Eco-friendly walnut shell powder based facile fabrication of biogenic Ag-nanodisks, and their interaction with bovine serum albumin.

Walnut shell biomass was used for the extraction of juglone by water as a solvent at room temperature. Upon addition of AgNO₃ to a dye solution, prefect transparent pale brown color develops within the reaction time. UV-visible spectroscopy revealed the appearance of surface plasmon absorption (SRP) peak at 410 nm for spherical silver nanoparticles (AgNPs). Transmission electron microscopy suggested the formation of spherical and truncated triangular nano-plate geometry of AgNPs with average diameter 25 nm. Juglone-surfactant interactions (micellization and incorporation) have been studied spectrophotometrically by using cationic cetyltrimethylammonium bromide (CTAB). The presence of CTAB has significant impacts on size, shape and the size distribution of AgNPs. The nucleation, growth, and adsorption processes depend on the [CTAB]. It also catalyzes the Ag⁺ ions reduction by juglone with a rate enhancement of ca. 100-fold. Activation parameters (activation energy, enthalpy of activation and entropy of activation) were evaluated to the synthesis of silver nano-disks. Antioxidant activity of juglone was accessed by the scavenging effect on DPPH radical. Silver nanoparticles was also used as quencher to determine their interaction with bovine serum albumin (BSA). The quenching constant were found to be 1.4 × 10³ M^-1 L s^-1 and 4.8 × 10³ M^-1 L s^-1 for two BSA concentrations.