Abstract
In this work, the assessment of Azadirachta indica, Tagetes erecta, Chrysanthemum morifolium, and Lentinula edodes extracts as catalysts for the green synthesis of zinc oxide nanoparticles (ZnO NPs) was performed. The photocatalytic properties of ZnO NPs were investigated by the photodegradation of methylene blue (MB) dye under sunlight irradiation. UV-visible (UV-Vis) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Thermogravimetric (TGA), and Brunauer-Emmett-Teller analysis (BET) were used for the characterization of samples. The XRD results indicate that all synthesized nanoparticles have a hexagonal wurtzite crystalline structure, which was confirmed by TEM. Further, TEM analysis proved the formation of spherical and hemispherical nanoparticles of ZnO with a size in the range of 14–32 nm, which were found in aggregate shape; such a size was well below the size of the particles synthesized with no extract (~43 nm). ZnO NPs produced with Tagetes erecta and Lentinula edodes showed the best photocatalytic activity, matching with the maximum adsorbed MB molecules (45.41 and 58.73%, respectively). MB was completely degraded in 45 min using Tagetes erecta and 120 min using Lentinula edodes when subjected to solar irradiation.
Highlights
Zinc oxide nanoparticles (ZnO NPs) are one of the nanostructured materials of greatest interest due to their wide range of applications in pharmaceutical [1], electronic [2], medical [3], power generation [4], and environmental [5] fields, which is due to their multiple properties such as semiconductors, pyroelectrics, piezoelectrics, catalysts, optoelectronics [6], antimicrobial, and anticancer activity [1].Zinc oxide is an environmentally friendly and abundant-in-nature semiconductor with n-type conductivity and a wide band gap of 3.3 eV
NPs with no extract, Tagetes erecta, Lentinula edodes, Azadirachta indica, and Chrysanthemum morifolium, respectively. It is well-known that bulk ZnO has a band gap of 3.37 eV [21], and the decrease in the band gap energy found here can be related to the presence of defect states caused by the botanical extracts, as well as by their influence on size control during nanoparticle formation [5]
The nanoparticles synthesized without botanical extract showed catalytic activity, being able to degrade the model dye in 150 min
Summary
Zinc oxide is an environmentally friendly and abundant-in-nature semiconductor with n-type conductivity and a wide band gap of 3.3 eV. ZnO has been extensively used in the photocatalytic degradation of organic pollutants owing to its good quantum efficiency, wide band gap, and nontoxic nature [7]. The advantage of this semiconductor is that the ZnO can absorb a significant fraction of the solar spectrum compared with other photocatalysts such as TiO2. Solar light consists of less than 5% UV radiation, which is why it is necessary to improve this efficiency by modifying its band gap
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