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Article

Treatment of Water Contaminated with Diesel Using Carbon Nanotubes

1
Dipartimento di Ingegneria Meccanica, Energetica e Gestionale, Università della Calabria, I-87036 Arcavacata di Rende, CS, Italy
2
Dipartimento di Farmacia e Scienze della Salute e della Nutrizione, Università della Calabria, I-87036 Arcavacata di Rende, CS, Italy
3
Dipartimento di Ingegneria per l’Ambiente, Università della Calabria, I-87036 Arcavacata di Rende, CS, Italy
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(10), 6226; https://doi.org/10.3390/app13106226
Submission received: 28 April 2023 / Revised: 15 May 2023 / Accepted: 18 May 2023 / Published: 19 May 2023
(This article belongs to the Special Issue Green Nanotechnology and Its Application in Wastewater Treatment)

Abstract

:
The purpose of this research was to evaluate the adsorbent properties of carbon nanotubes by investigating, in particular, the possibility of their use in the purification of water contaminated with automotive diesel, caused, in most cases, as a result of spillage from underground tanks, leaks from pipelines, traffic accidents, etc. In particular, we investigated whether the high molecular weights of the hydrocarbon molecules present in diesel could influence the adsorption capacity of carbon nanotubes. Initial systems consisting of water and diesel were treated with different amounts of carbon nanotubes. The final post-adsorption phases were characterized using NMR analysis, FT-IR spectroscopy and TG-DTG-DTA thermal analysis. Carbon nanotubes showed great efficiency in the adsorption of diesel, the possibility of their reuse in several adsorption cycles and the consequent recovery of the adsorbed diesel and of the treated water.

1. Introduction

Environmental pollution is a consequence of both civil and industrial anthropic activities and, as such, is highly widespread, even affecting areas of great naturalistic value. It does not spare soils, groundwater [1,2,3], surface waters, marine environments [4,5,6,7] and atmosphere [8,9]. The impact of pollution often has very serious consequences on human health [10], the balance of ecosystems, the livability of habitats, food chains [11,12], the landscape, the soils, the agriculture and, last but not least, biodiversity as a whole [13,14]. In recent years, in order to stem and contrast environmental pollution, research has been carried out in various sectors, such as in the production of eco-sustainable materials [15,16,17,18,19], in the synthesis and preparation of new photodegrading materials capable of degrading pollutants [20,21,22,23,24,25] and adsorbents for water purification [26,27,28].
The problem of contaminated sites assumes an extremely relevant importance in the context of environmental risk and public health [29]. Soil pollution from petroleum products can mainly affect the soil and subsoil [30,31,32].
The main mechanisms that arise when the contamination affects the surface area are: wind transport, oxidative/photochemical degradation, leaching and transport by meteoric or surface water, with the possibility of penetrating the subsoil. Penetrating into the subsoil, a petroleum product in the liquid phase tends to drain due to gravity: the air and the interstitial water are displaced with the consequent establishment of transport, transformation and interaction phenomena, which are a function of the characteristics of the soil and of the chemical-physical properties of the individual pollutants. The penetration of pollutants into the subsoil depends on the soil structure and the type of substance. A sandy soil will be more vulnerable to polluting agents, while a clayey soil will act as an obstacle, although, due to industrialization, the number of chemical substances that can penetrate the soil and consequently the underlying groundwater has significantly increased [33,34,35]. Diesel fuel is a common fuel, consisting of a mixture of liquid hydrocarbons, from 13 to 18 carbon atoms. It is obtained via the fractional distillation of petroleum with an average outlet temperature from the fractionation tower of approximately 350 °C and a higher flash point than petrol. It was used for the first time in the motoring field, as fuel for diesel engines, between 1893 and 1897 by Rudolf Diesel, in the experimentation phases that led to the development of the engine that still bears his name.
There are numerous cases of accidents involving significant contaminations of diesel or, in general, of other fuels of petroleum origin. Spills at sea and in coastal areas, due to the capsizing or stranding of tankers, represent the most striking situations in terms of the seriousness of the damage caused to the environment, although the problem, albeit to a lesser extent but more frequently, also affects other sectors of transport. Transportation, transfer and storage represent situations in which diesel fuel may accidentally spill into the environment [36,37,38]. The treatment of environments contaminated with accidental oil spills is often very expensive and difficult. In recent years, research and studies have been carried out to improve and develop new methods for the rehabilitation of areas contaminated with hydrocarbons. Generally, the main methods of remediation of areas contaminated with hydrocarbons are based on biological, chemical and physical phytoremediation treatments. Constructed wetlands, as is known, use plants for the decontamination of polluted sites. However, it is a method that can hardly be used in cases that require an immediate decontaminating action [39,40]. Biological treatments use indigenous microorganisms for the biodegradation of hydrocarbon pollutants. 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 Sumio Iijima 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, π-π 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.

