Selective Adsorption of Quercetin by the Sol-Gel Surface Molecularly Imprinted Polymer

Abstract

Quercetin, as one of the most biologically active natural flavonoids, is widely found in various vegetables, fruits and Chinese herbs. In this work, molecularly imprinted polymer (MIP) was synthesized through surface molecular imprinting technology with sol-gel polymerization mechanism on SiO2 at room temperature using quercetin as the template, SiO2 as the supporter, 3-aminopropyltriethoxysilane (APTES) as the functional monomer, and tetraethoxysilane (TEOS) as the cross-linker. The prepared MIP was characterized via scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption measurements to validate its surface morphology, structure and functionality. SEM images revealed that the morphology of MIP was rough and spherical with the particle size of 260 nm larger than that of the support SiO2. In the FTIR spectra of MIP, the band around 1499 cm−1 and 2932 cm−1 were assigned to N−H and C-H groups, respectively. The results indicated that the imprinted polymer layers were grafted on the surface of SiO2 and the MIP had been successfully prepared. Since the specific surface area and pore volume of MIP were markedly higher than those of NIP and SiO2 and were 52.10 m2 g−1 and 0.150 cm3 g−1, respectively, it was evident that the imprinting process created corresponding imprinted cavities and porosity. The MIP for adsorbing quercetin was evaluated by static adsorption experiment. The results indicated that the adsorption equilibrium could be reached within 90 min and the maximum adsorption capacity was as high as 35.70 mg/g. The mechanism for adsorption kinetics and isotherm of MIP for quercetin was proved to conform the pseudo-second-order kinetics model (R2 = 0.9930) and the Freundlich isotherm model (R2 = 0.9999), respectively, revealing that chemical adsorption and heterogeneous surface with multilayer adsorption dominated. In contrast to non-imprinted polymer (NIP), the MIP demonstrated high selectivity and specific recognition towards quercetin whose selectivity coefficients for quercetin relative to biochanin A were 1.61. Furthermore, the adsorption capacity of MIP can be maintaining above 90% after five regeneration cycles, indicating brilliant reusability and potential application for selective adsorption of quercetin.

Adsorption and Recognition Property of Tyrosine Molecularly Imprinted Polymer Prepared via Electron Beam Irradiation

“…The regeneration property of MIPs is crucial in practical industrial application. The reusability and the stability of the obtained MIP was determined by measuring the adsorption capacity of the MIP for L-Tyr repeatedly after each adsorption-desorption cycle under the same conditions [38,40]. The adsorption capacity of the MIP, which was reused five times, is shown in Figure 12, which demonstrates that the obtained MIP has excellent stability with a negligible decrease in adsorption capacity.…”

“…The results indicate that the adsorption of L-Tyr with an MIP is very fast, within 0.5 h, and higher capacity was observed for high initial concentration at adsorption equilibrium. In addition, a longer time was needed to reach adsorption equilibrium for the high concentration, demonstrating that the adsorption process is dependent on concentration [37,38].…”

Hydrophilic molecularly imprinted phenol-amine-formaldehyde resins

“…It was shown that in the presence of polyethylene glycol (porogen) with an average molecular mass of 10000 Da, the sorption capacity of quercetin by the molecularly-imprinted sample was ~5 µmol/g, the specific surface area was 288.1 m 2 /g, and the imprinting factor was 1.41. It was shown that recovery of quercetin (21-43%) is slightly lower, but the imprinting factor (1.4) is not inferior to that of the similar methods for extracting phenolic compounds [26] and dyes [29] with resorcinol-melamine-formaldehyde and phenol-formaldehyde resins, as well as quercetin with surface-imprinted polymers [30,31]. Modeling of the kinetics and isotherms of quercetin rebinding by the samples, obtained in the presence of polyethylene glycol of different average molecular mass, showed compliance with the pseudo-second-order model and the Freundlich model describing an inhomogeneous surface.…”

Preparation and Application Progress of Imprinted Polymers

“…The detection accuracy of the obtained sensor was relatively good, with a recovery rate of 92–117% for practical samples. The sol–gel approach was used for the fabrication of quercetin-based SIPs ( Figure 9 ) [ 101 ], the adsorption could reach equilibrium within 90 min, with a maximum adsorption capacity of 35.7 mg/g. The mechanism for adsorption isotherm and kinetics of SIPs was proved to obey the Freunflich isotherm model and pseudo-second-order kinetics model.…”