Carbon Quantum Dot-Modified ZnO Nanomaterials for Photocatalytic and Antibacterial Applications

Abstract

The emerging pollutant discharge of organic contaminants, synthetic dyes, pharmaceutical remains, and pathogenic microorganisms in water bodies has raised a critical demand for multifunctional nanotechnology-based materials that can simultaneously degrade pollutants and inactivate microorganisms. Due to its various properties such as low-cost, environmentalfriendly, chemical stability, photocatalytic and antibacterial activity, zinc oxide (ZnO) is one of the most widely studied semiconductor nanomaterials. The practical efficiency of pure ZnO is however limited by its wide band gap, its poor absorption in the visible light, its high rate of recombination of the electron–hole pairs generated by the light, and possible photo corrosion during prolonged irradiation. Carbon quantum dots (CQDs) are a novel type of 0D carbon nanomaterials with superior properties of photoluminescence, tuneable surface chemistry, water dispersibility, electron transferring capacity, low toxicity and visible light harvesting capacity, receiving significant attention. The modification of ZnO with CQDs is therefore expected to be an effective approach to improve photocatalytic and antibacterial activity. CQDs exhibit enhanced visible-light utilization, generation of reactive oxygen species, and act as photosensitizers, electron reservoirs, charge-transfer mediators and surface modifiers. CQDmodified ZnO can decompose organic pollutants like methylene blue, rhodamine B, methyl orange, phenolic compounds, pesticides, and pharmaceutical contaminants in photocatalytic systems. In the antibacterial application, the CQD-ZnO nanocomposites inhibit the bacterial growth by oxidative stress, cell membrane disruption, release of Zn²⁺ ions and intracellular damage. The properties, synthesis methods, characterization approaches, photocatalytic mechanism, antibacterial pathways, challenges and future prospects of CQD modified ZnO nanomaterials discussed. Their potential as sustainable multi-functional materials for wastewater treatment, environmental remediation and antimicrobial surface applications are highlighted.