Preparation of carbon nanotubes by catalytic pyrolysis of waste plastics and its growth mechanism
Plastics are widely used in all corners of life because of their excellent plasticity,durability and corrosion resistance.However,the use of plastic in the process of plastic caused serious pollution to the environment due to difficult to degrade,low recycling rate and other shortcomings.In this paper,low-density polyethylene(LDPE)was used as raw material and nickel nitrate was used as catalyst precursor to prepare polyethylene plastics into high-value carbon nanotubes(CNTs)by one-step pyrolysis,and their structures and growth mechanisms were characterized and analyzed by X-ray diffraction,scanning electron microscopy,transmission electron microscopy and gas chromatography-mass spectrometry.The effects of pyrolysis temperature(600-900℃)and nickel nitrate addition(0.5%—2.0%)on the structure and morphology of CNTs were investigated.The results indicated that the CNTs with good morphological structure were prepared at a temperature of 800℃and the amount of nickel nitrate added was 1.0%of the mass of polyethylene plastic.The CNTs were multi-walled carbon nanotubes with high graphitization,the length was 5-15μm,the average outer diameter of the tubes was(28.43±0.56)nm,the average inner diameter was(11.03±0.61)nm and the layer spacing was 0.340nm,which was close to the optimal graphite layer spacing of carbon nanotubes(d=0.3354nm).The growth mechanism and model of CNTs were investigated by combining gas chromatography-mass spectrometry,and the growth model of CNTs was dissected as the apical growth model.The prepared CNTs were used to remove microplastics from wastewater and showed good removal performance,realizing"waste to waste".In this study,LDPE were used as raw materials to obtain CNTs with excellent morphology and structure by one-step pyrolysis,which realized the high-quality utilization of plastics and provided a reference for the utilization of other similar wastes.
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