Synthesis And Properties Of Graphene Oxide-based Nanocomposite Hydrogels

Superabsorbent hydrogels are three-dimensional functional polymer materials composing of highly hydrophilic crosslinked macromolecular chains that are able to swell and retain a significant portion of water when placed in an aqueous medium,which makes them have potential applications in water retention in arid regions as well as ecological remediation,etc..However,conventional hydrogels show some disadvantages in terms of their poor nature of absorption/retention of water and salt resistance,thus,limits their practical application in a large scale.Graphene oxide(GO),a two-dimensional and single atomic layered carbon material,has many hydrophilic oxygenated functional groups,including hydroxyl(-OH),carbonyl(-C=O),and carboxyl(-COOH),which enables it not only has a strong hydrophilic,but also easy to interact with other functional groups for preparation of nanocomposite materials and hydrogels.In this project,the GO-based composite hydrogels were prepared by the in-situ polymerization or copolymerization and using GO as nanofillers.And then,we studied the water absorption properties of the as-prepared GO-based nanocomposite hydrogels in water and saline environment as well as the impacts of GO layers connected by covalent bonding in superabsorbent nanocomposite polymer chains for stretching,curling or collapsing properties of the polymer networks.The main contents and results are enclosed as follows.(1)Two kinds of GO-based hydrogels,poly(acrylic acid)-GO(PAA-GO)and poly acrylamide-GO(PAM-GO)hydrogels were prepared using GO as an nanofillers,N,N-methylene bisacrylamide as a crosslinker,ammonium persulfate as an initiator,acrylic acid and acrylamide as monomers.The GO was distributed evenly in polymer matrix.The addition of GO can greatly improve the adsorption water properties of hydrogels,because the graphene oxide provids a large number of hydrophilic groups and formed three-dimensional network by combination with the polymer.It also can be seen that the water absorption capacity of the hydrogel increased first and then decreased with the increase of the amount of initiator.The amount of crosslinking agent was inversely proportional to the water absorption capacity of the hydrogel.The GO sheets act as a ‘‘non-ionic’’ nanofiller in the polymeric and resist against the collapse of the polyelectrolytic networks and improves the salt resistance of the hydrogel composites.In organic solution,the GO nanofillers can also improve the absorption capacity of PAA-GO and PAM-GO.On the one hand,the interaction between the hydrophilic oxgen-containing groups on GO and polymer chains enhance the intensity of networks.On the other hand,GO nanosheets act as “house-of-cards” to prevent the extrusion of water from the networks.(2)The poly(acrylic acid-co-acrylamide)/graphene oxide(PAAM-GO)hydrogels were prepared by using GO as nanofillers,N,N-methylene bisacrylamide as a crosslinker,ammonium persulfate as an initiator,acrylic acid and acrylamide as copolymer monomers.The resulting PAAM-GO hydrogels show three-dimensional network structure.The content of initiator,monomers ratio,the content of crosslinker and the concentration of GO used in the process for the formation of hydrogels have a great influence on the adsorption properties of PAAM-GO.The as-prepared hydrogel composites exhibit high water adsorption capacity of 197 g g-1 with initiator content of 64 mg,crosslinker content of 12.8 mg,the molar ratios(AA to AM)of 0.5,GO concentration of 0.5 mg m L-1.The GO nanosheets improves the adsorption water properties of the hydrogel composites.Such improvement in the water absorbencies of PAAM-GO should be attributed to the fact that the GO sheets act as a ‘‘non-ionic’’ nanofiller in the polymeric and resist against the collapse of the polyelectrolytic networks.(3)The poly(acrylic acid)-modified GO hydrogels were prepared by using the p-phenylenediamine modified GO as nanofillers,N,N-methylene bisacrylamide as a crosslinker,ammonium persulfate as an initiator,acrylic acid as monomer.The addition of the modified GO can effectively improve the overall adsorption properties of the hydrogel composites.(4)The PAM/PEG-GO/ODA hydrogels were prepared by in situ polymerization and using eighteen alkyl amine modified graphene oxide(GO/ODA)as fillers under ambient conditions.The addition of GO/ODA can dramatically enhance the salt resistance and water absorption capacity of the hydrogels.Among them,the salt resistance of PAM/PEG-GO/ODA hydrogels in aqueous Ca Cl2 solution can be increased by 60%.When the content of GO/ODA was 5 wt%,the absorption capacity reached up to 61 g g-1.The PAM/PEG-GO/ODA hydrogels with hydrophilicity and hydrophobicity make them have good selectivity for removal of the water from oils.The water removal rate is more than 99%.(5)The PVA/PVP-GO interpenetration aerogel networks were prepared by freeze drying method.The content of GO has great influence of the pore structure of the as-prepared PVA/PVP-GO hydrogels.In a lower concentration of GO,the aerogel exhibited many larger pores,but with the increase of GO concentration the pore structure of aerogel was decreased and showed penetrating honeycomb structure.Compared to PVA/PVP aerogel,the PVA/PVP-GO shows excellent adsorption properties due to the addition of GO which can prevente the collapsing of the structure of aerogels,thus enhancing the salt resistance of the aerogels.Taking advantages of the unique macroporous structure and the hydrophilic and hydrophobic properties,the PVA/PVP-GO can be used to removal of water in diesel oil and the water content decreased from 0.094 g g-1 to 37.95 ppm.