Preparation Of Microcrystalline Cellulose Based Aerogel And Its Application For Adsorption Of Heavy Metals And Degradation Of Dyes

Wastewater remediation has currently been a worldly issue and an urgent task for environmental work in China.Aerogel,the world's lightest solid material,has been called as one wonder material of the 21^st century.Aerogel has a great many of favorable properties such as developed channel structure,low density,high ratio surface,high porosity,low thermal conductivity and high adsorption properties,holding great promises for drug delivery,adsorption and separation,sound adsorption,thermal insulation,catalytic degradation and tissue repair.Aiming at the serious heavy metal ions and dye pollution problems at present,we chose two biomasses Microcrystalline Cellulose?MCC?and Sodium Alginate?SA?as aerogel components,for they are sufficient,safe,environmentally friendly and biodegradable.In this work,we designed a high-strengh,multi-purpose and renewable multiscale aerogel based on MCC and SA.DAO-MCC?Diamidoxime MCC,abbreviate“DAO-MCC”?was prepared with MCC as the subtrate,ammonium cerium nitrate as the initiator,and the monomer2-cyan-3-ethoxyl-ethyl acrylate?EMCA?was loaded via the free radical induced grafting,followed by the amidoximation reaction.The DAO-MCC can effectively remove Cu²⁺,Pb²⁺,Cr³⁺and Cd²⁺by the chelation between the diaminoximed functional groups and metal ions,and the adsorption process followed Pseudo-second-order model with the Langmuir Q_max of 165,222.5,143.1 and 177.9 mg/g,respectively.Compared with MCC,the Q_max of DAO-MCC for the four metal ions increased 4.2,5.5,6.7 and 7 times.Regeneration experiments exhibited DAO-MCC can still reserve above 86%of their initial adsorption capacities after five consecutive regeneration cycles for the four metal ions,demonstrating the high-efficient,benign and renewable adsorption nature of DAO-MCC.To achieve the versatility,the hierarchical bionanocomposite DAO-MCC@MnO₂ was prepared based on redox principle with DAO-MCC as substrate.The adsorption results shown that the Q_max of DAO-MCC@MnO₂ for Cu²⁺,Pb²⁺,Cr³⁺and Cd²⁺increased 30.5,29.7,28.6 and 37.3 mg/g compared with MCC.Moreover,the DAO-MCC@MnO₂ can also degrade the dyes.In brief,the DAO-MCC@MnO₂ integrated the adsorptive advantages of diamidoxime groups and degradation efficiency of MnO₂ nanoparticles.The high-strength,multi-functional and reproducible multiscale DAO-MCC@MnO₂/SA?DMMS?aerogel was constructed with the micro-scale DAO-MCC@MnO₂ as the gel“framework”and SA molecular chains as the nano flexible“bond”.The aerogel was equipped with open channels,abundant active groups and excellent structural stability,and the hierarchical network,density,porosity,mechanical strength and elastic recovery can be regulated through adjusting the addition of DAO-MCC@MnO₂.The characterizations demonstrated that 2 h was needed for DMMS-40 hydrogel to reach a complete gel,and its density and porosity would be 37 mg/cm³ and 91%.The compressive strength and modulus of DMMS-40 aerogel reached 289 and 338 kPa,and it still can support 271.3 kPa at the 5^th compression.The adsorption results displayed that the DMMS-40 aerogel can reach the maximum adsorption amount at initial pH environments of Cu²⁺,Pb²⁺,Cr³⁺and Cd²⁺solutions after adsorption for 120 min.The adsorption process followed Pseudo-second-order model,and the Langmuir isotherm can fit the experimental data batter with the Q_max of 219.8,325.9,214.7 and 275 mg/g for Cu²⁺,Pb²⁺,Cr³⁺and Cd²⁺,respectively,indicating the monolayer adsorption model.Moreover,at the same concentration,the competition order of adsorbability was:Pb²⁺>Cd²⁺>Cu²⁺>Cr³⁺.The analysis demonstrated that some of the adsorption capacity was derived from the functional groups of DAO-MCC@MnO₂ and SA components,which can generate chemical actions or electrostatic interactions with metal ions.The other possible adsorbability was contributed by the unidirectional porous structure of aerogel,which provided a good channel for the physical diffusion and transmission of metal ions.After 5 consecutive adsorption-desorption cycles,the DMMS aerogel still can remain its shape,and retain above 78%of their initial adsorption amouts,proving the DMMS aerogel can be used as a recyclable adsorption material.The degradation experiment showed that the DMMS-40 aerogel had prominent degradation efficiency for MB,CR,MO and RhB dyes.When pH=4⁵,the addition of aerogel and H₂O₂ were 90 mg and 3 m L,the maximum degradation can be reached within60 min for CR?90.2%?and MO?95.4%?,and 120 min for MB?92.9%?and RhB?88.4%?.The degradation mechanism shown that the H₂O₂ was decomposed into·OH,·O₂^-,and·HO₂ free radicals by MnO₂ nanoparticles of DMMS aerogel,and these free radicals had powerful oxidative powers that break down the dyes into CO₂,H₂O,or other small molecules.After 5 cycles of degradation,DMMS aerogels can maintain 81.9%of the initial MO degradation rate,demonstrating the DMMS aerogel can be used for cyclic degradation of dyes.In conclusion,DMMS aerogel has excellent adsorbability for heavy metal ions and prominient catalytic degradation performance for dyes.After recycling for several times,the aerogel can still remain its framework,confirming its characteristics of high-strength,multi-function and renewablity.Therefore,the research results of this thesis provide theoretical basis and technical guidance for application of wastewater purification.