Tao Mei

Formation and morphology control of nanoparticlesvia solution routes in an autoclave

Formation and morphology control of nanomaterials is a crucial issue in nanoscience research in the exploitation of novel properties. This article presents a review of some research activities on the formation and morphology control of nanoparticlesvia solution routes in an autoclave over the last decade. Several solution systems, including hydrothermal, solvothermal and mixed solvothermal routes, are specifically discussed and highlighted. A helical belt template mechanism was proposed for the formation of the Te nanotubes in aqueous ammonia. Assisted by the surfactant of sodium dodecyl benzenesulfonate (SDBS), nickel nanobelts were hydrothermally synthesized. Ethylenediamine (En) and n-butylamine can be used as shape controllers to one-dimensional (1D) semiconductor nanostructures in the solvothermal process. The phase of metastable and stable MnS crystallites can be controlled by solvothermal reaction in various solvents. Selective preparation of 1D to 3D CdS nanostructures was achieved by controlling the volume ratio of the mixed solvents. With poly(vinylpyrrolidone) (PVP) serving as a soft template, the transformation from nanowires to nanotubes, then to nanowires was observed in the mixed solvents of distilled water and ethanolamine (EA).

Synchronously synthesized core–shell LiNi1/3Co1/3Mn1/3O2/carbon nanocomposites as cathode materials for high performance lithium ion batteries

LiNi1/3Co1/3Mn1/3O2/carbon core–shell nanocomposites with sizes of ∼100 nm and carbon shell thicknesses of ∼6 nm are obtained by a modified Pechini process, in which LiNi1/3Co1/3Mn1/3O2 is formed synchronously with a carbon coating in the presence of polyethylene glycol-600. Electrochemical measurements show that the nanocomposites deliver a stable discharge capacity of 175 mA h g−1 at 1 C and a capacity decay rate of <3% after 100 cycles. The effects of synthesis temperature on the electrochemical performance of the nanocomposites are examined, which shows that the discharge capacities increase from 154 to 175 mA h g−1 as the temperature increases from 800 to 1000 °C. Meanwhile, the electrochemical performances of the nanocomposites with carbon content varying from 0 to 20.8% are examined. Among these composites, that with 15.5% carbon content exhibits the highest and most stable discharge behaviour at 1 C for 100 cycles.

Hierarchical architectured MnCO3 microdumbbells: facile synthesis and enhanced performance for lithium ion batteries

Hierarchical architectured MnCO3 microdumbbells and lamellar structured MnCO3 nanosheets were selectively synthesized by a facile reflux route. Hierarchical architectured MnCO3 microdumbbells (approximately 0.5–1.5 μm in length and 0.3–0.9 μm in width) were composed of nanoparticles, while the lamellar structured MnCO3 nanosheets had uniform length of approximately 400 nm. Both structures were employed as anode active materials in lithium ion batteries. Experimental results showed that the hierarchical architectured MnCO3 microdumbbells exhibited superior electrochemical performances compared with the lamellar structured MnCO3 nanosheets. At a current rate of 0.5 C, the reversible capacity of the hierarchical architectured MnCO3 microdumbbell electrode after 100 cycles was 775 mA h g−1, while the lamellar structured MnCO3 nanosheets electrode was only 50 mA h g−1 after 100 cycles. The superior electrochemical behavior of hierarchical architectured MnCO3 microdumbbell materials could be ascribed to the unique micro-nano assembly structure, simultaneously cushioning the volume change, maintaining the electrode integrity, and offering a short diffusion distance.

Low-temperature and one-pot synthesis of sulfurized graphene nanosheets via in situ doping and their superior electrocatalytic activity for oxygen reduction reaction

The chemical doping of foreign atoms and functional moieties is a significant strategy for tailoring the electronic properties and enhancing the catalytic ability of graphene. However, the general approaches to the synthesis of heteroatom-doped graphene often involve chemical vapor deposition (CVD) and/or thermal annealing performed at high temperature under gas phases, which require special instruments and tedious process. In this study, we have developed a low temperature, economical, and facile one-pot hydrothermal method to synthesise sulfur-doped reduced graphene oxide (S-RGO) nanosheets, in which the sodium sulfide (Na2S) was employed not only as a sulfur source but also as a reductant to reduce the graphene oxide (GO) simultaneously with sulfur (S) being in situ doped into graphene frameworks. The as-prepared S-RGO has a high S content (4.19 at%), as well as high-quality sulfurated species (mainly as C–S–C–), and possesses numerous open edge sites and defects on its surface, which are beneficial for the improved ORR catalytic activity. Electrochemical characterizations clearly demonstrated the excellent electrical conductivity and superior electrocatalytic activity of S-RGO for oxygen reduction reaction (ORR), coupled with considerably enhanced stability and methanol tolerance compared to the commercial Pt/C catalyst. The present low temperature and one-pot approach provides the possibility for the synthesis of S-RGO at the Gram-scale for its application in electronic nanodevices and electrode materials for fuel cells.

