Preparation Of Modified Lignin-based Adsorbent And Its Application In Wastewater Treatment

Lignin has attracted increasing attention in recent decades due to its biodegradable,renewable,and environmentally friendly.Native lignin molecule contains many functional groups which suggests it has the potential to prepare various kinds of functional materials.Unfortunately,due to its complicated primary structure,poor solubility,low reactivity and high resistance,only a relatively small portion of lignin isolated from lignocellulosic biomass was already used commercially.Recently,in order to maximize its full value,great academic interest has been devoted to develop lignin-based products to explore the high value-added utilization of lignin resources.Herein,a series of lignin-based composite materials were synthesized via a green method from lignin and derivatives and used in the field of wastewater treatment,in order to provide support for achieving the efficient utilization of lignin.1-ethyl-3-methylimidazolium acetate?[Emim][OAc]?was elected as novel pretreatment solvent for enhancing the sulfonated efficiency of alkali lignin.The optimal conditions of dissolution were as follows:moisture content of lignin was 5%,353.15 K and 120 min,for which a higher solubility?399.5 g/L?of lignin in[Emim][OAc]was obtained.The spectras of³¹P-NMR clearly shown the major hydroxyl groups?the hydroxyl group of aliphatic,condensed phenolic,p-hydroxy-phenyl and guaiacyl?in lignin samples were from aliphatic regions.Compared with AL,these results of RL represent increases by 27.18%,14.39%,50%and 25.79%,respectively.Importantly,the water solubility and sulfonated degree of RL were increased by 14.6%and 33.6%,respectively.Such results imply that[Emim][OAc]pretreatment could improve the sulfonation efficiency and make the development of lignin-based products a real possibility.Hydrogels from alkaline lignin were prepared and shown to display unique swelling.Variable lignin contents?6.25 wt%,10.00 wt%,12.50 wt%,and 14.29 wt%?were successfully grafted with both N,N'-methylenebisacrylamide?MBA?and acrylamide?AM?.Ionic liquids such as 1-ethyl-3-methylimidazolium acetate?[Emim][OAc]?were used to avoid harsh,unfriendly solvents.All materials were characterized using X-ray diffraction?XRD?,FT-IR spectroscopy,Scanning electron microscope?SEM?,Thermogravimetric analysis?TGA?,and swellability.The swelling behaviors of the hydrogels were noticeably influenced by their lignin content.The degree of equilibrium swelling?the maximum swelling degree?decreased with increasing content of lignin.The highest swelling degree?1,650%?was obtained at 6.25wt%lignin.Kinetics revealed that the swelling behaviors of hydrogels were well-fitted by the Schott model.A new solid adsorbent,lignosulfonate-graphene oxide-acrylamide?LS-GO-AM?ternary composite hydrogel possessing good mechanical strength and high dye adsorption capacity,was prepared by a simple polymerization,and used for the removal of dyes from aqueous solution.The adsorption property of a model dye,methylene blue?MB?,onto the hydrogel was studied.The effects of adsorption time,initial pH,and concentration were investigated.When the initial MB concentration was 3 mg·L^-1 at an LS-GO-AM concentration of 4 g·L^-1,the absorption was 98.36%while the solution was nearly decolorized.Moreover,adsorption kinetic and equilibrium data were described well with pseudo-second-order and Langmuir isotherm models for MB adsorption.The LS-GO-AM composite hydrogel with enhanced mechanical strength could be easily separated from the reaction system.A novel adsorbent with 3D network structures for removal of hexavalent chromium?Cr?VI??from aqueous solutions has been successfully synthesized via incorporation of lignosulfonate?LS?into graphene oxide by a simple self-assembly method.The adsorption properties of Cr?VI?onto the lignosulfonate/graphene composites?LSG?were investigated,such as contact time,initial pH,and concentration were investigated.The results showed adsorption kinetic and equilibrium data were could be described well with pseudo-second-order and Langmuir isotherm models for Cr?VI?adsorption.The adsorption capacity of the composite for Cr?VI?was 601.2 mg/g.The modification of graphene oxide with LS was proved to significantly improve its adsorption sites,resulting in excellent NPEs removal efficiency from bleaching wastwater.Removal of NPEs could be effectively reduced the decomposition of hydrogen peroxide,thus to improve the efficiency of bleaching.Importantly,more than eighty percent of NPEs could be completely removed from the system through the LSG treatment,thereby avoiding using chelating agent.The results of this research indicated that the LSG could be successfully used for the removal of NPEs from bleaching wastwater.