The Experts below are selected from a list of 822 Experts worldwide ranked by ideXlab platform

Atsushi Takagaki - One of the best experts on this subject based on the ideXlab platform.

  • effects of post thermal treatments of ball milled Boron Nitrides on solid base catalysis
    Catalysis Today, 2020
    Co-Authors: Atsushi Takagaki
    Abstract:

    Abstract Ball-milled hexagonal Boron nitride was investigated as a solid base catalyst. The ball-milled Boron Nitrides were heated in a vacuum or air and used for Knoevenagel condensation. Measurements by X-ray diffraction, nitrogen adsorption, thermogravimetry-mass spectrometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy indicated that the heat treatment under vacuum hardly changed the physicochemical properties including crystal structure and surface composition whereas the heat treatment in air significantly altered the properties due to the formation of B2O3. The number of basic sites increased with the increase of the evacuation temperature. The Boron Nitrides after evacuation gave moderate product yield for Knoevenagel condensation of benzaldehyde with malononitrile at 40 °C. The Boron Nitrides after calcination showed different activity, dependent on the calcination temperature. The Boron nitride after ball-milling, followed by calcination at 300 °C exhibited the highest activity. The catalytic activity was not directly related to the base amount and the surface areas, suggesting that acid-base bifunctionality plays an important role in Knoevenagel condensation using the ball-milled Boron nitride catalysts.

  • effects of ball milling treatment on physicochemical properties and solid base activity of hexagonal Boron Nitrides
    Catalysis Science & Technology, 2019
    Co-Authors: Shoichiro Namba, Atsushi Takagaki, Keiko Jimura, Shigenobu Hayashi, Ryuji Kikuchi, Ted S Oyama
    Abstract:

    Hexagonal Boron nitride (h-BN) was ball-milled at various rotation speeds (150–600 rpm) using a planetary ball-mill. Ball-milling disrupted the layered structure of the h-BN, resulting in significant increases of surface area. Ball-milling at 400 rpm gave the highest surface area of 412 m2 g−1 while higher rotation speeds decreased the surface areas due to agglomeration. Moreover, ball-milling resulted in the emergence of amino- and hydroxyl groups on the surface which were observed by Fourier transform infrared spectroscopy, and partial oxidation of the surface Boron by the formation of B–OH groups was confirmed by X-ray photoelectron spectroscopy. The appearance of trigonal B–O and tetrahedral B–O was observed by Boron-11 magic-angle spinning nuclear magnetic resonance spectroscopy. The number of base sites was increased with the increase of rotation speeds of milling, corresponding to the formation of amino groups. The ball-milled h-BN showed catalytic activity for the nitroaldol reaction between nitromethane and benzaldehyde in which the h-BN milled at 400 rpm exhibited the highest reaction rate and turnover frequency. In addition, the ball-milled h-BN could convert glucose with the formation of fructose at 40 °C whereas pristine h-BN showed no activity. The base sites were mainly responsible for the catalytic activity.

Bingqing Wei - One of the best experts on this subject based on the ideXlab platform.

  • dual functionalities of few layered Boron Nitrides in the design and implementation of ca oh 2 nanomaterials toward an efficient wall painting fireproofing and consolidation
    ACS Applied Materials & Interfaces, 2019
    Co-Authors: Jinmeng Zhu, Jia Wang, Yuanyuan Zhang, Yijian Cao, Mara Camaiti, Bingqing Wei
    Abstract:

    Preserving ancient wall paintings from damage has become a challenge over the years. Nanosized calcium hydroxide (Ca(OH)2) has been identified as a promising material to preserve wall paintings. However, the synthesis of nanosized Ca(OH)2 is extremely difficult. Here, we demonstrate a breakthrough in wall painting protection enabled by Boron nitride nanosheets (BNNSs) through strategic synthesis Ca(OH)2-BNNS nanohybrids using an aqueous method. The BNNS have two significant functionalities in the design and implementation of the Ca(OH)2 nanomaterials. First, the introduction of BNNS results in the successful synthesis of uniform and nanosized Ca(OH)2 (∼80 nm) in the nanohybrids, which can be attributed to the supersaturation-induced "etching-stripping" mechanism. More interestingly and importantly, a unique gradient penetration structure is strategically formed when applying Ca(OH)2-BNNS hybrids on the wall paintings, i.e., the BNNS-rich layer will be at the surface of wall painting, whereas Ca(OH)2 nanomaterials prefer to penetrate deep in to the wall paintings. This gradient structure will allow the BNNS-rich layer to protect the wall paintings from fire, which is the first report to date among the protection materials for wall paintings; at the same time, nanosized Ca(OH)2 shows superior wall painting consolidation strength compared to commercial Ca(OH)2 material. These results endow new applications of the newly emerging two-dimensional nanomaterials for protecting cultural heritage.

