Preparation of novel magnetic molecular imprinted polymers nanospheres via reversible addition – fragmentation chain transfer polymerization for selective and efficient determination of tetrabromobisphenol A
Graphical abstract
Introduction
Tetrabromobisphenol A (TBBPA) as an important brominated flame retardant [1] is widely used in polycarbonate, phenolic resin, and epoxy resin, and is also used as additive type flame retardant with Sb2O3 in engineering plastics industry [2]. However, TBBPA is potential a persistent organic pollutant [3]. Many studies have shown that TBBPA has the potential toxicity as an endocrine disruptor, neurotoxicity and immune toxicity and other toxicological effects [4]. The determination of TBBPA in various matrixes has drawn much attention in recent years. Various analytical strategies have been proposed for detecting TBBPA in different samples for the past few years. At present, some methods with high sensitivity and accuracy, such as chromatographic and related techniques have been widely used to detect and quantify TBBPA and corresponding compounds. Owing to the low concentration of TBBPA and the complexity of the matrix, sample preparation prior to instrumental analysis is often urgently required.
Molecularly imprinted polymers (MIPs) are tailor-made artificial receptors with high affinity and selectivity for the template molecule [5], [6], which are usually prepared through the copolymerization of one or several functional monomers and cross-linkers in the presence of template molecules. In the highly cross-linked polymer matrix, the obtained MIPs possess the imprinted binding sites after the template molecules was removed, which are designed to be complementary to the template molecule in size, shape and chemical functionality. These binding sites have excellent affinity and specificity toward the targeted analytes, which are in favor of rebinding the template molecules from a mixture of the template molecules and other compounds with similar structure [7]. MIPs have been successfully applied in the field of chem/biosensors [8], [9], solid-phase extraction and solid-phase microextraction[10], [11], [12], [13], drug delivery, artificial enzyme inhibitor/antibody [14], [15], [16] and catalysis [17], [18] due to its special recognition ability.
Bulk polymerization or precipitation polymerization is the traditional methods to prepare MIPs [19], [20], [21]. The MIPs prepared through bulk polymerization are obliged to be smashed, ground and sieved in order to obtain useful particles, which leading to a poor yield. Furthermore, the MIPs prepared by these methods meet some critical disadvantages, such as the leakage of the template molecule and poor site availability, which are caused by the residual template molecules and the recognition sites deeply buried in the polymer substrate.
Surface molecularly imprinted polymers (SMIPs) are a strategy to immobilize the recognition sites on the surface of solid matrix, which has been recently acquainted for their distinct advantages over the ordinary MIPs, such as more approachable binding sites, adequate selectivity, faster mass transfer rate and binding rate [22], [23], [24], [25]. Recently, radical polymerization is a common approach to prepare SMIPs. However, as the side reactions, such as chain termination and transfer, it is difficult to control the rate of chain propagation and causes a broad size distribution of the polymer in traditional radical polymerization.
Because of the insignificant chain termination and slower reaction rate, controlled/living radical polymerization (CLRP) can overcome the shortcomings of the commonly used free radical polymerization where undesired chain transfer and termination occur during MIP preparation. CLRP includes atom transfer radical polymerization (ATRP) [26], nitroxide-mediated polymerization (NMP) [27], and RAFT polymerization [28]. Among these, the reaction condition of RAFT polymerization is mild and there is no metal catalyst was used. It is also compatible with almost all of the conventional radical polymerization monomers and enables post polymerization modification with other functional monomers. All of these make RAFT polymerization as a most attractive approach in preparing SMIPs [29].
Nanoparticles, especially magnetic nanoparticles serve as a promising support for surface imprinting owing to their large specific surface area, which can provide more recognition sites [30]. The magnetic imprinted nanospheres could be easily isolated from solutions with the help of external magnet after selectively recognizing the template molecule in complex matrix. There are few of reports focused on the preparation TBBPA imprinted polymer beads and detection it with chromatographic techniques [4], [31]. Both Hu [4] and Xie [31] groups reported prepare TBBPA imprinted SMIPs using SiO2 as substrate and tetraethoxysilane (TEOS) as cross-linkers and 3-aminopropyltriethoxysilane (APTES) as functional monomers. The obtained SMIPs difficult isolated from liquid medium after recognition process due to the absence of magnetic core. The combining the merits of RAFT polymerization and magnetic nanospheres to constructing MIPs of TBBPA has not been reported yet.
In this work, we incorporated the advantages of magnetic nanoparticles and RAFT polymerization to develop a new type of core-shell magnetic TBBPA-imprinted nanoparticles. The obtained core-shell magnetic molecularly imprinted polymers were characterized by transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). It was also used as an adsorbent to evaluate its ability in selective recognition TBBPA.
Section snippets
Materials
Sodium citrate, sodium acetate, FeCl3, sodium ascorbate, 2-bromobutyric acid (98%), 4-(N,N-dimethylamino)pyridine (DMAP), Propargyl alcohol and N-(3-(dimethylamino)propyl)-N′-ethylcarbodiimide hydrochloride (EDC) were obtained from Energy Chemical Industry Co. Ltd. (Shanghai, China). 4-vinylbenzylchloride (VBC), 4-Vinylpyridine (4-VP) and ethylene glycol dimethacrylate (EGDMA) were purchased from Alfa Aesar and purified by distillation under vacuum. 2,2′-Azobisisobutyronitrile (AIBN) was
Characterization
Fig. 1 illustrates the principle to synthesize Fe3O4@MIP nanoparticles. First, the citrate groups stabilized Fe3O4 nanospheres were prepared by hydrothermal method. Fe3O4 nanoparticles were then functionalized with MPS to make vinyl groups grafted to the surface of Fe3O4 particles by a simple Stöber method in the mixture of ethanol and water in the presence of ammonia. Subsequently, the Fe3O4@PVBC nanospheres were prepared via distillation–precipitation polymerization of 4-vinylbenzyl chloride
Conclusion
Based on the strategy of the surface imprinting, a novel magnetic Fe3O4@MIP with core-shell structure was prepared via the combination of click chemistry and RAFT polymerization in order to rapidly enrich and separate of TBBPA. The magnetic surface imprinted nanoparticles reveal satisfactory binding capacity, short absorption equilibrium time and specific recognition toward TBBPA. Fe3O4@MIP particles could be easily and quickly separated from the suspension by using an external magnetic field
Acknowledgements
This paper is dedicated to the memory of Professor Yanfeng Li.
The authors would like to express their appreciation for research funding provided by the National Natural Science Foundation of China (No.21374045, No.21074049) and the National Science Foundation for Fostering Talents in Basic Research of the National Natural Science Foundation of China (Grant No. J1103307).
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