Application of Graphene-Carbon Nanotube

Aerogels in OilSpill Clean-up

Vedant Makwana1 , Anish Singh2

Applied Petroleum Engineering - Upstream

Petroleum and Earth Sciences Department

University of Petroleum and Energy Studies

Dehradun, India

vedant.makwana@stu.upes.ac.in1

singh.anish2010@gmail.com2

Simran K Singh3

Geo-Informatics Engineering

Petroleum and Earth Sciences Department

University of Petroleum and Energy Studies

Dehradun, India

simranksingh208@gmail.com3

Abstract— To address oil spillage and chemical leakage

accidents, the development of efficient sorbent materials is of

global importance. Spilled oil characterizes a menace to the

aquatic ecosystem and the whole environment in broad-

spectrum and requires timely cleanup. Among all the

obtainable technologies, oil sorption has attracted the most

attention because of its simplicity and high level of

effectiveness. The key for the development of this technology is

convenient fabrication of high-performance oil sorbents that

can be used repeatedly. In this work, a fast microwave

irradiation-mediated approach has been proposed for

manufacturing multiwall carbon nanotube (MWCNTs)–

graphene hybrid aerogels, in which MWCNTs are vertically

anchored on the surface of cell walls of graphene aerogels. The

hybrid monoliths show super hydrophobicity and

superoleophilicity, a large pore volume, a large pore size, and

excellent compressibility, demonstrating outstanding

performance for recyclable oil sorption.

Lightweight materials that are both highly compressible

and resilient under large cyclic strains can be used in cleaning

oil spills. Graphene coated Carbon nanotubes offer a

combination of elasticity, mechanical resilience and low

density, and these properties have been exploited in nanotube-

based aerogels.

This paper proposes the use of Graphene Coated Carbon

Nanotubes Aerogels in Oil Spill Clean-up as a replacement for

of the current bungling technology.

Keywords—Oil Spillage ; Graphene ; Nano-Tubes

I. INTRODUCTION

To address oil spillage and chemical leakage accidents, the development of efficient sorbent materials is of global importance. Spilled oil characterizes a menace to the aquatic ecosystem and the whole environment in broad-spectrum and requires timely cleanup. Among all the obtainable technologies, oil sorption has attracted the most attention because of its simplicity and high level of effectiveness. The key for the development of this technology is convenient fabrication of high-performance oil sorbents that can be used repeatedly. In this work, a fast microwave irradiation-

mediated approach has been proposed for manufacturing multiwall carbon nanotube (MWCNTs)–graphene hybrid aerogels, in which MWCNTs are vertically anchored on the surface of cell walls of graphene aerogels. The hybrid monoliths show super hydrophobicity and superoleophilicity, a large pore volume, a large pore size, and excellent compressibility, demonstrating outstanding performance for recyclable oil sorption.

Lightweight materials that are both highly compressible and resilient under large cyclic strains can be used in cleaning oil spills. Graphene coated Carbon nanotubes offer a combination of elasticity, mechanical resilience and low density, and these properties have been exploited in nanotube-based aerogels.

This paper proposes the use of Graphene Coated Carbon Nanotubes Aerogels in Oil Spill Clean-up as a replacement for of the current bungling technology.

II. BYGONE DAYS OF THE CONVENTIONAL TECHNOLOGY

Over the past years numerous solutions have been

proposed for dealing with the problem of oil spills. These

include:

A. Mechanical Containment or Recovery

Mechanical containment or recovery is the primary line of defense against oil spills. Containment and recovery equipment includes a variety of booms, barriers, and skimmers, as well as natural and synthetic sorbent materials. Booms are floating, physical barriers to oil, made of plastic, metal, or other materials, which slow the spread of oil and keep it contained. Skilled teams deploy booms using mooring systems, such as anchors and land lines. Skimmers are boats and other devices that can remove oil from the sea surface before it reaches sensitive areas along a coastline. Sometimes, two boats will tow a collection boom, allowing oil to concentrate within the boom, where it is then picked up by a skimmer. Mechanical containment is used to capture and store the spilled oil until it can be disposed of properly.

