Ion-exchange properties of microdispersed sintered detonation nanodiamond

The adsorption of transition metal cations and inorganic anions from aqueous solutions on microdispersed sintered detonation nanodiamond (MSDN) is systematically studied. The selectivity series Fe³⁺ > Al³⁺ > Cu²⁺ > Mn²⁺ > Zn²⁺ > Cd²⁺ > Co²⁺ > Ni²⁺ with maximum adsorption capacity between 2 and 5 µmol g⁻¹ is obtained. It is found that anions may significantly contribute to the adsorption of transition metal cations, so the adsorption of CH₃COO⁻, Cl⁻, B₄O₇ ²⁻, ClO₄ ⁻, I⁻, SO₄ ²⁻, C₂O₄ ²⁻, PO₄ ³⁻ is also studied. For the first time, dominating adsorption of anions over cations is demonstrated for detonation nanodiamond. The maximum anion-exchange capacity of 50–150 µmol g⁻¹ is found for MSDN. Beside of electrostatic interactions, the formation of complexes with hydroxyl groups and interaction with metal impurities contribute to the adsorption of B₄O₇ ²⁻ and PO₄ ³⁻, respectively. Therefore, anion exchange selectivity of MSDN is different from that observed for common anion exchange resins. In all cases, the adsorption on MSDN obeys Langmuir law. The pH effect on the adsorption of SO₄ ²⁻, PO₄ ³⁻ and B₄O₇ ²⁻ is different from that observed for other anions due to specific interactions.