Abstract: Carbon quantum dots (CQD) were employed as dopants to enhance the photocatalytic efficiency of Nb₂ O₅ by decreasing the bandgap energy and prolonging the lifetime of the photogenerated exciton by in-creasing conductivity. X-ray diffraction (XRD), N₂ porosimetry, scanning electron microscopy (SEM), elec-trochemical impedance spectroscopy (EIS), photoacoustic spectroscopy (PAS), X-ray photoelectron spec-troscopy (XPS), Dynamic Light Scattering (DLS), zeta potential, and atomic force microscopy (AFM) were used to characterize the synthesized nanostructures. The residues from acerola processing were converted into CQD with an average size of 2.56 nm, as confirmed by AFM and the high fluorescence quantum yield of 43.32 %. N₂ physisorption results showed that the CQD were deposited on the surface of Nb₂ O₅, re-ducing the specific surface area (SBET) from 122 ±2.0 to 29 ±1.3 m^²g^-1. The photocatalytic performance of CQD/Nb₂ O₅ was superior to that of the control materials under UV-vis light irradiation, as there was a decrease in the bandgap energy (Eg) from 2.78 to 1.93 eV. This decrease in Eg led to a significant increase in the apparent rate constant (kapp) of the MG dye from 1.90 ×10^-3 s^-1 to 42.2 ×10^-3 s^-1, demonstrating that the presence of CQD can effectively separate the photogenerated charge carriers, as it was observed from the increase in conductivity showed by Nyquist diagram.

Key words: Acerola bagasse, Malachite green, Carbon dots, Photocatalyst, Chemical kinetics