Preparation,characterization And The Adsorption Characteristics Of Lignin/silica Nano Composites

Currently,bioethanol as a substitute for petrol obtained widespread concern from country to country.Food could be reduced due to the use of food to produce bioethanol,so the research of the use of agricultural waste such as corn stalks,grasses and wheats bran to produce cellulosic ethanol is increasing.Cellulosic ethanol is mainly obtained through hydrolysis and enzymolysis of sugar components in stalk.In this process,large amounts of residues will be produced and these residues are mainly burned to recover energy,which not only fail to improve economic efficiency,but also hinder the promotion and application of cellulosic ethanol.In this paper,the concept of biomass refining as a starting point,the main components of cellulosic ethanol residue were analyzed systematically to achieve the purpose of application.Four kinds of lignin were extracted from the fermented residues of corn stalks by inorganic methods and organic methods.The molecular weight and structure of the extracted lignin were studied by gel permeation chromatography,infrared spectroscopy and quantitative¹³C-NMR spectra.The results showed that the four kinds of extracted lignin were all mainly low molecular weight lignin and GSH-type lignin with presence of the primary structure ofβ-O-4,β-β,β-5,and the lignin extracted with organic solvents haved more syringl and condensed guaiacyl.Since silicon can be dissolved in alkaline solution,using NaOH aqueous solution as the reaction solvent,the optimum conditions for preparing the extract contained more silicon were determined through condition experiments,which were NaOH 7%,reaction time 1h,reaction temperature 60℃and solid-liquid ratio 1:25.The amorphous silica with high whiteness was prepared by slowly adding 2%HCl（volume fraction）to the extract.The SEM images and DLS showed that the prepared silica had a homogeneous distribution of particle size and the particle size was nanoscale.The XPS analysis indicated that the purity of nanosilica was 96.09%.Lignin and silica were main components in cellulosic ethanol residue and they could be joined together by formed hydrogen bonds,so the lignin/silica nano composites were prepared by extraction of the silica from the residues of corn stalks with NaOH aqueous solution and followed by precipitation with hydrochloric acid.The results of condition experiments showed that the nano lignin/silica composites with excellent properties were prepared with a pH of 7.0and a reaction temperature of 60℃.The prepared composite under optimum conditions was spherical in shape,easily to be dispersed and exhibited excellent thermal stability than lignin,and the particle size of composite was nanoscale.The BET analysis indicated that this composite had a high specific surface area（394.88 m²/g）and a uniform morphological distribution,and the adsorption isotherm of the composite belongedⅣtype.Experiments of using lignin/silica nano composites to adsorb methylene blue found that temperature and pH had a great influence on the adsorption experiments.The decolorization rate of methylene blue increased with improving temperature and pH,but the temperature was not higher than 35℃.Therefore,this adsorption experiment should be carried out in an alkaline environment with a reaction temperature of 35℃.Experiments of respectively using lignin/silica nano composites,silica and lignin to adsorb methylene blue found that lignin/silica nano composites had a best effect on the decolorization rate of methylene blue in these three substances because of its large specific surface area.