserves 614.4 C g−1, exhibiting an excellent rate capacity and a good capacitance retention of 90.3% after 3000 cycles at 10 A g−1. Furthermore, asymmetric supercapacitor based on the Ni3S2/NiS@Ni3S4 hybrid and reduced graphene oxide shows high power density, high energy density and long cycling lifespan.

Flowerlike NiCo2S4 Hollow Sub-Microspheres with Mesoporous Nanoshells Support Pd Nanoparticles for Enhanced Hydrogen Evolution Reaction Electrocatalysis in Both Acidic and Alkaline Conditions.

Flowerlike NiCo2S4 hollow sub-microspheres are synthesized through Cu2O templates to support Pd nanoparticles as high-efficiency catalysts for the hydrogen evolution reaction (HER). The diameter and shell size of NiCo2S4 hollow sub-microspheres are about 400 and 16 nm, respectively. In addition, the surface of the shells is constructed by petallike nanosheets. About 3 nm Pd particles uniformly incorporate with the flowerlike NiCo2S4 hollow sub-microsphere to form the NiCo2S4/Pd heterostructure. The NiCo2S4/Pd catalysts exhibit significantly lower overpotential of only 87 and 83 mV at 10 mA/cm2 for the HER in both acidic and alkaline conditions, respectively, relative to NiCo2S4 (247, 226 mV) and Pd (175, 385 mV) catalysts. Besides, the NiCo2S4/Pd catalysts also exhibit excellent stability of HER in these two conditions. The superior HER performance of NiCo2S4/Pd might be resulted from the unique architecture of metal nanoparticles anchored on the bimetallic sulfide flowerlike hollow sub-microspheres, which could provide high surface area, lots of active sites, strong synergetic effect, and stable structure.

Cyclic microwave radiation synthesis, photoconductivity, and optical properties of CuInS2 hollow sub-microspheres

CuInS2 powder was synthesized by a cyclic microwave irradiation method using l-cysteine as a sulfur source. The effect of microwave power (180–600 W) on the purity, morphology, and particle size of the synthesized powders was investigated. X-ray diffraction (XRD) analysis showed that the synthesized powders were pure CuInS2 with a tetragonal structure. Transmission electron microscopy (TEM) analysis revealed that the CuInS2 powder synthesized at 180 W composed of solid microspheres with a diameter of about 250 nm. Increasing the microwave power to 300 W and 450 W transformed some of the sub-microspheres into hollow sub-microspheres. At 600 W, all of the CuInS2 sub-microspheres were hollow. Based on time-dependent experiment, formation mechanisms of the CuInS2 solid and hollow sub-microspheres were discussed. The photoconductivity of the CuInS2 hollow sub-microspheres was greater than that of the CuInS2 solid sub-microspheres, suggesting that the CuInS2 hollow sub-microspheres were favorable to increase current carrier concentration and to improve electron transport. UV–vis diffuse reflectance spectrum (UV–vis DRS) of the CuInS2 hollow sub-microspheres showed strong absorption intensity with a direct band gap energy of 1.48 eV, which is potentially useful in solar-light driven applications.

Efficient hierarchical mixed Pd/SnO2 porous architecture deposited microheater for low power ethanol gas sensor

A novel gas microsensor combining SnO2 submicron/nanostructured porous sensitive film with Micro-Electro-Mechanical systems (MEMS) microheater was successfully fabricated. The film was made of hierarchically mixed Pd/SnO2 (HM-PTO) composites composed of Pd/SnO2 hollow submicrospheres (Pd/SnO2-HSs) and Pd/SnO2 nanoparticles (Pd/SnO2-NPs) deposited on the microheater platform using the microdispensing method. The as-prepared HM-PTO sensors exhibited high sensitivities, fast response/recovery rates, good selectivity, reliable reversibility, and relevant stability towards ethanol at low power consumption. The resulting superior sensing performances were attributed to the unique hierarchical structure. The internal void architecture of Pd/SnO2-HSs provided large specific surface areas, proper mesopore size distribution, large number of active adsorption/interaction sites, as well as promoted the chemisorption and dissociation of gas molecules due Pd-doping to yield superior gas response. In particular, the nano-sized SnO2 particles ensured the uniform deposition of the materials to yield enhanced local conductivities, and possibly faster phase transfer reactions responsible for the extremely good response/recovery performance. This simple fabrication procedure combined with high sensing performances look promising for the development of hierarchical morphologies of novel materials for gas sensing applications.