  • Dual Functionalities of Few-Layered Boron Nitrides in the Design and Implementation of Ca(OH)2 Nanomaterials toward an Efficient Wall Painting Fireproofing and Consolidation
    2019
    Co-Authors: Jinmeng Zhu, Jia Wang, Yuanyuan Zhang, Yijian Cao, Mara Camaiti, Bingqing Wei
    Abstract:

    Preserving ancient wall paintings from damage has become a challenge over the years. Nanosized calcium hydroxide (Ca­(OH)2) has been identified as a promising material to preserve wall paintings. However, the synthesis of nanosized Ca­(OH)2 is extremely difficult. Here, we demonstrate a breakthrough in wall painting protection enabled by Boron nitride nanosheets (BNNSs) through strategic synthesis Ca­(OH)2-BNNS nanohybrids using an aqueous method. The BNNS have two significant functionalities in the design and implementation of the Ca­(OH)2 nanomaterials. First, the introduction of BNNS results in the successful synthesis of uniform and nanosized Ca­(OH)2 (∼80 nm) in the nanohybrids, which can be attributed to the supersaturation-induced “etching–stripping” mechanism. More interestingly and importantly, a unique gradient penetration structure is strategically formed when applying Ca­(OH)2-BNNS hybrids on the wall paintings, i.e., the BNNS-rich layer will be at the surface of wall painting, whereas Ca­(OH)2 nanomaterials prefer to penetrate deep in to the wall paintings. This gradient structure will allow the BNNS-rich layer to protect the wall paintings from fire, which is the first report to date among the protection materials for wall paintings; at the same time, nanosized Ca­(OH)2 shows superior wall painting consolidation strength compared to commercial Ca­(OH)2 material. These results endow new applications of the newly emerging two-dimensional nanomaterials for protecting cultural heritage

Mustafa Culha - One of the best experts on this subject based on the ideXlab platform.

  • Transferrin-Mediated Glioblastoma Cell Targeting of Hexagonal Boron Nitrides
    Plasmonics, 2020
    Co-Authors: Melis Emanet, Ozlem şen, Mustafa Culha
    Abstract:

    Hexagonal Boron Nitrides (hBNs) are promising nanomaterials with their high Boron content, non-toxic nature in inactive form, high chemical stability, and mechanical strength. However, their hydrophobic nature limits their use in biomedical applications. Therefore, the hBNs have been functionalized with DSPE-PEG-NH_2 to increase their colloidal stability and circulation time in bloodstream as well as to provide active sites on their surface for further functionalization with tumor-targeting agents. Then, further functionalization of the DSPE-PEG-hBNs with transferrin (TfR) was applied for selective targeting of transferrin receptors overexpressed by brain tumor cells. After that, the cellular interaction and biocompatibility of the structure was investigated on glioblastoma multiforme (U87MG) cancer cells. The cellular investigations showed that transferrin functionalization of the DSPE-PEG-hBNs increased their uptake by glioblastoma cancer cells and decreased cell viability due to the enhanced cellular internalization. Based on the data, the TfR-DSPE-PEG-hBNs are promising agents to evaluate them in drug carrying and targeting applications. Graphical Abstract

  • hexagonal Boron Nitrides reduce the oxidative stress on cells
    Nanotechnology, 2020
    Co-Authors: Irem Culha Taskin, Melis Emanet, Mustafa Culha, Bayram Yilmaz
    Abstract:

    : The molecular stress caused by a drug administered to treat a disorder on healthy cells appears as a side effect. In this study, we aim to understand the potential of hexagonal Boron Nitrides (hBNs) as a therapeutic agent to relieve the cellular stress exerted by drugs. First, the cytotoxicity of hBNs and their possible degradation product, boric acid (BA), on the embryonic mouse hippocampal cell line mHippo E-14 was assessed in a wide concentration range (4.4-440 μg ml-1) of Boron including hBNs and BA for 24 and 72 h exposure. Then, cell cycle, reactive oxygen species generation, cell death mechanism and apoptotic body formation in nuclei with hBN and BA exposure were evaluated at increased concentrations and incubation times. Finally, the cells, exposed to doxorubicin (DOX), an anti-cancer chemotherapy drug, to exert oxidative stress, were treated with hBNs and BA. The results indicate that hBNs decrease the oxidative stress at the concentrations that are nontoxic to cells. The study suggests that hBNs can open new venues for their investigation to reduce or eliminate the adverse effects of toxic drugs used in the treatment of several fatal diseases including neurological disorders and cancer with their slow degradation feature.

