(101a) Enhancing the Hydrolytic Stability of Porous Boron Nitride for Use in Industrial Molecular Separations

Industrial separation processes account for 10-15% of the global energy consumption¹. The energy cost of large-scale gas and liquid separation processes like distillation could be significantly reduced by moving towards adsorption processes. An example of an inorganic adsorbent is porous boron nitride (BN): this material exhibits high surface area and porosity, and benefits from greater oxidative and thermal stability than carbonaceous adsorbents². In this work, we are exploring the potential of porous BN as an efficient and moisture-resistant adsorbent for molecular separations at industrial scale.

Recently, our group developed a new method to produce porous BN with enhanced surface area, tuneable porosity³ and promising liquid and gas separations performance. To further advance the use of porous BN, we must investigate its moisture stability, which appears limited based on preliminary work⁴. Considering this aspect, we developed two functionalisation routes to modify the surface of porous BN and enhance its hydrophobicity and resistance to moisture. The first route involves direct silylation of porous BN powder followed by pelletisation, whereas the second route uses chemical vapour deposition on porous BN pellets. A range of spectroscopic and analytical tools was used to characterise samples, including FTIR, XRD, XPS, TGA, SEM-EDX and N₂ sorption. To monitor the changes in hydrophobicity, we submitted samples to different levels of humidity, relevant to storage and sorption testing conditions. After this, we used N₂ sorption to probe the impact on surface area and porosity, as well as FTIR and XRD to check any changes in chemistry. Our results point to the efficiency of the approach to produce moisture-resistant BN-based adsorbents.

In parallel, we investigated the formation mechanism of porous BN via the analytical and spectroscopic characterisation of intermediates synthesised at different temperatures. In particular, solid-state NMR and Synchrotron-based X-ray absorption spectroscopy were used. The results of this study not only provide insight on how to tune the porosity of the material, but also on how to improve the hydrolytic stability discussed above. Therefore, this research paves the way for scaling up the synthesis of porous BN towards industrial applications.

References

1. Sholl, D. S.; Lively, R. P., Seven chemical separations to change the world. Nature 2016, 532 (7600), 435-437.

2. Jiang, X.-F.; Weng, Q.; Wang, X.-B.; Li, X.; Zhang, J.; Golberg, D.; Bando, Y., Recent Progress on Fabrications and Applications of Boron Nitride Nanomaterials: A Review. Journal of Materials Science & Technology 2015, 31 (6), 589-598.

3. Marchesini, S.; McGilvery, C. M.; Bailey, J.; Petit, C., Template-Free Synthesis of Highly Porous Boron Nitride: Insights into Pore Network Design and Impact on Gas Sorption. ACS Nano 2017, 11 (10), 10003-10011.

4. Shankar, R.; Marchesini, S.; Petit, C., Enhanced Hydrolytic Stability of Porous Boron Nitride via the Control of Crystallinity, Porosity, and Chemical Composition. The Journal of Physical Chemistry C 2019, 123 (7), 4282-4290.