Over the last decades, 2D or few-layer materials have been the subject of extensive research by chemists, physicists and material scientists. Due to their physical and chemical character (e.g. large surface area, unique electrochemical properties and unusual mechanical stability), 2D materials exhibit enormous potential for various types of applications ranging from electrode materials to bio/chemical sensors and biomedical research. Their electronic structure and reactivity can be tuned by modifying their surface (e.g. element doping) or the crystal lattice (introduction of vacancies), which allows the tuning of bandgaps and surface reactivity for catalytic applications. While there is a plethora of multi-element 2D materials (e.g. boron nitride or transition metal dichalcogenides), the number of mono-elemental 2D materials is limited, the most prominent example being graphene. However, the main disadvantage of graphene in electronics or as an electrocatalyst is its susceptibility to oxidation and the lack of a bandgap (not being a semiconductor).
This PhD project will focus on the design of innovative black phosphorus (BP) materials. BP is the most stable allotrope of phosphorus and crystallizes in a layered, puckered honeycomb structure. Theoretical studies predict that the bandgap of BP materials closely correlates with the number of layers. Therefore, few-layered black phosphorus (FLBP) exhibits enormous potential e.g. for optoelectronics and electrocatalysis. Due to its high carrier mobility, thickness-dependent direct bandgap and anisotropic physical properties, FLBP has also been considered for important applications such as sensors, batteries, photonics and transistors.
The successful candidate will gain a high level of inorganic synthetic skills (e.g. handling air-sensitive compounds, material processing, precursor synthesis). Besides the synthesis of bulk BP and exfoliation to produce FLBP, the student will work on the in-situ surface-functionalization of FLBP sheets. By modifying the surface of the BP flakes we will i) improve their stability towards oxygen and moisture, ii) create stable dispersions in aqueous and non-aqueous media iii) change their electronic properties (e.g. bandgap) and iv) create unprecedented (catalytic) surface reactivity. The lone pairs located on each P atom endow the layered BP structure with a unique (Lewis basic) reactivity and can serve as a functionalisation anchor. Electrophilic reagents can form Lewis pair donor-acceptor interactions that will bind them to the materials’ surface and introduce functional groups. Furthermore, we will reduce metal salts (e.g. Bi, Au, Ag) in-situ on the BP surface to dope it with metal nanoparticles.
To gain a fundamental understanding of the new materials’ properties, their thorough characterisation is very important. Thus, the student will be introduced to a wide range of analytical skills (e.g. XPS, XRD, SEM, TEM, AFM and Raman spectroscopy). Bandgaps will be probed using photoluminescence (PL) & NIR spectroscopy, and dispersion stability by dynamic light scattering (DLS) and Zeta potential measurements.
Finally, the student will investigate the catalytic potential of BP composites. For example, such “tuned” FLBP materials are potential catalysts for the transition-metal free photochemical or electrochemical activation of carbon dioxide to convert it into valuable chemical compounds, such as methane (CH4), formic acid (HCOOH) or methanol (H3COH). Together with a world-class collaborating group (University of Stockholm) we will develop catalytic membranes and photo-electrodes by thin-film deposition onto suitable substrates (such as zeolites or transparent glass-slides).