Zr-based Metal-organic Framework [Zr6O4(OH)4(3.2b-ttdc)6] for Effective Mercury (II) Sorption from Water
Authors: Shuvaeva Olga V. , Volynkin Sergey S. , Romanova Tamara E. 
Published: January 2025

Abstract:
The objective of this work is to study MOFs with ligands containing thienothiophene
groups as linkers and evaluate their practical application as sorbents for mercury removal from water.
This evaluation will be compared with MOFs containing 2,6-naphthalenedicarboxylic acid and
terephthalic acid linkers.
The study of Hg2+ sorption from solutions was carried out by shaking the MOFs (10 mg) with the
solution at 25 °C for 24 hours. Determination of chemical elements in solutions was performed using
an Agilent 8800 triple quadrupole ICP-MS spectrometer (ICP-QQQ) equipped with an octopole reaction-
collision cell in a standard configuration.
Within 24 hours, 97.8% of Hg2+ ions were removed from the solution, even at an initial Hg2+ concentration
as low as 1 mg·L-1. An important part of the work was studying the possibility Zr-ttdc regeneration
for repeated use. Using iodide solution as a desorbing agent proved more productive, ensuring
the desorption of Hg2+ through competitive complex formation due to the high stability constants
of the corresponding mercury complexes. With a 0.1 M potassium iodide solution at pH 6.5, 99% of
the sorbed mercury was desorbed in one desorption cycle.
The efficiency of [Zr6O4(OH)4([3.2-b]ttdc)6] in adsorbing mercury from aqueous solutions was thoroughly
evaluated and compared to [Zr6O4(OH)4(bdc)6] and [Zr6O4(OH)4(2.6-ndc)6], which lack sulfur-
containing linkers. The findings highlight the potential of functionalized MOFs for water purification
as well as application in analytical chemistry for the concentration of mercury. Notably,
[Zr6O4(OH)4([3.2-b]ttdc)6] demonstrated stability in water in a wide pH range, underscoring its
promise for diverse environmental chemistry applications.

result:
In this study, investigation of a new member of the MOFs family with thienylthiophenic acid (H2ttdc) as a dicarboxylate bridging ligand, were conducted. To elucidate the mechanism of mercury sorption by MOFs, a series of experiments were performed using sorbents based on various organic blocks, including 2,6-naphthalenedicarboxylic acid, thieno[3,2-b]thiophenic acid, and terephthalic acid. To evaluate the kinetics of the adsorption process, the effect of contact time on the sorption efficiency was studied. Within 24 hours, 97.8% of Hg2+ ions were removed from the solution, even at an initial Hg2+ concentration as low as 1 mg∙L-1. This demonstrates the high sorption efficiency of Hg2+ by Zr-ttdc from aqueous solutions. Depending on the source, a number of other elements (Cu, Pb, Zn, Fe, Mn, etc.) may also be present. Their influence on the efficiency of mercury sorption under optimal conditions was studied and it was shown that interfering effects from cations are practically absent. The situation is completely different for anions. Due to competitive complex formation, mercury sorption can be suppressed. It was shown that anions such as nitrate, sulfate, formate, and acetate at concentrations of 100 mg·L-1 do not affect mercury sorption efficiency. However, in the presence of chloride or iodide, sorption is suppressed. In the case of chloride, the sorption efficiency decreases to 90% and below when the chloride concentration in the solution is 50 mg/L and higher. An important part of the work was studying the possibility Zr-ttdc regeneration for repeated use. Using iodide solution as a desorbing agent proved more productive, ensuring desorption of Hg2+ through competitive complex formation due to the high stability constants of the corresponding mercury complexes. With a 0.1 M potassium iodide solution at pH 6.5, 99% of the sorbed mercury was desorbed in one desorption cycle. The feasibility of reusing the sorbent was demonstrated with potassium iodide solution regeneration over 6 sorption-desorption cycles.