October 2021 – Seminar

Dr. Gellert Mezei, Removal of anionic contaminants from water using nanojars

Zoom Event – Email edwardwthomas@gmail.com for an invite to event

Selective binding and transport of highly hydrophilic anions is ubiquitous in
nature, as anion binding proteins can differentiate between similar anions with
over a million-fold efficiency. While comparable selectivity has occasionally been
achieved for certain anions using small, artificial receptors, the selective binding
of certain anions, such as sulfate in the presence of carbonate, remains a very
challenging task. Nanojars have emerged as a new class of anion binding and
extraction agents of unparalleled efficiency. Nanojars are neutral, nano-sized
toroidal copper(II)-hydroxide/pyrazolate assemblies comprised of a series of
homologous oligomerization isomers of the formula [anion{Cu(OH)(pz)} n ] (Cu n ; n
= 26−36; pz = pyrazolate, C 3 H 3 N 2 – ), which strongly bind hydrophilic anions such as
carbonate, sulfate and phosphate, as well as the toxic anions arsenate and
chromate. By using a combination of single-crystal X-ray crystallography,
electrospray-ionization mass spectrometry (ESI-MS) and 1 H-NMR spectroscopy, it
has been determined that the various Cu n nanojars are based on a combination of
three or four [Cu(OH)(pz)] m metallamacrocycles (m = 6−14, except 11), tightly held
together by a network of hydrogen bonding and Cu-O interactions.
Two challenging problems in the field of anion binding and extraction have
been successfully addressed by using nanojars as extraction agents. First, nanojars
are able to extract even the most hydrophilic anions, such as carbonate and
sulfate, from water into aliphatic hydrocarbons. Second, nanojars are able to
selectively extract strongly hydrophilic anions in the presence of less hydrophilic
anions. Moreover, rigidification of the nanojar outer shell by tethering pairs of
pyrazole ligands together leads to further increase of selectivity. Nanojars
prepared with tethered pyrazole ligands of the formula pz(CH 2 ) x pz selectively bind
either carbonate (when x = 2) or sulfate anions (when x = 3). Anion extraction
studies have shown that by using nanojars, the concentration of arsenate and
chromate ions in aqueous media can be lowered below EPA-permitted levels in
drinking water. Furthermore, nanojars can be used for the selective sequestering
of CO 2 from the air in the presence of other atmospheric gases by conversion to
carbonate.