Sustainable and industrially scalable ultrasonic liquid phase exfoliation technologies for manufacturing 2D advanced functional materials (EcoUltra2D)

Ultrasonic cavitation and streaming are widely used in the chemical, food, oil, drag and paint processing industries. The generation of cavitation bubbles though ultrasound (US) is a powerful technique that induces physico-mechanical and physico-chemical effects in multiphase systems contained in liquid media. When imploding, cavitation bubbles produce high-speed liquid jets (300-1000 m/s) accompanied by high pressure (100-1000 MPa) and local temperature spikes (up to 10000 K). Pulsating bubbles impose high-frequency pressure pulses of several MPa in magnitude. These basic phenomena are involved in specific and in many cases poorly understood mechanisms that are used as a working tool, for instance, for manufacturing two-dimensional (2D) nanomaterials, and exploited for various other applications in industry.

Two-dimensional (2D) nanomaterials, such as graphene, MoS2, WS2, h-BN, h-BCN, and other layered materials are being heralded as unique materials that may help overcome current and future societal challenges related to energy generation, thermal management, and storage and in the healthcare sectors. Despite intense research, the successful exploitation and integration of 2D materials in next generation technologies where faster, thinner, and stronger devices are needed is still hampered by the issues associated with the scalability, reproducibility, and sustainability of current manufacturing techniques, aimed at generating uniform and high-quality 2D materials. For example, most current production processes of 2D materials are limited to batch-processing and require large quantities of harmful solvents and surfactants for the shearing or ultrasonication to work, bearing the risk of causing much harm to the environment, whilst the resulting structures are often limited in size and to few layer 2D materials with monolayers only at the edges of the exfoliated structures.

Here, we propose to overturn the current exfoliation technological paradigm by giving the ultrasound-induced mechanisms the leading role in the exfoliation of layered materials. The scientific novelty lies in establishing the precise mechanisms of ultrasonic exfoliation through advanced and bespoke in situ synchrotron X-ray ultrahigh speed imaging techniques (up to million frames per second), small-angle neutron scattering, precise acoustic measurements, advanced ex situ characterisation, and multi-scale modelling methods. The technological step-change advance lies in developing a scalable and environmentally friendly process with focus on using water as the liquid medium (minimising the amount of special, expensive, and harmful additives), and reducing the processing time from tens of hours to minutes whilst increasing yield and size of the 2D sheets.

The processing part of the project will concentrate on the development of an innovative reactor, controlled ultrasonication, optimisation of processing parameters, and the selection of suitable eco-friendly additives in order to achieve the most efficient exfoliation and dispersion in terms of the lateral size, shape, quality, flake thickness, and yield of the nanosheets. The properties of these 2D functional materials will be tested and benchmarked against commercially available 2D materials and employed in batteries and thermal management applications.

This project is driven by the technological need to expand the use and increase the efficiency of ultrasonic processing (USP) in nanomaterials manufacturing, and more specifically in the production of 2D materials that may play a pivotal role in the 21st Century manufacturing. The lack of fundamental knowledge of the underlying mechanisms hinders currently the up-scaling of sono-processing approaches. In this research we will pioneer the use of environment friendly engineering approaches to large-scale nanomaterials manufacturing and, by providing new tools and approaches, our proposed research will contribute to the wider nanoscience research and ultrasound processing communities as well as to industries that use ultrasound processing techniques.

Functional materials in particular have been highlighted by EPSRC as one of its priority areas. The UK has been an international leader in this field. With past EPSRC support and support of the European Commission and the European Research Council the applicants have already established a leading track record in carbon and non-carbon nanomaterials as well as in ultrasonic technologies and advanced characterisation.

We can now address the next challenge: to demonstrate exquisite control during large-scale processing of nanostructures. We expect that our proposed research will lead to a new generation of functional materials that will find their way in applications including batteries, touch-screen displays, and molecular transistors to mention but a few. This work will be of interest to a wide range of companies in the UK and worldwide (such as Designer Carbon Materials Ltd, Tata Steel (Graphene Technology), who will be partners in the project) and may also lead to new start-ups.

The technological step-change advance of this research is in developing a scalable and environment friendly process with the focus on eliminated or minimising the amount of specialised, expensive and harmful additions, and minimising the processing time with simultaneous increase in the yield and size of 2D sheets; opening novel avenues towards 2D materials exploitation.

To maintain UK's competitiveness in industry and academia, the training needs are high and with this project we are addressing this challenge through the training of the post-doctoral researchers employed by this project. Moreover, three PhD students funded through EPSRC DTA studentships at Oxford and by Oxford Brookes will be educated within the PhD studies on "The chemical functionalisation of nanomaterials" and "On the fundamental mechanisms of ultrasonic assisted liquid phase exfoliation of two dimensional nanomaterials", respectively; experiencing also direct exposure to procedures employed to bridge research and development work.
The success of the project will allow us to engage industrial companies in further, more applied research and in implementation of the results through different funding schemes. The results can be directly used by R&D centres and industry for the up-scaling of pilot results on processing of 2D nanomaterials to the industrial production of functional, electronic materials, chemically-active materials, sensing and bio-active materials, composites; and the models and fundamental knowledge developed will be used to advance and optimise new sono-technologies.

All participating investigators have experience in research programmes funded by the EPSRC, the EU, and UK and overseas industry concerning novel technologies and nanomaterials. Through those links as well as high-ranking publications and conferences, the outcomes of the project will reach the main academic and industrial beneficiaries.