However this method has its own drawbacks. These include:

It is an expensive and complex method of oil recovery.

It is a labour intensive method.

The recovered oil needs further treatment.

This method is efficient in selected weather conditions.

It requires perennial maintenance.

This method is incompetent.

B. Chemical Agents Recovery

Chemical and biological methods can be used in conjunction with mechanical means for containing and cleaning up oil spills. Dispersing agents and gelling agents are most useful in helping to keep oil from reaching shorelines and other sensitive habitats. However, the use of chemical dispersants for response to oil spills has remained a controversial subject in many countries, despite the fact that it is one of the more efficient/proven methods. This is because:

Dispersion process moves oil from surface to water column. This exposes water column & near shore shallow bottom-dwelling organisms to oil.

Both dispersants and dispersed oil particles are toxic to some marine organisms

Effectiveness of dispersant is dependent on type of oil spilled, weather conditions & how quickly the dispersant is applied onto oil slick.

Heavier oils or highly emulsified oils are less amenable to successful dispersion.

C. Insitu Burning

In situ burning, or ISB, is a technique sometimes used by

people responding to an oil spill. In situ burning involves the

controlled burning of oil that has spilled from a vessel or a

facility, at the location of the spill.

However, use of this technique leads to the loss of valuable

oil resources.

III. NEED FOR INNOVATIVE TECHNOLOGY

Conventional techniques are not adequate to solve the problem of massive oil spills. In recent years, nanotechnology has emerged as a potential source of novel solutions to many of the world's outstanding problems. Although the application of nanotechnology for oil spill cleanup is still in its nascent stage, it offers great promise for the future. In the last couple of years, there has been particularly growing interest worldwide in exploring ways of finding suitable solutions to clean up oil spills through use of nanomaterials. Graphene coated Carbon-based aerogels have attracted interest in various fields due to their unique physical properties, such as low apparent density, porosity, and specific surface area.

As sorbent materials, graphene/CNT hybrid foam, and exhibit very high sorption capacities, good recyclability and environmental friendliness.

IV. BENEFITS OF GRAPHENE CNT TREATMENT

A. Ultralow Density and High Porosity: Because of the

ultralow density, the hybrid structures still exhibit a

high porosity of up to 99%.This increases its oil

absorbing power.

B. Excellent mechanical stability: Graphene, a material

that is very strong and extremely elastic, bouncing back

after being compressed. It can also absorb up to 900

times its own weight in oil and do so quickly.

C. Can work in varied Temperatures: CNT/GA can work

in both high as well as low temperatures, making them

effective in working in different environment, like the

arid and the Polar Regions.

D. High hydrophobicity and Superoleophilicity: Due to its

high affinity towards Oil and Low affinity towards

water, it serves as an effective Oil/Chemical absorbing

agent.(Figure 7)

E. Environment Friendly: As this sponge does not react

with the chemicals and oil, it can simply absorb the oil

and be taken out without harming the marine

environment.

F. Recyclable: The graphene-coated aerogel exhibits no

change in mechanical properties after more than 1X106

compressive cycles, and its original shape can be

recovered quickly after compression release.

V. COMPARATIVE ANALYSIS : GRAPHENE CARBON NANO-

TUBE AEROGELS OVER CNT’S

All nanotube-based foams and aerogels developed so far

undergo structural collapse or significant plastic deformation with a reduction in compressive strength, when they are subjected to cyclic strain. Hence, an inelastic aerogel made of single-walled carbon nanotubes can be transformed into a super elastic material by coating it with between one and five layers of graphene nanoplates. The graphene-coated aerogel exhibits no change in mechanical properties after more than 1 × 106 compressive cycles, and its original shape can be recovered quickly after compression release.

