Novel aqueous two-phase systems containing polymer-based deep eutectic solvent and citrate salts for high-performance extraction of dyes

Abstract

• ATPs containing DESs and sodium or potassium citrate were studied. • The effects of salt and temperature on phase separation were discussed. • The ATPSs were used for extraction of methyl orange, methylene blue and congo red. • Higher extraction efficiency was obtained with congo red than the other dyes. The release of synthetic dyes into the aquatic environment, cause to both economic and environmental concerns owing to its pernicious effect. Until now, various dyes removal methodologies have been developed much attention in separation fields. Aqueous two-phase systems (ATPSs) are considered as utmost important and significant method for the separation field because the main component of the two phases is water. In the current study, the ATPSs have been constructed by either polypropylene glycol 400 (PPG 400 ) or deep eutectic solvent (DES) based on PPG 400 and tetrabutylammonium bromide (TBAB) with two citrate salts (sodium or potassium). These systems have been applied to explore their capability for the partitioning and separation of the dyes namely methyl orange (MO), methylene blue (MB), and congo red (CR) from aqueous media. The binodal data were experimentally measured by the clouding point method at temperatures T = (298.15, 303.15, 308.15, and 313.15) K under 85 kPa. The obtained partition coefficients ( K ) and extraction efficiencies ( EE %) demonstrate that the mentioned dyes preferentially were distributed into the PPG 400 or DES-rich phase. The measured binodal data were fitted by two semi-empirical Merchuk and Zafarani-Moattar et al. equations. The salt effect indicates that the ability of Na + is more than K + , which follows the Hofmeister series and can be related to the ions Gibbs free energy of hydration ( Δ G hyd ). Finally, it can be observed that the potential of the studied dyes to transfer into the top phase obeyed the following trend: CR > MO > MB in all the studied systems and the ATPSs methodology provided a high degree of dye removal (98%) from the water.