Characterization of ultrasonic-treated corn crop biomass using imaging, spectral and thermal techniques: a review

The corn crop biomass (CB) is widely used as a feedstock for biochemicals such as lactic acid, succinic acid, citric acid, xanthan gum, and biofuels likely bioethanol, butanol, and biogas. Since CB provides a resistive structure for enzymatic and microbial attack, ultrasonic treatment can assist to break the recalcitrance structure. Several techniques such as imaging (atomic force microscopy—AFM; scanning electron microscopy—SEM), spectroscopy (energy-dispersive X-ray spectroscopy—EDX; Fourier transform infrared spectroscopy—FTIR; Raman spectroscopy; X-ray diffraction—XRD), and thermal (TGA) were studied to characterize the ultrasonicated CB. A detailed analysis of different techniques on their potential benefits will assist the researchers to select a suitable technique to optimize the ultrasonication for various applications. The basic mechanisms behind ultrasonication, benefits, downsides, practical considerations, and factors that should be deliberated in the future studies are discussed. Sonication enhanced the hemicellulose and cellulose yield, saccharification rate, and delignification of CB. AFM, EDX, FTIR, Raman spectroscopy, SEM, TGA, and XRD described the variations in topographical features, elemental composition, molecular structure, microstructure, thermal steadiness, and degree of crystallinity, respectively, of the ultrasonicated CB. The quantitative crystallinity of CB can be analyzed through XRD and Raman spectroscopy, whereas the qualitative crystallinity and molecular structural comparisons are studied using FTIR. Imaging techniques can provide important aspects such as lignin relocalization and cell wall delamination. Integrating EDX with SEM is beneficial to determine the elemental percentage composition altered in CB due to ultrasonication.