Loading...
Discerning the chemical reactivity of covalent surface-functionalized ordered mesoporous carbon nanoparticles through oxidative coupling and organolithium mediated approaches
Kovach, Nolan Christopher
Kovach, Nolan Christopher
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2024
Date Submitted
Keywords
Collections
Files
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
Porous carbons materials are particularly attractive to study and utilize due to their high surface area, chemical resistance towards high and low pHs, and inherent thermal & electrical conductivity. However, many porous carbons are relatively devoid of reactive surface chemical functionality, primarily comprising sp2 C-C bonds (both planar or strained/curved) and sp3 C-H bonds, being both inherently hydrophobic and nonreactive towards chemical attack.
Post-synthetic modifications instill new chemical groups on carbon surfaces to imbue new functionality. Covalently modified carbons are preferred to retain surface functionality over time relative to leachable non-covalently surface bound adsorbates. Catalyst and adsorbent regeneration, as well as operating conditions for electrodes call for the immersion of carbon into acid or base at concentrations which can degrade some material surfaces. Despite there being many covalently modified carbon materials, there is a dearth of knowledge regarding pH ranges which these can operate while retaining surface functionality.
Ordered mesoporous carbon (OMC) hard templated from mesoporous silica nanoparticles were selected for primary amine surface modification by two methods—wet chemical oxidation and organolithium activation—to explore differences in etheric and carbon-carbon surface bonding. The former method installs surface hydroxyls through the Fenton reaction which then undergo a Williamson ether-like synthesis to furnish ether bonds. The latter technique furnishes C-C bonds be means of an alkyllithium to deprotonate C-H moieties on the carbon surface followed by an SN2 reaction with an electrophile.
OMC and hydroxylated OMC were reacted with haloethylamines, giving rise to surface ethylamine groups appended by C-C and C-O-C bonds, respectively. Particle stability and surface amine presence were examined before and after immersion in in pH 14 (in sodium hydroxide) and pH 0-3 (in hydrochloric acid). Particle physical characterization included nitrogen sorption, low-angle X-ray diffraction, and both scanning and transmission electron microscopy. The primary amine moiety was qualitatively identified by point-of-zero charge and quantified by a 4-nitrobenzaldehyde colorimetric assay, enabling the amine density on the OMC materials to be calculated. The aminated OMCs were proven to retain catalytic activity over multiple reaction cycles as a heterogeneous base catalyst for the Knoevenagel condensation reaction. Most importantly, the acid and base immersion results directly inform which pH environments these types of covalently modified OMC materials can, and cannot be used in. Knowledge from this dissertation’s research campaign may inspire scientists developing other types of functional carbon materials to consider their work beyond the scope of a singular application.
Associated Publications
Rights
Copyright of the original work is retained by the author.