Qing Huang

Photoluminescent Ti3C2 MXene Quantum Dots for Multicolor Cellular Imaging

The fabrication of photoluminescent Ti3 C2 MXene quantum dots (MQDs) by a facile hydrothermal method is reported, which may greatly extend the applications of MXene-based materials. Interestingly, the as-prepared MQDs show excitation-dependent photoluminescence spectra with quantum yields of up to ≈10% due to strong quantum confinement. The applications of MQDs as biocompatible multicolor cellular imaging probes and zinc ion sensors are demonstrated.

Sintering and thermal properties of multiwalled carbon nanotube–BaTiO3 composites

Densified multiwalled carbon nanotube (MWNT)–BaTiO3 composites were successfully fabricated through a spark plasma sintering (SPS) method. The influences of sintering temperature, annealing time, and the content of carbon nanotubes on the densification of composites were studied in detail. The morphology of fracture surface was observed using field emission scanning electron microscope (FE-SEM). Through analyzing the temperature dependent shrinkage rate, we found that the incorporation of carbon nanotubes can effectively accelerate the densification process of MWNT–BaTiO3 composites. Excellent electrical and thermal conductivity of MWNTs were proposed to account for this unexpected sintering behavior. Thermal properties of MWNT–BaTiO3 composites, including specific heat capacity, thermal diffusivity, and thermal conductivity, were also principally investigated. The experimental results show that the thermal diffusivity and thermal conductivity both unusually decreased although the specific heat capacity increased after adding CNTs into composites. It was suggested that the interfacial thermal barrier between CNTs and the BaTiO3 matrix plays a crucial role in determining the thermal conductivity of bulk composites. A simplified effective medium approximation formulation was used to simulate and predict the thermal conductivity of the MWNT–BaTiO3 composite, but only fitted well with the measured values for low CNTs content (2.45 vol%). The reason for this deviation was proposed and needs further work to make it clear thoroughly.

Loading Actinides in Multilayered Structures for Nuclear Waste Treatment: The First Case Study of Uranium Capture with Vanadium Carbide MXene

Efficient nuclear waste treatment and environmental management are important hurdles that need to be overcome if nuclear energy is to become more widely used. Herein, we demonstrate the first case of using two-dimensional (2D) multilayered V2CTx nanosheets prepared by HF etching of V2AlC to remove actinides from aqueous solutions. The V2CTx material is found to be a highly efficient uranium (U(VI)) sorbent, evidenced by a high uptake capacity of 174 mg g(-1), fast sorption kinetics, and desirable selectivity. Fitting of the sorption isotherm indicated that the sorption followed a heterogeneous adsorption model, most probably due to the presence of heterogeneous adsorption sites. Density functional theory calculations, in combination with X-ray absorption fine structure characterizations, suggest that the uranyl ions prefer to coordinate with hydroxyl groups bonded to the V-sites of the nanosheets via forming bidentate inner-sphere complexes.

Synthesis and Electrochemical Properties of Two-Dimensional Hafnium Carbide

We demonstrate fabrication of a two-dimensional Hf-containing MXene, Hf3C2Tz, by selective etching of a layered parent Hf3[Al(Si)]4C6 compound. A substitutional solution of Si on Al sites effectively weakened the interfacial adhesion between Hf-C and Al(Si)-C sublayers within the unit cell of the parent compound, facilitating the subsequent selective etching. The underlying mechanism of the Si-alloying-facilitated etching process is thoroughly studied by first-principles density functional calculations. The result showed that more valence electrons of Si than Al weaken the adhesive energy of the etching interface. The MXenes were determined to be flexible and conductive. Moreover, this 2D Hf-containing MXene material showed reversible volumetric capacities of 1567 and 504 mAh cm-3 for lithium and sodium ions batteries, respectively, at a current density of 200 mAg-1 after 200 cycles. Thus, Hf3C2Tz MXenes with a 2D structure are candidate anode materials for metal-ion intercalation, especially for applications where size matters.

Bioactive calcium sulfate/magnesium phosphate cement for bone substitute applications.

A novel calcium sulfate/magnesium phosphate cement (CSMPC) composite was prepared and studied in the present work. The physical properties including the phases, the microstructures, the setting properties and the compressive strengths of the CSMPCs were studied. The bio-performances of the CSMPCs were comprehensively evaluated using in vitro simulated body fluid (SBF) method and in vitro cell culture. The dependence of the physical and chemical properties of the CSMPC on its composition and microstructure was studied in detail. It is found that the CSMPC composites exhibited mediate setting times (6-12 min) compared to the calcium sulfate (CS) and the magnesium phosphate cement (MPC). They showed an encapsulation structure in which the unconverted hexagonal prism CSH particles were embedded in the xerogel-like MPC matrix. The phase compositions and the mechanical properties of the CSMPCs were closely related to the content of MPC and the hardening process. The CSMPCs exhibited excellent bioactivity and good biocompatibility to support the cells to attach and proliferate on the surface. The CSMPC composite has the potential to serve as bone grafts for the bone regeneration.

