Preparation Of Porous Carbon Materials Based On Lignin And Its Research On Removal Hexavalent Chromium From Water

With the increase of the population and the rapid advancement of the national economy,the water quality crisis is more and more serious in our country.Hexavalent chromium Cr?VI?,one of the most poisonous heavy metal ions,is commonly in industrial wastewater that from the textile printing and dyeing,electroplating and leather industry.Lignin is a renewable resource and a three dimensional polymer whic h can provide quantities of aromatic compounds,accounting for 15 % to 36 % of the plant,less than cellulose.Alkali lignin?AL?is a waste product of the pulp and paper industry and seldom utilized so that pollute the water environment.As the lignin contains many active groups,it can be used for chemical modification to synthesis functional materials to removal heavy metal ions from water.In this paper,we were prepared mesoporous magnetic materials,two series of photocatalysts with Bi₂O₃ and PEI-?-Fe₂O₃/Bi₂O₃ composite material to removal the hexavalent chromium Cr?VI?from water.This work was divided into three sections:?1?With alkali lignin?AL?as raw material,the polyethleneimine?PEI?and Fe₃O₄ functionalized magnetic carbon nanoparticles?PCN?were successfully prepared by ball grinding and thermal condensation methods.The new synthesis materials were characterized by TEM,SEM,EDS,FT-IR and XPS,which showed that the obtained products were honeycomb-like porous carbon as well as amino and Fe₃O₄ attached onto the surface of lignin.The porous structure with PEI and Fe₃O₄ was developed for enhanced the quantity of adsorption and reduction of toxic hexavalent chromium Cr?VI?to non-toxic trivalent chromium Cr?III?.Solution pH exhibited an obvious impact on the adsorption and the maximum adsorption equilibrium quantity?160 mg g-1?occurred at pH 2.0.?2?In present work,a series of photocatalysts with Bi₂O₃ nanoparticles coated on the surface of lignin as a cocatalyst through a facile one-step hydrothermal process in an alkaline sodium hydroxide/urea solution system.In the incipient stage,carbonyl oxygen of polyvinylpyrrolidone?PVP?formed Bi-PVP complexes through the coordinative bonding and slowly released Bi³⁺ that react with hydroxyl provided by lignin.The obtained products were characterized by TEM,SEM,EDS,XPS,XRD and UV-vis spectroscopy.The results demonstrated that photocatalysts demonstrated highly efficient fluorescent property due to Bi₂O₃ nanoparticles loaded.Adsorption experiments of Cr?VI?indicated that photocatalysts composed in urea solution show much higher catalytic activity compared to the sodium hydroxide solution,and the maximum catalytic activity occurred at pH 2.0.This work not only provides a potential way to retrieve the alkali lignin,but also puts a novel method for further study.?3?To further improve the photocatalyic capability of the Bi₂O₃/PCN,?-Fe₂O₃-Bi₂O₃/PCN composites were successfully synthesized by ball grinding and hydrothermal methods.The obtained products were characterized by TEM,SEM,EDS,XPS,XRD and fluorescent spectroscopy.The results indicated that the hierarchically structured ?-Fe₂O₃-Bi₂O₃ nanoparticles loaded on the surface of lignin and C@?-Fe₂O₃-Bi₂O₃ composites exhibited a higher visible light photocatalytic activity than Bi₂O₃/PCN.Owing to property of ?-Fe₂O₃ enhance the migration rate of photoelectrons and the effective separation of electron-hole pairs,the excellent coupling effect of ?-Fe₂O₃ and Bi₂O₃ improved the photocatalytic activity.This work provided wide applications in the field of environment treatment.