In
this work, we investigated SO2 absorption by deep
eutectic solvents (DESs) formed by 1-ethyl-3-methylimidazolium chloride
(EmimCl) and ethylene glycol (EG) under different conditions. DESs
with different molar ratios of EmimCl and EG (from 2:1 to 1:2) were
prepared. The results showed that all the EmimCl-EG solvents were
very efficient for SO2 capture. It was demonstrated that
the SO2 solubility increased with increasing concentrations
of EmimCl in DESs. The effects of temperature and SO2 partial
pressure were also investigated. The Emim-EG (2:1) solvent could absorb
1.15 (53 wt %) g SO2/g solvent at 20 °C and 1.0 atm,
a much higher capacity than that of other DESs reported to date under
the same conditions. Moreover, the SO2 desorption temperature
of the solvents could be tuned by changing the composition of the
solvents, and all the EmimCl-EG solvents showed excellent reversibility.
Nuclear magnetic resonance and Fourier transform infrared spectra
showed the interactions of the solvents and SO2.
In
this work, the anion-functionalized deep eutectic solvents (DESs)
comprising solid organic salt tetraethylammonium tetrazolate ([N2222][Tetz]) and ethylene glycol (EG) at a molar ratio 1:2
were synthesized to capture SO2. DESs [N2222][Tetz]-EG(1:2) could capture 0.853 g of SO2/g solvent
(4.31 mol SO2/mol solvent) at 1.0 atm and 20 °C. Interestingly,
[N2222][Tetz]-EG(1:2) exhibited a high SO2 absorption
capacity of 0.140 g of SO2/g solvent (0.708 mol SO2/mol solvent) at 2000 ppm, which was much higher than the
absorption capacity (0.002 g of SO2/g solvent or 0.009
mol SO2/mol solvent) of non-functionalized DESs consisting
of tetraethylammonium chloride ([N2222][Cl])-EG(1:2) under
the same conditions. Moreover, [N2222][Tetz]-EG(1:2) can
be reused and showed good reversibility. Nuclear magnetic resonance
and Fourier transform infrared results indicated that the high SO2 absorption capacity of [N2222][Tetz]-EG(1:2) was
due to the chemical reaction between SO2 and anion [Tetz]−, and the SO2 absorption enthalpy of [N2222][Tetz]-EG(1:2) was −52.7 kJ/mol which also confirmed
the strong interaction between SO2 and [N2222][Tetz]-EG(1:2).
Despite the great achievements of advanced photoredox catalysis for organic‐synthetic reactions, the literature is rather vague with respect to reaction quantum yields – the number of product molecules per absorbed photon. This stands in contrast to the clear and commonly used chemical yield as standard parameter to quantify the efficiency of chemical reactions. We applied an opto‐electronic device to measure the reaction quantum yields of a reference reaction in a rapid and facile way, which revealed that this parameter cannot be regarded as a single, isolated value. A so far undescribed strong dependence of the reaction quantum yield on the incident light power and the irradiation time was revealed. The light input even decides on the interplay of the closed photoredox catalytic cycle and the radical chain propagation. The reaction kinetics were modelled in full detail to obtain important insight into the general description of photoredox catalytic mechanisms.
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