Tyrosine-Immobilized Montmorillonite: An Efficient Adsorbent for Removal of Pb²⁺ and Cu²⁺ from Aqueous Solution

Herein, a new effective material, tyrosine-functionalized montmorillonite (Tyr-Mt), was prepared and used in the adsorption of Pb²⁺ and Cu²⁺ ions. Tyr-Mt is synthesized by modifying sodium montmorillonite (Na-Mt) with l-tyrosine. The X-ray diffraction, ζ-potential, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller, and thermal analysis results showed that the modifier was successfully inserted into the interlayer of montmorillonite. In single-ion systems, various parameters were thoroughly evaluated, such as the amount of the modifier, pH value, the initial concentration of M²⁺, and contact time, affecting the adsorption processes in sodium montmorillonite (Na-Mt) and Tyr-Mt composites. The adsorption experiments of Pb²⁺ and Cu²⁺ showed that the adsorption effect of Tyr-Mt was better than that of Na-Mt. The balanced adsorption of Pb²⁺ by Tyr-Mt was 106.21 (higher than that by Na-Mt, 89.08 mg/g) and of Cu²⁺ was 28.31 mg/g (higher than that by Na-Mt, 23.93 mg/g). The adsorption model conforms to the Langmuir model, indicating that the active sites on the adsorbent surface are the same. The kinetics conforms to the pseudo-second-order kinetics, and the adsorption process is a spontaneous endothermic process. In the binary co-adsorption system, the adsorption capacity for heavy metal ions was lower than that in a single adsorption system. Tyr-Mt is used in the adsorption of heavy ions due to its high efficiency and low cost. This study will provide a simple and convenient method for the application of other modified clays to achieve high adsorption capacity for toxic cations in soil and aqueous solutions.