Polymer Pendant Crown Thioethers for Removal of Mercury from Acidic Waste Streams-Characterization and Extraction Performance

Abstract

The removal and immobilization of mercury(II) ions from industrial waste streams is a difficult and expensive problem requiring a robust extractant that is resistant to corrosive conditions. We have now developed an acid-resistant thiacrown polymer that has potential utility as a selective and cost-effective Hg2+ extractant. A new crown thioether, 2-hydroxymethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-OH), was synthesized through reaction of 2,3-dimercapto-1-propanol with 4,7,10-trithiatridecane-1,13-di-p-toluenesulfonate; then treated with thionyl chloride to form 2-chloromethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-Cl); followed by conversion to 2-(N-methyl)aminomethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-NHMe), through reaction with methylamine. The synthesis of the 4-vinylbenzyl-substituted thiacrown was readily accomplished by treating with 4-vinylbenzyl chloride. Co-polymerization of the 4-vinylbenzyl-substituted thiacrown with DVB (80% divinylbenzene) using AIBN as the radical initiator generated the highly cross-linked crown thioether polymer. The polymer based material was tested for Hg(II) extraction activity from acidic solutions. The material was found to extract 95+% of the Hg in a pH range of around 1.5 to over 6.0, with contact times of less than 30 min and in the presence of high concentration of competing ions such as Pb, Cd, Al, and Fe. The spent polymer could also be stripped of the Hg2+ and reused without sufficient loss of loading capacity. Characterization of the binding sites by XPS and XAS show only some of the S atoms in the thiacrown participate in the binding of Hg. Our results indicate this polymer has the potential to treat highly acidic wastes efficiently. This thiacrown polymer is far more effective in extracting Hg2+ from aqueous solution than previously reported Hg2+ extrac-tants, not only being very fast and efficient and selective, but also independent of pH.

Metal Complexation of Thiacrown Ether Macrocycles by Electrospray Ionization Mass Spectrometry

“…Thiacrown ethers have been attached through covalent linkages to various linker groups which allow them to be incorporated into polymers. In these previous studies, macrocycles with sulfur heteroatoms were incorporated into a polymer by a lariat covalent linkage via an amine nitrogen or ether oxygen on the macrocycle. − Thiacrown ether macrocycle-based agents have recently been patented for use in extracting heavy metals for wastewater remediation. , Heavy metal extraction agents could be further improved by using structures that minimize the solubility in an aqueous environment and yet are able to efficiently extract the desired metal ion from the wastewater. For use in acidic, alkaline, or flowing systems, a rugged linkage to a stationary phase is desirable for the extracting agent.…”

Metallathiacrown Ethers: Synthesis and Characterization of Transition-Metal Complexes Containing α,ω-Bis(phosphite)-Polythioether Ligands and an Evaluation of Their Soft Metal Binding Capabilities

“…Due to the propensity of the sulfur atoms in thiacrown ethers to bind soft metal cations and small molecules, − the ability of the new metallathiacrown ethers 1 – 3 to bind group X soft metal chlorides of the type MCl 2 (M = Pd, Pt) has been evaluated using 31 P­{ 1 H} and 1 H NMR spectroscopy. Surprisingly, no changes in either the 31 P­{ 1 H} or 1 H NMR spectra were observed upon addition of PdCl 2 to solutions of 1 – 3 , suggesting that PdCl 2 does not strongly bind to the metallathiacrown ethers.…”

“…Due to their excellent selectivities for binding small molecules and metal cations, crown ethers have been studied for many years by both organic and inorganic chemists alike. − Modification of the crown ether ring with various functional groups has been used to provide additional donor sites, increase selectivity for specific substrates, or add a spectroscopic probe. − The heteroatom donor sites in these compounds have also been varied to enhance selectivities for specific classes of metal cations and metal-containing small molecules. For instance, hard metals such as the alkali metals show an increased selectivity for hard donor atoms such as oxygen (crown ether) and nitrogen (azacrown ether), , whereas metals such as those found in the fifth and sixth rows of the periodic table more strongly bind to soft donor atoms such as sulfur (thiacrown ether). − Due to their soft donor capability, thiacrown ethers, in particular, have found a wide variety of applications from toxic heavy metal sensing and removal agents to nanomaterials and anticancer agents. − …”

New Tin Templates for the Synthesis of Macrocyclic Polythiaether−Polythiaester Ligands

“…Novel macrocycles are currently being developed and evaluated for use as selective recyclable ligands for extraction of heavy metals from contaminated waters. , Both acyclic sulfur-containing ligands and cyclic crown thiaethers have been used in such applications. The addition of an aliphatic cage structure to crown thiaethers has resulted in several macrocycles that are insoluble in protic solvents such as water and methanol…”