Synthesis, modification, and characterization of hydroxide-derived nanomaterials

Mary Qin G. Hassig

doi:10.17918/00011087

Discovered in 2020, Quaternary ammonium hydroxide Derived Nanomaterials, QDNs, are a family of easily synthesized, low-dimensional, transition metal oxides. Typically, QDNs are formed by reacting a transition metal precursor with a highly concentrated, symmetric quaternary ammonium hydroxide aqueous solution under standard pressure and almost ambient temperatures. Most of the work featured herein focuses on expanding the realm of possibilities for synthesizing members of this family. A significant amount of the work done here is on a two-dimensional, manganese oxide-based QDN with a birnessite structure, henceforth referred to as Quaternary Derived Birnessite, QDB. This investigation is primarily driven by the desire to both increase the processing space of QDNs in general, and to increase the safety around making them by moving away from tetramethylammonium hydroxide, TMAOH, as the primary reactant. Some successes were found in synthesizing QDBs with other symmetric quaternary ammonium hydroxides. However, not any hydroxide worked, leading to questions on the requirements necessary to form QDB. These questions led to success in synthesizing birnessite with the inexpensive, widely available, non-toxic, manganese oxide, Mn₃O₄, in combination with alkali metal hydroxides, through the addition of an oxidizing agent. Also studied is QDB's ability to easily ion-exchange cations as other birnessites are known to do. Through ion exchange, QDBs were able to find application in toxic dye adsorption, outperforming other forms of birnessite by more than a factor of five in tests performed with rhodamine 6G. Additionally, after exchanging the hazardous TMA⁺ cations with Li⁺ a biocompatible material was obtained. This work continues by investigating the reaction between titanium diboride, TiB₂, and TMAOH that results in the titanium oxide-based QDN, 1 Dimensional Lepidocrocite, 1DL. Here the reaction mechanism(s) for the formation of 1DL is probed. And for the first time, the importance of carbon dioxide to the reaction kinetics was elucidated. This study also concluded that in the case of TiB₂, 1DL can be synthesized with much lower concentrations of TMAOH than previously used, creating a material that is functionally, structurally, and optically identical to the standard 1DL, but with a different morphology. This thesis concludes with a study to expand the family of QDNs out of only transition metal precursors, finding success in synthesizing what can be characterized as a two-dimensional silicon dioxide, formed by reacting Si and TMAOH for a couple of hours, under ambient pressure. The Si-based QDN is being tentatively assigned to a silica-only zeolite precursor, formed without long reaction times or the need for solvothermal methods.

Synthesis, modification, and characterization of hydroxide-derived nanomaterials

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Synthesis, modification, and characterization of hydroxide-derived nanomaterials

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