Fabrication and characterization of antibacterial nanoparticles supported on hierarchical hybrid substrates

The effectiveness of many nanomaterial- based devices depends upon their available surface area. Isolated nanoparticles (NPs) can offer high- surface area, but are prone to environmental loss and pollution. Whereas those supported on solid substrates are limited by the specific surface area (SSA) of the support. The SSA limitation of traditional supports can be addressed by attaching NPs on specially designed hierarchical structures having unusually high SSA, thereby maximizing the nanomaterial advantage with- out the risks of using loose nano-powders. In this research, hierarchical structures were fabricated by grafting carbon nanotubes (CNT) on carbon and subsequently decorated with strongly attached silver nanoparticles (AgNP) via controlled reduction of silver salts in the presence of reducing and capping agents. Microstructure characterization revealed that along with other processing parameters, reduction temperature can be used to control NP morphology. For this substrate morphology, fine and uniformly dispersed AgNP were obtained at 60 C, whereas significant particle coalescence and increase in parti- cle size occurred at 80 C. Mechanical durability of AgNP-CNT attachments on the substrate was tested in harsh ultrasonic conditions and found to be impres- sive, with no detectable AgNP loss even when the larger substrate begins to fail. The antibacterial effectiveness of these structures was tested in multiple testing modes against Gram-negative Escherichia coli (E. coli, JM109). It was seen in each case that AgNP attached on CNT-grafted hierarchical substrates showed significantly higher reduction of E. coli com- pared to AgNP attached directly on the starting porous supports without CNT grafting. These results indicate that AgNP attached to hierarchal hybrid supports can lead to compact and powerful antibacterial devices for chemical-free disinfection devices of the future.