Synthesis Of Surface Imprinted Sorbents Upon Silicon-based Micro/Nano Materials And Study On The Selective Recognition/Separation Of Phenolic Endocrine Disruptors

With the widespread use of phenolic fine chemical industrial raw materials, pesticide, preservatives, molluscicide and antioxidants in the industrial and agricultural production, the pollutions from phenolic endocrine disruptors (PEDs) are serious in a few parts of China. Moreover, the toxicity, environmental persistence, bioaccumulation and estrogenic activity of PEDs have aroused wide public concern. In regular monitoring, adsorption that utilizes sorbents is an efficient and economically feasible method for the removal of PEDs. Currently, sorbents such as activated carbon, modified clay materials, biosorbents and sewage sludge all have the disadvantages of low selectivity, small adsorption capacity and long equilibrium time.Molecular imprinting technology (MIT) is a promising method to prepare synthetic materials with molecular recognition ability, namely molecularly imprinted polymers (MIPs). And the artificial receptor-like binding sites in MIPs having the size and shape complimentary to the template molecule. Traditionally, MIPs, obtained by bulk polymerization, exhibit highly selective recognition but with low capacity and poor site accessibility to the target molecules, as the extraction of template molecules embedded inside the thick polymer network is quite difficult due to the high cross-linking nature of MIPs. By establishing the molecular recognition system to be located at or near the surface of support materials, surface imprinting technique provides a promising solution to improve the adsorption capacity and recognition kinetics by reducing permanent entrapment of the template. Micro/nano silicon-based materials have the potential to be adopted as the imprinting support materials because of their low cost, chemical stability, large surface area together with readily obtainable property.In this study, the natural silicon-based materials (attapulgite and halloysite nanotubes) and synthetic silicon-based materials (silica gel and fly-ash-cenospheres) were adopted as the imprinting support. Then the MIPs, magnetic molecularly imprinted polymers (MMIPs), temperature responsive and magnetic molecularly imprinted polymers (TMMIPs) were prepared by surface imprinting technology incorporating with the graft copolymerization technology, magnetic material separation method and temperature responsive adsorption/release technology, respectively. By various of characterization, the crystalline phase, morphology, magnetism, structure, chemical composition and surface property of as-prepared imprinted sorbents were investigated. And their behaviours of selective rocognition and separation of several typical PEDs were studied by the batch mode operations. Moreover, the recognition mechanism, adsorption equilibrium and kinetics were discussed in detail.The main conclusions included the following items:1. Synthesis of MIPs upon silicon-based materials by graft copolymerization and research of applications in selective adsorption and separation PEDs(1) Polyaniline/silica gel composites (PAS) were prepared by in situ fast polymerization method. Using PAS, grafted amido and 2,6-dichlorophenol (2,6-DCP) as the support, functional monomer and template, respectively, MIPs were synthesized by graft copolymerization. Then the MIPs were characterized, and the results demonstrated agglomerate shape possessed of mesopores, and the good compatibility was obtained between the PAS and imprinted layer. The results of batch adsorption experiments suggested that pH 7.0 and the 3.0% volume of methanol in testing solution were the optimal adsorption conditions. The Langmuir isotherm model was fitted to the equilibrium data better than the other models, and the monolayer adsorption capacity of MIPs were 43.59 mg/g,58.99 mg/g and 63.83 mg/g at 298 K,308 K and 318 K, respectively. The kinetic properties of MIPs were well described by the pseudo-second-order equation. Moreover, intraparticle diffusion coefficient (k\) and pore diffusion coefficient (D2) of MIPs elevated with the increased of 2,6-DCP concentration and temperature of medium, while increased the 2,6-DCP concentration was found to reduce film diffusion. Furthermore, the values of film diffusion coefficient (D1) were lower than those of D2, indicating the diffusion process was controlled by film diffusion. The selectivity of the MIPs also demonstrates high affinity for 2,6-DCP over related phenolic compounds, and the recognition activity was excellent than that of non-imprinted polymers (NIPs).(2) In order to improve the selectivity in the presence of polar solvents, especially water,β-cyclodextrin (β-CD), possessing of a hydrophilic exterior and hydrophobic internal cavity, was used to prepare the (3-cyclodextrin/attapulgite composites (β-CD/ATP). Usingβ-CD/ATP, graftedβ-CD and 2,4-dichlorophenol (2,4-DCP) as the support, functional monomer and template, respectively, MIPs were synthesized by graft copolymerization. Then the MIPs was characterized, and the results demonstrated uniformLy sized microspheres with the diameter of 4.0 um, and the good compatibility was obtained between theβ-CD/ATP and imprinted layer. The results of batch adsorption experiments suggested that pH 2.0 in testing solution was the optimal adsorption condition, and hydrogen bonding was the main recognition mechanism. The Langmuir isotherm model was fitted to the equilibrium data better than the other models, and the monolayer adsorption capacity of MIPs were 62.14 mg/g,70.95 mg/g and 77.96 mg/g at 298 K,308 K and 318 K, respectively. The kinetic properties of MMIPs were well described by the pseudo-second-order