Hierarchical SnO 2 hollow sub-microspheres for panchromatic PbS quantum dot-sensitized solar cells

Abstract In contrast with the commonly used TiO 2 or ZnO electron transporters, SnO 2 , which possesses relatively low conduction band and high electron-mobility, is expected to facilitate the extraction of photogenerated electrons from quantum dots (QDs) to oxides in quantum dot-sensitized solar cells (QDSCs), especially for those narrow band gap QDs (e.g., PbS). In this work, hierarchical SnO 2 hollow sub-microspheres have been synthesized by a facile one-step hydrothermal process, and further studied for near infrared responsive PbS QDSCs. Morphology and structure characterizations reveal that these sub-micrometer-sized spheres (150–200 nm) with hollow interiors are assembled by numerous packed nanograins. The nanometer-sized grains ensure large specific surface area (∼69.2 m 2 g −1 ) and pore size (∼19 nm) for high QD loading, while the sub-micrometer-sized spheres function as efficient light scatters and robust electron transporting structures. As a result, these superior features make such hierarchical SnO 2 architectures very promising candidates for photovoltaic application. Based on the multifunctional photoelectrode constructed with hierarchical SnO 2 hollow architectures, an appreciable power conversion efficiency up to 1.34% has been achieved for a PbS QDSC, coupled with interface engineering through TiO 2 coating and CdS passivation. This work offers a promising design for developing high performance QDSCs.

Mesocrystalline Zn-Doped Fe3O4 Hollow Submicrospheres: Formation Mechanism and Enhanced Photo-Fenton Catalytic Performance.

Uniform and magnetic recyclable mesocrystalline Zn-doped Fe3O4 hollow submicrospheres (HSMSs) were successfully synthesized via a simple one-pot solvothermal route and were used for efficient heterogeneous photo-Fenton catalyst. XRD, XPS, Raman spectroscopy, Mössbauer spectroscopy, SEM, HRTEM, and EDX analyses revealed that the shell of HSMSs is highly porous and assembled by oriented attachment of magnetite nanocrystal building blocks with Zn-rich surfaces. Furthermore, a possible formation mechanism of mesocrystalline hollow materials was proposed. First, Fe3O4 mesocrystals were assembled by oriented nanocrystals, and a Zn-rich amorphous shell grew on the surfaces. Then, Zn gradually diffused into Fe3O4 crystals to form Zn-doped Fe3O4 due to the Kirkendall effect with increasing the reaction time. Meanwhile, the inner nanocrystals would be dissolved, and outer particles would grow larger owing to the Ostwald ripening process, leading to the formation of a hollow structure with porous shell. The Zn-doped Fe3O4 HSMSs exhibited high and stable photo-Fenton activity for degradation of rhodamine B (RhB) and cephalexin under visible-light irradiation in the presence of H2O2, which results from their hollow mesocrystal structure and Zn doping. It could be easily separated and reused by an external magnetic field. The results suggested that the as-obtained magnetite hollow mesocrystals could be a promising catalyst in the photo-Fenton process.

Heterojunction construction between TiO2 hollowsphere and ZnIn2S4 flower for photocatalysis application

In the past few years, more and more efforts have been made on designing novel and efficient semiconductor-based heterojunction photocatalyst to maximize the capture and conversion efficiency of solar energy. In this work, unique TiO2 hollow sub-microspheres (THSs) and ZnIn2S4 (ZIS) flower-like microspheres were combined through a facile hydrothermal method and novelly applied in photocatalytic metronidazole (MTZ) degradation. The effects of THSs on the physicochemical properties and photocatalytic performance of ZIS were systemically investigated, and the optimal weight ratio of THS and ZIS in the composite was found. Furthermore, various technologies such as photoluminescence (PL), surface photovoltage spectra (SPS) and electrochemical impedance spectra (EIS) were used to verify the intimate contact and highly-efficient charge-carriers transfer between THS and ZIS components. The underlying photocatalysis mechanism was also carefully surveyed and proposed through hydroxyl radicals (OH) monitoring and radical trapping experiments.

