In the past decade, porous boron nitride (BN) has proven promising as a novel class of inorganic materials in the field of separations and particularly adsorption. Owing to its high surface area and thermal stability, porous BN has been researched for CO2 capture and water cleaning, for instance. However, most research remains at laboratory scale due to a lack of understanding of the formation mechanism of porous BN, which is still largely a ‘black box’ and prevents scale-up. Partial reaction pathways have been unveiled, but they omit critical steps in the formation, including the porosity development, which is key to adsorption. To unlock the potential of porous BN at a larger scale, we have investigated its formation from the perspective of both chemical formation and porosity development. We have characterised reaction intermediates obtained at different temperatures with a range of analytical and spectroscopic tools. Using these analyses, we propose a mechanism that highlights the key stages of BN formation and its porosity, including the intermediates and gaseous species formed in the process. We identified that the formation of non-porous carbon nitride is crucial to form porous BN with release of porogens, such as HCN and CO2. This work paves the way for scaled-up processes to use porous BN to its full potential at industrial level for gas and liquid separations.
Supporting Information _Formation Mechanism and Porosity Development in Porous Boron Nitride
Additional chemical aspects of the reaction precursors (boric acid, melamine and urea) and carbon nitride. Comparison of porous BN obtained with and without final dwell time at 1050 °C. Additional 11B solid-state NMR spectra and associated Density Functional Theory (DFT) calculations. 13C solid-state NMR spectra from some intermediates and carbon nitride. Additional O-K edge NEXAFS results. FTIR and TG-MS results highlighting the roles of melamine and urea as N-precursors in the synthesis of porous BN.