  • stimulatory effect of hexagonal Boron Nitrides in wound healing
    ACS Applied Bio Materials, 2019
    Co-Authors: Ozlem şen, Melis Emanet, Mustafa Culha
    Abstract:

    There is an increased interest in the use of hexagonal Boron Nitrides (hBNs) in medicine due to their unique properties that include low toxicity, absorption of UV light and neutrons, high chemical...

  • biocompatibility evaluation of hexagonal Boron Nitrides on healthy mouse hippocampal cell line and their positive effect on stressed cells
    Beilstein Archives, 2019
    Co-Authors: Irem Culha Taskin, Melis Emanet, Mustafa Culha, Bayram Yilmaz
    Abstract:

    In this study, hexagonal Boron Nitrides (hBNs) and their degradation product, boric acid (BA), are comparatively evaluated to investigate their biocompatibility and oxidative stress relieving effects on embryonic mouse hippocampal cell line (mHippoE-14). First, cell viability is assessed for a wide concentration range of 4.40-440 μg/mL of Boron (B) containing hBNs and BA for 24 and 72 h exposures. Then, cell cycle, reactive oxygen species (ROS) generation, and cell death mechanisms are investigated at a concentration range of 4.4-44 μg/mL with increased incubation times. Finally, the influence of hBNs and BA on apoptotic body formation is monitored to analyze their nuclei integrity with confocal microscopy. Both hBNs and BA are found to be not cytotoxic at lower than 22 µg/mL B containing concentrations, and hBNs are much less cytotoxic compared to BA. At low concentration of hBNs, no detectable change in cell cycle, ROS production and DNA damage are observed. The study was further extended by exposing the cells to doxorubicin (DOX) to cause stress on cells before treating with hBNs and BA to investigate their positive effect on cellular metabolism. It is found that both hBNs and BA helps to increase the cell viability after the exposure to DOX. The results are envisioning the exploitation of hBNs as biocompatible agents for their possible biomedical applications including mitigating oxidative stress caused by various drugs used for neurological diseases and brain cancers. Since hBNs slowly degrade in biological media, they can be used as a controlled B releasing agent as compared to ionic BA in addition to their nanocarrier feature.

  • one step synthesis of hexagonal Boron Nitrides their crystallinity and biodegradation
    Frontiers in Bioengineering and Biotechnology, 2018
    Co-Authors: Ozlem şen, Melis Emanet, Mustafa Culha
    Abstract:

    Hexagonal Boron Nitrides (hBNs) have recently been investigated for several novel applications due to their unique properties such as biocompatibility, superhydrophobicity, electrical insulation, and thermal and chemical stability. In addition, their biodegradation products have recently reported to have therapeutic effect on certain cancer types. hBNs are easily synthesized from Boron and nitrogen precursors at moderately low temperatures. However, crystallinity and yield vary depending on the type of precursor, reaction temperature, and duration. In this study, a simple one-step hBNs synthesis method is reported without a catalyst, which might be an undesired contaminant for biomedical applications. The influence of Boron precursors (boric acid, colemanite, or Boron trioxide) on hBNs crystallinity, stability, and biodegradation in suspensions containing oxidative and hydrolytic degradation agents is investigated with the aim of their possible application in biomedicine. We found that the choice of Boron precursor is a critically important parameter controlling the hBNs crystallinity and dependently influencing the biodegradation rate.

Dmitri Golberg - One of the best experts on this subject based on the ideXlab platform.

  • highly water soluble porous and biocompatible Boron Nitrides for anticancer drug delivery
    ACS Nano, 2014
    Co-Authors: Qunhong Weng, Xuebin Wang, Yoshio Bando, Binju Wang, Nobutaka Hanagata, Xia Li, Xi Wang, Xiangfen Jiang, Dmitri Golberg
    Abstract:

    Developing materials for "Nano-vehicles" with clinically approved drugs encapsulated is envisaged to enhance drug therapeutic effects and reduce the adverse effects. However, design and preparation of the biomaterials that are porous, nontoxic, soluble, and stable in physiological solutions and could be easily functionalized for effective drug deliveries are still challenging. Here, we report an original and simple thermal substitution method to fabricate perfectly water-soluble and porous Boron nitride (BN) materials featuring unprecedentedly high hydroxylation degrees. These hydroxylated BNs are biocompatible and can effectively load anticancer drugs (e.g., doxorubicin, DOX) up to contents three times exceeding their own weight. The same or even fewer drugs that are loaded on such BN carriers exhibit much higher potency for reducing the viability of LNCaP cancer cells than free drugs.

