The product from filtration was washed with ethanol to obtain a hydrothermally treated specimen, or washed with 0.1 N HNO3 solution at 25 °C to reach pH values of 6 and 1.7 to obtain other specimens.
The product from filtration was washed withethanol to obtain a hydrothermally treated specimen, or washedwith 0.1 N HNO3 solution at 25 °C to reach pH values of 6 and 1.7to obtain other specimens.