ИСТИНА

High specific surface area and functional surface composition of detonation nanodiamonds allow the modification of nanodiamonds surface with different compounds either by chemical synthesis or adsorption [1]. Pretreatment of nanodiamonds sets the functional composition of the surface and provides its positive or negative zeta potential in the aqueous suspension. Previously, we have shown that being quaternary ammonium base the surface active drug (Myramistin) can adsorb on both positively and negatively charged nanodiamonds [2,3]. To reveal the mechanism of the adsorption process we studied the adsorption of three representatives of a homologous series of alkyltrimethylammonium bromides (dodecyl, tetradecyl and hexadecyl) on nanodiamonds of positive and negative zeta potential. The amount of the surfactant on nanodiamond surface was determined using tritium labeled compounds that were obtained by means of tritium thermal activation method [4]. Nanodiamonds produced by PlasmaChem were used in this study. Nanodiamond powder was used as received as well as subjected to air annealing at 450°C during 1 hour. The suspension of single-digit nanodiamond (SDND, PlasmaChem) was used as received. Nanodiamond powder was suspended in water as it was described in ref [2]. Nanodiamonds were characterized by means of FTIR, BET and TEM. The suspensions were also characterized by DLS. It was found that nanodiamond subjected to air annealing and SDND possess negative value of zeta potential as well as it functional composition was very close. The adsorption experiments were carried out according to the procedure described previously [2,3]. For all types nanodiamonds we obtained adsorption isotherms of alkyltrimethylammonium bromides of Langmuir type. It reached plateau region at concentration value close to critical micelle concentration. However, the value of maximum adsorption was decrease with molecular weight growth. For nanodimonds that were subjected to air annealing and SDND the isotherms were identical and maximum adsorption obtained for these samples was as much as 30 times higher than maximum adsorption on nanodiamonds of positive zeta potential. The reversibility of adsorption of alkyltrimethylammonium bromides was determined in water and in 0.9% NaCl. For all samples it was found that desorption in water is negligible while in presence of salt the desorption reached 57% suggesting the dominant role of electrostatic interactions in the adsorption process. We also control value of zeta potential as a function of surface concentration of alkyltrimethylammonium bromides surface concentration. We have found that all types of nanodiamonds are stabilized in the aqueous suspension when the adsorption reaches plateau region. This work was supported by Russian Foundation for Basic Research (grant # 17-03-00985). References Neburkova J., Vavra J., Cigler P. 1. Current Opinion Solid State Mater. Sci. (2017) 21, 43. 2. Chernysheva M.G., Popov A.G., Tashlitsky V.N., Badun G.A. Colloids Surface A. (2019), 565, 25. 3. Chernysheva M.G., Alexeev M.E., Myasnikov I.Yu, Popov A.G., Badun G.A. Abstr. 13th Int. Conf.Advanced Carbon Nanostructures (ACNS'2017), p. 42. 4. Badun G.A., Chernysheva M.G., Ksenofontov A.L. Radiochimica Acta. (2012), 100, 401.