Sustainable preparation of oxidized graphitic material from wheat straw using a deep eutectic solvent for superactivity of cellulase

Abstract

Relatively greener methods for the direct and single-step conversion of abundantly available biomass into oxidized graphitic material should be developed for promoting the utilization of such materials in different applications. Herein, a new sustainable method for low-temperature (∼60 °C), single-step and fast (in 30 minutes) conversion of wheat straw into an oxidized graphitic material under microwave irradiation using a deep eutectic solvent (DES) comprising ZnCl₂ and lactic acid (LA) has been established. The prepared graphitic material has been regenerated from DES using water as an antisolvent and characterized for its inherent structure. The extent of oxidation of the graphitic material has been investigated using Fourier-transform infrared (FTIR), ¹³C nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) techniques. Subsequently, the graphitic material has been utilized as a nano-support for the immobilization of cellulase, which showed a 17-fold enhancement in enzymatic activity. Such an enhancement in enzymatic activity is assigned to the favourable synergistic forces of interaction between the substrate, graphitic material and cellulase. The ease of dissolution of wheat straw in DES and its conversion to the oxidized graphitic material, which acts as an enzyme-friendly host, represents an environment friendly and economical way to utilize wheat straw.