Layered silicate RUB-15 for efficient removal of UO22+ and heavy metal ions by ion-exchange

Abstract

Remediation of water systems containing radionuclides and heavy metals is important to human health. In this work, two-dimensional layered silicate RUB-15 was fabricated by a straightforward and scalable hydrothermal method and then applied in water remediation for the first time. The layered silicate RUB-15 exhibited high adsorption abilities and efficient adsorption rates for not only UO₂²⁺ but also heavy metal ions (Pb²⁺ and Cd²⁺). The maximum adsorption capacities for UO₂²⁺, Pb²⁺ and Cd²⁺ of RUB-15 were 152, 338 and 190 mg g⁻¹, respectively. A pseudo-second-order reaction is observed on RUB-15 and the highest distribution coefficient K_d value reached was 1.42 × 10⁴ mL g⁻¹. XRD, EDX and XPS analyses proved that the ion-exchange between UO₂²⁺ (or Pb²⁺ and Cd²⁺) and tetramethylammonium (TMA) cations inside the interlayer space of RUB-15 was the key adsorption mechanism. The abundant TMA cations inside RUB-15 supplied sufficient ion-exchange sites for the contaminant, and the large interlayer spacing of RUB-15 (1.4 nm) assured efficient ion diffusion rates. The multiple advantages of RUB-15, such as good dispersion in water, low cost, high adsorption capacities for heavy metal ions and UO₂²⁺ ions and efficient regeneration made the layered silicate RUB-15 a promising adsorbent in water treatment applications.