Controlled Synthesis Of Nanomaterials Research Articles

Research Progress in the Preparation of Transition Metal Sulfide Materials and Their Supercapacitor Performance.

Transition metal sulfides are widely used in supercapacitor electrode materials and exhibit excellent performance because of their rich variety, low price, and high theoretical specific capacity. At present, the main methods to prepare transition metal sulfides include the hydrothermal method and the electrochemical method. In order to further improve their electrochemical performance, two aspects can be addressed. Firstly, by controllable synthesis of nanomaterials, porous structures and large surface areas can be achieved, thereby improving ion transport efficiency. Secondly, by combining transition metal sulfides with other energy storage materials, such as carbon materials and metal oxides, the synergy between different materials can be fully utilized. However, future research still needs to address some challenges. In order to guide further in-depth research, it is necessary to combine the current research-derived knowledge and propose a direction for future development of transition metal sulfide electrode materials.

Controllable design, synthesis and characterization of nanostructured rare earth metal oxides

Abstract Rare earth metal oxide nanomaterials have drawn much attention in recent decades due to their unique properties and promising applications in catalysis, chemical and biological sensing, separation, and optical devices. Because of the strong structure–property correlation, controllable synthesis of nanomaterials with desired properties has long been the most important topic in nanoscience and nanotechnology and still maintains a grand challenge. A variety of methods, involving chemical, physical, and hybrid method, have been developed to precisely control nanomaterials, including size, shape, dimensionality, crystal structure, composition, and homogeneity. These nanostructural parameters play essential roles in determining the final properties of functional nanomaterials. Full understanding of nanomaterial properties through characterization is vital in elucidating the fundamental principles in synthesis and applications. It allows researchers to discover the correlations between the reaction parameters and nanomaterial properties, offers valuable insights in improving synthetic routes, and provokes new design strategies for nanostructures. In application systems, it extrapolates the structure–activity relationship and reaction mechanism and helps to establish quality model for similar reaction processes. The purpose of this chapter is to provide a comprehensive overview and a practical guide of rare earth oxide nanomaterial design and characterization, with special focus on the well-established synthetic methods and the conventional and advanced analytical techniques. This chapter addresses each synthetic method with its advantages and certain disadvantages, and specifically provides synthetic strategies, typical procedures and features of resulting nanomaterials for the widely-used chemical methods, such as hydrothermal, solvothermal, sol–gel, co-precipitation, thermal decomposition, etc. For the nanomaterial characterization, a practical guide for each technique is addressed, including working principle, applications, materials requirements, experimental design and data analysis. In particular, electron and force microscopy are illuminated for their powerful functions in determining size, shape, and crystal structure, while X-ray based techniques are discussed for crystalline, electronic, and atomic structural determination for oxide nanomaterials. Additionally, the advanced characterization methodologies of synchrotron-based techniques and in situ methods are included. These non-traditional methods become more and more popular because of their capabilities of offering unusual nanostructural information, short experiment time, and in-depth problem solution. Graphical Abstract:

Liquid Cell Transmission Electron Microscopy Study of Platinum Iron Nanocrystal Growth and Shape Evolution

We study solution growth of platinum iron nanocrystals in situ in a liquid cell by using transmission electron microscopy. By varying the oleylamine concentration, we observed that platinum iron nanoparticle growth follows different trajectories with diverse shape evolution. With 20% oleylamine, three stages of growth were observed: (i) nucleation and growth of platinum iron nanoparticles in the precursor solution; (ii) nanowire formation by shape-directed nanoparticle attachment; and (iii) breakdown or shrinkage of the nanowires into individual nanoparticles with large size distribution. With 30% oleylamine, formation of platinum iron nanowires similar to that with 20% oleylamine was observed. However, those nanowires do not break down or shrink, which suggests that nanowires are stabilized by oleylamine as surfactant binding on the surface. With 50% oleylamine, after the individual nanoparticles are formed, they do not merge into nanowires. The shape of the nanoparticle is strongly influenced by the neighboring nanoparticles due to stereo-hindrance effects. Real-time observation of the dynamic growth process sheds light on the controllable synthesis of nanomaterials.

Facile Synthesis of TiO<SUB>2</SUB> Nanocrystals Using NH<SUB>4</SUB>F as Morphology-Controlling Agent and Its Influences on Photocatalytic Activity

Controllable synthesis of nanomaterials with different morphologies can significantly affect their properties. Here we report that the morphology and facet orientation of TiO2 nanocrystals can be readily modulated via a hydrothermal method using a simple morphology-controlling agent of NH4F. The photocatalytic activity of resultant TiO2 has been evaluated by photodegradation of methyl orange. The results indicate that the introduction of NH4F can be used to modulate the mophology and, thereby, the photocatalytic activity of TiO2. The obtained TiO2 with high-energy facet, small size, and large surface area can exhibit an improved photocatalytic efficiency, which may be promising for real application.

6-Fold-Symmetrical AlN Hierarchical Nanostructures: Synthesis and Field-Emission Properties

The controllable synthesis of nanomaterials with unique morphologies and sizes has attracted increasing interest because of the shape-dependent properties of the nanomaterials. In this article, we report the synthesis of the new 6-fold-symmetrical AlN hierarchical nanostructures including urchinlike and flowerlike ones assembled by AlN nanoneedles through the chemical reaction between AlCl3 and NH3 with the vaporization temperature of AlCl3 between 120 and 165 °C and the reaction temperature higher than 1050 °C. The morphologies, sizes, and densities of the AlN nanostructures could be controllably modulated by changing the reaction temperature and the vapor pressure of AlCl3. The formation mechanism of the AlN hierarchical nanostructures has been discussed on the basis of the change in the AlCl3 vapor pressure and the morphological evolution of the intermediate products. The shape-dependent properties of the AlN products have been observed, and the urchinlike nanostructures showed better optical and field-emission properties in comparison with the flowerlike ones. These results indicate the potential applications of the 6-fold-symmetrical AlN hierarchical nanostructures in optoelectronic and field-emission devices.

Combinatorial two-dimensional architectures from nanocrystal building blocks: controlled assembly and their applications

Promoted by the controllable synthesis of nanomaterials, nanocrystal self-assembly has attracted much attention for both scientific interest and potential applications. In this article, we highlight the recent advances in applying the breath figure (BF) method—a traditional technique to prepare patterned porous polymer films—to nanocrystal self-assembly. This new combined strategy leads to hierarchically ordered structures from nanocrystal superlattices to micrometer patterns, showing appealing prospects in various fields.