The encapsulated particles were finally dispersed in urea solution at a concentration of 0.1 M. The mixtures were then heated to 95 °C and dried at the same temperature for 24 h to obtain the solid sample (assigned as as-prepared-1, as-prepared-2, and as-prepared-3, respectively). Then the as-prepared samples were further calcined at 550 °C in air for 2 h. The resulting samples were denoted as CuO/MS, NiO/MS, and Co3O4/MS, respectively.