Biosynthesized pure CuO, N-CuO, Zn-CuO, and N-Zn-CuO nanoparticles for photocatalytic activity: Enhanced optical properties through bandgap engineering

In the era of science and technology, nanoscience has explored the potential of nanoparticles (NPs) due to their extraordinary properties at nanoscale compared to those of bulk materials. Modifying metal oxide semiconductors through innovative and sustainable approaches is crucial to meet specific requirements for targeted applications. Herein, semiconductor modified N-Zn-codoped CuO NPs was successfully synthesized as highly efficient photocatalyst using Pycnostachys Abyssinica Fresen plant leaf extract as a bioreducing and capping agent for the degradation of methylene blue (MB) under natural sunlight irradiation. Additionally, pure CuO NPs, N-CuO NPs, and Zn-CuO NPs were also biosynthesized for comparison. Characterization via UV Vis, XRD, SEM, and FT-IR revealed that N-Zn codoping narrowed the band gap (1.72–1.07 eV), reduced the crystallite size (38.995–31.929 nm), distorted the monoclinic crystal lattice (rhombus- and diamond-like shapes with an average particle size of 2.25 µm to an irregular shape with an average size of 2.75 µm), and redshifted the Cu O characteristic peaks (617–529 cm −1 ) of CuO NPs, confirming the successful incorporation of dopants into CuO NPs. The effects of key parameters on the photocatalytic degradation efficiency of all biosynthesized NPs were investigated. The optimal conditions for maximum degradation of N-Zn-CuO NPs were a 3 % dopant concentration for both N and Zn, a 120 mg photocatalyst dosage, a pH of 11, a 20 ppm initial dye concentration and a 30-minute reaction time. The photocatalytic activity toward MB dye degradation after 30 minutes of exposure to sunlight was 99.75 % for the N-Zn-CuO NPs, outperforming that of the pure CuO NPs (95.76 %), N-CuO NPs (97.93 %), and Zn-CuO NPs (98.26 %) under optimal conditions. The enhanced photocatalytic performance of N-Zn-CuO NPs is attributed to their tailored optical properties, leading to improved charge separation and reduced recombination. Kinetic studies revealed a strong fit (R 2 =0.99799) with the BMG kinetic model for N-ZnCuO NPs, indicating surface-mediated degradation of MB. Furthermore, the nanocatalysts exhibited excellent reusability and stability over four cycles. These findings highlight the potential of biosynthesized N-Zn-CuO NPs as highly efficient, simple, ecofriendly and sustainable solutions for the degradation of organic pollutants. • Modifying MOS through innovative approaches is crucial to meet specific requirements for targeted applications. • Semiconductor modified N-Zn-codoped CuO NPs was successfully synthesized as highly efficient photocatalyst using PA extract. • UV-Vis and XRD confirmed codoping, modifying the band gap from 1.72 eV to 1.07 eV and reducing crystallite size to 31.93 nm. • At optimal condition, N-Zn-CuO NPs degraded 99.75 % of MB in 30 mins of sunlight, surpassing pure CuO, N-CuO, & Zn-CuO NPs. • Doping & codoping not only improved the photocatalytic activity of CuO NPs but also enhanced their stability & reusability.