Synthesis and Characterization of ZnO/CuO Nanocomposites Decorated with Carbon Dots for Photocatalytic Degradation of MB and Antibacterial Applications

Abstract

Zinc oxide nanoparticles (ZnO-NPs) are gaining significant attention due to their catalytic and antibacterial properties. However, their effectiveness in pure form is limited by several factors, including a large energy bandgap, high exciton binding energy, electron-hole recombination, poor absorption of visible light, and insufficient photocatalytic activity. To address these challenges, we propose the incorporation of transition metal oxides, such as copper (II) oxide (CuO), along with trace amounts of carbon nanomaterials. This study focuses on enhancing the photocatalytic degradation of methylene blue (MB) dye by adding only 9% CuO nanoparticles and 2% carbon dots (C-dots) to the ZnO-NPs. The inclusion of these materials reduced the energy bandgap of ZnO-NPs from 3.08 eV to 2.51 eV, leading to a significant improvement in their photocatalytic activity. Our results indicated that nearly complete degradation of MB (98.7%) was achieved within 60 min of visible light irradiation when 70 mg of the C-dot decorated ZnO/CuO composite was used. This performance is considerably better than that of the pure ZnO-NPs, which only degraded 76.16% of the MB dye after the same duration of light exposure. Additionally, the incorporation of CuO and C-dots significantly enhanced the antibacterial activity of ZnO-NPs against selected gram-positive and gram-negative bacteria. The zones of inhibition for B.Seraus, E.coli, S.typhi and S.ureus were 8±0.25, 12±0.20, 13±0.10, and 10±0.30 mm, respectively, evaluated against ZnO-NPs. Also the zones of inhibition for B.Seraus, E.coli, S.typhi and S.ureus were 14±0.20, 17±0.20, 18±0.15, 16±0.35mm, respectively, evaluated against ZnO/CuO@C-dot-NCs. The substantial improvement in both photocatalytic and antibacterial effectiveness can be attributed to enhanced surface charge and stability. To our knowledge, this represents the most significant improvement in photocatalytic and antibacterial efficacy achieved by adding small amounts of C-dot material to ZnO/CuO nanocomposites.