Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemical Engineering and Materials Science

First Advisor

Guangzhao Mao

Abstract

This study focuses on fabrication of hybrid nanostructures using gold nanoparticles (AuNP) as seeds and partially oxidized potassium tetracyanoplatinate, known as Krogmann’s salt (KCP), and later this method will be employed to manufacture a prototype sensor for detecting different vapors. Nanocrystals are synthesized using electrochemical method with the aim to have more control over the size and shape of the charge transfer salt based on the seed mediated nucleation method. AuNP seeds are prepared on highly ordered pyrolytic graphite (HOPG) substrate by the electrocrystallization method. An aqueous solution of 0.05 to 1 mM Hydrogen tetrachloroaurate (HAuCl4) with 0.1 mM (Potassium chloride) KCl as the supporting electrolyte was prepared. The electrodeposition of the AuNPs was monitored by Cyclic Voltammetry (CV) and analyzed by Atomic Force Microscopy (AFM). The results show that the most dominant factor to control the AuNP size is the HAuCl4 concentration. Deposition time and applied potential are the other factors controlling the electrodeposition. The smallest particle size was observed with the lowest HAuCl4 concentration. The synthesis of K1.75Pt(CN)4.1.5H2O rods is conducted according to literature on bare HOPG with a concentration of 0.07 M of K2Pt(CN)4 in DI water and a potential pulse of 1.5V (vs SCE ) for 0.1s. Needle shaped crystals with a size range of 600 nm to 5µm in length and 100-500nm in width were synthesized on the bare HOPG. When the experiment was conducted with the same conditions on AuNP decorated HOPG, in result the average diameter and length of the rods were reduced significantly that matches our hypothesis based on seed-mediated nucleation theory. The results will help to have a better understanding of seed-mediated nucleation theory for producing nanoparticles of the desired size and shape, and also introduce a new way of manufacturing future nanosensors and nanoelectrods. Next, micro sized crystals were synthesized using the same method with longer deposition time on patterned Cr/Au electrodes. The conductivity of the KCP crystals was measured in exposure of different vapors. The results show dramatic conductivity change after introducing the vapors to the sensor, and also it shows a rapid respond and more sensitivity compare to commercial sensors .They proves that this prototype can be a reliable and cheap replacement of available sensors in different applications.

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