Preparation and Removal Performance of Magnetic Polymer for Carbamazepine and Oxcarbazepine

Using surface molecular imprinting and magnetic responsive imprinting techniques, we prepared a dual-template magnetic molecularly imprinted polymer (CBZ/OXC-MIPs) with specific recognition for Carbamazepine (CBZ) and Oxcarbazepine (OXC). The anhydride (IA) was selected as the functional monomer through annealing simulation algorithms. The preparation of CBZ/OXC-MIPs was optimized based on the ratio of template molecules to functional monomers, the amount of crosslinking agent and solvent, and the ratio of CBZ to OXC. Characterization analysis indicated that the imprinted polymer was successfully prepared, exhibiting magnetic properties and a porous structure with pore sizes predominantly distributed between 1-2nm. Adsorption experiments showed that the adsorption process of CBZ/OXC-MIPs conformed to the Freundlich model, indicating the presence of high and low affinity adsorption sites. The adsorption reached optimal equilibrium in about 30 minutes, consistent with pseudo-second-order kinetics. CBZ/OXC-MIPs demonstrated specific recognition in competitive adsorption, with a decrease in adsorption capacity of 3.39% after 10 regenerations. Molecular simulation and characterization indicated that selective adsorption primarily relies on van der Waals forces, hydrogen bonding, and electrostatic interactions.

In recent years, the detection of residues of pharmaceuticals and personal care products (PPCPs) in natural water bodies has emerged as a new issue of trace environmental pollutants. PPCPs primarily enter groundwater and surface water in the form of leachate from solid waste or metabolites during production or daily life.

This study employed surface molecular imprinting, magnetic responsive imprinting, and dual-template molecular imprinting techniques to prepare a dual-template magnetic molecularly imprinted polymer CBZ/OXC-MIPs with specific recognition capability and high adsorption performance for CBZ and its ketone derivative OXC. The preparation conditions for CBZ/OXC-MIPs were optimized, and the adsorption performance of the imprinted polymer was studied. Combining simulation results and characterization techniques, the adsorption mechanism of the imprinted polymer was analyzed from the perspectives of structural effects, energy effects, hydrogen bonding effects, and electrostatic effects.

Based on commonly used functional monomers in previous studies, and following the principle of selecting acidic or neutral monomers based on basic template molecules (CBZ and OXC), five initial functional monomers were chosen. Using Materials Studio 8.0 molecular simulation software, the initial conformations of IA, 2-Hydroxyethyl methacrylate (2HEMA), Methacrylic Acid (MAA), Acrylic Acid (AA), and Methyl Methacrylate (MMA) with CBZ and OXC were constructed. The molar ratio of CBZ, OXC, and functional monomers was set to 1:1:4.

Figure 1a shows the effect of the crosslinking agent EGDMA at 15, 20, 25, and 30mmol on the removal rate and adsorption of CBZ/OXC-mips for CBZ and OXC. When the total amount of template molecules CBZ and OXC is 1mmol, with ratios of 4:1, 7:3, 3:2, 1:1, 2:3, and 3:7, the adsorption and removal rates of CBZ and OXC were analyzed (Figure 1b). The effect of the molar ratio of template molecules CBZ and OXC to functional monomer IA at 1:1, 1:2, 1:4, 1:6, and 1:8 was studied on the adsorption efficiency of CBZ/OXC-mips for CBZ and OXC (Figure 1c). The effect of acetonitrile addition on the adsorption performance of CBZ/OXC-MIPs is shown in Figure 1d.

The FTIR spectra of the polymer are shown in Figure 2. The characteristic vibrational absorption peaks of the Fe-O bond appear at 587cm−1, 579cm−1, and 576cm−1, indicating that both CBZ/OXC-MIPs and SiO2-modified nano Fe3O4 possess magnetic properties.

The XRD patterns of Fe3O4, Fe3O4@SiO2, and CBZ/OXC-MIPs are shown in Figure 3.

The SEM images show that CBZ/OXC-MIPs are relatively uniform spherical particles with a diameter of about 70nm (Figure 4a). The overall structure of CBZ/OXC-MIPs is loose. The polymer system has numerous pores, which facilitate the adsorption and elution regeneration of pollutants. In contrast, NIPs are spherical particles with a diameter of about 100nm (Figure 4b), larger than CBZ/OXC-MIPs. Furthermore, compared to CBZ/OXC-MIPs, NIPs are more tightly packed, with fewer pores in the polymer system, resulting in a smaller specific surface area and weaker adsorption capacity than CBZ/OXC-MIPs.

