Simultaneous carbonization and sulfonation of microcrystalline cellulose to obtain solid acid catalyst and carbon quantum dots

Lignocellulosic materials have been successfully used in the production of solid acid catalysts (SACs), generally prepared in two steps: Biomass thermal or hydrothermal carbonization followed by sulfonation. The process' supernatant is usually discarded; however, this liquid fraction may contain potentially important substances. In this work, the production of SACs was carried out by simultaneous carbonization/sulfonation of Microcrystalline Cellulose (MCC) by direct reaction with concentrated sulfuric acid. The obtained catalyst have excellent characteristics, with an ionic exchange capacity of 1.3 mmol g−1. The SAC's catalytic activity was evaluated in oleic acid esterification with methanol in a molar ratio of 1:20, yielding up to 80 % conversion in 6 h of reaction at 65 °C. The supernatant showed the presence of carbon dots (CD) characterized by solution UV/Vis spectra pattern and Fluorimetry assays. Thus, the presented process allows obtaining SACs and CDs that can act as catalysts in a series of physicochemical processes.