Nanomaterials, which show large reflectivity for external radiation, are of general interest in science and technology. We report a result from our ongoing research on the reflection of low-energy neutrons from powders of detonation diamond nanoparticles. Our previous work showed a large probability for quasispecular reflection of neutrons from this medium. The model of neutron scattering from nanoparticles, which we have developed, suggests two ways to increase the quasispecular reflection probability: (1) the reduction of incoherent scattering by substitution of hydrogen with fluorine inside the nanoparticles, and (2) the sharpening of the neutron optical potential step by removal of amorphous sp2 carbon from the nanoparticle shells. We present experimental results on scattering of slow neutrons from both raw and fluorinated diamond nanoparticles with amorphous sp2 carbon removed by gas-solid fluorination. These results show a clear increase in quasispecular reflection probability.