Tailored Zeolitic Imidazolate Framework (TSC‐ZIF) for water purification: Evaluating TSC‐ZIF affinity towards heavy metal ions in multi‐metal solutions

Abstract

In response to the growing concerns surrounding water pollution and the presence of multiple metal ions in environmental matrices, we conducted a comprehensive study to explore the potential of a thiosemicarbazone Schiff base in the Zeolitic Imidazolate Framework (TSC‐ZIF‐1) as an efficient adsorbent for removing harmful metal ions from aqueous solutions. Our investigation assessed the adsorption capacity and efficiency of TSC‐ZIF 1 towards three key metal ions—Hg(II), Ag(I), and Pb(II)—in homo‐ionic, tertiary, and multi‐metal ion systems. TSC‐ZIF 1 exhibited unprecedented adsorption behavior towards all three metal ions in the homo‐ionic system, with the Langmuir isotherm models fitting well (R2 ~ 0.98 to 0.99). The maximum adsorption capacities were found to be 1,667 mg/g for Hg(II), as previously reported; 285 mg/g for Ag(I); and 769 mg/g for Pb(II); these values serve as baseline values. Subsequently, we conducted a comparative analysis for a tertiary system, Hg(II)/Ag(I)/Pb(II), where the three metals co‐existed in one solution. The adsorption capacity for each metal ion was reduced to varying extents; notably, the adsorption capacity for Pb(II) experienced the most significant reduction, reaching a qm value of 57 mg/g, representing an ~93% decrease compared to the homo‐ionic metal system. Conversely, the adsorption capacity for Ag(I) exhibited a minor decrease of ~3%. Despite a decrease in the adsorption capacity for Hg(II) by approximately 34%, the removal capacity remains the highest among the other metals. Our investigation of the competitive adsorption among the metal ions in the Hg(II)/Ag(I)/Pb(II) system revealed an antagonistic effect, indicating strong adsorption competition for available sites on TSC‐ZIF 1. When extending this study to a more complex multi‐metal ion system containing six metal ions, TSC‐ZIF 1 exhibited high selectivity (higher than 60% removal) towards Hg(II), Ag(I), and Pb(II) in a multi‐ionic system, including Hg(II), Ag(I), Pb(II), Cd(II), Ni(II), and Mg(II).