Synergistic enhancement of photocatalytic, antioxidant, and antimicrobial activities in nitrogen and phosphorus dual-doped ZnO nanoparticles

Abstract

• Co-doping ZnO nanoparticles with nitrogen and phosphorus reduces the band gap from 2.92 eV to 2.53 eV, enhancing visible-light photocatalytic activity. • ZnO nanocomposites degraded 97.7% of methylene blue within 80 minutes, surpassing pure ZnO-NPs due to improved surface properties. • Antioxidant tests showed increased radical scavenging with higher nanocomposite concentrations, indicating effective oxidation inhibition via electron transfer. • The nanocomposites have antimicrobial activity comparable to pure and doped ZnO-NPs, with combined formulations showing enhanced efficacy. Nanotechnology has a wide range of applications across various fields, including photocatalysis, medicine, antioxidants, and antimicrobials. Zinc oxide nanoparticles (ZnO-NPs) are among the most extensively studied nanomaterials due to their versatile properties. However, in their pure form, ZnO-NPs possess a wide band gap, which limits their absorption of visible light and results in low photocatalytic efficiency. To overcome these limitations, ZnO-NPs were characterized using several techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, and scanning electron microscopy (SEM). By introducing small amounts of nitrogen and phosphorus through co-doping, the band gap of ZnO-NPs was effectively reduced from 2.92 eV to 2.53 eV, leading to a significant enhancement in photocatalytic activity. The co-doped ZnO-NPs demonstrated exceptional performance, achieving 97.5% degradation of a 50 mL Methylene Blue dye solution within only 80 minutes using 50 mg of catalyst. This represents a substantial improvement compared to pure ZnO-NPs under identical conditions. The enhanced photocatalytic performance is attributed to increased surface charge stability and improved surface properties resulting from co-doping. Additionally, the antioxidant activity of the synthesized nanoparticles and nanocomposites was evaluated using DPPH radical scavenging assays. Results showed increased radical scavenging with higher concentrations, with IC50 values of approximately 91 mg/L for pristine ZnO-NPs and 57 mg/L for N&P co-doped ZnO-NPs. These findings suggest that the nanocomposites can effectively inhibit oxidation through electron transfer mechanisms involving n→π* transitions. Regarding antimicrobial activity, the nanocomposites exhibited effects comparable to pure ZnO-NPs, N-doped, and P-doped ZnO-NPs. Notably, the combination of ZnO-NPs and co-doped nanoparticles demonstrated superior antimicrobial efficacy.