Magnetic Porous Molecularly Imprinted Polymers Based on Surface Precipitation Polymerization and Mesoporous SiO2 Layer as Sacrificial Support for Efficient and Selective Extraction and Determination of Chlorogenic Acid in Duzhong Brick Tea.

Magnetic porous molecularly imprinted polymers (MPMIPs) for rapid and efficient selective recognition of chlorogenic acid (CGA) were effectively prepared based on surface precipitation polymerization using CGA as template, 4-vinylpyridine (4-VP) as functional monomer, and mesoporous SiO2 (mSiO2) layer as sacrificial support. A computational simulation by evaluation of electronic binding energy is used to optimize the stoichiometric ratio between CGA and 4-VP (1:5), which reduced the duration of laboratory trials. The porous MIP shell and the rid of solid MIPs by magnet gave MPMIPs high binding capacity (42.22 mg/g) and fast kinetic binding (35 min). Adsorption behavior between CGA and MPMIPs followed Langmuir equation and pseudo-first-order reaction kinetics. Furthermore, the obtained MPMIPs as solid phase adsorbents coupled with high performance liquid chromatography (HPLC) were employed for selective extraction and determination of CGA (2.93 ± 0.11 mg/g) in Duzhong brick tea. The recoveries from 91.8% to 104.2%, and the limit of detection (LOD) at 0.8 µg/mL were obtained. The linear range (2.0⁻150.0 µg/mL) was wide with R² > 0.999. Overall, this study provided an efficient approach for fabrication of well-constructed MPMIPs for fast and selective recognition and determination of CGA from complex samples.

Weaving microscale wool ball-like hollow covalent organic polymers from nanorods for efficient adsorption and sensing.

Microscale covalent organic polymers with a unique 3D hollow wool ball-like morphology have been woven from 1D nanorods by a cascade emulsion strategy with a large surface area (284 m2 g-1), which showed great potential for simultaneous removal (Qmax, 358.15 mg g-1) and fluorescent detection (detection limit, 8.0 µg L-1) of bisphenol A.

Hydrophobic-force-driven adsorption of bisphenol A from aqueous solution by polyethylene glycol diacrylate hydrogel microsphere.

Polyethylene glycol diacrylate (PEGDA) hydrogel microsphere was synthesized by UV-assisted reverse emulsion polymerization as an efficient adsorbent for water purification. Optical microscopy and TEM proved its spherical and hollow structure, while XRD pattern proved that it was amorphous with limited crystallinity. Abundant oxygen-containing functional groups such as hydroxyl were detected by FTIR. The hydrogels exhibited low swelling capacities ranging from 0.19 to 0.77 g/g in water and would decrease in salty solutions. The effects of operation parameters on the bisphenol A (BPA) adsorption were studied, including the polymer composition between PEGDA and polyethylene glycol methacrylate (PEGMA), initial concentration of BPA, pH, and operation temperature. The resulting hydrogel, especially for PDM2 (the ratio between PEGDA and PEGMA is 2), was able to effectively enrich BPA in water. The adsorption capacity was nearly stable below pH 8.0 and decreased when beyond 8.0. Thermodynamic parameters reflected that BPA adsorbed by hydrogel was a spontaneous (ΔG0 < 0) and exothermic (ΔH0 < 0) progress. The adsorption capacity increased with the increase of the concentration of NaCl, exhibiting salinity-enhanced adsorption capacity driven by hydrophobic force. Excellent results were also achieved by applying hydrogel for spiked real surface waters, which accounted for more than 91% compared to simulated solution. As-prepared hydrogel was expected to be good candidate for treatment of endocrine disruptors with lower solubility in water.

Effective synthesis of magnetic porous molecularly imprinted polymers for efficient and selective extraction of cinnamic acid from apple juices.

An effective strategy was proposed to prepare novel magnetic porous molecularly imprinted polymers (MPMIPs) for highly selective extraction of cinnamic acid (CMA) from complex matrices. Characterization and various parameters affecting adsorption and desorption behaviors were investigated. Results revealed adsorption behavior between CMA and MPMIPs followed Freundlich equation adsorption isotherm with a maximum adsorption capacity at 4.35mg/g and pseudo-second-order reaction kinetics with equilibrium time at 60min. Subsequently, MPMIPs were successfully used to selectively extract CMA from apple juice with a relatively satisfactory recovery (92.7-101.4%). Coupling with high-performance liquid chromatography and ultraviolet detection (HPLC-UV), the limit of detection (LOD) for CMA was 0.006µg/mL, and the linear range (0.02-10µg/mL) was wide with correlation coefficient at 0.9995. Finally, the contents of CMA in two kinds of apple juices were determined as 0.132 and 0.120µg/mL. Results indicated the superiority of MPMIPs in the selective extraction field.