equation. Moreover, MIPs demonstrated higher affinity for target 2,4-DCP and excellent regeneration property.2. Synthesis of MMIPs upon silicon-based materials and research of applications in selective adsorption and separation PEDs(1) Via encapsulation of attapulgite/Fe3O4 magnetic particles (ATP/Fe3O4), the MMIPs were synthesized for the selective recognition of 2,4-DCP. MMIPs were characterized, and the results demonstrated claviform shape with an imprinted polymer film (thickness of about 16 nm), and exhibited magnetic property (Ms=5.67 emu/g) and thermal stability. Batch mode adsorption studies were carried out to investigate the specific binding capacity, binding kinetics and recognition specificity. The Langmuir isotherm model was fitted to the equilibrium data better than the other models, and the monolayer adsorption capacity of MMIPs were 145.79 mg/g 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 towards 2,4-DCP over structurally related phenolic compounds. In addition, MMIPs could be regenerated, and their adsorption capacity in the fifth use was about 7.53%loss in 2,4-DCP solution. Moreover, MMIPs were successfully applied to the selective solid phase extraction of 2,4-DCP from environmental water samples.(2) Magnetic nanoparticles were attached to carboxylic acid functionalized halloysite nanotubes (COOH-HNTs) by high-temperature reaction of ferric triacetylacetonate in 1-methyl-2-pyrrolidone. Based on magnetic halloysite nanotubes particles (MHNTs), MMIPs were synthesized for the selective recognition of 2,4,6-trichlorophenol (6-TCP). MMIPs were characterized, and the results demonstrated with an imprinted polymer film (5.0-15 nm) and exhibited magnetic property (Ms=2.74 emu/g) 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 other model, and the monolayer adsorption capacity of MMIPs was 246.73 mg/g 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 6-TCP over structurally related phenolic compounds, and hydrogen bonds between 6-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 6-TCP solution, about 16.1% loss in coexisting phenolic compound solution. The MMIPs prepared were successfully applied to the selective solid phase extraction of 6-TCP from environmental samples.(3) Magnetic composites (MCs) were achieved via coating a chitosan layer containing y-Fe2O3 nanoparticles onto the surface of aldehyde-functionalized fly-ash-cenospheres. Based on these MCs, MMIPs were further synthesized and characterized, and used to selectively recognise bisphenol A (BPA) molecules. MMIPs were characterized, and the results demonstrated that these spherical shaped MMIPs particles had magnetic sensitivity (Ms=2.221 emu/g) and magnetic stability. Batch mode adsorption studies were carried out to investigate the specific adsorption equilibrium, kinetics and selective recognition. The Langmuir isotherm model was fitted well to the equilibrium data of the MMIPs, and the monolayer adsorption capacity of the MMIPs was 135.1 mg/g at 298 K. The kinetic properties of the MMIPs were well described by the pseudo-second-order equation. Selective recognition experiments demonstrated the high affinity and selectivity of MMIPs towards BPA over competitive phenolic compounds, and hydrogen bonding was proved to be mainly responsible for the recognition mechanism.3. Synthesis of TMMIPs upon silicon-based materials and research of applications in selective recognition and release PEDs(1) FesCVHalloysite 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, TMMIPs were further synthesized by adopting 2,4,5-trichlorophenol (5-TCP) and N-isopropylacrylamide (NIPAM) as the template molecules and temperature responsive monomer, respectively. TMMIPs were characterized and the results indicated that the TMMIPs exhibit magnetic sensitivity (Ms=2.026 emu/g), magnetic stability and thermal stability and excellent temperature responsive behavior. The molecular interaction between 5-TCP and MAA was investigated by 1H-NMR spectroscopy and ultraviolet absorption spectroscopy, which suggested that hydrogen bonding may be largely responsible for the recognition mechanism. The TMMIPs were then applied to selectively recognise and release 5-TCP molecules at 60℃and 20℃, respectively. The maximum amount of binding at 60℃was 197.8 mg/g for TMMIPs. At 20℃, about 32.3%-42.7% of 5-TCP adsorbed by TMMIPs was released. The kinetic results suggested that the TMMIPs possessed of a faster adsorption and recognition of 5-TCP than that of temperature responsive and magnetic non-imprinted polymers (TMNIPs). The selective recognition experiments demonstrated the high affinity and selectivity of TMMIPs towards 5-TCP over competitive phenolic compounds.(2) 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 the methacrylic acid-functionalized MHNTs (MAA-MHNTs). By decorating the MAA-MHNTs with temperature responsive monomer N-isopropylacrylamide (NIPAM), TMMIPs based on the obtained NIPAM-MHNTs were synthesized by a surface imprinting technique. The results of characterization indicated that TMMIPs exhibited magnetic sensitivity (Ms= 1.758 emu/g), magnetic stability, thermal stability and obvious temperature responsive behavior. Then the TMMIPs were applied to switched recognition and release 5-TCP by changing the medium temperature. TMMIPs showed outstanding recognition ability towards the imprint species under high temperature conditions, the maximum amount of binding at 60℃was 197.7 mg/g for TMMIPs. At 20℃, a portion of captured 5-TCP was released from the swelled TMMIPs. The kinetic results suggested that the TMMIPs possessed of a faster adsorption and recognition of 5-TCP than that of TMNIPs. The selective analysis demonstrated high affinity and selectivity of TMMIIPs towards 5-TCP over competitive phenolic compounds.