Development of Separation and Concentration of a Trace of Substance by Thermo-sensitive Heteropolymer Gels

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The adsorption property of the polyampholyte gel composed of sodium styrene sulfate (SSS) and vinylbenzyl trimethylammonium chloride (VBTA) has been investigated at different temperatures with hydrophobic aromatic compounds as adsorbate. Using the N-isopropylacrylamide (NIPA) gel, the corresponding experiments were also carried out for comparison. At room temperature, the NIPA gel hardly adsorbed the aromatic compounds, while it adsorbed them at higher temperatures. In contrast with the adsorption behavior of the NIPA gel, the adsorption amounts of the aromatic compounds for the SSS-VBTA gel decreased with increasing temperature. Also, it has been demonstrated that the SSS-VBTA gel can repeatedly adsorb bisphenol-A at 298 K and desorb it at 353 K by the temperature-swing operation : this adsorption/desorption behavior of the SSS-VBTA gel is diametrically opposite to that of the NIPA gel. This shows that the SSS-VBTA gel is much more suitable for the adsorption removal of the hydrophobic aromatic compounds from very dilute aqueous solutions, because a vast amount of energy is required for heating a large amount of water to adsorb the hydrophobic compounds using the NIPA gel. The SSS-VBTA gel which was grafted on the innersurface of porous silica gel particles showed ad-and desorption reversibly for hydrophobic aromatic compounds under the temperature-swing operation.