Abstract:

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.

Key words: waste plastic, carbon nanotubes (CNTs), growth mechanism

摘要：

塑料因优异的易塑性、持久性、耐腐蚀等被广泛应用于生活中的各个角落。然而塑料在使用过程由于难降解、回收利用率低等缺点对环境造成严重污染。本文以低密度聚乙烯（LDPE）为原料，以硝酸镍为催化剂前体，通过一步热解法将聚乙烯塑料制备成具有高价值的碳纳米管（CNTs），通过X射线衍射、扫描电镜、透射电镜及气相色谱-质谱等技术对其结构和生长机制进行表征与分析。研究热解温度（600~900℃）和硝酸镍加入量（0.5%~2.0%）对CNTs结构形貌的影响。结果表明，在温度为800℃、硝酸镍质量分数1.0%的条件下制备得到形貌结构较好的CNTs。该条件下CNTs为多壁碳纳米管，石墨化度较高，长度为5~15μm，管平均外径为(28.43±0.56)nm，平均内径为(11.03±0.61)nm，层间距为0.340nm，接近碳纳米管的最理想的石墨层间距（d=0.3354nm）。结合气相色谱-质谱技术研究了CNTs的生长机理与模型，剖析出CNTs为顶端生长模型。将制备的CNTs用于去除废水中的微塑料并表现出了较好的去除性能，实现了“以废治废”。本研究以LDPE为原料采用一步热解法得到形貌结构优异的CNTs，实现了塑料的高质化利用，并为其他相似废弃物的利用提供了借鉴。

关键词: 废塑料, 碳纳米管, 生长机理