Valorization of Rice Husk through the Development of New Materials of Silica Functionalized with Phthaloyl Diamide Ligands: Characterization, Isomer Effect, Ag+ Adsorption Investigation, and Antibacterial Activity

Abstract Silica was obtained from rice husk, a low-cost and abundant agricultural waste, and chemically modified with three phthaloyl diamide ligand isomers, aiming to develop new materials with adsorptive and antibacterial potential. The prepared adsorbents were fully characterized, confirming the successful functionalization. The isomeric structure of the ligands significantly influenced both the uniformity and extent of functionalization and the Ag+ adsorption efficiency. The Ag+ adsorption was favored at pH 5.0 and room temperature, and the adsorption rate was very fast, reaching equilibrium in about 15 min. The maximum adsorption capacity was 19.94 mg g–1. Antibacterial tests demonstrated that the Ag+-loaded adsorbent exhibited marked antibacterial activity against Escherichia coli, highlighting the dual functionality of the synthesized material. These results underscore the potential of phthaloyl-modified rice husk-derived silica as a novel and effective material for integrated Ag+ removal and antibacterial protection.