Standing porous ZnO nanoplate-built hollow microspheres and kinetically controlled dissolution/crystal growth mechanism

The standing porous nanoplate-built ZnO hollow microspheres with micro/nanostructure are fabricated based on a modified hydrothermal strategy, using citrate as structural director, and subsequent annealing treatment. The hollow spheres are composed of the vertically standing and cross-linked single crystalline porous nanoplates with the exposed surface of nonpolar (10(ar 1)0) planes. Experiments have revealed the structural evolution: the formation of amorphous spheres in the initial reaction stage, followed by surface crystallization and nanoplate outward growth accompanied by inward dissolution of the amorphous spheres. Citrate in the precursor solution plays a dominant role in the formation of such porous ZnO hollow spheres. A model is presented, based on citrate-induced amorphous sphere formation and kinetically controlled dissolution and crystal growth. The model describes the formation of the hollow spheres, thermodynamically and kinetically.