Facile Preparation And Characterization Of A Novel Magnetic Adsorbent And For Fulvic Acid And Hexavalent Chromium Removal

With the rapid economic development and continuous improvement of people's living standards,the problem of water pollution is severe increasingly.Fe3O4 is a kind of spinel ferrite with good magnetic and biocompatibility.Chitosan and ?-CD are inexpensive and easy to be degarded and contain a variety of function groups.Therefore Fe3O4 was modified by chitosan and ?-CD.The natural organic matter fulvic acid and inorganic heavy metal Cr(VI)were selected as the target pollutants for exploring the performance and mechanism of FA and Cr(VI)by ?-CD@CS MNPs.In this paper,?-cyclodextrin chitosan magnetic nanoparticles(?-CD@CS MNPs)were facilely synthesized by an ex situ co-precipitation method.The adsorbent was characterized using mutiple techniques and its performance for fulvic acid(FA)removal from solution was investigated.The SEM and TEM image indicated that the shape of ?-CD@CS MNPs was uniform size of(52±3)nm.X-ray powder diffraction(XRD)analysis showed that the magnetic phase in ?-CD@CS MNPs was spinel magnetite.The absorbent has super-paramagnetic and saturation magnetization of 62 emu×g-1.Meanwhile,the effect of p H,adsorbent content,temperature,initial concentration and adsorption time on adsorption capacity was studied.The results showed that the practical adsorption capacity for FA was51.35 mg×g-1 at p H 7.0±0.1 under 25 ?,and the adsorption equilibrium was reached in 600 min.The adsorption process was endothermic reaction.Furthermore,the experimental data showed that the adsorption behavior of ?-CD@CS MNPs for FA fitted Langmuir isotherm model and pseudo-second-order model.The presence of cations(K+?Ca2+)contributes to the adsorption of FA by ?-CD@CS MNPs,with the order of Ca2+>K+.In addition,the adsorption behavior of Cr(VI)by ?-CD@CS MNPs was studied.With the help of FTIR,XRD,VSM and XPS characterization methods,Cr(VI)was proved to be absorbed on ?-CD@CS MNPs with no valence state change of chromium element,the adsorbent had complete crystal structure and stable magnetism before and after adsorption.Meanwhile,the effect of p H,adsorbent content,temperature,initial concentration andadsorption time on adsorption capacity was studied.The results showed that the practical adsorption capacity for Cr(VI)was 31.60 mg × g-1 at p H 3.0±0.1 under 25 ?,and the adsorption equilibrium was generally reached in 50 min.The adsorption process was endothermic reaction.Furthermore,the experimental data showed that the adsorption behavior of ?-CD@CS MNPs for FA fitted pseudo-second-order model and Freudlich isotherm model.The presence of anionic(Cl-?NO3-)is not conductive to the adsorption of Cr(VI)by ?-CD@CS MNPs,with the order of NO3-> Cl-.Moreover,the presence of fulvic acid didn't significantly promote the removal of Cr(VI)by ?-CD@CS MNPs,but in the process of adsorption,there is valence state change of chromium element.Adsorption mechanism of FA and Cr(VI)may involved electrostatic interaction,hydrogen bonding and hydrophobic interaction,as well as inclusion interaction which contributed to the host-guest interactions between ?-CD molecules and organic contaminant.