Enhanced Visible-Light-Driven Photocatalytic Activity of Zinc Oxide Nanorods-Encapsulated Carbon Quantum Dot

Zinc Oxide (ZnO) nanorods are a promising material for photocatalysis, but their performance is still limited by low light absorption and electron-hole pair recombination. The addition of Carbon Quantum Dots (CQDs) can enhance the photocatalytic activity of ZnO nanorods. This research aims to determine the effect of Carbon Quantum Dot (CQD) variation on the ZnO nanorod/CQD nanocomposite's photocatalytic performance, structure, morphology, and optical properties. The composite was synthesized by the hydrothermal method with varying weight percentages (wt%) of CQDs: 0%, 1%, 5%, and 10%. Characterization was performed using XRD, SEM-EDX, UV-Vis, and photodegradation tests on methylene blue (MB) and Congo red (CR) dyes under UV irradiation. The XRD results show a decrease in crystal size with the addition of CQDs up to 5%, along with an increase in porosity and particle size observed by SEM analysis. With the addition of CQDs, the UV-Vis spectrum shows an extension of ZnO absorption to higher wavelengths and a change in the band gap, with the lowest value of 3.68 eV at 5% CQDs. The photocatalytic activity of ZnO nanorods with an irradiation time of 240 minutes against MB showed a degradation of 86.4% with a degradation rate (k) of 0.00408 min⁻¹, followed by the addition of CQDs sequentially at 99.4% (k = 0.00913 min⁻¹), 91.5% (k = 0.00914 min⁻¹), and 89.26% (k = 0.00860 min⁻¹). Meanwhile, with the CR dye at an irradiation time of 120 minutes, the degradation was 86.21% with a degradation rate (k) of 0.01652 min⁻¹. The sequential addition of CQDs resulted in degradation of 95.92% (k = 0.02856 min⁻¹), 90.43% (k = 0.02543 min⁻¹), and 88.72% (k = 0.02504 min⁻¹). The addition of CQDs has been proven to enhance the photocatalytic performance of ZnO nanorods.