Carbon-based nanomaterials production from environmental pollutant byproducts: A Review

Abstract

Carbon dioxide (CO2) and fly ash are known to be harmful to the environment. While some of their beneficiations have reached maturity for the chemical industry, their application in the synthesis of carbon nanomaterials (CNMs) such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are still limited. This review focuses on the application of CO2 as a carbon source and fly ash as both catalyst and carbon source for the synthesis of CNMs. Various methods used for the production of CNMs from CO2 and fly ash such as chemical reactions, chemical vapour deposition (CVD) and electrolysis are discussed. Characterization techniques (Scanning Electron Microscope, Transmission Electron Microscopy, Thermogravimetric Analysis, Raman spectroscopy, and Energy Dispersive Spectroscopy) were used to access the quality of the synthesized CNMs. Double helical and bamboo CNTs were among the morphologies found from the chemical reaction method, the type of reductant was found to influence the morphology and high pressure is required. The CVD method gave higher yields of CNTs with various morphologies (CNT-ribbons, Straight and coiled CNTs) and required high temperatures. An unusual CNT morphology was observed in the electrolysis method, which looks like cotton wool called a CNT-wool. Highly crystalline nanomaterials in good yields without the use of high pressures and temperatures were also observed with the electrolysis method. The choice of method should be based on the preferred morphology, yield and product quality.