2. Materials and Methods

2.1. Materials

Carbon nanotubes are the same as those used in our previous works, where they have been extensively characterized and to which we refer for further details [74,75,76]. Briefly summarizing, carbon nanotubes (CNTs) were obtained with the CCVD (Catalytic Chemical Vapor Deposition) synthesis method. They had a specific BET surface equal to 108.78 m2/g and a purity of 95%.
The diesel used in the experimentation is of the type intended for motor vehicles and is of a commercial nature. Its density is equal to 0.835 g/mL.

2.2. Instruments

The characterization of the phases was carried out through various chemical-physical methods.
In particular, the carbon nanotubes after the adsorption tests were characterized through FTIR spectrometry and TG-DTG/DTA thermal analysis. Thermal analyses were performed with Shimadzu TG/DTG instrument in an air flow of 50 mL/min, with a heating rate of 10 °C/min. The FTIR measurements were performed with a Jasco 430 FT-IR spectrometer on pellets obtained with 2 mg of carbon nanotubes and 200 mg of KBr (spectroscopic grade), in a range of 500–4000 cm−1 with a resolution of 2 cm−1.
The filtrations obtained after the adsorption and subsequent filtration tests were analyzed by 13C high-resolution NMR analysis. NMR spectra were recorded at 25.0 ± 0.1 °C on a Bruker Avance 300 spectrometer at 75.475 MHz and processed using Bruker software XWIN-NMR, version number 3.0.

2.3. Adsorption Tests

To evaluate the adsorbent properties of the CNTs, in order to purify the water contaminated by diesel, a two-phase system was initially prepared consisting of known quantities of water and diesel.
Subsequently, the adsorption tests were carried out by introducing variable quantities of CNTs into the two-phase system.
The whole was stirred at a constant speed, for a precise time and in a well-sealed container to avoid evaporation phenomena. At the end of the programmed adsorption time, the CNTs were separated from the biphasic system under examination by means of filtration. In particular, the filtration was performed using a paper filter (Whatman) and a flask for collecting the filtrate, the latter connected to a vacuum pump.
The final filtrate obtained was collected in a graduated cylinder to measure the volume reduction in the diesel phase. The nanotubes obtained after filtration were subsequently characterized (Figure 1).
During the tests, the quantities of carbon nanotubes and adsorption times were varied, while the diesel/water ratio and stirring speed remained constant. Table 1 shows, in detail, the experimental parameters used in the experimentation.

2.4. Cyclic Adsorption/Desorption Tests

To evaluate the release and regenerative capabilities of carbon nanotubes compared to diesel, cyclic adsorption/desorption tests were performed. The desorption tests were carried out via extraction with acetone.
Each cycle was made up of four consecutive phases:
(1)
Adsorption: each adsorption test was carried out at room temperature and under stirring for 60 min.
(2)
Post-adsorption filtration: after the programmed adsorption time, the carbon nanotubes were separated from the filtration system, the liquid phases obtained (immiscible) were placed in a graduated burette and the quantities of water and diesel were measured residually.
(3)
Desorption: it was carried out by proceeding with an extraction with acetone of the gas oil adsorbed by the carbon nanotubes. In particular, the nanotubes recovered in the previous phase were inserted into 30 mL of acetone, stirred for 60 min in a well-sealed container at a temperature of about 40 °C.
(4)
Post-desorption filtration: At the end of the programmed extraction time, the CNTs were separated through filtration using a vacuum pump. The liquid phase obtained was placed in a graduated burette, and the volumes were measured.
The nanotubes recovered after the desorption phase, after having been left for 24 h at room temperature, were used for another cycle, inserting them into a system again consisting of 10 mL of gas oil and 40 mL of water.

