Deposition kinetics and electrochemical properties of tannic acid on gold and silica

• Tannic acid adsorbs as very thin films on silica and gold.
• These films allow for the reduction of Ag+ cations.
• The reduction kinetics of Ag+ is a slow first order process.
• Tannic acid films are impermeable to hexacyanoferrate anions.

Tannic acid and other polyphenols adsorb spontaneously on almost all kinds of surfaces to yield hydrophilic coatings. However, the deposition kinetics of tannic acid as a function of its solution concentration has not yet been well characterized. Such fundamental aspects are of the highest importance for the protection against corrosion and other applications. Herein, it is shown by means of quartz crystal microbalance with dissipation monitoring that tannic acid (TA) deposition on gold and silica yield to monolayers independently of the TA concentration between 0.1 and 50 mg mL−1. Significant but only partial desorption occurs when the film is put again in the presence of sodium acetate buffer. The reduction of Ag+ cations in silver particles in the presence of tannic acid films is a slow and silver concentration dependent process. In addition TA monolayer films deposited on gold become impermeable to potassium hexacyanoferrate. This shows the high homogeneity and compacity of spontaneously deposited TA monolayers on silver and polycrystalline gold.

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