Mehrnoush Khavarian

FLOATING CATALYST CVD SYNTHESIS OF CARBON NANOTUBES USING IRON (III) CHLORIDE: INFLUENCES OF THE GROWTH PARAMETERS

Carbon nanotubes (CNTs) were synthesized by a low-cost floating catalyst (FC) chemical vapor deposition (CVD) method in a horizontal reactor. It was found that iron (III) chloride (FeCl3) is a high efficient FC precursor for methane CVD to grow CNTs. In this study, the effects of reaction temperature and flow ratio of methane to nitrogen (CH4:N2) on the morphology of the CNTs were investigated. The morphological analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that increasing the reaction temperature and flow ratio of CH4:N2 grew CNTs of larger diameters. Energy dispersive X-ray (EDX) and thermogravimetric analysis (TGA) were employed to study the purity of the produced CNTs. As shown by the TGA, the highest yield of 74.19% was recorded for the CNTs grown at 1000°C and flow ratio CH4:N2 of 300:200.

IRON (III) CHLORIDE AS FLOATING CATALYST PRECURSOR TO PRODUCE MULTI-WALLED CARBON NANOTUBES FROM METHANE

Multi-walled carbon nanotubes (MWCNTs) were prepared by floating catalyst (FC) method, using methane as a carbon source and iron (III) chloride (FeCl3) as a catalyst precursor, followed by purification with air oxidation and acid treatment. The as-grown and purified MWCNTs were characterized by transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry analysis and Raman spectroscopy. The average inner and outer diameters of the MWCNTs were 25 and 39 nm, respectively. The purity and yield of the purified MWCNTs were more than 92% and 71% weight fraction, respectively.

Effects of Growth Parameters on the Morphology of Aligned Carbon Nanotubes Synthesized by Floating Catalyst and the Growth Model

Aligned carbon nanotubes (CNTs) were grown in a simple designed horizontal quartz tube reactor from chemical vapor deposition (CVD) using ferrocene as floating catalyst (FC). FC-CVD process was performed using methane as carbon source under nitrogen flow without introducing hydrogen. Aligned CNTs with an average length of ca. 10 μm were produced at reaction temperatures in a range of 950–1100°C and methane flow rate of 250–450 sccm for 60 minutes. The diameter of CNTs was influenced by the size of iron catalyst particles formed in the reactor. A conceptual model of CNT formation and its growth mechanism were proposed in this study.

Effects of Reaction Temperature on CO2 Reforming of CH4 over Multi-Walled Carbon Nanotubes Catalyst with Co-Mo-MgO Nanoparticles

The utilization of greenhousegases, such as carbon dioxide (CO2) and methane (CH4), is among the most important challenges in the energy research field. The catalytic activity behavior of CO2 reforming of CH4 (CRM) over synthesized multi-walled carbon nanotubes (MWCNTs) with Co-Mo and MgO nanoparticles was investigated. Based on conversion of reactants and production of syngas, the synthesized Co-Mo-MgO/MWCNTs were found to be a suitable catalyst for the CRM reaction. The CH4 and CO2 conversions were greatly influenced by the reaction temperature in the range of 750-1000 °C. The catalyst exhibited high activity and stability during 10 h reaction time with 82.68% conversion of CH4 at 950 °C respectively,without significant deactivation. The reaction rate of CH4 and CO2 over carbon nanotubes was affected significantly by the reaction temperature.The syngas ratio was close to unity and no carbon deposition over the catalyst was observed after the termination of the reaction.

Effects of Temperature on the Synthesis of Carbon Nanotubes by FeCl3 as a Floating Catalyst Precursor

The influence of temperature on the growth of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) using FeCl3 as a floating catalyst (FC) precursor and methane as a carbon source was studied. FeCl3 was found to be an efficient FC precursor for methane CVD into CNTs without the need of introducing hydrogen in feed. The optimum temperature for growing CNTs was 1050°C, giving off 80% yield of CNTs. The electron microscopy analysis shows that the produced CNTs possessed the average diameter of 30 nm and Raman scattering reveals the low ID/IG ratio of 0.62, indicating the presence of high graphitized structure.

