Into the unknown: Exploring the surface chemistry of black phosphorus

Abstract

Black phosphorus (bP), a layered 2D allotrope of elemental phosphorus, is a promising material for electronic and catalytic applications, among others, due to its direct, tunable bandgap, high carrier mobility, and relatively reactive basal plane. Although reactivity, likely originating from the surface lone pairs, occurs adventitiously, our understanding of bP chemistry remains limited. Facile methods to functionalize the surface and probe the resulting modified nanosheets are scarce: previous reports of bP functionalization suffer from oxidative degradation of exfoliated nanosheets, low signal-to-noise ratios, and minimal changes in characteristic bP features post-functionalization. When functionalization is reported, further investigation into the stoichiometric chemistry of the modified nanosheets is rare, limiting rational application of bP materials. This work dives into the intersection of molecular phosphine chemistry and materials design to investigate the fundamental chemistry of bP through covalent functionalization and to apply these principles to fabricate a bP-supported hydroformylation catalyst. In Chapter 2, clear covalent bonds between nitrene functional groups and the bP surface are demonstrated via infrared spectroscopy and 15N isotopic labeling. In Chapter 3, the ligand character of bP (Tolman electronic parameter, buried volume) in an organometallic complex is investigated using discrete metal carbonyl functional groups. Finally, strategies developed herein are applied in Chapter 4 to synthesize and study the reactivity of a novel bP-supported hydroformylation catalyst. The body of work presented herein establishes a detailed understanding of bP surface chemistry and demonstrates its applications as a novel and chemically interesting support.