l -Ascorbic Acid-Enabled Integrated Hydrothermal Process for the Selective Coproduction of xylooligosaccharides, Carbon Quantum Dots, and Fermentable Sugars from Corncob

This study presents a green bifunctional l-ascorbic acid (ascorbic acid (ASA)) agent to assist hydrothermal pretreatment of corncob to address challenges in enhancing xylooligosaccharide (XOS) production and enzymatic hydrolysis performance. Under the optimized conditions (2% ASA, 150 °C, 70 min), a maximum XOS yield of 58.14% (based on xylan in raw corncob) was obtained. Enzymatic hydrolysis of the pretreated residue with only 10 FPU/g cellulase gave glucose and xylose yields of 97.32% and 89.17%, respectively. The XOS-rich hydrolysate was purified with 10% activated carbon (AC) (96.54% adsorption) and fractionated by ethanol gradient elution (94.74% recovery). Additionally, carbon quantum dots prepared from the XOS-separated spent liquor by AC adsorption from XOS hydrolysate showed bright blue fluorescence under UV, peaking at a 380 nm excitation. Therefore, this integrated strategy enables high-value utilization of corncob biomass for advanced biorefinery applications.