Enhanced catalytic activity and thermal stability of 2,4-dichlorophenol hydroxylase by using microwave irradiation and imidazolium ionic liquid for 2,4-dichlorophenol removal

Abstract

Enzymatic removal of 2,4-dichlorophenol (2,4-DCP) has become more attractive recently due to its high efficiency, low cost and environmental benefits. A highly active 2,4-DCP hydroxylase for 2,4-DCP removal was obtained and used in 2,4-DCP removal by employing microwave irradiation as a heating mode and ionic liquid (IL) as an additive. Both [EMIM][PF₆] (1-ethyl-3-methylimidazolium hexafluorophosphate) and microwave irradiation were found to increase the 2,4-DCP removal efficiency and the thermal stability of 2,4-DCP hydroxylase, and a further incremental effect of microwave irradiation and [EMIM][PF₆] on improving the 2,4-DCP removal efficiency and enzymatic thermal stability was observed. Conditions for 2,4-DCP removal were optimized and the removal of 2,4-DCP was completed in 15 min at 25 °C with 0.66 ± 0.015 U mg⁻¹ enzyme activity under the optimum conditions, much faster than the present enzymatic removal route, which took several hours for complete 2,4-DCP removal. Only 30 min were required for complete 2,4-DCP removal by using the 2,4-DCP hydroxylase at 4 °C, indicating its psychrotrophic adaptability. These results showed that the use of 2,4-DCP hydroxylase under microwave in [EMIM][PF₆] is a fast, efficient and environmentally benign method for the removal of 2,4-DCP, and this method can be used over a wide temperature range.