Liangxu Lin

Creating high yield water soluble luminescent graphene quantum dots via exfoliating and disintegrating carbon nanotubes and graphite flakes

We have developed an effective method to exfoliate and disintegrate multi-walled carbon nanotubes and graphite flakes. With this technique, high yield production of luminescent graphene quantum dots with high quantum yield and low oxidization can be achieved.

Fabrication of Luminescent Monolayered Tungsten Dichalcogenides Quantum Dots with Giant Spin-Valley Coupling

A high yield (>36 wt %) method has been developed of preparing monolayered tungsten dichalcogenide (WS2) quantum dots (QDs) with lateral size ∼8-15 nm from multilayered WS2 flakes. The monolayered WS2 QDs are, like monolayered WS2 sheets, direct semiconductors despite the flake precursors being an indirect semiconductor. However, the QDs have a significantly larger direct transition energy (3.16 eV) compared to the sheets (2.1 eV) and enhanced photoluminescence (PL; quantum yield ∼4%) in the blue-green spectral region at room temperature. UV/vis measurements reveal a giant spin-valley coupling of the monolayered WS2 QDs at around 570 meV, which is larger than that of monolayered WS2 sheets (∼400 meV). This spin-valley coupling was further confirmed by PL as direct transitions from the conduction band minimum to split valence band energy levels, leading to multiple luminescence peaks centered at around 369 (3.36 eV) and 461 nm (2.69 eV, also contributed by a new defect level). The discovery of giant spin-valley coupling and the strong luminescence of the monolayered WS2 QDs make them potentially of interests for the applications in semiconductor-based spintronics, conceptual valley-based electronics, quantum information technology and optoelectronic devices. However, we also demonstrate that the fabricated monolayered WS2 QDs can be a nontoxic fluorescent label for high contrast bioimaging application.

Fabrication and Luminescence of Monolayered Boron Nitride Quantum Dots

Monolayered boron nitride (BN) quantum dots (QDs; lateral size ≈10 nm) are fabricated using a novel method. Unlike monolayered BN sheets, these BN QDs exhibit blue-green luminescence due to defects formed during preparation. This optical behavior adds significant functionality to a material that is already receiving much attention. It is further shown that the QDs are nontoxic to biological cells and well suited to bio-imaging.

Sulfur-Depleted Monolayered Molybdenum Disulfide Nanocrystals for Superelectrochemical Hydrogen Evolution Reaction

Catalytically driven electrochemical hydrogen evolution reaction (HER) of monolayered molybdenum disulfide (MoS2) is usually highly suppressed by the scarcity of edges and low electrical conductivity. Here, we show how the catalytic performance of MoS2 monolayers can be improved dramatically by catalyst size reduction and surface sulfur (S) depletion. Monolayered MoS2 nanocrystals (NCs) (2-25 nm) produced via exfoliating and disintegrating their bulk counterparts showed improved catalysis rates over monolayer sheets because of their increased edge ratios and metallicity. Subsequent S depletion of these NCs further improved the metallicity and made Mo atoms on the basal plane become catalytically active. As a result, the S-depleted NCs with low mass (∼1.2 μg) showed super high catalytic performance on HER with a low Tafel slope of ∼29 mV/decade, overpotentials of 60-75 mV, and high current densities jx (where x is in mV) of j150 = 9.64 mA·cm(-2) and j200 = 52.13 mA·cm(-2). We have found that higher production rates of H2 could not be achieved by adding more NC layers since HER only happens on the topmost surface and the charge mobility decreases dramatically. These difficulties can be largely alleviated by creating a hybrid structure of NCs immobilized onto three-dimensional graphene to provide a very high surface exposure of the catalyst for electrochemical HER, resulting in very high current densities of j150 = 49.5 mA·cm(-2) and j200 = 232 mA·cm(-2) with ∼14.3 μg of NCs. Our experimental and theoretical studies show how careful design and modification of nanoscale materials/structures can result in highly efficient catalysis. There may be considerable opportunities in the broader family of transition metal dichalcogenides beyond just MoS2 to develop highly efficient atomically thin catalysts. These could offer cheap and effective replacement of precious metal catalysts in clean energy production.

