Fabrication of Anisotropic Silver Nanoplatelets on the Surface of TiO2 Fibers for Enhanced Photocatalysis of a Chemical Warfare Agent Simulant, Methyl Paraoxon

Among the world's most deadly toxins are a class of organophosphates that are used as chemical warfare agents (CWAs). It is imperative to continue to develop novel means for mitigation and protection against these chemical threats. Sensitizing the surface of metal oxide semiconductors with plasmonic nanoparticles for photocatalytic degradation of chemical threats has been a prominent area of research in recent years. Anisotropic silver nanoplateles were purposefully grown on the surface of TiO2 fibers, in order to determine the impact of silver nanoparticle shape on (1) the generation of hot electrons by the silver, (2) the subsequent transfer of those electrons from the silver into the TiO2, and (3) the photocatalytic behavior of the Ag–TiO2 composite. To elucidate the charge injection properties of the composites, transient absorption experiments (pump–probe experiments) were undertaken. These involved pumping the composite samples with a range of discrete visible wavelengths and probing the composite within the intraband transitions of the TiO2. As a complement to these experiments, the photocatalytic properties of the Ag–TiO2 composite fibers were studied via the photocatalytic hydrolysis of methyl paraoxon, a chemical warfare agent simulant. This involved exposure of the methyl paraoxon to either red, green, blue, or white LED illumination. For both the transient absorption and photocatalytic experiments, maximum efficiency was observed for those scenarios in which the resonance of the silver platelets most closely matched the wavelength of incident radiation. Furthermore, the composite with silver nanoplatelets clearly outperformed its counterpart with silver nanospheres, in terms of both charge injection and photocatalytic behavior. We believe these results shall serve as a basis for future catalytic research in which the resonance of anisotropic plasmonic nanoparticles (in a given composite) shall be designed to match the wavelength of incident radiation.