3. Results

3.1. Adsorption Kinetics

The following Figure 2a–d show the adsorption kinetics for systems characterized by 40 mL of distilled water, 10 mL of diesel and 0.3, 0.5, 0.7 and 1.0 g of carbon nanotubes, respectively.
The % of adsorption was calculated as [(Vol.Diesel init. − Vol.Diesel final.)/Vol.Diesel init.] × 100, where the initial volume of diesel represents the amount of diesel before the adsorption process, and the final volume represents the amount of diesel still present in the system after the adsorption process.
Using 0.3 g of non-purified carbon nanotubes (Figure 2a), it can immediately be seen that the adsorption rate is very high, so much so that we can state that the phenomenon is kinetically immediate. However, a percentage of diesel adsorption equal to 100% is not observed. In fact, the maximum value is around 80%. The evaluation of the percentage of adsorption remains almost constant, even for long times. By increasing the amount of nanotubes to 0.5 g (Figure 2b), the results obtained are very similar to the previous case in the first 15 min. At longer times, the behavior is different; in fact, the percentage value of adsorption stands at about 90% after 30 min to reach about 100% of adsorbed diesel fuel after 60 min. Thus, 0.3 g of nanotubes is insufficient for almost total adsorption of the nanotubes, which, in this case, reaches saturation after about 20 min. Further, 0.5 g of nanotubes, being a greater quantity than the previous ones, does not reach saturation and is able to totally adsorb, although with longer times compared to the subsequent systems, which have higher quantities of nanotubes.
By increasing the quantities of carbon nanotubes to 0.7 and 1.0 g, respectively (Figure 2c,d), the usual immediate “triggering” of the adsorption phenomenon is highlighted in just 2.5 min and the achievement of the maximum adsorbed quantity of diesel fuel.
These data lead us to think that 0.7 g of CNTs can already be considered as a suitable quantity to obtain the full adsorption of diesel fuel in water. Using 1 g of CNTs, on the other hand, the system has an excess aliquot of carbon nanotubes not needed by the process.
Figure 3 reports the adsorption capacity of carbon nanotubes. The adsorption capacity was calculated as the ratio of the variation in diesel volumes with respect to the grams of nanotubes used (qe = Vol.Diesel init. − Vol.Diesel final.)/g CNTs).
As the system was stirred, the carbon nanotubes transferred mainly into the diesel phase, and as the amount of carbon nanotubes in the system increased, the CNT agglomeration phenomena were increasingly visible to the naked eye. This agglomeration phenomenon has already been reported in the literature [75].
All this leads to the incomplete availability of the adsorption sites and, consequently, a decrease in the adsorption capacity of the carbon nanotubes. An excess of carbon nanotubes, therefore, does not lead to an increase in adsorption capacity. The maximum adsorption capacity is reached in almost all cases within the first 15 min and then stabilizes. In particular, for the system with the lowest content of carbon nanotubes (0.3 g), the highest adsorption capacity value recorded is equal to 27 and is reached after about 15 min. The system with the highest carbon nanotube content has a maximum adsorption capacity value of 10 after 15 min.
Although carbon nanotubes, diesel and water have different densities, on average, of 1.35 g/cm3, 0.835 g/cm3 and 1 g/cm3, respectively, the dispersion of the phases mainly occurs through the hydrophobic nature of the nanotubes. In fact, carbon nanotubes in the absence of functional groups, as carbon nanotubes used in this experimental work, show a predominantly hydrophobic nature. In this case, the interaction with extremely polar molecules, such as water, is very weak, while the interaction with low-polarity organic molecules, such as those present in diesel fuel, is favored. This explains the preferential adsorption of carbon nanotubes towards diesel organic molecules.

