Biosynthesis and characterization of MnO2 and Zn/Mn2O4 NPs using Ziziphus spina-Christi aqueous leaves extract: Effect of decoration on photodegradation activity against various organic dyes

An aqueous leaf extract of Ziziphus spina-Christi is used to synthesize manganese oxide nanoparticles (MnO2 NPs) and zinc-coated manganese oxide nanoparticles (Zn/Mn2O4 NC). The study aims to investigate the photocatalytic degradation efficiency of MnO2 NPs and Zn/Mn2O4 NC in relation to the azo dyes methylene blue (MB), m-Toluidine (mT), and P-Toluidine (pT). X-ray diffraction analysis (XRD) confirmed the crystalline nature of the biosynthesized MnO2 NPs and Zn/Mn2O4, revealing their respective crystallite sizes to be approximately 14.65 nm and 22.97 nm. The scanning electron microscope (SEM) images demonstrated that the MnO2 NPs exhibit a tetragonal and spherical shape, while the Zn/Mn2O4 particles possess a spherical shape. UV–vis spectroscopy measurements indicated that the MnO2 NPs and Zn/Mn2O4 exhibit indirect bandgaps with energy values of 1.46 eV and 1.14 eV, respectively. Fourier transform infrared (FTIR) analysis revealed the presence of organic compounds containing CO and OH groups, such as carbohydrates, phenolic acids, tannins, and flavonoids derived from Ziziphus spina-Christi, suggesting a high likelihood of stability for the biosynthetic MnO2 and Zn/Mn2O4 materials. Interestingly, the photocatalytic degradation of the biosynthetic MnO2 and Zn/Mn2O4 provided good efficacy against the Methylene Blue (MB), m-Toluidine (mT), and P-Toluidine (pT) where the Zn/Mn2O4 exhibit an excellent degradation were 99.2, 99.8 and 98.4 % after 75 min. The biosynthetic MnO2 NPs and Zn/Mn2O4 NCs resulting from using aqueous ZSCLE were cost-effective and eco-friendly, and the decoration of MnO2 NPs by Zn improved their effectiveness.