Preparation Of Magnetic Spartina Alterniflora Adsorbent Functionalized With Sulfonic Acid Group And Its Adsorption Properties For Heavy Metals And Dyes From Waters

Spartina alterniflora is an invasive plant with strong interspecific competition.Since its introduction in China in the 1960s,it has rapidly expanded population size and spatial distribution,which have erupted in Jiangsu,Zhejiang,and Guangdong,threatening local ecosystems and coastal aquaculture.It is practical to use a large number of Spartina alterniflora for resource utilization.The straw of Spartina alterniflora is rich in cellulose,which can be modified to improve the processing property and applied to the field of sewage treatment.This paper used the adsorption method to treat methylene blue,methyl violet,Cu?II?and Hg?II?in aqueous solution.The raw material Spartina alterniflora is an invasive species with strong ecological tolerance and interspecific competition.Sulfonic cellulose is synthesized by grafting AMPS?2-acrylamido-2-methyl-1-propanesulfonic acid?on the cellulose rich in straw,and then combined with Fe₃O₄.The adsorbent is magnetic,easy to separate,and has excellent adsorption property,which not only treat wastewater but aiso realize resource utilization of invasive species.The optimum reaction conditions of sulfonic acid group modification were investigated by orthogonal experiment and single factor experiment.The SEM,XRD,FTIR,XPS and magnetic analysis methods were used to study the changes of Spartina alterniflora in the modification.The relationship between the dosage of adsorbent,the pH of the solution,the adsorption temperature,the adsorption time and the adsorption property was obtained through the static adsorption experiment of dyes and heavy metal ions by magnetic adsorbent.Adsorption kinetics,adsorption isotherm and adsorption thermodynamic model were used to further explore the static adsorption mechanism.The effects of column height,flow rate and concentration on the breakthrough curve were investigated by dynamic adsorption experiments,and the Thomas model and the Yoon-Nelson model were fitted.The main conclusions are as follows:?1?The optimal modification conditions of magnetic Spartina alterniflora adsorbent?MSMSA?as follows:The influence degree of the factors,the modification temperature>the dosage of AMPS>initiator concentration>modification time;Spartina alterniflora,1.6g;initiator KMnO₄,348.0mmol/L;AMPS,4.8g;reaction temperature,313K;reaction time,3h;the mass ratio of magnetic Fe₃O₄ and sulfonic Spartina alterniflora,1:3.SEM analysis showed that Spartina alterniflora changed from smooth surface to loose porous;It was found that the symmetric stretching vibration peak and the asymmetric stretching vibration peak of S=O appeared at 1161cm-1 and 1318cm-1respectively by FTIR analysis.It was found by XPS analysis that there was the S2p peak?164ev?in Spartina alterniflora.FTIR and XPS analysis proved that sulfonic acid groups were successfully grafted onto Spartina alterniflora;XRD analysis showed that the peak position corresponding to Fe₃O₄ appeared in MSMSA and the hysteresis loop analysis showed that MSMSA had superparamagnetism,indicating that Spartina alterniflora and Fe₃O₄ were successfully combined and the adsorbent had magnetic.The results showed that removal rate of dyes and heavy metals by MSMSA were 30%and 50%higher than those without modification.The adsorption property of the magnetic Spartina alterniflora adsorbent is greatly improved,and it is easy to separate from liquid.?2?Static adsorption results of dyes and heavy metal ions by MSMSA as follows:For the adsorption of methylene blue and methyl violet solution,the optimal dosage of MSMSA is 0.5g/L.For the adsorption of Cu?II?and Hg?II?solutions,the optimal dosage of MSMSA is 2g/L.The optimum adsorption pH for methylene blue and methyl violet is 8 and the optimum adsorption pH for Cu?II?and Hg?II?solution is 5;the adsorption capacity increased and the adsorption equilibrium time became shorter as the temperature increased.After 3times of adsorption-desorption experiments,the removal rate of MSMSA was slightly reduced,but still higher than 91%.The adsorption kinetics analysis showed that the adsorption of MSMSA for the four kinds of pollutants were fitted with pseudo-second-order kinetic model?R²>0.999?.The saturated adsorption capacity calculated by the quasi-secondary equation was also closer to the actual experimental adsorption amount,and the adsorption process was mainly chemical adsorption;Adsorption isotherm analysis showed that the adsorption of methylene blue,methyl violet and Hg?II?were fitted with the Langmuir isotherm,which belongs to monolayer adsorption,while the adsorption of Cu?II?was more suitable for the Freundlich adsorption isotherm model.After the adsorbent adsorbs the first layer of Cu?II?on the surface,multi-layer adsorption can still be carried out due to the presence of van der Waals force.MSMSA had the highest saturated adsorption capacity for methylene blue,methyl violet,Cu?II?and Hg?II?at 323 K,which were188.68,185.18,27.38 and 25.92mg/g,respectively.Thermodynamic analysis showed that the adsorption of pollutants by MSMSA is a spontaneous irreversible process,which is an endothermic reaction,and the increase of temperature is beneficial to the adsorption.?3?The dynamic adsorption of heavy metal ions by MSMSA showed that when the column height was increased,the flow rate and concentration were decreased,the penetration time was prolonged and the removal rate was increased.The correlation coefficient of the Thomas and the Yoon-Nelson model fitting curve was greater than 0.947.The equilibrium adsorption capacity calculated by the two models were similar to the actual data obtained,and both of them described the dynamic adsorption process well.The axial diffusion of the adsorption column is not speed limit step.The packed column could be regenerated with hydrochloric acid,and The adsorption capacity of the packed column for the third time is about 88%of the first time.After 3 times of dynamic adsorption,it maintained good adsorption property.