3.2. Thermal Characterization of Post-Adsorption Carbon Nanotubes

Figure 4a shows a typical trend of the TG and DTG thermal curves of a sample of nanotubes used in the diesel adsorption process. Regardless of the quantities of nanotubes used during the test, the TG and DTG curves always presented the same profile. In particular, an initial weight loss at about 200 °C, not present in the original CNTs, i.e., before being used in the adsorption process, can be seen, referable to the loss of the adsorbed gas oil. The thermal analyses of the original nanotubes before the adsorption tests are reported in our previous articles [61,68]. A second weight loss is visible at about 600 °C, a typical behavior of carbon nanotubes attributable to their combustion. The DTG curve has two minima at these two temperatures.
Figure 4b shows the DTA thermal curve of the same sample. At about 220 °C, there is an endothermic peak due to the loss through evaporation of the adsorbed gas oil. An exothermic peak at 600 °C confirms that the nanotubes used in the experimental process are in no way chemically “attacked” by the gas oil itself, given that they maintain the same combustion temperature as the pre-adsorption samples and, therefore, the same degree of graphitization.

3.3. NMR Characterization

Figure 5a–c report the 13C-NMR spectra carried out on the filtrate of the systems containing different quantities of carbon nanotubes. The samples obtained after a treatment time of 5 min were taken into consideration, since the previously reported data show that these times represent a fair compromise between short times and high diesel abatement percentages.
The analyses were carried out on the samples containing the quantities of nanotubes of 0.3, 0.5 and 1.0 g, respectively, because these are representative of the entire range of the quantities of nanotubes used, these being the lowest, medium and highest values, respectively.
After the established treatment period, the nanotubes were removed from the vacuum filtration system, and the resulting filtrate was characterized. The filtrate appeared as a single phase, with all visible diesel adsorbed.
The reported spectra show weak signals in a range of 10–50 ppm, referable to the presence of hydrocarbons [68], which denote only traces of diesel, thus confirming the high efficiency of carbon nanotubes in diesel adsorption.
Furthermore, the 13C-NMR spectra show that by increasing the quantity of nanotubes in the adsorption treatment, the signals associated with the presence of diesel become increasingly weak, confirming a greater purification of the treated water.

3.4. FT-IR Characterization

Figure 6 shows the FT-IR spectra of carbon nanotubes before the adsorption process (Figure 6a) and post-adsorption for systems containing 0.3 and 1.0 g of carbon nanotubes (Figure 6b,c).
In particular, Figure 6a highlights the classic bands at about 1382, 1639 and 2023 cm−1, due to different C–C bonds present in the graphitic structure of carbon nanotubes. Furthermore, the band at about 3449 cm−1 should be highlighted, relating to –OH groups, which, in different quantities, are linked to the CNTs. The presence of this band can be attributed exclusively to humidity and negligible oxidative effects of the material.
From the spectra relating to the post-adsorption nanotubes, all the bands present in the nanotubes before the adsorption process are highlighted, testifying the good resistance of the carbon nanotubes in the presence of diesel. Furthermore, in addition to the previous ones, there are bands in a range of 2800–3050 cm−1, attributable to the presence of aliphatic groups, which confirm the adsorbent action of carbon nanotubes compared to diesel, the latter being rich in hydrocarbon compounds. Comparing the spectra reported in Figure 6b,c, it is evident that the lines attributable to hydrocarbon compounds are more intense as the quantity of carbon nanotubes used in the adsorption process increases.

