Controlled Growth of Metal Nanoparticles on Multi-Walled Carbon Nanotubes for Chemical Sensing Applications

Abstract

We have grown nanoparticles of gold, silver, copper, cobalt and nickel on the surface of carbon nanotubes which are deposited by CVD on gold wires bearing a nickel catalyst layer. A study of the CVD reaction as a function of time revealed that one-minute and ten-minute deposition times yielded qualitatively similar coatings. Metal nanoparticles were grown from electroplating solutions by using the nanotube-coated wire as the working electrode and running a galvanostatic, electrochemical deposition. For gold depositions, we were able to show that varying the conditions of current, plating bath concentration and deposition time allowed control of the size of the deposited nanoparticles within the range of 10 – 150 nm. The morphology of the gold nanoparticles was approximately spherical, except under unique conditions where spiked spheroids, also known as nano-urchins, were observed. By using the gold nanoparticle-decorated CNT electrode as one plate in a parallel-plate capacitor, we were able to show a change in electrical properties, such as capacitance, by comparing voltammograms before and after exposure of the electrode to a dilute solution of organic thiols. This demonstrates the potential utility of the electrode structure as a chemical detector. The two SEM images below show typical results. On the left, CVD carbon nanotube growth prior to electrodeposition of metal nanoparticles; note the presence of nickel catalyst particles at nanotube tips. On the right, carbon nanotube sample after electrodeposition of gold nanoparticles. Figure 1