Effective solvothermal deoxidization of graphene oxide using solid sulphur as a reducing agent

Functional group free graphene materials with high electronic conductivities were prepared via solvothermal reaction of solid sulphur (S) and graphene oxide (GO) in a H2O–NMP or H2O–DMF (1 : 1 in volume ratio) solvent at 110 °C for 10 h. Ultraviolet-visible (UV/Vis) analysis revealed that S exhibited strong reductive ability in a boiling GO aqueous solution. Its reducing effect could be further enhanced by using NMP or DMF as a surfactant to adjust the solvent surface tension close to the surface energy of graphene. UV/Vis and X-ray photoelectron spectroscopy (XPS) results confirmed that the electronic structure of graphene had been completely restored and the oxygen contents reduced remarkably. No graphitic stacking between the reduced GO (RGO) was found. As-prepared RGO products also exhibited good dispersivities in various solvents. Moreover, it was inter-convertible between their different forms: agglomerates, simply air dried bulk solids and films and well-dispersed suspensions.

Investigating the bioavailability of graphene quantum dots in lung tissues via Fourier transform infrared spectroscopy

Biomolecular fractions affect the fate and behaviour of quantum dots (QDs) in living systems but how the interactions between biomolecules and QDs affect the bioavailability of QDs is a major knowledge gap in risk assessment analysis. The transport of QDs after release into a living organism is a complex process. The majority accumulate in the lungs where they can directly affect the inhalation process and lung architecture. Here, we investigate the bioavailability of graphene quantum dots (GQDs) to the lungs of rats by measuring the alterations in macromolecular fractions via Fourier transform infrared spectroscopy (FTIR). GQDs were intravenously injected into the rats in a dose-dependent manner (low (5 mg kg−1) and high (15 mg kg−1) doses of GQDs per body weight of rat) for 7 days. The lung tissues were isolated, processed and haematoxylin–eosin stained for histological analysis to identify cell death. Key biochemical differences were identified by spectral signatures: pronounced changes in cholesterol were found in two cases of low and high doses; a change in phosphorylation profile of substrate proteins in the tissues was observed in low dose at 24 h. This is the first time biomolecules have been measured in biological tissue using FTIR to investigate the biocompatibility of foreign material. We found that highly accurate toxicological changes can be investigated with FTIR measurements of tissue sections. As a result, FTIR could form the basis of a non-invasive pre-diagnostic tool for predicting the toxicity of GQDs.

Simple growth of BCNO@C core shell fibres and luminescent BCNO tubes

A novel core shell structure (BCNO@C with C core and BCNO shell) has been prepared using a simple heating reaction. These fibres have a diameter around 100–300 nm with lengths up to hundreds of micrometres. To create BCNO@C fibres, the C fibres (cores) were first grown using Ni particle catalysts before adding BCNO shells. Simple burning of the core shell fibres led to the formation of novel B0.43C0.23N0.27O0.07 tubes. Unlike the BCN tubes grown from the substitution of C tubes, the BCNO tubes here have a homogenous structure with luminescence centered at around 386 nm (from 290–700 nm), which was mainly contributed to by the 1,3-B centers, carbene structures and BO2− species. The method used here is suitable to being adapted in the future to tune the electronic structure of BCN based materials.

Synthesis of hierarchically porous mullite ceramics with improved thermal insulation via foam-gelcasting combined with pore former addition

ABSTRACT To further improve the thermal insulation performance of porous mullite ceramics used in important industrial sectors, a combined foam-gelcasting and pore-former addition approach was investigated in this work, by which hierarchical porous mullite ceramics with excellent properties, in particular, thermal insulation property, were prepared. Both mesopores (2–50 nm) and macropores (117.8–202.7 μm) were formed in porous mullite ceramics resultant from 2 h firing at 1300°C with various amounts of submicron-sized CaCO3 pore former. The former mainly arose from the decomposition of CaCO3, and the latter from the foam-gelcasting process. The porous samples prepared with CaCO3 addition had low linear shrinkage of 2.35–4.83%, high porosity of 72.98–79.07% and high compressive strength of 5.52–14.82 MPa. Most importantly, they also exhibited a very low thermal-conductivity, e.g. 0.114 W m−1 K−1 at 200°C, which was much lower than in the cases of their counterparts prepared via the conventional foam-gelcasting route.

Bio-imaging of lung diseases using luminescent graphene nanocrystals

In this study, we report for the first time the spectral and passive targeting features of Graphene Nanocrystals (GNCs) in biological cells. The analysis of the exposure of GNCs to histological specimen has been performed using fluorescence imaging. The nanocrystals have been exposed to rat animal models in a time and dose dependent manner, and lung tissues have been analyzed to demonstrate the enhanced permeability, retention effect and selectivity of GNCs in lung tumors.