Carbon Nanotubes as a Resourceful Product Derived from Waste Plastic—A Review

Abstract

Generation of wastes increases exponentially with the advancement of lifestyle, and out of different types of wastes in this planet, a behemoth portion of the waste is constituted of varying polymers. Researches are going on to mitigate this threat of leviathan quantities of waste plastics around the globe. Landfilling and incineration are one of the ways to eradicate the problems related to waste polymers but the processes of landfilling and incineration are not that amenable techniques. The process of incineration favours the recovery of energy but both social and economic limitations associated with it has made the process quite incompetent. Hence, it is imperative to find a new way to mitigate this problem. In the past decade, researchers after strenuous investigations have found that recycling of plastics can be utilized as one of the cardinal ways to mitigate the threat of the large quantity of waste plastics. Additionally, it has also been revealed that wastes’ plastics can serve the purpose of being one of the consequential precursors of carbonaceous feeds that can be recycled under appropriate reacting conditions to produce carbon nanotubes (CNTs) of varying forms and qualities and also to meet the challenge of finite nature of fossil fuels. CNTs possess an exceptional chemical, mechanical, thermal and electrical properties which have attracted great scientific and technological interests to explore it for realistic and practical applications. CNTs with these unique properties have found numerous applications in various genres of science and technology innovations. Several methods have been developed and reported that is followed to synthesize CNTs of different forms under proper reacting conditions in the presence of suitable catalysts (nickel based, cobalt based, iron based, etc.). Different forms of CNTs are available among which the production of multiwall carbon nanotubes (MWCNTs) from waste polymers is feasible and satisfactory. Though there are various methods available for synthesis of CNTs, benchmark and feasible method for CNTs synthesis is yet to be reported. In depth, investigations are required to carry out to develop a feasible method that will utilize either virgin or waste plastics as the carbon precursors to synthesize CNTs, taking all the parameters under consideration influencing both the quality and quantity of it. The questions that need to find answer are—What are the parameters influencing the mechanism of growth of both the forms of CNTs (SWCNTs/MWCNTs) from plastics (virgin and waste)? How can the decomposition temperature be reduced to make the process not only efficient in terms of saving energy but also in terms of abjuring the formation of both dioxins and furans? How to make the process more feasible so that it can be a good alternative to improvise the quality of CNTs from wastes’ plastics? In this paper, a review has been presented discussing various methods available till date for synthesis of CNTs from virgin and waste polymers ranging from polyethylene, polypropylene and polyethylene terephthalate to polyvinyl alcohol. Finally, the paper proposes an optimal route for the production of CNTs from plastics. It is evident that the genre of converting low-valued materials to value-added products such as carbon nanotubes that can be explored for various applications is not only a promising route in terms of recycling technology but also in terms of sustainability