Pristine detonation nanodiamonds as regenerable adsorbents for metal cations

The usability of pristine (not functionalized by grafting) detonation nanodiamonds as reversible and repeatedly regenerated adsorbents for metal cations was shown by examples of sorption of cadmium, zinc, nickel, and copper from aqueous solutions. Various pristine nanodiamond surface treatments are discussed. The procedure of oxidative sintering with nitric acid at 250 °C provided a surface with an increased number of carboxyl groups with a sorption capacity above 100 μmol/g for all test cations. Sorption isotherms for test metals (copper, nickel, zinc, and cadmium) can be divided into two distinct parts: a lower part for concentrations of up to 10–15 mmol/L belong to the Langmuir L5 type by Giles and absorption free energies are 8–12 kJ/mol according to the Dubinin–Radushkevich model, evidencing a primarily chemisorption mechanism of the studied cations on micropores in ND surface. The parts of curves above 10–15 mmol/L are described with linear equations, free energies of absorption are 4–6 kJ/mol by Dubinin–Radushkevich that are assigned to physisorption in mesopores. A procedure for the surface regeneration, which is based a similar sintering treatment with nitric acid, was developed. It provided sorption parameters not degraded compared to the starting material; and the regeneration process is repeatable at least for 10 cycles. [Display omitted] •Use of nanodiamonds as regenerable cationic sorbents is shown.•Nitric-acid treatment at 250 °C provided sorption capacity above 100 μmol/g.•Langmuir sorption isotherms are shown; absorption free energies are 8–12 kJ/mol according to Dubinin–Radushkevich model.•A regeneration procedure is based on a similar treatment with nitric acid. Sorption parameters of nanodiamonds after regeneration are not degraded.•Regeneration process is repeatable.