Jiangdong Dai

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.

A simple and sensitive surface molecularly imprinted polymers based fluorescence sensor for detection of λ-Cyhalothrin.

In this study, surface molecularly imprinted YVO4:Eu(3+) nanoparticles with molecular recognitive optosensing activity were successfully prepared by precipitation polymerization using λ-Cyhalothrin (LC) as template molecules, methacrylic acid and ethylene glycol dimethacrylate as the polymerization precursors which could complex with template molecules, and the material has been characterized by SEM, TEM, FT-IR, XRD, TGA and so on. Meanwhile, the as-prepared core-shell structured nanocomposite (YVO4:Eu(3+)@MIPs), which was composed of lanthanide doped YVO4:Eu(3+) as fluorescent signal and surface molecular imprinted polymers as molecular selective recognition sites, could selectively and sensitively optosense the template molecules. After the experimental conditions were optimized, two linear relationship were obtained covering the concentration range of 2.0-10.0 μM and 10.0-90.0 μM, and the limit of detection (LOD) for LC was found to be 1.76 μM. Furthermore, a possible mechanism was put forward to explain the fluorescence quenching of YVO4:Eu(3+)@MIPs. More importantly, the obtained sensor was proven to be suitable for the detection of residues of LC in real examples. And the excellent performance of this sensor will facilitate future development of rapid and high-efficiency detection of LC.

Removal of cefalexin using yeast surface-imprinted polymer prepared by atom transfer radical polymerization.

The first use of yeast as a support in the molecular imprinting field combined with atom transfer radical polymerization was described. Then, the as-prepared molecularly imprinted polymers were characterized by Fourier transmission infrared spectrometry, scanning electron microscope, thermogravimetric analysis, and elemental analysis. The obtained imprinted polymers demonstrated elliptical-shaped particles with the thickness of imprinting layer of 0.63 μm. The batch mode experiments were adopted to investigate the adsorption equilibrium, kinetics, and selectivity. The kinetic properties of imprinted polymers were well described by the pseudo-second-order kinetic equation, indicating the chemical process was the rate-limiting step for the adsorption of cefalexin (CFX). The equilibrium data were well fitted by the Freundlich isotherm, and the multimolecular layers adsorption capacity of imprinted polymers was 34.07 mg g(-1) at 298 K. The selectivity analysis suggested that the imprinted polymers exhibited excellent selective recognition for CFX in the presence of other compounds with related structure. Finally, the analytical method based on the imprinted polymers extraction coupled with high-performance liquid chromatograph was successfully used for CFX analysis in spiked pork and water samples.

Luminescence functionalization of porous silica nanospheres by YVO4:Eu3+ for the efficient recognition of λ-cyhalothrin in aqueous media

Porous silica nanospheres were fabricated using a facile surface-protected etching strategy. Polyvinylpyrrolidone (PVP) was used as a protecting polymer adsorbed on the surface of silica nanospheres and NaOH was employed as an etching agent. Owing to the protective action of PVP and inhomogeneous etching, mesopores were created in the silica nanospheres. Then, based on a simple and economical wet-chemical route, highly luminescent YVO4:Eu3+ nanocrystals were then integrated onto the nanospheres to form a highly luminescent mSiO2/YVO4:Eu3+ composite material. This material, which combined the mesoporous structure of SiO2 and the strong red luminescence property of YVO4:Eu3+, could be used as a novel optosensing system. The structure, morphology, porosity, and optical properties of the materials were well characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption, and photoluminescence spectra, and the optical stability and effect of pH on mSiO2/YVO4:Eu3+ were also evaluated. It was observed that λ-cyhalothrin (LC) could quench the luminescence of mSiO2/YVO4:Eu3+ in a concentration-dependent manner, which was best described by a Stern–Volmer-type equation. This study therefore demonstrated that the composite material could be potentially used as a probe to monitor the residues of LC in water.