Eco-friendly exfoliation of bismuth oxide nanoplatelets with non-layered crystal structures for functional elastomer nanocomposites

Two-dimensional (2D) metal oxide nanoplatelets with high aspect ratio and unique physicochemical features hold great potential for diverse functional applications. However, two challenges remain: (i) preparation of nanoplatelets from non-layered oxides needs improvement as it mostly involves organic solvents; and (ii) stacking and aggregation can be severe during polymer processing, e.g. melt-compounding. Bi₂O₃ herein was investigated as a representative model. 2D Bi₂O₃ nanoplatelets (BONs) with a lateral size of 0.74 ± 0.37 μm and a thickness of 15.46 ± 8.30 nm were successfully produced in deionized water through liquid-phase mechanical exfoliation. XRD showed anisotropic crystallite size reduction. For example, the size reduction of 13.37 nm along (120) plane was substantially greater than the other major planes. BON paste was added by melt compounding to prepare elastomer nanocomposites. BONs with a relatively uniform dispersion improved the mechanical properties. Simulations revealed that BONs could redistribute local stress fields effectively, leading to an enhancement in the overall tensile response. Through tensile-fractured surface analysis, the enhancement is due to (i) the well dispersed BONs (interparticle distance reduced from 24.96 ± 10.32 μm to 9.00 ± 2.94 μm), (ii) their 2D structural advantage and (iii) improved interfacial interaction. The nanocomposite at 3.3 vol% BONs exhibited a shielding efficiency of 68.01% against 80 kVp X-rays, a linear attenuation coefficient (μ) of 3.83 cm⁻¹, a mass attenuation coefficient (μₘ) of 3.14 cm² g⁻¹ and a half-value layer (HVL) of 0.18 cm. This work establishes a sustainable route for producing metal oxide nanoplatelets and functional elastomer nanocomposites.