Microwave-assisted rapid synthesis of anisotropic Ag nanoparticles by solid state transformation

S. Navaladian, B. Viswanathan, T. K. Varadarajan and R. P. Viswanath

 

 

Microwave irradiation is used to synthesize anisotropic silver nanoparticles via decomposition of silver oxalate in a glycol medium using polyvinyl pyrolidone as the capping agent. The concentration of Ag nanoparticles formed by thermal decomposition shows to be higher than that of polyol-reduced Ag nanoparticles. These nanoparticles have been characterized and show an average of size around 30 nm following irradiation for 75s and 5-6 nm after 60s. Ethylene glycol (EG) was found to be a better medium than diethylene glycol (DEG). Microwave-assisted synthesis is manifold faster than conventional heating.

 

Methods

 

Characterization of silver oxalate was carried out using a powder x-ray diffraction (XRD), Perkin Elmer thermo-gravimetric analysis (TGA)7 and an FEI (Model: Quanta 200) scanning electron microscope (SEM). Irradiation was carried out in a Panosonic Inverter (1100 W, 2.45 GHz) microwave oven. Collodial Ag nanoparticles were characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM).

 

Key Findings

 

1.) Nanoparticle size can be manipulated by microwave exposure.

2.) Suggest that SPR band of nanoparticles vary depending on dielectric constant,         refractive index and size.

3.) Suggest mechanism for nanoparticle growth: Ag₂C₂O₄ (s) à 2 Ag(s) + 2 CO₂

4.) Suggest that EG is a more suitable dielectric medium than DEG which is due to the smaller size of EG to effectively enter pores of silver oxalate and reduce Ag⁺ on surface.

The effect of laser power on the formation of carbon nanotubes prepared in CO2continuous wave laser ablation at room temperature

H. Zhang et al. I Physica B 325 (2003) 224-229

Introduction

The synthesis of carbon nanotubes has generated a number of useable facile methods most of which employ the use of high temperature atmospheres.  However, the findings suggest a novel method of Carbon nanotube formation that mitigates  the concern of high temperature reactions.  Single-walled carbon nanotubes (SWCNT) were prepared by continuous wave CO₂ laser ablation without the application of additional heat to the materials.  TEM and Raman Spectra were used to assess the effects  of varied laser power on the growth and diameter distributions of the newly formed tubes.  The continuous laser source was generated by laser vaporization in laser power from 500 to 850 W and compared to previous literature.

Key Findings

1.       Carbon nanotubes are able to be formed at room temperature using infrared laser with wavelengths of 10.6 µm.

2.       Direct relationship found between SWCNT diameter and laser power. At lower laser power (below 500W) bamboo-shaped CNT’s are reported.

3.       SWCNT’s produced in different excitations wavelengths  (632.8nm v. 488nm) produce varied spectra when pulsed with continuous CO₂ laser.  Information suggest the these results are conducive to carbon nanotube diameter

4.       Spectra show diameter distribution ranging from 1.1 to 1.6nm.

Functionalization of Single-Walled Carbon Nanotubes with 1,4-Benzenediamine Using a Diazonium Reaction

Mark D. Ellison* and Patrick J. Gasda

J. Phys. Chem. C 2008, 112, 738-740

 Purpose

To functionalize single walled carbon nanotubes (SWCNT) using a phenyl amine group in a single step diazonium reaction process. Amines NH2 prove versatile and this facile functionalization allows for a variety of future reactions.

Method

The reaction process required that purified SWCNT be mixed with an aromatic compound containing an amine substituent in heat that is concentrated and purified. Functionalization was verified using 
Fourier Transform Infrared (FT-IR), Raman and UV/vis spectroscopies.

Key Findings

1.) Previous methods employed usage of multiple steps of which would either include fluorination prior to amine addition or the reaction of an amine following addition of carboxylic groups.

2.) Using 1, 4-benzenediamine it is possible to attach the molecule resulting in an attached benzene ring with an amine group para to the SWCNT.

3.) Stretches conducive to N-H in FT-IR spectrum were detected at 3737 and 3664cm-1, respectively. These stretches were shown to be 200 cm-1 higher than the starting material suggesting possible attachment.

4.) Raman spectra indicated sidewall functionalization due to significant intensity in the D band.

5.) UV/vis spectra illustrate peak resulting from transitions between van Hove singularities. There were no discernable peaks in the functionalized SWCNT which coincides with previous literature.

Key words: van Hove singularities-a variation in the density of states (DOS) of a solid. In two dimensions the DOS is logarithmically divergent and in one dimension the DOS itself is infinite where gradient energy is zero.

Carbon Nanotubes: Synthesis, Integration, and Properties

by Hongjie Dai

Accounts of Chemical Research, 35, NO. 12 (2002)

Purpose of Study:

This investigation examines manipulation of single-walled carbon nanotubes (SWNT) growth using CVD method of production to acquire enhanced understanding of CNT properties and growth.

Methods
Utilization of the chemical vapor deposition method (CVD) elmininates the need for solid- state carbon precursors, forms CNT at lower temperature of (500-1000), and incorporates usage of hydrocarbon gases for source carbon atoms and metal catalyst particles. Carbon nanotube synthesis by CVD involves heating a catalyst material in a furnace while flowing the hydrocarbon gas through the tube reactor. The catalyst particles nucleate nanotube growth and can be used to attain further specificity of growth for both multi-walled and single-walled nanotubes.

Key Features

1.)The polarizability of SWNT’s has allowed used of electric fields to control growth direction.

2.) The use of Fe⁺³ as catalyst particle has been introduced to the CVD method of synthesis and allowed extraction of nanoparticle-nanotube relationship which deduces that tube growth rises upward from the nanoparticle. Further, using TEM and AFM theory suggest that SWNT diameters are closely determined by catalytic particle diameter.

3.)The SWNT experiences improved conductivity under O₂ and N₂.

4.)A method has been devised to functionalize SWNT noncovalently and preserve the sp² structures and their electronic properties. These attachments include π-stacking of 1-pyrenebutanoic acid succinimidyl ester onto the SWNT sidewalls and prove highly stable leading to functionalization with succinimidyl ester groups.