Smart Adsorbents Functionalized with Thermoresponsive Polymers for Selective Adsorption and Energy-Saving Regeneration

Abstract

Selective adsorption and energy-saving regeneration are two important issues for adsorptive separation. However, it is impossible for traditional adsorbents with changeless pore properties to realize both of them. In this study, a strategy was proposed to design and fabricate a new generation of adsorbents via grafting the thermoresponsive polymers (TPs), namely, poly(N-isopropylacrymide) (PNIPAM), onto the pore surface of mesoporous silica SBA-15. The TPs disperse homogeneously in pore space and act as molecular switches which are reversibly closed or opened with the change of temperature. At the temperature of adsorption below the lower critical solution temperature (LCST), TPs are extended as a result of their extensive hydrogen bonding interactions with water and the molecular switches are closed. It is easier for smaller adsorbates to enter than larger ones, and the selective adsorption can be consequently realized. At the temperature of desorption (above LCST), TPs shrink owing to their hydrogen bonding between polymer molecules and promote desorption of adsorbates owing to the opened molecular switches. The smart adsorbent can thus realize selective adsorption and energy-saving desorption responsive to adsorption/desorption conditions by tunable pore properties. This is impossible for traditional adsorbents with changeless pores, although selective adsorption and energy-saving regeneration are extremely desired for adsorptive separation.