This review sums up the techniques used for the synthesis of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon nanospheres (CNSs) by employing catalysts of natural origin. Establishing large-scale production and commercial applications of CNTs for a sustainable society is still of high apprehension. In this regard, one of the major factors is the starting materials such as precursors and catalyst sources. However, natural materials contain a minor quantity of metals or metal oxides and could be employed as a catalyst source for the synthesis of CNTs, providing the possibility to replace expensive catalyst sources. A large number of successful studies have been completed so far and confirm that these developed methods for carbon nanomaterials synthesis exhibiting high quality from common natural materials are not only possible but, most importantly, promising and scalable. This review also highlights purification methods and recent promising applications of as-synthesized CNTs.
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