Insights into the role of Phosphate Group to vastly improve adsorption of Thorium and Uranium by Triptycene Based Knitted Aryl Polymer Network

Abstract

We demonstrated efficient and selective removal of Th (IV) and U(VI) from aqueous solutions by engaging a triptycene based knitted aryl polymer (KAP). The adsorption efficiency is governed by multiple parameters including pH (2-10), initial ion concentrations (25-800 ppm), adsorbent characteristics, and the presence of competing ions (Cu2+, Sr²⁺, Co²⁺, K⁺, Na+, Zn²⁺and Cs⁺) in solution. The specially designed KAP (TP_DPP) consisted of nanopores (surface area of 480 m2 g-1) with P=O groups that can potentially interact with Th and U resulting in 760 mg/g and 644 mg/g absorption capacities, respectively. Maximum adsorption was achieved at pH 6 for both Th(IV) and U(VI) indicating a balance between favourable ion speciation and deprotonated, highly interactive phosphate functional groups on the TP_DPP framework. The TP_DPP also registered a distribution coefficient Kd of 106 mL/g for Th and 105 for U. γ-irradiated TP_DPP (50, 100, 200, and 300 kGy) retained excellent adsorption capacities for both Th(IV) and U(VI). Chemical stability was tested by treating TP_DPP with acidic and basic solutions before adsorption experiments. The reduction of Th uptake varied from 1.2% in presence of Sr2+ to maximum of 4.2 % in presence of Co2+. The effect of interfering ions on reduction of U uptake varied from 0.6% in presence of Na to maximum of 13 % in presence of Cu2+. This work highlights TP_DPP as a superior adsorbent for Th and U removal, offering a sustainable and effective solution for nuclear waste management and groundwater remediation.