Synthesis, characterization and formation process of transition metal oxide nanotubes using carbon nanofibers as templates

A six-fold difference in structure results in a six-order difference in conductivity: silica shell nanoarchitectonics on carbon black particles

Carbon black (Ketchen Black with a particle size of several tens of nm) was coated with silica with a varied thickness of 2 and 12 nm. Carbon/silica core-shell particles were grafted with the γ-methacryloxypropylsilyl group to be homogeneously dispersed into a poly(methyl methacrylate) film. The electrical conductivity of the poly(methyl methacrylate) films containing carbon/silica particles was successfully controlled by the thickness of the silica layer; silica coating with 2 nm thickness gave a conducting film, while that with 12 nm thickness gave a less conducting film with a remarkable difference on the order of 10⁶ (in volume conductivity).

Facile synthesis of nanostructured perovskites by precursor accumulation on nanocarbons

Perovskite-type oxides have impacted various research fields, including materials and energy science. Despite their vast potential in various applications, general and simple synthesis methods for nano-perovskites remain limited. Herein, various nano-perovskites were synthesized by a facile approach involving the use of nanocarbons. The calcination of the nanocarbon deposited with metal salts yielded nano-perovskites, emulating the morphology of nanocarbons. The accumulation of precursors (i.e., metal salts) on the surface of the nanocarbon during the evaporation of the solvent is the key step in which the precursors are homogeneously mixed prior to calcination. The homogeneity of the precursors facilitated low-temperature calcination that resulted in the formation of nano-perovskites. Various nano-perovskites, including LaMnO₃, LaCoO₃, LaFeO₃, LaNiO₃, LaAlO₃, LaGaO₃, CaMnO₃, BaMnO₃, SrMnO₃, La_0.7Sr_0.3FeO₃, La₂CuO₄, and Ca₂Fe₂O₅, were successfully synthesized, demonstrating the simplicity and novelty of the method for the general synthesis of nano-perovskites.

Precursor accumulation on nanocarbons for the synthesis of LaCoO3 nanoparticles as electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction (OER) is a key step in energy storage devices. Lanthanum cobaltite (LaCoO₃) perovskite is an active catalyst for OER in alkaline solutions, and it is expected to be a low-cost alternative to the state-of-the-art catalysts (IrO₂ and RuO₂) because transition metals are abundant and inexpensive. For efficient catalysis with LaCoO₃, nanosized LaCoO₃ with a high surface area is desirable for increasing the number of catalytically active sites. In this study, we developed a novel synthetic route for LaCoO₃ nanoparticles by accumulating the precursor molecules over nanocarbons. This precursor accumulation (PA) method for LaCoO₃ nanoparticle synthesis is simple and involves the following steps: (1) a commercially available carbon powder is soaked in a solution of the nitrate salts of lanthanum and cobalt and (2) the sample is dried and calcined in air. The LaCoO₃ nanoparticles prepared by the PA method have a high specific surface area (12 m² g⁻¹), comparable to that of conventional LaCoO₃ nanoparticles. The morphology of the LaCoO₃ nanoparticles is affected by the nanocarbon type, and LaCoO₃ nanoparticles with diameters of less than 100 nm were obtained when carbon black (Ketjen black) was used as the support. Further, the sulfur impurities in nanocarbons significantly influence the formation of the perovskite structure. The prepared LaCoO₃ nanoparticles show excellent OER activity owing to their high surface area and perovskite structure. The Tafel slope of these LaCoO₃ nanoparticles is as low as that of the previously reported active LaCoO₃ catalyst. The results strongly suggest that the PA method provides nanosized LaCoO₃ without requiring the precise control of chemical reactions, harsh conditions, and/or special apparatus, indicating that it is promising for producing active OER catalysts at a large scale.

A simple synthetic process for LaCoO₃ nanoparticles based on the accumulation of precursors on nanocarbon supports was presented. The LaCoO₃ nanoparticles showed excellent OER activity owing to their high surface area and perovskite structure.

