Green Synthesis of Silver Nanoparticles Using Chitosan in Carbonic acid Solutions: Effect of Pressure and Temperature on the Structure and Antimicrobial Properties

Composite chitosan films containing stabilized silver nanoparticles were synthesized using aqueous solutions of carbonic acid (i.e., water saturated with carbon dioxide) under varying pressure (6–50 MPa) and temperature conditions (25–90 °C). Carbonic acid is a biocompatible and antimicrobial medium. The influence of various factors, such as the molar ratio of chitosan to silver, pressure variations, and temperature, on the structural properties of the composite chitosan/silver composites was studied systematically using transmission electron microscopy (TEM) and X-ray diffractometry (XRD). A correlation was identified between the characteristics of the water saturation with carbon dioxide (pressure and temperature of the carbonic acid solution) and the structural features of the composite films. All films exhibited small silver nanoparticles measuring 1–2 nm in diameter. At specific pressure and temperature values, a phase of larger nanoparticles with sizes in the tens of nanometers was also present within the chitosan matrix. The relationship between the structure of the produced films and their antimicrobial properties has been established.