Preparation Of Hydrogel Composites And Their Adsorption Mechanism For Heavy Metals

Heavy metal pollutants in industrial wastewater pose a serious threat to people's lives and health,so the problem of heavy metal pollution needs to be solved urgently.The adsorption method has the advantages of low cost,simple operation and high efficiency,and has been widely used in heavy metal sewage treatment.Hydrogel has become a research hotspot in the field of water treatment.This project aims to prepare new hydrogel materials with simple operation,strong adsorption capacity and recyclability.Copolymer Polyacrylic acid chitosan hydrogels(PAA-CS),Polyacrylamide cellulose hydrogels(PAM-CMC),poly(dimethylaminoethyl methacrylate)cellulose hydrogels(DMA-CMC)and poly(dimethylaminoethyl methacrylate)vinyl pyridine hydrogels(DMA-VP)were prepared by free radical polymerization,their physical and chemical properties,such as morphology,functional groups and swelling rate,were characterized,and their adsorption behaviors and mechanisms for heavy metal ions(taking Cu(II)and Cr(VI)as examples)were investigated,the effects of temperature,p H value of solution and interference of Ca(II)on the adsorption of heavy metal ions were studied.The main conclusions are summarized as follows:1.PAA-CS hydrogels with three-dimensional network pore structure and cross-linked chitosan were prepared by free radical polymerization using acrylic acid(AA)and chitosan(CS)as co-monomers.The swelling range of PAA-CS was 1.9-5.8.The results of heavy metal adsorption experiments show that the maximum amounts of Cu(II)and Cr(VI)adsorbed by PAA-CS hydrogel are 352 mg/g and 156.8 mg/g,respectively,the adsorption of Cu(II)and Cr(VI)on PAA hydrogel was 1.46 and 3.12times as much as that on PAA hydrogel.The adsorption process is mainly the electrostatic and coordination effect produced by-COOH and-OH in heavy metal ions and hydrogels.After three cycles of regeneration,more than 70%of the original adsorption capacity can still be maintained.2.PAM-CMC hydrogels with three-dimensional network pore structure were successfully synthesized by free radical polymerization using acrylamide and carboxymethyl cellulose as copolymerization monomers.The results of heavy metal adsorption experiments show that the adsorption of Cu(II)and Cr(VI)on PAM-CMC hydrogel accords with the Langmuir isothermal adsorption process,and the theoretical maximum adsorption amounts are 260.1 mg/g and 196.7 mg/g,the adsorption capacity of the gel was increased obviously.The adsorption mainly takes place on-COOH and-NH₂,and mainly involves coordination and electrostatic interactions.After 3 cycles of regeneration,PAM-CMC hydrogel still has the adsorption capacity of more than 65%of its original value.3.DMA-CMC and DMA-VP hydrogels were prepared by free radical polymerization of dimethylaminoethyl methacrylate with carboxymethyl cellulose and4-vinylpyridine,respectively.DMA-CMC hydrogel and DMA-VP Hydrogel also have three-dimensional network pore structure.The adsorption experiments of Cu(II)and Cr(VI)showed that the adsorption processes of DMA-CMC hydrogel and DMA-VP hydrogel were consistent with the first-order kinetic Langmuir equation,and the dominant processes were mass transfer and diffusion processes,the maximum adsorption capacity was 296.2 mg/g and 424.6 mg/g,281.3 mg/g and 265.2 mg/G respectively.The adsorption properties of DMA-CMC hydrogel for Cu and Cr were better than those of DMA-VP hydrogel.The adsorption mainly takes place on the carboxyl,amino and pyridine rings,and mainly involves coordination and electrostatic interactions.After three cycles of regeneration,the two hydrogels still possessed more than 60%of the original value.4.The adsorption processes of PAA,PAA-CS,PAM,PAM-CMC hydrogels for Cu(II)and Cr(VI)follow the second-order kinetic model.The adsorption of Cu(II)and Cr(VI)onto DMA-CMC and DMA-VP hydrogels followed a first-order kinetic model.In addition,all hydrogels were more suitable for Langmuir isothermal adsorption model,and PAA-CS and DMA-CMC hydrogels were the best for Cu(II)and Cr(VI),421.2mg/g and 424.6 mg/g,respectively.The adsorption order of hydrogels to four heavy metal ions was Cu(II)>Cr(?)>Zn(II)>Mg(II),which was mainly influenced by electronegativity.