First-principles analysis of transition metal nitrates in oxide host sensor materials

Abstract

The warfighter is often tasked with the responsibility of investigating possible rogue laboratories, searching for materials that can be used to build or develop weapons that can range from improvised explosive devices to chemical warfare agents for direct attack. Currently, the warfighter’s primary method of chemical detection comes in the form of colorimetric paper. It is a mid-20th century technology that comes in the form of a paper detection system that, like litmus, changes color according to the reagent detected. This method doesn’t come without its limitations. This work aims to provide a convenient, reliable and cost-efficient alternative to current detection methods, while allowing for a wider range of chemical activity. Preliminary work with inorganic oxides, such as zeolites, have shown promise as a framework for a colorimetric sensor with the potential to be portable, provide high selectivity and specific chemical information in the form of unique color changes. The aluminosilicate zeolite explored uses a hydrogen counter-ion and is composed of corner sharing Si/Al tetrahedrons, allowing for multiple bonding orientations which produce a 3D framework of multiple pores of various sizes as well as producing various polytypes. By decorating this zeolite framework with various metal nitrates [Co(NO₃)₂, Cu(NO₃)₂, Ni(NO₃)₂] and exposing the resulting materials to chemical threats, color changes have been noted. Using density functional theory, we can model these metal nitrate and zeolite interactions. This multifaceted work will explore the structural nature of the aluminosilicate zeolite being explored, the adsorptive interactions that occur between the zeolite and the metal nitrates and determine the spectroscopic changes that occur as a result of these interactions. Modeling the transition metal and zeolite interactions, along with the calculation of the electronic band structures of these materials will give us insight into the light absorbing nature of these combinations, allowing us to determine the nature of the color change observed.