Pin Hsiang Chiu

Electrochemically Controlling the Size of Gold Nanoparticles

This work demonstrates the electrochemical synthesis of nanoscale gold particles using a surfactant solution. Tetradodecylammonium bromide (TTAB) surfactant was applied to stabilize the gold clusters. Experimental results reveal that the size of the produced gold nanoparticles is controlled by the amount of TTAB surfactant, the current density, and the growth temperature. The size of the gold nanoparticles can be controlled in the range 58.3-8.3 nm. The particle size decreases as the amount of TTAB increases from 1 to 90 mg. The optimal current density in this study was 3 mA/cm 2 . The size of the produced nanoparticles increases linearly with the growth temperature from 25 to 60°C. The gold nanoparticles were observed by transmission electron microscopy, ultraviolet-visible spectrometry, and X-ray photoelectron spectroscopy. A mechanism for electrochemically controlling the size of the gold nanoparticles is presented.

Synthesis of the Gold Nanocubes by Electrochemical Technique

This investigation demonstrates the rapid synthesis of a large quantity of uniform-sized gold nanocubes by an electrochemical method, using a surfactant solution and acetone. A redshift is observed in ultraviolet-visible absorption spectra as the shape of gold nanoparticles changes from spherical to cubic. The selected area electron diffraction patterns reveal that the gold nanocubes are single crystalline with lattice constant a = 4.068 A. The nanocube edge is about 30 nm long. The gold nanocubes are truncated structures, as revealed by high-resolution transmission electron microscopy analysis. The effect of acetone addition on the shape of particles is also discussed.

Characterization and Synthesis of GSCS Nanoparticles by Sol–Gel Method with Controlling of Adding Water Amount

In this article, gold-silica composite nanoparticles with a core-shell structure are successfully fabricated using a simple sol-gel method without using primer, surfactant, or surface modification of the core. The reactions solution at room temperature is prepared by tetraethyl orthosilicate (TEOS), isopropanol, ammonia, and water. The growth of gold-silica core-shell (GSCS) nanoparticles involved the base-catalyzed hydrolysis of TEOS and subsequent condensation of silica onto the surface of gold nanoparticles. Silica is observed to be sol phase without adding water in the reaction solution. Thus, these silica sols could not be uniformly coated onto the surface of gold nanoparticles. To investigate the influence of water on the synthesis of GSCS nanoparticles, the amount of water was varied in the range of 1 to 9 mL. It was found that the thickness of the silica shell could be formed in the range of 10 to 120 nm, and the UV-visible optical absorption measurement revealed a pronounced redshift of the surface plasmon resonance band from 528 to 537 nm. Furthermore, the analysis of the reaction solution pH indicated that the silica shell cannot be coated at pH > 10.85. The growth of silica could be increased substantially to form the thicker silica shell within the pH of the reaction solution from 10.85 to 10.06. However, the reaction solution in the lightly alkaline condition is suitable for the growth of silica.

The novel formation of barium titanate nanodendrites

The barium titanate (BaTiO3) nanoparticles with novel dendrite-like structures have been successfully fabricated via a simple coprecipitation method, the so-called BaTiO3 nanodendrites (BTNDs). This method was remarkable, fast, simple, and scalable. The growth solution is prepared by barium chloride (BaCl2), titanium tetrachloride (TiCl4), and oxalic acid. The shape and size of BaTiO3 depend on the amount of added BaCl2 solvent. To investigate the influence of amount of BaCl2 on BTNDs, the amount of BaCl2 was varied in the range from 3 to 6 mL. The role of BaCl2 is found to have remarkable influence on the morphology, crystallite size, and formation of dendrite-like structures. The thickness and length of the central stem of BTND were ~300 nm and ~20 μm, respectively. The branchings were found to occur at irregular intervals along the main stem. Besides, the formation mechanism of BTND is proposed and discussed.

Fabrication of Gold Nanocubes by the Electrochemical Method

This paper demonstrates synthesis of gold nanocubes with uniform size about 30 nm by a simple electrochemical method. The surfactant cetyltrimethylammonium bromide (CTAB) and tetradodecylammonium bromide (TTAB) were used as the stabilizer and micelle template to control the size and shape of gold nanocubes. In this study, acetone solvent was injected to the electrolyte solution with surfactant, changing the surfactant micelle-template, leading to the formation of gold nanocubes. The gold nanocubes have a surface plasmon resonance (SPR) band at a wavelength of about 530 nm. The gold nanodumbbells have been determined to be single-crystalline with a face-centered cubic (fcc) structure by X-ray diffraction (XRD) analysis.

Electrochemical formation of gold nanodendrites by the additive toluene solvent

Gold nanodendrites (GDs) are successfully fabricated via a simple electrochemical method (ECM) using micelle templates formed by two surfactants with various amounts of toluene solvent, the primary surfactant being hexadecyltrimethylammonium bromide (CTAB) and the cosurfactant being tetradodecylammonium bromide (TTAB). To investigate the influence of toluene solvent on the GDs, the amount of toluene solvent was varied in the range from 10 to 50 μL. It was found that the shape of particles was changed from sphere to dendritic shape, and the UV–vis optical absorption measurement revealed a pronounced red shift of the surface plasmon resonance (SPR) peak from 525 to 540 nm. The selected-area electron diffraction (SAED) patterns reveal that GDs are single crystalline with lattice constant a = 4.072 Å. The GDs have been determined to be pure gold with a face-centered cubic (fcc) structure.

Synthesis of the Gold Nanocubes by Electrochemical Method with Surfactant Solution and Acetone Solvent Addition

Monodispersed gold nanocubes of highly uniform size were fabricated by a simple electrochemical method. The lengths of the edges of the gold nanocubes were about 30 nm. The growth solution was prepared from two cationic surfactant solutions as micelle templates with added acetone solvent. The primary surfactant was hexadecyltrimethylammonium bromide (CTAB) and the co-surfactant was tetradodecylammonium bromide (TTAB).

Synthesis of Core@Shell Composites with Gold Nanoparticles Trapped inside Ceramic Silica Shells by the Sol-Gel Method

This paper describes a sol-gel (SG) method for the coating of gold nanoparticles with uniform shells of amorphous silica. The thickness of silica could be conveniently controlled in the range of 10 to 120 nm by increasing the amount of water. Although spherical gold nanoparticles generally have a surface plasmon resonance (SPR) at a wavelength of about 520 nm, a spherical gold core with a silica shell offers a very highly tunable SPR wavelength depending on the thickness of the silica shell.

Synthesis of Gold Nanodogbones by the Seed Mediated Growth Method with Addition of Vitamin C Solvent

A simple seeded mediated growth (SMG) method with addition of vitamin C solvent to prepare novel gold nanodogbones is reported. In SMG method, gold nanodogbones are produced in reasonable yield by chemical reducing HAuCl4 in surfactant solution, with small seed gold particles added as nucleation centers for the preparation of large size nanoparticles. Besides, the surfactant absorbs strongly (as a bilayer) along the crystal face of the nanoparticle. The surfactant is usually considered to be a soft micelle-template, which controls the size and shape of the nanoparticles. In this study, the role of vitamin C is found to alter gold nanoparticles shape from rod structures to dogbone-like structures. The aspect ratio of gold nanodogbones can be easily controlled by addition amount of vitamin C solvent from 10 to 30 µL.