Exploring the Mechanisms of the Early Stages of the Formation of Silver Nanoparticles and the Role of Organic Additives

Silver nanoparticle synthesis using organic reducing and stabilizing agents is essential in target oriented materials design for various applications such as medicine, electronics, and catalysis. Here, we explored the mechanisms of the silver nucleation process with silver nitrate as a precursor and trisodium citrate and poly(acrylic acid) (PAA) as both reducing and stabilizing agents. The thesis is thereby subdivided into three parts. Firstly, we studied the dual role of trisodium citrate in reducing silver ions and stabilizing nanoparticles. Using potentiometric titration and the law of mass action, we explored how pH-dependent speciation leads to silver and citrate ion association under light exclusion and moderate temperature to prevent Ag(0) reduction. Amorphous silver citrate is formed initially, which has not been reported previously, to the best of our knowledge. In the second part, we investigated a new calcination method for silver citrate precursors using PAA as an inhibitor to extend nucleation time, resulting in pure amorphous silver citrate, which significantly increases surface area and catalytic performance of the obtained Ag(0)-based materials. The calcination of amorphous silver citrate appears to significantly influence the surface chemistry and catalytic efficiency of silver nanoparticles, as evidenced by the reduction of 4 nitrophenol to 4-aminophenol, a reaction relevant to water treatment. Finally, we systematically studied how silver nanoparticle formation in concentrated PAA environments under UV irradiation depends on PAA and silver ion concentrations. Potentiometric titration and spectroscopy reveal that the Ag+ - PAA system exhibits distinct states of coacervates/complexes, free ions, and, at high silver concentrations, likely dense liquid polymer states prior to solid silver polyacrylate formation. Nanoparticles formed under different conditions vary in growth and ripening. PAA not only stabilizes the particles but also creates distinct environments for precursor reduction, enabling additional control over nanoparticle size, which is critical for optical properties, such as producing bimodal distributions relevant for applications. Overall, these findings highlight significant scientific and industrial potential, offering a versatile method to produce porous monolithic silver and silver nanoparticles for catalysis, medicine, and environmental applications such as drug delivery and antioxidants. By advancing the understanding of silver nanoparticle synthesis, this work opens new avenues for progress in nanotechnology and related fields.