Surface Polarity Determination of ZnO Spherical Particles Synthesized via Solvothermal Route

Abstract

ZnO monodispersed microspheres exhibiting only a c(þ)-plane on the surface were successfully synthesized by a novel soft-chemical solvothermal method with ethylene glycol (EG) and hexamethylenetetramine. The concentration of EG plays a critical role in the formation of these spherical particles. The spherical particles are dense and have hierarchical structure, where small crystallites are radially aligned along the c-axis. The polarity was determined using convergent-beam electron diffraction, and we established that the whole surface of the microspheres is a c(þ)-plane.

Hierarchical structures of ZnO spherical particles synthesized solvothermally

“…As the EG/W ratio increased, the sizes of the constituent plates and of the hole in ZnO doughnuts decreased, and at EG/W = 5, almost spherical particles with a small hole were obtained. Table 2 shows the effect of the EG/W ratio on the morphology of ZnO in our experiments [38]. At EG/W < 1, the precipitates were hexagonal and contained an unknown phase.…”

“…Various conditions have been used in the glycol-assisted solvothermal synthesis of ZnO particles with hierarchical structure [27][28][29][30][31][32][33][34][35][36][37][38][39], and the concentration of glycol was found to play a key role in the microstructure of ZnO particles. Table 1 lists the preparation conditions of spheroidal ZnO particles using EG and DEG, and the scanning electron microscopy (SEM) images of ZnO particles are shown in figure 3.…”

“…Recently, our group reported the synthesis of ZnO spherical particles using EG and hexamethylenetetramine (HMT) [38]. HMT is often employed to produce ZnO powders and films in aqueous solutions with a homogeneous precipitation method [21,22].…”

“…Urea was used for increasing the pH of the solvent, which is similar to our usage of HMT [38]. ZnO rods were grown when the solvent contained EG, DEG or tetraethylene glycol.…”

“…We have clearly observed the hierarchical structure in spherical ZnO particles. Figure 5 shows SEM images of particles prepared in the 87.5 vol.% EG solution and the corresponding illustrations [38]. They are probably fragments of ZnO spheres broken by ultrasonic treatment.…”