Single-pot green synthesis of novel thiol-engineered iron thiomalate (Fe-TA) metal organic framework for selective adsorption of mercury in water

Abstract

A novel thiol-functionalized iron thiomalate metal organic framework (Fe-TA) was synthesized using a facile, single step and green coprecipitation route. The synthesis procedure was optimized and it was proven to be an exclusive way over conventional hydrothermal method. This newly reported MOF was characterized in detail using XRD, FTIR, FESEM, EDX, BET, and Zetasizer to determine the morphological and compositional properties that indicated to the amorphous nature of Fe-TA. The MOF demonstrated high adsorption of aqueous inorganic mercury that was thoroughly explored in varying range of experimental conditions, namely, adsorbent dose, solution pH, feed Hg concentration, temperature, and time to analyze the adsorption isotherms along with the kinetic and thermodynamic parameters. The maximum capacity was evaluated as 1223 mg/g at 298 K using the Langmuir isotherm model and the adsorption followed pseudo-second order kinetics. XPS analysis was used to confirm chemisorption as the governing mechanism by strong lone pair interactions between S and Hg forming a Hg-S complex. The high negative zeta potential of Fe-TA (-18 mV) aided in strong electrostatic interactions with Hg²⁺ favoring the adsorption process. The selective affinity (K_d: 5.35 × 10⁵ mL/g) and substantial regenerative quality (>93%) of the adsorbent was also reported.