Monocrystalline synthetic nanodiamond powders (MSY 0-0.03, MSY 0-0.05, MSY 0-0.100, MSY 0.150, and MSY 0-0.200) were purchased from Microdiamant AG. The diamond particles were annealed in air at 450 o C for 3-4 h. Afterwards, the particles were treated with a mixture of concentrated hydrochloric acid and nitric acid at 100 o C for 2 h. The recovered nanoparticles were subsequently treated with 0.2 M sodium hydroxide solution at 100 o C for 2 h.