| The process of leather making generates large amount of chrome-containing wastewater and dyeing wastewater. These pollutants will bring about environmental pollution as well as the waste of resource. In this research, the collagen fiber extracted from the acid sheepskin was modified by the hyperbranched polymer with multi-functional groups and three dimensional branching structures. The novel effective adsorption materials were prepared and applied in the treatment of Cr(III)and dye solution. The adsorption properties as well as the adsorption mechanism were studied to elucidate the relationship between the structure of the adsorption materials and the adsorption properties. The studies make the fundamental works of research and development of novel tanning auxiliary agents and dyeing auxiliary to improve the absorptivity of tanning agent and dye molecular.The acid relaxation collagen fiber(CF) was prepared by acid swelling method to remove the interfibrillar substance and mechanical function. Firstly, the acrylic acid methyl ester(MA) and ethyl three amine(DETA) were used as the raw materials to prepare the terminal-amino hyperbranched polymer(HBPN). By using the glutaraldehyde as crosslinking agent, the HBPN was grafted onto the surface of CF to prepare the terminal-amino hyperbranched polymer modified collagen fiber adsorption material(CF-HBPN). Secondly, we choose glyoxalic acid as the terminal modified agent to prepare the terminal-carboxyl hyperbranched polymer modified collagen fiber adsorption material(CF-HBPC). The active functional groups content of pristine collagen fiber and modified collagen fiber were determined by chemical analysis methods, namely, the salicylic aldehyde method for the amino group’s content and Boehm titrimetry for the carboxyl group’s content. At the same time, the Fourier transform infrared spectroscopy(FT-IR), X-ray photoelectron-spectroscopy(XPS), the specific surface area analyzer, Field-emission scanning electron microscope(SEM)were employed to characterize the structure and surface morphology of CF, CF-HBPN and CF-HBPC.The appropriate modification conditions were optimized by orthogonal experiment method. Experimental results showed that the optimum concentration of glyoxylic acid was 0.133g·L-1, the reaction temperature was 45℃, the reaction p H of the system was 6.5 and the reaction time was 3h. The reaction rate between CF-HBPN and glyoxylic acid was 30.11mg·g-1 under these conditions. The amino content of CF-HBPN was 5.45% and it increased by 32.6% than that of CF. After carboxyl modification, the carboxyl group’s content of CF-HBPC increased by 20.08% when compared with CF. The adsorption peak of carboxyl carbonyl appeared at the 1730cm-1 in the FT-IR spectra of CF-HBPC, indicating the terminal modification reaction was succeeded. The BET specific surface area of CF and CF-HBPC were 0.6062m2·g-1 and 0.9613m2·g-1. After the glyoxylic acid modification, the intermolecular hydrogen bonding of CF-HBPN was broke. The triple-helical structure bonding strength decreased and became loose. The peptide chain extended and the thermal denaturation temperature decreased. Above all, the CF-HBPC was prepared as the designed route.The simulated Cr(III) containing solution was prepared to study the adsorption properties of the collagen fiber based adsorption materials. The influence of p H, temperature, the dosage of the adsorption material and initial concentration of the solution to the adsorption efficiency of CF, CF-HBPN and CF-HBPC were studied, respectively. The pseudo first order kinetic model, pseudo second order kinetic model and intra particle diffusion model were employed to fit the experimental adsorption kinetic data. Moreover, the Langmuir, Freundlich and Temkin adsorption isotherm models were used to fit the experimental adsorption isotherm data. The FT-IR, SEM-EDS, X-ray diffraction analysis( XRD) analysis were employed to characterize the variations of the adsorption materials before and after Cr(III) adsorption. The results indicated that when the optimal p H was 4.5, the adsorption capacity of CF-HBPC was 75.02mg·g-1. It was 158.1% higher than that of CF. For a certain volume of Cr(III) containing solution, the adsorption capacity increased with the increase of initial concentrations of the solution, and decreased with the increase of the dosage of the adsorption material. The Cr(III) removal rate decreased with the increase of initial concentration of Cr(III) containing solution. Moreover, it increased with the increase of the dosage of adsorbent material. The adsorption kinetic study results indicated that the Pseudo second order model was suitable to describe the adsorption kinetic of CF-HBPN and CF-HBPC toward Cr(III). The adsorption thermodynamics of CF-HBPC was studied, too. The Langmuir isotherm was much better to describe the adsorption isotherm of CF-HBPC to Cr(III). Therefore, the adsorption process is single layer adsorption and the adsorption sites were distributed on the surface of the adsorption material uniformly. The adsorption probability is identical. The FT-IR analysis indicated that the carboxyl functional group was involved in the adsorption process. The fluorescence intensity of CF-HBPN-Cr( III) and CF-HBPC-Cr(III) increased when compared with CF-HBPN and CF-HBPC. It meant new complex state was generated during the adsorption process. The EDS analysis showed that the Cr content in the CF-Cr(III), CF-HBPN-Cr(III) and CF-HBPC-Cr(III) were 1.91%, 2.62% and 5.24%, respectively. It could be concluded that with the inducement of hyperbranched polymer and multi-functional groups, the adsorption capacity of CF increased. The Cr OOH characteristic absorption peak appeared at 26.5° in the XRD spectrum of CF-Cr(III).In order to study the relationship between the structure of adsorption material and the adsorption properties of the adsorption material, the HBPN was grafted onto the surface of CF-HBPN by glutaraldehyde to prepare the second generation of terminal-amino hyperbranched polymer collagen fiber adsorption material( CF-HBPN-II). The appropriate modification conditions were optimized by orthogonal experiment experiment method. Experimental results showed that the optimum reaction temperature was 60℃, the reaction p H of glyoxylic acid was 9.0, the reaction time of glutaraldehyde was 130 min and the concentration of glutaraldehyde was 2.51g·L-1. The potentiometric titration results indicated that the total amine, the tertiary amine, primary and secondery amine content were 9.3116mmol·g-1, 1.8608mmol·g-1, 7.4508mmol·g-1, respectively. The isoelectric point of CF-HBPN was 8.399. The amino content of CF-HBPN-II increased because the histidine content of CF-HBPN-II increased during the amino acid analysis. The BET specific surface area of CF-HBPN and CF-HBPN-II were 0.5873m2·g-1 and 0.6870m2·g-1.The adsorption properties of CF, CF-HBPN and CF-HBPN-II toward acid black dye( Isolan black 2S-LD) were investigated by static adsorption experiments. The experimental results indicated that when the p H of dye solution was 3.0, the adsorption capacities and the removal rate were 325.11mg·g-1 and 99.64%. The pseudo second order kinetic fitted the adsorption kinetic of CF-HBPN toward dye better. The adsorption process was endothermic and spontaneous. The FT-IR, XPS and SEM-EDS analysis indicated that the N groups were protonated by obtaining the H+ and show electrostatic attraction to anionic dye. The fluorescence intensity decreased after dye adsorption. The distilled water and 0.1mol·L-1 Na OH were used as the desorption agent to study the desorption properties of CF-HBPN and CF-HBPN-II. The experimental results indicated that the desorption efficiency of distilled water was low, namely, only 1% of the dye molecule was desorbed. The supralan yellow can be desorbed by 0.1mol·L-1 Na OH largely, namely, 54.98% for CF-HBPN and 74.44% for CF-HBPN-II. |
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