Hollow Mesoporous Structure Research Articles

Synthesis and superparamagnetism of Fe3O4 hollow nano-microspheres

Fe3O4 nanomaterials have received great attention due to their many applications in tumor diagnosis and tumor heat therapy based on their good biocompatibility, magnetic targeting ability and superparamagnetic properties to avoid magnetic reunion in the process of magnetic targeting. Most of superparamagnetic nanoparticles obtained by traditional methods exhibit lower saturation magnetization (MS), because of their small particle sizes. Enlarging the particle size is favorable to increase the MS of magnetic particles. However, the superparamagnetism of the particle could be lost with the increase of particle size. This is not favorable to the targeting delivery of magnetic particles. For this purpose, in this paper, novel Fe3O4 nano-microspheres with mesoporous hollow structure are successfully synthesized by a facile hydrothermal method from the FeCl36 H2O, sodium citrate, urea, and polyacrylamide as additive, the reaction temperature is 200℃ and reaction time is 12 h. The crystal structure and purity of the resulting products are examined by powder X-ray diffraction (XRD). The morphologies of the products are studied by using scanning electron microscopy (SEM) and transmission electron microscopic (TEM). The magnetic properties of Fe3O4 nano-microspheres are evaluated with a vibrating sample magnetometer. The morphology evolution process and possible formation mechanism of Fe3O4 nano-microspheres are investigated. The findings are as follows:all XRD peaks of the hollow Fe3O4 nano-microspheres could be assigned to the spinel-type Fe3O4. The SEM and TEM images reveal that the products are mesoporous hollow Fe3O4 nano-microspheres and possess hierarchical structure, in which large microspheres (160 nm) are self-assembled by smaller Fe3O4 initial crystals (18 nm). It is found that the synthetic time of Fe3O4 nano-microspheres is considerable for the formation of the Fe3O4 hierarchical structure, and that the dispersion and sphericity of Fe3O4 nano-microspheres are the best when reaction time is 12 h. The formation of hierarchical hollow structure is believed to be due to the Ostwald ripening process, in which the initial crystals redissolve and regrow. Furthermore, the magnetic measurement results show that as-prepared hollow Fe3O4 nano-microspheres exhibit typical superparamagnetic properties whose initial crystal size is in the range of superparamagnetic region. Meanwhile, MS is about 73.3 emu/g at room temperature, which is significantly greater than that of traditional small superparamagnetic nanoparticles and compact solid nano-microspheres. The high saturation magnetization of hollow Fe3O4 nano-microspheres originates from a high crystallinity with primary grain, lager size and hierarchical structure. The results indicate that the as-prepared Fe3O4 hollow nano-microspheres are dispersed, water-soluble, homogeneous in particle diameter, and superparamagnetic, and can be used in targeted anticancer drug delivery and tumor heat therapy.

Synthesis and characterization of mesoporous and hollow-mesoporous MxFe3-xO4 (M=Mg, Mn, Fe, Co, Ni, Cu, Zn) microspheres for microwave-triggered controllable drug delivery

Spinel ferrites can be used in magnetic targeting and microwave heating and can therefore be used for targeted and controllable drug delivery. We used the cetyltrimethylammonium bromide-assisted solvothermal method to synthesize a series of spinel ferrites (MxFe3-xO4, M=Mg, Mn, Fe, Co, Ni, Cu, Zn) with a mesoporous or hollow-mesoporous structure suitable for direct drug loading and the particle diameters ranging from 200 to 350 nm. We investigated the effects of M2+ cation on the morphology and properties of these products by analyzing their transmission electron microscopy images, mesoporous properties, magnetic properties, and microwave responses. We chose hollow-mesoporous MxFe3-xO4 (M=Fe, Co, Zn) nanoparticles, which had better overall properties, for the drug VP16 (etoposide) loading and microwave-controlled release. The CoxFe3-xO4 and Fe3O4 particles trapped 61.5 and 64.8%, respectively, of the VP16, which were higher than that (60.4%) of ZnxFe3-xO4. Controllable drug release by these simple magnetic nanocarriers can be achieved by microwave irradiation, and VP16-loaded CoxFe3-xO4 released the most VP16 molecules (more than 50% after 1 h and 69.1% after 6 h) under microwave irradiation. Our results confirm the favorable drug loading and microwave-controlled delivery by these ferrites, and lay a theoretical foundation to promote clinical application of the targeted controllable drug delivery system.

