Zwitterionic ammonium-sulfonato grafted cellulose for efficient thallium removal and adsorption mechanism study

Thallium (Tl) has posed serious impacts on human being concerning increasingly serious pollution in aqueous environments. However, little information on removal method than conventional heavy metals have been available. In the present work, zwitterionic N-(3-sulfonato-1-propyl)-N,N-dimethylammonium grafted cellulose fibre (DMAE-PS) has been fabricated. The chemical component, thermal stability and surface properties of as-prepared materials are identified by FT-IR, elemental analysis, TGA, XRD, BET and SEM. DMAE-PS is shown to be very efficient for removing Tl(I) from water samples with a loading capacity of 274.7 mg (Tl(I))·g^-1 (DMAE-PS)_, representing one of the best performances among bio-mass derived materials. The adsorption is consistent with the Freundlich model following a pseudo-second order (K₂ = 4.36 × 10^-4 g·mg^-1·min^-1, R² = 0.999) and two-step intra-particle diffusion kinetics. The selectivity towards Tl(I) is also remarkably, 1-2 orders (distribution ratio K_Tl/M = 14.85-289.29) of magnitude larger than competing metals (Zn²⁺, Cr³⁺, Mn²⁺, Cu²⁺ and Cd²⁺). The SEM, XPS and UV-visible spectrum collectively reveal that -SO₃^--Tl(I) ionic interaction is probably the main driving force for specific adsorption, which shows a high stability against pH variation. The fabricated DMAE-PS is a sustainable bio-adsorbent with synthetic availability, high removing capacity and strong selectivity, therefore, potentially feasible in treatment of Tl(I) polluted environmental samples.