# Treatment of Water Contaminated with Diesel Using Carbon Nanotubes
## 1 Introduction
These methods have shown promising results, although high-molecular-weight hydrocarbons have shown a lower reactivity to microorganisms [41; 42; 43]. Chemical treatments are often difficult, as the pollutants, as in the case of oil, are hydrocarbon mixtures of different chemical natures and, therefore, require distinct treatments [44; 45]. Accidental spillages of large quantities of hydrocarbons in extensive marine areas often require physical methods, such as dredging and harvesting by floating dams and cleaning using high-pressure pumps and washers [46]. The containment of accidental spills of hydrocarbons into the environment, by means of the physical method of adsorption, represents an excellent solution, especially when this involves aquifer systems. Adsorption is based on processes capable of separating the contaminant from the solid or liquid matrix and obtaining them in concentrated form, subsequently destined for treatment or final disposal [47; 48; 49]. The fact that these are purely physical interventions, i.e., without the addition of chemical reagents, could be seen as an advantage, as it greatly reduces the risk of secondary contamination. Numerous studies on the use of adsorbents for the treatment of hydrocarbon-contaminated sites are reported in the literature. Different adsorbent materials can be used, such as microporous materials [50; 51], biochar [52; 53; 54], chitosans [55] and activated carbons [56]. Carbon nanotubes represent an important class of adsorbent material [57; 58; 59; 60; 61; 62]. Carbon nanotubes were studied as early as the early 1950s, but only in 1991 were they identified with certainty by the scientist [PERSON] of the NEC Fundamental Research Laboratory of Tsukaba (Japan) as a by-product of the production of fullerene by electric arc [63; 64]. In particular, carbon nanotubes appear as tubular structures with a diameter in the order of tens of nanometers, derived from the winding of a graphite sheet of atomic thickness [65]. The study of the physical properties of nanotubes has highlighted exceptional properties for which carbon nanotubes have numerous applications in several areas, including chemistry, biology, purification, medicine, electronics and optics [66; 67]. Recent studies report that carbon nanotubes have shown large adsorptive capacities in the purification of petrol-contaminated water [68; 69; 70; 71]. Carbon nanotubes can interact with inorganic contaminants through several mechanisms, such as surface complexation, electrostatic interaction, ion exchange, physical adsorption and precipitation. In the case of organic pollutants, as in the case of organic molecules present in diesel, in addition to physical adsorption, \(\pi\)-\(\pi\) and electrostatic interactions play an important role in adsorption [72]. As is known, gasoline is a lighter liquid, which is obtained via distillation immediately after the gases separate, while diesel is heavier and is found below gasoline in the distillation column. From a chemical point of view, gasoline is composed of volatile hydrocarbons, and this is why, if left in the open air, a part of it evaporates. Diesel fuel, being denser and oilier, is not, but for this very reason, it freezes at low temperatures. Gasoline is also more flammable than diesel. Gasoline and diesel contain hundreds of different hydrocarbon molecules. Gasoline contains mainly alkanes, alkenes and aromatics, with a number of carbon atoms ranging from 4 to 12. Diesel fuel, on the other hand, consists mainly of paraffins, aromatics and naphthenes, with several carbon atoms between 12 and 20 [73]. In the present study, we intended to test whether carbon nanotubes present in the treatment of diesel-contaminated water have the same effectiveness that they show in gasoline-contaminated water. In particular, if the presence of molecular weight in diesel fuel is greater than that present in gasoline, it can affect the adsorption capacity of carbon nanotubes.