Over-activity and stability of laccase using ionic liquids: screening and application in dye decolorization

Abstract

The use of a wide range of water miscible and immiscible ionic liquids (ILs) as reaction media for ABTS (2,2′-azino-bis(3ethylbenzothiazoline-6-sulfonic acid) diammonium salt) oxidation by Trametes versicolor laccase was studied. Thirteen ILs were shown to be suitable media for the laccase oxidation reaction, increasing the activity with respect to conventional media. Among them, the water-miscible IL choline dihydrogen phosphate [Chol][H 2 PO 4 ] allowed over-laccase activity with an enhancement rate of 451% at 25°C and pH 7.0. This ionic liquid improved the stability of the enzyme in the face of high temperature and high pH, while storage at room 10 temperature in aqueous medium was increased up to 4.5 times. Moreover, it was found that its use in the reaction medium for decolourizing dyes (antraquinonic and azoic) using laccase increased the decolourization rate by up to 216% and 137% for the azoic dyes Acid Black 1 and Remazol Brillant Blue R, respectively. A high decolorization rate was also obtained for a mix of dyes (80% within 8 h). To understand the effect of [Chol][H 2 PO 4 ] on the secondary protein structure of the laccase, several spectroscopic techniques were used 15 such as Circular Dichroism (CD), Fourier transform infrared (FT-IR) and Fluorescence, all of which demonstrated that the β sheets structure was affected. A shift to α-helix structure [Chol][H 2 PO 4 ] could be responsible of the enhancement of the enzyme activity observed at 300 mM 55properties of ILs, including their hydrophobicity, density, viscosity, melting point, polarity and solvent miscibility, can be finely tuned by selecting appropriate combinations of cations and anions, while an optimal IL can be designed for each specific enzymatic reaction system. Interest in these compounds, often 60 heralded as the green, high-tech media of the future, is still increasing rapidly, not only in biocatalysis but also in chemical catalysis, separation technology and analytical applications 13, 14 . Recently, the use of ILs with laccases has also been described as an efficient non-conventional catalyst system in applications such 65 as wood treatment and phenol degradation 3, 5 . On the other hand,Textile manufacturing involves the discharge of highly colored synthetic dye effluents which are aesthetically displeasing and can damage the receiving water body by impeding the penetration of light 15 . The strict environmental 70 legislation of European countries does not permit their release since they can have very severe consequences on river courses, including reducing photosynthetic activity and dissolved oxygen concentrations 16 . The great importance of effluent treatment has been underlined in many research-works 17 . In the textile 75 industry, a wide variety of dyes colors have been extensively used for textile industry, anthraquinonic and azoic dyes could be

Enhanced decolorization of aqueous dye solutions by a high quality copolymer flocculant

“…The value of n indicates the type of isotherm to be favorable (n > 1), unfavorable (n < 1), linear (n = 1). The high values of n (n > 2) at equilibrium at all 10 the temperature conditions indicated that biosorption of the dyes onto the CATCA flocculant were favorable processes. Temkin isotherm and the R-P isotherm constants and the correlation coefficients are listed in Table S1-S4 (in supporting information).…”

“…According to Chiou and Yoshida 27 charge dominates the surface of CATCS and strong electrostatic attraction exists between the positively charged surface of CATCS and negatively charged dyes. As the pH increased, the positive charge on CATCS reduced which made electrostatic attraction force decline and the existence of excess OHions will 10 compete with dye anions for the adsorption sites 29 , therefore prevented the adsorption of dye anions on the adsorbent surface.…”

“…The constant K a was determined by plotting ln(q e /Ce) versus q e 10 and extrapolating zero q e 40 . The plot of lnK a as a function of 1/T yields a straight line from which ΔH and ΔS were calculated from the slope and intercept, respectively.…”

“…However, with increasing diversity of 30 industrial products, the ingredients of dye wastewater have become more and more intricate in recent years, which make color removal one of the most difficult tasks 6, 7 . Methods for processing dye wastewater involve physical, chemical and biological approaches [8][9][10][11] . Techniques such as 35 adsorption, coagulation, chemical oxidation ， electrolysis, and biological treatment, have been extensively applied in dye wastewater treatment.…”

“…Thermodynamics and kinetics of the decolorization process was investigated in details and the decolorization mechanism of CATCS was determined. 10 …”