Synthesis of multi-walled carbon nanotubes via pyrolysis of plastic waste using a two-stage process

The pyrolysis of different plastic waste types such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET) and polystyrene (PS) for producing multi-walled carbon nanotubes (MWCNTs) using a two-stage process has been investigated. Firstly, the cracking of plastic wastes was carried out at a temperature of 700°C to produce hydrocarbon gases. In the second stage, the produced hydrocarbon gases were decomposed at 650°C on the surface of the Ni-Mo/Al₂O₃ catalyst to form CNTs. Various analytical tools such as XRD, TPR, TGA, Raman spectroscopy and TEM were used to describe both the fresh catalyst and the obtained CNTs. The results showed that the amount of the hydrocarbon gases was related to the type of plastic waste and hence the CNT yield. Accordingly, LDPE or PP was decomposed to produce the largest gases yield of 72.5 or 70.7 wt%, respectively. As a result, a large CNTs yield of 5.8 and 5 g/g_cat can be achieved by pyrolysis of PP and LDPE waste, respectively. However, a small yield of CNTs with little quality and low purity was obtained by using PS or PET waste as the carbon feedstock.     

SO_2促进的碳纳米管负载V_2O_5催化剂用于NH_3选择性还原NO

采用透射电镜(TEM)、X射线光电子能谱(XPS)、红外光谱(FT-IR)、SCR反应和程序升温脱附(TPD)等手段研究了碳纳米管(CNTs)担载的五氧化二钒(V2O5/CNTs)催化剂的形貌、表面形态以及SO2对选择催化NO还原活性的影响.结果表明,SO2对V2O5/CNTs催化剂的催化活性具有明显的促进作用,其促进作用源于SO2在催化剂表面的吸附.吸附的SO2主要位于碳表面而非钒表面,而且这种促进作用与V2O5和碳表面之间协同作用有关.     

Synthesis of titanium dioxide nanotubes via one-step dynamic hydrothermal process

Titanium dioxide (TiO₂) nanotubes were synthesized via one-step dynamic hydrothermal process from commercial TiO₂ powder. The effects of NaOH concentration, reaction time, reaction temperature, stirring process and washing on the morphology, and the exchange ions of the nanotubes were investigated. The morphology of the nanotubes was characterized in detail with transmission electron microscopy and scanning electron microscope. In the dynamic hydrothermal process, stirring can reduce the reaction time of transformation from particles to nanotubes. The nanotubes were formed when the expected reaction temperature reached to 130 °C. Energy dispersive X-ray analysis was used to determine the exchange of sodium ions and protons in washing process. The Na⁺ ions attached in the nanotubes were removed completely by HCl aqueous solution and deionized water treatments. X-ray diffraction patterns showed the titanate phase of the as-synthesized sample and anatase phase of TiO₂ nanotubes after calcination process at 400 °C for 2 h.     

Deposition of metal nanoparticles on carbon nanotubes via hexane modified water-in-CO2 microemulsion at room temperature

Carbon nanotube-supported metallic nanoparticles (Pd, Rh, and bimetallic Pd-Rh) with diameters in the range 2-10 nm can be synthesized by hydrogen reduction of metal ions dissolved in the water core of a CO2 microemulsion in liquid CO2 at room temperature. The microemulsion is stabilized by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and dissolved in liquid CO2 with the aid of hexane as a modifier. The metal nanoparticles synthesized in the microemulsion can be deposited on surfaces of multi-walled carbon nanotubes (MWCNTs) by stirring in the liquid CO2 phase. This simple method produces uniformly distributed metal nanoparticles on surfaces of the MWCNTs with high yields. The carbon nanotube-supported Pd/Rh bimetallic nanoparticles exhibit high catalytic activities for hydrogenation of aromatic compounds and can be reused without losing catalytic activity.     

