Recent Research Progress in Stimuli-Responsive Graphene Materials

Graphene is a kind of two-dimensional carbon nano-material with hexagonal honeycomb lattice, which is formed by the hybridization of carbon atoms in sp² electron orbit. The atoms in graphene layer are connected together by σ bond, and the free electrons form a large area of conjugated π bond. This structural feature endows graphene with excellent electrical properties, mechanical properties, optical properties and thermal conductivity, making graphene be a " rising star” material which has attracted enormous attentions. With the rapid development of this field, the research focus has been shifting to controlled fabrication of graphene materials by chemical or physical modifications aiming to achieve specific applications in different advanced systems. Stimuli-responsive systems are of great theoretical and practical interests because of their spontaneously response to environmental changes. Polymer-based stimuli-responsive materials have the disadvantages of poor mechanical strength and insufficient environment stability. In contrast, graphene-based materials are stable, mechanically strong, electrically and thermally conductive, making them be attractive building discrete for the fabrication of stimuli-responsive materials. Stimuli-responsive graphene materials can be obtained by modifying graphene with specific polymers, small molecules or nano-particles through covalent or non-covalent interactions. These polymers or small molecules are typically able to response to external stimulus. Therefore, the functionalized graphene-based materials are sensitive to a series of stimulus, including temperature, pH, electrical field, light, gas molecule, solvent molecule, magnetic field or even multiple signals. In this review, the fabrication methods and related applications of stimuli-responsive graphene materials functionalized by the corresponding polymers, small molecules or nano-particles are outlined. These stimuli-responsive graphene systems present great theoretical and practical interests in a wide range of fields, such as actuators, switches, chemical or strain sensors, self-healing materials, photothermal therapy and controlled drug/gene delivery, etc. Moreover, the deficiencies of the existing stimuli-responsive graphene materials are summarized as well. The future application and development directions of the stimuli-responsive graphene materials are proposed.