Moreover, the coating does not affect the structural integrity of the nanotubes or the compressibility and porosity of the nanotube network. The coating also increases Young's modulus and energy storage modulus by a factor of ~6, and the loss modulus by a factor of ~3. The super elasticity and complete fatigue resistance of Graphene coated CNTs can be attributed to the graphene coating strengthening the existing crosslinking points or ‘nodes’ in the aerogel. (Figure 4)

VI. SYNTHESIS OF GRAPHENE CARBON NANO-TUBE

AEROGELS

First, a functionalized graphene aerogel (FGA) via an ethylene-diamine-functionalized approach with a high porosity and large pore sizes was exposed under MWI (Microwave Irradiation) to give rise to ULGA (Ultralight Graphene Aerogel).Afterward, ULGA was coated with ferrocene by impregnating it in an acetone solution of ferrocene and drying naturally, where π−π interactions between them can drive the uniform distribution of ferrocene on ULGA. Lastly, additional MWI was involved to produce rapid in situ superheating of ULGA, resulting in the decomposition of ferrocene into iron particles and cyclopentadienyl, which serve as the catalyst and carbon source, respectively, for the growth of CNTs, leading to the

formation of CNT/GA hybrid structure. A freeze-drying method that involved freeze-drying solutions of carbon nanotubes and graphene to create a carbon sponge that can be adjusted to any shape. (Figure 1)

The other process can be describes, as mechanically enhanced aerogels of graphene sheets and carbon nanotubes (CNTs) were prepared via hydrothermal reduction of graphene oxide and CNTs in the presence of ferrous ions (FeSO4 solution). The resultant graphene–CNT aerogels possess a 3-D network of carbon structures containing micro-sized pores and α-FeOOH nanorods within the matrix.

The synthesis of an ultracompressible, superelastic aerogel by coating the struts and nodes of a single-walled carbon nanotube network with one- to few-layer graphene had been demonstrated. These aerogels are capable of withstanding significant (>90%) compressive strain without plastic deformation over many cycles. In addition, they have a highly porous and conductive structure with very large specific surface area, properties which are ideal for supercapacitor applications.

VII. PHYSICAL PROPERTIES OF CNT/GA

The as-prepared CNT/GA aerogel has a very low

apparent density of ca. 0.18 mg/ cm3, which is much less than those of the traditional carbon aerogels (100–800 mg/cubic cm) and hydrophobic nano-cellulose aerogels (20–30 mg /cubic cm).

Because it is porous and highly hydrophobic, it can adsorb organic solvents and oils—up to 900 times its own weight. It draws oil out of an oil/water mixture with high efficiency and selectivity, leaving behind pure water (Figure 2)

A piece of CNT/GA aerogel with a volume of 5.3 cm can stand stably on top of a dandelion without deforming it (Figure 3). The CNT/GA aerogel porosity is estimated to be 99%. A single gram of aerogel able to absorb up to 68.8 grams of organic material (such as oil) per second. The extraordinary heat- and fire-resistance of this material are particularly noteworthy: repeated treatment with the flame of a torch caused no changes in its form or inner three-dimensional pore structure.

VIII. PRACTICALITY IN OIL SPILL CLEAN-UP

The prepared aerogels exhibit outstanding adsorption

performance for the removal of petroleum products, fats and

organic solvents especially under continuous vacuum

regime showing adsorption capacity of 28L of oil per gram

of aerogel.

Graphene, a material that is very strong and extremely

elastic, bouncing back after being compressed. It can also

absorb up to 900 times its own weight in oil and do so

quickly. A very interesting application of this aerogel is in

oil spills – a single gram of aerogel able to absorb up to 68.8

grams of organic material (such as oil) per second. Thus,

pieces of CNT/GA can be used to clean oil spill.

IX. TEST AND DEMONSTRATIONS OF GRAPHENE COATED

CNTS

Due to its low apparent density, excellent mechanical

stability, high porosity, and hydrophobicity /superoleophilicity, the CNT/GA aerogel is an ideal candidate for the sorption of oils and other organic pollutants.

When a small piece of the CNT/GA aerogel was placed on the surface of oil-water mixtures, the oil layer (dyed with Sudan III) immediately started shrinking and disappeared completely after a few minutes (Figure 2). Similarly, when the CNT/GA aerogel was held to approach phenoxin (also dyed with Sudan III) under water, the phenoxin droplets were rapidly absorbed by the aerogel upon contact.

