Formation Of Hollow Spheres Research Articles

All roads lead to Rome: Trace water-dominated the formation of nanosheet-assembled hollow metal-organic frameworks for high performance supercapacitors

Controlling the structure of metal-organic frameworks (MOFs) is a crucial strategy to enhance electrochemical performance. In this work, nanosheet-assembled hollow Ni-MOF spheres are synthesized by controlling the transition states through a facile trace water-assisted solvothermal method. During the research, it is found that water in the system, whether from the precursor Ni(NO3)2·6H2O or from an additional source, is a key influencing factor that can regulate the reaction process to control structural changes. Theoretical calculations prove that the water present in the reaction system can affect the distribution of terephthalic acid (TPA) and Ni2+, indicating that trace water can provide an accelerating effect. The nanosheet-assembled sphere shells can expose more active surface area, and the hollow structure can prevent the restacking of nanosheets and shorten the charge transport path. Based on these structural advantages, the prepared Ni-TPA MOF electrode achieves a high specific capacitance of 1010 F g−1 at 1 A g−1 and a 61 % rate capability at 20 A g−1. This work offers a feasible and highly effective strategy to design nanosheet-assembled hollow MOF spheres for high-performance supercapacitors and helps to understand the key factors influencing the formation of hollow MOF spheres.

Luminescent hollow spherical nanoparticles with enhanced imaging contrast through hydrogen bonding connected micelles

Herein, we propose an innovative method for synthesizing luminescent hollow spherical nanoparticles. Our method involves the construction of hydrogen bonding connected micelles (HBCMs) utilizing inter-polymer complexes of poly(styrene-alt-hydroxyphenylmaleimide)/poly(4-vinylpyridine) (poly(S-alt-HPMI)/P4VP), which could undergo self-assembly, resulting in the formation of core/shell nanostructures in the selective solvent. The aim was to incorporate two types of fluorescent compounds, namely tris(4–bromophenyl)amine (TPA–Br3) and 1,1,2,2–tetrakis(4–bromophenyl)ethene (TPE–Br4), as the cross-linkers to enhance the shell structures of HBCMs and using dimethylformamide (DMF) was employed to remove the core structures, aiming to pursue the formation of luminescent hollow spheres. Transmission electron microscopy (TEM) images confirmed the formation of self-assembled spherical structures formed by poly(S-alt-HPMI)/P4VP inter-polymer complexes. The morphological features, hydrogen bonding interactions, particle sizes, cross-linking reactions, core removal, and thermal properties were thoroughly investigated by TEM, atomic force microscope (AFM), dynamic light scattering (DLS) instrument, Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) analyses. Moreover, the optical properties were also explored by fluorescence microscope and photoluminescence (PL). This evidence indicates that the HBCMs could be directly cross-linked with TPA–Br3 or TPE–Br4 and subsequently transformed into hollow spheres by the addition of DMF. Fluorescent particles featuring hollow spheres could be prepared successfully without traditional dye staining or labeling. This advancement holds promising potential for applications in nano-carriers with improved imaging contrast.

Mn‐doping ensuring cobalt silicate hollow spheres with boosted electrochemical property for hybrid supercapacitors

AbstractRecently, transition metal silicates (TMSs) have garnered significant attention as promising candidates for electrode materials in supercapacitors (SCs), especially cobalt silicate (Co2SiO4, CoSi) related materials. However, due to the poor conductivity and narrow potential range of CoSi, its electrochemical properties are not fully developed and far from desirable. Herein, to enhance the electrochemical properties of CoSi, hollow spheres of Mn‐doped CoSi (CoMnSi) were fabricated through a hydrothermal method. The dopant Mn facilitates the formation of CoMnSi hollow spheres assembled by nanosheets and these nanosheets connect with each other to form the core‐shell hollow architecture. The effect of the Mn/Co ratio on the electrochemical properties of CoSi has been investigated. CoMnSi‐2 (Mn/Co = 1/9) displays the specific capacitance of 495 F g−1 at 0.5 A g−1, surpassing to that of CoSi (279 F g−1 at 0.5 A g−1) and manganese silicate (denoted as MnSi, 38 F g−1 at 0.5 A g−1). The CoMnSi‐2//active carbon hybrid supercapacitor (CoMnSi‐2//AC HSC) achieves the specific capacitance with 181 mF cm−2 (151 F g−1) at 1 mA cm−2 and energy density with 0.644 Wh m−2 at 2 W m−2. The device displays a practical application by powering the LED lamp circuit bulb working for more than 25 min repeatedly. The performance achieved by CoMnSi is superior to some state‐of‐the‐art electrode materials of TMSs. Density functional theory calculations have provided evidence that Mn‐doping enhances the electronic conductivity and reduces the electron transport barrier of CoSi, boosting its electrochemical properties. This work supplies a strategy for tailoring structures of TMSs to enhance their electrochemical performance.

