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Carbon nano tube is a very strong material, but there are some drawbacks. The material is expensive to produce and it is difficult to assemble because of its extremely small size. The material is also not very good at heat conduction, so it is not suitable for many applications.

Carbon nano tubes are also vulnerable to oxidation, which can limit their durability and usefulness. The material also can not easily be recycled, so if used in applications it may be difficult to dispose of properly. Finally, although carbon nano tubes are incredibly strong and lightweight, the material is difficult to treat for impurities and other defects.

The most problems of carbon nano tube are toxicity exposure and the cost specially single wall carbon nano tube

Carbon nanotubes (CNTs) possess remarkable electrical, mechanical, and thermal properties, making them highly promising for various applications. Nonetheless, CNTs also face several challenges and problems that hinder their widespread use. Some of the most significant issues include synthesis difficulties, purification challenges, structural defects, toxicity concerns, and scalability limitations. Overcoming these challenges will require continued research and development in the field of carbon nanotubes.

One of the most important issues is that we are not yet about its toxicity.

I recommend you read this article: https://www.sciencedaily.com/releases/2011/01/110118092134.htm#:~:text=Carbon%20nanotubes%2C%20which%20are%20extremely,cancer%2C%20according%20to%20new%20research.

Ahmed Kadhim Hussein Apart from the points mentioned above, dispersion is also a major problem.CNTs tend to aggregate and form bundles, which can limit their effectiveness in certain applications, such as in composites and coatings.

Carbon nanotubes (CNTs) are cylindrical large molecules consisting of a hexagonal arrangement of hybridized carbon atoms, which may by formed by rolling up a single sheet of graphene (single-walled carbon nanotubes, SWCNTs) or by rolling up multiple sheets of graphene (multiwalled carbon nanotubes, MWCNTs).

Carbon nanotubes are used to make bullet- proof jackets. Carbon nanotubes can be used to make aircraft and spacecraft bodies. Carbon nanotubes can be used to build high-performance nanoscaled thin-film transistors to replace silicon-based transistors because of the semiconducting properties of carbon nanotubes.Carbon nanotubes can exhibit remarkable electrical conductivity, while others are semiconductors. They also have exceptional tensile strength and thermal conductivity because of their nanostructure and strength of the bonds between carbon atoms. In addition, they can be chemically modified.

Carbon Nanotubes Properties:

• CNTs have high thermal conductivity.
• CNTs have high electrical conductivity.
• CNTs aspect ratio.
• CNTs are very elastic ~18% elongation to failure.
• CNTs have very high tensile strength.
• CNTs are highly flexible — can be bent considerably without damage.
• CNTs have a low thermal expansion coefficient.

carbon nanotubes atoms are agglomerated with each by vanderwall forces and strong pi pi interactions, so deagglomeration is main challenge faced while using CNT but to overcome this we use ultrasonication.

Next, main problem we faced is its cost; it’s is very expensive.

There are some issues which depends on there applications.

So, clarify for what purpose you want to use CNTs?

May be some issues which are main obstacles for specific application but it may have good advantages in another application

The state-of-art and key problems of carbon nanotube (CNT) based polymer composites (CNT/polymer composites) including CNT/polymer structural composites and CNT/polymer functional composites are reviewed. Based on the results reported up to now, CNTs can be an effective reinforcement for polymer matrices, and the tensile strength and elastic modulus of CNT/polymer composites can reach as high as 3600 MPa and 80 GPa, respectively. CNT/polymer composites are also promising functional composite materials with improved electrical and thermal conductivity, etc. Due to their multi-functional properties, CNT/polymer composites are expected to be used as low weight structural materials, optical devices, thermal interface materials, electric components, electromagnetic absorption materials, etc. However, the full potential of CNT/polymer composites still remains to be realized. A few key problems, such as how to prepare structurecontrollable CNTs with high purity and consistently dependable high performance, how to break up entangled or bundled CNTs and then uniformly disperse and align them within a polymer matrix, how to improve the load transfer from matrix to CNT reinforcement, etc, still exist and need to be solved in order to realize the wide applications of these advanced composites.