A. Test 1 : Sorption Capacity

To further demonstrate the sorption ability of CNT/GA

aerogel, CNT/GA was tested on the basis of sorption capacities for different commercial petroleum products (e.g., gasoline, diesel oil, pump oil, etc.) and toxic organic solvents (e.g., bromobenzene, THF, n-hexane, etc.).

The sorption efficiency can be assessed by weight gain, defined as

Wt %=( Weight after saturated sorption – initial weight)/initial weight

Study Data

The CNT/GA aerogel showed outstanding sorption ability for these liquids. In general, the sorption capacities range from 51 to 139 times the weight of the CNT/GA aerogel for a variety of oils and organic solvents). The organics were mainly stored in the macro pores of the CNT/GA aerogels, so the differences of sorption capacities were related to the densities of organic liquids.

The sorption capacities of CNT/GA are superior to those of activated carbon (< 1 times), marshmallow-like macroporous gels (6–14 times), graphene/α-FeOOH aerogel (13–27 times), micro-porous polymers (< 33 times), and our previously reported PDMS-coated carbonaceous nanofiber aerogel (40–115 times); and CNT sponge (80–180 times).

B. Test 2 : Sorption Kinetics

The sorption kinetics of CNT/GA aerogel to four organic

liquids were investigated. The sorption capacity Qt of each organic liquid was plotted as a function of the sorption time (Figure 8).

Study Data

The sorption capacities increase with sorption time until saturation. The saturation sorption time of low-viscosity organic solvents (ethanol and phenoxin) is much shorter than that of high-viscosity oils (soybean oil and diesel oil); the saturation sorption time of the two organic solvents is less than 30 s, while it takes more than 900 s to reach saturation for the two oils.

The kinetics can be described by a second-order model

1/Qm-Qt=1/Qm +Kt

Where Q indicates the saturated sorption capacity, Qt is the amount of sorption at time t, t represents the sorption time, and K is the sorption constant that is viscosity-dependent.

The fitting values of Qm are nearly equal to the weight gains further indicating an excellent agreement between the sorption kinetics model and experimental data.

C. Test 3 : Sorption of Oil Under Harsh Conditions

In addition to sorbents suitable to face oil leakage

accidents under ambient conditions, there is a need for materials working effectively.

Under harsh conditions, such as high or low temperatures, traditional sorbents (such as polyurethane-based and polyethylene-based materials) cannot be used at temperatures above 200 degree C, and others will become very brittle at low temperatures. In this regard, our CNT/GA aerogel exhibits exceptional features.

To test sorption capacity of Graphene coated Carbon Nanotube Aerogels under Extreme Temperatures. After continuous 30 s of such extreme heating, it was immediately immersed into liquid nitrogen (Liq. N2).

Study Data

When exposed to an ethanol flame, the CNT/GA aerogel did not support any burning and remained inert (After ca. 30 s of such extreme heating, it was immediately immersed into liquid nitrogen. No decomposition or material change occurred; even upon repetition of this treatment for several times, the shape, volume, and inherent 3D porous structure of CNT/GA aerogel remained unchanged, demonstrating that the CNT/GA aerogel can withstand extreme temperatures and rapid temperature change.

Further, thermogravimetric analysis (TGA) shows that the CNT/GA aerogel has a weight loss of less than 8% at a temperature of up to 850 degree C in N2 and can tolerate a high temperature of approximately 400 o C in air.

After the CNT/GA aerogel was heated in an ethanol flame or frozen in N2 for five minutes, it still exhibited a good mechanical property and supported at least 500 times its own weight. There was only a slight difference among the original, burned, and freezed samples in the compressive strain– stress test .(Meanwhile, the high and low temperature treatments had no obvious influence on the hydrophobic and oleophilic properties of the CNT/GA aerogel. As the sorption properties are insensitive to temperatures, the CNT/GA aerogel is considered to be an ideal oil sorbent for dealing with accidents.

Hot soybean oil (164.7 o C) and cold ethanol (2103.2 o C) are absorbed by the CNT/GA aerogel equally completely as room temperature. Limited only by the measuring range of our thermometer, even hotter (e.g., 400 0 C) and colder (e.g., 2196 o C) organic liquids were also absorbed by our CNT/GA aerogel, demonstrating overall excellent performance over a wide temperature range. These results indicate that the CNT/GA aerogel can be used in some special situations, such as oil spillage in the polar zone and high or low temperature organic solvents leakage accidents, for which conventional sorbent materials.

