Abstract
We report on the synthesis of alpha manganese dioxide (α-MnO2) nanorods using natural extracts from Vitis vinifera grape stems and Malus domestica ‘Cortland’ apple peels. We used a two-step method to produce highly crystalline α-MnO2 nanorods: (1) reduction of KMnO4 in the presence of natural extracts to initiate the nucleation process; and (2) a thermal treatment to enable further solid-state growth of the nuclei. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) images provided direct evidence of the morphology of the nanorods and these images were used to propose nucleation and growth mechanisms. We found that the α-MnO2 nanorods synthesized using natural extracts exhibit structural and magnetic properties similar to those of nanoparticles synthesized via traditional chemical routes. Furthermore, Fourier transform infrared (FTIR) shows that the particle growth of the α-MnO2 nanorods appears to be controlled by the presence of natural capping agents during the thermal treatment. We also evaluated the catalytic activity of the nanorods in the degradation of aqueous solutions of indigo carmine dye, highlighting the potential use of these materials to clean dye-polluted water.
Highlights
During the past decade, the synthesis of anisotropic metal oxide nanoparticles has attracted considerable attention because of their unique size- and shape-dependent properties [1,2,3]
According to the X-ray diffraction (XRD) patterns, the crystallinity of the synthesized products improves with further calcination at 600 ◦C and 800 ◦C, and this behavior is consistent with prior observations for the synthesis of α-MnO2 nanocrystals [50,51,52]
It is important to note that regardless of the natural extract used for the synthesis, the calcinated samples at 800 ◦C exhibit an increase in the peak intensity and a decrease in peak broadening when compared to the same samples calcinated at 600 ◦C
Summary
The synthesis of anisotropic metal oxide nanoparticles has attracted considerable attention because of their unique size- and shape-dependent properties [1,2,3]. Self-assembly processes driven by diverse interactions can generate a myriad of nanostructures by using nanocrystals as building blocks Shape control of these structures can be achieved by tuning some of the synthesis parameters such as temperature, type of ligands, and interaction of the ligands with the precursors and/or the nanoparticles [4,5,6]. Among the variety of possible shapes, nanorods are some of the most studied anisotropic materials as the combination of chemically induced growth and shape anisotropy can offer an additional level of control during self-assembly processes driven by structural and chemical selectivity [9,10]. There are no studies exploring the use of natural extracts for the oriented growth of highly crystalline alpha manganese dioxide (α-MnO2) nanorods, which is the main topic of this paper. The synthesis method reported here may be extended to a wide variety of other metal oxide nanomaterials
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