The milling process was carried out in a planetary ball-milling machine (PM100, Retsch Co., Germany) using a wet milling method with ultrapure water as the solvent. ... 10 g, ultrapure water (50 mL), and 180 g zirconium balls (2 mm) were placed in a 200 mL capacity zirconia jar and milled at 350 r/min for 0, 5, 10, and 15 h, respectively. The ...Web