Optimized preparation, thermal characterization and microwave absorption properties of deep eutectic solvents made by choline chloride and hydrated salts of alkali earth metals

In this manuscript, we provided insights into the preparation of Deep Eutectic Solvents (DESs) made by choline chloride and MgCl2·6H2O or CaCl2·6H2O, proposed as green solvents for the valorization of biomasses, and we performed an extensive evaluation of their thermal properties. In particular, we highlighted the use of a microwave (MW) coaxial antenna as a rapid, efficient, and eco-friendly heating probe, which can reduce the preparation time up to 40 times with respect to conventional heating without altering the final properties of the product. The thermal properties of the DESs were extensively studied by Differential Scanning Calorimetry and High-Resolution Thermogravimetry with analysis of the evolved gas by Fourier Transformed Infra-Red spectroscopy, with the aim to obtain important information on their thermal stability and thermal degradation mechanism. The experimental data also allowed us to obtain indirect evidence of the hydrogen bonding network formed in DES nanostructures. Finally, the evaluation of the samples’ capability to absorb MWs allowed us to classify them as good MW absorbers, highlighting their potential for future applications in MW-assisted processes.