Metal–Organic Frameworks Bearing Dense Alkyl Thiol for the Efficient Degradation and Concomitant Removal of Toxic Cr(VI)

Abstract

Highly efficient removal of toxic Cr(VI) from aqueous media remains a crucial concern for ecosystem protection and public health. Herein, we demonstrated a new approach to solve this issue by constructing alkyl thiolcontaining Zr-based metal−organic framework (MOF) adsorbents using simple and inexpensive mercaptosuccinic acid (MSA) and meso-dimercaptosuccinic acid (DMSA) as ligands. These chemically stable MOFs could be prepared in an uncomplicated, green, cost-effective, and scalable way. The interaction mechanism between alkyl thiol groups in MOFs and Cr(VI) was investigated in detail. Thanks to the formation of a Cr(VI)−thiolate complex and the oxidation of thiol groups, these designed MOFs not only exhibited high Cr(VI) adsorption capacities (202.0 and 138.7 mg/g for Zr-MSA and Zr-DMSA, respectively) but also displayed the immobilization ability for concomitant resultant Cr(III). Even in the presence of high concentrations of possibly coexistent interfering ions, the thiol-containing MOFs can still work effectively to decontaminate the Cr(VI) species. In addition, the strategy of introducing thiol groups into MOFs for Cr(VI) reduction and concomitant Cr(III) immobilization is universal for other MOFs, as verified by thiol-containing UiO-66 and MOF-808 prepared by a one-pot method. Therefore, our work not only produces several effective Cr(VI) adsorbents but also sets a general guideline for the construction of Cr(VI) adsorbents by introducing thiol groups into porous materials.

Modulated synthesis of thiol-functionalized fcu and hcp UiO-66(Zr) for the removal of silver(i) ions from water

“…51 In 2019 Yang et al had briefly noted the idea of using mercaptoacetic acid as a modulator for the synthesis of a thiol-modified UiO-66 but concentrated on the use of thiol-modified mercaptosuccinate and dimercaptosuccinate linkers for the removal of chromates. 13 The powder X-ray diffraction (PXRD) patterns of UiO-66-MAc-X match the simulated pattern of fcu UiO-66 for X = 10, 30, 50 (Fig. 1).…”

“…Therefore, it corresponds well to previous reported uptake behaviors for the capture of Ag(I) and other heavy metal ions like Hg(II) with MOFs. 24,11,13 a) b) c) d) The uptake depends on the incorporated sulfur amount, which is around 1.5times higher in UiO-66-MAc-50eq over -100eq as determined in the CHNS analysis.…”

“…5 They are promising materials for applications in catalysis, 6 gas storage/separation 7 and for drug delivery. 8 Functionalized zirconium MOFs (Zr-MOFs), especially UiO-66, 9,10 a relatively water-stable MOF with the organic linker benzene-1,4-dicarboxylate (BDC 2-), 4 showed a promising potential for wastewater treatment as it is capable of removing heavy metal ions of mercury 11,12 and chromium 13 or other impurities. 14,15,16,17,24 In addition UiO-66 is regarded as non-toxic which is of great importance for the purification of water.…”

“…18,19,20 Thiol-modified Zr-MOFs should be useful for the uptake or removal of soft Lewis-acid metal cations like Hg 2+ and Ag + from water. To this day few thiol modifications of UiO-66 are reported in literature and were synthesized from thiolfunctionalized linkers 12,13,21 through postsynthetic linker exchange or linker modification. 12 Yee et al described the synthesis with 2,5-dimercapto-1,4-benzenedicarboxylic acid (H 2 DMBD), yielding UiO-66 type MOF which they tested for the removal of Hg 2+ .…”

“…21,22,23 Yang et al reported two UiO-type MOFs with the organic linkers mercaptosuccinic acid (MSA) and dimercaptosuccinic acid (DMSA) forming zirconium fumarate analogs Zr-MSA and Zr-DMSA with ~12 wt% sulfur for Zr-MSA and surface areas of 513 m 2 /g and 275 m 2 /g, respectively. 13 Just recently Ding et al postsynthetically introduced rhodanine into UiO-66 (UiO-66-Rd) and amino-functionalized UiO-66-NH 2 (UiO-66-NH 2 -Rd). The functionalized MOFs showed BET surface areas of 518-606 m 2 /g, sulfur contents of less than 5 wt%, and achieved high uptakes of silver from aqueous solution but at the expense of a decrease of crystallinity in PXRD and BET surface area.…”