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.