Mesoporous black N-TiO2−x hollow spheres as efficient visible-light-driven photocatalysts

Mesoporous black N-TiO2−x hollow spheres are successfully fabricated through a facile evaporation-induced self-assembly (EISA) process, coupled with an etching procedure and an in-situ solid-state chemical reduction strategy. The resultant black N-TiO2−x hollow spheres with high crystallinity possess a narrow band gap of ∼2.37 eV, a large specific surface area of ∼128 m2 g−1, and a well defined hollow sphere structure, which exhibit excellent visible-light-driven photocatalytic performance for degradation of phenol, reduction of Cr(IV), and hydrogen production. The photocatalytic reaction apparent rate constants (k) of the black N-TiO2−x for phenol degradation and Cr(IV) reduction are ∼5 and 6 times higher than that of pristine TiO2, and hydrogen production rate for N-TiO2−x is ∼160 μmol h−1, which is ∼7 folds higher than that of pristine one. The excellent photocatalytic and photoreduction property can be attributed to the synergy effect of N and Ti3+ codoping narrowing the band gap, the high specific surface area offering more surface active sites, and the mesoporous hollow structure favoring light harvesting and refraction.

Hyper-Cross-Linking Mediated Self-Assembly Strategy To Synthesize Hollow Microporous Organic Nanospheres.

Hollow microporous organic nanospheres (H-MONs) are prepared by using polylactide-b-polystyrene diblock copolymers (PLA-b-PS) as the precursor via a hyper-cross-linking mediated self-assembly strategy, in which the hyper-cross-linking PS block forms the microporous organic shell framework, and the degradable PLA block produces the hollow mesoporous core structure. The formation mechanism, morphology, and porosity parameters of the resulting H-MONs are systematically investigated. Moreover, based on the hyper-cross-linking generated rigid microporous organic frameworks, hollow microporous carbon nanospheres (H-MCNs) can be achieved by further pyrolysis progress. The obtained H-MCNs as electrode materials of a supercapacitor exhibit excellent electrochemical performance with specific capacitances of up to 145 F g-1 at 0.2 A g-1, with almost no capacitance loss even after 5000 cycles at 10 A g-1. More especially, H-MONs can be further act as "nanoreactors" for the synthesis of Fe3O4 nanoparticles within hollow cores to construct magnetic core-shell Fe3O4@H-MONs nanocomposite materials. Our strategy represents a new avenue for the preparation of hollow morphology-controlled microporous organic polymers with various potential applications.

Synthesis of hollow and mesoporous structured NaYF4:Yb,Er upconversion luminescent nanoparticles for targeted drug delivery

In this paper, we demonstrated a one-step template-free strategy to fabricate a hollow mesoporous structured NaYF4:Yb,Er nanoparticles with excellent upconversion luminescence. Folic acid (FA), a commonly used cancer-targeting agent, was conjugated on the surface of the nanoparticles based on the presence of free amine groups, which were labeled as NaYF4:Yb,Er-FA HMUCNPs. The properties were extensively studied, which indicated the obtained samples showed a typical hollow mesoporous structure and excellent upconversion luminescence that were useful for cell imaging and drug delivery. The L929 cells viability, hemolysis assay and coagulation test demonstrated good biocompatibility of the samples. The anti-cancer drug doxorubicin hydrochloride (DOX) storage/release properties were demonstrated to be pH-responsive, in which, the drug release might be beneficial at the reduced pH for targeted release and controlled therapy. Moreover, it was found that DOX-loaded NaYF4:Yb,Er-FA HMUCNPs exhibited greater cytotoxicity to KB cells than free DOX due to the specific cell uptake by KB cells via folate receptor-mediate endocytosis. Therefore, the multifunctional nanoparticles combining upconversion luminescent property and hollow mesoporous structure have potential for simultaneous targeted anti-cancer drug delivery and cell imaging.

