Fabrication Of Bioinspired Molecularly Imprinted Nanocomposite Membrane In Selective Separation And Enrichment Of Environmental And Biological Samples

Membrane separation technology (MST) is the frontier technology of separation science in chemical disciplines,MST is a new technology that the substances was separated according to the membrane's pore size. MST as a new separation technology is widely investigated in recent years. However, there often need several distinct requirements to meet the membrane performance in the membrane separation processes, it requires both high selectivity flux and good contamination resistance.Therefore, development of novel membrane materials with specific needs is the key to solve the issue for green fine chemical industry and novel MST applications.The molecularly imprinted membranes (MIMs) rise in response to the proper time and conditions which combine the molecular imprinting technique (MIT) with MST for the selective separation of target molecules from mixture and the structural analogues.In addition, dopamine can polymerize and affix to all kinds of inorganic and organic materials through the generation of strong noncovalent and covalent linkages with surfaces. Meanwhile, there is the reason to believe that the metallic nanoparticles with high chemical stability and anti-fouling properties can be uniformly dispersed and tightly bound onto the PDA-modified versatile membrane platform. Therefore,research into combinations of this PDA-modified versatile membrane platform and MIMs for the preparation of molecularly imprinted nanocomposite membrane materials would effectively improve the structural stability, reproducibility and selectivity.In this paper, focusing on molecularly imprinted membrane technology and bionic dopamine self-polymerization-composite modification technology, combining with the surface modification process of the nanocomposite materials, put forward the preparation of bioinspired molecularly imprinted nanocomposite membranes which was used in the study of selective purification and separation researches. With porous poly (vinylidene fluoride) (PVDF). membrane and regenerated cellulose (RC)membrane as the basal membranes, the molecularly imprinted nanocomposite membranes were prepared by using the advantages of PDA platform for secondary reaction, and selecting different molecular (artemisinin, m-cresol, propranolol,ovalbumin) as template molecules,using a variety of surface imprinting polymer technology to synthesis of different kinds, and then they were applied to selective separation of a variety of target molecules. Studying on the static adsorption capacities and selective permeation performance towards different template molecules of the as-prepared bioinspired molecularly imprinted nanocomposite membranes, and discussing the possible recognition and mass-transfer mechanism in detail. The main study results of this thesis are as follows:1. Preparation of molecularly imprinted composite membranes by surface-initiated polymerization method for the selective separation and enrichment(1) The molecularly imprinted composite membranes (MIMs) were prepared via a one-pot atom transfer radical polymerization (AGET ATRP) method based on porous PVDF membrane with artemisinin (Ars) as template molecule. The as-prepared MIMs were then used for the selective recognition and separation of Ars molecules. The surface structure and morphology of the as-prepared MIMs were characterized by ATR-FTIR and SEM. The isothermal adsorption curve of MIMs was well fitted by the Langmuir model, suggesting the monolayer adsorption capacities of MIMs. The selective permeation results indicated that MIMs has higher permeability coefficients for artemether than that of Ars compared to the NIMs, indicating that the MIMs had special selectivity to Ars due to their strong interaction with Ars. The perm-selectivity result also showed that the transport mechanism of MIMs for Ars was accordance with the retarded permeation mechanism of molecularly imprinted membrane materials.(2) Taking the enhancement of adsorption capacity and separation performance as starting points, combining with surface graft copolymerization method, a two-step modification process was performed on the RC membranes to obtain the surface functional monomer modified structure by using 3-aminopropyltriethoxysilane(APTES) and acryloyl chloride (AC). Then, the surface functional monomer modified molecularly imprinted membranes (FMIMs) were prepared by using Ars as template molecule. The physicochemical properties such as surface morphology, elementary composition, and chemical bonding of the as-prepared FMIMs were characterized by SEM and XPS. The selective permeation results indicated that FMIMs has higher permeability coefficients for artemether than that of Ars compared to the FNIMs (the permeability coefficient ?=10.60), indicating that the FMIMs had special selectivity to Ars due to their strong interaction with Ars, which caused the blocking permeation of Ars through the FMIMs, which would play a great role in promoting the separation and purification of Ars.2. Preparation of bioinspired molecularly imprinted nanocomposite membranes through the organic/inorganic nanoparticles doping process for the selective separation study(1) A polydopamine (PDA)-based secondary reaction platform was initially obtained based on RC membranes (PDA@RC) by using the dopamine (DA)self-polymerization-composite modification technique. And then the surface functional SiO2 nanoparticles were modified onto the PDA@RC surface through a solvothermal method. The organic-inorganic molecularly imprinted nanocomposite membranes (MINCMs) were' prepared by using Ars as template molecule. The physicochemical properties such as surface morphology, elementary composition, and chemical bonding of the as-prepared FMIMs were characterized by SEM, XPS, and ATR-FTIR. The static adsorption results indicated that the maximum adsorption capacity of MINCMs was 54 mg/g, and the permeation experiments stated that the as-prepared MINCMs had excellent selective separation and enrichment of Ars, the transport mechanism of MINCMs for Ars was accordance with the retarded permeation mechanism.