Development and chemical tuning of novel 2D ultrathin polydopamine membranes

In 2007, a new synthetic melanin, polydopamine (PDA), was first reported in the scientific literature, triggering a period of intensive research into its structure and properties. Over the last decade, this biomimetic polymer has attracted considerable interest, mainly due to its interesting adhesive, optical, electrical and photocatalytic properties. In the field of materials engineering, attempts have been made to use PDA, for example, for antibacterial protection, construction of biosensors, drug carriers and water purification. The ability of polydopamine-based heterostructures to efficiently photocatalytically degrade water has also recently been demonstrated. This discovery was made by a team of scientists from the Centre for NanoBioMedicine (CNBM) in collaboration with national and international partners. In the heterojunction thus constructed, polydopamine was deposited from solution directly onto the semiconductor surface. During the polymerisation process, suspended nanoparticles and aggregates (clusters) of PDA are also formed in solution, but a relatively new and unexplored area is the ability of polydopamine to form thin films at the liquid/gas (solution/air) interface under appropriate synthesis conditions, i.e. slow solution stirring and constant but low gas exchange. According to recent literature reports, such membranes can be 50 to 200 nm thick (5-20 x 10-5 mm) and have different properties compared to polydopamine formed in solution under the influence of oxygen dissolved in water. Importantly, they may have completely different applications to polydopamine thin films deposited directly on substrates, due to the different structure and physicochemical properties of PDA, the nature of the bond formed with the substrate, and possible other as yet undiscovered advantages. Recently, a paper was published by CNBM researchers showing for the first time that such membranes can have a 2D or near 2D structure. This is a groundbreaking discovery and opens up completely new and fascinating possibilities in the field of nanocomposites. The project is therefore aimed at the materials engineering and chemistry communities, and it is planned to use international scientific conferences and high-impact scientific journals as a means of communication. The aim of this project is to optimise the process for obtaining the membranes described above (towards improved homogeneity and reduced thickness), using very low concentrations of reactants, and to chemically modify them using suitable oxidation mixtures based on transition metal salts and hydrogen peroxide. Each of these steps will be followed by a series of in-depth structural and nanostructural studies. The use of very low concentrations of reactants is expected to increase the efficiency of the process and thus meet the objectives of green chemistry. In order to optimise the membrane production process, it is also planned to improve the so-called scooping method, i.e. the application of membranes directly from solution onto a pre-prepared substrate. To do this, a completely new process is planned, namely the formation of an intermediate layer between the solution in which polymerisation takes place and the membrane on its surface. The project will use advanced materials testing techniques such as grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), Raman spectroscopy, visible reflectance spectroscopy, near and mid-infrared spectroscopy and X-ray photoelectron spectrometry (XPS). This will help to understand the formation of membranes at the liquid/gas interface, the influence of oxidative mixtures on process yields, the structure and properties of the resulting membranes, and to extend knowledge of the chemical structure of polydopamine, which is still not fully described.