Straight-chained thermo-responsive polymer with high chelating group content for heavy metal ion recovery

A straight-chained thermo-responsive adsorbent with high chelating group content was synthesized to obtain high adsorption capacity for the recovery of heavy metal ions. 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. Detailed examinations of the effect of chelating group content and the concentration of heavy metal ion on the thermo-responsive properties and adsorption/desorption characteristics were also performed. The results exhibited that although the poly(NIPAM-co-AA)with high AA content (more than 27.3 mol%) lost a thermo-response at pH 5.0, when the poly(NIPAM-co-AA) adsorbed Cu(II), even the copolymer with 60 mol% AA exhibited thermo-response. This result indicates that the 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. A detailed examination of the effect of AA content, Cu concentration and temperature on adsorption/desorption behavior of the poly(NIPAM-co-AA) suggested that the copolymer exhibited the Langmuir type adsorption, but the adsorption capacity at above LCST (60 degrees C) was larger than that at below LCST (10 degrees C). It was also found that the temperature change did not affect the saturated adsorption capacity, Q(s), but affected the affinity constant, K. Based on the obtained saturated adsorption capacity, Q(s) and the affinity constant, K, the desorbed amount, Delta Q and the desorption ratio of Cu(II), R, were calculated for the AA introduction amount of 0-60 mol% and for Cu(II) equilibrium concentration of 0-20 mol/m(3). The results showed that both of Delta Q and desorption ratio were largely influenced by both AA content and Cu(II) concentration. (C) 2010 Elsevier B.V. All rights reserved.