In situ repair of graphene defects and enhancement of its reinforcement effect in polyvinyl alcohol hydrogels

Defects cause unexpected and unsatisfactory effects in graphene when it is used as a reinforcement in composites. Herein, gamma-ray irradiation was introduced as a facile and efficient method to simultaneously repair the defects of reduced graphene oxide (rGO) and enhance the reinforcement effect of graphene in a polyvinyl alcohol (PVA) matrix. Under the action of gamma-ray irradiation, the surfaces of rGO were activated and free radicals were produced on PVA chains. At higher irradiation doses, random chain scissions of the PVA main-chain were linked with the reactive groups around the edge of defects on the rGO, leading to the repair of the crystalline graphene, which was evidenced by the decrease of ID/IG and stronger 2D bands of the irradiated PVA/rGO hydrogel composites. Thus, the reinforcement effect of graphene is enhanced by gamma-ray irradiation. The tensile and compressive strength of the PVA/rGO hydrogel composites achieved their maximum values at irradiation doses of 100 kGy and 150 kGy, respectively, which were 44% and 171% higher than the nonirradiated composites, and 113% and 336% higher than those of pure PVA hydrogel, respectively.