Provided are plasma processes for producing graphene nanosheets comprising injecting into a thermal zone of a plasma a carbon-containing substance at a velocity of at least 60 m/s standard temperature and pressure STP to nucleate the graphene nanosheets, and quenching the graphene nanosheets with a quench gas of no more than 1000° C. The injecting of the carbon-containing substance may be carried out using a plurality of jets. The graphene nanosheets may have a Raman G/D ratio greater than or equal to 3 and a 2D/G ratio greater than or equal to 0.8, as measured using an incident laser wavelength of 514 nm. The graphene nanosheets may be produced at a rate of at least 80 g/h. The graphene nanosheets can have a polyaromatic hydrocarbon concentration of less than about 0.7% by weight.