Feifei Cao

Facile hydrothermal synthesis and electrochemical properties of orthorhombic LiMnO2 cathode materials for rechargeable lithium batteries

Pure-phase, LiMn2O4-mixed and aluminum-doped orthorhombic LiMnO2 (o-LiMnO2) cathode materials with high discharge capacity and excellent cyclic stability were prepared by one-step hydrothermal reaction of MnCl2, EDTA, LiOH, AlCl3 and NaClO solutions. Chemical composition and aluminum content were affected by temperature and the concentration of LiOH, NaClO and AlCl3. A mixed phase of Mn3O4 and o-LiMnO2, pure-phase o-LiMnO2, and a mixed phase of o-LiMnO2 and LiMn2O4 were formed with increasing the concentration of NaClO from 0.08 to 0.25 mol L−1 at 180 °C for 24 h. Adding EDTA and NaClO facilitated the formation of o-LiMnO2. Al/Mn molar percent ratios in doped o-LiMnO2 were 0.34, 0.58, 0.91, and 1.22 when Al/Mn molar ratios in hydrothermal system were controlled at 0.05, 0.10, 0.15, and 0.20, respectively. Mixing LiMn2O4 and doping Al improved the discharge capacity and cyclic stability of o-LiMnO2. o-LiMnO2, the mixture with an o-LiMnO2/LiMn2O4 mass ratio of 2.45, and doped o-LiMnO2 with an Al/Mn molar percent ratio of 0.58 exhibited initial discharge capacities of 76, 139, and 82 mA h g−1, and cycling capacities of 124, 144, and 156 mA h g−1 after 100 cycles, respectively. This work facilitates the preparation and electrochemical performance improvement of o-LiMnO2.

Basophilic green fluorescent carbon nanoparticles derived from benzoxazine for the detection of Cr(VI) in a strongly alkaline environment

Fluorescent probes for heavy or transition metal ions in extreme environments are crucially important for practical use. In this work, basophilic green fluorescent carbon nanoparticles (G-CNPs) were synthesized by one-pot hydrothermal treatment of benzoxazine in NaOH aqueous solution. These G-CNPs showed favorable dispersibility in strongly alkaline conditions due to the abundant functional groups on their surface. Based on their good photoluminescence properties and excellent stability, the G-CNPs could be used to detect Cr(VI) in a strongly alkaline environment (pH = 14) through a fluorescence quenching effect. This detection process was achieved selectively among 17 anions within 30 seconds and the limitation was 0.58 μM (S/N = 3). It was revealed that the fluorescence turn-off process was caused by the inner filter effect (IFE) of Cr(VI). This study developed efficient fluorescence sensors based on fluorescent carbon nanoparticles, which could be used in strongly alkaline environments.

Self-assembly of birnessite nanoflowers by staged three-dimensional oriented attachment

Birnessite (layer-type Mn(III, IV) oxides with ordered sheet stacking) is the most common mineral species of manganese (Mn) oxides and has been demonstrated to be among the strongest sorbents and oxidants in surface environments. The morphology of birnessite is one of the key factors affecting its reactivity. Either biotic or abiotic birnessite samples usually consist of nanoflower-like crystals. However, the governing factors and mechanisms of morphological evolution of the nanoflower-shaped birnessite remain poorly understood. In this work, birnessite nanoflowers, as a natural birnessite analog, were synthesized and the intermediate products during birnessite crystallization were captured by instant freezing using liquid nitrogen. The processes and mechanisms of crystal growth of birnessite nanoflowers were investigated using a combination of high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that primary hexagonal nanoflakes rapidly agglomerate to form nuclei-like substrates at the initial stages, and subsequently, these nanoflakes aggregate laterally and link serially on the substrates to form nanopetals through both rotation and edge-to-edge oriented attachment (OA) mechanism. This process is likely driven by hydrogen bonding between unsaturated O atoms at the edge planes of [MnO6] sheets. Meanwhile, the OA mechanism along the (001) plane is likely driven by Coulombic interactions and hydrogen bonding during the assembly process of the adjacent nanopetals. The morphological evolution occurred by the staged three-dimensional OA process that plays an essential role in the self-assembly of flower-like birnessite crystals. These findings provide further understanding of how nanoparticle assembly is directed to achieving desired shapes and sizes by fabricating nanomaterials through three-dimensional OA processes.

