Synthesis and characterization of superparamagnetic poly(urea-formaldehyde) adsorbents and their use for adsorption of flavonoids from Glycyrrhiza uralensis Fisch

Abstract

Superparamagnetic spherical poly(urea-formaldehyde) (PUF) adsorbents were synthesized and their selective adsorption for licorice flavonoids was investigated in this paper. The magnetite (Fe 3 O 4 ) nanoparticles were prepared by co-precipitation of ferrous and ferric salts. Then the magnetic adsorbents with PUF shell were synthesized by reversed phase suspension polymerization. The spherical adsorbents have an average diameter of 50 µm and exhibit superparamagnetic characteristics. The saturation magnetization of the adsorbents was 15.1 emu/g. The sorption and desorption properties of licorice flavonoids on the adsorbents were studied. The result shows that the adsorbents have high adsorption capacity (about 16.7 mg/g (adsorbent)). The adsorption data of flavonoids generally obeys the Langmuir isotherm equation. The adsorption can reach equilibrium rapidly and depends strongly on the pH of the feed solution. The concentration of licorice flavonoids after desorption can reach 25.12% in the desorbed fraction with 75% ethanol solution, which is higher than the 21.9% of commercial macroporous resin XDA-1. HPLC showed that liquiritin, one of main flavonoids in the licorice, was retained in this fraction, while glycyrrhizic acid (GA) can be almost removed from this fraction.Abbreviations a adsorption equilibrium constant A adsorption ratio (%) C d flavonoids concentration of desorption solution (mg/ml) C e equilibrium concentration of flavonoids in the adsorption solution (mg/ml) C o initial concentration of flavonoids in the adsorption solution (mg/ml) D desorption ration (%) GA glycyrrhizic acid PUF poly(urea-formaldehyde) Q e adsorption capacity at adsorption equilibrium (mg/g adsorbents) Q m saturation adsorption capacity (mg/g adsorbents) V d volume of desorption solution (ml) V i volume of initial solution (ml) W weight of the dry adsorbents (g)

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