A New Type Of Flame Method That Can Be Used To Prepare Graphene And Flawedgraphene

Graphene is a sp²-bonded carbon nanostructure with a hexagonal honeycomb pattern in a two-dimensional plane.Such unique structure makes graphene exhibting exceptional electrical,mechanical,optical,and thermal properties.Therefore,it has a wide range of applications such as electronics,heat dissipation,energy storage,etc.Recent studies demonstrate that by introducing defects into graphene lattice,the physical and chemical properties of graphene can be tuned,enabling its applications in the fields of ultrafiltration,catalyst,sensor,and so on.Current methods for preparing graphene include mechanical exfoliation,chemical vapor deposition（CVD）,epitaxial growth,plasma and flame synthesis,etc.Irradiation and chemical treatment are the main methods to introduce defects within exfoliated or CVD-grown pristine graphene.The irradiation methods such as ion bombardment and oxygen plasma can’t afford large-area film treatment and scale-up manufacturing.Chemical treatments face challenges in controllability and contamination.CVD as the most mature method for manufacturing large-area graphene provides a solution by utilizing the intrinsic defects generated during crystal growth to modify the properties of graphene.However,the density of defects tends to be extremely low for CVD-grown graphene.Therefore,it’s urgent to develop a method that can directly manufacture large-area graphene with tunable properties of defects to meet the rising needs for the applications of defective graphene.This work introduces a novel flame-based method that can be used to synthesize graphene with tunable defective levels.A microscale inverse-diffusion flame array is designed for graphene synthesis.Ansys Fluent is employed to simulate the designated microscale inverse-diffusion flame array flame structures under different conditions.The effects of flame equivalent ratio,the concentration of species,flow speed on the flame structure,profiles of temperature and precursor species are studied.The conditions suitable for graphene growth are demonstrated.An experimental setup,including the burner body,gas pipelines,mass flow controller,sample holder,thermocouple,and tail gas treatment unit is built with a relevant patent applied.The simulation results reveal that the equivalence ratio suitable for the graphene growth is ranging from 3 to 4 with a corresponding oxidizer flow rate of 1m/s（oxygen 25-30%）or 0.8m/s（oxygen 30-35%）.Moreover,by studying the profile of chemical species under such conditions,CH₃,CH₂,and C₂H_x are found to be the dominant hydrocarbon species in the temperature range of graphene growth.The flame configurations are optimized according to the simulation results and graphene film is synthesized on catalytic substrates under the optimal conditions.Graphene sample is further etched via the in-situ hydrogen annealing.The density of defects within flame-synthesized graphene can be increased by as much as 12.25 times after annealing.Such method achieves the preparation of graphene with tunable defects using only one setup instead of the current two-step routes relying on both CVD synthesis and irradiation etching systems.The novel flame-based method exhibits advantages in cost,efficiency,and film size,which meets the requirements of large-scale manufacturing.