3.5. Adsorption/Desorption Cycles

Three consecutive cycles of adsorption and desorption were performed to test the possibility of regeneration of the carbon nanotubes and to evaluate a possible recovery of the adsorbed gas oil.
The % adsorption was calculated in the same way as reported in the previous paragraph (3.1), while the percentage of desorption was calculated with the following expression (Vol.final diesel desorbed/Vol.initial diesel adsorbed) × 100, where Vol.final diesel desorbed represents the volume of diesel obtained after the desorption process while Vol.initial diesel adsorbed represents the volume of diesel initially adsorbed.
In particular, the system consisting of 10 mL of diesel, 40 mL of water and 0.5 g of carbon nanotubes was taken as a reference, as it was simpler in terms of experimental operation and equally effective for evaluating the desorption and adsorption process.
The data shown in Figure 7, first of all, show that the % of adsorption decreases as the number of cycles increases; therefore, there is a decrease in the quantities of diesel fuel adsorbed as the cycles progress. In particular, there is a decrease in the % adsorption of about 5% in the second cycle and of about 8% in the third cycle. All this can be motivated by a small quantity of diesel, which cannot desorb during the desorption phase and which is retained inside the nanotubes.
Most likely, this small amount of diesel that is retained is the one that is most inside the carbon nanotubes and that cannot be easily desorbed and would need drastic extraction methods. Furthermore, it is also possible to attribute this slight decrease in the % of adsorption to a small loss of the carbon nanotubes following the operations carried out during the cycles. However, it should be emphasized that this decrease in % adsorption remains low and is, therefore, acceptable.
The % of diesel desorbed is always lower than the quantity adsorbed, with values ranging between 9 and 15%; in this case, the previous hypothesis relating to a small quantity of diesel, which is withheld, is confirmed. The acetone extraction method probably does not allow for total desorption. It is possible and desirable that alternative methods could lead to total desorption.
As is known, the choice of solvent is mainly guided by considerations, such as high solvent power towards the components to be transferred, easy separability and availability at low costs. It is likely that other solvents may have higher solvent extraction power for diesel, but in this experimental research, we chose a solvent that would allow for an adequate compromise between solvent power and availability at low costs.
Finally, there is a decrease in the percentage of desorption as the number of cycles increases.
In general, it is difficult to identify an adsorption and desorption threshold for nanotubes as these are certainly conditioned by the nature of the species being adsorbed as well as by times and operating conditions. Compared to our case study, however, it is possible to outline the following operating capacities of the nanotubes used: with 0.7 g of CNTs, at room temperature, after only 2.5 min, all 10 mL of diesel is adsorbed. As far as desorption is concerned, the first desorption cycle has only a 5% loss of recovered diesel.

4. Conclusions

The results obtained allow the following conclusions to be drawn:
Carbon nanotubes have shown a high diesel adsorption capacity. The high molecular weights of the hydrocarbon molecules present in the diesel did not create resistance and were adsorbed by the carbon nanotubes without obvious problems.
The adsorption rates were quite high, and maximum adsorption was reached within a few minutes. In particular, in the system that used 10 mL of diesel/40 mL of water and 0.7 g of carbon nanotubes, within 2.5 min, almost 100% of diesel was adsorbed. The quantities of carbon nanotubes to be used proved to be an important parameter to consider and evaluate. Exceeding the optimal amount of carbon nanotubes to use for a system does not result in improved adsorption. This can be attributed to carbon nanotube agglomeration phenomena, which become increasingly significant as the quantities of the latter increase, making it difficult for the large molecules present in diesel to reach the carbon nanotube adsorption sites.
Both gasoline and diesel contain hundreds of different hydrocarbon molecules. As is known, however, the organic molecules constituting diesel are, on average, larger than those present in gasoline [68]. It is possible to hypothesize that adsorption mechanisms, both of diesel and gasoline, are similar, mainly due to physical adsorption, π-π and electrostatic interactions. The different dimensions of the molecules do not lead to substantial variations in the adsorption processes. However, a more evident difference is observed in the agglomeration phenomena, which are more evident in the case of diesel. Probably, this can be justified with a higher density of diesel (830–950 kg/m3) than of gasoline (700–800 kg/m3).
The adsorption and desorption cycles showed that carbon nanotubes can allow for the recovery of adsorbed diesel and their reuse with losses of low-adsorption-efficiency percentages. In particular, after the second cycle, there was a loss of 5% and 8% in the third, compared to the amount of diesel adsorbed in the first cycle.
The present research represents only a preliminary study to test the possibility of using carbon nanotubes as adsorbent materials in the purification of diesel-contaminated water. Surely, other studies and insights are needed, but the results obtained, being encouraging, will hopefully motivate other researchers.