Hydrothermal Synthesis of Bismuth Ferrite Hollow Spheres with Enhanced Visible-Light Photocatalytic Activity.

In recent years, semiconductor hollow spheres have gained much attention due to their unique combination of morphological, chemical, and physico-chemical properties. In this work, we report for the first time the synthesis of BiFeO3 hollow spheres by a facile hydrothermal treatment method. The mechanism of formation of pure phase BiFeO3 hollow spheres is investigated systematically by variation of synthetic parameters such as temperature and time, ratio and amount of precursors, pressure, and calcination procedures. The samples were characterized by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and UV-vis diffuse reflectance spectroscopy. We observe that the purity and morphology of the synthesized materials are very sensitive to synthesis parameters. In general, the chemically and morphologically very robust hollow spheres have diameters in the range of 200 nm to 2 μm and a wall thickness of 50-200 nm. The synthesized BiFeO3 hollow spheres were applied as catalysts in the photodegradation of the model pollutant Rhodamine B under visible-light irradiation. Notably, the photocatalyst demonstrated exceptionally high removal efficiencies leading to complete degradation of the dye in less than 150 min at neutral pH. The superior efficiencies of the synthesized material are attributed to the unique features of hollow spheres. The active species in the photocatalytic process have been identified by trapping experiments.

Solvent-Driven Self-Organization of Meso-Substituted Porphyrins: Morphological Analysis from Fluorescence Lifetime Imaging Microscopy.

A morphological analysis of different thin films of meso-tetra-p-(di-p-phenylamino)phenylporphyrin, H2T(TPA)4P, was made by fluorescence lifetime imaging microscopy (FLIM) and scanning electron microscopy (SEM). A comprehensive study of H2T(TPA)4P was undertaken through UV/vis absorption and fluorescence techniques in different solvents, solvent mixtures and in thin films. In solution, occurrence of intramolecular energy transfer from the triphenylamine (TPA) moieties to the porphyrin core, with quenching efficiencies in the order of 94-97%, is observed. The energy transfer rate constants are determined assuming Förster's dipole-dipole and Dexter's electron exchange mechanisms. In drop-cast-prepared thin films, from samples with different solvent mixtures, the photoluminescence (PL) quantum yield (ΦPL) decreases ∼1 order of magnitude compared to the solution behavior. FLIM and SEM experiments showed the self-organization and morphology of H2T(TPA)4P in thin films to be highly dependent on the solvent mixture used to prepare the film. In chloroform, the solvent's evaporation results in the formation of elongated and overlapped microrod structures. Introduction of a cosolvent, namely, a polar cosolvent, promotes changes in the morphology of the self-assembled structures, with the formation of three-dimensional spherical structures and hollow spheres. H2T(TPA)4P dispersed in a polymer matrix shows enhanced ΦPL values when compared to the drop-cast films. FLIM images showed coexistence of three different states or domains: aggregated, interface, and nonaggregated or less-aggregated states. This work highlights the importance of FLIM in the morphological characterization of heterogeneous films, together with the photophysical characterization of nano- and microdomains.

Chiral Binaphthalene Building Blocks for Self-Assembled Nanoscale CPL Emitters.