  • Boron nitride porous microbelts for hydrogen storage
    ACS Nano, 2013
    Co-Authors: Qunhong Weng, Xuebin Wang, Yoshio Bando, Dmitri Golberg
    Abstract:

    Layered Boron Nitrides (BNs) are usually viewed as excellent protective coatings and reinforcing materials due to their chemical inertness and high mechanical strength. However, the attention paid to their potential applications in gas sorption, especially in case of hydrogen, has obviously been insufficient. Herein, a novel BN material (i.e., porous microbelts), with the highest specific surface area ever reported for any BN system, up to 1488 m2 g–1, is obtained through one-step template-free reaction of a Boron acid–melamine precursor with ammonia. Comprehensive high-resolution transmission electron microscopy, X-ray diffraction, and Raman characterizations all confirm that the obtained BN phase is partially disordered, shows an enlarged average spacing between adjacent (0002) layers (d0002 = 0.38 nm, compared to normal 0.33 nm for a bulk layered BN), and belongs to an intermediate state between hexagonal (h-BN) and amorphous (a-BN) phases. By changing the synthesis temperatures, the textures of obtain...

  • high resolution analytical electron microscopy of Boron Nitrides laser heated at high pressure
    Journal of Electron Microscopy, 1997
    Co-Authors: Dmitri Golberg, Yoshio Bando, M I Eremets, Keiji Kurashima, Takashi Tamiya, Kenichi Takemura, Hitoshi Yusa
    Abstract:

    High-resolution transmission electron microscopy and electron energy loss spectroscopy have been carried out for cubic and hexagonal Boron Nitrides (BN) laser heated in argon or nitrogen media at pressures of 5-11 GPa in a diamond anvil cell. In particular, recrystallized products of irradiation from a fluid phase in the form of tiny flakes have been investigated. The observations revealed perfect crystallinity (either of cubic or hexagonal BN) in flakes recrystallized from the fluid and traces of melting in the bulk. Multishelled circular and polygonal BN nanotubes, which did not contain any additional inclusions, were found after laser heating of cubic and hexagonal BN in nitrogen. The nanotubes typically exhibited 3-10 shells, a characteristic inner dimension in cross-section of 2-6 nm and stoichiometry of B/N ~1. They were found to have grown either from a cubic BN matrix or from a mixture of amorphous + turbostratic + hexagonal BN, which had recrystalized on the specimens' surface from the fluid phase.

Takuya Morishita - One of the best experts on this subject based on the ideXlab platform.

  • highly thermally conductive and electrically insulating polymer nanocomposites with Boron nitride nanosheet ionic liquid complexes
    RSC Advances, 2017
    Co-Authors: Takuya Morishita, Naoko Takahashi
    Abstract:

    Highly thermally conductive and electrically insulating polymer materials are eagerly anticipated for thermal management of various applications including next-generation power electronic devices. Herein, Boron nitride nanosheet (BNNS)/ionic liquid (IL)/polymer composites with high thermal conductivity (TC) and high electrical insulation were fabricated. BNNSs were exfoliated and noncovalently functionalized with ILs by one-step route using liquid-phase exfoliation of hexagonal Boron Nitrides in ILs. ILs improved exfoliation by physical adsorption on BNNS surfaces, forming highly soluble few-layered BNNS/IL complexes with high yields. The use of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) gave sufficient amounts of BNNS/[bmim][PF6] complexes for fabrication of BNNS/IL/polymer composites. Then BNNS/[bmim][PF6]/poly(methyl methacrylate) (PMMA) composite films were prepared using a simple wet-process, significantly enhancing both through-plane and in-plane TCs. The through-plane and in-plane TCs of the BNNS/[bmim][PF6]/PMMA composite films containing 50 wt% (≈34 vol%) BNNS reached approx. 5.4 W m−1 K−1 and approx. 7.3 W m−1 K−1, respectively. The through-plane TC is superior to those of previously reported BNNS/thermoplastic (TP) polymer composites with similar BNNS loadings. This high through-plane TC derives from randomly dispersed BNNSs and good affinity between PMMA and [bmim][PF6] on the BNNS surface. The optimum functionalization ratio (FR, [bmim][PF6]/BNNS mass ratio) found for enhancing the TC represents a balance of increased compatibility of BNNS/PMMA and a decrease of TC caused by extra amorphous [bmim][PF6]. Furthermore, the combination of IL and polymer matrix species is important. The through-plane TC of BNNS/[bmim][PF6]/polybutylene terephthalate (PBT) composite films containing 50 wt% BNNS was extremely high (approx. 5.8 W m−1 K−1), although that of BNNS/[bmim][PF6]/polycarbonate (PC) composite films was very low (approx. 1.2 W m−1 K−1) because of the lower affinity of [bmim][PF6] with PC. Moreover, the volume resistivity of the BNNS/[bmim][PF6]/TP polymer composites was improved compared with that of h-BN/TP polymer composites. The BNNS/IL/polymer composites are extremely promising for various applications requiring highly TC and electrical insulation.

