surface structure of the disc samples prepared was analyzed using
a scanning electron microscope (JSM-IT-100, Jeol, Japan). The samples
were first coated with gold in a gold sputter (QUORUM) for 90 s at
a 10 mA current. The SEM analysis was done to examine the surface
homogeneity and porosities. The images were taken at magnifications
of 100×, 1000×, and 3000×, with the voltage kept at
20 kV.