Preparation Of Alkali-Modified MXene/Cellulose Composite Aerogel For The Treatment Of Dyeing Wastewater

Many environmental issues,especially water pollution,have attracted worldwide attention.As a large textile printing and dyeing country,China discharges a large amount of printing and dyeing wastewater every year.Especially,the printing and dyeing wastewater contains a large amount of organic and heavy metal pollutants,which not only seriously damage the ecological environment but also cause harm to human health.Therefore,it is an urgent task to develop an efficient,inexpensive,and sustainable material for reducing water pollution and treating dye wastewater.Due to its unique layered structure and abundant surface functional groups,MXene has received a lot of research in the field of dye adsorption in recent years.In particular,the alkali modified MXene（Alk-MXene）surface after sodium hydroxide modification and activation has more abundant negative charges,which interact with the positively charged cationic dye methylene blue dye to achieve the effect of removing the dye.In addition,as a common biological substrate adsorption material,cellulose has been widely used in the field of printing and dyeing wastewater treatment due to its good dispersion,easy recovery,and environmental friendliness.Therefore,the MXene/cellulose（MXene/MCC）composite aerogels obtained by doping MXene two-dimensional nanostructured materials into the three-dimensional framework of cellulose aerogels can significantly improve the adsorption capacity of cellulose aerogels for dyes.Therefore,in this paper,microcrystalline cellulose is used as the raw material for gel network to prepare cellulose solution by low-temperature freezing and thawing method,and then the cellulose is freeze-dried to obtain aerogel（MCC）;Secondly,MXene was prepared by mild etching method and Alk MXene was obtained by alkali modification after MXene was obtained.Then,two kinds of two-dimensional structural nanomaterials with different properties were doped into cellulose,and MXene/cellulose and Alk MXene/fibroin（Alk MXene/MCC）composite aerogels with different mass concentrations were prepared by compounding and freeze-drying;Deeply and systematically study the adsorption performance of dyes,select the cationic dye methylene blue dye（MB）as the pollution source,study the adsorption performance of three materials,such as MCC,MXene/MCC,and Alk-MXene/MCC,from the aspects of adsorbent quality,adsorption time to the adsorbent,environmental temperature,and other factors,and establish an adsorption kinetic model to study their adsorption mechanism.The specific research content is as follows:（1）Preparation,structure and performance regulation of MXene and alkali modified MXeneMXene materials were prepared using Ti₃Al C₂ as raw material,hydrochloric acid（HCl）and lithium fluoride（Li F）as etching systems,using indirect and mild etching methods.During this process,the optimal etching system conditions were selected by adjusting the molar concentration of hydrochloric acid.In addition,on the basis of obtaining the original MXene,sodium hydroxide is used for alkali modification,and Alk MXene with different alkali modification degrees is obtained by using different molar concentrations of sodium hydroxide.Scanning electron microscopy,Fourier transform infrared spectroscopy,and EDS elemental analysis were used to characterize its microscopic composition and chemical properties.It was proved that the layered structure of MXene was most obvious in a mild etching system using indirect methods when the molar concentration of hydrochloric acid was 12 M.In the Alk MXene modified by alkali,the microstructure of the original MXene material did not change with the infiltration of alkali.Therefore,nano materials with this new two-dimensional structure have been successfully prepared by this method.（2）Preparation of alkali modified MXene/cellulose composite aerogel and its structure and performance regulationUsing microcrystalline cellulose as raw material,the cellulose solution was obtained through low-temperature freezing and thawing.Using MXene and Alk-MXene at different mass concentrations as single factor variables,the optimal synthesis method of composite cellulose was optimized.The field emission electron microscope（SEM）technology is used to combine the multi-stage pore characteristics of porous materials to realize the controllable adjustment of the micro nano morphology and structure of the multi-stage porous materials.The composite cellulose aerogel has a three-dimensional network pore structure,and the pores are interconnected.By means of infrared spectrum,X-ray diffraction,energy spectrum and thermogravimetry,it is verified that the composite aerogel still maintains its basic crystal structure and stable atomic composition when doped with nano materials.After comprehensive consideration of the microstructure characteristics of composite cellulose and the adsorption of subsequent dyes,it was finally selected that when the mass concentration of MXene doped was1.5%,the composite aerogel was light and highly porous,with a porosity of 89%.Its micro morphology and structure had good performance,which could become an efficient adsorbent material（3）Adsorption of Methylene Blue on Alkali Modified MXene/Cellulose Composite AerogelUsing the above prepared MCC,MXene/MCC,Alk-MXene/MCC as adsorption materials,taking the quality of adsorption materials,contact time,environmental temperature,etc.as factors,the prepared composite aerogel was treated with methylene blue dye by controlling the variable method.In addition,the effect of photo catalysis on the adsorption effect was studied,and its adsorption performance was studied.Quasi first order and quasi second order kinetic models were established to fit the entire adsorption process,Study its adsorption mechanism.The results showed that the adsorption effect of the composite aerogel doped with MXene was much higher than that of the pure cellulose aerogel gel,the adsorption effect of the composite aerogel obtained by alkali modified MXene was higher than that of the composite aerogel obtained by unmodified MXene,and the adsorption effect of the composite aerogel after photocatalysis was much higher than that of the composite aerogel without photocatalysis.After fitting the adsorption kinetic model,it was found that the theoretical parameter values obtained by fitting the quasi second order kinetic model after adsorption equilibrium were closer to the results of adsorption test parameters,and the fitting results showed that chemical adsorption was the key to the entire adsorption process.Comprehensively,Alk-MXene/MCC composite aerogel has high dye treatment capacity and can effectively absorb methylene blue dye,thus achieving efficient dye treatment effect.At the same time,it can also save time and economic costs,making it have a great application prospect in dye treatment,providing strategic support for the preparation of efficient adsorbents.