Carbon Nanotube Sponges

Carbon nanotubes are nanoscale structures having remarkable properties in both mechanical and electronic areas.

Carbon nanotubes are highly conductive, and they are very elongated nanostructures excellently interacting with electromagnetic radiations. They have the finest electronic and mechanical properties.

Introduction

Until now, CNT-based macrostructures are in various forms, such as sheets or long fibers yarned from CNT forests and thin films or bucky-papers in which density, alignment, and permeability of the Carbon nanotubes can be personalized. Most significantly, high porosity, huge surface area, and lightweight of materials based on CNT make it a capable applicant for applications in the environmental field such as filtration, separation, and absorption. Carbon nanotubes have many benefits, including stronger interactions of chemical-nanotube, high absorption capacity, fast equilibrium rates, and tailored surface chemistry. CNT's are limited to the absorption or separation of diluted, despite their remarkable properties.

A sponge bulk-like material comprising of interconnected CNT skeletons that are self-assembled. In a densified state, sponges swell rapidly when organic solvents come in contact with them. CNTs sponges absorb a wide variety of oils and solutions with good recyclability, excellent specificity, and capacity to absorb up to 180 times its personal weight, the magnitude of 2 orders higher than activated carbon. The Carbon nanotube sponges contain both nano- and micro-sized pores and can absorb sticky, heavy oils and fluids without any difficulty. CNT Sponges are oil-loving and water-hating. That's why a sponge ball floats on a water pool in an exclusive 'floating-and-cleaning' manner. Also, these sponges can be compressed because of pressure into handy portable balls that swells immediately on the addition of oil or ethanol.

An Overview of Carbon Nanotube 

Regardless of the striking physical characteristics of Carbon nanotubes and thorough hard-work in this field, the progress in environmental applications is restricted to the absorption or separation of the molecules and diluted ions. In this article, we inform you about the production of a sponge bulk-like material comprising of skeletons of CNT that are self-assembled and interconnected with a density of the lightest aerogels, having porosity >99%, high flexibility in structure and robustness, pristine form, and wettability to organics. CNT's absorb a wide variety of oils and solvents with outstanding recyclability, selectivity, and capable of absorbing up to 180 times its weight, two orders of magnitude higher than activated carbon. The sponge can be used for potential environmental applications such as cleanup of the spill in large-area and water remediation. This article focuses on explaining the excellent characteristics and properties of carbon nanotubes sponges.

Carbon Nanotube Sponges

Carbon nanotube sponges are extremely lightweight nanomaterials created by random and self-supporting 3-dimensional networks. Carbon Nanotube sponges can be distorted into any shape elastically and compressed recurrently in liquid or air without collapsing. CNT sponges are way lighter than water because of such density, and because the sponges naturally repel water, saturated sponges can be collected for recycling. Carbon nanotube sponges can be used multiple times by either being compressed, or the solvent can be burned off to remove the solvent from its structure. The density of sponge can be amplified by 20 times.

CNT sponges, a 3D sponge-like solid is produced by a method of CVD, using ferrocene and 1,2-dichlorobenzene (as a catalyst precursor) and source of carbon, respectively. CNT's don't only have tremendous mechanical properties but also has a high electrical conductivity that has been informed in the latest publications and has shown promise in environmental applications like flexible and compressible conductors, smart materials, sensors, and nanocomposites. Through our latest outcomes, we have observed that the best suitable usages are in the large-area oil spill cleanup, purification of water, and treatment of waste oil.

Properties of Carbon Nanotube Sponges

In comparison to other conventional cellular materials, Carbon nanotube sponges openly display excellent mechanical properties and great stability: high strength to weight ratio, super-elasticity, thermo-mechanical durability in a broad range of temperature, negligible stress relaxation under high pressure, excellent resistance against fatigue, after more than 3.5 × 106 cycles and frequency-invariant electro-mechanical stability under mechanical compression. The structure of the sponge is uniform with superior mechanical strength, excellent flexibility, high porosity, and low density. The CNT sponge comprises of Carbon nanotubes that are self-assembled into an interconnected, porous 3D framework, according to Scanning electron microscopy characterization. These are nanotubes of multi-walled with a diameter of 30 to 50 nm and length of 10-100s of micrometers, representing that CNT has multiple layers in the sponge, which is cm thick. The production of the sponge is scalable as the growth rate didn't slow down during the process. CNT sponge is also springy and compliant. It can be twisted or bent to a large amount without breaking, and then recover to its almost original shape. Another thing that guarantees that there is going to be no structural collapse under compressive loading is the strong force of binding between neighboring nanotubes. The sponges can sustain complete volume recovery without plastic deformations. The absorption and filling of the pores by solvents are advantageous for them to regain their old original shape and size. Reversible absorption and solvent removal provide an easy way for recycled use. Carbon nanotube sponges determine its capacities to absorb highly up-to eight to one hundred eighty times its weight for a wide variety of oils and solvents, for liquids with higher density, like chloroform.

