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 O2 plasma treatment (O2-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 O2-LDPT. By adding H2 during O2-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 O2/H2-LDPT.