“…Therefore, a series of methods was successfully developed, such as hydrothermal method [9], solvothermal method [10] and silica-protected calcination [11]. In these preparation processes, the hard (SiO 2 spheres [12], Fe 2 O 3 particles [13], carbon spheres [14], polymer latex spheres [15], etc.) and soft sacrificial templates (vesicles [16], emulsions [17], and micelles [18]) are usually required, which lead to high cost, complex steps, long reaction time, stringent conditions and pollutants generated from the elimination of the templates.…”