Effect of two-step calcination on the formation of nickel oxide hollow nanofibers

Abstract

1D (one-dimensional) hollow nanofibers are of great technological interest. Their formation can be controlled by tuning the calcination process. However, the formation mechanism through the control of the burning stage is still debated in the literature. Herein, the influence of calcination in two steps on the morphology of hollow nanofibers of nickel oxide (NiO), prepared by solution blow spinning (SBS) technique, was investigated. A systematic study using a variety of characterization techniques suggests that a prolonged residence time in the initial step of calcination produces nanofibers with a better definition of the hollow region with better control of tubular wall thickness. Statistically, the calcination methodology studied here does not affect the outer diameter of nanofibers, as shown by Analysis of Variance (ANOVA) and Tukey’s method. According to our findings, the formation mechanism is influenced by gas diffusion and phase separation during fiber spinning and heat treatment, which suggests that neither the Kirkendall effect nor the Ostwald ripening process can be solely responsible for the formation hollow fibers. These findings contribute to a better understanding of the formation of metal-oxide hollow nanofibers induced by heat treatment.