Hollow mesoporous structured molecularly imprinted polymers for highly sensitive and selective detection of estrogens from food samples

Novel hollow mesoporous molecularly imprinted polymers (HM-MIPs) were proposed for highly selective and sensitive detection of estrogens in food samples. HM-MIPs were prepared by one-pot surface imprinting method using17β-estradiol (E2) as template followed by chemical selective etching to remove solid silica core. Transmission electron microscopy coupled with N2 adsorption experiment confirmed the successful formation of hollow mesoporous structure. Binding adsorption experiment indicated that HM-MIPs have high binding capacity and fast mass transfer property, and class selective recognition of estrogens is possible by E2 imprinted HM-MIPs. HM-MIPs-SPE-HPLC was employed to enrich and detect E1, E2 and E3 in cucumber, milk powder and grass carp samples. Satisfactory recoveries in the range of 85.6%–101.2% and relative standard deviation lower than 4.3% were obtained. The limits of detection for these estrogens were in the range of 33–22ngL−1. Thus, HM-MIPs-SPE method proved to be an accuracy and practical platform for detection of estrogens in food samples.

A targeted drug delivery system based on folic acid-functionalized upconversion luminescent nanoparticles.

In this paper, multifunctional upconversion luminescent NaYF4:Yb,Er nanoparticles with excellent hollow mesoporous structure were first fabricated. The effects of various reaction conditions on the morphology and size of the as-prepared samples were investigated in detail and Ostwald ripening effect was adapted to explain the formation mechanism of the HMUCNPs. Then, folic acid, a well-known ligand for the selective targeting of drugs into tumor cells, was conjugated to the surface of the hollow mesoporous structured upconversion luminescent nanoparticles (HMUCNPs) via amide reaction for targeted delivery of anticancer drugs so as to enhance the therapeutic efficacy. The properties were extensively studied, which indicated the obtained samples showed a typical hollow mesoporous structure and excellent upconversion luminescence that were useful for cell imaging and drug delivery. Drug storage/release properties were demonstrated to be pH responsive, in which the drug release might be beneficial at the reduced pH in certain cancerous tissues for targeted release and controlled therapy at the pathological sites. Meanwhile, DOX-NaYF4:Yb,Er-FA HMUCNPs exhibited greater cytotoxicity than free doxorubicin hydrochloride because folic acid-conjugated HMUCNPs can be specifically taken up by FR-positive KB cells via a receptor-mediated endocytosis. Therefore, the folic acid-functionalized nanoparticles combining upconversion luminescent property and hollow mesoporous structure have potential for simultaneous targeted anticancer drug delivery and cell imaging.

Water-promoted zeolitic imidazolate framework-67 transformation to Ni–Co layered double hydroxide hollow microsphere for supercapacitor electrode material

Hollow Ni–Co layered double hydroxide (LDH) was synthesized with rhombic dodecahedral zeolitic imidazolate framework-67 (ZIF-67) as self-sacrificed template and cobalt precursor. Water was found to be very important role on the formation of Ni–Co LDH hollow microstructure. As a supercapacitor electrode material, the obtained hollow Ni–Co LDH delivered a high specific capacitance of 1530 F g−1 at the current density of 1.0 A g−1 and good cycle performance, which can be ascribed to its hollow mesoporous structure composed of the Ni–Co LDH nanosheets and high specific surface area. Combined with the AC negative electrodes, the assembled asymmetric supercapacitors performed an energy density of 27.5 Wh kg−1 at the power density of 375 W kg−1.

Near-infrared light-mediated DOX-UCNPs@mHTiO2 nanocomposite for chemo/photodynamic therapy and imaging

Recently, incorporating multiple components into one nanoplatform for anticancer theranostics has attracted most attention. Herein, a rattle-structured nanocomposite by using UCNPs (NaYF4:Yb,Tm@NaYF4) as core coated with hollow mesoporous TiO2 (UCNPs@mHTiO2) was constructed as the nanocarrier. First, UCNPs@SiO2@TiO2 was prepared, by a selective etching method to remove SiO2 shell, to make sure the hollow mesoporous structure and high surface area (347m2g−1) of UCNPs@mHTiO2. Under near-infrared (NIR) light irradiation, the UV emission can excite TiO2 to produce ROS and to realize photodynamic therapy (PDT). In addition, the hollow structure offers space to store antitumor drug molecules (doxorubicin, DOX) and this nanocomposite also exhibits the improved DOX release in mildly acidic environment, which could greatly promote chemotherapy efficiency. Moreover, the luminescence resonance energy transfer (LRET) from UCNPs to DOX, owing to the effective distance restricted by the cavity, can be used to monitor the intercellular drug release kinetics. HeLa cells were used as the model cancer cells and the detailed cell experiments show the enhanced cytotoxicity, ascribing to the synergistic effect of chemotherapy and PDT. Therefore, the novel multifunctional nanocomposite, combining with chemotherapy, PDT, and imaging, should be a potential candidate in anticancer field.