The introduction of biuret hydrogen-bonding sites onto chiral binaphthalene-based chromophores was investigated as a route to sub-micron-sized, vesicle-like aggregates endowed with chiroptical properties. The synthesis was conducted from the corresponding chiral 4,4'-dibromo-1,1'-bis(2-naphthol) via Suzuki-Miyaura coupling to afford luminescent chromophores whose emission spectrum could be tuned from blue to yellow-green through extension of the conjugation. For all compounds, the spontaneous formation of hollow spheres with a diameter of ca. 200-800 nm was evidenced by scanning electron microscopy, along with strong asymmetry in the circularly polarized absorption spectra. For some compounds, the emission also displayed circular polarization with values of glum = ca. 10-3 which could be increased upon aggregation.

Self-Templated Synthesis of Triphenylene-Based Uniform Hollow Spherical Two-Dimensional Covalent Organic Frameworks for Drug Delivery

Constructing two-dimensional covalent organic frameworks (2DCOFs) with a desirable crystalline structure and morphology is promising but remains a significant challenge. Herein, we report self-templated synthesis of uniform hollow spherical 2DCOFs based on 2,3,6,7,10,11-hexakis(4-aminophenyl) triphenylene. A detailed time-dependent study of hollow sphere formation reveals an intriguing transformation from initial homogeneous solid spheres into uniform hollow spheres with the Ostwald ripening mechanism. Impressively, the resultant spherical 2DCOFs are composed of high crystallinity nanosheets and even hexagonal single crystals, as demonstrated by transmission electron microscopy. Thanks to its uniform morphology and high crystallinity, the pore volume of the obtained 2DCOFs is up to 1.947 cm3 g–1, which makes it function as superior nanocarriers for efficient controlled drug delivery. This result provides an avenue for improving COFs’ performance by regulating their morphology.

L-buthionine sulfoximine encapsulated hollow calcium peroxide as a chloroperoxidase nanocarrier for enhanced enzyme dynamic therapy

The appropriate design of multifunctional nanocarriers for chloroperoxidase (CPO) delivery and the simultaneous improvement of the efficiency of enzyme dynamic therapy (EDT) remain significant challenges. Herein, we report a facile one-step route to obtain a multifunctional nanocarrier for the formation of sodium hyaluronate-modified hollow calcium peroxide spheres with encapsulated L-buthionine sulfoximine (BSO), followed by delivery of CPO for enhanced EDT. After effective accumulation at the tumor sites, the nanocomposite rapidly decomposes and releases Ca2+, BSO molecules, CPO, and concurrently generates a large volume of hydrogen peroxide (H2O2) in the endogenous tumor microenvironment (TME). BSO molecules inhibit the biosynthesis of glutathione (GSH) by inactivating γ-glutamyl cysteine synthetase. Due to BSO-induced GSH depletion and self-supply of H2O2, the EDT efficiency of CPO was significantly enhanced to achieve high tumor therapy efficiency. Additionally, overloaded Ca2+ caused mitochondrial damage and amplified the oxidative stress. Moreover, calcification resulted from the unbalanced calcium transport channel caused by enhanced oxidative stress, accelerating tumor apoptosis and improving the efficacy of computed tomography (CT) imaging visual tumor therapy. This simple and efficient design for multifunctional nanocomposites will likely take an important place in the field of combined tumor therapeutics.

Formation of monoclinic α-Bi2O3 nanosheet-assembled hollow spheres as a high-performance electrode for supercapacitor

Formation of monoclinic α-Bi2O3 nanosheet-assembled hollow spheres as a high-performance electrode for supercapacitor

Formation of gold hollow spheres by rapid heating–cooling process

Formation of gold hollow spheres by rapid heating–cooling process

Dissolvable microgel-templated macroporous hydrogels for controlled cell assembly

