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

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 (similar to 60 degrees 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), C-13 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.

Automated summary

In order to promote the utilization of abundant biomass in various applications, greener methods for direct conversion into oxidized graphitic materials should be developed. This study presents a new sustainable method for the low-temperature and fast conversion of wheat straw into oxidized graphitic material using a deep eutectic solvent and microwave irradiation. The resulting graphitic material exhibited enhanced enzymatic activity as a nano-support for cellulase immobilization. The ease of dissolution of wheat straw in the deep eutectic solvent and its conversion to enzyme-friendly oxidized graphitic material represents an environmentally friendly and economical approach.