Sub-Nano Confined Matter at High Pressures

I will talk about a very intriguing research field, joining high pressure science of simple molecular sys-tems to the amazing world of zeolites. I will first present a review on several novel compounds obtained by react-ing dense simple carbon bearing molecular systems at GPa or tens of GPa, strongly confined in the sub-nanopores of two non-catalytic, pure SiO2 zeolites: silicalite-1 and ZSM-22. The purely pressure induced reaction products are: a disordered silicon carbonate [1], and polymer/zeolite sub-nanocomposites such as poly-ethylene/zeolite [2], poly-acetylene/zeolite [3,4], and polyCO/zeolite [4,5]. These composites, which are 1D systems in the case of ZSM-22 as the confining host system, have remarkable interest for fundamental phys-ics and chemistry, and also for potential applications in mechanics, electronics, photonics and energy storage. On a more physical ground, confining dense simple systems at high pressures, at the Angstrom scale, pro-duced novel and exotic sub-nanophases of these sys-tems. Indeed, I will present results on a recently ob-tained dense and highly disordered form of molecular nitrogen, sub-nanoconfined in silicalite-1 under pres-sure, up to 50 GPa [6]. In this form, N2-N2 interactions and, consequently, distances are found to be very close to those of bulk N2 at the same pressures. This result provides a rationale for the polymerization of the simple C-bearing molecules occurring in the channels of the non-catalytic zeolites under pressure, where the pressure threshold was found to be very similar to that observed in bulk samples. We also predict the formation of strongly confined pol-ymeric, non-molecular nitrogen forms in zeolites above 1 Mbar. Finally, I will present results on a freshly dis-covered sub-nano phase of dense O2, confined in ZSM-22 above 10 GPa [7]. This exotic phase is made of 1D stacked clusters, dimers or tetramers, of O2 molecules driven by the 1D host channels of the ZSM-22 zeolite, and it occurs in the same pressure range where, in bulk solid oxygen, the O8 tetramer was observed several years ago [8,9]. Investigations were performed using diamond anvil cells, optical spectroscopy, and X-ray diffraction. References: [1] M. Santoro, et al., Proc. Natl. Acad. Sci. U. S. A. 108, 7689 (2011). [2] M. Santoro, et al., Nature Communications 4, 1557 (2013). [3] D. Scelta, et al., Chem. Mater. 26, 2249-2255 (2014). [4] M. Santoro, et al., Chem. Mater. 28, (2016). [5] M. Santoro, et al., Chem. Mater. 27, 6486 (2015). [6] M. Santoro, et al., J. Phys. Chem. Lett. 8, 2406 (2017). [7] M. Santoro, et al., in preparation. [8] Lundegaard et al., Nature 443, 201 (2006). [9] Fujihisa et al., Phys. Rev. Lett. 97, 085503 (2006).