Preparation Of Polydopamine Modified Dialdehyde Chitosan And Its Adsorption Properties For Carmine Dye

With the development of industry,dyes are widely used in various fields such as textiles and packaging,and the treatment of dye wastewater has become a major problem in the field of wastewater treatment.Adsorption is one of the most promising technologies in dye wastewater treatment,and chitosan(CS)is currently one of the most popular raw materials for preparing adsorbents.The unmodified CS has disadvantages such as poor solubility and small adsorption capacity.Therefore,in this study,sodium periodate was used as the oxidant first,and the C2 and C3 positions of CS were analyzed by oxidation modification method and freeze-drying method.Through selective oxidation,dialdehyde chitosan(DCS)adsorbents with different degrees of oxidation were prepared;then polydopamine(PDA)was formed by self-polymerization of dopamine(DA)oxidation and then grafted with DCS to obtain polydopamine modified Dialdehyde chitosan(PDA-DCS)adsorbent.Taking the anionic dye carmine as a simulated dye wastewater,the adsorption process and adsorption mechanism of the dye wastewater by DCS and PDA-DCS were studied,and the adsorption process and adsorption mechanism were discussed,which has certain guiding significance for industrial application.The main research contents and results of the paper are as follows:1.Characterize DCS and PDA-DCS.SEM analysis showed that compared with the unmodified CS,the porosity of the oxidized DCS increased,and the PDA-DCS further presented a multi-layer porous structure;FTIR analysis showed that the DCS was successfully oxidized to form aldehyde groups,and the PDA in the PDA-DCS It was successfully grafted with DCS;XRD analysis showed that the crystallinity of DCS and PDA-DCS were lower than those before modification;TG analysis showed that the thermal stability of DCS was lower than that of CS,and the thermal stability of PDA-DCS was lower than that of DCS.There is a certain improvement.2.The effects of various factors on the adsorption performance of DCS and PDA-DCS were explored through adsorption experiments,and the reusability of PDA-DCS was analyzed.The experimental results show that the adsorption performance of DCS＿2:1 and PDA-DCS＿2:1 with the substance ratio of chitosan and sodium periodate of 2:1 is the best;the adsorption capacities of DCS and PDA-DCS both increase first with the increase of p H.and then gradually decreased,and the optimal adsorption p H of PDA-DCS was higher than that of DCS,and the optimal adsorption p H of PDA-DCS was 3;the adsorption capacity of DCS increased rapidly within the initial 60 min,and the adsorption capacity reached the equilibrium point at 120 min,while the adsorption capacity of PDA-DCS increased rapidly within the initial 30 min,and the adsorption capacity basically reached equilibrium at 80 min.The adsorption rate of PDA-DCS was significantly improved compared with DCS;The adsorption capacity increased with the increase of the initial concentration,and reached a relative saturation state when the carmine concentration was 400 and 500 mg/L,respectively.The reusability analysis experiment showed that after five consecutive adsorption-desorption cycles,the adsorption capacity of PDA-DCS remained in a good state,which was easy to achieve regeneration and reuse.3.The adsorption kinetics fitting analysis shows that the adsorption process of DCS and PDA-DCS to carmine dyes are in line with the pseudo-second-order adsorption kinetic model;the adsorption isotherm fitting results show that DCS and PDA-DCS are suitable for Langmuir adsorption Isotherm model;adsorption thermodynamic analysis shows that the adsorption process of DCS and PDA-DCS is a spontaneous exothermic reaction and the degree of freedom of the adsorption system increases when the adsorption is equilibrium.Under the optimal adsorption process conditions,the maximum adsorption capacity of DCS for carmine dye was 992.4 mg/g,and the maximum adsorption capacity of PDA-DCS for carmine dye was 1194.4 mg/g.Comparing the adsorbent PDA-DCS with other adsorbents that have been studied for the adsorption of carmine,the results show that the adsorption capacity of PDA-DCS is at a higher level.