The simultaneous synthesis of carbon dots and carbon spheres with tunable sizes using a vertical chemical vapour deposition method

Abstract

Herein we report on the direct synthesis of solid hydrophobic carbon dots (CDs) and simultaneously carbon spheres (CSs), using a vertical chemical  vapour deposition (CVD) reactor. The HRTEM data indicated that the CDs and CSs originated from different carbon building blocks indicated that the CDs  and CSs originated from different carbon building blocks. The CDs were obtained by reacting acetylene (C₂H₂) and Ar mixtures at high flow rates (≥500  sccm) and high temperatures (800–1000°C). TEM studies indicated that the CDs produced were graphene-like quantum dots that increased in size from c.  3 nm to 8 nm as the Ar flow rate (constant C₂H₂ flow rate) was decreased, while small solid CSs (c. 100 nm) were also synthesised in the process. The  CSs had a typical spherical layered structure with no graphitic core. A mechanism to rationalise the observation that the CDs and CSs grew  simultaneously by different pathways with no formation of intermediate-sized particles is given