Preparation And Adsorption Characterization Of Nanocellulose Aerogel

With the improvement of China’s modernization,the rapid development of industry and the continuous growth of population,the problem of water quality damage makes mankind face a more severe test.Synthetic dyes,heavy metal ions and other pollutants in water resources have caused serious harm to human health,animals and the environment.Because these pollutants are highly toxic and difficult to degrade,it is urgent to remove them from wastewater.Adsorption is one of the common methods for wastewater treatment because of its advantages of cheap raw materials,intelligible implementation steps and recyclability.In recent years,cellulose,as a kind of green and environment-friendly material,has attracted the attention of many researchers.At the same time,cellulose aerogels prepared from cellulose,as adsorbent for high specific surface area,also have great potential in the adsorption of dyes and heavy metals in wastewater.However,the poor mechanical properties and adsorbable contaminants of pure cellulose aerogels are relatively single,which greatly limits their application in the field of water pollution adsorption.In this paper,softwood kraft pulp is used as the initial raw material,oxidized by the TEMPO oxidation method,and then subjected to high-pressure homogenization to obtain oxidized cellulose nanofibrils（TOCN）.The TOCN is characterized by TEM,and the results show that the TOCN is elongated.Shape and intertwined with each other to form a network structure.Different aerogels were prepared using it as the framework material.The main research contents are as follows:（1）The TOCN/PVA/M-K10 aerogels（TPMA）with excellent mechanical properties and good dye adsorption properties were prepared by modification and freeze drying with TOCN as the backbone carrier by adding polyvinyl alcohol（PVA）and montmorillonite K10（M-K10）.SEM showed that the microstructure of the TOCN/PVA/M-K10 aerogel was reticulated porous structure.FTIR,XRD and XPS characterization confirmed the formation of chemical crosslinking,and the cyclic compression test confirmed the TPMA.The TPMA has perfect shape recovery rate both in air and under water.When the maximum strain is 60%,the TPMA can maintain 93%of the initial height after 100cycles of compression.At the same time,TPMA has a low density of 19.32 mg cm^-3.Dye adsorption test showed that TPMA had excellent adsorption properties for methylene blue（MB）.At 20 mg L^-1 initial concentration,the removal rate was more than 80%and the maximum adsorption capacity was 2.28 mg g^-1.At the same time,the influence of aerogel dosage,initial p H value of solution,inorganic salt content and contact time on the adsorption performance of TPMA.And the adsorption kinetics and adsorption isotherms of TPMA adsorbed MB were also studied.The recycling characteristics of TPMA were also investigated.The results showed that the more TPMA was used,the lower the adsorption capacity of MB,but the higher the removal rate of MB.The adsorption capacity of MB increased with the increase of p H.When p H reached 7,the adsorption capacity reached the maximum.The removal rate of MB was proportional to the concentration of inorganic salt,and reached the adsorption equilibrium in 120 minutes.The adsorption results of MB followed pseudo second order adsorption kinetics and Freundlich adsorption isotherm After four cycles of adsorption desorption,the initial adsorption capacity is still 60%.In conclusion,TPMA is a good dye adsorbent.（2）Using TOCN as the backbone carrier,the basic TOCN/PVA aerogel（TPA）was prepared by adding PVA for modification and freeze-drying.ZIF-8 and ZIF-67 were grown on the surface of TPA to prepare ZIF-8 aerogels（ZIF-8A）and ZIF-67 aerogels（ZIF-67A）with good adsorption performance for heavy metal ions.SEM showed that there was a dense layer of ZIF-8 and ZIF-67 nanoparticles on the surface of ZIF-8A and ZIF-67A.The FTIR,XRD,and XPS characterizations confirmed the successful growth of both.The adsorption test of heavy metal ion solutions found that ZIF-8A and ZIF-67A has strong adsorption performance for Cu²⁺and Pb²⁺.When ZIF-8A adsorbs Cu²⁺and Pb²⁺,the maximum adsorption capacity reaches 12.5 and 16.3 mg g^-1,and the adsorption efficiency reaches 50%and 65%;when ZIF-67A adsorbs Cu²⁺and Pb²⁺,the maximum adsorption capacity reaches 15.1 and 19.8 mg g^-1,and the adsorption efficiency reaches60%and 79%.At the same time,the adsorption kinetics and regeneration performance of ZIF-8A and ZIF-67A on Cu²⁺and Pb²⁺were also studied.The results showed that the adsorption of Cu²⁺and Pb²⁺by ZIF-8A and ZIF-67A conformed to the pseudo second order adsorption kinetics and both have good regeneration and reuse performance.Taken together,ZIF-8A and ZIF-67A are two reliable choices for heavy metal ion adsorbents.