Synthesis of carbon nanotubes

Carbon nanotubes play a fundamental role in the rapidly developing field of nanoscience and nanotechnology because of their unique properties and high potential for applications. In this article, the different synthesis methods of carbon nanotubes (both multi-walled and single-walled) are reviewed. From the industrial point of view, the chemical vapor deposition method has shown advantages over laser vaporization and electric arc discharge methods. This article also presents recent work in the controlled synthesis of carbon nanotubes with ordered architectures. Special carbon nanotube configurations, such as nanocoils, nanohorns, bamboo-shaped and carbon cylinder made up from carbon nanotubes are also discussed.     

Physico-chemical studies of amorphous carbon nanotubes synthesized at low temperature

This work provides better understanding on the nature of amorphous carbon nanotubes, which are synthesized via a simple chemical route. Amorphous carbon nanotubes (α-CNTs) are successfully synthesized by heating a mixture of ferrocene and ammonium chloride at temperature as low as 200 °C and are treated with hydrochloric acid. Transmission and field emission scanning electron microscopy techniques are performed to examine the morphology and dimension of the samples. X-ray diffraction tests confirm the amorphous structure of the nanotubes. The Fourier transform infrared spectroscopy and Raman studies indicate that the treated α-CNTs consist of many defective walls and are more amorphous compared with the untreated α-CNTs. Ultraviolet–visible absorption studies reveal that the untreated and treated α-CNTs exhibit plasmon absorbance with high bandgaps of 4 eV and 4.35 eV, respectively.     

Synthesis and characterization of polyurethane-grafted single-walled carbon nanotubes via click chemistry

Polyurethane (PU)-grafted carbon nanotubes were synthesized by the coupling of alkyne moiety decorated single walled carbon nanotube (SWCNT) with azide moiety containing PU using Cu(I) catalyzed Huisgen [3 + 2] cycloaddition click chemistry. The azide moiety containing poly(s-caprolactone)diol was synthesized by ring-opening polymerization and further used for PU synthesis. Alkyne-functionalizion of SWCNT was completed by the reaction of p-aminophenyl propargyl ether with SWCNT using a solvent free diazotization procedure. Nuclear magnetic resonance, Fourier transform infrared, and Raman spectroscopic measurements confirmed the functionalization of SWCNT. Scanning electron microscopy and transmission electron microscopy images showed an excellent dispersion of SWCNTs, and specially debundling of SWCNTs could be observed due to polymer assisted dispersion. A quantitative grafting was successfully achieved even at high content of functional groups.     

Deposition of metallic nanoparticles on carbon nanotubes via a fast evaporation process

A new technique was developed for the deposition of colloidal metal nanoparticles on carbon nanotubes. It involves fast evaporation of a suspension containing sonochemically functionalized carbon nanotubes and colloidal nanoparticles. It was demonstrated that metallic nanoparticles with different sizes and concentrations can be deposited on the carbon nanotubes with only a few agglomerates. The technique does not seem to be limited by what the nanoparticles are, and therefore would be applicable to the deposition of other nanoparticles on carbon nanotubes. PtPd and CoPt(3) alloy nanoparticles were used to demonstrate the deposition process. It was found that the surfactants used to disperse the nanoparticles can hinder the nanoparticle deposition. When the nanoparticles were washed with ethanol, they could be well deposited on the carbon nanotubes. The obtained carbon nanotube supported metal nanoparticles were characterized by transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and cyclic voltammetry.     

Synthesis of carbon nanotubes at low temperature by filament assisted atmospheric CVD and their field emission characteristics

Multiwalled carbon nanotubes (MWNTs) were synthesized using a hot filament assisted chemical vapor deposition (CVD) at the atmospheric pressure at a substrate temperature of 550 °C. The size of nanotubes was controlled by changing the size of catalyst particles. The structure and composition of these nanotubes were investigated using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The electron field emission current of MWNTs was also measured. It was found that the nanotubes with smaller the diameter had higher the emission current levels though synthesis conditions except catalyst particles were the same. These as-grown MWNTs had emission current densities of 6.5 mA/cm² and 2.5 mA/cm² at 1 V/μm for 5-8 nm and 20 nm size carbon nanotube samples, respectively. The results indicated that the MWNTs synthesized had low emission threshold voltages and high emission current levels that are favorable properties for field emission-based display device applications.     

