Superabsorbent graphene oxide/carbon nanotube hybrid Poly(acrylic acid-co-acrylamide) hydrogels for efficient salinity gradient energy harvest

Abstract

Hydrogels can be employed to recover salinity gradient (SG) energy as they can exhibit reversible swelling and shrinking behaviors in alternate freshwater and sea water. The swelling ratio and mechanic property of hydrogels are essential for the SG energy harvest. Herein, different amounts of graphene oxide (GO) or carbon nanotube (CNT) were successfully introduced to the matrix of poly(acrylic acid-co-acrylamide) (PAAM) hydrogels. Compared to the original PAAM hydrogels, both the swelling property and mechanic strength of the GO/CNT hybrid PAAM hydrogels were significantly enhanced. Although the CNT/PAAM hydrogels exhibited relatively higher swelling ratio (1578 g g−1) than that of GO/PAAM (1423 g g−1), the highest SG energy recovery was obtained by using GO/PAAM hydrogels (7.07 J g−1). The reason was due to the better mechanical strength of GO/PAAM hydrogels, which resulted from the covalent bonds between the extensive oxygenated functional groups in GO and the polymeric chains. Moreover, excellent reproducibility was observed with GO/PAAM hydrogels over 10 cycles because of their highly structure integrity. These results demonstrated that GO/CNT hybrid hydrogels are efficient for SG energy recovery attributed to the high swelling ability as well as the strong mechanical property.