Catalyst effect on carbon nanomaterials production by chemical vapor deposition

Carbon nanomaterials (CNMs) such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have attract many interests due to their unique mechanical, chemical, electrical, magnetic, thermal and other properties. They have been applied in various fields such as electronics, medicine and catalysis. Intense research effort have been undertaken to synthesis CNTs at a reasonable cost. Currently chemical vapor deposition (CVD) is the most widely used method, which is promising way for large scale production and high purity of CNMs at low cost and easy to handle. Catalyst used in CVD method give high significant role in determination of the yield and the types of CNTs produced. Iron oxide (Fe2O3) and nickel oxide (NiO) powder have been used to investigate the growth of CNMs. The samples were growth by using methanol as a precursor at temperature 700 °C for 30 minutes deposition time. As a result, CNTs can be found grow at small size of catalyst (less 10 nm). Bigger size of catalyst (above 20 nm) lead to encapsulated of metal carbide. Amorphous carbon was formed around the catalyst that have size in micro scale. All sample were analyzed using high resolution transmission electron microscopy (HRTEM) images and energy dispersive X-ray (EDX). Thus, the study of catalyst during CVD process are important for a better understanding of CNM growth

Hydrogen gas sensing of TiO2/MWCNT thick film via screen-printing technique

Titanium dioxide is a well-known sensing material for sensing gas, especially hydrogen, while the carbon nanotube is able to operate the gas sensor at room temperature. This study combined both characteristics and investigated varying operating temperatures and different hydrogen concentrations on the sensor response. To prepare the gas sensor sensing film, an organic binder was mixed with TiO2/MWCNT. Then, using a screen-printing method, the mixture was deposited on the alumina substrate. Annealing was done using air at 500°C and then using nitrogen at 600°C, for 30 min each. FESEM, EDX, and XRD were used to characterise the structural and morphological analysis of the sensing film. The operating temperature was varied at 100°C, 200°C, and 300°C and the hydrogen concentration varied from 100 - 1000 ppm. When exposed to hydrogen, the gas sensor showed decreased current, and vice versa when exposed to nitrogen. Therefore, the gas sensor can be categorised as a p-type gas sensor. The sensor was able to sense 500-1000 ppm of hydrogen at operating temperatures of 100°C and 200°C. The gas sensor was able to sense lower concentrations of hydrogen at 300°C i.e. 100-1000 ppm hydrogen; thus the optimal operating temperature for the gas sensor in this study is 300°C

Effect of PVP as a capping agent in single reaction synthesis of nanocomposite soft/hard ferrite nanoparticles

Nanocomposite magnets consist of soft and hard ferrite phases are known as an exchange spring magnet when they are sufficiently spin exchange coupled. Hard and soft ferrites offer high value of coercivity, Hc and saturation magnetization, Ms respectively. In order to obtain a better permanent magnet, both soft and hard ferrite phases need to be “exchange coupled”. The nanoparticles were prepared by a simple one-pot technique of 80% soft phase and 20% hard phase. This technique involves a single reaction mixture of metal nitrates and aqueous solution of varied amounts of polyvinylpyrrolidone (PVP). The heat treatment applied was at 800 °C for 3 h. The synthesized composites were characterized by Transmission Electron Microscope (TEM), Fourier Transform Infra-red (FT-IR), Energy Dispersive X-Ray (EDX), X-ray diffraction (XRD) and Vibrating sample magnetometer (VSM). The coexistence of two phases, Ni0.5Zn0.5Fe2O4 and SrFe12O19 were observed by XRD patterns. It also verified by the EDX that no impurities detected. The magnetic properties of nanocomposite ferrites for 0.06 g/ml PVP gives a better properties of Hc 932 G and Ms 39.0 emu/g with average particle size obtained from FESEM was 49.2 nm. The concentration of PVP used gives effect on the magnetic properties of the samples

Novel poly (3, 4-ethylenedioxythiophene)/reduced graphene oxide incorporated with manganese oxide/iron oxide for supercapacitor device

