A simple one-step process, Tollens method, has been used for synthesis of silver NPs with a controlled size. This green synthesis technique involves reduction of Ag(NH3)2+ (as Tollens reagent) by an aldehyde (101). In the modified Tollens procedure, silver ions are reduced by saccharides in the presence of ammonia, yielding silver nanoparticle films (50-200 nm), silver hydrosols (20-50 nm) and silver NPs of different shapes. In this method, ammonia concentration and nature of the reducing agent play an important role in controlling size and morphology of silver NPs. It was revealed that the smallest particles were formed at the lowest ammonia concentration. Glucose and the lowest ammonia concentration (5 mM) resulted in the smallest average particle size of 57 nm with an intense maximum of surface plasmon absorbance at 420 nm. Moreover, increase in NH3 from 0.005 M to 0.2 M resulted in a simultaneous increase in particle size and polydispersity (102). Silver NPs with controllable sizes were synthesized by reduction of [Ag(NH3)2]+ with glucose, galactose, maltose, and lactose (103).
The nanoparticle synthesis was carried out at various ammonia concentrations (0.005-0.20 M) and pH conditions of 11.5-13.0 resulting in average particle sizes of 25-450 nm. The particle size was increased by increasing (NH3), and the difference in structure of reducing agent (monosaccharides and disaccharides) and pH (particles obtained at pH 11.5 were smaller than those at pH 12.5) influenced the particle size. Polydispersity also decreased by lowering the pH. Produced silver NPs were stabilized and protected by sodium dodecyl sulfate (SDS), polyoxyethylene sorbitane monooleate (Tween 80), and polyvinylpyrrolidone (PVP 360) (104,105).