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Carbon – Ice Composite Materials: Water Structure and Dynamics at the Carbon Interface

Periodic Reporting for period 2 - CARBONICE (Carbon – Ice Composite Materials: Water Structure and Dynamics at the Carbon Interface)

Reporting period: 2018-12-01 to 2020-05-31

Carbon and water in its various states of matter make up a substantial proportion of our Universe. The two materials are highly dissimilar with respect to their chemical and physical properties. Elemental carbon is even often referred to as a hydrophobic, ‘water-hating’ material. Yet, the two materials often coexist and critical yet poorly understood processes take place at the interface between these unlike chemical species. This includes the hydration shells of hydrophobic moieties in biomolecules, clathrate hydrate materials where water molecules crystallise around hydrophobic guest species as well as icy comets which are often black due to the presence of carbon at their surfaces.

The aim of the CARBONICE project is to investigate the interface and interplay between water and carbon in detail. Using new and innovative experimental strategies, the water molecule will be placed in a variety of different yet highly relevant carbon environments. This will give us unprecedented insights into how water hydrates hydrophobic species which is highly important in the context of hydrophobic interactions. Investigations into how carbon species influence phase transitions of ice will give new insights into crystallisation phenomena but will also reveal the factors that lead to the formation of either ferro- or antiferroelectric ices. Creating carbon – ice composites in the lab as they exist on comets will enable us to understand the complex weather cycles on comets and may help explaining the unusual surface features recently identified by the Rosetta space probe.

In summary, this truly multidisciplinary project opens up a new spyhole to critically important processes at the water – carbon interface. The results will have an impact on the space, atmospheric and general materials sciences but will also be highly relevant with respect to further optimising the computer models of water as well as understanding the properties of water in nano-confinements and how it drives biological processes.
To pursue the aims of the CARBONICE project, we now have two fully functioning vacuum chambers available fully equipped with quartz-crystal microbalances and mass-spectrometers in order to achieve the low-temperature co-deposition of amorphous ice and carbonaceous species. In line with the objectives of the proposal, a number of major achievements have already been realised.

Mixtures of carbon species and amorphous ice prepared so far include C60 fullerene, tetraphenylmethane and adamantane. But, we have also conducted a systematic study into the desorption of gaseous species from amorphous ice including methane, argon, helium and carbon dioxide (J. Chem. Phys. 151 (2019) 134505). This crucial study highlighted the best way to deposit the amorphous ice and we used the various gas species as probes for detecting macroscopic and microscopic changes of the amorphous matrix upon heating in vacuum. The importance of baffling the flow of the water vapour was also highlighted by this study, which will be of fundamental importance for future work. Clathrate hydrate formation was observed for adamantane but not fullerene, which provides an important insight for future work. Interestingly, the active species with respect to clathrate hydrate formation seems to be the stacking-disordered ice after crystallisation and not the amorphous matrix. Both C60 and adamantane were found to influence the crystallisation of the amorphous matrix. C60, in particular, has a major impact on the crystallisation and also the glass transition of the amorphous ice. Furthermore, we could show that ‘blankets’ of C60 on top of amorphous ice alters its desorption properties. This is an important finding with respect to explaining weather cycles of comets. The C60 work is currently being written up for publication. Regarding using adamantane as a ‘nanoprobe’ for detecting structural changes within the amorphous ice including clathrate hydrate formation, we have conducted a successful neutron diffraction experiment. The data is currently analysed. As a new analytical tool for quantifying stacking disorder in ice I, we have presented a new method based on pair-distribution-function analysis which will benefit the project (J. Appl. Cryst. 51 (2018) 1211-1220).

We have also developed detailed procedures for producing a variety of carbon films for adsorption / desorption studies. One PhD student now works full time on this part of the project. In this sense, very good progress has been made with WPs 2, 3 and 4, and it is clear what the future directions for these WPs will be. The focus of WP1 is now to analyse the neutron diffraction data of adamantane / amorphous ice mixtures. The student working on WP2 has now started using tetraphenylmethane as guest species and investigates the adamantane clathrate hydrate formation in detail. Work from WP3 on hydrogen ordering phase transitions has resulted in three publications: ‘Deep glassy states’ of ice were discovered (Chem. Sci. 10 (2019) 515-523), we have presented a comprehensive benchmarking study on the effects of a wide range of acid and base dopants (J. Chem. Phys. 148 (2018) 244507) and recently published a combined neutron spectroscopy / diffraction study on deep glassy ice VI (J. Phys. Chem. Lett. 11 (2020) 1106-1111).

In addition to the carbon species, we have realised that ammonium fluoride is a highly interesting guest species as well. As part of WP3, we could show ammonium fluoride is a hydrogen-disordering agent for ice (J. Phys. Chem. C 123 (2019) 16486-16492). Beyond primary research outputs, the PI of CARBONICE has also written an invited highlight article on the discovery of a new methane clathrate hydrate (Proc. Natl. Acad. Sci. USA 116 (2019) 16164-16166), a topic closely overlapping with the aims of CARBONICE, and a general review article on the recent advances in the exploration of water’s phase diagram (J. Chem. Phys. 150 (2019) 060901).

As part of work on WP4, a new preparation procedure for graphene oxide has been published (ChemistrySelect 3 (2018) 6972-6978) and some of our carbon materials were supplied to collaborators, which resulted in a joint article on using graphene materials in light-harvesting (Nanoscale 10 (2018) 19678-19683) and medical applications (Chem. Sci. 10 (2019) 8880-8888). The environment created by WP4 has also helped a PhD student (outside CARBONICE) to fill carbon nanotubes with elemental arsenic, which resulted in the discovery of two new allotropes of this main group element (Angew. Chem. Int. Ed. 57 (2018) 11649-11653 & Inorg. Chem. 58 (2019) 15216-15224). In summary, we have made very good progress with respect to WPs 2-4, and work in the second half of the project can now aim at completing the various WPs.
The work carried out in the CARBONICE project is very much state-of-the-art. This is illustrated, for example, by the recent discovery of deep glassy states of ice. By the end of the project, we aim to obtain a full understanding of the behaviour of water at the carbon interface. This includes structural as well as dynamic aspect. Specifically, we aim to discover new inclusion compounds (ie clathrate hydrates), influence the phase transitions of ice with respect to stacking disorder and ferro-/antiferroelectricity, understand how the structures of carbon materials affect the ad- and desorption of water under conditions relevant for comets, and gain insights into how water hydrates large carbonaceous hydrophobes.