Single‐Feedstock Valorization of Rice Husk Into Cellulose Nanocrystal/Lysine‐Doped Carbon Dot Hybrid Nanocarriers for pH‐Responsive Tetracycline Delivery

Sustainable conversion of agricultural residues into functional nanomaterials offers new opportunities for biomass valorization and advanced biomedical applications. Herein, we report a single‐feedstock strategy for converting rice husk into cellulose nanocrystals (CNCs) and lysine‐doped carbon dots (L‐CDs), followed by their integration into a hybrid nanocarrier system. CNCs were obtained through alkali bleaching and sulfuric acid hydrolysis, while L‐CDs were synthesized via hydrothermal carbonization with in situ lysine doping. The resulting CNC/L‐CD hybrid exhibited excitation‐dependent photoluminescence, enhanced thermal stability, altered surface charge, and an increased optical bandgap (4.91 eV). Spectroscopic and surface analyses confirmed successful hybrid formation through electrostatic and hydrogen bonding interactions. To evaluate drug delivery performance, the CNC/L‐CD hybrid was incorporated into sodium alginate (SA) beads for tetracycline loading and release studies. SA‐CNC beads showed the highest tetracycline loading capacity (7.56 mg g ⁻¹ ), whereas SA‐CNC/L‐CD beads exhibited enhanced pH‐responsive release behavior under physiologically relevant conditions. The released tetracycline retained antibacterial activity against Escherichia coli , Staphylococcus aureus , and Salmonella typhimurium . Control experiments confirmed that unloaded carrier materials exhibited no intrinsic antibacterial activity. These findings demonstrate the potential of rice husk‐derived CNC/L‐CD hybrids as sustainable nanocarriers for pH‐responsive tetracycline delivery and highlight a practical route for transforming agricultural waste into value‐added biomedical materials.