Thermochromism, stability and thermodynamics of cobalt(ii) complexes in newly synthesized nitrate based ionic liquid and its photostability

Abstract

In this work a 1-(2-hydroxyethyl)-3-methylimidazolium nitrate ionic liquid, [HO(CH2)2mim]NO3, has been synthesized in order to serve as a new thermochromic material upon addition of cobalt(II) ions. Spectrophotometric measurements of a series of cobalt(II) nitrate and cobalt(II) chloride solutions in [HO(CH2)2mim]NO3 at 298.15, 308.15, 318.15, 328.15, and 338.15 K, were performed. Based on the recorded spectra, the overall stability constants and thermodynamic parameters for the cobalt(II) associations with chloride and nitrate ions were calculated. The thermodynamic calculations suggest that thermochromism is not observed in the ionic medium due to a small entropy change during the replacement of nitrate with chloride ions in the co-ordination sphere of cobalt(II). The absence of the molecular solvent was also the reason for the lack of thermochromism. Thus, cobalt(II) solutions in [HO(CH2)2mim]NO3 and water mixtures were studied as a new and green medium that can be used for the auto-regulation of the light intensity and shade protection. The investigated system with water upon addition of cobalt(II) was found to be a far more efficient and responsive thermochromic medium for all of the studied systems up until now. The structure of [HO(CH2)2mim]NO3 was confirmed by both (1)H NMR and IR spectroscopy. Also, the efficiency of different advanced oxidation processes (UV-induced photolysis, UV/H2O2 photolysis, heterogeneous photocatalysis using TiO2 Degussa P25 and TiO2 with 7.24%, w/w Fe catalysts) for [HO(CH2)2mim]NO3 degradation were investigated. The reaction intermediates formed during the photo-oxidation process were identified using LC-ESI-MS/MS and (1)H NMR techniques.

Advanced oxidation processes for the removal of [bmim][Sal] third generation ionic liquids: effect of water matrices and intermediates identification

“…On the other hand, the [Sal] À showed UV absorption at a broader range between 200 and 335 nm, with three absorption maxima at 205, 236, and the lowest at 303 nm. Since the UV radiation of used lamp below of closely 275 nm cannot pass through Pyrex glass, 25 no direct photolysis of [bmim] + could be expected. Also, observing the radiation of lamp which passed through the wall of the reactor and the absorption spectrum of absorbed radiation by [Sal] À in the range of 275 to 335 nm, a direct photolysis of the [Sal] À could be possible.…”

“…Thus, it is very important to nd an efficient method for a complete and safe removal of ionic liquids from the environment. [23][24][25] The advanced oxidation processes (AOPs), for example, UVA/H 2 O 2 , UVA/Fe 2+ /H 2 O 2 , and UVA/TiO 2 are potentially useful for wastewater treating because they generate hydroxyl radicals, [26][27][28] a powerful nonspecic oxidant, and can provide an almost total degradation. 29 Among numerous AOPs, Fenton's process is one of the promising technologies because of the high oxidation potential and relatively low cost.…”

Thermochromism and switchable paramagnetism of cobalt(ii) in thiocyanate ionic liquids

“…1,[9][10][11][12] While ionic liquid systems with thermochromism related to changes in coordination of the metal centre have previously been reported, this has either been in the presence of additives or molecular solvents, or the magnetic properties were not investigated. [13][14][15][16][17] Here, we report on solutions of cobalt(II)isothiocyanate in thiocyanate ILs that show reversible switching of the cobalt(II) speciation from tetrahedral [Co(NCS)4] 2at room temperature to octahedral [Co(NCS)6] 4at temperatures around 233 K. These temperature-dependent changes in the co-ordination environment are accompanied by reversible changes in colour (blue to red) and by significant changes of the effective magnetic moment of these fluids. The IL acts as a reservoir for the thiocyanate anions, enabling a reversible equilibrium, which in turn results in a reversible temperature-dependent switching of the coordination environment; hence a reversible switching of the magnetic moment.…”

High‐performance liquid chromatography/high‐resolution mass spectrometry for the characterization of transformation products of ionic liquids

“…Ionic liquids (ILs) are a subject of active research in the field of alternative solvents, being promoted as “green chemistry” replacements to traditional solvents used in industry . The great interest in these compounds relies on their attractive properties such as low vapour pressures and flammability, chemical and thermal stability, high ionic conductivity, wide electrochemical potential window and ability to behave as catalysts …”

“…1 The great interest in these compounds relies on their attractive properties such as low vapour pressures and flammability, chemical and thermal stability, high ionic conductivity, wide electrochemical potential window and ability to behave as catalysts. [2][3][4] Only few studies have reported on the environmental fate of ILs. 5 Photochemistry is a potentially important attenuation route influencing the fate of ILs in surface waters.…”