Stnthesis Of Magnetic N-vinylformamide Grafted Starch And Its Application In Copper-nickel-chromium Heavy Metal Ions By Adsorption Separation

In this paper,a novel bio-based adsorbent with magnetic starch grafted N-vinylformamide was synthesized.N-vinylformamide（NVF）was grafted onto the pregelatinized starch（PGS）to form NVF-grafted starch（CSA）;The magnetic nano-triiron oxide surface coated with hydrated manganese dioxide to obtain modified nanoparticles（NFs）;A novel magnetic starch（M-CSA）was combined from CSA and NFs in aqueous solution by sonication.The adsorption mechanism and separation performance by CSA,NFs and M-CSA of Cu²⁺,Ni²⁺and Cr₂O₇^2-metal ions were investigated.Firstly,using cyclohexanone and sodium bromate as initiators,N-vinyl formamide was grafted of pre-gelatinized starch to form NVF grafted starch.Meanwhile,the adsorption performance of different concentrations of Cu²⁺,Ni²⁺and Cr₂O₇^2-was analyzed using the adsorbent CSA.The structures of CSA was characterized by FTIR,SEM,¹H-NMR and conductivity measurements.The adsorption mechanism by CSA was investigated by FTIR and XPS.The results showed that NVF was successfully grafted onto the pregelatinized starch,and CSA had the ability to adsorb Cu²⁺,Ni²⁺and Cr₂O₇^2-from aqueous solutions with high.CSA adsorbed 28.00 mg/g Cu²⁺in 0.3 g/l copper solution,1.17 mg/g Ni²⁺in 0.02 g/l nickel solution and 3.03 mg/g Cr₂O₇^2-in 0.08 g/l potassium dichromate solution.Secondly,Fe₃O₄surface was coated by Mn O₂formed by in-situ chemical reaction between KMn O₄and Mn SO₄to obtain modified nanoparticles.Meanwhile,Fe₃O₄reacted with Mn SO₄in the presence of KMn O₄to form Fe₃Mn₃O₈.The adsorption performance and adsorption mechanism of Cu²⁺,Ni²⁺and Cr₂O₇^2-were analyzed using the adsorbent NFs.The results showed that the hydrated manganese dioxide was successfully coated onto the surface of magnetic Fe₃O₄nanoparticles with uniform coating and no serious accumulation,while the compound Fe₃Mn₃O₈was formed.At the same time,NFs showed the effect of increased dispersion in aqueous solution and increased adsorption capacity of heavy metal ions in adsorbed aqueous solution.NFs adsorbed 312.20 mg/g Cu²⁺in 3.8 g/l copper solution,30.51 mg/g Ni²⁺in 0.6 g/l nickel solution and 42.97 mg/g Cr₂O₇^2-in 1.2 g/l potassium dichromate solution.Finally,CSA and NFs were sonicated in aqueous solution,and the combination of NFs and CSA occurred to obtain magnetic starch.The chemical structure analysis and the adsorption mechanism of M-CSA were also investigated.The results showed that CSA and NFs were successfully combined into M-CSA,and the combined adsorption capacity of M-CSA had the ability to adsorb Cu²⁺,Ni²⁺and Cr₂O₇^2-from aqueous solutions with high.M-CSA adsorbed 274.68 mg/g Cu²⁺in 3.0 g/l copper solution,8.92 mg/g Ni²⁺in 0.5 g/l nickel solution and 36.53 mg/g Cr₂O₇^2-in 1.2 g/l potassium dichromate solution.The adsorption experiments showed that the newly developed biosorbent M-CSA had a good recyclability.The adsorption ability of M-CSA was substantially improved by EDTA-2Na modification.The results of M-CSA after four adsorption cycles showed that the adsorption capacity could still be maintained at about 50.5%of the original adsorption capacity for Cu²⁺,and the adsorption capacity exceeded the original adsorption capacity for Ni²⁺and Cr₂O₇^2-.