Phytofabrication of silver nanoparticles from Illicium verum fruit extract and its role in Cr +6 removal: a comparative analysis

Herein, using Illicium verum (IV) aqueous fruit extract, spherical shape silver nanoparticles (IV-AgNPs) of 40 nm average size with typical SPR at 422 nm were synthesised through the one-pot chemical reduction method. In the presence of Cr+6, IV-AgNPs rapidly changed from yellow to pink colour, with immediate SPR quench at 422 nm and new peak appearance at 510 nm, suggesting carboxylate groups involvement in AgNPs synthesis and Cr+6 interaction, respectively. Clusters were formed in Cr+6 presence; as a result, IV-AgNPs' zeta potentials changed from −24.1 to 14 mV. Moreover, with the lowest limit of detection (22.1 nM), IV-AgNPs displayed higher potential for Cr+6 adsorption in aqueous medium. The Langmuir isotherm predicts monolayer adsorption on a homogeneous surface of both adsorbents via chemisorption kinetics with adsorption capacity of 1511.65 and 720.35 mg/g for IV-AgNPs and IV fruit extract, respectively. Calculated thermodynamic values of -∆G°, +∆H°, and +∆S° indicate spontaneity, randomness, and endothermicity of the adsorbate system(s). Akaike information criterion ranking alignment and kinetics equilibrium for adsorbents showed that the Elovich plot and intra-particle diffusion produced the best output in comparison to other models. These findings indicate adsorption dynamics are controllable for both adsorbents, but the size-dependent properties of IV-AgNPs significantly improve interaction efficiency for Cr+6 adsorption.