Plant extract-based liquid phase exfoliation enables one-step green production of two-dimensional heterostructure nanohybrids capable of dramatic improvement in polymer properties

Abstract

Synthesis of nanoscale materials is urgent with an increasing demand due to their valuable applications in various industries including medicine and aerospace. To advance green and sustainable nanomaterial synthesis, this study employed liquid-phase exfoliation techniques using bath sonication with gallnut and coffee waste as plant extracts to develop two-dimensional (2D) nanomaterials: functionalized few-layer graphene (FFG), h-boron nitride nanosheets (BNNs), functionalized few-layer borophene (FFB), and MXenes, from graphite, h-boron nitride, boron, and HF-etched Ti₃AlC₂, respectively, as well as their hybrids BNN/FFG, BNN/FFB, FFG/MXene, BNN/MXene, FFG/FFB, and FFB/MXene. When incorporated at 1 wt%, these nanomaterials and nanohybrids significantly improved both the mechanical properties and thermal stability of polyvinyl alcohol (PVA) and chitosan films. Specifically, the resulting hybrid nanocomposite films outperformed pure PVA in terms of tensile strength (35.1 ± 0.6 MPa) and Young's modulus (862.4 ± 42.4 MPa) with a 3.25- and 6.5-fold increase, respectively. In addition, the reinforcement of nanomaterials into the films increased the initial decomposition temperatures up to 50%. Furthermore, utilizing the graphene production process, we performed a life cycle assessment of this technology focusing on three impact categories: energy use, biogenicity, and land transformation. Commercial exfoliating solvents are much more costly than our plant extracts, according to an economic analysis of the costs related to the use of plant and coffee waste extracts in comparison to other exfoliating solvents. To date, this is the first study to successfully synthesize FFB, MXenes, and their hybrids with FFG and BNN using gallnut or coffee extract-mediated liquid phase exfoliation. The established method of nanohybrid preparation provides a simple, energy-efficient, and environmentally friendly approach that can be adapted for the design and synthesis of a wide range of functional hybrid nanomaterials with diverse applications.