Synthesis and Characterization of Silver Nanoparticles

AgNPs were prepared in water by a chemical reduction method. Reagents for the syntheses were of analytical purity and used without further purification: silver nitrate (AgNO₃, purity 99.999%, Sigma-Aldrich), sodium citrate (C₆H₅Na₃O₇·2H₂O, purity 99.0%, Sigma-Aldrich), tannic acid (C₇₆H₅₂O₄₆, Fluka), deionized water (Deionizer Millipore Simplicity system). All solutions of reacting materials were prepared using deionized water. Before use, all glassware was cleaned in a bath of aqua regia solution and rinsed thoroughly using deionized water. The syntheses were carried out using a constant molar ratio of silver nitrate to sodium citrate and tannic acid. For AgNP syntheses with sodium citrate, the molar ratio of silver nitrate to sodium citrate was 1:7; for AgNP syntheses with tannic acid, the ratio of silver nitrate to tannic acid was 1:2; for AgNP syntheses with a mixture of sodium citrate and tannic acid, the ratio of silver nitrate, sodium citrate and tannic acid was 1:7:2. The concentration of silver ions in all solutions was 100 ppm. The syntheses of AgNPs were carried out both at room temperature and at 100 °C. The syntheses at room temperature were carried out by the addition of a sodium citrate and tannic acid mixture to the aqueous solution of silver nitrate. In the case of syntheses at 100 °C, silver nitrate was first heated to its boiling point under reflux and then a mixture of sodium citrate and tannic acid was introduced to the reaction mixture. The solution was heated for additional 15 min and cooled to room temperature. The conditions of syntheses and chemicals used in the preparation of AgNPs are presented in Table 1.Table 1

The conditions of syntheses and chemicals used in the preparation of AgNPs

Sample	Temperature of the synthesis	Reagents
		Silver nitrate	Sodium citrate (SC)	Tannic acid (TA)
Colloid SC	Room temp.	0.0164%; 95.80 g	4%; 4.20 g	X
Colloid SC*	100 °C
Colloid TA	Room temp.	0.0158%; 99.35 g	X	5%; 0.63 g
Colloid TA*	100 °C
Colloid SC–TA	Room temp.	0.0165%; 95.15 g	4%; 4.20 g	5%; 0.63 g
Colloid SC–TA*	100 °C

X—reagent was not used in the synthesis procedure