On the transition of reaction pathway during microwave plasma gas‐phase synthesis of graphene nanosheets: From amorphous to highly crystalline structure

Fourier‐transform infrared spectroscopy and proton‐transfer‐reaction–mass spectrometry are used in a complementary way to study gas‐phase processes during decomposition of ethanol in a microwave plasma torch. Decomposition products (C, C2 and simple hydrocarbons) reassemble into higher hydrocarbons and graphene nuclei and further grow into graphene nanosheets (GNS). Depending on microwave power, ethanol flow rate and molecular gas admixture, the material structure changes from amorphous to crystalline. The presence of C2n + 1H y species was found to be responsible for the formation of defects in the GNS structure. O2 and H2 admixtures change the gas temperature axial profile and consequently modify reaction pathways influencing growth and production rate of GNS. Determination of reaction pathway selectivity enables us to predict whether high‐quality or defective GNS are produced. Exceptionally stable geometry of the microwave plasma torch was reached by a separate external injection of hydrocarbon precursor into the microwave (MW) filament primary ignited and sustained in a pure argon atmosphere. Two discharge zones are visibly distinguished, representing a green‐glowing hot plasma zone emitted by C2 molecule and an orange‐glowing assembly zone, where graphene is formed. The gas temperature axial profile changes with MW power or addition of molecular admixture into the plasma, substantially affecting the geometry, and consequently the quality of synthesised graphene nanosheets can be engineered.