According to the latest IUPAC classification, the nitrogen adsorption-desorption curve of CBZ/OXC-MIPs is a type II isotherm (Figure 5a). The BJH desorption dV/dD curve (Figure 5b) shows that the pore size distribution of CBZ/OXC-MIPs is mostly between 1-2nm, indicating that micropores occupy a large portion of the pore volume, thus CBZ/OXC-MIPs have a high specific surface area and adsorption capacity.

The adsorption capacity of the polymer for pollutants increases with concentration (Figure 6). The fitting results of the isothermal model and isothermal adsorption parameters are shown in Figure 6.

Through Scatchard model analysis, the Scatchard fitting graph of MIPs shows two lines with different slopes (Figure 7a).

The intraparticle diffusion curve of the polymer exhibits multiple linearity (Figure 8), indicating that the controlling steps for the adsorption rate differ at each stage.

From Figure 9, it can be seen that in a single system, the removal rate of CBZ/OXC-mips for CBZ is higher than that for OXC. This may be due to the fact that CBZ has one less carbonyl group than OXC, resulting in smaller molecular weight and volume, allowing CBZ to enter the interior of CBZ/OXC-mips and bind with the imprinting sites left by OXC.

Using a ternary mixed solution of CBZ, OXC, and DIC, the specific adsorption of CBZ/OXC-mips for CBZ and OXC was further studied. As shown in Figure 10, in the presence of DIC, MIPs still exhibit good adsorption selectivity for target pollutants CBZ and OXC.

Compared to ultra-pure water, the removal rate of CBZ/OXC-mips for CBZ and OXC in the effluent only slightly decreased (Figure 11).

The thermodynamic results of the polymer are shown in Figure 12.

After 10 cycles of adsorption-elution-reabsorption, the adsorption capacities of CBZ/OXC-MIPs, CBZ-mips, OXC-MIPs, and NIPs decreased to 9.15mg/g (a decrease of 3.39%), 8.37mg/g (a decrease of 4.23%), 7.68mg/g (a decrease of 5.39%), and 4.78mg/g (a decrease of 5.61%) respectively (Figure 13).

As shown in Figure 14, the CBZ/OXC-MIPs imprinting system forms intermolecular and intramolecular hydrogen bonds.

As shown in Figure 15, the in-plane bending vibration peaks of the amide C=O-N appear at 646cm−1 and 1531cm−1, while the vibrational absorption peak of the carbonyl C=O appears at 1690cm−1, indicating that CBZ and OXC are adsorbed on the surface of CBZ/OXC-mips.

The dissociation constants pKa of CBZ and OXC are 13.9 and 13.73, respectively. The zero charge point of CBZ/OXC-MIPs is 4.03 (Figure 16). Therefore, when the solution pH < 4.0, CBZ/OXC-mips carries a positive charge and is electrostatically repelled by CBZ and OXC with protonated amide groups, leading to a decrease in adsorption capacity.

By utilizing surface molecular imprinting technology and magnetic responsive imprinting technology, with CBZ and OXC as template molecules, IA as the functional monomer, Fe3O4@SiO2 as the carrier, EGDMA as the crosslinking agent, and AIBN as the initiator, we successfully synthesized CBZ/OXC-mips. Using annealing simulation algorithms to optimize the functional monomer, the preparation of CBZ/OXC-mips was optimized with a ratio of CBZ and OXC to IA of 1:2, EGDMA and acetonitrile amounts of 25mmol, 60mL, and the ratio of CBZ to OXC as 1:1. The structure, morphology, and composition of CBZ/OXC-mip were characterized using FTIR, XRD, SEM, and BET analysis. The results indicated that CBZ/OXC-MIPs possess magnetic properties and a loose porous structure. The pore size is primarily distributed between 1-2nm, with a specific surface area of 266.97m2/g. The adsorption process of CBZ/OXC-MIPs conforms to the Freundlich law. Optimal equilibrium is reached in about 30 minutes, consistent with pseudo-second-order kinetics. The adsorption performance of CBZ/OXC-MIPs surpasses that of single-template polymers (CBZ-mips and OXC-MIPs). The adsorption process is spontaneous, endothermic, and entropy-increasing. CBZ/OXC-MIPs exhibit excellent specific adsorption capability, with a decrease in adsorption capacity of 3.39% after 10 regenerations. Molecular simulation and characterization analysis results indicate that van der Waals forces, hydrogen bonding, and electrostatic interactions play significant roles in the specific adsorption of CBZ/OXC-mips for CBZ and OXC.

Article Details:

https://doi.org/10.1016/j.seppur.2022.122556