Ultrasound-Combined Pre-Hydrolysis Preparation of Soybean Hull Nanocellulose and Its Characterization

• Soybean hull waste valorization: A sustainable route to high-value nanocellulose (NCs). • Different acids enable controllable preparation of NCs with tailored properties. • NCs feature spherical morphology, crystallinity exceeding 50%, and small particle size. • The prepared NCs exhibit enhanced thermal stability, favoring practical applications. • NCs serve as a promising bio-based nanomaterial with broad application potential. Transforming agricultural waste into nanocellulose offers a sustainable approach to mitigate environmental pollution and enhance the economic value of biowaste. Nanocellulose was isolated from soybean seed coat waste—remaining after ammonium oxalate microwave extraction of polysaccharides—by employing a combined method of acid pretreatment (sulfuric, hydrochloric, and citric acids) and ultrasonic dispersion. This approach provides an innovative strategy for the valorization of agricultural waste. The prepared NC were systematically characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), coupled with water-holding capacity (WHC), emulsification properties, and static water contact angle (WCA). FTIR results confirmed the effective removal of lignin and hemicellulose impurities, along with enhanced hydroxyl accessibility and strengthened hydrogen bonding interactions. SEM and AFM analyses revealed that all NC samples exhibited spherical morphology with diameters