Controlled synthesis of reduced graphene oxide-carbon nanotube hybrids and their aqueous behavior

This paper reports the controlled synthesis of reduced graphene oxide-carbon nanotube (rGO-CNT) hybrids and their aqueous behavior. The CNTs were suspended in an aqueous dispersion of GO, and the GO-CNT hybrids were reduced in situ in a controlled fashion using nascent hydrogen. Several hybrids with oxygen content ranging from 26 to 2% were synthesized. The properties of the hybrids with low degree of reduction were closer to GO while those with high degree of reduction were closer to CNTs. Solubility, dispersibility, hydrophobicity, critical coagulation concentration (CCC value), and Zeta potential of the hybrids were studied and compared. Solubility of GO-CNT hybrid decreased from 6.2 to 0 mu g/ml after reducing oxygen content to 2%. Dispersibility of hybrids also decreased from 7.1 to 0.5 mu g/ml after GO reduction. CCC value of hybrids in the presence of NaCl decreased from 16 in unreduced GO-CNT hybrid to 6 for one containing 7% oxygen, and equivalent decrease in the presence of MgCl2 was from 3 to 1. Additionally, as expected, the hydrophobicity of hybrids increased on reduction and the hydrophobicity index increased from - 3.2 to 7.4% as oxygen concentration decreased from 26 to 2%.