Study On Preparation And Wastewater Treatment Mechanism Of Core-shell Structure Double-loaded Hydrogels

With the improvement of human living standards and the development of industrial technology,the types of organic pollutants such as dyes are increasing,the components have become more complex,and the impact on the environment has also be increased.Hydrogels are three-dimensional networks formed by cross-linking polymers.Due to their large specific surface area,high carrier strength and high controllability,it can be used as adsorption material and immobilized embedded material in the field of wastewater treatment.Polymer materials commonly used in dye wastewater treatment which are difficult to be biodegraded,and other chemical substances introduced into the preparation process will cause secondary pollution.The refractory pollutants in wastewater can not be completely and efficiently removed by adsorption or degradation of hydrogels or a microorganism at a time.The research based on this background,in view of the pending of methylene blue and crystal violet dye wastewater,the core-shell structure double-loaded hydrogels are prepared by the natural polymers and synthetic polymers,they can adsorption,and use the microbial degradation and light catalytic fractional multiple step by step to remove pollutants,degradation efficiency thoroughly.This research can provide new ideas and new technology for dye wastewater treatment.The main contents and conclusions of this paper are as follows:(1)Using polyvinyl alcohol(PVA),hydroxyethyl cellulose(HEC)and sodium alginate(SA)as substrates,a synthetic PVA/HEC-SA/Ca2+double-layer core-shell structure hydrogels were prepared.The morphology and structure were observed and characterized by SEM,FTIR and XPS.The results show that the dense shell structure is formed by the cross-linking between ions;the freeze-thaw cycle strengthens the hydrogen bond cross-linking of PVA and HEC to build a loose and porous network structure in the core,and the carboxyl groups in the shell and the hydroxyl groups in the core are cross-linked to form a stable structure.The preparation process was optimized by response surface method,and the best preparation conditions were obtained when the mass ratio HEC/PVA is 0.73,the crosslinking time was 0.55 h,the SA concentration was 3.29%,and the addition amount of CaCl2 was 0.9 g,the swelling rate reached the highest 5795.54%..(2)The core was loaded with yeasts(YE),and nano titanium dioxide(TiO2 NPS)was embedded in the shell to prepare the double-loaded core-shell structure hydrogels Observation of the morphology by SEM shows that the core-shell structure is clear and demonstrable,as evidenced by microscope photos,the existence of YE in the core was verified.XRD analysis results proved the loading of TiO2 NPs in the shell.At the same time,FTIR and XPS verified the existence of interaction forces between the molecules of the core-shell structure.The effect of core-shell hydrogels on the removal of methylene blue(MB)dye was studied under different loading loads.The higher the loading amount of TiO2 NPS in the shell,the maximum degradation of MB reached 96.65%.However,the degradation of MB increased firstly and then decreased with the increase of the loading amount of YE,and reached the maximum of 92.15%.(3)The removal of methylene blue(MB)and crystal violet(CV)dyes by the double-loaded core-shell structure hydrogels.According to the fitting results and the measurement of FTIR and Zeta potential,the removal of dyes by the hydrogels includes adsorption,microbial catalysis and photocatalytic degradation.The adsorption conforms to the pseudo-second-order kinetic model and the Langmuir model.The MB and CV are mainly degraded from macromolecules to small molecules by attacking their benzene ring structure,C=N,C-N,C=S and other functional groups,which are further degraded by mineralization of small molecules.The determination of TOC in dyes further proves that dye wastewater is degraded rather than simply decolorized.(4)Cyclic degradation experiments show that the degradation rates of MB and CV were still 68.97%and 61.21%after 4 times of cyclic degradation.The effect was relatively stable,which could be used for recycling wastewater treatment.In addition,the double-loaded core-shell structure hydrogels can be degraded by cellulose degrading enzymes after use without causing secondary pollution to the environment.