Fabrication Of Adsorption Materials Of Cellulose-based For Heavy Metal Ions And Study Of Their Adsorption Performance

Cellulose is one of the natural polymer synthesized through photosynthesis. It is in harmony with the nature ecosystem circulation system, and can completely regenerate, is a kind of huge reserves of natural resources. Cellulose have abundant functional groups, which prone to physical and chemical modification, and also has the advantage such as biodegradability, biocompatibility and safety. Cellulose is valuable resources and wealth which endowed to human by nature. Nature can synthesize cellulose of about 180 billion tons per year through photosynthesis, but the cellulose used by human accounts for less than 10% of the total cellulose on the earth by far, causing the tremendous waste of resources. Hyperbranched polymer containing a large number of active end functional group, moleculars has fewer coils and it is difficult to crystallization. Hyperbranched polymer has good performance, low viscosity and high chemical reactivity, etc. In addition, the synthesis of hyperbranched polymer has some advantages, such as simple operation, synthesis of low cost, which make an attractive prospect of application of hyperbranched polymer.In this study, cotton fibers and cellulose diacetate nanofibers(CDA) were modified by amino-end hyperbranched polymer HBP-NH2, and two kinds of heavy metal adsorption materials CF-NH2 and CDA-NH2 were preparied. The Prepared heavy metal adsorption materials CF-NH2 and CDA-NH2 were analysed by SEM, FT-IR and XPS to characterize the combination of HBP-NH2 to cotton fibers and CDA nanofibers. Heavy metal adsorption materials CF-NH2 and CDA-NH2 were used to adsorpt copper ions, which existing in the form of Cu2+ cation in solulution. And they were also used to adsorpt chromium ions, which existing mainly in the form of Cr2O72-, Cr O42-, HCr O4- anion in solulution.The research results showed that HBP-NH2 was grafted onto cotton fibers and CDA nanofibers by the role of the glutaraldehyde crosslinking after a series of pretreatment, and two kinds of heavy metal adsorption materials CF-NH2 and CDA-NH2 were preparied successfully modified by HBP-NH2.SEM images shows that the surface of cotton fibers and CDA nanofibers which were modified by HBP-NH2 were covered with a layer of crosslinking layer, which shows that HBP-NH2 was banded onto cotton fibers and CDA nanofibers by chemical graft crosslinking.The analysis of FT-IR shows that the characteristic absorption peaks of C=N appears at 1637.27 cm-1 of cotton fibers modified by HBP-NH2, the stretching vibration peak of primary amine-N-H appears at 1619.91 cm-1, and the characteristics of the aliphatic amine absorption peaks appear at 1227.76 cm-1, 1202.62 cm-1 and 1058.73 cm-1, which show that HBP-NH2 was bonded onto cotton fibers successfully. The characteristic absorption peak of C=N appears at 1637.34 cm-1 of CDA nanofibers modified by HBP-NH2, which confirmed that the schiff base was produced by the reaction of the glutaraldehyde and ammonia. There are free-NH2,-NH and association-NH2,-NH formed N-H stretching vibration absorption peak by the overlapping at absorption frequency between 3500~3100 cm-1. Primary amine N-H bending vibration absorption peak appears at 1558.27 cm-1. absorption frequency between 1350~400 cm-1 is fingerprint area, the organic amine C-H stretching vibration peak appears at 1157.13 cm-1 and 1114.70 cm-1, which further confirmed that HBP-NH2 was bonded onto CDA nanofibers successfully.The analysis of XPS also shows that obvious N1 s photoelectron spectral lines appears at 396 e V of the surface of cotton fibers modified by HBP-NH2, and obvious N1 s photoelectron spectral lines appears at 398.2 e V of the surface of CDA nanofiber modified by HBP-NH2, which further confirmed that HBP-NH2 was bonded to the surface of cotton fibers and CDA nanofibers successfully by crosslinking of the glutaraldehyde.The static adsorption of Heavy metal experiments showed that adsorption ability of cotton fibers modified with HBP-NH2(CF-NH2) to Cu(II) and Cr(VI) ion has greatly improved comparing with the ordinary cotton fibers and the oxidated cotton fibers. When the p H value of solution was 5.0, the adsorption capacity of CF-NH2 to Cu(II) was strongest, and the adsorption quantity was biggest. When the p H value of solution was 4.0, the adsorption capacity of CF-NH2 to Cr(VI) ions reached the maximum. Comparing with the ordinary CDA nanofibers, adsorption ability of CDA nanofibers modified with HBP-NH2(CDA-NH2) to Cu(II) and Cr(VI) ion has greatly improved. When the p H value of solution was 5.59, there is abundent amino functional groups to high degree of proton, leading to more free amino functional ligand and heavy metal Cu(II) ion, at the same time amino functional groups on the free electron to attract ability will be further strengthened, the adsorption capacity of CDA-NH2 to Cu(II) was strongest, and the adsorption quantity was biggest. When the p H value of solution was 4.0, the adsorption capacity of CDA-NH2 to Cr(VI) ions reached the maximum.Adsorption isotherm experiments showed that the adsorption of CF-NH2 and CDA-NH2 for Cu(II) and Cr(VI) ion is mainly chemical adsorption, and the influence of solution temperature on the adsorbent adsorption capacity is little, and the adsorption of heavy metals can be performed at room temperature. Adsorption isotherms of CF-NH2 and CDA-NH2 to Cu(II) and Cr(VI) ions have good fitting with Langmuir equation under different temperatures, linear correlation coefficients are greater than 0.99. The fitting results show that the adsorption of CF-NH2 and CDA-NH2 to Cu(II) and Cr(VI) ion is an exothermic process, belongs to the chemical adsorption. The adsorption of CF-NH2 and CDA-NH2 to Cu(II) and Cr(VI) ion is multilayer adsorption, and it has a good adsorption capability of CF-NH2 and CDA-NH2 to cation Cu2+ and anionic HCr O4- ion in aqueous solution.Adsorption kinetics experiments showed that the adsorption kinetics of CF-NH2 and CDA-NH2 to Cu(II) and Cr(VI) ions have good regression effect with Lagergren quasi secondary dynamics equation, and the dynamics equation of quasi secondary regression linear correlation coefficients are greater than 0.99, are better than the first order kinetics equation of regression results. Calculated adsorption balance numerical values using secondary dynamics equation on Cu(II) and Cr(VI) ions are very close to experimental values, which show that adsorption of CF-NH2 and CDA-NH2 for Cu(II) and Cr(VI) ion conforms to the secondary adsorption dynamics, the adsorption process of CF-NH2 and CDA-NH2 for Cu(II) and Cr(VI) ion belongs to the chemical adsorption.In addition, amino content of two kind heavy metal adsorption materials CF-NH2 and CDA-NH2 is 0.305% and 7.531%, respectively. As the adsorption of the two kind heavy metal adsorption materials is mainly chemical adsorption, which makes CDA-NH2 has a higher adsorption capacity for Cu(II), Cr(VI) ions than CF-NH2.