Preparation and formation mechanism of ZnO supported hollow SiO2 nanoparticle by an interfacial reaction through micropores

Abstract

Abstract A ZnO supported hollow SiO 2 (ZnO/h-SiO 2 ) composite nanoparticle with a strong yellow emission has been prepared using the Zn(OAc) 2 precursor with a catalytic amount of NaOH. A single nano-sized ZnO having defective oxygen homogeneously dispersed on the SiO 2 shell. How this desired structure was achieved is discussed by comparison of three carrier nanoparticles of h-SiO 2 , calcite core–SiO 2 shell (CS), and dense SiO 2 (d-SiO 2 ) which have several spaces where the precursor solution was trapped. That is, h-SiO 2 has a micropore/hollow interior/interspace among the particles, CS has a micropore/interspace, and d-SiO 2 only has an interspace. On the CS carrier, similar ZnO single nanoparticles were dispersed and the ZnO/CS composite showed a strong yellow emission. On the d-SiO 2 carrier, aggregated ZnO nanoparticles were localized on part of the SiO 2 surface. Consequently, the existence of micropores is the key structure to obtain the ZnO nanoparticle dispersion. During penetration of the ZnO precursor into the hollow interior through the micropores, dissociated Zn 2+ ions adsorb on the SiO 2 surface. Hydroxide ions (OH − ) of NaOH then make contact with the adsorbed Zn 2+ on the SiO 2 shell to form ZnO. The micropore could work as a mold to prevent excess growth of the ZnO. The strong emission was also contributed by defects among the siloxane bonds in the SiO 2 shell due to its light scattering ability. The obtained ZnO/h-SiO 2 can be useful as a yellow phosphor of a white light emitting diode (LED).