(2) Taking the enhancement of adsorption rate and performance of concentration and separation as starting points, inspired by the highly bioadhesive performance of PDA, the m-cresol imprinted SiO2 nanocomposite was synthesized by using DA as both the functional monomer and crosslinking agent (m-cresol-imprinted PDA@SiO2).And then the urgently desired molecularly imprinted nanocomposite membranes(MINCMs) were prepared by developing a simple "bio-glue" imprinted strategy: by simply immersing the m-cresol-imprinted PDA@SiO2 into the PVDF casting solution accompanied by persistently mechanically stirring, a highly bio-adhered and homo-dispersedly distributed structure could be generated into MINCMs during a phase inversion process. The surface structure and morphology of the as-prepared MINCMs and nanocomposites were characterized. As to the perm-selectivity results:MINCMs processed a much lower transport flux of m-cresol than that of m-cresol and 2,4-DP, which should be mainly attributed to the presence of sterically complementary imprinting cavities of m-cresol molecules that hindered the transport of m-cresol via binding/desorption onto recognition sites in MINCMs. While other substances (p-cresol and 2,4-DP) presented no specific interactions with MINCMs,thus facilitating the transport by convection or diffusion. The excellent separation performance (perm-selectivity factor is 3.477) along with the low preparation consumed and green, quick, facile synthesis conditions make the as-prepared MINCMs attractive in broad technological applications for various areas.(3) Inspired by the PDA-modified methodology, dopamine can concurrently polymerize into pDA and deposit at the surface of SiO2, the nanospheres were then modified by Ag via reduced reaction of Ag+ by catechol-induced to obtain the Ag-PDA@SiO2 in mild conditions. After that, the initiator-fixed nanoparticles(Br-Ag-PDA@SiO2) were easily obtained by using 2-bromopropionyl bromide and trimethylamine as the catalytic system. The key design of our synthetic strategy was to incorporate the multilevel nanocomposite structure (Br-Ag-PDA@SiO2) into the porous PVDF scaffold such that the active domain is actually formed inside the porous support. The molecularly imprinted nanocomposite membranes (MINCMs)were finally prepared via a photoinitiated atom transfer radical polymerization (ATRP)method by using propranolol as template molecule, acrylamide (AM) and methacrylic acid (MAA) as functional monomers. To prove recognition specificity of the MINCMs, O-pivaloylpropranolol (Opl) and O-acetylpropranolol (Oal) were chosen for comparison and imprinted, and similar recognition selectivity was observed dependent on the template molecule. The permeation results indicated that the as-prepared MINCMs had excellent selective separation and enrichment performance of propranolol. Therefore, this novel bioinspired synthesis method will open a new direction to manipulation of molecularly imprinted membrane materials and provide a simple yet convenient way to selective separation of propranolol.3. Preparation of multilayer molecularly imprinted nanocomposite membranes by using the PDA-based versatile membrane platform for the selective separation study(1) Taking the enhancement of adsorption capacity and separation rate as starting points, combining with PDA-based method and nanocomposite modified process, the novel multi-component metal-organic molecularly imprinted nanocomposite membrane (MMO-MIM) was prepared via a surface-initiated sol-gel imprinted procedure based on porous PVDF membrane by using m-cresol as template molecule.The as-prepared MMO-MIM not only exhibits rapid adsorption dynamics, but also possesses excellent separation performance(?MMO-MIM/MMO-NIM and ?m-cresol/2,4-DP are higher than 2.6 and 4.0,respectively) of templates. In addition, all synthesis procedures were conducted in aqueous or ethanol solution at ambient temperature.(2) Based on two aspects of selective separation of biomacromolecule and applications of the surface effect, a PDA modified surface was initially obtained by using porous RC membrane as the basement membrane (PDA@RC). And then, a two-step functionalization approach was developed on a PDA-inspired porous surface to obtain the uniformly bound SiO2/Ag nanosheet structure (Ag-SiO2@PDA@RC).The novel Ag/SiO2/organic hybrid MIMs (ASO-MIMs) was then prepared via a redox-initiated imprinted polymerization procedure by using ovalbumin (Ova) as template molecule, and the as-prepared ASO-MIMs were then applied to the selective separation of Ova and surface cell adhesion behavior research. The surface structure and morphology of the as-prepared ASO-MIMs were characterized by SEM, TEM,XPS, and ATR-FTIR. The Ova-bound ASO-MIMs were used to investigate the surface cell adhesion performance. The relative morphological observations of the adhered cells and in vitro viability tests show no significant difference between the ASO-MIMs binding with 13.6 mg/g Ova (13.6-ASO-MIMs) and bare glass,indicating the excellent biocompatibility of the 13.6-ASO-MIMs. Furthermore, the permeation factors ?ASO-NIMsIASO-MIMs were all more than 3.5 in the whole permeation experiments, clearly demonstrating the presence of specific recognition sites in the ASO-MIMs. Therefore, the transport mechanism of ASO-MIMs for Ova was accordance with the retarded permeation mechanism, which provided convincing theoretical foundation and applications for biomacromolecules imprinted technique.Collectively, the Ova-bound ASO-MIMs could be demonstrated as a versatile membrane with improved durability, regeneration ability, and biocompatibility.