Preparation And Adsorption Application Of The Novel Chitosan Hydrogel

Recently,the water pollution has been more and more serious,which has been attracted more and more attention.Some contaminants are able to be accumulated through food chain,which causes a threat to human health,ecological safety and environmental stability.Chitosan,as an emerging adsorbent in the field of water treatment,has attracted much attention around the world.Owing to the diverse preparation methods,chitosan-based materials possess different physicochemical properties and can be applied to remove different pollutants,which are effective,stable and selective.Compared with some chitosan-based materials applying to remove cations(e.g.heavy metals),there are much less attentions that are paid to remove anions,such as perfluorooctanoic acid(PFOA)and nitrate.PFOA,existing as organic anions in water,possesses high chemical stability and is hard to be removed by biological and chemical treatments so traditional municipal technologies can not effectively remove PFOA.And nitrate,existing as inorganic anions in water,possesses high water-solubility and has caused lots of contaminations around the world.Therefore,the development of a chitosan-based material that is able to effectively remove PFOA and nitrate with high stability is valuable for the anions’removal and possesses a prosperous application.In this study,Chitosan-ethylene glycol hydrogel(CEGH)was synthesized using the repeated freezing-thawing procedure.The removal effects of PFOA representing organic anions and nitrate representing inorganic anions onto CEGH were studied.Adsorption isotherms and kinetics were used to explore the adsorption performance.SEM,FTIR,XPS and thermogravimetric analysis were applied to indicate CEGH’s physicochemical properties and removal mechanisms.The main contents and results of CEGH to remove PFOA in water are as follows:(1)CEGH has a rough surface and possesses abundant N-H and O-H functional groups,which are effective to remove PFOA.(2)Freundlich-Langmuir model was best to fit isotherms,which had a R~2(0.964)close to 1.Based on the Freundlich-Langmuir model,the maximum sorption capacity was 1275.9 mg/g,which much higher than the adsorption capacities of other adsorbents in previous studies.(3)The equilibrium was reached at 10 h.Pseudo-first-order model had the best fit with R~2 of 0.96.(4)The initial p H value of sample solution and reaction temperature played vital roles in adsorption process of PFOA removal.With the increase of p H,the adsorption capacity decreased significantly.And with the reaction temperature increasing,the adsorption capacity increased.(5)Experimental data and characterizations results clearly indicated protonated amine led to ionic hydrogen bond of PFOA onto CEGH.The main contents and results of CEGH to remove nitrate in water are as follows:(1)The N-H and O-H functional groups on CEGH surface were beneficial to the removal of nitrate.(2)Langmuir model was best to fit isotherms with R~2(0.98).Theoretically,the maximum sorption capacity of nitrate onto CEGH was 49.04 mg/g,which higher than those of previous adsorbents.(3)With the reaction time increasing,adsorption capacity increased and the equilibrium time was about 10 h.Pseudo-second-order model was best to fit kinetics with R~2(0.994).(4)p H,reaction temperature and co-existing anions could make influence on the adsorption process.The adsorption decreased with p H or temperature increasing.Co-existing anions all made negative influences on nitrate adsorption on CEGH due to the competitive adsorption.And the more charge the anions carried,the more serious the inhibition for the removal of anions was.(5)Experimental data and characterizations results clearly showed the N-H and O-H on CEGH were able to cause polar attraction to nitrate,which was beneficial to the removal process.When p H was low,electrostatic attraction and ionic hydrogen bond interaction were also generated to improve the adsorption capacity owing to the existence of H+.This study showed that CEGH was effective to remove PFOA and nitrate,which was valuable for the future removal of anions and constituted a stepping stone to the development of relative materials and practical application.