Mesenchymal stem cells (MSCs)-based therapies have been widely used to promote tissue regeneration and to modulate immune/inflammatory response. The therapeutic potential of MSCs can be further improved by forming multi-cellular spheroids. Meanwhile, hydrogels with macroporous structures are advantageous for improving mass transport properties for the cell-laden matrices. Herein, we report the fabrication of MSC-laden macroporous hydrogel scaffolds through incorporating rapidly dissolvable spherical cell-laden microgels. Dissolvable microgels were fabricated by tandem droplet-microfluidics and thiol-norbornene photopolymerization using a novel fast-degrading macromer poly(ethylene glycol)-norbornene-dopamine (PEGNB-Dopa). The cell-laden PEGNB-Dopa microgels were subsequently encapsulated within another bulk hydrogel matrix, whose porous structure was generated efficiently by the rapid degradation of the PEGNB-Dopa microgels. The cytocompatibility of this in situ pore-forming approach was demonstrated with multiple cell types. Furthermore, adjusting the stiffness and cell adhesiveness of the bulk hydrogels afforded the formation of solid cell spheroids or hollow spheres. The assembly of solid or hollow MSC spheroids led to differential activation of AKT pathway. Finally, MSCs solid spheroids formed in situ within the macroporous hydrogels exhibited robust secretion of HGF, VEGF-A, IL-6, IL-8, and TIMP-2. In summary, this platform provides an innovative method for forming cell-laden macroporous hydrogels for a variety of future biomedical applications.

Supramolecular gating of TADF process in self-assembled nano-spheres for high-resolution OLED applications.

Acridine-based donor-acceptor chromophores exhibiting E-type delayed fluorescence were substituted with bis-biuret H-bonding motifs to induce the formation of hollow spheres which can be deposited from solution to form the active component of OLED devices. In solution, the contribution of the delayed component is sensitive to disruption of the aggregates.

Formation of hierarchical Co-decorated Mo2C hollow spheres for enhanced hydrogen evolution

Formation of hierarchical Co-decorated Mo2C hollow spheres for enhanced hydrogen evolution

Hierarchical Porous, N-Containing Carbon Supports for High Loading Sulfur Cathodes.

The lithium-polysulfide (LiPS) dissolution from the cathode to the organic electrolyte is the main challenge for high-energy-density lithium-sulfur batteries (LSBs). Herein, we present a multi-functional porous carbon, melamine cyanurate (MCA)-glucose-derived carbon (MGC), with superior porosity, electrical conductivity, and polysulfide affinity as an efficient sulfur support to mitigate the shuttle effect. MGC is prepared via a reactive templating approach, wherein the organic MCA crystals are utilized as the pore-/micro-structure-directing agent and nitrogen source. The homogeneous coating of spherical MCA crystal particles with glucose followed by carbonization at 600 °C leads to the formation of hierarchical porous hollow carbon spheres with abundant pyridinic N-functional groups without losing their microstructural ordering. Moreover, MGC enables facile penetration and intensive anchoring of LiPS, especially under high loading sulfur conditions. Consequently, the MGC cathode exhibited a high areal capacity of 5.79 mAh cm−2 at 1 mA cm−2 and high loading sulfur of 6.0 mg cm−2 with a minor capacity decay rate of 0.18% per cycle for 100 cycles.

Self-templated formation of cobalt-embedded hollow N-doped carbon spheres for efficient oxygen reduction

The slow kinetics at the cathode of oxygen reduction reaction (ORR) seriously limits the efficiencies of fuel cells and metal-air batteries. Pt, the state-of-the-art ORR electrocatalyst, suffers from high cost, low earth abundance, and poor stability. Here a self-templated strategy based on metal-organic frameworks (MOFs) is proposed for the fabrication of hollow nitrogen-doped carbon spheres that are embedded with cobalt nanoparticles (Co/HNC). The Co/HNC manifests better ORR activities, methanol tolerance, and stability than commercial Pt/C. The high ORR performance of Co/NHC can be attributed to the hollow structure which provides enlarged electrochemically active surface area, the formation of more Co-N species, and the introduction of defects. This work highlights the significance of rational engineering of MOFs for enhanced ORR activity and stability and offers new routes to the design and synthesis of high-performance electrocatalysts.

