Biomass-Derived Boron-Doped Carbon Quantum Dots with Tunable Electronic Structure and Enhanced Bioactivity: A Combined Experimental and DFT Study

Boron-doped carbon quantum dots (B-CQDs) have been synthesized via a sustainable hydrothermal method using banana peel biomass and boric acid as precursors. Uniform spherical dots with an average size of 2 nm after doping have been revealed through an electron microscope. Optical studies showed a red shift in absorption and photoluminescence peaks. Tauc’s plot revealed band gap reduction from 2.73 eV (CQDs) to 2.33 eV (B-CQDs) after boron incorporation due to the modification in the electronic structure. The doped CQDs exhibit enhanced electrochemical capacitance (78 F g –1 at 0.5 A g –1 ) and improved antibacterial efficiency against Escherichia coli with MIC values of 3.0 mg mL –1 . They also maintained excellent cytocompatibility, with over 90% cell viability in the 3T3-L1 fibroblast cell line. DFT simulations supported the experimental findings by revealing that asymmetric boron doping introduces defect states near the Fermi level, thereby reducing the HOMO–LUMO gap. Both experimental and theoretical analysis indicate that boron incorporation alters the electronic configuration. The synergy between green hydrothermal synthesis and electronic modification highlights B-CQDs as eco-friendly nanomaterials for bioelectronic and antimicrobial applications.