Controllable Fabrication of Rare-Earth-Doped Gd₂O₂SO₄@SiO₂ Double-Shell Hollow Spheres for Efficient Upconversion Luminescence and Magnetic Resonance Imaging

Uniform hollow spheres of Yb and Er codoped Gd₂O₂SO₄ (noted as Gd₂O₂SO₄:Yb,Er) have been developed as novel bifunctional contrast agents for efficient upconversion optical and magnetic resonance imaging (MRI) for the first time. Gd-containing organic precursory spheres were first obtained by a facile hydrothermal process. Owing to the innate hydrophilic nature of the precursory spheres, surface modification with a layer of stable and biocompatible silica could be readily achieved through the Stöber sol–gel method and subsequent calcination. The morphology and thickness of the silica shell can be tailored by adjusting the reaction time. Compared with Gd₂O₂SO₄:Yb,Er hollow spheres without silica coating, well-dispersed Gd₂O₂SO₄:Yb,Er@SiO₂ double-shell hollow spheres could generate intense upconversion fluorescence, and showed a significant contrast enhancement of T1-weighted MRI both <i>in vitro</i> and <i>in vivo</i>. These gadolinium oxysulfate-based hollow spheres are thus regarded as a new type of potential bimodal optical-MRI contrast agents

Advanced Supercapacitors Based on α‑Ni(OH)₂ Nanoplates/Graphene Composite Electrodes with High Energy and Power Density

In order to solve the lack of energy sources, researchers devote themselves to the study of green renewable and economical supercapacitors. We demonstrate herein that the α-Ni­(OH)₂ nanoplates/graphene composites are fabricated as active electrodes in supercapacitors with excellent cycling stability, high energy density, and power density. The advantages of graphene can complement the shortcomings of α-Ni­(OH)₂ nanoplates to compose a novel composite. The α-Ni­(OH)₂ nanoplates/graphene composite presents a high specific capacitance of 1954 F g^–1 at 5 A g^–1. The reason for the improving performance is attributed to graphene, which provides an improved conductivity and increased specific surface area by interweaving with α-Ni­(OH)₂ nanoplates. It is particularly worth mentioning that the assembled asymmetric supercapacitor cells yield a high specific capacitance of 309 F g^–1 at 5 A g^–1 and light a 2 V LED sustainable for about 7 min, which may bring great prospects for further fundamental research and potential applications in energy storage devices

Liquid Phase Exfoliation of MoS₂ Assisted by Formamide Solvothermal Treatment and Enhanced Electrocatalytic Activity Based on (H₃Mo₁₂O₄₀P/MoS₂)_n Multilayer Structure

In this work, MoS₂ nanosheets were obtained successfully using the liquid phase exfoliation method assisted by formamide solvothermal treatment. The exfoliation efficiency in <i>N</i>-methyl-2-pyrrolidone (NMP) was enhanced by the synergetic effect of easier intercalation of polar solvent and higher repulsive force of the treated bulk MoS₂. The exfoliated MoS₂ nanosheets were assembled alternately with H₃Mo₁₂O₄₀P (PMo₁₂) into a multilayer heterostructure by the layer-by-layer (LBL) method, in which PMo₁₂ with high electron mobility bridges the adjacent catalytically active MoS₂ layers. Based on the heterostructure, the electrocatalytic performance for hydrogen evolution was substantially enhanced over multilayer MoS₂ nanosheets alone. Moreover, it was found that the electrocatalytic performance was influenced by the layer number, indicating that an optimum balance between the mass transfer (MoS₂ layer) and electron conductivity (PMo₁₂ layer) was needed for the construction of efficient electrocatalysts. In addition, the electrocatalytic performance of the multilayers (MoS₂)_n and (PMo₁₂/MoS₂)_n could be improved by oxygen plasma treatment, which might be ascribed to the increased number of edges and defects in MoS₂ nanosheets. This work not only provides a facile method to exfoliate MoS₂ with higher efficiency, but also offers a feasible strategy to build up high-performance electrocatalysts by rationally assembling nanosheets and polyoxometalate species at the nanoscale level