Saad Anthony, Mills Rollie, Wan Hongyi, Mottaleb M Abdul, Ormsbee Lindell, Bhattacharyya Dibakar
Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506-0046.
College of Medicine, University of Kentucky, Lexington, Kentucky 40506-0046.
J Memb Sci. 2020 Apr 1;599. doi: 10.1016/j.memsci.2020.117821. Epub 2020 Jan 17.
Perfluorochemicals (PFCs) are emerging contaminants in various water sources. Responsive polymers provide a new avenue for PFC adsorption/desorption from water. Poly-N-isopropylacrylamide's (PNIPAm's) temperature-responsive behavior and hydrophilic/hydrophobic transition is leveraged for reversible adsorption and desorption of PFCs. Adsorption of PFOA (perfluoro-octanoic acid) onto PNIPAm hydrogels yielded Freundlich distribution coefficients (K) of 0.073 L/g at 35 °C (above LCST) and 0.026 L/g at 22°C. Kinetic studies yielded second order rate constants (k) of 0.012 g/mg/h for adsorption and 12.6 g/mg/h for desorption, with initial rates of 28 mg/g/h and 41 mg/g/h, respectively. Interaction parameters of PNIPAm's functional groups in its different conformational states, as well as the hydrophobic fluorinated carbon tails and hydrophilic head groups of PFOA are used to describe relative adsorption. Polyvinylidene difluoride (PVDF) provides a robust membrane structure for the commercial viability of polymeric adsorbents. Temperature swing adsorption of PFOA using PNIPAm functionalized PVDF membrane pores showed consistent adsorption and desorption capacity over 5 cycles. PFOA desorption percentage of 60% was obtained in pure water at temperatures below PNIPAm's lower critical solution temperature (LCST) while 13% desorption was obtained at temperatures above the LCST, thus showing the importance of the LCST on desorption performance.
全氟化合物（PFCs）是各类水源中新兴的污染物。响应性聚合物为从水中吸附/解吸PFCs提供了一条新途径。聚N-异丙基丙烯酰胺（PNIPAm）的温度响应行为及其亲水/疏水转变被用于PFCs的可逆吸附和解吸。全氟辛酸（PFOA）在PNIPAm水凝胶上的吸附在35°C（高于最低临界溶液温度）时产生的弗伦德利希分配系数（K）为0.073 L/g，在22°C时为0.026 L/g。动力学研究得出吸附的二级速率常数（k）为0.012 g/mg/h，解吸的二级速率常数为12.6 g/mg/h，初始速率分别为28 mg/g/h和41 mg/g/h。PNIPAm不同构象状态下官能团的相互作用参数，以及PFOA的疏水氟化碳链尾和亲水头基，被用来描述相对吸附情况。聚偏二氟乙烯（PVDF）为聚合物吸附剂的商业可行性提供了坚固的膜结构。使用PNIPAm功能化的PVDF膜孔对PFOA进行变温吸附，在5个循环中显示出一致的吸附和解吸能力。在低于PNIPAm最低临界溶液温度（LCST）的纯水中，PFOA的解吸率为60%，而在高于LCST的温度下解吸率为13%，从而表明LCST对解吸性能的重要性。
