Evaluation of Immobilized Titanium Dioxide-Silver-Hydroxyapatite Nanoparticles and Colloidal Silver for Water Disinfection

Abstract

Titanium dioxide nanoparticles combined with silver and hydroxyapatite (TiO₂-Ag-Hap) form a photocatalytic composite capable of oxidizing and mineralizing a wide spectrum of microbiological and chemical contaminants in water, while silver nanoparticles have long been employed for their antimicrobial properties. These materials were evaluated through an iterative series of experiments that evaluated microbial reduction, material formulation, method of application, surface-interface interactions, and reusability. The TiO₂ formulation was assessed as an antimicrobial film coated onto fabric and ceramic beads in three experimental designs: a gravity filtration column, a portable treatment capsule, and a static chamber. Colloidal floating Ag nanoparticles in solution were also assessed. Reduction of Escherichia coli, Klebsiella terrigena, MS2 bacteriophage, and Rotavirus was evaluated though standard culture-based methods. Significant microbial reduction was only observed in the static open pan design for the TiO₂-Ag-HAp materials. Colloidal silver was more effective and caused a 5 log reduction of K. terrigena, within 60 minutes, and a 5 and 4 log reduction of MS2 within 120 and 90 minutes respectively in initial trials. The anti-microbial properties of both materials were apparent, but further investigations are necessary to assess the potential of the materials for integration and development in water treatment technologies.