Adsorption Of Dyes From Water By Cyclodextrin-based Nanocomposites

The wastewater containing dyes not only results in the unrecoverable environmental pollution,but also has serious teratogenic and carcinogenic harm to human body.Therefore,the removal of dyes is an important issue for organic wastewater treatment.β-cyclodextrin(β-CD)is a kind of oligosaccharide with biological activity,which is often used as adsorbent because of its more adsorption active sites and special hydrophobic cavity structure.However,β-cyclodextrin is soluble in water,so it is necessary to modify it to enhance adsorption effect.In this paper,four kinds of adsorbent precursors,H-β-CDP,P-β-CDP,M-β-CDP and I-β-CDP,were synthesized,respectively,with four diisocyanate derivatives,that is,hexamethylene diisocyanate(HDI),p-phenyldiisocyanate(PPDI),diphenylmethane diisocyanate(MDI)and isophorone diisocyanate(IPDI)via crosslinking.These four adsorbents were used to adsorb methylene blue,rhodamine B and methyl orange,respectively.It suggests that P-β-CDP showed the most excellent adsorption effect,followed by M-β-CDP.The P-β-CDP was further modified by ethylenediaminetetraacetic acid(EDTA)to fabricate P-E-β-CDP to improve the hydrophicity of the material.P-β-CDP,M-β-CDP and P-E-β-CDP were characterized,respectively,by Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),thermogravimetric analysis(TGA),specific surface area test,water contact angle test and scanning electron microscopy(SEM).The adsorption experiments of methylene blue and rhodamine B were carried out with three adsorption materials,and the effects of initial concentration of the dye,adsorption time,p H and temperature on the adsorption capacity were investigated.The results indicate that the p H had a greater adsorption effect on methylene blue,but less one on rhodamine B.The adsorption kinetics and the adsorption isotherm model were analysized and fitted,respectively.It reveals that the adsorption process was strongly correlated with the pseudo-second-order kinetics equation and the Langmuir isotherm model,indicating that the adsorption process was a monolayer adsorption model dominated by chemisorption.The maximum adsorption capacity of P-β-CDP was 736.2mg/g when the initial concentration of Rhodamine B was 900mg/L.That of M-β-CDP was93.73mg/g when the initial concentration of methylene blue was 143.25mg/L.