| Heavy metal ions(HMIs)and Dye molecules(DMs)are two most typical pollutants in industrial wastewater,which need to be treated and recovered before discharge to avoid environmental damage and resource waste.In the past,the treatment technology of these two pollutants has the problems of high energy consumption,incomplete treatment and low recovery.Membrane separation technology is an efficient treatment technology to avoid the above problems.Calcium Alginate(CA)hydrogel membrane is a new type of adsorption separation membrane,which can remove HMIs and DMs effectively.In this paper,GO/CA modified composite hydrogel membrane was prepared by using Graphene Oxide(GO)modification,and its preparation characteristics,property characterization,pollutant removal effect and mechanism were explored.The main research results are as follows:(1)GO nanomaterials were prepared by improved Hummers method,and their properties were characterized by TEM,XRD,FT-IR methods.The results showed that the GO nanomaterials were lamellar and gossamer.The interlayer spacing between graphite powder and GO was 0.340 nm and 0.871 nm,respectively.There are obvious characteristic peaks of hydroxyl and carboxyl group in prepared GO.The abo ve results show that the prepared GO meets the requirements of being CA hydrogel membrane modification material.(2)In this study,calcium chloride was used as the crosslinking agent,urea as the pore-forming agent,and GO nanoparticles were added to prepare GO/CA modified composite hydrogel membranes with different GO mass fractions by multi-component crosslinking method,and their comprehensive characteristics were explored.The composite membranes were characterized by SEM,TEM,AFM,FT-IR and XRD,and their mechanical properties,water flux and anti-pollution properties were determined.The results showed that GO was uniformly combined with calcium alginate,and the preparation of GO/CA modified composite hydrogel membrane was successful.The variation rules of cross section stratification structure,water flux,flux recovery rate and mechanical properties of the composite membrane with GO mass fraction were obtained.The composite membrane with GO mass fraction of 0.3wt%had the best comprehensive performance.(3)In order to explore the separation performance of different GO/CA modified composite hydrogel membranes,the composite membranes were subjected to direct filtration experiments,direct adsorption experiments and post-adsorption filtration experiments with Malachite Green(MG).The results show that the removal rate of MG by direct filtration of the composite membrane can reach 100%,which is mainly due to the adsorption of the composite membrane.The composite membrane with a GO mass fraction of 0.3wt% also presented the optimal adsorption performance and the highest saturation interception rate.Adsorption not only affects the treatment effect in the early stage,but also affects the interception rate after the adsorption saturation in the later stage,thus affecting the overall effect of filtration.Therefore,it is very important to deeply explore the adsorption optimization and the improvement of the composite membrane using effect of adsorption mechanism.(4)The adsorption performance and mechanism of GO/CA modified composite hydrogel membrane on four kinds of DMs with different structures and properties were investigated,and the influences of p H,initial dye concentration,contact time and temperature on the adsorption capacity were determined.Adsorption kinetics,isotherm and thermodynamics were introduced to explore the mechanism of adsorption separation.The results show that the adsorption equilibrium of the four DMs satisfies the Langmuir model and is a single layer adsorption.p H has a great influence on the electrical properties of the membrane surface,which has a significant influence on the adsorption capacity.The increase of initial DMs concentration,contact time and temperature is conducive to adsorption.(5)In order to explore the adsorption performance and mechanism of composite membranes on four different properties of HMIs,the composite membranes before and after adsorption were characterized.The effects of p H,initial concentration,temperature,contact time and cycle times on adsorption were measured.The adsorption kinetic model was introduced to analyze the adsorption mechanism.The changes of adsorption amount with p H,ion concentration,time and temperature were obtained.The results show that the adsorption of four kinds of HMIs on the composite membrane is more in line with the pseudo-second-order kinetic model,indicating that the adsorption of HMIs is affected by the concentration of multiple components.The results of the reproducibility study showed that after five adsorption-desorption cycles,the adsorption capacity of Pb(II),Cd(II)and Cu(II)on the composite membrane could still maintain more than 80%,and the adsorption capacity of Cr(III)was 56% of the original adsorption capacity.This is because: according to the theory of hard and soft acids and bases,Pb(II)and Cu(II)are boundary acids,Cd(II)is soft acid,Cr(III)is hard acid,and both carboxyl and hydroxyl groups are hard bases.According to Pearson’s law of acid-base reaction,hard base and hard acid will form a strong bond,so Cr(III)adsorption on the composite membrane is relatively difficult to desorption.(6)the maximum adsorption capacity of the four DMs was 1134.0(neutral red,NR),1074.3(methylene blue,MB),348.7(rhodamine B,RB),268.8(methyl orange,MO)mg/L,respectively.The maximum adsorption capacities of HMIs were 327.9(Pb(II)),177.4(Cd(II)),119.2(Cu(II))and 118.6(Cr(III))mg/g,respectively.The difference of adsorption amount between the two types of pollutants is mainly caused by the difference of relative mass,electrification and charge amount of the pollutants.Thermodynamic analysis shows that the adsorption of DMs and HMIs by the composite membrane is a spontaneous endothermic process,and the adsorption amount is positively correlated with the temperature.The experimental results show that the prepared hydrophilic GO/CA modified composite hydrogel membrane has a good removal effect on DMs and HMIs in water.In the early stage of filtration,the adsorption function of the composite membrane plays a leading role.Through the study of the adsorption mechanism,it can be known that the GO/CA modified composite hydrogel membrane has electrostatic attraction,ion exchange,van der Waals force and hydrogen bond effect on the adsorption mechanism of the two kinds of pollutants,and it also has a co-application on HMIs.After adsorption saturation,the electrostatic repulsion between pollutants plays a leading role. |
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