High-capacity hollow porous dummy molecular imprinted polymers using ionic liquid as functional monomer for selective recognition of salicylic acid.

The existence of strong intramolecular hydrogen bond in salicylic acid (SA) weakens its intermolecular hydrogen bonding with functional monomer, then it is a challenge work to fabricate molecularly imprinted polymers (MIPs) for SA recognition with high capacity and good selectivity. Here, hollow porous dummy MIPs (HPDMIPs) were prepared using benzoic acid (BA) as dummy template, ionic liquid (i.e. 1-vinyl-3-methylimidazolium chloride) as functional monomer, and MCM-48 as sacrificial support. Factors that affected adsorption, such as type of template and porogen, mole ratio of template-functional monomer-cross-linker and type of binding solvent, were optimized in detail. Multiple strong interactions between SA and ionic liquid in HPDMIPs deduced higher binding capacity (29.75mg/g), imprinting factor (5.61) and selectivity than any previously reported MIPs by traditional or surface imprinting technology. The large surface area (543.9m2/g) with hollow porous structure resulted in faster kinetic binding (25min). The equilibrium data fitted well to Freundlich equation and the adsorption process could be described by pseudo-second order model. Finally, HPDMIPs were successfully applied to selectively extract and enrich SA from Actinidia chinensis with a relatively high recovery (84.6-94.5%).

Synthesis and characterization of hollow porous molecular imprinted polymers for the selective extraction and determination of caffeic acid in fruit samples.

Hollow porous molecular imprinted polymers (HPMIPs) were prepared using caffeic acid (CA) as template, 4-vinylpyridine (4-VP) as functional monomer, and MCM-48 as sacrificial support. Large surface area (562.7m2/g) of HPMIPs resulted in high binding capacity (27.26mg/g) and fast kinetic binding (40min) in comparison with solid MIPs. Equilibrium data fitted well to Freundlich equation, and adsorption process with multi-diffusion mechanisms could be described by pseudo-second order model. Selectivity of HPMIPs was favorable. Finally, HPMIPs were successfully used to rapidly and selectively extract CA from fruits with a relatively satisfactory recovery (87.1-101.3%). Coupling with HPLC, contents of CA in kiwifruit, apple, papaya and waxberry were less than 1.0µg/g fresh fruit. Results indicated the superiority of HPMIPs in the separation field.

Hollow porous ionic liquids composite polymers based solid phase extraction coupled online with high performance liquid chromatography for selective analysis of hydrophilic hydroxybenzoic acids from complex samples.

Polar and hydrophilic properties of hydroxybenzoic acids usually made them coelute with interferences in high performance liquid chromatography (HPLC) analysis. Then selective analysis of them was necessary. Herein, hollow porous ionic liquids composite polymers (PILs) based solid phase extraction (SPE) was firstly fabricated and coupled online with HPLC for selective analysis of hydroxybenzoic acids from complex matrices. Hollow porous PILs were firstly synthesized using Mobil Composition of Matter No. 48 (MCM-48) spheres as sacrificial support, 1-vinyl-3-methylimidazolium chloride (VMIM+Cl-) as monomer, and ethylene glycol dimethacrylate (EGDMA) as cross-linker. Various parameters affecting synthesis, adsorption and desorption behaviors were investigated and optimized. Steady-state adsorption studies showed the resulting hollow porous PILs exhibited high adsorption capacity, fast adsorption kinetics, and excellent specific adsorption. Subsequently, the application of online SPE system was studied by selective analysis of protocatechuic acid (PCA), 4-hydroxybenzoic acid (4-HBA), and vanillic acid (VA) from Pollen Typha angustifolia. The obtained limit of detection (LOD) varied from 0.002 to 0.01µg/mL, the linear range (0.05-5.0µg/mL) was wide with correlation coefficient (R) from 0.9982 to 0.9994, and the average recoveries at three spiking levels ranged from 82.7 to 102.4%, with column-to-column relative standard deviation (RSD) below 8.1%. The proposed online method showed good accuracy, precision, specificity and convenience, which opened up a universal and efficient route for selective analysis of hydroxybenzoic acids from complex samples.

Hollow molecular imprinted polymers towards rapid, effective and selective extraction of caffeic acid from fruits.