Nanocomposite Membranes for Liquid and Gas Separations from the Perspective of Nanostructure Dimensions

One of the critical aspects in the design of nanocomposite membrane is the selection of a well-matched pair of nanomaterials and a polymer matrix that suits their intended application. By making use of the fascinating flexibility of nanoscale materials, the functionalities of the resultant nanocomposite membranes can be tailored. The unique features demonstrated by nanomaterials are closely related to their dimensions, hence a greater attention is deserved for this critical aspect. Recognizing the impressive research efforts devoted to fine-tuning the nanocomposite membranes for a broad range of applications including gas and liquid separation, this review intends to discuss the selection criteria of nanostructured materials from the perspective of their dimensions for the production of high-performing nanocomposite membranes. Based on their dimension classifications, an overview of the characteristics of nanomaterials used for the development of nanocomposite membranes is presented. The advantages and roles of these nanomaterials in advancing the performance of the resultant nanocomposite membranes for gas and liquid separation are reviewed. By highlighting the importance of dimensions of nanomaterials that account for their intriguing structural and physical properties, the potential of these nanomaterials in the development of nanocomposite membranes can be fully harnessed.

Coating of Silica Nanolayers on Carbon Nanofibers via the Precursor Accumulation Method

Surface modification of nanocarbons, for example, by coating with oxide nanolayers, is a research topic of significant interest because of the drastic changes in the physicochemical properties of the modified nanocarbons. One simple method of creating these oxide nanolayer coatings on nanocarbons is the precursor accumulation (PA) technique, which entails the following: (1) a precursor solution is added dropwise onto nanocarbon powder; (2) the solvent is dried, leaving the accumulated precursor on the nanocarbon surface; and (3) hydrolysis or decomposition of the precursor in air leads to the formation of oxide nanolayers on the nanocarbons. In this study, tetraethoxysilane (TEOS) was used as a precursor for coating silica nanolayers onto carbon nanofibers (CNFs). TEOS is so stable that it hardly undergoes hydrolysis on the surface of pristine CNFs. By treating CNFs with H₂SO₄/HNO₃, acidic functional groups were introduced onto the CNF surfaces. Silica nanolayers were successfully synthesized on these acid-treated CNFs via PA coating because the acidic functional groups catalyzed the hydrolysis of TEOS accumulated on the CNF surfaces. Scanning transmission electron microscopy indicated that the thickness of silica layer is approximately several nanometers. Pore size distribution analysis for the silica nanolayer suggested the presence of nanopores with 3-5 nm. The TEOS molecules could have accessed the functional groups through the nanopore; therefore, the number of silica nanolayers formed increased with the number of PA coatings. Finally, we compared the PA coating with conventional sol-gel and atomic layer deposition techniques.

Synthesis of Carbon Nanofibers on C-Fiber Textiles by Thermal CVD Using Fe Catalyst

This research was conducted to synthesize carbon nanofibers on C-fiber textiles by thermal CVD using Fe catalyst. The substrate which was a carbon textile consisting of non woven carbon fibers and attached graphite particles, was oxidized by nitric acid before the deposition process. Hydroxyl groups were created on the C-fiber textile due to the oxidization step. Fe (III) hydroxide was subsequently deposited on the oxidized surface of the C-fiber textile. To deposit ferric particles two different methods were tested: i) deposition-precipitation, ii) dip-coating. For the experiments using both type of catalyst deposition the weight ratio of Fe to C-fiber textile was also varied. Ferric particles were reduced to iron after deposition by using H2/N2gas and CNFs were grown by flowing ethylene gas. Properties of carbon nanofibers created like this were analyzed through Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), N2-sorption (BET), X-Ray Diffraction (XRD), and X-ray Photoelectron Spectoscopy (XPS). In the case of deposition-precipitation method the result shows that the diameter of carbon nanofibers grew up to 40~60nm and 30~55nm at which the weight ratios of Fe catalyst to C-fiber textiles are 1:30 and 1:70 respectively. If Fe particles were deposited by dip-coating method, the diameter of carbon nanofibers grew up to 40~60nm and 25~30nm for the ratios of Fe catalyst to C-fiber textiles 1:10 and 1:30.

Controlled synthesis of one-dimensional inorganic nanostructures using pre-existing one-dimensional nanostructures as templates

Template-directed strategy has become one of the most popular methods for the fabrication of one-dimensional (1D) nanostructures with uniform size and controllable physical dimensions in recent years. This Review article describes the recent progress in the synthesis of 1D inorganic nanostructures by using suitable templates. A brief survey on the templating method based on the organic templates and porous membrane is firstly given. Then, the article is focused on recent emerging synthetic strategies by templating against the pre-existing 1D nanostructures using different physical and chemical transformation techniques, including epitaxial growth, nonepitaxial growth, direct chemical transformation, solid-state interfacial diffusion reaction, and so on. The important reactivity role of the 1D nanostructures will be emphasized in such transformation process. Finally, we conclude this paper with some perspectives and outlook on this research topic.