Preparation of large-area graphene oxide sheets with a high density of carboxyl groups using O2/H2 low-damage plasma

We have used low-damage O-2 plastha treatment (O-2-LDPT), with chemically reactive radicals generated in an inductively coupled plasma system equipped with a complementary filter, to prepare large-area graphene oxide (GO) sheets. Raman spectroscopy and X-ray photoelectron spectroscopy demonstrated that oxidative functionalities were formed on the graphene surfaces. However,,the carboxyl group, which is the most important functional group for biological applications, only occupied about 6.1% of the GO sheets formed using O-2-LDPT. By adding H-2 during O-2-LDPT, the compositional ratio of carboxyl group could be greatly increased to 10.8%. Optical emission spectroscopy revealed that this enhancement was achieved because of the presence of hydroxyl radicals in O-2/H-2-LDPT. (C) 2016 Elsevier B.V. All rights reserved.