Temperature-swing adsorption of 4-isopropylphenol and bisphenol A onto a poly(N-isopropylacrylamide)/silica gel composite

Abstract

Poly( N -isopropylacrylamide) (poly(NIPA)) is a thermosensitive polymer, with a lower critical solution temperature (LCST) of ~33 °C in water. Herein, a poly(NIPA)/silica gel composite was developed as an adsorbent for the temperature-swing adsorption (TSA) of organic pollutants in aqueous media. Poly(NIPA) was grafted onto a millimeter-sized silica gel by silane coupling, followed by free radical polymerization. The composite reversibly adsorbed/desorbed organic pollutants such as bisphenol A and 4-isopropylphenol by changing the temperature across the LCST range to modulate the hydrophilicity/hydrophobicity of poly(NIPA). The adsorption isotherms and kinetics were evaluated through a batch experiment. A continuous TSA process using a fixed-bed column with adsorption at 40 °C followed by desorption at 20 °C was demonstrated. The associated breakthrough curve was predicted by a mathematical analysis involving the Henry constant and effective diffusivity. The composite overcomes drawbacks such as a low mechanical strength and thermosensitive volume change of conventional poly(NIPA) gels. Thus, this study provides a strategy for preparing an environmentally friendly adsorbent and designing an adsorption process for wastewater treatment and conservation of water environments. • A thermosensitive poly( N -isopropylacrylamide)/silica gel composite was developed. • The composite adsorbed/desorbed organic pollutants with a change in temperature. • The adsorption isotherms and kinetics were investigated. • A continuous temperature-swing adsorption process was demonstrated and designed. • It is an environment-friendly way for wastewater treatment and water conservation.