Functionalization of Black Phosphorus with Inorganic Reagents

Since its first reported exfoliation in 2014, the interest in black phosphorus has grown dramatically. The direct band gap, the high carrier mobility and the large specific surface area of BP open up great opportunities in different topical sectors of physics and chemistry including catalysis. As each phosphorus atom in BP has an sp3 hybridization and is bearing a lone-pair, an effective approach to surface modification could encompass the coordination of transition metal fragments. In this thesis, the functionalization of exfoliated black phosphorus (2D BP) with different palladium precursors is presented. In particular, a new nanohybrid was obtained growing Pd NPs in situ on 2D BP. The new material, named Pd/BP, was characterized by means of different spectroscopic techniques and electron microscopy measurements. The existence of Pd‒P bonds of 2.26(3) Å between peripheral Pd atoms of the nanoparticles and BP flakes was revealed via EXAFS measurements, highlighting the ability of 2D BP to act as an effective ligand toward the surface of metal NPs. The nanohybrid Pd/BP was used successfully as heterogeneous catalyst in the liquid phase hydrogenation of chloronitrobenzene to chloroaniline, resulting extremely selective in the process. Remarkably, comparative studies carried out with Pd NPs supported on carbon as reference material, revealed that the use of BP as support is crucial to reach higher selectivity. Following a distinct approach, the functionalization of 2D BP was accomplished by addition of the organometallic precursor [Pd(C3H5)Cl]2 to 2D BP. In-depth solid state characterization carried out by means of powder XRD and solid state 31P CP-MAS NMR allowed to unravel the nature of the new material. HAADF-STEM microscopy performed at atomic level was exploited to probe the morphology of the flakes, revealing the existence of a uniform distribution of the metal within 2D BP, with no formation of metal aggregates, such as Pd NPs. EXAFS measurements, together with DFT simulations, revealed the existence of unprecedented interlayer Pd‒Pd dimers, bridging two BP layers. Consistently with morphological and structural analysis, testing the material (named Pd2/BP) in the benchmark hydrogenation of C=C and C≡C bonds, the metal sites resulted inaccessible to organic substrates. Conversely, preliminary studies on the application of Pd2/BP in the hydrogen evolution reaction (HER) from acidic medium, pointed out a strong enhancement in electrocatalytic activity compared to pristine 2D BP.