Synthesis and Characterization of a Novel Hybrid Material Titanium Amino Tris(methylenephosphonic acid) and Its Application as a Cation Exchanger

In the present work, a novel hybrid ion-exchange material was synthesized by a sol–gel route, by treating titanium tetrachloride with claw-type amino tris­(methylenephosphonic acid) (ATMP) to give titanium amino tris­(methylenephosphonic acid) (Ti-ATMP). Ti-ATMP was characterized by elemental analysis (ICP-AES and C, H, N analysis), spectral analysis (FTIR), thermal analysis (TGA), XRD, SEM, and EDX spectroscopy, including physicochemical and ion-exchange characteristics. The equilibrium exchange of transition-metal ions (viz., Cu²⁺, Ni²⁺, Co²⁺ Zn²⁺) and heavy-metal ions (viz., Pb²⁺,Cd²⁺, Hg²⁺) with the H⁺ ions contained in ATMP was studied at constant ionic strength and varying temperatures, and various thermodynamic parameters such as the equilibrium constant (<i>K</i>), standard Gibbs free energy (Δ<i>G</i>°), enthalpy (Δ<i>H</i>°), and entropy (Δ<i>S</i>°) were evaluated. The Nernst–Planck equation was used to study the ion-exchange kinetics, and various kinetic parameters, namely, the self-diffusion coefficient (<i>D</i>₀), energy of activation (<i>E</i>_a), and entropy of activation (Δ<i>S</i>*), were evaluated under conditions favoring a particle-diffusion-controlled mechanism. Metal-ion adsorptions with variations in concentration and temperature were studied using the Langmuir and Freundlich adsorption isotherms. The distribution coefficient (<i>K</i>_d) and breakthrough capacity (BTC) values for transition- and heavy-metal ions were determined. Based on <i>K</i>_d (mL·g^–1), the selectivity order for metal ions toward Ti-ATMP was found to be Cu²⁺ (19820) > Zn²⁺(3280) > Co²⁺ (2630) > Ni²⁺ (2390) among transition-metal ions and Pb²⁺ (3590) > Cd²⁺ (2340) > Hg²⁺ (610) among the heavy-metal ions. The elution behavior of these metal ions was studied using different acids and electrolytes. A study on regeneration and reuse of the ion exchanger Ti-ATMP shows that it is effective up to five cycles without much decline in performance, which indicates that Ti-ATMP has good potential for use as a cation exchanger