Newly synthesised diglycolamide functionalised silica gel with terminal 2-ethylhexyl alkyl chain, Silica-DGA (2EH) having high ligand density for adsorption of trivalent actinide and lanthanide from acidic medium

Abstract

A novel diglycolamide resin with 2-ethylhexyl terminal alkyl chain functionalised to silica gel was synthesised and characterised by ATR-FTIR, SEM, TG/DSC, & ¹³C (CP/MAS) solid state NMR techniques. Effective functionalization of the organic ligand upon silica gel was confirmed from the two carbonyl stretching frequencies at 1735 cm⁻¹ and 1619 cm⁻¹ in the FTIR spectrum and carbonyl carbon atom signal at 170 ppm in ¹³C (CP/MAS) solid state NMR spectrum. Thermo gravimetric measurement showed 17.3 ± 0.2 % (W/W) weight loss corresponding to the ligand loading value of 425 µmol/g. The resin showed very high uptake of trivalent lanthanide and actinide ions from 4.0 M HNO₃ medium and very low distribution of Cs & Sr; K_d ∼ 1.1×10³ mL/g for Am(III), ∼ 1.41×10³ mL/g for Eu(III), ∼2.5 mL/g for Sr and 1.53 mL/g for Cs. FTIR spectroscopic study of the Eu³⁺ adsorbed resin showed single carbonyl stretching frequency at 1654 cm⁻¹, instead of the two carbonyl stretching frequencies in fresh silica-DGA(2EH) resin indicating complexation through carbonyl oxygen. Very low K_d of ∼1.2–5.1 mL/g for lanthanides/actinides from 4.0 M HNO₃ containing water soluble DGA namely N, N, N, N, Tetraethyldiglycolamide (TEDGA) in the concentration range 0.3–0.1 M indicates 99 % back adsorption feasibility.