Organic waste from orange peels was synthesized into carbon nanodots (CDs) using a microwaveassisted method to serve as photocatalysts for purifying industrial liquid waste. The CDs were
characterized using photoluminescence (PL), ultraviolet-visible (UV-Vis) spectroscopy, Fouriertransform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and time-resolved
photoluminescence (TRPL). The characterization results revealed that the CDs exhibit fluorescence at
a wavelength of 509 nm with a lifetime of 56 ns. Additionally, three absorption peaks were observed:
one at 230 nm, attributed to C=C bonds in the core state, and two at 276 nm and 320 nm, associated
with C-N and C-O bonds in the surface state. The photocatalyst solution was synthesized by combining
CDs with TiO2 to enhance pollutant absorption. This photocatalyst was applied to the degradation of
methylene blue in liquid waste. Significant degradation of the methylene blue dye was observed over
varying exposure times (0, 6, 12, 18, and 24 hours) under direct sunlight. UV-Vis analysis revealed a
wavelength shift, a decrease in the energy gap, and an increase in particle size, attributed to quantum
effects. Furthermore, the dye degradation efficiency increased with longer exposure, rising from 56.6%
to 83% over 18 hours of sunlight. These findings demonstrate that optimizing the optical properties of
CDs in combination with TiO2 is an effective, economical, and environmentally friendly approach for
industrial liquid waste purification.