基于非水解sol-gel法的碳热还原氮化合成氮化铝超细粉体

以无水氯化铝和异丙醚为原料,采用非水解溶胶-凝胶法制备出氧化铝凝胶。其经800℃煅烧才析出少量γ-Al2O3晶体,γ-Al2O3向α-Al2O3晶型转变在1200℃附近,经900℃煅烧后比表面积仍高达145m2/g,具有介孔结构。以该高活性氧化铝凝胶作为铝源,采用碳热还原氮化工艺合成氮化铝粉体。结果表明,氧化铝凝胶经300℃预煅烧,按n(C)/n(Al)=7.8与碳黑混合,在流量80mL/min高纯N2中,于1450℃还原氮化2h便可合成出平均粒径在400nm的高纯六方相AlN粉体。     

Low temperature synthesis of multi-walled carbon nanotubes via a sonochemical/hydrothermal method

In this investigation, multi-walled carbon nanotubes (MWCNTs) have been prepared by a facile sonochemical/hydrothermal method. MWCNTs have been hydrothermally fabricated with using dichloromethane, cobalt chloride and metallic lithium as starting materials in 5 mol/lit NaOH aqueous solution. Ultrasonic pre-treatment of the solution mixture had an important step prior to the hydrothermal condition, which could generate a considerable amount of multi-walled carbon nanotubes for the subsequent hydrothermal growth. Finally, high pure MWCNTs with lengths of 2-5 μm and diameters of 60 ± 20 nm could be synthesized at as low temperature as 160 °C. As a matter of fact, the method of sonochemical/hydrothermal guarantees the production of multi-walled carbon nanotubes (MWCNTs) for different applications, especially reinforcement materials.     

Multi-branching carbon nanotubes via self-seeded catalysts

A novel multi-branching carbon nanotube (CNT) structure is synthesized by direct current plasma enhanced chemical vapor deposition. The structure consists of aligned CNTs which have branches of smaller diameters growing aligned along a direction perpendicular to the original CNT. The mechanism of branching is explained in terms of a self-seeding of Ni catalyst which is transferred by sputtering from the original catalyst particles in the backbone CNTs to the walls of those CNTs. It is also shown that the branching induced a large increase in surface area and total nanotube length and can be beneficial in supporting very fine Pt nanoparticles for fuel cell and other catalytic applications. Such an array of Y-junction nanostructures could be useful for the fabrication of a high-density array of nanoelectronics switches and transistors.     

Oxygen reduction activity of carbon nitride supported on carbon nanotubes

Fuel cells offer an alternative to burning fossil fuels, but use platinum as a catalyst which is expensive and scarce. Cheap, alternative catalysts could enable fuel cells to become serious contenders in the green energy sector. One promising class of catalyst for electrochemical oxygen reduction is iron-containing, nanostructured, nitrogen-doped carbon. The catalytic activity of such N-doped carbons has improved vastly over the years bringing industrial applications ever closer. Stoichiometric carbon nitride powder has only been observed in recent years. It has nitrogen content up to 57% and as such is an extremely interesting material to work with. The electrochemical activity of carbon nitride has already been explored, confirming that iron is not a necessary ingredient for 4-electron oxygen reduction. Here, we synthesize carbon nitride on a carbon nanotube support and subject it to high temperature treatment in an effort to increase the surface area and conductivity. The results lend insight into the mechanism of oxygen reduction and show the potential for carbon nanotube-supported carbon nitride to be used as a catalyst to replace platinum in fuel cells.     

