Abstract Our research is directed towards finding inroad(s) for conversion of detonation nanodiamond to more standard nanopowder with, first of all, enhancement of chemical and phase purity and, secondly, establish monofunctional surface termination. We have designed and tested a novel approach to detonation nanodiamond purification and surface functionalization, using a high temperature treatment in hydrogen-(H2, NH3) and chlorine-containing (Cl2, CCl4) gaseous media. A serious reduction in Al, Cr, Si and Fe content in nanodiamond was achieved by Cl2 treatment at 850 °C. Moreover a drastic decrease in the hydrophility (by a factor of 20) from annealing in a CCl4 / Ar mixture is demonstrated. Other remarkable features after high temperature treatment in H2 and NH3 are being studied by independent characterization techniques (chemical analyses; pH-measurements, FTIR-, Raman-, and ESR spectroscopy), indicating profound nanodiamond modification and prescribed functionalization are possible.