Author Contributions

Conceptualization, P.D.L. and A.M.; methodology, P.D.L. and C.S.; validation, P.D.L., C.S. and A.M.; formal analysis, P.D.L. and C.S.; investigation, P.D.L. and C.S.; writing—review and editing, P.D.L.; supervision, P.D.L., A.M. and J.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Acknowledgments

We dedicate a particular memory to Ing. Mario Vassallo, who contributed to this research but whose life was cut short.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Phases of adsorption tests on water/diesel systems with different amounts of carbon nanotubes.
Figure 1. Phases of adsorption tests on water/diesel systems with different amounts of carbon nanotubes.
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Figure 2. Percentage of diesel adsorbed as a function of time and of different quantities of carbon nanotubes (a) 0.3; (b) 0.5; (c) 0.7; (d) 1.0 (g).
Figure 2. Percentage of diesel adsorbed as a function of time and of different quantities of carbon nanotubes (a) 0.3; (b) 0.5; (c) 0.7; (d) 1.0 (g).
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Figure 3. Adsorption capacity (qe = mL Dieselads/gCNTs) in the different systems consisting of 40 mL water + 10 mL diesel and different quantities of carbon nanotubes: 0.3; 0.5; 0.7; 1.0 g. The results obtained show that the qe values decrease as the amount of carbon nanotubes used in the adsorption systems increases. This is probably due to the agglomeration phenomenon of carbon nanotubes, which becomes increasingly significant as their quantities increase.
Figure 3. Adsorption capacity (qe = mL Dieselads/gCNTs) in the different systems consisting of 40 mL water + 10 mL diesel and different quantities of carbon nanotubes: 0.3; 0.5; 0.7; 1.0 g. The results obtained show that the qe values decrease as the amount of carbon nanotubes used in the adsorption systems increases. This is probably due to the agglomeration phenomenon of carbon nanotubes, which becomes increasingly significant as their quantities increase.
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Figure 4. TG, DTG (a) and DTA (b) curves of a sample of CNTs after the diesel adsorption process.
Figure 4. TG, DTG (a) and DTA (b) curves of a sample of CNTs after the diesel adsorption process.
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Figure 5. 13C-NMR spectra of the liquid phase for systems containing 0.3 g (a), 0.5 g (b) and 1 g (c) of CNTs after 5 min of treatment.
Figure 5. 13C-NMR spectra of the liquid phase for systems containing 0.3 g (a), 0.5 g (b) and 1 g (c) of CNTs after 5 min of treatment.
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Figure 6. FT-IR spectra of pre-adsorption (a) and post-adsorption carbon nanotubes for systems with 0.3 g (b) and 1.0 g (c) carbon nanotubes.
Figure 6. FT-IR spectra of pre-adsorption (a) and post-adsorption carbon nanotubes for systems with 0.3 g (b) and 1.0 g (c) carbon nanotubes.
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Figure 7. Percentage of adsorbent and desorbed diesel as a function of the number of cycles in adsorbance/desorbance.
Figure 7. Percentage of adsorbent and desorbed diesel as a function of the number of cycles in adsorbance/desorbance.
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Table 1. Composition and experimental variables used in adsorption tests.
Table 1. Composition and experimental variables used in adsorption tests.
Experimental Parameters
Water [mL]40
Diesel [mL]10
Rotation speed [rpm]350
Carbon Nanotubes [g]0.3; 0.5; 0.7; 1
Adsorption time [min]2.5; 5; 15; 30; 45; 60; 120
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De Luca, P.; Siciliano, C.; B.Nagy, J.; Macario, A. Treatment of Water Contaminated with Diesel Using Carbon Nanotubes. Appl. Sci. 2023, 13, 6226. https://doi.org/10.3390/app13106226

AMA Style

De Luca P, Siciliano C, B.Nagy J, Macario A. Treatment of Water Contaminated with Diesel Using Carbon Nanotubes. Applied Sciences. 2023; 13(10):6226. https://doi.org/10.3390/app13106226

Chicago/Turabian Style

De Luca, Pierantonio, Carlo Siciliano, Janos B.Nagy, and Anastasia Macario. 2023. "Treatment of Water Contaminated with Diesel Using Carbon Nanotubes" Applied Sciences 13, no. 10: 6226. https://doi.org/10.3390/app13106226

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