Multiple pH-responsive graphene composites by non-covalent modification with chitosan.

Multiple pH-sensitive composites have been prepared through non-covalently functionalizing chemically converted graphene (CCG) with chitosan. Chtiosan exhibits as polybases and CCG shows characteristics of polyacids. Owing to the synergistic effects of chitosan and CCG, chitosan decorated graphene (CS-G) presents a multiple pH-responsive behavior that it can be dispersed well whether in acidic or in basic solution but aggregated in near-neutral solution. After CS-G was modified through a controlled deposition and cross-linking process of chitosan, the resultant cross-linked chitosan decorated graphene (CLCS-G) can be converted to a different pH-sensitive material that disperses only in acidic solution. Both CS-G and CLCS-G present a reversible switching between dispersed and aggregated states with pH as a stimulus. The unique pH response mechanisms of CS-G and CLCS-G have been further investigated by zeta potential analysis. Based on the unique pH-responsive property of CS-G, a stable and repeatable pH-driven switch was developed for monitoring pH change.