Formation of hollow silica spheres from molecular silica sols

Hollow silica microspheres have been obtained in a surfactantfree templating process at neutral pH from silica sol of 2–10 nm globular organic–inorganic silica particles with exposed hydrophobic siloxane part as well as hydrophilic reactive silanol groups. Due to small diffusion coefficient and amphiphilic nature, the sol particles stabilize an oil–water interface quickly. Initially they assemble via noncovalent interaction into a stable shell and then condense covalently, with fast initial stabilization/dispersion of oil–water emulsion improving the control and simplifying the microsphere formation process.

The novel p-Co3O4/n-I-Fe2O3 nano hollow spheres with the enhanced photocatalytic activity

The iodine doped α-Fe2O3 hollow spheres combined with Co3O4 were firstly prepared by a two-step method. The catalysts with the structure of p-Co3O4/n-I-Fe2O3 HS exhibited excellent photo-degradation activity under visible irradiation. More than 94% RhB was degraded within 10 min, the reaction rate constant was calculated to 0.303 min−1 which was 10.7 times higher than pure Fe2O3 particles. The iodine doping decreased the surface electron impedance and enhanced the separation of photo-induced carriers. The formation of hollow spheres increased the specific surface area of the catalysts as expected. The p-n junction further promoted carriers separation and the Fenton reaction.

Scalable preparation of individual, uniform hyper-crosslinked polyimide hollow spheres through solid-state powder foaming: The power of network manipulation

Here in this study, for the first time, we revealed that the introduction of network structure can unprecedented preventing the inter-sphere fusing of spheres, thus provided a scalable solid-state powder foaming process for the synthesis of uniform hyper-crosslinked high performance polyimide (PI) hollow spheres. The pore sizes can be fine-tuned by controlling the solvent residuum amounts. The fast-increasing viscosity of framework nylon-salt-type monomers under foaming temperature is responsible for the formation of individual PI hollow spheres instead of fused foams. The research revealed the framework manipulation as a new strategy for the facile preparation of high performance polymer hollow structures.

Formation of graphene-wrapped multi-shelled NiGa2O4 hollow spheres and graphene-wrapped yolk-shell NiFe2O4 hollow spheres derived from metal-organic frameworks for high-performance hybrid supercapacitors.

To construct a supercapacitor (SC) with considerable performance, synthesis of an electrode material with a highly porous structure is necessary. Herein, an efficient metal-organic framework (MOF)-derived procedure is offered to construct a graphene wrapped multi-shelled NiGa2O4 hollow sphere (GW-MSNGOHS) positive electrode material and a graphene-wrapped yolk-shell NiFe2O4 hollow sphere (GW-YS-NFOHS) negative electrode material with a highly porous nature in SCs. The GW-MSNGOHS and GW-YS-NFOHS electrodes exhibit excellent capacities (∼411.25 mA h g-1 and 254.25 mA h g-1, respectively, at 1 A g-1), reasonable rate performances (75.85%, and 62.7%, respectively), and outstanding cyclability (98.9% and 90.9%, respectively). Benefiting from the reasonably engineered negative and positive electrodes, the fabricated asymmetric device (GW-MSNGOHS//GW-YS-NFOHS) can show an excellent energy density (ED) of 118.97 W h kg-1 at a power density (PD) of 1702 W kg-1, an exceptional robustness of 92.1%, and an excellent capacity (Cs) of 140.2 mA g-1.

Patchy Templated Synthesis of Macroporous Colloidal Hollow Spheres and Their Application as Catalytic Microreactors.

Porous colloidal hollow spheres have been applied to diversified fields over the past few decades. However, developing simple and efficient methods to prepare such porous hollow spheres with macro pores remains a challenge. To address this problem, we present a patchy templated synthesis route, which can be used to prepare such colloidal hollow spheres that have macro pores through the shells. This was achieved by using patchy poly(styrene-co-sodium styrenesulfonate) spheres as the template and poly(allylamine hydrochloride) as binding molecules. SiO2 can site-selectively only grow on one kind of patch, resulting in the formation of porous hollow spheres. The pore sizes can be tuned from ∼50 to 400 nm. The resulting porous hollow spheres have a Janus character so that Au nanoparticles can only be attached to the interior surfaces in situ, which can be used as catalytic microreactors and show the catalytic performance of pore size dependence.