In-situ fabrication of ionic liquids/MIL-68(In)–NH2 photocatalyst for improving visible-light photocatalytic degradation of doxycycline hydrochloride

Metal-organic framework (MOFs)-based composites have been popular in photocatalysis due to their outstanding physicochemical properties, such as large surface area, high activity and good transmission properties. Herein, a method of ionic liquids (ILs)-assisted synthesis of IL/MIL-68(In)-NH2 composite materials were proposed, and composites were used for visible light catalytic degradation of doxycycline hydrochloride (DOXH). The effects of four kinds of ionic liquids on the structure and photocatalytic properties of the composites were explored, including diethylenetriamine acetate ([DETA][OAc]), diethylenetriamine hexafluorophosphate ([DETA][PF6]), 1-ethyl-3-methylimidazole acetate ([EMIM][OAc]) and 1-ethyl-3-methylimidazole hexafluorophosphate ([EMIM][PF6]). The results show that the introduction of different ionic liquids affects the grain growth of MOFs material and photocatalytic activity. Among them, ILDAc/MIL-68(In)-NH2 samples showed the highest photocatalytic activity. 92% removal rate of doxycycline hydrochloride and kinetic degradation constant (0.00918 min-1) was observed under the optimal addition of ILDAc (10 wt%), which was 4.6 times that of MIL-68(In)-NH2. The enhancement was attributed to a combined effect of efficient adsorption at low concentration, an increase of active sites, and efficient charge transfer. In addition, the effects of pH and initial concentration were investigated. Finally, the photocatalytic mechanism of DOXH was elucidated, and the possible intermediate products and degradation pathways were discussed. Considering the excellent photostability and ultra-fast photodegradation of ILDAc/MIL-68(In)-NH2, this study opens up a new prospect for the preparation of ionic liquids functionalized MOFs with wide practical application value.