Petrochemical residue-derived silica-supported titania-magnesium catalysts for the photocatalytic degradation of imidazolium ionic liquids in water

The ionic liquids 1-n-butyl-3-methylimidazolium chloride (C(4)MImCl), 1-n-butyl-3-methylimidazolium hexafluorophosphate (C(4)MImPF(6)), 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C(4)MImNTf(2)), 1-n-butyl-2,3-dimethylimidazolium chloride (C(4)MImCl) and 1-n-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide (C(4)MMImNTf(2)) were degraded under UV and visible radiation in the presence of a silica-supported photocatalyst (SiTi), which was derived from a petrochemical residual catalyst slurry rich in titanium and magnesium. These ionic liquid advanced oxidation processes were studied by UV spectroscopy and electrospray ionization mass spectrometry. After 120 min of irradiation, 50.2, 48.7, 45.3, 40.7 and 35.3% of C(4)MImCl, C(4)MImPF(6) , C(4)MImNTf(2) , C(4)MMImCl and C(4)MImNTf(2) were degraded under UV and 45.4, 43.6, 40.2, 36.8 and 32.7% of C(4)MImCl, C(4)MImPF(6) , C(4)MImNTf(2) , C(4)MMImCl and C(4)MImNTf(2) were degraded under visible light, respectively. The commercial titania P25 catalyst degraded 66.3 and 50.2% of C(4)MImCl under UV and visible radiation, respectively. Regarding the stability of photocatalyst SiTi, it was reused five times with only minor loss of catalytic activity. Doping of SiTi with 25 wt% Mg2+/SiO2 resulted in improved degradation values of 64.6% (UV irradiation) and 65.3% (visible irradiation) of C(4)MImCl. Cytotoxicity assays (MTT reduction and Neutral Red incorporation) on NIH/3T3 cells after 24 h of irradiation of C(4)MImCl indicated the absence of in vitro cytotoxicity. Altogether, this study opens new opportunities for the management of petrochemical waste, providing access to effective and stable heterogeneous photocatalysts for the degradation of imidazolium ionic liquids.