Hui Hang

Fabrication and Evaluation of Magnetic/Hollow Double-Shelled Imprinted Sorbents Formed by Pickering Emulsion Polymerization

Magnetic/hollow double-shelled imprinted polymers (MH-MIPs) were synthesized by Pickering emulsion polymerization. In this method, attapulgite (ATP) particles were used as stabilizers to establish a stable oil-in-water emulsion, and a few hydrophilic Fe3O4 nanoparticles were allowed to be magnetic separation carriers. The imprinting system was fabricated by radical polymerization in the presence of the functional and polymeric monomers in the oil phase. The results of characterization indicated that MH-MIPs exhibited magnetic sensitivity (Ms = 4.76 emu g(-1)), thermal stability (especially below 200 °C), and hollow structure and were composed of exterior ATP shells and interior imprinted polymers shells. Then MH-MIPs were evaluated as sorbents for the selective binding of λ-cyhalothrin as a result of their magnetism, enhanced mechanical strength, hydrophilic surface, and recognition ability. The kinetic properties of MH-MIPs were well described by the pseudo-second-order equation, indicating that the chemical process could be the rate-limiting step in the adsorption process for λ-cyhalothrin. The equilibrium adsorption capacity of MH-MIPs was 60.06 μmol g(-1) at 25 °C, and the Langmuir isotherm model gave a better fit to the experimental data, indicating the monolayer molecular adsorption for λ-cyhalothrin. The selective recognition experiments also demonstrated the high affinity and selectivity of MH-MIIPs toward λ-cyhalothrin over fenvalerate and diethyl phthalate.

Selective recognition of 2,4,5-trichlorophenol by temperature responsive and magnetic molecularly imprinted polymers based on halloysite nanotubes

Fe3O4/Halloysite nanotube magnetic composites (MHNTs) were firstly prepared via an effective polyol-medium solvothermal method, and then the surface of the MHNTs was endowed with reactive vinyl groups through modification with 3-(methacryloyloxy)propyl trimethoxysilane (MPS). Based on the MHNTs-MPS, temperature responsive and magnetic molecularly imprinted polymers (t-MMIPs) were further synthesized by adopting methacrylic acid (MAA) and N-isopropylacrylamide (NIPAM) as the functional monomer and temperature responsive monomer, respectively. The as-prepared t-MMIPs were characterized by FT-IR, TEM, TGA and VSM, which indicated that the t-MMIPs exhibit magnetic sensitivity (Ms = 2.026 emu g−1), magnetic stability (especially in the pH range of 4.0–8.0) and thermal stability and are composed of an imprinted layer. The molecular interaction between 2,4,5-trichlorophenol (TCP) and MAA was investigated by 1H-NMR spectroscopy and ultraviolet absorption spectroscopy, which suggest that hydrogen bonding may be largely responsible for the recognition mechanism. The t-MMIPs were then applied to selectively recognise and release TCP molecules at 60 °C and 20 °C, respectively. The maximum amount of binding at 60 °C was 197.8 mg g−1 and 122.6 mg g−1 for t-MMIPs and temperature responsive and magnetic non-imprinted polymers (t-MNIPs), respectively. At 20 °C, about 32.3%–42.7% of TCP adsorbed by t-MMIPs was released, whereas 25.3%–39.9% of TCP was released by t-MNIPs. The selective recognition experiments demonstrated the high affinity and selectivity of t-MMIPs towards TCP over competitive phenolic compounds, and the specific recognition of binding sites may be based on the distinct size, structure and functional group to the template molecules.

Switched recognition and release ability of temperature responsive molecularly imprinted polymers based on magnetic halloysite nanotubes

CoFe2O4/halloysite nanotube magnetic composites (MHNTs) were firstly achieved via a wet impregnation technique, and then a thermal polymerization under (NH4)2S2O8 chain initiation in water was employed to obtain methacrylic acid-functionalized MHNTs (MAA-MHNTs). By decorating the MAA-MHNTs with the temperature responsive monomer N-isopropylacrylamide (NIPAM), a novel temperature responsive molecularly imprinted material based on the obtained NIPAM-MHNTs (TMMIPs) was synthesized by a surface imprinting technique. The results of characterization indicated that the TMMIPs exhibited magnetic sensitivity (Ms = 1.758 emu g−1), magnetic stability (in the pH range of 2.0–8.0), thermal stability (especially below 200 °C) and contained a temperature responsive imprinted layer (the lower critical solution temperature was 33.96 °C). Then the TMMIPs were applied to switched recognition and release of 2,4,5-trichlorophenol molecules (5-TCP) by changing the medium temperature. TMMIPs showed outstanding recognition ability towards the imprinted species under high temperature conditions (such as 60 °C), due to the loss of hydration and a collapsed state of inter-poly(N-isopropylacrylamide), which resulted in the formation of a specific structure between 5-TCP and the polymer network. In contrast, at relatively low temperatures (such as 20 °C), the captured 5-TCP was released from the swelled TMMIPs, which resulted from increasing the distance between 5-TCP and the polymer network. The selective analysis demonstrated the high affinity and selectivity of TMMIPs towards 5-TCP over competitive phenolic compounds, and the specific recognition of binding sites may be based on the distinct size, structure and functional groups of the template molecules.

