Dye-contaminated wastewater from the textile industry and petrochemical waste oil (PWO) constitute a very serious threat to the environment. The presence of dyes in water inhibits penetration of sunlight, decreasing the photosynthetic processes of aquatic plants, resulting in the disruption of aquatic ecosystems. Moreover, organic dyes are known to have adverse effects on the human health, which presents a risk to the sources of clean drinking water. On the other hand, petrochemical waste oil is difficult to degrade and contains heavy metals and harmful additives. When dumped on landfills, waste oil may seep through the soil and find its way to bodies of water. Recycling technologies are still underdeveloped, and treatment proves to be expensive. Thus, it is crucial to improve the alternative upcycling technology of petrochemical waste oil. Herein, carbon nanotubes (CNT) were synthesized from PWO by simple catalytic vapor deposition (CVD). These CNTs were then used for systematic study on the removal of cationic and anionic dyes from wastewater. Dye removal by the as-synthesized CNT was Langmuir-type adsorption and followed the pseudo-second-order rate model for both the cationic and anionic dyes. Factors like solid-to-liquid ratio, initial dye concentration, and removal efficiency were investigated. CNT from PWO showed a relatively short adsorption time of less than an hour (t~60 min) for both types of dye and demonstrated very high dye adsorption capacities (qm). Hence, this study opens the possibility of using the PWO-derived CNT for large-scale dye-contaminated wastewater treatment.