Preparation Of Carbon Nanomaterials By Pyrolysis Of Plastic Polymers

With the gradually increasing production and use of plastic products in the world year by year,the environmental problems caused by discarded plastic products are becoming more and more serious.Due to high cost,serious environmental pollution,and waste of land resources,traditional waste plastic disposal methods such as incineration and landfill could not meet people's pursuit of an energy-saving and environmentally friendly society.Therefore,it is extremely urgent to develop a high utilization rate and environmentally friendly plastic recycling method.Chemical recycling is the most promising method for recycling waste plastics due to its high utilization rate of hydrocarbon atoms and controllable structure of recycled products.Its main process is to transform raw waste plastic materials into high value-added products through thermal cracking and a series of catalytic reactions.Carbon nanomaterials are widely used in many fields such as energy and environment due to their unique physical structure and chemical properties.Among the methods for preparing carbon nanomaterials,chemical vapor deposition is the main method for preparing carbon nanomaterials in large quantities because of its controllable parameters,low cost and simple operation.Compared with the extensive use of liquid and gas as carbon source,report on using solid carbon source in chemical vapor deposition process for carbon nanotubes synthesis remains scarce.This work revolves around the chemical recycling of waste plastics,and aims to use solid carbon sources such as polymer particles and waste plastic products to prepare high valueadded carbon nanomaterials through chemical vapor deposition.The main work contents are as follows:(1)Using two-stage chemical vapor deposition equipment and powdery magnesium oxide supported cobalt as catalyst,polyethylene terephthalate,high density polyethylene,polyvinyl chloride,low density polyethylene,polypropylene,polystyrene and polycarbonate were selected as carbon sources to achieve the bulk growth of carbon nanotubes.Polyethylene terephthalate,high density polyethylene,low density polyethylene,polypropylene and polystyrene were used to achieve high quality and high yield growth of single-walled carbon nanotubes.Raman spectroscopy and UV-vis-NIR absorption spectroscopy characterizations demonstrated that the single-walled carbon nanotubes catalyzed by different plastic polymers have similar diameter and chiral distribution.The success in single-walled carbon nanotube growth is correlated with the strong interaction between the reduced metal cobalt and the magnesium oxide support.The catalytically active cobalt nanoparticles are firmly anchored on the surface of the magnesium oxide support,preventing the particle aggregation and subsequent formation of large-diameter particles.In this work,cobalt nanoparticles are the active component for nucleating and growing single-walled carbon nanotubes.Besides,using magnesium oxide powders as growth template and polypropylene as carbon source,we have prepared graphene shell structures with high degree of graphitization and controllable number of layers by chemical vapor deposition.This work not only transforms plastic polymer to high value-added carbon nanomaterials,but also enriches the recycling and treatment approaches of waste plastics.(2)In order to further investigate the catalytic behavior of metal nanoparticles attached to magnesium oxide powders in the growth of single-walled carbon nanotubes,palladium nanoparticles prepared by microwave reduction method and supported on magnesium oxide support were designed as powder catalyst.High purity carbon monoxide was used as carbon source to grow high quality single-walled carbon nanotubes at high temperatures.Raman spectroscopy,UV-vis-NIR absorption spectroscopy and fluorescence spectroscopy characterization results show that singlewalled carbon nanotubes synthesized from palladium catalyst has a narrow chirality distribution,this is mainly due to the high melting point of palladium nanoparticles.They can maintain a high dispersibility on the carrier surfaces at a high growth temperature,thereby realizing the synthesis of single-walled carbon nanotubes with a narrow diameter distribution.This work extends the use of unconventional metal as active catalyst for the growth of single-walled carbon nanotubes,and provides an experimental basis for further exploring the growth mechanism of single-walled carbon nanotubes.