Evaluation of zinc-doped mesoporous hydroxyapatite microspheres for the construction of a novel biomimetic scaffold optimized for bone augmentation.

Biomaterials with high osteogenic activity are desirable for sufficient healing of bone defects resulting from trauma, tumor, infection, and congenital abnormalities. Synthetic materials mimicking the structure and composition of human trabecular bone are of considerable potential in bone augmentation. In the present study, a zinc (Zn)-doped mesoporous hydroxyapatite microspheres (Zn-MHMs)/collagen scaffold (Zn-MHMs/Coll) was developed through a lyophilization fabrication process and designed to mimic the trabecular bone. The Zn-MHMs were synthesized through a microwave-hydrothermal method by using creatine phosphate as an organic phosphorus source. Zn-MHMs that consist of hydroxyapatite nanosheets showed relatively uniform spherical morphology, mesoporous hollow structure, high specific surface area, and homogeneous Zn distribution. They were additionally investigated as a drug nanocarrier, which was efficient in drug delivery and presented a pH-responsive drug release behavior. Furthermore, they were incorporated into the collagen matrix to construct a biomimetic scaffold optimized for bone tissue regeneration. The Zn-MHMs/Coll scaffolds showed an interconnected pore structure in the range of 100–300 μm and a sustained release of Zn ions. More importantly, the Zn-MHMs/Coll scaffolds could enhance the osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells. Finally, the bone defect repair results of critical-sized femoral condyle defect rat model demonstrated that the Zn-MHMs/Coll scaffolds could enhance bone regeneration compared with the Coll or MHMs/Coll scaffolds. The results suggest that the biomimetic Zn-MHMs/Coll scaffolds may be of enormous potential in bone repair and regeneration.

Role of Li + ions on the luminescence properties in water dispersible mesoporous CaF 2 : Eu 3 + nanocrystals

Polyvinyl pyrrolidone- (PVP) and ethylene glycol- (EG) coated water dispersible mesoporous CaF2:Eu3+,Li+ nanocrystals were synthesized by a simple one-pot hydrothermal method. The role of Li+ ions on the morphology and spectra in the CaF2 nanocrystals have been reported. The synthesized nanocrystals were monodisperse with regular sphere-like shapes and exhibited obvious hollow mesoporous structure. The results from x-ray photoelectron spectroscopy determined the successful incorporation of Eu3+ ions and Li+ ions into the CaF2 host lattice. The excitation and emission intensity of Eu3+ enhanced with Li+ concentration until 7 mol.%. The nanocrystals could disperse in water for more than a month due to the EG and PVP molecules coated over the nanocrystals.

Achieving excellent activity and stability for oxygen reduction electrocatalysis by hollow mesoporous iron–nitrogen-doped graphitic carbon spheres

Fe–N–C graphitic spheres preparedvia in situpolymerization and functionalization possess both chemical functions (Fe–Nx-coordinated moieties) and hollow mesoporous structures, demonstrating exceptional activity and stability for the 4e−oxygen reduction reaction in both acidic and alkaline media.

Degradable Hollow Mesoporous Silicon/Carbon Nanoparticles for Photoacoustic Imaging-Guided Highly Effective Chemo-Thermal Tumor Therapy in Vitro and in Vivo.

