where water molecules are dissociated into hydrogen (H•) and hydroxyl radicals (OH•), respectively. The alcohol (CH3CH2OH) denotes the radicals scavenger, ethanol, (CH3CHOH•) is the secondary radical and (CH3COH^) is the deprotonated form. The measures of pH of the H2PtCl6 initial solution and after sonication revealed that it was maintained in acid conditions at pH = 5.
Fig. 1b exhibits the UV–vis spectrum of the AgNO3 solution obtained during 7 h of ultrasound. An absorption band related to the plasmon resonance of silver nanoparticles appears at a wavelength that varies between 420 and 430 nm (indicated in the plot). The position and intensity of the plasmon band depend on the particle dimensions [24,25]. The initial and final pH of the AgNO3 solution was maintained neutral (pH = 7). The reduction of silver by sonication can be expressed following the two pathways described by