Mixing nitrogen-containing compounds for synthesis of porous boron nitride for improved porosity, surface functionality, and solid base catalytic activity

Porous boron nitride was synthesized using boric acid with urea and/or hexamethylenetetramine (HMTA) via pyrolysis method. X-ray diffraction and Fourier transform infrared measurements indicated that the synthesized boron nitride has a turbostratic structure with both amino and hydroxyl group on the surface. The synthesis using a mixture of two nitrogen-containing precursors was found to not only significantly increase the porosity, but also improve the surface functionality. X-ray photoelectron spectroscopy and B K-edge and O K-edge X-ray absorption fine structure measurements revealed that the proportion of amino and hydroxyl groups on the surface increased with increasing concentration of HMTA during synthesis. Solid-state ¹¹B nuclear magnetic resonance spectroscopy indicated that all samples contained trigonal B-N, trigonal B-O and tetrahedral B-O sites, and that samples prepared with high concentrations of HMTA had less tetrahedral B-O sites, suppressing the formation of BOx species as byproducts. Solid base catalytic activity was evaluated through Knoevenagel condensation, and the catalytic performance was significantly improved by synthesizing boron nitride catalyst using a mixture of the two nitrogen-containing precursors. The enhancement of the activity was influenced by the development of the pore structure as well as the emergence of functional groups on the surface.