Study On Preparation And Adsorption Properties Of Magnetic Polyethylenimine Functionalized Steam-exploded Rice Straw

Many of industrial production process will produce a large number of Lead,Chromium and other heavy metal-containing wastewater.These wastewater has become an important source of environmental pollution,meanwhile directly or indirectly been harmful to human’s health.Adsorption is a commonly used technology for wastewater treatment due to its simplicity for design,easy operation and low technological equipment and operation cost.At present,activated carbon is among the most widely used adsorbents,but it is expensive and difficult to regenerate.Therefore,it is of great significance to develop new bio-absorbent materials with low price.In this paper,magnetic polyethylenimine functionalized steam-exploded rice straw（Fe₃O₄-PEI-SERS）was successfully prepared by crosslinking polyethylenimine（PEI）and steam-exploded rice straw（SERS）with glutaraldehyde,meanwhile coating magnetic Fe₃O₄.Its structure and properties were characterized.The adsorption potentials of Fe₃O₄-PEI-SERS for the removal of Pb（Ⅱ）and Cr（Ⅵ）were investigated.,This study has some theoretical and practical significance for the development and application of the adsorbents from agricultural straw.The main research contents and results are shown as follows:1.Research on the preparation of Fe₃O₄-PEI-SERSTo obtain the optimal preparation conditions,the effects of rice straw dosage,PEI dosage,glutaraldehyde dosage,NaOH dosage,reaction temperature and time on the yield and adsorption performance of Fe₃O₄-PEI-SERS were done.The results showed that the optimal conditions were obtained with 0.15g of SERS,1.3mL of PEI solution（30%in water）,6mL of 2.5%Glutaraldehyde solution,0.2g of NaOH,0.04g of Fe₃O₄,reaction temperature of 45℃ and reaction tine 3h.2.Characterization of Fe₃O₄-PEI-SERSThe structure and properties of Fe₃O₄-PEI-SERS were characterized by using scanning electron microscope（SEM）,X-ray diffraction（XRD）,Fourier infrared spectrum（FT-IR）,X-ray photoelectron spectroscopy（XPS）and Vibrating Sample Magnetometer（VSM）.The SEM image showed that the adsorbent had a relatively fluffy structure,in which a large amount of straw cellulose was intertwined,and single cellulose surface has a large number of attachments.The results of FT-IR and XPS analysis showed that PEI has been successfully modified on SERS.According to the results of XRD,the crystal structure of Fe₃O₄ was not changed during the preparation.The saturated magnetization value was measured to be 4.88 emu/g,therefore,the Fe₃O₄-PEI-SERS could be easily separated from the aqueous solution by an external magnetic field.3.Research on the adsorption of Pb（Ⅱ）onto Fe₃O₄-PEI-SERSThe influences on pH,adsorption time,adsorbent dose,initial Pb（Ⅱ）concentration and temperature of solution were carried out with Fe₃O₄-PEI-SERS as an adsorbent.The related adsorption mechanism was discussed.The results show that:The adsorption of Pb（Ⅱ）by Fe₃O₄-PEI-SERS had a strong pH dependence.The adsorption time had a significant effect on the adsorption efficiency of Pb（Ⅱ）,and the adsorption reached equilibrium at 180 min.The adsorption process is in accordance with the pseudo-second order model.Langmuir and Freundlich models both can well describe the adsorption behavior of Pb（Ⅱ）on the Fe₃O₄-PEI-SERS.The maximum adsorption capacities at 20,30 and 40OC were 192.31,200.00 and 212.77 mg/g,respectively.This adsorption is an entropy increase,spontaneous and endothermic process because of AG⁰<0,△H⁰>0 and △AS⁰>0.Repeating experiments showed that the adsorbent can maintain a high adsorption capacity after 5 consecutive adsorption/desorption experiments by using 0.1 mol/L EDTA as the desorption agent.4.Research on the adsorption of Cr（Ⅳ）onto Fe₃O₄-PEI-SERSThe influences on pH,adsorption time,adsorbent dose,initial Cr（Ⅵ）concentration and temperature of solution were carried out with Fe₃O₄-PEI-SERS as an adsorbent.The related adsorption mechanism was discussed.The results show that:The adsorption of Cr（Ⅵ）on Fe₃O₄-PEI-SERS had a strong pH dependence.At pH=2,the removal of Cr（Ⅵ）reached the maximum.The adsorption equilibrium time was related to initial Cr（Ⅵ）concentration and observed to be 1 and 6 h for of 200 and 300 mg/L of Cr（Ⅵ）,respectively.The adsorption process was in accordance with the pseudo-second order model,indicating that the reaction was mainly controlled by chemical adsorption.Compared with Freundlich model,Langmuir model can better describe the adsorption behavior of Cr（Ⅵ）on Fe₃O₄-PEI-SERS when adsorbing.The maximum adsorption capacities at 25,35 and 45℃ were 280.11,317.46 and 338.98 mg/g,respectively.The adsorption is an entropy increase,spontaneous and endothermic process because of △G⁰<0,△H⁰>0 and △S⁰>0.Repeating experiments showed that the adsorbent can maintain a high adsorption capacity after 5 consecutive adsorption/desorption experiments by using 0.5 mol/L NaOH as the desorption agent.which indicates that Fe₃O₄-PEI-SERS has good stability,reproducibility and reusability.