Electron beam-assisted exfoliation of boron nitride and covalent functionalization

Abstract

A facile, scalable exfoliation technique is still required for further modification to cater to any potential application for two-dimensional boron nitride. This paper discusses the radiation-assisted exfoliation of hexagonal boron nitride (h-BN) using electron beam irradiation and followed by functionalization with phosphoric acid 2-hydroxyethyl methacrylate ester (PA) to facilitate targeted applications. h-BN is dispersed in NaOH solution and subjected to mild sonication to facilitate ion intercalation between the layers. The sonicated h-BN solution was exposed to electron beam irradiation for BNNS exfoliation. The degree of exfoliation was measured in terms of d-spacing derived from XRD using Bragg's law. The effect of irradiation dose, energy, NaOH concentration, and mass of h-BN, on exfoliation degree was investigated. XRD analysis was used to compute the d-spacing, crystallinity, and crystal size of h-BN after irradiation. The d-spacing attained for pristine h- BN was 0.334 nm, however it increases to 0.337 nm upon irradiation at 100 kGy doses, 3 MeV of energy, and 0.1 g of h-BN in 80 mL of 30 % NaOH solution. The occurrence of radiation-assisted exfoliation and its mechanism were supported by FTIR, TGA, Raman, FESEM, XPS, AFM, and TEM analyses. The exfoliated BN was functionalized with PA. The degree of functionalization was measured by phosphoric density (mmol/g) via the acid-base titration method. The effect of PA concentration, reaction temperature and mass on phosphoric density was also investigated. The highest phosphoric density attained was approximately 13.32 mmol/g at 10 % PA, 0.1 g of exfoliated BN, 80 °C, and 5 h. The incorporation of PA onto exfoliated BN was further confirmed by XRD, FTIR, TGA, Raman, FESEM-EDX, and XPS analyses. Conclusively, this study reveals a facile dual-step exfoliation and functionalization technique of h-BN nanosheet through radiation assisted exfoliation technique.