Abstract
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•A new method for oil fly ash (OFA) treatment to produce CNTs is described.•Pre-sintering the OFA at 400 °C is a very effective treatment method to grow CNTs.•The optimum conditions to provide uniform, well defined CNTs were determined.•Bamboo like nanotubes with zigzag curved walls are observed in these CNTs.•This method is suitable for the mass scale production of low cost CNTs.
Oil fly ash (OFA) is a byproduct generated by the burning of heavy crude oil in factories and power plants. Millions of tons of OFA is produced annually worldwide and is mostly treated as solid waste. Extensive efforts have been made to utilize OFA and reduce its environmental effects. Recently, OFA has been found to be a suitable catalyst and co-precursor for carbon nanotube (CNTs) production. However, the treatment methods used are expensive and time consuming. Here, we describe a new method for OFA treatment and provide optimized growth conditions for CNTs production. Pre-sintering of OFA at elevated temperatures (400–450 °C) in air or vacuum using a chemical vapor deposition (CVD) tube furnace (80–100 min) is a very effective treatment method for CNTs growth under optimum growth conditions. The optimum parameters for CNTs growth were growth temperature, gas pressure, gas flow rate, and growth time. Well-defined, thin nanotubes with diameters of 20–40 nm were produced. Bamboo-like nanotubes with zigzag curved walls were also observed in the produced CNTs. The weight percentage of the produced CNTs was approximately twice that of the treated OFA. Consequently, the pre-sintering method exhibited suitability for the mass production of CNTs. Thus, large quantities of the nanomaterial can be supplied for use in various applications, e.g., polymer composites, the rubber industry, construction materials, and lubricant additives.