1. Its high cost.

2. A high entanglement of CNT–CNT due to a strong π–π stacking interaction has resulted in poor interfacial interactions between CNT and a polymer.

3. Deagglomeration of CNT atoms is the main challenge.

It's solubility issue in polar solvents.

Not sure what the question is really about, "What are the most problems..." is very vague.

One issue is that the well reputed material properties are only valid for very high quality (high crystallinity) nanotubes. The manufacturing processes of such high quality materials are not easy to upscale, and only small volumes at a high cost can be made with the sought material properties.

Instead the readily available, mass produced, materials have properties that are very far from the ideal material, thus hampering large use of carbon nanotubes in applications that require the ideal, intrinsic, properties. This issue is similar to what has happened to graphene, the ideal material has many promising properties, but the commercially available material is far from the ideal, free of defects and single-sheet, graphene.

Hence there cannot be any large commercial use for any of these materials until there are well defined material standards and material characterisation methods.

Consistency on the Quality from batch to bacth, has been a chanllenges for sacling up production.

The high purity necessary to have the required properties is difficult to obtain on an industrial scale

Expensive , Consistency in quality and prone to induce cancerous cells

Concerning single-walled carbon nanotubes (SWCNTs), one of the main problem is the separation of chiralities of individual tubes after growth by chemical vapor deposition (CVD). The CVD of SWCNTs is the best method to obtain clean tubes with few defects and high quality (which is verified by Raman spectroscopy), but a lot of different kinds of tubes (chiralities of (n,m)-SWCNTs) are usually obtained. Some of the tubes can be metallic and other semiconducting depending on the (n,m) chirality (ex: (6,5)-SWCNT is chiral and semiconducting). Depending on the application, specific type is required: for example, only semiconducting SWCNTs are desired if used as field electric transistors (to replace Si-based transistor technologies), or more metallic tubes if used as conductive electrode.

In this regard, a lot of effort are being made to separate the tubes with various methods: CVD with specific nanoparticles used as catalyst with precise size or geometry (by great control of pressure, temperature and gases such as reducing H2 or carbon source, thus chemical, cinematic and thermodynamic aspects play interconnected and complex roles during CVD), the other approach is to separate the SWNTs with polymers or by centrifugation or similar mechanical approaches. But while in the first case reproducible and reliable CVD process leading to 100% of single chirality of tube was never achieved yet, in the other case the separation (chemical or mechanical) often leads to problem such as difficulty to purify or to keep the tubes without damages (broken C-C bonds, etc.).

If you're interested in mechanically strong nanotubes, multi-walled nanotubes have better properties than single-walled carbon nanotubes (which has better opto-electronic properties).

Hope this helps.

Carbon nanotubes (CNTs) are cylindrical large molecules consisting of a hexagonal arrangement of hybridized carbon atoms, which may by formed by rolling up a single sheet of graphene (single-walled carbon nanotubes, SWCNTs) or by rolling up multiple sheets of graphene (multiwalled carbon nanotubes, MWCNTs). CNTs are made up of concentric cylinders of graphite layers. CNTs are used to improve the thermal stability, hardness, and electrical conductivity of polymeric composites. Initially Lai et al.

Carbon nanotubes are utilized in energy storage, device modelling, automotive parts, boat hulls, sporting goods, water filters, thin-film electronics, coatings, actuators, and electromagnetic shields.

Carbon nanotubes are used to make bullet- proof jackets. Carbon nanotubes can be used to make aircraft and spacecraft bodies. Carbon nanotubes can be used to build high-performance nanoscaled thin-film transistors to replace silicon-based transistors because of the semiconducting properties of carbon nanotubes.

NTs have extraordinary electrical conductivity, heat conductivity, and mechanical properties. They are probably the best electron field-emitter possible. They are polymers of pure carbon and can be reacted and manipulated using the well-known and tremendously rich chemistry of carbon