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

Abstract

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 °C) was larger than that at below LCST (10 °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, Δ 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 Δ Q and desorption ratio were largely influenced by both AA content and Cu(II) concentration.