Transformation of polymer-ZnO core-shell nanofibers into ZnO hollow nanofibers: Intrinsic defect reorganization in ZnO and its influence on the photocatalysis

Photocatalytic activity (PCA) on semiconductors is known to be majorly influenced by specific surface area and intrinsic lattice defects of the catalyst. In this report, we tested the efficiencies of 1D ZnO catalysts of varying fiber diameter (80. nm and 650. nm of inner diameter) in two formats, viz. core-shell and hollow nanofibers, where the former is calcined to yield the latter. These nanofibrous catalysts were produced by combining electrospinning and atomic layer deposition processes which were then subjected to thorough characterization including photoluminescence (PL) unveiling the details of intrinsic defects/densities. During the thermal treatment, intrinsic defects are reorganized and as a result a new PL band is observed apart from some significant changes in the intensities of other emissions. The densities of various intrinsic defects from PL are compared for all samples and juxtaposed with the PCA. Careful scrutiny of the various results suggested an anti-correlation between surface area and PCA; i.e., higher surface area does not necessarily imply better PCA. Beyond a limit, the most deterministic factor would be the density of surface defects rather than the specific surface area. The results of this study enable the researchers to fabricate 1D semiconductor photocatalysts while striking the balance between surface area and density of defects.