Preparation Of Nanocellulose-based Gel Materials And Removal Of Cr(Ⅵ)

Chromium is a common metal contaminant,mainly from industries such as textile dyeing,leather tanning,metal polishing and electroplating.In recent years,with the rapid development of the economy and the steady progress of industrialization,the harm caused by chromium pollution has become increasingly serious.Among them,Cr（VI）poses a serious threat to human health and the entire ecological environment due to its carcinogenicity,teratogenicity and mutagenicity,as well as high solubility and fluidity.The preparation of low-cost,high-efficiency and large-scale adsorbents for the treatment of Cr（VI）is a top priority.In this paper,composite gel materials with cellulose nanofibrils（CNFs）as the matrix were prepared by chemical crosslinking,physical-chemical crosslinking and in situ chemical oxidation,and the Cr（VI）pollution in the aqueous environment was treated by static adsorption,dynamic adsorption and adsorption-reduction.The main research contents are as follows:（1）CNFs/PEI composite hydrogels（CPHs）were prepared by chemical crosslinking using wheat straw-based CNFs and polyethylenimine（PEI）as raw materials and epichlorohydrin（ECH）as crosslinking agent.The SEM results showed that the microscopic morphology of the composite hydrogel was a honeycomb macroporous network structure,and infrared spectroscopy and elemental analysis showed that CPHs hydrogels carried a large number of amino groups.CPH₁₃ composite hydrogel was used for the static adsorption of Cr（VI）in water,and the results showed that when the p H value was 2,the adsorption effect of Cr（VI）was the best.The results of adsorption kinetics and isothermal equations show that the adsorption kinetics conform to the quasi-secondary kinetic model,and the adsorption isothermal equations conform to the Langmuir model,and the maximum adsorption capacity of Cr（VI）is 117.1 mg/g and 123.5 mg/g at temperatures of 25°C and 35°C,respectively.After three adsorption-desorption cycles,the adsorption capacity can reach more than 70%of the initial adsorption capacity,indicating that CPHs hydrogels have certain regeneration and recycling performance.（2）Using wheat straw-based CNFs as raw materials,a resilient sponge CNFs/PEI composite aerogels（CPAs）were prepared by a combination of physico-chemical crosslinking.CPAs were characterized by SEM,FT-IR,SEM-EDS,CHNS elemental analysis,BET,mechanical property test,zeta potential.The obtained CPAs have the advantages of porous structure,high wet strength and good shape recovery performance in water,which is conducive to dynamic adsorption of Cr（VI）in fixed bed.The optimized CPA₁₁ has good adsorption performance for Cr（VI）,and the theoretical maximum adsorption capacity is 710.10 mg/g.XPS and FT-IR were used to analyze the adsorption mechanism of Cr（VI）as electrostatic attraction,chemical reduction and chelation.CPA₁₁ retains 90%of its initial absorption capacity after 5adsorption-desorption cycles.The results of fixed bedpost experiments show that the breakthrough curve of the adsorption process under different conditions is in good agreement with the Thomas model.The lower flow rate,lower influent concentration,and higher column height were conducive to the dynamic adsorption process of Cr（VI）by CPA₁₁.（3）A CPA@PPy-F photosensitive composite gel material was prepared by in situ oxidation of pyrrole（Py）using Fe Cl₃ as oxidant.SEM,FT-IR,UV-vis,and XPS were used to characterize gel materials.By comparing dark conditions and light conditions,the adsorption,in-situ reduction,cyclic adsorption performance and cyclic adsorption mechanism of Cr（VI）of this composite aerogel were studied.The results showed that the content of Cr（III）in the gel under photocatalytic conditions was 72.33%,which was 1.43 times higher than that under dark conditions,and the light conditions could promote the in-situ reduction of Cr（VI）.The results of cyclic adsorption experiments showed that after 6 cycles of adsorption,the cyclic adsorption capacity of CPA@PPy-F to Cr（VI）was 64.97%higher than that of dark treatment,indicating that the CPA@PPy-F of Cr（III）could provide a new adsorption site for Cr（VI）.