Biodiesel production from waste cooking oil by immobilized lipase on superparamagnetic Fe3O4 hollow sub-microspheres

Superparamagnetic Fe3O4 hollow sub-microspheres (FHSM) with strong response to an external magnet were prepared via a solvothermal method, followed by acid etching. Lipase from Candida sp. 99–125 was directly immobilized onto the amino-functional FHSM by simple adsorption, without glutaraldehyde linkage. The immobilized lipase was used to catalyze the esterification/transesterification of waste cooking oil with methanol to produce fatty acid methyl ester (FAME), a major source of biodiesel. FAME yield exceeded 93.4% over a wide range of temperatures from 10 to 40 °C. Notably, stability was clearly improved at the lower temperatures, in particular, giving a FAME yield of 89.6% after eight cycles of use at 10 °C.

Solvothermal Synthesis of Single-Crystal Magnetite Hollow Sub-Microspheres: A Novel Formation Mechanism and Magnetic Properties

In this paper, single-crystal magnetite hollow sub-microspheres with a narrow diameter distribution are synthesized through a simple solvothermal process in ethylene glycol in the presence of urea and a small amount of water. The determining role of water in the solvothermal synthesis is studied. It is found that a small amount of water is crucial for the formation of the magnetite hollow spheres. A novel formation mechanism of the magnetite hollow spheres is proposed based on the bubble-assisted Ostwald ripening. It is believed that the appropriate amount of CO2 gas bubbles produced in situ by urea hydrolysis is crucial for the formation of hollow spheres. Because of the existence of gas microbubbles, magnetite solid spheres with a loose core and compact shell form, which is the key factor for the following inside-out Ostwald ripening and the formation of the hollow spheres. Thus, by simple changing of the water dosage, magnetite hollow spheres with different diameters and shell thicknesses are obtained controllably. The magnetic properties of the obtained magnetite hollow spheres are studied. It is found that the saturation magnetization of the magnetite hollow sub-microspheres decreases with the increasing shell thickness, whereas the coercivity and remanent magnetization increase with increasing shell thickness.

One-step hydrothermal synthesis of (CuIn)0.2Zn1.6S2 hollow sub-microspheres for efficient visible-light-driven photocatalytic hydrogen generation

(CuIn)0.2Zn1.6S2 (CIZS) hollow sub-microspheres were prepared by a simple one-step hydrothermal method using thioacetamide (TAA) as a sulfur source. It was demonstrated that the amount of TAA played a key role on the morphology of CIZS samples. Low amount of TAA led to the formation of solid sub-microspheres. Nevertheless, high amount of TAA gave rise to the growth of hollow sub-microspheres, which could be elucidated by a bubble template mechanism. The morphology transition, as well as the reduced crystallite size, led to the increased specific surface area with the increased amount of TAA. Meanwhile, the defect states in CIZS samples were gradually decreased, when the amount of TAA was increased. The improved specific surface area and decreased defects of CIZS products contributed to higher efficiencies of charge separation and surface chemical reaction. The photocatalytic performance of CIZS photocatalysts was closely influenced by the amount of TAA. CIZS samples prepared with 5 g of TAA showed the highest hydrogen production rate, with the apparent quantum yield of 11.5% at 420 nm. It was summarized that the superior photocatalytic activity should be attributed to the larger specific surface area, decreased defects and relatively clean surface. This work not only provided a simple route to prepare hollow-structured photocatalysts, but also demonstrated the importance of sulfur source on photocatalytic properties of metal sulfide photocatalysts.