Preparation Of Novel Composite Superabsorbent Beads Based On Natural Sodium Alginate And Nanoclayand Their Properties

In recent years,with the proposal of"ecological priority,high-quality development"and the carbon peaking and carbon neutrality goal,green development has become the subject of the present era.However,the rapid development of modern industry inevitably brings environmental pollution problems,and the water pollution situation is still very serious,which seriously threatens the safety of the ecological environment and people’s lives and health.Therefore,it has become a continuous pursuit of people to seek suitable methods to remove pollutants in water bodies,thereby obtaining clean and safe water.Adsorption has attracted more and more attention in recent years in both academia and industry due to its simplicity,high efficiency,and complete removal of pollutants in water without generating new chemical substances.At present,the research on adsorbents has made significant progress,but the development of adsorbents with high adsorption capacity,high removal rate,and environmental friendliness is still in its infancy.In order to develop environmentally friendly high-performance adsorbents that are easy to be recycled and reused,in this thesis,the SA grafted polyacrylamide/sepiolite（SP）composite beads were synthesized in aqueous solution using sodium alginate（SA）as matrix by a green polymerization reaction in a"beads reactor".The composite beads with all natural components were prepared by compounding SA,polyaspartic acid（PASP）and natural nano-clay rectorite（RE）.The structures of the prepared beads were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）.The adsorption properties of the microspheres for dyes such as methylene blue（MB）,basic fuchsin（BF）and heavy metal ions such as Pb（II）in pure water and natural waters were systematically evaluated.The effects of the synthetic conditions,composition and adsorption parameters on the adsorption capacity and removal rate of the microspheres were investigated.The adsorption behavior and mechanism were investigated by fitting the experimental data with adsorption isotherm and kinetic models and structural characterization of adsorbent after adsorption.The main research contents and results are as follows:（1）Using SA,acrylamide（AM）,N,N’-methylenebisacrylamide（MBA）,ammonium persulfate（APS）,sepiolite（SP）and gelatin（GE）as precursor of reactants,the precursor is dropped into the Ca Cl₂solution,so that the surface of the droplet is immediately cross-linked with Ca²⁺ions to form a microcapsule,and the reactant is wrapped inside the microcapsule.Under the condition of heating,the initiator APS in the microencapsulation is decomposed to generate free radicals,which triggers the graft copolymerization and cross-linking reaction of AM and SA,forming SA-grafted polymer composite bead with cross-linking network structure,rich functional groups,excellent single adsorption or co-adsorption capacity,easy separation and other advantages.The adsorption capacities of MB,BF and Pb（II）on the best composite bead is390.78,1425.65 and 533.91 mg/g,respectively.After adsorption by composite beads,the removal rates of MB,BF and Pb（II）in the solution reached 99.71%,99.99%and 99.97%,respectively.In addition,the adsorption microspheres can remove 99.22%of BF and 93.06%of Pb（II）in BF/Pb（II）mixed solution（BF concentration:100 mg/L;Pb（II）concentration:50 mg/L）（2）Using natural SA,PASP and natural nanoclay RE as raw materials,an all-natural composite bead（SA/PASP/RE）with network structure,rich functional groups and high adsorption efficiency was prepared by Ca²⁺crosslinking.Structural characterization results show that appropriate amount of RE can be uniformly dispersed in the polymer network,while excessive amount of RE was physically filled in the polymer.When RE content was 0.6%,the adsorption capacity of MB and Pb（II）on the composite bead reached 849 mg/g and 312 mg/g,respectively.When RE content is 43%,the removal rate of MB and Pb（II）reaches 99.96%and 99.98%,respectively（the corresponding adsorption capacity reached 666.69 mg/g and 193.05 mg/g,respectively）.Moreover,the adsorption efficiency of MB and Pb（II）in natural water is also high.After 5 times of desorption-regeneration,the adsorption rate still reaches85.6%.The composite beads have the advantages of high adsorption capacity,high removal rate,recyclability and environmental friendliness,and so have application prospects in removal of pollutants.