Electrospun ZnO nanofibers (ZNF) have received increased attention as photocatalysts owing to their potential for incredible performance. However, uncertainty still exists in determining the correlation between grain boundaries (GBs) and photocatalytic activity. Therefore, effective thought has been put into engineering the GBs to convert ZNF into a promising photocatalyst. Herein, the obtained electrospun ZnO structures are composed of nanograins, which are connected to each other in an ordered manner. In-depth studies have revealed that the growth of nanograins severely altered the morphology of ZNF and GB areas at higher annealing temperatures ranging from 500 degrees C to 1000 degrees C. Based on the morphological features and their structural evolution, the obtained structures are named as ZnO nanofibers-1 (ZNF-1,500 degrees C), ZnO hollow tubes (ZHT, 600 degrees C), ZnO nanofibers-2 (ZNF-2, 700 degrees C), ZnO bamboo structured fibers (ZBF, 800 degrees C), ZnO segmented fibers (ZSF, 900 degrees C) and ZnO nanoparticles (ZNP, 1000 degrees C). A strong correlation between the inherent emission features of ZNF and their peak positions have been detected with the GB. The comparative degradation efficiency of methylene blue (MB) has been studied and the results showed that the ZNF-1 with highly stacked nanograins containing rich grain boundaries demonstrated similar to 6 times higher efficiency than other structures. In addition, it has been shown to have a strong effect towards the degradation of Rhodamine B (Rh B) and 4-nitro-phenol (4-NP). A critical parameter for improving the photocatalytic activity is found to be the GB mediated defects, which are proposed to be oxygen/zinc vacancies at nanograin fusion interfaces, while supposedly maintaining its fibrous structure, wherein no relationship has been drawn implying the direct domination of morphology, surface area and defect.
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