Synthesis of nitrogen-doped ZnO particles by decomposition of zinc nitrate hexahydrate in molten ammonium salts

The N-doped ZnO was prepared by heating a mixture of zinc nitrate hexahydrate [Zn(NO₃)₂·6 H₂O] and ammonium salt at 623 K for 1 h in air. The mixture of zinc nitrate hydrate and ammonium salt formed a homogeneous molten salt at 623 K, and the homogeneous dispersion of the metal ions and ammonium ions contributed to the N-doping. In particular, when the mixture of zinc nitrate hydrate and ammonium acetate (CH₃COONH₄) was heated at 623 K, the doped amount of nitrogen was higher than with the mixture of zinc nitrate hydrate and NH₄NO₄. The acetate anion (CH₃COO⁻) restricted the oxidation reaction of nitrate anion (NO₃⁻). Furthermore, Al- and N-co-doped ZnO particles were obtained by heating the mixture of zinc nitrate hydrate, aluminum nitrate hydrate, and ammonium acetate. The Al and N co-doping effectively increased the doped amount of nitrogen. The spontaneous formation of ZnO lattice and the nitrogen source in the molten salt and the homogeneous dispersion of Zn₂⁺ ions and Al₃⁺ ions contributed to the increase in the amount of doped nitrogen.