Rapid and selective extraction and enrichment of trace bioactive analytes from complex matrices were of significant importance for efficient and accurate quantification. Here, novel hollow molecular imprinted polymers (HMIPs) were prepared using caffeic acid (CA) as template, 4-vinylpyridine (4-VP) as functional monomer, and Fe3O4@SiO2 as sacrificial support. Fourier transform infrared spectrometer (FT-IR), transmission electron microscopy (TEM), nitrogen adsorption and thermo-gravimetric analysis (TGA) were used to verify the successful synthesis of HMIPs. Hollow structure with large surface area (325.8m2/g) made most recognition sites locate on the surface of HMIPs, resulting in high binding capacity (21.10mg/g) and fast kinetic binding (35min) in comparison with magnetic MIPs (MMIPs) and solid MIPs. The equilibrium data fitted well to Freundlich equation and the adsorption process could be described by pseudo-second order model. The selectivity performance of HMIPs was favorable. Finally, HMIPs were successfully used as adsorbent to rapidly and selectively extract and enrich CA from fruits with a relatively satisfactory recovery (85.6-103.5%). Coupling with high-performance liquid chromatography (HPLC), the content of CA in four kinds of fruits (kiwifruit, apple, papaya and waxberry) was determined as less than 1.0µg/g fresh fruit. Results indicated the superiority of HMIPs in the selective extraction of target compound from complex matrices.

Boronate affinity-based surface molecularly imprinted polymers using glucose as fragment template for excellent recognition of glucosides.

Rapid and efficient extraction of bioactive glycosides from complex natural origins poses a difficult challenge, and then is often inherent bottleneck for their highly utilization. Herein, we propose a strategy to fabricate boronate affinity based surface molecularly imprinted polymers (MIPs) for excellent recognition of glucosides. d-glucose was used as fragment template. Boronic acid, dynamic covalent binding with d-glucose under different pH conditions, was selected as functional monomer to improve specificity. Fe3O4 solid core for surface imprinting using tetraethyl orthosilicate (TEOS) as crosslinker could control imprinted shell thickness for favorable adsorption capacity and satisfactory mass transfer rate, improve hydrophilicity, separate easily by a magnet. Model adsorption studies showed that the resulting MIPs show specific recognition of glucosides. The equilibrium data fitted well to Langmuir equation and the adsorption process could be described by pseudo-second order model. Furthermore, the MIPs were successfully applied for selective extraction of three flavonoid glucosides (daidzin, glycitin, and genistin) from soybean. Results indicated that selective extraction of glucosides from complex aqueous media based on the prepared MIPs is simple, rapid, efficient and specific. Moreover, this method opens up a universal route for imprinting saccharide with cis-diol group for glycosides recognition.

High-capacity magnetic hollow porous molecularly imprinted polymers for specific extraction of protocatechuic acid.

Magnetic hollow porous molecularly imprinted polymers (HPMIPs) with high binding capacity, fast mass transfer, and easy magnetic separation have been fabricated for the first time. In this method, HPMIPs was firstly synthesized using protocatechuic acid (PCA) as template, 4-vinylpyridine (4-VP) as functional monomer, glycidilmethacrylate (GMA) as co-monomer, and MCM-48 as sacrificial support. After that, epoxide ring of GMA was opened for chemisorbing Fe3O4 nanoparticles to prepare magnetic HPMIPs. The results of characterization indicated that magnetic HPMIPs exhibited large surface area (548m(2)/g) with hollow porous structure and magnetic sensitivity (magnetic saturation at 2.9emu/g). The following adsorption characteristics investigation exhibited surprisingly higher adsorption capacity (37.7mg/g), and faster kinetic binding (25min) than any previously reported PCA imprinted MIPs by traditional or surface imprinting technology. The equilibrium data fitted well to Langmuir equation and the adsorption process could be described by pseudo-second order model. The selective recognition experiments also demonstrated the high selectivity of magnetic HPMIPs towards PCA over analogues. The results of the real sample analysis confirmed the superiority of the proposed magnetic HPMIPs for selective and efficient enrichment of trace PCA from complex matrices.

Novel molecular imprinted polymers over magnetic mesoporous silica microspheres for selective and efficient determination of protocatechuic acid in Syzygium aromaticum.

Improving sites accessibility can increase the binding efficiency of molecular imprinted polymers (MIPs). In this work, we firstly synthesized MIPs over magnetic mesoporous silica microspheres (Fe3O4@mSiO2@MIPs) for the selective recognition of protocatechuic acid (PCA). The resulting Fe3O4@mSiO2@MIPs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR), thermo-gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), and vibration sample magnetometer (VSM), and evaluated by adsorption isotherms/kinetics and competitive adsorption. The maximum adsorption capacity of PCA on Fe3O4@mSiO2@MIPs was 17.2mg/g (2.3 times that on Fe3O4@SiO2@MIPs). In addition, Fe3O4@mSiO2@MIPs showed a short equilibrium time (140min), rapid magnetic separation (5s) and high stability (retained 94.4% after six cycles). Subsequently, Fe3O4@mSiO2@MIPs were successfully applied for the selective and efficient determination of PCA (29.3µg/g) from Syzygium aromaticum. Conclusively, we combined three advantages into Fe3O4@mSiO2@MIPs, namely, Fe3O4 core for quick separation, mSiO2 layer for enough accessible sites, and surface imprinting MIPs for fast binding and excellent selectivity, to extract PCA from complex systems.