X. OIL-UPTAKE AND RECYCLABILITY STUDIES OF THE

CNT/GA AEROGELS

The recyclability of CNT/GA, is in high demand in oil cleanup applications. The sorbed oils can be easily harvested by compressing the carbon mat and mechanically extruding the sorbed oil (Figure 5).

The oil gradually squeezes out from the monolith under compression. The sorption and desorption processes of different oils are different, and the recovery percentage by compression is also viscosity-dependent; ethyl acetate with the lowest viscosity shows 90% recovery, while the most viscous pump oil exhibits a recovery of 72% for the first cycle.

Considering multiple sorption−desorption cycles for diesel fuel, where 70% of the saturated sorption capacity can be maintained over many cycles. Surprisingly, the recovery ratio increases to almost 100% after the second cycle. Because of the interaction between oils and the monolith, part of the volume has been occupied by oil, which cannot be regenerated by mechanical extrusion, but the remaining pores can be fully utilized in cyclic applications. Thus, the full reclaim of sorbed oils is shown after the first cycle.

XI. CONCLUSION

In summary, we have developed a novel and simple method to fabricate macroscopic CNT/GA aerogels composed of interconnected 3D networks of nanofibers on a large scale. The CNT/GA aerogel possesses unique physical features, such as low apparent density, high porosity, excellent mechanical stability, high hydrophobicity and superoleophilicity.

As an oil sorbent, the CNT/GA aerogel exhibits high sorption capacity, excellent recyclability and high selectivity.

Importantly, the sorption performance of the CNT/GA aerogel can be maintained over a wide temperature range, from liquid nitrogen temperature up to ca. 400oC, which extends its potential applications.

XII. TABLES AND FIGURES

Figure 1: Synthesis of Graphene coated Carbon Nanotube Aerogels

Figure 2:( a) the sequential photographs of the CNT/GA Aerogel absorbing diesel oil on water surface. (b) Sorption capacities of CNT/GA

aerogels for various organic liquids in terms of weight gain. (c) Schematic diagram of the CNT/GA aerogel recycling process by heat treatment

method. (d) The sorption recyclability of CNT/GA aerogel over ten cycles.

Figure 3: A graphene carbon nanotube aerogels placed on a flower

Figure 4: Graphene coated nanotube aerogel Vs Nanotube Aerogel

Figure 5: Recyclability of Graphene Carbon Nanotube Aerogels

Figure 6: High-magnification images for Graphene Carbon Nanotube Aerogels

Figure 7: Water droplets as quasi-sphere and soybean on the surface of

CNT/GA

Figure 8: Sorption kinetics of four organic liquids: (a) ethanol, (b) phenoxin, (c) soybean oil, and (d) diesel oil.

Figure 9: Microstructure of graphene-coated single-walled carbon nanotube aerogels.

Table 1: Pore volumes of CNT/GA aerogels calculated from the uptake of various organic liquids.

Weight gain (g g-1) Density (g cm-3) Pore volume (cm3 g-1)

Gasoline 61.14 0.73 84.33

Diesel oil 74.82 0.83 89.87

Pump oil 86.34 0.87 99.24

Sesame oil 92.92 0.92 89.84

Soybean oil 90.19 0.93 97.37

Ethanol 71.47 0.79 90.47

Bromobenzene 124.55 1.5 83.03

Chloroform 120.17 1.5 80.11

Phenoxin 139.08 1.6 86.93

THF 78.94 0.89 88.70

n-hexane 51.55 0.66 78.18

Acetone 71.24 0.8 89.05

Table 2: Fitting parameters of sorption kinetics of four organic liquids. Table 3: Fitting parameters of sorption kinetics of four organic liquids.

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Organic liquids K (s-1) Qm (%)

Ethanol 1.1063×10-2 7285.5

Phenoxin 1.7648×10-2 13827

Diesel oil 2.0669×10-4 7712.0

Soybean oil 5.3708×10-4 8893.2