Hydrothermal synthesis of layered Li1.81H0.19Ti2O5·xH2O nanosheets and their transformation to single-crystalline Li4Ti5O12 nanosheets as the anode materials for Li-ion batteries

Lithium titanate oxide hydrate (Li1.81H0.19Ti2O5·xH2O) nanosheets were prepared via simple hydrothermal treatment of the low cost tetrabutyl titanate in LiOH solution. The orthorhombic Li1.81H0.19Ti2O5·xH2O nanosheets with thickness less than 10 nm were single crystalline and grew along the (100) facet. Time-dependent experiments confirmed that the formation of Li1.81H0.19Ti2O5·xH2O nanosheets underwent a hydrolysis–Kirkendall effect–Ostwald ripening process. As these Li1.81H0.19Ti2O5·xH2O nanosheets calcined at 500 °C for 2 h, the Li4Ti5O12 nanosheets with thickness of 10–20 nm were synthesized. The Li4Ti5O12 nanosheets were single crystalline and grew along the (110) facet. As an anode material for rechargeable lithium-ion batteries, Li4Ti5O12 nanosheets delivered an initial discharge capacity of 183 mAh g−1 together with a discharge capacity of 160 mAh g−1 after 100 cycles at 1 C. The discharge capacity could reach up to 120 mAh g−1 even after 300 cycles at 10 C. The morphology of nanosheets with large BET value (155.5 m2 g−1) and the high lithium-ion diffusion coefficient (1.51 × 10−8 cm2 s−1) could be favorable for the enhanced high-rate performance.

Size-controlled PdO/graphene oxides and their reduction products with high catalytic activity

A simple two-step method for the preparation of Pd nanoparticles supported on reduced graphene oxide (Pd/RGO) is reported. Well-dispersed and size-controlled Pd/RGO was synthesized through reduction of PdO nanoparticles on graphene oxide (PdO/GO) with hydrazine hydrate and ammonia at 80 °C for 4 hours. The PdO/GO was successfully prepared by mixing GO and Pd(NO3)2 aqueous solution together without adding any additional chemicals. The sizes and morphologies of PdO nanoparticles can be controlled by changing the concentrations of Pd(NO3)2, reaction temperatures and times. The results suggest that a small scale increase of the loadings of Pd supported on RGO can significantly improve the catalytic activity of Pd/RGO, and the stability is much better than that of commercial Pd/C catalysts for methanol electrooxidation and the Suzuki reaction.

Thermal Stability-Enhanced and High-Efficiency Planar Perovskite Solar Cells with Interface Passivation

As the electron transport layer (ETL) of perovskite solar cells, oxide semiconductor zinc oxide (ZnO) has been attracting great attention due to its relatively high mobility, optical transparency, low-temperature fabrication, and good environment stability. However, the nature of ZnO will react with the patron on methylamine, which would deteriorate the performance of cells. Although many methods, including high-temperature annealing, doping, and surface modification, have been studied to improve the efficiency and stability of perovskite solar cells with ZnO ETL, devices remain relatively low in efficiency and stability. Herein, we adopted a novel multistep annealing method to deposit a porous PbI2 film and improved the quality and uniformity of perovskite films. The cells with ZnO ETL were fabricated at the temperature of <150 °C by solution processing. The power conversion efficiency (PCE) of the device fabricated by the novel annealing method increased from 15.5 to 17.5%. To enhance the thermal stability of CH3NH3PbI3 (MAPbI3) on the ZnO surface, a thin layer of small molecule [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was inserted between the ZnO layer and perovskite film. Interestingly, the PCE of PCBM-passivated cells could reach nearly 19.1%. To our best knowledge, this is the highest PCE value of ZnO-based perovskite solar cells until now. More importantly, PCBM modification could effectively suppress the decomposition of MAPbI3 and improve the thermal stability of cells. Therefore, the ZnO is a promising candidate of electron transport material for perovskite solar cells in future applications.

Solid state synthesis of nitride, carbide and boride nanocrystals in an autoclave

This feature article provides a brief overview of the latest developments in the solid state synthesis of various nitride, carbide and boride nanocrystals in an autoclave at mild temperatures. An additive assisted route was developed for nitride, carbide and boride nanocrystals. In the presence of S powder, 3C–SiC nanocrystals were obtained utilizing waste plastics and Si powder at 350–500 °C. With the assistance of I2, rare-earth and alkaline-earth hexaboride nanocrystals were prepared at temperatures below 400 °C. As N-aminothiourea and iodine were added to the system containing Si and NaN3, β-Si3N4 nanorods and α,β-Si3N4 nanoparticles could be prepared at 60 °C. A ternary nitride of MgSiN2 can also be prepared at 350–500 °C using Si, Mg, and NaN3 as reactants.

One-pot synthesis of carbon nanoribbons and their enhanced lithium storage performance

Carbon nanoribbons are obtained on a large scale by an easy one-pot pathway. The nanoribbons, which have thicknesses of ∼5 nm, widths of ∼500 nm and lengths exceeding 15 μm, are prepared from ferrocene and Mg(CH3COO)2·4H2O at 600 °C for 10 h. The Raman spectrum of the as-obtained sample indicates that it possesses a mass of disorder and defects. X-ray photoelectron spectroscopy (XPS) results show that the nanoribbons are doped by nitrogen at an atomic percentage of 2.09%. The specific surface area of the sample is measured to be as large as 1240 m2 g−1. In the charge–discharge experiments of secondary lithium ion batteries, the carbon nanoribbons demonstrate a stable reversible capacity of 750 mA h g−1 after 300 cycles at 0.5 A g−1, suggesting that the as-prepared carbon nanoribbons have potential applications as electrode materials in electronic devices.

Synthesis of disk-like LiNi1/3Co1/3Mn1/3O2 nanoplates with exposed (001) planes and their enhanced rate performance in a lithium ion battery

With the addition of span 85, disk-like LiNi1/3Co1/3Mn1/3O2 nanoplates with exposed (001) planes were synthesized using a simple Pechini method. The diameter of the disk-like LiNi1/3Co1/3Mn1/3O2 nanoplates was approximately 50 nm while the thickness was around 3 nm. This result showed that the mixture of liquid surfactants played a key role in the change of morphology of the LiNi1/3Co1/3Mn1/3O2 nanoplates. This kind of cathode material, which was applied in a lithium ion battery, achieved a high specific capacity of 165 mA h g−1 at 2C after 200 cycles, together with a capacity retention ratio of 98.2%.