The development of nanoscaled theranostic agents for cancer combination therapies has received intensive attention in recent years. In this report, a degradable hollow mesoporous PEG-Si/C-DOX NP is designed and fabricated for pH-responsive, photoacoustic imaging-guided highly effective chemo-thermal combination therapy. The intrinsic hollow mesoporous structure endows the as-synthesized nanoparticles (NPs) with a high drug loading capacity (31.1%). Under NIR (808 nm) irradiation, the photothermal conversion efficiency of the Si/C NPs is as high as 40.7%. Preferential accumulation of the PEG-Si/C-DOX NPs around tumor tissue was demonstrated with photoacoustic images. Cellular internalization of the NPs and release of the DOX in nuclei are shown with fluorescent images. With efficient NIR photothermal conversion and high DOX loading capacity, the PEG-Si/C-DOX NPs are demonstrated to have remarkable cancer-cell-killing ability and to achieve complete in vivo tumor elimination via combinational chemo-thermal therapy. Last but not least, the NPs show good biodegradability and biosafety, making them a promising candidate for multifunctional drug delivery and cancer theranostic.

A microwave-triggered controllable drug delivery system based on hollow-mesoporous cobalt ferrite magnetic nanoparticles

Facile synthesis and smart designs of multifuctional nanocarriers would make them more potential in the practical application of drug delivery for cancer treatment. In this study, we synthesized hollow-mesoporous cobalt ferrite (H-mCoxFe3−xO4) nanoparticles by a cetyltrimethylammonium bromide (CTAB)-assisted solvothermal method. The resulting monodisperse CoxFe3−xO4 microspheres are 280 nm in diameter with fine uniformity and hollow-mesoporous structure, and they possess a fairly high surface area of 58.03 m2/g, a pore volume of 0.13 cm3/g, an average pore size of 7.21 nm, and are suitable for drug loading. This material has a high magnetization saturation value (42.2 emu/g) for drug targeting and its sodium chloride suspension could raise to 50 °C from room temperature in 180 s. The drug release process shows that the release rate under the microwave irradiation was faster than that under stirring condition, and about 64% VP16 was released after six on/off microwave treatment cycles. So these multifunctional H-mCoxFe3−xO4 nanoparticles with single material are expected to provide the research foundation for using as drug carrier themselves for drug loading, magnetic targeting, and microwave-triggered controllable release.

Hollow structured CoSn(OH)6-supported Pt for effective room-temperature oxidation of gaseous formaldehyde

Uniform CoSn(OH)6 hollow nanoboxes and the derivative with Pt loading (Pt/CoSn(OH)6) were herein synthesized and characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). SEM and TEM analyses showed that CoSn(OH)6 possessed mesoporous hollow structure and Pt nanoparticles with size of 2–8[Formula: see text]nm were uniformly dispersed on the surface of CoSn(OH)6 nanoboxes. The performances of the catalysts for the formaldehyde (HCHO) removal at room temperature were evaluated. These Pt/CoSn(OH)6 catalysts exhibited a remarkable catalytic activity as well as stability for room-temperature oxidative decomposition of gaseous HCHO, while the corresponding CoSn(OH)6 only showed adsorption. The synergetic effect between the highly dispersed Pt nanoparticles and the CoSn(OH)6 nanoboxes with mesoporous hollow structure, a large surface area and abundant surface hydroxyl groups is considered to be the main reason for the observed high catalytic activity of Pt/CoSn(OH)6.

Facile and tunable synthesis of hierarchical mesoporous silica materials ranging from flower structure with wrinkled edges to hollow structure with coarse surface

Mesoporous silica materials have attracted great attention in many fields. However, facile and tunable synthesis of hierarchical mesoporous silica structures is still a big challenge, and thus the development of them still lags behind. Herein, well-defined mesoporous silica flower structure with wrinkled edges and mesoporous silica hollow structure with coarse surface were synthesized simply by using poly(vinylpyrrolidone) and hexadecylamine as cotemplates in different water/ethanol solvent systems. The shape evolution from flower to hollow can be easily realized by tuning the volume ratio of water to ethanol, and the yields of both materials can reach gram scale. The formation mechanisms of mesoporous silica flower and hollow structures were also experimentally investigated and discussed. These novel hierarchical structures having unique physicochemical properties may bring many interesting insights into scientific research and technological application.

