SYNTHESIS, CHARACTERIZATION, AND PHOTOTHERMAL PROPERTIES OF PLASMONIC METAL NITRIDE NANOPARTICLES

Abstract

Plasmonic materials have been widely used for applications such as photothermal therapy, chemical and biological sensing, energy generation and conversion devices. Most common plasmonic nanomaterials are composed of noble metals, Au and Ag. However, these materials are expensive and hinder applications that require large-scale synthesis. The nanostructures of Au and Ag are susceptible to sintering when used as solar concentrators and Ag can oxidize under ambient conditions, further limiting the practical use of these metals. As an alternative to noble metals, theoretical investigations have shown transition metal nitrides to be promising alternatives. Transition metal nitrides (TMNs) are relatively inexpensive, have high melting points and therefore can possess thermal stability, and their refractory nature can render chemical stability and mechanical hardness. However, these TMNs have not been thoroughly investigated experimentally. The focus of this doctoral work is to synthesize plasmonic TMN nanostructures, examine their properties, and compare them to well-established noble metal (Au and Ag) plasmonic materials. Free-standing and water-dispersible group IVB (Ti, Zr, and Hf) nitrides were synthesized using a solid-state metathesis reaction between the respective transition metal oxides and magnesium nitride. The nanoparticles were characterized using XRD, SEM, TEM, DLS, and XPS. Additionally, the optical properties were investigated using absorbance spectroscopy. The photothermal properties of group IVB TMNs were investigated using an 850 nm LED source and their performance was compared to Au nanorods. The long-term oxidative and chemical stability of group IVB TMNs were also investigated. Furthermore, the group IVB TMNs were successfully synthesized using a solid-gas approach by reacting the respective transition metal oxides with Mg under the flow of N2 gas. The solid-state metathesis reaction was used to synthesize plasmonic Cr2N successfully, and the resulting nanoparticles were characterized using various techniques. The LSPR peak of plasmonic Cr2N is in the deep UV region, therefore EELS loss probability maps were used to probe the plasmonic responses. Additionally, the chemical stability of Cr2N colloidal suspension at different pH was also investigated. Moreover, the photothermal properties of Cr2N using a 365 nm LED source were investigated. These studies suggest the possibility of using Cr2N for water treatment and disinfection applications.