Metallogel Synthesis from Cu(II) Complex with Benzotriazole-5-carboxylic Acid for Enhanced Congo Red Dye Adsorption and Anion Exchange

A new metallogel was assembled by Cu(II) and benzotriazole-5-carboxylic acid (H₂btca) as gelators via a solvothermal method. The study of various parameters influencing the metallogelation process, including solvent types, metal ions, counter-anions, and the mole ratios of gelators, was investigated. The morphology and surface properties of xerogels were characterized by FTIR, FE-SEM, and EDX techniques. The xerogel demonstrated selective adsorption of anionic dyes, particularly Congo red dye (CR), with a removal efficiency of 98%. The comprehensive study of the adsorption process coincides with the pseudo-second-order model, the Langmuir isotherm, and the spontaneous exothermic process. The adsorption capacity of CR is 666.4 mg·g^–1. The dye adsorption mechanism was investigated. Furthermore, the synthesis of Cu-metallogels can be achieved with various anionic species, including NO₃^–, ClO₄^–, and BF₄^–, allowing for the development of reversible anion exchange behaviors.