Synthesis of core–shell structured Ag3PO4@benzoxazine soft gel nanocomposites and their photocatalytic performance

In the investigation of photocatalysis, it remains a significant challenge to improve the interface properties and enhance the stability of photocatalysts. To address this challenge, we have prepared core–shell structured Ag3PO4@benzoxazine soft gel nanocomposites, in which Ag3PO4 nanoparticles are coated with uniform benzoxazine monomers via a facile solution self-assembly method. The benzoxazine monomers are attached to the surface of Ag3PO4 nanoparticles by coordination interaction between the amino group of the benzoxazine monomers and Ag+ ions on the surface of Ag3PO4, and the soft gel shell is formed via the interaction of hydrogen bonds between the benzoxazine monomers. The nanocomposites exhibit higher visible-light photocatalytic stability than the bare Ag3PO4 nanoparticles under the same reaction conditions. Both experimental evidence and electrochemical calculations reveal that the high photocatalytic stability of Ag3PO4@benzoxazine soft gel nanocomposites mainly originates from the silver amine complex ion formed in the interface between the core and the shell. The integration of photocatalysts with the advantages of soft gels can provide a new way to improve the interface properties of Ag3PO4 catalyst and facilitate the realization of the long-standing goal of performing chemical synthesis using sunlight.

pH controlled green luminescent carbon dots derived from benzoxazine monomers for the fluorescence turn-on and turn-off detection

Emerging carbon dots (CDs) are widely used as fluorescent probes in biological and environmental fields, nevertheless, the control of CDs based on different detection mechanisms is rarely reported. In this paper, green luminescent CDs (G-CDs) were prepared by a facile hydrothermal treatment of benzoxazine monomers (BZM). The obtained G-CDs showed pH dependent photoluminescence, which could be designed as fluorescence turn-on and turn-off sensors. The G-CDs exhibited weak photoluminescence at pHu202f=u202f7.0 and could be turned on by Zn(II) selectively with the limitation of 0.32u202fμM in the concentration range from 1 to 100u202fμM. When pHu202f=u202f10.0, Cr(VI) could quench the strong fluorescence of G-CDs efficiently, and the limit of detection was 0.99u202fμM with a linear range of 1-50u202fμM. Furthermore, the fluorescence turn-on and turn-off performance of G-CDs was attributed to the intramolecular charge transfer (ICT) of Zn(II) and the inner filter effect (IFE) of Cr(VI), respectively. The excellent probes were successfully applied for the detection of Zn(II) in biological system and Cr(VI) in environment.

Application of the correct design of successive self-nucleation and annealing (SSA) to study the stereo-defects and its distribution of homo- and co-polypropylene

The stereo-defects and its distribution of four homo- and co-polypropylene samples with different processing properties were studied through the correct design Successive Self-Nucleation and Annealing (SSA), and other characterization methods such as Differential Scanning Calorimetry (DSC), Gel Permeation Chromatography (GPC), Temperature Rising Elution Fractionation (TREF), respectively. Firstly, the preliminary characterization found that the two homo-polypropylene or co-polypropylene samples had the similar mechanical and thermal properties, and the SSA results also revealed the internal microstructure of the different kind of polypropylene was almost exactly the same, representing the alike isotactic sequence length, the fractions weight of the isotactic sequence, and the isotactic sequence length distribution of the same kind of polypropylene. Compared with the homo-polypropylene, the DSC, GPC, and TREF tests indicated there were difference in the properties of the co-polypropylene samples, revealing the disparities in molecular chain microstructure. The SSA results after the correct Ts for each sample showed there were obvious differences in the (statistical) lamellar thickness and its distribution and the fractions weight of different fractions after SSA treatment, further revealing the microstructure difference on the isotactic sequence length, and the isotactic sequence length distribution of homo- and co-polypropylene samples. Besides, the correct design SSA also indicated the polar copolymer monomer had a great influence on the high isotactic component in co-polypropylene microstructure.