Magnetic ZnO surface-imprinted polymers prepared by ARGET ATRP and the application for antibiotics selective recognition

This paper reports a molecularly imprinted polymers (MIPs) based fluorescence sensor which is synthesized by grafting MIP layers on the surface of ZnO nanorods embedded γ-Fe2O3 nanoparticles via activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). Methacrylic acid (MAA, functional monomer), 3-(trimethoxysilyl)propyl mathacrylate (MPS) modified γ-Fe2O3 (γ-Fe2O3/MPS, assistant magnetic monomer) and ethylene glycol dimethacrylate (EGDMA, cross-linking monomer) were co-polymerized in anisole at 313 K in the presence of sulfamethazine as a template molecule. Sulfamethazine was then solvent-extracted to obtain ZnO-grafted molecularly imprinted polymers (ZnO-MIPs). ZnO-MIPs were characterized by FE-SEM, TEM, FT-IR, TGA/DSC, VSM, fluorescence spectroscopy and Raman spectroscopy. It was observed that sulfamethazine can quench the luminescence of ZnO-MIPs in a concentration-dependent manner that can be described by a Stern–Volmer-type equation. ZnO-MIPs were used to determine sulfamethazine in a spiked pork sample with good recognition ability. This study therefore demonstrates the potential application in the recognition and separation of antibiotics based on molecularly imprinted polymers.

Selective separation of lambdacyhalothrin by porous/magnetic molecularly imprinted polymers prepared by Pickering emulsion polymerization

Porous/magnetic molecularly imprinted polymers (PM-MIPs) were prepared by Pickering emulsion polymerization. The reaction was carried out in an oil/water emulsion using magnetic halloysite nanotubes as the stabilizer instead of a toxic surfactant. In the oil phase, the imprinting process was conducted by radical polymerization of functional and cross-linked monomers, and porogen chloroform generated steam under the high reaction temperature, which resulted in some pores decorated with easily accessible molecular binding sites within the as-made PM-MIPs. The characterization demonstrated that the PM-MIPs were porous and magnetic inorganic-polymer composite microparticles with magnetic sensitivity (M(s) = 0.7448 emu/g), thermal stability (below 473 K) and magnetic stability (over the pH range of 2.0-8.0). The PM-MIPs were used as a sorbent for the selective binding of lambdacyhalothrin (LC) and rapidly separated under an external magnetic field. The Freundlich isotherm model gave a good fit to the experimental data. The adsorption kinetics of the PM-MIPs was well described by pseudo-second-order kinetics, indicating that the chemical process could be the rate-limiting step in the adsorption of LC. The selective recognition experiments exhibited the outstanding selective adsorption effect of the PM-MIPs for target LC. Moreover, the PM-MIPs regeneration without significant loss in adsorption capacity was demonstrated by at least four repeated cycles.

Magnetic molecularly imprinted microcapsules derived from Pickering emulsion polymerization and their novel adsorption characteristics for λ-cyhalothrin

Magnetic molecularly imprinted microcapsules (MMIMs) were synthesized by Pickering emulsion polymerization. In this work, an oil-in-water Pickering emulsion stabilized by halloysite nanotubes (HNTs) was first established in the presence of a few hydrophilic Fe3O4 nanoparticles as magnetic separation carriers. The imprinting system was fabricated by radical polymerization and subsequent combination with functional and polymeric monomers in the oil phase. The formation mechanism of the Pickering emulsion and MMIMs is discussed in detail, and the as-prepared MMIMs are successfully evaluated as sorbents for the recognition of λ-cyhalothrin. The results demonstrated that the MMIMs exhibited magnetic sensitivity (Ms = 8.45 emu g−1), a hollow structure, a semipermeable external surface and excellent robustness. The batch mode experiments proved that the imprinting effect synchronously improved the adsorption kinetics and equilibrium for the MMIMs. The selective recognition experiments also suggested high affinity and selectivity of MMIMs towards λ-cyhalothrin over fenvalerate and diethyl phthalate.