(16a) Straight-Chained Thermo-Responsive Polymer for Heavy Metal Ion Recovery

A straight-chained thermo-responsive polymer for heavy metal ions recovery was developed. The polymer was synthesized through free radical copolymerization of N-isopropylacrylamide (NIPAM) as a thermo-responsive element and acrylic acid (AA) as an interactive element. The thermo-response of poly NIPAM was weaken by incorporating of AA due to the hydrophilicity of AA, and poly (NIPAM-co-AA) containing more than 27.3 mol% of AA lost the thermo-response at pH 5.0. However, despite the high AA amount, the poly (NIPAM-co-AA) with even 60 mol% AA exhibited the thermo-response when the poly (NIPAM-co-AA) adsorbed Cu(II). This result indicates that poly (NIPAM-co-AA) can exhibit considerably higher adsorption capacity (1 order higher) due to higher introduction amount of the interactive element compared to the previously reported cross-linked thermo-responsive adsorbents. The experimental results of Cu(II) adsorption and desorption on the obtained copolymers showed that the Cu(II) adsorption behavior of poly (NIPAM-co-AA) can be explained by the Langmuir model adsorption. However, different from normal physical adsorption, the adsorbed amount of Cu(II) on the copolymer increased with the temperature raise. Also, the reversible control of the adsorption and desorption of Cu(II) was achieved by temperature swing between 10 and 60 ºC. It was suggested that the conformational changes of poly NIPAM contributed the adsorption/desorption behavior of Cu(II). The desorbed amount and desorption ratio of Cu(II) was finally calculated by using the results of Langmuir analysis. The result showed that the desorbed amount and desorption ratio were largely influenced by both AA content and Cu(II) concentration.