Unleashing the potential of Boratrane and Silatrane: A game-changing approach for enhanced boron- and silicon- incorporation in phenol-formaldehyde resins and their thermal stability

Abstract

In this study, we present an innovative and cost-effective method for the preparation of phenolic resin (PR) containing boron and silicon (BPR and BSiPR) using boratrane and silatrane. Through a one-pot synthesis via a sol-gel process, 3BPR and 3B5SiPR are successfully synthesized, utilizing boratrane and silatrane as the sources of boron and silicon. Our results demonstrate the effective introduction of boron and silicon elements into the PR matrix through the formation of BO4 (borate) and SiO4 (silicate) structures, as evidenced by Cph-O-B and B-O-Si linkages. Notably, the utilization of boratrane in the synthesis of 3BPR leads to the formation of a uniform structure of BO4, as confirmed by 11B-NMR analysis. Furthermore, the resulting resins exhibit an improved char yield of 72 % at 900 °C. The formation of borate and silicate species effectively reduces the content of phenolic hydroxyl groups, thus contributing to a decrease in weight loss during the carbonization process. Additionally, the migration of boron and silicon into the carbon structure promotes the formation of B4C and B8C crystal structures, resulting in the carbonization of resins and the formation of a graphene-like structure, as confirmed by Raman spectroscopy, which exhibits a broad 2D-band. The obtained carbon materials possess both Lewis acid and basic sites. The presence of Lewis acid sites was characterized through pyridine-adsorbed FTIR, while the Lewis basic sites and CO2 absorption were examined via TPD-CO2 analysis. The CO2 absorption capacities of 3BPR and 3B5SiPR were found to be 0.475 and 0.518 mmol/g, respectively.