Geng Zhang

Facile Synthesis of Carbon-Coated Spinel Li4Ti5O12/Rutile-TiO2 Composites as an Improved Anode Material in Full Lithium-Ion Batteries with LiFePO4@N-Doped Carbon Cathode

The spinel Li4Ti5O12/rutile-TiO2@carbon (LTO-RTO@C) composites were fabricated via a hydrothermal method combined with calcination treatment employing glucose as carbon source. The carbon coating layer and the in situ formed rutile-TiO2 can effectively enhance the electric conductivity and provide quick Li+ diffusion pathways for Li4Ti5O12. When used as an anode material for lithium-ion batteries, the rate capability and cycling stability of LTO-RTO@C composites were improved in comparison with those of pure Li4Ti5O12 or Li4Ti5O12/rutile-TiO2. Moreover, the potential of approximately 1.8 V rechargeable full lithium-ion batteries has been achieved by utilizing an LTO-RTO@C anode and a LiFePO4@N-doped carbon cathode.

Improved Electrochemical Performance of LiFePO4@N-Doped Carbon Nanocomposites Using Polybenzoxazine as Nitrogen and Carbon Sources

Polybenzoxazine is used as a novel carbon and nitrogen source for coating LiFePO4 to obtain LiFePO4@nitrogen-doped carbon (LFP@NC) nanocomposites. The nitrogen-doped graphene-like carbon that is in situ coated on nanometer-sized LiFePO4 particles can effectively enhance the electrical conductivity and provide fast Li+ transport paths. When used as a cathode material for lithium-ion batteries, the LFP@NC nanocomposite (88.4 wt % of LiFePO4) exhibits a favorable rate performance and stable cycling performance.

Co nanoparticles/Co, N, S tri-doped graphene templated from in-situ formed Co, S co-doped g-C3N4 as an active bifunctional electrocatalyst for overall water splitting

The development of high-performance electrocatalyst with earth-abundant elements for water-splitting is a key factor to improve its cost efficiency. Herein, a noble metal-free bifunctional electrocatalyst was synthesized by a facile pyrolysis method using sucrose, urea, Co(NO3)2 and sulfur powder as raw materials. During the fabrication process, Co, S co-doped graphitic carbon nitride (g-C3N4) was first produced, and then this in-situ-formed template further induced the generation of a Co, N, S tri-doped graphene coupled with Co nanoparticles (NPs) in the following pyrolysis process. The effect of pyrolysis temperature (700, 800, and 900 °C) on the physical properties and electrochemical performances of the final product was studied. Thanks to the increased number of graphene layer encapsulated Co NPs, higher graphitization degree of carbon matrix and the existence of hierarchical macro/meso pores, the composite electrocatalyst prepared under 900 °C presented the best activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with outstanding long-term durability. This work presented a facile method for the fabrication of non-noble-metal-based carbon composite from in-situ-formed template and also demonstrated a potential bifunctional electrocatalyst for the future investigation and application.

Fabrication of a highly dispersed Pd core @Pt shell electrocatalyst for the oxygen reduction reaction

ABSTRACT Core-shell nanostructures have been widely investigated to improve the electrocatalytic performance of platinum. However, organic precursors, surfactants or high temperature are usually necessary during the preparation procedure. Unfortunately, these requirements limit the application of these methods on a large scale. Herein, a Pd core @Pt shell nanostructure was fabricated through the reduction of K 2 PtCl 4 by dissociated hydrogen at room temperature without the assistance of either a surfactant or a high-boiling point solvent. The shell thickness of this nanostructure was successfully controlled by varying the amount of K 2 PtCl 4 ; core-shell nanoparticles with a shell thickness of 0.45, 0.75 and 0.90 nm were obtained, as determined by TEM. The remarkable crystallinity and epitaxial growth of the Pd core @Pt shell nanostructure were revealed by HRTEM and EDS. According to ICP and XPS, surface segregation of Pt was established. The impressive ORR performance was attributed to the weak adsorption strength of the OH ads species, which resulted from the electron transfer impact between the Pd core and Pt shell . The facile and clean preparation method can be used to prepare other core-shell nanostructures under a mild atmosphere.

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.

Shape-controlled synthesis of Pd nanocrystals in an aqueous solution by using amphiphilic triblock copolymers as both the stabilizer and the reductant

Palladium nanocrystals (NCs) are highly useful functional materials in many applications, and the performances of Pd NCs were strongly depended on the crystalline facet exposed on their surface. In this work, Pd NCs were synthesized in aqueous solutions by using Na2PdCl4 as the precursor, citric acid as the capping agent, and Pluronic F127 as both stabilizer and reductant. By adjusting the reaction parameters, Pd cuboctahedrons, octahedrons, and triangular nanoplates with well-defined facets can be produced. This study provides a new pathway for the shape-controlled preparation of noble metal NCs.

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 pH = 7.0 and could be turned on by Zn(II) selectively with the limitation of 0.32 μM in the concentration range from 1 to 100 μM. When pH = 10.0, Cr(VI) could quench the strong fluorescence of G-CDs efficiently, and the limit of detection was 0.99 μM with a linear range of 1-50 μM. 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.

ArticleFabrication of a highly dispersed Pdcore@Ptshell electrocatalyst for the oxygen reduction reaction

ABSTRACT Core-shell nanostructures have been widely investigated to improve the electrocatalytic performance of platinum. However, organic precursors, surfactants or high temperature are usually necessary during the preparation procedure. Unfortunately, these requirements limit the application of these methods on a large scale. Herein, a Pd core @Pt shell nanostructure was fabricated through the reduction of K 2 PtCl 4 by dissociated hydrogen at room temperature without the assistance of either a surfactant or a high-boiling point solvent. The shell thickness of this nanostructure was successfully controlled by varying the amount of K 2 PtCl 4 ; core-shell nanoparticles with a shell thickness of 0.45, 0.75 and 0.90 nm were obtained, as determined by TEM. The remarkable crystallinity and epitaxial growth of the Pd core @Pt shell nanostructure were revealed by HRTEM and EDS. According to ICP and XPS, surface segregation of Pt was established. The impressive ORR performance was attributed to the weak adsorption strength of the OH ads species, which resulted from the electron transfer impact between the Pd core and Pt shell . The facile and clean preparation method can be used to prepare other core-shell nanostructures under a mild atmosphere.