Green synthesis of saponin-capped copper (II) oxide (CuO) nanoparticles and their efficacy in photocatalytic dye degradation

In recent years, green synthesis of nanoparticles coated with different phytochemicals has emerged as a sustainable approach with multifaceted applications. Green nanoparticles can be synthesized in an environment-friendly way while retaining all the advantages of traditional nanoparticles and more. In this study, a novel saponin-capped copper oxide nanoparticle system was synthesized. Saponin, a secondary metabolite in numerous plants, offers eco-friendly and sustainable alternatives for a wide range of biomedical applications. Saponin was isolated from soapnut in an aqueous medium and a standard protocol for green synthesis of saponin-capped copper oxide nanoparticles was optimized. The synthesized nanoparticles were characterized using various techniques and tested for their ability to photocatalyze the degradation of methylene blue, a toxic synthetic dye. X-ray diffraction confirmed the formation of CuO in both samples and UV–Vis and Fourier transform infrared spectroscopies confirmed the presence of saponin in the green-synthesised samples. Scanning electron microscopic analysis of the samples revealed the formation of bigger nano-spheroids for bare CuO (average diameter 244.1 ± 36.3 nm) and smaller irregular clusters for saponin-capped CuO (average length 147.1 ± 41.6 nm). Both these nanostructures were formed by the accumulation of smaller nanoparticles (<30 nm). Through efficient photocatalytic degradation of methylene blue in water, nanoparticles extended a simple and eco-friendly route for environmental remediation and water purification. Saponin-capped CuO nanoparticles catalyzed 86.32 % degradation of the dye, significantly higher than that degraded by bare copper oxide nanoparticles (13.14 %). The results signified the enhanced potential of the saponin-capped nanoparticles compared to the bare CuO ones as nano-photocatalyst.