Basic Problems Of Physical Chemistry About Synthesis Process For Au Colloid

Gold colloids have attracted great interest because of their unique physical and chemical properties, which render them ideal candidates in the fields of photonics, optoelectronics, sensor, information storage, catalyst, biolabeling, magnetic ferrofluids, and medicine. Very interestingly, some properties of gold colloids, such as surface plasmon resonances (SPR) and catalytic activity depend sensitively on their size and shape; therefore, great efforts have been devoted to the controllable synthesis of Au colloids, in which aqueous HAuCl₄ is the most commonly used Au precursor. The pH of aqueous HAuCl₄ usually varies in different approaches for the synthesis of Au colloids; however, the speciation of aqueous HAuCl₄ affected by the pH has seldom been considered as a factor influencing the nucleation and growth of Au colloids.Recently, the pH dependent speciation of aqueous HAuCl₄ have been frequently discussed during the course of preparing supported Au catalysts. Moreau et al. calculated the relative equilibrium concentration of gold complex as a function of pH of aqueous HAuCl₄ with a constant Cl- concentration of 2.5×10^-3 mol L^-1. Although it is known that HAuCl₄ undergoes pH-dependent hydrolysis, the unambiguous speciation of aqueous HAuCl₄ as a function of pH still lacks, particularly at high pH.In this thesis, we employed ion chromatography to examine the speciation of aqueous HAuCl₄ as a function of pH. The concentration of free Cl- in the aqueous solution as the product of HAuCl₄ hydrolysis was quantitatively determined by ion chromatography, which thus enabled us to determine the speciation of aqueous HAuCl₄ at different pH.We also investigated the reduction of aqueous HAuCl₄ at various pH values by ascorbic acid (VC) in the presence of sodium benzenesulfonate (SDBS) and found that the speciation of HAuCl₄ has great influence on the size and thus properties of Au colloids. Au colloids exhibiting the localized surface plasmon resonance in the near- infrared (NIR) region were facilely synthesized at high pH. The size dependent Au-SDBS interactions were also observed and discussed.Meanwhile, we further research some influencing factors of the nucleation and growth of Au colloids, such as species and concentration of protective agent.