Owing to their simplicity and ease of synthesis, carbon nanotubes (CNTs) have captivated attention of researchers. Many engineering applications have investigated the new features of nanostructured carbon nanotubes, such as large surface area, stiffness and durability. CNTs have opened up new opportunities for environmental improvement, pollution management and application in a variety of fields. Multiple types of pollution are produced as a result of population growth, urbanization and industrialization. CNTs are used to solve a variety of challenges, including environmental difficulties, water pollution, biomedical applications, and so on. It becomes an unavoidable present and future material. Different applications of CNTs have been presented in this review paper. CNTs are potential material having number of uses, including water purification, drug delivery, preservatives, catalysis, genetic engineering and artificial implants which are reviewed in this review article. This paper is presenting an explicit and systematic progress of CNTs for water treatment, medicinal uses drug delivery, artificial implants and so on, and a multitude of CNT applications in broad disciplines and their purification methods have been covered. The issues related to synthesis technologies, purification technology, bio-medicinal application and catalytic property of CNTs within the framework of different engineering applications and environmental impact are discussed in this study.

    Abstract
        Graphical abstract
    1 Introduction
    2 Structure
        2.1 On the basis of number of layers
        2.2 On the basis of rolling angle
        2.3 On the basis of structure of CNTs
    3 Properties of CNTs
    4 Preparation techniques
        4.1 Electric-arc discharge (EAD)
        4.2 Laser vaporization (LV)
        4.3 Chemical vapor deposition (CVD)
        4.4 Plasma-enhanced chemical vapor deposition (PECVD)
        4.5 Catalytic pyrolysis of hydrocarbon (CPH)
        4.6 Alcohol catalytic chemical vapor deposition (ACCVD)
        4.7 Hydrothermal methods (HM)
        4.8 CNTs’ growth mechanism
        4.9 Comparison among CNTs synthesis methods
    5 Purification of CNTs
        5.1 Sonication, filtration and annealing by surfactants
        5.2 Air oxidation
        5.3 Acid refluxing
    6 Characterization of CNTs
        6.1 Raman spectroscopy (RS)
        6.2 X-ray photoelectron spectroscopy (XPS)
        6.3 Fourier-transform infrared spectroscopy (FT-IR)
        6.4 Thermogravimetric analysis (TGA)
        6.5 Scanning and transmission electron microscopy (SEM and TEM)
    7 Applications of CNTs
        7.1 Drug delivery
        7.2 CNTs for water treatment
    8 Limitations of CNTs
    9 Future perspective
    10 Conclusion
    Acknowledgements 
    References

• Faiza Asghar(Department of Chemistry, University of Wah)
• Babar Murtaza(Riphah Institute of Pharmaceutical Sciences, Riphah International University)
• Bushra Shakoor(Department of Chemistry, University of Wah)
• Nabtahil Iqbal(Department of Chemistry, University of Wah)
• Maria Shafique(Department of Chemistry, University of Wah)
• Rafia Murtaza(Department of Chemistry, University of Wah)
• Ian Sydney Butler(Department of Chemistry, McGill University)