Ni(II) triggered sensing and reversible uptake of ammonia by tetrazole based Ni(II) metallogel: A one-pot mechanistic approach

Abstract

The release of ammonia gas and its removal through traditional approaches is a critical challenge inhibiting the sustainability of chemical industries. The quest to improve sustainability has triggered interest to develop chemoprobe and reusable adsorbent for toxic gases such as ammonia. The present study offers the first example of a novel one-pot synthesis of a stable Ni(II)metallogel (Ni(II)MG) from 1, 4 adiponitrile and sodium azide. The Ni(II)MG is composed of Ni(II) coordinated with four in-situ formed CN-Tz (5-(1H-tetrazol-5-yl)pentanenitrile) ligands and two water molecules forming predominant octahedral geometry. The Ni(II)MG has good strength, and viscoelastic, thixotropic, and self-healing properties. The Ni(II)MG and its xerogel (Ni(II)XG) have been thoroughly characterized and utilized for ammonia sensing and reversible adsorption at ambient condition. The mesoporous nature and presence of hydrogen-bonded water molecules in the pores make this material effective for reversible adsorption of ammonia. The lewis acidic Ni(II) increases the cloud network of hydrogen-bonded water molecules and triggers the coordinated water molecules to activate hydrogen-bonded water molecules for binding the ammonia molecules. The Ni(II) triggered extended hydrogen bonding through coordinated water molecule is also supported by DFT studies. The Ni(II)XG shows good ammonia adsorption capacity (8 mmol/gm) which is confirmed by TPD studies. The properties of Ni(II)XG are found to be intact after ammonia adsorption even after 20 cycles. Hence, it could be a promising low cost, sustainable and reusable material as a chemoprobe for removal of ammonia.