Selective Recognition of 2,4,6-Trichlorophenol by Molecularly Imprinted Polymers Based on Magnetic Halloysite Nanotubes Composites

Magnetic nanoparticles were attached to carboxylic acid functionalized halloysite nanotubes (HNTs-COOH) by high-temperature reaction of ferric triacetylacetonate in 1-methyl-2-pyrrolidone. Then, based on magnetic halloysite nanotubes particles (MHNTs), the magnetic molecularly imprinted polymers (MMIPs) were synthesized for the selective recognition of 2,4,6-trichlorophenol (TCP). MMIPs were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) analysis, thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), elemental analysis, and Raman spectroscopy. MMIPs were demonstrated with an imprinted polymer film (5.0-15.0 nm) and exhibited magnetic property (M-s = 2.74 emu g(-1)) and thermal stability. Batch mode adsorption studies were carried out to investigate the specific adsorption equilibrium, kinetics, and selective recognition. The Langmuir isotherm model was fitted to the equilibrium data better than the Freundlich model, and the monolayer adsorption capacity of MMIPs was 246.73 mg g(-1) at 298 K. The kinetic properties of MMIPs were well-described by the pseudo-second-order equation, initial adsorption rate, and half-adsorption time. The selective recognition experiments demonstrated high affinity and selectivity toward TCP over structurally related phenolic compounds, and hydrogen bonds between TCP and methacrylic acid (MAA) were mainly responsible for the recognition mechanism. In addition, MMIPs could be regenerated, and their adsorption capacity in the fifth use was about 11.0% loss in pure TCP solution, about 16.1% loss in coexisting phenolic compound solution. The MMIPs prepared were successfully applied to the separation of TCP from environmental samples.