Reactive Nanoparticles Immobilized In Temperature- Responsive Hydrogel for Toxic Organics Degradation

The application of temperature responsive hydrogels for nano-scale catalytic reactions is an emerging and attractive area because of the combination of their individual unique features: temperature responsive tunability of the hydrogel and the high catalytic reactivity of the nano material. Inspired by these advantages, for the first time we successfully integrated the features of temperature responsive hydrogels in biology and biomedicine, and extended the application to the area of toxic organic dechlorination from water. Compared to the traditional water dechlorination treatment by using nanoparticles in bulk phase which are environmental harmful, the temperature responsive hydrogels immobilized nanoparticles are friendlier to the environment and reactivity controllable by the temperature.

In our method, the reactive Fe and Fe/Pd nanoparticles (about 40-70 nm) are entrapped and/or direct synthesized in the non-toxic hydrogel network which has two components: (1) N-isopropylacrylamide (NIPAAm) functioning as a reactivity-controller of the dechlorination through swelling and shrinking in response to temperature change; and (2) acrylic acid (AA) functioning as a scaffold to pick up and prevent the nanoparticles from leaching. Equilibrium adsorption of trichloroethylene (TCE) and 3,3',4,4',5-Pentachlorobiphenyl (PCB 126) through temperature responsive P(NIPAAm-AA) hydrogel indeed demonstrated higher partitioning for both compounds above lower critical solution temperature (LCST) as the enhancement of adsorption amount due to the hydrophobicity increase above LCST. Mass balance was calculated and indicated almost no loss of TCE and PCB 126. To prove the tunable reactivity, we performed dechlorination study with TCE below and above LCST. The reactivity indeed increased above LCST. The surface area normalized reaction rate (k_SA) for Fe/Pd (1.5 wt% as of Fe) immobilized in P(NIPAAm-AA) hydrogel indicated three-fold increase from 0.0156 to 0.0411 L/m²h. Since the reaction rates can be enhanced with the temperature increase, for comparison, dechlorination with Fe/Pd in solution phase has also been done and showed only two-fold increase of reactivity, which demonstrated the role of partitioning. The Fe/Pd NPs (2.1 wt% Pd) have been synthesized in situ in the hydrogel and used for PCB 126 degradation. Complete degradation has been achieved within 3 h, with biphenyl as the only product. 

This research was supported by NIEHS-SRP and by DOE-KRCEE.