Hydrophilic gallic acid-imprinted polymers over magnetic mesoporous silica microspheres with excellent molecular recognition ability in aqueous fruit juices.

Hydrophilic molecularly imprinted polymers (MIPs) for gallic acid (GA) were prepared with excellent recognition ability in an aqueous solution. The proposed MIPs were designed by self-polymerization of dopamine (DA) on magnetic mesoporous silica (Fe3O4@SiO2@mSiO2, MMS) using GA as template. Resulting Fe3O4@SiO2@mSiO2@MIPs (MMS-MIPs) were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), vibrating sample magnetometer (VSM), and evaluated by adsorption isotherms/kinetics and competitive adsorption. The adsorption behavior between GA and MMS-MIPs followed Langmuir and Sips adsorption isotherms with a maximum adsorption capacity at 88.7 mg/g and pseudo-second-order reaction kinetics with fast binding (equilibrium time at 100 min). In addition, MMS-MIPs showed rapid magnetic separation (10 s) and stability (retained 95.2% after six cycles). Subsequently, MMS-MIPs were applied for the selective extraction and determination of GA from grape, apple, peach and orange juices (4.02, 3.91, 5.97, and 0.67 µg/g, respectively). Generally, the described method may pave the way towards rationally designing more advanced hydrophilic MIPs.

Efficient determination of protocatechuic acid in fruit juices by selective and rapid magnetic molecular imprinted solid phase extraction coupled with HPLC.

Magnetic molecular imprinted polymers (MMIPs) have been prepared as solid phase material to selectively extract protocatechuic acid (PCA) from fruit juices with high capacity and fast binding kinetics. The resulting MMIPs were characterized by TEM, FT-IR, TGA, and VSM. The adsorption process between PCA and MMIPs followed Langumuir adsorption isotherm with maximum adsorption capacity at 7.5 mg/g and pseudo-second-order reaction kinetics with fast binding kinetics (equilibrium time at 40 min). In addition, the prepared MMIPs showed rapid magnetic separation (10 s) and reusability (retained 94.9% after six cycles). Subsequently, MMIPs were successfully applied for selective enrichment and determination of PCA from fruit juices (0.45 µg/mL in grape juice but not detected in apple juice, pineapple juice, orange juice, and peach juice) with satisfactory recoveries (92-107%). The results indicated that synthesized MMIPs can be used for efficient and selective extraction of PCA from complex matrices.

High-capacity thermo-responsive magnetic molecularly imprinted polymers for selective extraction of curcuminoids.

Thermo-responsive magnetic molecularly imprinted polymers (TMMIPs) for selective recognition of curcuminoids with high capacity and selectivity have firstly been developed. The resulting TMMIPs were characterized by TEM, FT-IR, TGA, VSM and UV, which indicated that TMMIPs showed thermo-responsiveness [lower critical solution temperature (LCST) at 33.71°C] and rapid magnetic separation (5s). The polymerization, adsorption and release conditions were optimized in detail to obtain the highest binding capacity, selectivity and release ratio. We found that the adopted thermo-responsive monomer [N-isopropylacrylamide (NIPAm)] could be considered not only as inert polymer backbone for thermo-responsiveness but also as functional co-monomers combination with basic monomer (4-VP) for more specific binding sites when ethanol was added in binding solution. The maximum adsorption capacity with highest selectivity of curcumin was 440.3µg/g (1.93 times that on MMIPs with no thermosensitivity) at 45°C (above LCST) in 20% (v/v) ethanol solution on shrunk TMMIPs, and the maximum release proportion was about 98% at 20°C (below LCST) in methanol-acetic acid (9/1, v/v) solution on swelled TMMIPs. The adsorption process between curcumin and TMMIPs followed Langumuir adsorption isotherm and pseudo-first-order reaction kinetics. The prepared TMMIPs also showed high reproducibility (RSD<6% for batch-to-batch evaluation) and stability (only 7% decrease after five cycles). Subsequently, the TMMIPs were successfully applied for selective extraction of curcuminoids from complex natural product, Curcuma longa.