Study of phase transformation behaviour of alumina through precipitation method

Alumina hydrates were prepared by the wet chemical method under different pH values and subsequently calcined through both conventional and microwave heating approaches. After calcination at 500xa0°C for 2xa0h, amorphous precursor was partially transformed to α-alumina. NH4NO3 remaining in the dried precursor without further washing after precipitation reaction was found to increase the transformation temperature, which is different from previous published results. Microwave calcination was also employed and can dramatically enhance the phase transformation rate in comparison with the conventional method. A combination of microwave heating and amorphous precursor may be a viable strategy to fabricate α-alumina at low temperatures rapidly.

Preparation of nanocrystalline-coated carbon nanotube/Ni0.5Zn0.5Fe2O4 composite with excellent electromagnetic property as microwave absorber

A combined precipitation-hydrothermal method was used to fabricate carbon nanotube/Ni0.5Zn0.5Fe2O4 ferrite composite powders. The phase, microstructure and electromagnetic properties of CNT/NiNi0.5Zn0.5Fe2O4 composites were investigated. After surface modification, The zeta potential value of CNTs could maintain at about -50mV when pH is higher than 8, which affords a suitable surface environment for in situ coating of NiNi0.5Zn0.5Fe2O4 nanocrystallines. With increasing CNTs content, the saturation magnetization of the composites is gradually reduced, while the complex magnetic permeability changes little. The complex dielectric constant of the composites is significantly increased when the concentration of CNTs approaches the percolation threshold value of 2 wt%. When CNTs content is 5 wt%, the reflection ratios are less than -10 dB within the frequency range 2-9 GHz, and the reflection ratios reach a minimum -32.5 dB at a frequency of about 3.9 GHz.

Engineering scaffolds integrated with calcium sulfate and oyster shell for enhanced bone tissue regeneration.

Engineering scaffolds combinging natural biomineral and artificially synthesized material hold promising potential for bone tissue regeneration. In this study, novel bioactive calcium sulfate/oyster shell (CS/OS) composites were prepared. Comparing to CS scaffold, the CS/OS composites with a controllable degradation rate displayed enhanced mineral nodule formation, higher alkaline phosphate (ALP) activity and increased proliferation rate while treated osteocytes. In CS/OS composites group, elevated mRNA levels of key osteogenic genes including bone morphogenetic protein-2 (BMP-2), runt-related transcription factor 2 (Runx2), osterix (Osx), and osteocalcin (OCN) were observed. Furthermore, The up-regulation of BMP-2 and type I collagen (COL-I) was observed for CS/OS composites relative to a CS group. Scaffolds were implanted into critical-sized femur cavity defects in rabbits to investigate the osteogenic capacity of the composites in vivo. The CS/OS scaffolds with proper suitable times and mechanical strength strongly promoted osteogenic tissue regeneration relative to the regeneration capacity of CS scaffolds, as indicated by the results of histological staining. These results suggest that the OS-modified CS engineering scaffolds with improved mechanical properties and bioactivity would facilitate the development of a new strategy for clinic bone defect regeneration.

Structures and Mechanical and Electronic Properties of the Ti2CO2 MXene Incorporated with Neighboring Elements (Sc, V, B and N)

Ti2CO2, as the representative MXene with semiconducting characteristics and ultrahigh carrier mobility, has attracted increasing attention in material science. Herein, various Ti2CO2 alloys with Ti displaced by neighboring elements Sc and V, or C by B and N are investigated in this paper based on the first-principles density functional calculations. The structures and mechanical and electronic properties are thoroughly studied for the configurations with varying alloying atom concentrations. The choices of alloying elements play a critical role in determining the lattice parameters and layer thickness. The Sc substitutions generally increase the lattice parameter but decrease the layer thickness. In contrast, the introduction of N presents slight influence on the structural parameters. The mechanical strength shows remarkable variations by introducing the alloying elements. The maximum elastic constant c11 is determined to be 425xa0GPa in (Ti0.25V0.75)2CO2, and the corresponding minimum value is only 104xa0GPa found in (Ti0.125Sc0.875)2CO2. With respect to the electronic properties, although B and Sc both present one less valance electron compared to their replaced elements C and Ti, it is easier to realize the p-type semiconductor in the configurations containing Sc. Both the V and N substitutions are capable of generating n-type semiconductors, but their optimal stoichiometric compositions are quite different. Among all the configurations investigated, only (Ti0.5V0.5)2CO2 and (Ti0.375V0.625)2CO2 are magnetic, with their magnetism determined to be 2.61xa0uB/cell and 1.52xa0uB/cell, respectively. Thus, the method of alloying neighboring elements provides an effective approach in manipulating the physical properties of the Ti2CO2, which might widen the possible applications of MXene materials.

Exploring the potential of exfoliated ternary ultrathin Ti4AlN3 nanosheets for fabricating hybrid patterned polymer brushes

Since the discovery of graphene, two-dimensional (2D) materials have been receiving increased attention. The quest for new 2D materials with unique structure and special properties has become urgent. Herein we report on the preparation of a new kind of ternary 2D material, Ti4AlN3 nanosheets, by liquid exfoliation of the corresponding laminated MAX phase. The obtained Ti4AlN3 nanosheets, bearing abundant surface groups, can be further used to fabricate micro-patterns via micro-contact printing (μCP) and subsequently functionalized through self-initiated photografting and photopolymerization (SIPGP) to achieve MAX-based hybrid patterned polymer brushes. Our work opens a door to explore the synthesis of 2D hybrid materials for functional applications based on the traditional MAX phases.