Yisi Liu

Graphene aerogel-supported and graphene quantum dots-modified γ-MnOOH nanotubes as a highly efficient electrocatalyst for oxygen reduction reaction

In this work, we demonstrate a facile strategy to synthesize a novel three-dimensional (3D) graphene aerogel-supported and graphene quantum dots-modified γ-MnOOH nanotubes as a highly efficient electrocatalyst. The structure, morphology, and chemical composition of γ-MnOOH@GA/GQDs are investigated by X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of catalysts is discussed by cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), and rotating disk electrode (RDE) measurements in O2-saturated 0.1 M KOH electrolyte. The γ-MnOOH@GA/GQDs hybrid exhibits more positive onset potential and half-wave potential, faster charge transfer, lower Tafel slope than that of γ-MnOOH@GA, GA and γ-MnOOH, and mainly undergoes a direct 4e− reaction pathway. Furthermore, its electrocatalytic performance is comparable with the commercial 20 wt% Pt/C, which is attributed to the unique 3D crumpled porous nanostructure of GA with large specific area and fast electron transport, and the synergic covalent coupling between the γ-MnOOH nanotubes and GA. More importantly, the GQDs structural defects can facilitate the adsorption of oxygen and charge transfer. As a highly efficient surface “sensitizer”, GQDs are modified on the γ-MnOOH surfaces to further boost the electrocatalytic property.

Calcium silicate/calcium aluminate composite biocement for bone restorative application: synthesis, characterisation and in vitro biocompatibility

Pure β-dicalcium silicate and monocalcium aluminate powder were prepared by Pechini method. A series of calcium silicate/calcium aluminate cements (CSC/CAC) were prepared. The setting time, crystalline phases, microstructures, compressive strength, cells attachment and silicon release of the cements were investigated. The results indicate that the setting time of CSC/CAC was shorter than that of either CSC or CAC. The hydration products in CSC/CAC composite are gehlenite (Ca2Al2SiO7·8H2O), calcium aluminate hydrate (Ca3Al2O6 × H2O), and katoite (Ca2Al2O6·6H2O). Platelike crystals were found in the microstructure. The liquid to powder ratio has a significant effect on the porosity and the strength of CSC/CAC. The MC3T3 cells attached well to the surfaces of CSC/CAC. However, the cells proliferation on the surface of 7S3A was better than that of 3S7A due to its higher silicon release. In general, CSC/CAC exhibits good biocompatibility and relative high strength, and may be suitable for some non-load bearing bone restorative applications.

Nickel ion removal by porous potassium magnesium titanate made from plate-like crystals

Plate-like potassium magnesium titanate (KMTO) powder prepared by molten salt growth method and the KMTO porous ceramic synthesised by polymeric sponge replication method were used as sorbents to remove nickel ions from wastewater. Both powder and porous ceramic were characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The maximum adsorption capacities of powder and porous ceramic were 96 and 24 mg g− 1 respectively at a pH value of 6 (25°C). However, the removal efficiencies of both could reach up to 99%. Moreover, the adsorption kinetics for the KMTO powder and the porous ceramics followed the pseudo-second-order kinetic model, and the equilibrium data for the KMTO powder fitted the Langmuir isothermal model well, while the porous ceramics fitted with the Freundlich model. The mechanism of the adsorption by the KMTO powder and the porous ceramic was ion exchange. It was also shown that the nickel saturated KMTO powder and the porous ceramics were stable in leaching tests.