extract the main material or chemicals and actions from the preparation process,only words not sentance:The SACs were prepared using an omnibearing planetary ball mill (CHISHUN, PMQW2). Analytical grades of TiO2 (P25, Degussa), MCln 
(M= Pd, Bi, Y, Er, Cu, Na, etc.) (99.9%), HCl (36–38%) and deionized water were used in the synthesis. Firstly, the support TiO2 (5.0 ×10− 2 mol) and MCln (5.0 n × 10− 5 mol, n = 1, 2, 3,…) were added into the agate grinding jar (250.0 ml) together with 15.0 ml H2O. Subsequently, the HCl (VHCl: Vwater=1:1) was added to adjust the overall pH to 0.0–4.0. Agate grinding balls of different sizes (6.0, 10.0, and 20.0 mm) were added and ground at 400 r/m for 12 h. Due to the choice of natural agate material (good heat dissipation) and 15.0 ml of water, the temperature of the whole ball milling process is < 35 ◦C,which can effectively prevent oxidation due to high temperature. Finally, the mixture was then taken out, washed and centrifuged repeatedly with 0.1 mol/L HCl and H2O, dried in an oven at 90 ◦C for 4 h. After grinding the solid into the fine powder, the final product single-metal MSA/TiO2 (M= Pd, Bi, Y, Er, Cu, Na, etc.) photocatalysts were obtained.