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Preparation of a Gold 3 Nitrate Precursor for Bottom-Up Ultrasonic Spray Pyrolysis

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gold 3 nitrate (H3NO3) is one of the least reactive salts of gold. It is usually prepared by adding it to acid, such as nitric acid or aqua regia. Alternatively, it can be formed by treating silver chloride with nitric acid in the presence of an excess of halide, such as chlorine or bromine. In the latter case, the resultant solution is commonly called acid gold nitrate or gold(III) nitrate, also known as nitratoauric acid and hydrogen tetranitratoaurate, respectively. It is an odorless, colorless compound.

Until recently, the preparation of a water-based precursor for bottom-up ultrasonic spray pyrolysis of gold nanoparticles was not feasible because of the low solubility of the Au(NO3)3 salt. However, this was overcome by using a special neutralizer, ammonium hydroxide (NH4OH), in the solution. This led to the in situ formation of low concentrations of NO2- and NO3- ions, which could be captured directly in deionized water. The resulting gold(III) nitrate was stable in deionized water for 9 months and prevented agglomeration and coagulation of the final collection state.

We have optimized the preparation of the Au(NO3)3 precursor for use in a spray pyrolysis system by selecting the optimal temperature ranges for the evaporation and reaction zones, and determining the optimal gas flow rates of the carrier (N2) and reducing (H2) gases to give sufficient residence times for the chemical conversion of the precursor into gold nanoparticles. The rheological properties of the precursor were evaluated by means of a Fungilab Smart Series Rheometer with a low viscosity adapter.