Synthesis and characterization of carbon nanotubes via ultrasonic spray pyrolysis method on zeolite

Ultrasonic spray pyrolysis method for the synthesis of carbon nanotubes (CNTs) has been investigated with zeolite supporting material. Single wall carbon nanotubes (SWCNTs) were obtained at 850 °C in nitrogen environment. Such deposition system makes it possible to grow CNTs without reducing agent at atmospheric pressure in a simple setup. Iron and cobalt acetate were used as catalyst and ethanol as carbon source for the synthesis of CNTs. Results show that nature of zeolite and cobalt concentration play important roles for SWCNTs production. Interestingly, we notice that in catalyst particles of sharp shape, nucleation of a nanotubes cap occurs dominantly in the forward direction.     

Synthesis of high-purity and high-crystallinity single-walled carbon nanotubes homogeneously dispersed by wet process

Field emission (FE) electron sources based on high-purity and high-crystallinity single-walled carbon nanotubes (hc-SWCNTs) are promising electronic devices from the viewpoint of industrial application. However, to utilize high-purity hc-SWCNTs as a component of electronic devices, it is necessary to homogeneously disperse hc-SWCNTs using a wet process. Shear force is required to break up aggregates of hc-SWCNTs to produce a film with uniformly dispersed hc-SWCNTs, but contaminants such as fine graphite in the aggregates disperse the shear force of hc-SWCNT bundles. Therefore, it is necessary to remove these contaminants to achieve the uniform dispersion of hc-SWCNTs. In this study, we have succeeded in the highly efficient synthesis of hc-SWCNTs with few contaminants by the arc discharge method using glass-like carbon as a raw material to produce SWCNTs. It was demonstrated that hc-SWCNTs with low foreign matter contamination can be uniformly dispersed without the need for wet dispersion tools such as a homogenizer and a jet mill. Moreover, the long-term stability of the current emitted by FE devices fabricated using the dispersed solution can be obtained.     

反应温度对碳纳米管的影响

本文利用化学气相沉积( CVD)法,以乙烯为碳源气体,二茂铁为催化剂,在二氧化硅上制备出一系列碳纳米管,并通过拉曼光谱和扫描电子显微镜( SEM)对其形貌、结构和组分进行表征,分析反应温度对碳纳米管的影响.研究发现:当反应温度为860℃时,有均匀的碳纳米管薄膜生成,其管径和长度分别达到104 nm和95 μm,同时结构缺陷少,非碳管杂质较少,纯度较高.     

Multi-walled carbon nanotubes produced by hydrogen DC arc discharge at elevated environment temperature

Multi-walled carbon nanotubes (MWCNTs) were synthesized by hydrogen DC arc discharge at elevated environment temperature. The sample collected from the soot on the inner wall of the arc discharge furnace was investigated using TEM, HRTEM and X-ray diffraction. The results show that environment temperature has a significant effect on the formation of MWCNTs in the soot in hydrogen atmosphere as well as the diameter of the tubes. When environment temperature in the furnace is higher than about 500 °C, MWCNTs can be formed on the furnace walls with a great quantity.     

Ester-functionalized single-walled carbon nanotubes via addition of haloformates

Herein, a versatile method to introduce ester functional groups to the surface of single-walled carbon nanotubes (SWCNTs) was defined. Ester-modified SWCNTs were prepared via the direct reaction of haloformates with reduced SWCNTs [(nBu–SWCNT ^n? ) Li _n ⁺ ] generated by n-butyl lithium. Ultraviolet–Visible–near infrared and Raman spectroscopy verified the evidence of covalent surface functionalization. Solubility of functionalized SWCNTs (f-SWCNTs) enhanced compared to purified SWCNTs. Gold tagging to positively charged SWCNTs displayed the presence and distribution of functional groups, confirming the conversion of esters into amides. f-SWCNTs were further characterized by thermo-gravimetric analysis coupled with mass spectrometry and fourier-transform infrared spectroscopy.