A carbon nanotube sponge is also an excellent thermal insulator with low density. The thermal conductivity of CNT sponge is less than other insulating materials like polymeric foams, and woods. Although CNT as individuals are great thermal conductors, the ultrahigh sponge's porosity makes it an excellent thermal insulator. In comparison with other conventional porous materials, Carbon nanotube sponges provide benefits like thermal stability, electrical conductivity, robustness, resistance against harsh environment, and it can influence a variety of usages, for instance, high strength-to-weight ratio composites, multifunctional structural media, sensors, electrodes, or membranes.

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Applications of Carbon Nanotube Sponges

Membranes with the tunable size of pores and density have high flux for water and gas, and selective molecular transport through pore functionalization. CNT sponges can be used as smart materials, nanocomposites, flexible and compressible conductors and sensors. Some of their application fields are explained below

Environmental Applications

CNT sponge has a high capacity to absorb liquid. The commercial fuel absorption test indicated that the sponge could absorb almost 1603% of its weight in fuel in less than 1 min, and the range increases to 1675% after 10 minutes. After every trial, burn the sponge at 300 °C temperature to eliminate fuel from the structure of the sponge. Both fuels are absorbed by the sponge, but the preference and the velocity for absorption are incredibly interrelated to the fluid's polarity. The 3D Carbon Nanotube sponge has a compelling a-polar character having a 146-degree contact angle, which is related to the defects in CNTs structure and the functional group's presence on the surface like COOH, OH, and CHO. The final result confirms that the CNT sponges that are made with magnesium ferrite have hopeful characteristics for environmental applications in the future, for instance, in marine disasters. They have a high capacity of absorbing non-organic compounds, a high non-polar character, a senior mechanical resistance to tensile and compression tests, and high permeability. They also displayed a high hydrophobic character and rapid absorption of a-polar fuels. These materials are very useful in preventing and controlling industrial chemical leaks, recovering the fluid resources that are polluted by oils, fluids, and many other applications.

For Oil Absorption

CNT sponges can be used in terms of oil absorption. These sponges have absorption capacity higher than 100 g g–1 for various oils and organics with viscosities of 3–200 cP, and they maintain absorption capacities of 20–40 g g–1 after ten absorption cycles. We can recover 98% of the absorbed oil if we squeeze the sponge or use the heat to burn the fat absorbed by the sponge. This process of absorption has been explained by a second-order kinetic model. This outcome explains that Carbon nanotube sponges are capable of oil absorbents with high recyclability. In densified or pristine form, CNT sponges can absorb kinds of oils thrown on the surface and then eliminate them. Sponge kept on growing more substantial due to the oil that's being consumed, and after up-taking all of it, the sponge which is floating on water has recovered its original size and shape. Wherever the sponge arrives, it immediately sucks the portion of oil that comes in contact, leading to a local white region around and behind exposed to freshwater. The sponge drifts to the area of rest oil film because of its oil-wetting and water-repelling properties, following to this distinctive capability of ''floating-and-cleaning'' which is mainly beneficial for oil spill cleanup. The sponge stretched, marking a clear area around it. The area of oil which has been cleaned is of about 800 times larger than the size of the initial densified sponge.

Improved Water Cleanup

A CNT sponge can soak up water contaminants. The CNT sulfur-doped sponges, also showed a high absorption capacity for oils, opening up the probability of utilizing it in cleanups of spilled oil and industrial accidents. Carbon nanotube sponges are hollow cylindrical structures comprised of a carbon sheet with excellent chemical, mechanical and thermal characteristics that have led to a display of applications from body armor to solar panels. CNT Sponges have been tested as perfect applicants for cleanup of wastewater. CNTs of mm or cm-scale, are easier to handle. CNTs sponge floats on water due to its porous structure and, once they are saturated with oil, oil can be eliminated by quickly squeezing the sponge and releasing the oil, the sponges can then be used again. The addition of sulfur in the sponge caused defects on the sponges surface that later enables ferrocene that was added in between the synthesis process. It was done to fill iron into the small capsules within a single carbon shell. Iron's presence means that the sponges can now be magnetically controlled with no need for any direct contact, solving the current problem of how to manage the CNT sponges when they are added onto the water's surface. These Carbon nanotube sponges can successfully remove a toxic organic solvent―dichlorobenzene―from water. CNT sponges can also absorb vegetable oil up to 150 times of its weight and can absorb engine oil to a slightly higher capacity.

Also, they can be used for human-motion detection in real-time. The sample of Carbon nanotube sponges was attached around a glove of rubber to spot fingers bending movements, allowing the discovery of the folded amplitude of fingers. Also, it traces the amplitude of fingers' motion. The use of such spongy sensors has benefits in both engineering and daily activities, for instance, remote controlling and health monitoring.

Conclusion

Carbon Nanotube Sponges are well known for their high porosity rate, low density, its ability to not break apart even at high compressions and load, its ability to absorb way more oil and fluid than its weight, and then getting re-used by removing the oil and fluids from the sponge. It is used in the environment to remove oil from the water surface, to clean up wastewater. They can also be used as sensors, electrodes, and compressible and flexible conductors.

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References

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