| Heavy metal pollution has become one of the main problems that seriously affect the harmonious development of freshwater resources in China.Cadmium as a common toxic heavy metal element in sewage,the excessive content will not only affect the growth and development of plants and animals,and the intake of the human body will cause functional damage to the liver and kidneys,cardiovascular damage and cancer and other major diseases,causing serious harm to the human body.Pumpkin in the deep processing process will produce a large number of pumpkin peel by-products,often used as waste disposal,the comprehensive use of low degree.Polysaccharides,as the main active ingredient of pumpkin,contain hydroxyl and carboxyl groups,which can react with metal ions and can be used for the adsorption of heavy metal ions,and have broad application prospects.Extracting polysaccharides from pumpkin peel for water pollution treatment has the advantages of low cost,low pollution to the environment and easy degradation..In this study,we intend to optimize the adsorption rate of cadmium by extracting polysaccharides from pumpkin peel and conduct structural characterization and stability studies,apply pumpkin peel polysaccharides to the treatment of heavy metals in wastewater,investigate its adsorption mechanism,and provide technical support for the development of new adsorbents.The main research contents and results are as follows.(1)Extraction of pumpkin peel polysaccharide(PPP)The extraction of PPP was carried out by hot water extraction method.The optimum extraction process was optimized by single-factor and response surface method: the materialliquid ratio was 1:18,the reaction temperature was 70 ℃,and the reaction time was 122 min,the yield of PPP was 24.5%.(2)Study on the adsorption performance of PPP on cadmiumThe adsorption performance of PPP on cadmium was studied by cadmium chloride method,and the best adsorption process was obtained by single-factor and response surface optimization: the weight ratio of pumpkin peel polysaccharide to cadmium chloride was22.5:1,the p H was 6.75,the adsorption temperature was 35 ℃,and the adsorption time was36 min,and the adsorption rate was 97.73%±0.20%.(3)Adsorption kinetics studyThe laws of cadmium ion adsorption by pumpkin peel polysaccharide were investigated by quasi primary kinetic equations and quasi secondary kinetic equations.The results showed that the maximum adsorption amount of cadmium ions adsorbed by pumpkin peel polysaccharide was 19.23 mg/g,which satisfied the quasi-secondary kinetic equation.(4)Structural characterization of PPP-CdThe structural characterization of PPP-Cd was carried out using spectral analysis,particle size and thermogravimetric analysis.The results showed that PPP-Cd was basically free of protein and nucleic acid.The particle size of pumpkin peel polysaccharide combined with cadmium increased from 142 nm to 164 nm,and the change of thermal stability was not obvious.(5)Stability study of PPP-CdThe stability analysis of PPP-Cd was studied by laser nanoparticle size analyzer,and the results showed that the temperature had the greatest influence on the stability of PPP-Cd,and the stability of PPP-Cd became better with the increase of storage temperature and the extension of storage time,and the storage effect in strong acid(p H=2)and neutral environment(p H=6)was poor. |
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