Modification And Adsorption Properties Of Nature Polysacharides

When heavy metals from various industrial activities enter aquatic systems they must be removed from the wastewater because of their significant threat to human health. Among the various techniques used for treatment of heavy metals in wastewater, adsorption is a promising alternative due to easy handling, lower operating costs, high efficiency for removing very low levels of heavy metals from dilute solutions, and there is no threat of secondary contamination. Starch and cellulose, the most common nature polymer, was modified to adsorb heavy metal ions and their adsorption properities were researched.Porous starch?PS? was modified with carbon disulfide?CD? and citric acid?CA? to obtain porous starch xanthate?PSX? and porous citrate starch?PCS?, which were characterized by scanning electron microscopy?SEM? and Fourier transform infrared spectroscopy?FTIR?. The xanthate and carboxylate groups once were attached to the walls of the porous structures, they could respectively form chelation and electrostatic interactions with heavy metal ions. The Pb²⁺ ion was selected as the model metal and its adsorption by PSXs and PCSs was characterized. The adsorption capacity was highly dependent on the CD/starch and CA/starch mole ratios used during preparation. The adsorption behavior of Pb²⁺ on PSXs and PCSs fit both the pseudo-second-order kinetic model and the Langmuir isotherm model well. The maximum adsorption capacity from the Langmuir isotherm equation reached 109.1 and 57.6 mg/g for PSX and PCS when preparation conditions were optimized, and the adsorption time was just 20 and 60 min, respectively. As monolithic materials, the obtained PSXand PCS could be easily separated out after the adsorption process. PSX and PCS might be used as effective adsorbents for removal of heavy metals from contaminated liquid. But porous structure was easily destroyed in aqueous systerm, cellulose was used instead subsequently.Porous celluloses?PCs? were successfully prepared by a simple process of freezing the cellulose solution in ionic liquid, followed by solvent exchange and drying at normal temperature instead of the supercritical drying. PCs were composed of cellulose sheets of low crystallinity, as evidenced by SEM, XRD, TGA and FTIR, oriented into unidirectional structures when the cellulose concentration was low?1%?. When the cellulose concentration was high?4%? the structure was twisted and randomly oriented. PCs had low apparent densities of 44 to 88 mg/cm3 and oil adsorption capacities ranging from 9.70 to 22.40 g/g?oil/PC? due to the ultralight porous structures. Oxidation of sodium periodate introduced dialdehyde groups into the porous structure. After the same reaction time, the aldehyde content of PC was much higher than the untreated cellulose counterpart. The resultant dialdehyde modified-PC had better urea adsorption than modified-viscose fiber. The high reactivity of PCs was related to the low crystallinity and porous structure.