Study On The Adsorption Properties Of Amino Terminated Hyperbranched Polyamide Modified Collagen Fiber Toward Cr(Ⅵ)

Cr （VI） is one of contaminants in the industrial wastewater understrict control of pollution. In this study, collagen fiber was used as aabsorbent to remove Cr（VI） from water at first. Effect of pH,temperature, absorbent dosage and initial concentration of Cr（VI） on itsremoval rate were studied in the batch mode. The results indicated thatthe modified collagen fiber was very effective for removal Cr（VI） fromwater. The removal rate of Cr（VI） increased with the decrease ofsolution pH value, and the maximum removal rate was attained at pHabout3.0. The increase of absorbent dosage would raise the removalefficiency, while it would simultaneously reduce the absorptioncapacity. Moreover, the removal of Cr（VI） was found to decrease withthe increasing of initial concentration of Cr（VI）. Whereas, the Cr（VI）uptake capacity increased with the rise of Cr（VI） initial concentrationuntil reaching saturation. The absorption equilibrium time was6h andthe optimum absorption temperature was40℃. The experimental resultsshowed that the isotherm adsorption followed the isothermal adsorptionmodel of Freundlich. The adsorption kinetics followed the mechanismof the lagrange pseudo-second-order equation. Furthermore, FourierTransform Infrared Spectroscopy （FT-IR） and Scanning ElectronMicroscope and Energy Dispersive Spectrometer （SEM-EDS） analysiswere employed to characterize CF before and after absorbing Cr（VI）.The mechanism involved in the absorption process was elucidatedwhich included the electrostatic absorption and ion exchange.Amino terminated hyperbranched polyamide（HPBN） which wassynthesized by diethylenetriamine（DETA） and methacrylate（MA） had alarge amount of active terminated amino groups and amide groups. Glutaraldehyde was used as crosslinking agent to graft HPBN onto CFto prepare hyperbranched polyamide amino modified collagen fiberabsorbent（CF-HBPN）. The influence of different conditions on theamino group content of CF-HBPN was studied. FT-IR, DifferentialScanning Calorimetry-Thermo Gravimetric Analyzer （DSC-TGA） andSEM-EDS modern analysis instruments were employed to analyze thestructure of CF-HBPN. The experimental results indicated that theoptimum reaction conditions on the preparation of absorbent were the n（-NH₂/CF）：n（-NH₂/HBPN）=1:0.7, the dosage of crosslinking agentwas0.533mL/gCF, the temperature was40℃and the reaction time was4h. Under these conditions, the amino content of CF-HBPN was3.27times higher than that of CF. Moreover, the experimental resultsshowed that the adsorption capacity of CF-HBPN on Cr（VI） was3.09times higher than that of CF.HBPN was used as a novel absorbent to remove Cr（VI） fromsimulated chrome solution. Various factors influencing the uptake ofCr（VI）, namely, quantity of absorbent, pH, the concentration of thesimulated chrome solution and the duration of treatment had beenstudied. The experimental result indicated that the modified collagenfiber was very effective for removing Cr（VI） from simulated chromesolution. The removal rate of Cr（VI） increased with the decrease ofsolution pH values. The maximum rate of removal was attained at pH3.0. The increase of absorbent dosage would raise the removalefficiency, but it would simultaneously reduce the adsorption capacity.Moreover, the removal rate of Cr（VI） was found to decrease with theincreasing of initial concentration of Cr（VI）. At pH3.0, the temperatureof30℃,0.4g·L^-1modified collagen fiber, the rate of removal couldreach99.57%. Whereas, the Cr（VI） uptake capacity increased with theincrease of Cr（VI） initial concentration until reaching saturation, whichwas found to be38.94mg·g^-1. Several desorption solutions were used toanalyze the desorption process while the0.18mol·L^-1NaOH solution wasthe best. The effect of coexisting ions on adsorption capacity ofCF-HBPN was small. Furthermore, X-ray Photoelectron Spectroscopy （XPS） as well as SEM-EDS analysis were employed to characterizeCF-HBPN, and further to elucidate the adsorption mechanism involvedin the process. XPS analysis revealed that the Cr（VI） combined on thesurface of modified collagen fiber and the protonation amino groupswere the functional groups in the adsorption process because of theelectrostatic power. SEM analysis revealed that the surface of modifiedcollagen fiber was rough and it had three-dimensional structures. EDSanalysis indicated that the adsorption process included ion exchange.The main adsorption mechanism were charge neutralization power andphysical absorption from three-dimensional structure of HBPN.The kinetics and isothermal of adsorption process of the CF-HBPNtoward Cr（VI） was studied. The adsorption equilibrium time was about6h. It showed that the removal of Cr（VI） by CF-HBPN followed theLagrange pseudo-second-order adsorption kinetics and Langmuirisothermal adsorption model. Adsorption process is endothermic andspontaneous process, and mainly controlled by the entropy change.