The confinement effect of layered double hydroxides on intercalated pyromellitic acidic anions and highly selective uranium extraction from simulated seawater

Abstract

Oxygen-rich pyromellitic acidic anions (PMA⁴⁻) have been intercalated into MgAl-layered double hydroxides to fabricate the MgAl–PMA–LDH (abbr. PMA–LDH) composite exhibiting excellent adsorption performance toward uranium (U(VI)). Benefiting from the large number of functional groups of –COO⁻, the PMA–LDH displays an extremely large maximum U adsorption capacity (q^U_m) of 352 mg g⁻¹ and an ultra-fast sorption rate, reaching uptakes of ∼97% within 30 min and >99% in 1 h at the initial U concentration (C^U₀) of 113 ppm. Over a very wide pH range of 5–11, high U removals (>93%) are achieved at C^U₀ = 105 ppm. Moreover, in the presence of highly concentrated competitive ions, ultra-high selectivity of UO₂²⁺ is observed, giving a very large distribution coefficient (K_d) of ∼10⁶ mL g⁻¹. Moreover, the PMA–LDH exhibits effective capture of UO₂²⁺ in contaminated simulated seawater, showing high uptakes of >93% at C^U₀ ∼ 10 ppm and >98% at C^U₀ ∼ 100 ppm. The dispersion effect of LDH layers may contribute to the increase of U adsorption capacity, and the confinement effect of LDH is conducive to the improvement of sorption selectivity toward U. The exploration of the interaction mechanism of UO₂²⁺ with PMA⁴⁻ confined within the LDH gallery offers an important basis for the fabrication of new kinds of organic/inorganic hybrid materials. The PMA–LDH is a highly effective adsorbent which can be applied to uranium extraction from seawater and uranium disposal in nuclear wastewater.