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Synthesis and characterization of carbon nanotube aerogel from waste engine oil via floating catalyst chemical vapor deposition for oil spill removal

Carbon nanotube (CNT) aerogel is a novel nanomaterial with three-dimensional (3D) 
macrostructure. The long CNTs assemble display high porosity, spinnability, 
structural stability, and good electrical conductivity. These characteristic represents a 
critical approach towards practical applications such as supercapacitors, gas storage, 
catalyst support, filtration, separation, biological sensors and oil spill removal. CNT 
aerogel is directly synthesized by floating catalyst chemical vapor deposition 
(FCCVD) using petrochemicals such as methane, cyclohexane, toluene or 
dichlorobenzene as a carbon source. Nevertheless, the high cost, depletion of the 
petrochemical products, and environmental aspects have brought the consideration of 
using waste engine oil (WEO) instead as a carbon source. This work is the first ever 
attempt to utilize WEO for CNT aerogel production. It was done via catalytic 
decomposition of WEO with ferrocene as a catalyst through FCCVD method. Prior to 
the reaction process, WEO was first filtered to remove dirt and any solid particles that 
might present. This was later followed by fractional distillation of the oil into different 
fractions which resulted in five (5) fractions. Gas chromatography-mass spectrometry 
(GC-MS) showed successful separation of low molecular weight hydrocarbons which 
was necessary for dissolving the catalyst, while Carbon-nitrogen-sulfur (CNS) 
analysis indicated that each fraction has more than 69% carbon, less than 0.2% 
nitrogen and less than 0.09% sulfur. The reaction was carried out at 1150 °C and 1200 
°C in hydrogen with a flowing rate of 550 - 650 mL min-1. The carbon source solution 
(10 mL) was continuously injected into the furnace tube at a feeding rate of 10 mL h- 
1 during one hour reaction time. It was found that all the synthesized CNT aerogel 
were multi-walled carbon nanotubes (MWCNTs) with 99.14% yield for CNT aerogel 
3 synthesized at 1150 °C. Interestingly, CNT aerogel 2-2 and CNT aerogel 3-2 
revealed graphenated carbon nanotubes (G-CNTs) structure obtained at reaction 
temperature 1200 °C. The CNT aerogels had a mesopore distribution with specific surface area in the range between 80.6 - 222.0 m2 g-1. Field emission scanning electron 
microscopy (FESEM) revealed randomly orientated to entangle thin multi-walled 
structure. Oil spill removal study was done by conducting benzene, toluene, and mxylene 
(BTX) as well as kerosene, diesel oil, palm oil and waste engine oil absorption 
of the synthesized CNTs. Results showed that CNT aerogel 5-2 gave the highest 
sorption capacity (Qe) for kerosene in both oil and oil/water system at 71.43 and 75.19 
(g g-1), respectively. Absorption capacity was sustained at 90% for benzene, toluene, 
and m-xylene, 93% for kerosene, 87% for diesel fuel, 68% for palm oil, and 65% for 
waste engine oil even after 10 absorption cycles. Therefore, it can be concluded that 
CNT aerogel were successfully prepared from WEO by using FCCVD method which 
produced MWCNT at 1150 °C and graphenated CNT aerogel at 1200 °C. The CNT 
aerogel showed an excellent sorption capacity for all tested solvents and oils in both 
oil and oil/water systems with commendable recycle performance.