| Spherical polyelectrolyte brushes (SPB) are systems in which polyelectrolyte chains are attached densely to spherical nanoparticales, which have been widely used for immobilize nanoparticles, proteins adsorption and separation due to their unique structure and characteristics. It is hard to remove the SPB from solution which has limited the application of SPB in the field of selective separation of dye wastes. It is known that CO2 has many applications in material science. One of the useful techniques is the gas antisolvent process, which has been widely used in many processes, such as extraction, fractionation, recrystallization of chemicals and micronization. In this paper, SPB can be separated from solution perfectly by the easy control of CO2 pressure. Therefore, in this contribution, it is possible to utilize SPB as a platform and compressed CO2 as antisolvent to separate dye wastes from organic solution.The main works and results are summarized as follows:1. The anionic SPB (PS-PAA) consisted of a polystyrene core and poly(acrylic acid) chains was synthesized. In this paper, novel method for highly selective separation methylene blue (MB) has been proposed which employed spherical polyelectrolyte brushes as adsorbent while compressed CO2 as antisolvent. Firstly, MB was absorbed byPS-PAA. Then, the PS-PAA and absorbed dyes can be precipitated simultaneously from organic solutions by the easy control of CO2 pressure. The effects of serveral parameters such as CO2 pressures, initial dye concentration, contact time and temperature on the separation efficiency have been determined. The kinetic data were well fitted to pseudo-second-order kinetic model and Weber’s intraparticle diffusion model indicated that intraparticle diffusion of MB was the not rate-limiting step in the adsorption process. The adsorption isotherm data were treated according to Langmuir and Freundlich models and the best fit was the Freundlich model.2. Cationic SPB, consisting of a polystyrene (PS) core and a poly (2-aminoethylmethacrylate hydrochloride) (PAEMH) shell densely grafted on the core surface, were synthesized by photoemulsion polymerization. PS-PAEMH was utilized as a platform and CO2 was used as an antisolvent to remove anionic dye, eosin Y (EY), from solution. Differnet techniques, such as FTIR, UV, DLS and phase state research, were used to study the process. The adsorption behavior of EY onto PS-PAEMH was highly dependent on CO2 pressure, contact time and initial concentration. The separation efficiency of dyes increas with the increasing of CO2 pressure and the adsorption capacity of PS-PAEMH increased with the increasing of initial EY concentration. Adsorption reached equilibrium after 20 min and the maximum adsorption capacity of PS-PAEMH is 335.20 mg/g which is larger than other adsorbents. PS-PAEMH can preferentially and thoroughly adsorb anionic dye from mixed dye solutions due to the electrostatic interaction between PS-PAEMH and EY. The absorbed dyes could be eluted by salt solutions, and the regenerated PS-PAEMH has highly adsorption capacity for EY even after five times.3. Nonionic SPB (PS-PNIPA) composed of a polystyrene (PS) core and poly (N-isopropylacrylamide) were successfully synthesized. Separation performances of PS-PNIPA for different dyes were studied. The PS-PNIPA exhibited a less adsorption of cationic dyes, anionic dyes and nonionic dyes. It proved that the binding of dyes onto SPB were dominated by electrostatic interaction in another way. |
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