O/C Ratio‐Driven Fluorescence Enhancement in Cellulose‐Derived Carbon Quantum Dots: Mechanistic Insights into Reaction Pathways

Abstract By regulating cellulose molecular weight through enzymatic hydrolysis to obtain different carbon precursors, three types of carbon quantum dots (CQDs) are synthesized via hydrothermal methods: cellulose enzyme‐hydrolyzed solids‐based carbon quantum dots (CES‐CQDs), cellulose enzyme‐hydrolyzed mixtures‐based carbon quantum dots (CEM‐CQDs), and cellulose hydrothermal degradation products‐based carbon quantum dots (CHD‐CQDs). By controlling the molecular weight of the cellulose precursor, the O/C ratio of the CQDs is systematically modulated from 0.25 to 0.61, resulting in a more than five‐fold increase in fluorescence intensity and an approximately seven‐fold improvement in quantum yield (QY). Density functional theory (DFT) calculations indicate that high O/C ratio enhances oscillator strength, thereby boosting fluorescence. Through a combination of experimental and density functional theory analyses, the formation mechanisms of cellulose‐derived CQDs are revealed to involve: primarily the auto‐etherification of 5‐hydroxymethylfurfural (5‐HMF), concurrently accompanied by esterification reactions between 5‐HMF and formic acid (FA), as well as aldol condensation reactions between 5‐HMF and levulinic acid (LA). This study elucidates the fundamental relationship between the molecular structure of cellulose precursors and the fluorescence properties of CQDs, providing a universal strategy for rationally designing high‐performance luminescent nanomaterials from renewable biomass.