Preparation And Adsorption Properties Of Cr(Ⅵ)Ion-imprinted Lignin Adsorbent

As a kind of rich storage natural polymer compound,lignin has been extensively studied by people.However,the development and utilization of lignin are limited by its complex structure and large steric hindrance.Most of lignin is discharged as waste or burned as low value fuel,which not only wastes resources,but also pollutes the environment.Therefore,the study of lignin modification is of great significance for the full development and utilization of lignin.Because the active functional groups on lignin can adsorb heavy metals,lignin can be used as a cheap adsorbent.However,there are few reports on the selective adsorption of heavy metals by lignin based adsorbents.In order to improve the adsorption performance of lignin-based adsorbents and broaden the utilization of lignin,a lignin ion-imprinted polymer was prepared by ion-imprinted technology in this paper.In order to improve the reactivity of lignin and the adsorption performance of adsorbent,lignin was depolymerized.Depolymerized lignin was used as raw material to prepare depolymerized lignin ion imprinted polymer.A bifunctional monomer ion-imprinted polymer was prepared by using acrylamide and methacrylic acid as functional monomers.The adsorption properties and mechanism of lignin ion-imprinted polymers were studied.The results are as follows:Sodium lignosulfonate ion-imprinted polymer(L-IIP)was prepared via graft copolymerization of sodium lignosulfonateand acrylamide,in the presence of Cr(VI)as template ion,acrylamide as functional monomer,N,N-methylene-bis-acrylamide as crosslinker.The maximum adsorption capacity of the prepared ion-imprinted polymer was 19.55 mg·g’1 in Cr(Ⅵ)solution with initial concentration of 800 mg/L and pH=2 at 25℃.The selectivity coefficients of sodium lignosulfonate ion-imprinted polymer in Cr(Ⅵ)/Cu(Ⅱ)and Cr(Ⅵ)/Cr(Ⅲ)mixed solutions were 5.925 and 7,respectively.In order to improve the adsorption performance of sodium lignosulfonate ion-imprinted adsorption materials,depolymerized sodium lignosulfonate ion-imprinted polymer(DL-IIP)was prepared via graft copolymerization of functional monomer methacrylic acid and depolymerized sodium lignin sulfonate with Cr(Ⅵ)as template ion and N,N-methylene-bis-acrylamide as crosslinking agent.The maximum adsorption capacity of the prepared ion-imprinted polymer was 24.28 mg·g-1 in Cr(Ⅵ)solution with initial concentration of 800 mg/L and pH=2 at 25℃.The adsorption selectivity coefficients of depolymerized sodium lignosulfonate ion-imprinted polymer in Cr(Ⅵ)/Cu(Ⅱ)and Cr(VI)/Cr(Ⅲ)mixed solutions were 8.05 and 5.24,respectively.In order to study the properties of bifunctional monomer ion-imprinted polymers,the bifunctional monomer ion-imprinted polymers(B-IIP)were prepared by using Cr(VI)as template ion,N,N-methylene-bis-acrylamide as crosslinking agent,acrylamide and methacrylic acid as functional monomers.The maximum adsorption capacity of the prepared ion-imprinted polymer was 24.59 mg·g-1 in Cr(VI)solution with initial concentration of 800 mg/L and pH=2 at 25℃.Under the synergistic effect of bifunctional monomers,bifunctional monomers ion-imprinted polymers showed better selective adsorption,and their adsorption selectivity coefficients in Cr(Ⅵ)/Cu(Ⅱ)and Cr(Ⅵ)/Cr(Ⅲ)mixed solutions were 9.42 and 12.59,respectively.The adsorption of Cr(VI)on three kinds of ion-imprinted polymers were described well with the pseudo-second-order model.The adsorption isotherms of Cr(VI)on the three ion-imprinted polymers were fitted to the Langmuir model.The three kinds of ion-imprinted polymers have good reusability,after five times of adsorption/desorption,the adsorption capacity of the three materials can still reach more than 80%of the maximum adsorption capacity.Lignin ion-imprinted adsorption materials have good adsorption performance,which provides a good application prospect for the further development and utilization of lignin.