Recent trends in graphene materials synthesized by CVD with various carbon precursors

AbstractGraphene is a single layer of carbon atoms arranged in an sp2-hybridized structure with properties far superior compared to other materials. Research and development in graphene synthesis have been rapidly growing the past few years, especially using chemical vapor deposition (CVD) over various types of carbon precursor. The nature and the type of carbon precursor is one important parameter of growth by CVD, especially for graphene production, since they can dramatically impact graphene growth yield and rate. However, effects of the used carbon precursor on graphene growth mechanisms are rarely discussed. In the course of large-scale and low-cost graphene preparation, this review on the recent trends regarding the utilization of diverse carbon precursors used to synthesize graphene via the CVD method is of great interest for development of improved or alternative synthesis methods. The details and the mechanisms involved in graphene synthesis using carbon precursors in the form of gaseous, liquids and solids are compared, analyzed and discussed thoroughly. In this review, we present a thorough overview on the impact and mechanisms of carbon precursors in achieving high-quality graphene with competitive edge in the near future.

Dispersion of Multi-Walled Carbon Nanotubes in Portland Cement Concrete Using Ultra-Sonication and Polycarboxylic Based Superplasticizer

The potential properties of carbon nanotube-cement based materials strongly depend on the dispersion of carbon nanotubes (CNTs) within the cement matrix and the bonding between CNTs and the hydrated cement. The homogeneous dispersion of CNTs in the cement matrix yet is one of the main challenges due to strong van der Waals forces between nanotubes. In this study, a polycarboxylic ether based superplasticizer and ultra-sonication technique was used for dispersion of multi-walled carbon nanotubes (MWCNTs). Portland cement concrete specimens with different concentrations of MWCNTs (0.04 and 0.1 % by the weight of cement), with and without the presence of superplasticizer were investigated. Compressive strength test results revealed a significant improvement in mechanical properties of sample containing 0.1 % MWCNTs and 0.2 % superplasticizer. Moreover, field emission scanning electron microscopy (FESEM) images of fractured surfaces of hardened specimens showed a good dispersion of MWCNTs within the cement matrix. This method was developed to facilitate the uniform dispersion of MWCNTs in the cementitious concrete for better reinforcement in nanoscale and mechanical properties enhancement by transfer of load between the nanotubes and matrix.

A review of carbon-based and non-carbon-based catalyst supports for the selective catalytic reduction of nitric oxide

Various types of carbon-based and non-carbon-based catalyst supports for nitric oxide (NO) removal through selective catalytic reduction (SCR) with ammonia are examined in this review. A number of carbon-based materials, such as carbon nanotubes (CNTs), activated carbon (AC), and graphene (GR) and non-carbon-based materials, such as Zeolite Socony Mobil–5 (ZSM-5), TiO2, and Al2O3 supported materials, were identified as the most up-to-date and recently used catalysts for the removal of NO gas. The main focus of this review is the study of catalyst preparation methods, as this is highly correlated to the behaviour of NO removal. The general mechanisms involved in the system, the Langmuir–Hinshelwood or Eley–Riedeal mechanism, are also discussed. Characterisation analysis affecting the surface and chemical structure of the catalyst is also detailed in this work. Finally, a few major conclusions are drawn and future directions for work on the advancement of the SCR-NH3 catalyst are suggested.

Understanding the performance and mechanism of Mg-containing oxides as support catalysts in the thermal dry reforming of methane

Dry reforming of methane (DRM) is one of the more promising methods for syngas (synthetic gas) production and co-utilization of methane and carbon dioxide, which are the main greenhouse gases. Magnesium is commonly applied in a Ni-based catalyst in DRM to improve catalyst performance and inhibit carbon deposition. The aim of this review is to gain better insight into recent developments on the use of Mg as a support or promoter for DRM catalysts. Its high basicity and high thermal stability make Mg suitable for introduction into the highly endothermic reaction of DRM. The introduction of Mg as a support or promoter for Ni-based catalysts allows for good metal dispersion on the catalyst surface, which consequently facilitates high catalytic activity and low catalyst deactivation. The mechanism of DRM and carbon formation and reduction are reviewed. This work further explores how different constraints, such as the synthesis method, metal loading, pretreatment, and operating conditions, influence the dry reforming reactions and product yields. In this review, different strategies for enhancing catalytic activity and the effect of metal dispersion on Mg-containing oxide catalysts are highlighted.