Controllable synthesis of nitrogen-doped hollow mesoporous carbon spheres using ionic liquids as template for supercapacitors

We have demonstrated a facile and controllable synthesis of monodispersed nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) using resorcinol/formaldehyde resin as a carbon precursor, tetraethyl orthosilicate as a structure-assistant agent, ionic liquids (ILs) as soft template, partial carbon sources, and nitrogen sources. The sizes and the architectures including hollow and yolk-shell of resultant carbon spheres can be efficiently controlled through the adjustment of the content of ILs. Alkyl chain length of the ILs also has an important effect on the formation of N-HMCSs. With proper alkyl chain length and content of ILs, the resultant N-HMCSs show monodispersed hollow spheres with high surface areas (up to 1158m2g−1), large pore volumes (up to 1.70cm3g−1), and uniform mesopore size (5.0nm). Combining the hollow mesoporous structure, high porosity, large surface area, and nitrogen functionality, the as-synthesized N-HMCSs have good supercapacitor performance with good capacitance (up to 159Fg−1) and favorable capacitance retention (88% capacitive retention after 5000 cycles).

NiO hollow microspheres interconnected by carbon nanotubes as an anode for lithium ion batteries

In this work, NiO hollow microspheres interconnected by multi-walled carbon nanotubes (MWCNTs) were prepared, characterized, and evaluated in terms of lithium ion storage properties. Characterization results showed that the NiO hollow microspheres were formed by self assembly of NiO nanoparticles promoted by MWCNTs, which connected the NiO microspheres to form a long-range network. Electrochemical measurement results showed a charge capacity as high as 597.2mAhg−1 when cycling at the rate 2C and maintained 85.3% capacity of 0.1C. After cycling for 100 times at 1C, it maintained a capacity of 692.3mAhg−1 with retention 89.3% of the initial capacity. The observed excellent electrochemical performance is attributed to the presence of MWCNTs interconnecting the NiO microspheres of the composite material, of which electronic conductivity was improved, and the mesoporous hollow structure effectively alleviated the volume changes to maintain the structural stability during cycling.

Hollow hydroxyapatite microsphere: a promising carrier for bone tissue engineering

Hydroxyapatite (HA) microsphere with abundant ordered mesoporous and large hollow structure was prepared at hydrothermal condition with the aid of citrate. The obtained microsphere was performed as a drug delivery carrier to evaluate its drug loading/releasing behaviour using alendronate (AL) as a model drug. Results revealed that HA particles performed high AL-loading capability (46.8 wt % with respect to the powdered starting materials) and excellent AL-releasing behaviour (sustained drug releasing profile without burst release). Besides, although a proliferation inhibition phenomenon was observed as HA and AL-loading HA (HA-AL) co-cultured with mesenchymal stem cells (MSCs) at the initial stage, after prolonging co-culture period, compared with HA and control group, HA-AL promoted the cells’ proliferation, meanwhile, it facilitated osteogenic differentiation of MSCs and enhanced the expression level of typical markers, all of that ensure HA microsphere is a promising carrier for bone repair.

Synthesis of N-Doped Hollow-Structured Mesoporous Carbon Nanospheres for High-Performance Supercapacitors.

We have demonstrated a facile and controllable synthesis of monodispersed N-doped hollow mesoporous carbon nanospheres (N-HMCSs) and yolk-shell hollow mesoporous carbon nanospheres (N-YSHMCSs) by a modified "silica-assisted" route. The synthesis process can be carried out by using resorcinol-formaldehyde resin as a carbon precursor, melamine as a nitrogen source, hexadecyl trimethylammonium chloride as a template, and silicate oligomers as structure-supporter. The morphological (i.e., particle size, shell thickness, cavity size, and core diameter) and textural features of the carbon nanospheres are easily controlled by varying the amount of ammonium. The resultant carbon nanospheres possess high surface areas (up to 2464 m(2) g(-1)), large pore volumes (up to 2.36 cm(3) g(-1)), and uniform mesopore size (∼2.4 nm for N-HMCSs, ∼ 4.5 nm for N-YSHMCSs). Through combining the hollow mesoporous structure, high porosity, large surface area, and N heteroatomic functionality, the as-synthesized N-doped hollow-structured carbon nanospheres manifest excellent supercapacitor performance with high capacitance (up to 240 F/g), favorable capacitance retention (97.0% capacitive retention after 5000 cycles), and high energy density (up to 11.1 Wh kg(-1)).