Shear-induced phase transition of nanocrystalline hexagonal boron nitride to wurtzitic structure at room temperature and lower pressure.

Disordered structures of boron nitride (BN), graphite, boron carbide (BC), and boron carbon nitride (BCN) systems are considered important precursor materials for synthesis of superhard phases in these systems. However, phase transformation of such materials can be achieved only at extreme pressure-temperature conditions, which is irrelevant to industrial applications. Here, the phase transition from disordered nanocrystalline hexagonal (h)BN to superhard wurtzitic (w)BN was found at room temperature under a pressure of 6.7 GPa after applying large plastic shear in a rotational diamond anvil cell (RDAC) monitored by in situ synchrotron X-ray diffraction (XRD) measurements. However, under hydrostatic compression to 52.8 GPa, the same hBN sample did not transform to wBN but probably underwent a reversible transformation to a high-pressure disordered phase with closed-packed buckled layers. The current phase-transition pressure is the lowest among all reported direct-phase transitions from hBN to wBN at room temperature. Usually, large plastic straining leads to disordering and amorphization; here, in contrast, highly disordered hBN transformed to crystalline wBN. The mechanisms of strain-induced phase transformation and the reasons for such a low transformation pressure are discussed. Our results demonstrate a potential of low pressure-room temperature synthesis of superhard materials under plastic shear from disordered or amorphous precursors. They also open a pathway of phase transformation of nanocrystalline materials and materials with disordered and amorphous structures under extensive shear.

A reduced graphene oxide based electrochemical biosensor for tyrosine detection.

In this paper, a 'green' and safe hydrothermal method has been used to reduce graphene oxide and produce hemin modified graphene nanosheet (HGN) based electrochemical biosensors for the determination of l-tyrosine levels. The as-fabricated HGN biosensors were characterized by UV-visible absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy (FTIR) spectra and thermogravimetric analysis (TGA). The experimental results indicated that hemin was successfully immobilized on the reduced graphene oxide nanosheet (rGO) through π-π interaction. TEM images and EDX results further confirmed the attachment of hemin on the rGO nanosheet. Cyclic voltammetry tests were carried out for the bare glass carbon electrode (GCE), the rGO electrode (rGO/GCE), and the hemin-rGO electrode (HGN/GCE). The HGN/GCE based biosensor exhibits a tyrosine detection linear range from 5 × 10(-7) M to 2 × 10(-5) M with a detection limitation of 7.5 × 10(-8) M at a signal-to-noise ratio of 3. The sensitivity of this biosensor is 133 times higher than that of the bare GCE. In comparison with other works, electroactive biosensors are easily fabricated, easily controlled and cost-effective. Moreover, the hemin-rGO based biosensors demonstrate higher stability, a broader detection linear range and better detection sensitivity. Study of the oxidation scheme reveals that the rGO enhances the electron transfer between the electrode and the hemin, and the existence of hemin groups effectively electrocatalyzes the oxidation of tyrosine. This study contributes to a widespread clinical application of nanomaterial based biosensor devices with a broader detection linear range, improved stability, enhanced sensitivity and reduced costs.

Porphyrin Immobilized Nanographene Oxide for Enhanced and Targeted Photothermal Therapy of Brain Cancer.

Brain cancer is a fatal disease that is difficult to treat because of poor targeting and low permeability of chemotherapeutic drugs through the blood brain barrier. In a comparison to current treatments, such as surgery followed by chemotherapy and/or radiotherapy, photothermal therapy is a remarkable noninvasive therapy developed in recent years. In this work, porphyrin immobilized nanographene oxide (PNG) was synthesized and bioconjugated with a peptide to achieve enhanced and targeted photothermal therapy for brain cancer. PNG was dispersed into the agar based artificial tissue model and demonstrated a photo-to-thermal conversion efficiency of 19.93% at a PNG concentration of only 0.5 wt %, with a heating rate of 0.6 °C/s at the beginning of irradiation. In comparison, 0.5 wt % graphene oxide (GO) indicated a photo-to-thermal conversion efficiency of 12.20% and a heating rate of 0.3 °C/s. To actively target brain tumor cells without harming healthy cells and tissues surrounding the laser path, a tripeptide l-arginyl-glycyl-l-aspartic (RGD) was further grafted to PNG. The photothermal therapy effects of PNG-RGD completely eliminated the tumor in vivo, indicating its excellent therapeutic effect for the treatment of brain cancer.

Synthesis of highly nanoporous YBO3 architecture via a co-precipitation approach and tunable luminescent properties.

We present a simple co-precipitation method to prepare highly nanoporous YBO(3) architecture using NaBO(3) · 4H(2)O as a boric source and 600°C as the annealing temperature. The reaction was carried out under an aqueous condition without any organic solvent, surfactant, or catalysts. The prepared samples were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photoluminescence of doped-nanoporous YBO(3):Eu(3+) was further investigated. It is expected that highly nanoporous YBO(3) architecture can be an ideal candidate for applications in catalysis, adsorption, and optoelectronic devices.