  • facile exfoliation and noncovalent superacid functionalization of Boron nitride nanosheets and their use for highly thermally conductive and electrically insulating polymer nanocomposites
    ACS Applied Materials & Interfaces, 2016
    Co-Authors: Takuya Morishita, Hirotaka Okamoto
    Abstract:

    There is an increasing demand for highly thermally conductive and electrically insulating polymer materials for next-generation electronic devices, power systems, and communication equipment. Boron nitride nanosheets (BNNSs) are insulating materials with extremely high thermal conductivity. However, BNNSs suffer from the lack of facile and low-cost methods for producing large volumes of BNNSs, and extremely low through-plane thermal conductivities of BNNS/polymer composites as compared to the in-plane thermal conductivities. Herein, highly soluble, noncovalently functionalized Boron nitride nanosheets (NF-BNNSs) with chlorosulfonic acid (CSA) were prepared by extremely facile and low-cost direct exfoliation of hexagonal Boron Nitrides (h-BNs), and acted as excellent nanofillers for dramatically improving both in- and through-plane thermal conductivities of insulating polymers. CSA is a cheap and versatile superacid with a large production volume. CSA showed strong physical adsorption on h-BN surfaces, giv...

  • Facile Exfoliation and Noncovalent Superacid Functionalization of Boron Nitride Nanosheets and Their Use for Highly Thermally Conductive and Electrically Insulating Polymer Nanocomposites
    2016
    Co-Authors: Takuya Morishita, Hirotaka Okamoto
    Abstract:

    There is an increasing demand for highly thermally conductive and electrically insulating polymer materials for next-generation electronic devices, power systems, and communication equipment. Boron nitride nanosheets (BNNSs) are insulating materials with extremely high thermal conductivity. However, BNNSs suffer from the lack of facile and low-cost methods for producing large volumes of BNNSs, and extremely low through-plane thermal conductivities of BNNS/polymer composites as compared to the in-plane thermal conductivities. Herein, highly soluble, noncovalently functionalized Boron nitride nanosheets (NF-BNNSs) with chlorosulfonic acid (CSA) were prepared by extremely facile and low-cost direct exfoliation of hexagonal Boron Nitrides (h-BNs), and acted as excellent nanofillers for dramatically improving both in- and through-plane thermal conductivities of insulating polymers. CSA is a cheap and versatile superacid with a large production volume. CSA showed strong physical adsorption on h-BN surfaces, giving few-layered NF-BNNSs in high yields (up to ∼25%). The crystallinity of the NF-BNNS was perfectly maintained even after CSA treatment. The physical adsorption of CSAs imparted high solubility for BNNSs in various organic solvents, yielding NF-BNNS uniformly dispersed-thermoplastic polymer composite films through a simple wet-process using predispersed NF-BNNS solutions. Random dispersion of NF-BNNSs in thermoplastic polymer films dramatically enhanced both the in- and through-plane thermal conductivities (>10 W m–1 K–1). The through-plane thermal conductivity of the NF-BNNS/polybutylene terephthalate (PBT) composite films was much greater (up to 11.0 W m–1 K–1) than those previously reported for BNNS/thermoplastic polymer composites (≤2.6 W m–1 K–1). These results are also due to an increase of interactions between the BNNS and polymer matrices, caused by physical adsorption of CSAs on BNNS surfaces. Moreover, the volume resistivity of the NF-BNNS/PBT composite films was significantly improved compared with pristine PBT. The NF-BNNS/polymer composites are very promising as highly thermally conductive and electrically insulating materials in various applications