Catalysts for vapor-phase deposition of multi-walled carbon nanotubes are considered. A method for synthesis of iron-containing catalyst by coprecipitation of aluminum, magnesium, and iron(II) hydroxides is suggested.Carbon nanotubes (CNT), which were only available in milligram amounts several years ago, are gradually becoming a product of large-tonnage synthesis. Simultaneously with the increase in the production scale, new application fields of CNT are being revealed. For example, Hyperion Catalysis International Co. (USA) manufactures CNT 10315 nm in diameter and CNT-containing polymeric formulations. Introduction of 235% CNT into polymeric materials makes them electrically conducting and thereby hinders accumulation of static electricity [1]. Mechanical properties of CNT-filled polymeric materials have been studied [23 4]. CNT and CNT-based composites are under intensive scientific and technological development in China [5310].According to the results of [9], the most valuable are fine CNT less than 20 nm in diameter. In the best variants reported in numerous publications devoted to synthesis of multi-walled CNT by the chemical vapor deposition technique, the CNT diameter is 10 320 nm. The authors of the present study are not aware of any method for obtaining multi-walled CNT with an average diameter of less than 10 nm.It is commonly believed, even though this issue remains insufficiently studied, that the diameter of a growing nanotube is determined by the size of the cluster of a catalytically active metal, e.g., iron, cobalt, or nickel. Presumably, the most efficient way to obtain and stabilize nanosize clusters of catalytically active metals is their immobilization on some highly dispersed or porous support, e.g., aluminum oxide, silicon, magnesium, or carbon. For this purpose, a dispersed support is impregnated with solutions of metal compounds (nitrates, acetylacetonates, salts of organic acids, etc.) On being introduced into a hot reactor, these compounds decompose to give, commonly, metal oxides, from which catalytically active metal clusters are formed in a reducing atmosphere (as a rule, a mixture of hydrogen and hydrocarbons). Such a procedure for fabrication of catalysts for synthesis of multi-walled CNT was described, e.g., in the patent [11]. Aluminum oxide with a particle size of about 10 nm was used as a highly dispersed support, and nitrates and acetylacetonates of iron, molybdenum, manganese, and chromium, and mixtures of these, as compounds of catalytically active metals. Ethylene mixed with hydrogen served as a source of carbon. The mass of the multi-walled CNT obtained was tens of times that of the catalytically active metals, and the diameter of the resulting CNT was in the range from 3.5 to 70 nm. The method described has the following disadvantage. As a result of impregnation and drying, particles of the material undergo aggregation and the size of metal oxide clusters formed in pyrolysis may markedly exceed the particle size of the highly dispersed support. Thus, the nanotubes obtain...

An effective polyhydroquinone/graphene nanocomposite was developed to remove Cu(II) and Zn(II) metal ions in water. The composite nanomaterial was characterized by FT‐IR, SEM, TEM, XRD, Raman spectroscopy, and thermo‐gravimetry. The surface of the material was heterogeneous with 10–20 nm particle size. The adsorption capacity of Cu(II) and Zn(II) metal ions were 40.9 and 24.8 μgg−1, respectively. The sorption followed Langmuir, Freundlich, Tempkin and D−Rs models. The process of adsorption was successfully described by pseudo‐second‐order model, thereby indicating the chemical nature of the main adsorption mechanism. Thus, it can be argued that the adsorption proceeded in a mixed‐diffusion mode, with a significant contribution of a large number of high affinity active sites located on the adsorbent surface. The uptake time was 60 and 15 minutes for Cu(II) and Zn(II) at pH 6.0; indicating fast hydro‐friendly nature and making the method applicable to solve water pollution in real life problems. Therefore, the reported method may be used to remove Cu(II) and Zn(II) metal ions in any water resource.

A novel mesoporous carbon nanostructured material was prepared and characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, thermogravimetry, and X-ray diffractometry. The material demonstrated high-speed and high-adsorption capacities of 827.5 and 2484.5 mg g–1 for methyl orange (MO) and malachite green (MG) dyes in 10 min. The kinetic data were fitted to pseudo-first- and pseudo-second-order, external and intraparticle diffusion, and Elovich models, whereas the isotherm data were adjusted to the Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, and Langmuir–Freundlich isotherms (Sips). It was found that MO and MG adsorption was limited by chemical interactions and mixed diffusion. Besides, the physical process was elucidated through free energy values (E = 2.56 and 0.049 kJ mol–1 for the MO and MG, respectively). Methyl orange adsorption mostly occurred through ion exchange and electrostatic interactions, and at lower MO concentrations, through chemical interactions and surface complexation as well. Malachite green adsorption took place only on lower-energy sites. Thus, it can be concluded that the adsorbent proposed herein possessed high-speed and high-adsorption capacity. Therefore, it can be considered as promising in removing the reported dye pollutants.

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