A new composite namely PEDOT/RGO/MnO₂/Fe₂O₃ was successfully developed from mixed metal oxides (MnO₂ and Fe₂O₃) incorporated with poly(3,4-ethylenedioxythiophene) (PEDOT) and reduced graphene oxide (RGO). The surface morphology of the prepared composite revealed that MnO₂ and Fe₂O₃ particles were successfully coated on the wrinkles and curly like-sheets of PEDOT/RGO in order to prevent aggregation of RGO layers and the composite was able to retain 80% of its initial specific capacitance in 1 M KCl. The PEDOT/RGO/MnO₂/Fe₂O₃ composite with Mn:Fe molar ratio of 2:3 displayed the highest specific capacitance of 287 F/g indicating that Mn:Fe molar ratio gives significant effect on the super capacitive performance of the composite. The specific capacitance of PEDOT/RGO/MnO₂/Fe₂O₃ was higher than the composites with monometallic oxide i.e. PEDOT/RGO/MnO₂ and PEDOT/RGO/Fe₂O₃. The PEDOT/RGO/MnO₂/Fe₂O₃ composite also revealed the lowest charge transfer resistance that leads to the superior supercapacitive performance. The specific energy and specific power of PEDOT/RGO/MnO₂/Fe₂O₃ composite were 11 Wh/kg and 1900 W/kg at 4 A/g, respectively. The results showed that the PEDOT/RGO/MnO₂/Fe₂O₃ composite is a promising electrode material for high-performance supercapacitor

Detecting hydrogen using TiO2-B2O3 at different operating temperature

Performance of TiO2-B2O3 gas sensor that annealed using nitrogen at 650°C for 30 minutes was observed and analyzed. The sensing film of the gas sensor was prepared by mixing TiO2-B2O3 with an organic binder. The sensing film was characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The gas sensor was exposed to hydrogen at a concentration of 100-1000 ppm with operating temperatures of 100°C and 200°C. However, no response was detected for 100 ppm at 100°C. But, as the operating temperature was increased to 200°C, the gas sensor indicated a good response for 100 ppm of hydrogen. The gas sensor exhibited p-type response based on decreased current when exposed to hydrogen. The sensitivity of gas sensor was calculated at 1.00, 2.18 and 3.58 for 100 ppm, 500 ppm and 1000 ppm respectively, at an operating temperature of 200°C

Electropolymerization of poly(3,4-ethylenedioxythiophene) onto polyvinyl alcohol-graphene quantum dot-cobalt oxide nanofiber composite for high-performance supercapacitor

Fabrication of highly conductive nanofiber by coating polyvinyl alcohol-graphene quantum dot-cobalt oxide (PVA-GQD-Co3O4) nanofiber composite with a conductive material, poly(3,4-ethylenedioxythiophene) (PEDOT) for supercapacitor was successfully prepared via two-step technique i.e. electrospinning and electropolymerization. The prepared electrode materials were characterized using FTIR, Raman and XRD analysis to confirm the structure of the electrospun nanofiber composite. The presence of cauliflower-like structure studied by FESEM revealed that PEDOT was uniformly coated on PVA-GQD-Co3O4 electrospun nanofibers. The PVA-GQD-Co3O4/PEDOT nanofiber composite exhibited a specific capacitance of 361.97 F/g, low equivalent series resistance (ESR) and excellent stability with retention of 96% after 1000 cycles. The PVA-GQD-Co3O4/PEDOT nanofiber composite also demonstrated a high specific energy and excellent specific power ranged from 16.51 to 19.98 Wh/kg and 496.10–2396.99 W/kg, as the current density increased from 1.0 to 5.0 A/g

Carbon nanotubes reinforced aluminum matrix composites – a review of processing techniques

Carbon nanotube reinforced aluminium matrix composites (Al-CNTs) have been widely used in aerospace and automotive industries where high quality and strength is required. The enhanced mechanical properties of Al-CNTs are closely related to processing technique due to challenges within production of these composite materials. In the current review, solid state processing techniques used for synthesizing Al-CNTs have been reviewed to provide an insight into the features and capabilities of each technique regarding the incorporation of CNT reinforcements. To conclude, the mechanical performance of Al-CNT composites is mainly decided by the capability of each technique in the dispersion of CNTs within the aluminum matrix

Incorporation of zinc oxide into carbon nanotube/graphite nanofiber as high performance supercapacitor electrode

An efficient and simple hydrothermal method has been developed to prepare Carbon nanotube/Graphite nanofiber/Zinc Oxide (CNT/GNF/ZnO) ternary composites which are employed as supercapacitor materials. The electrochemical measurements reveal that the introduction of ZnO into CNT/GNF can enhance the specific capacitance value up to 306 Fg−1 at 10 mVs−1, with 99.4% capacity retention. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) characterizations reveal that the combination of nanometer-sized CNT/GNF and random distribution of impregnated ZnO can form a highly conductive network. The improved supercapacitance property of CNT/GNF/ZnO can be ascribed to the synergistic effect between double layer capacitance of CNT/GNF and the pseudocapacitance of ZnO

Influence of B2O3 addition on the properties of TiO2 thick film at various annealing temperatures for hydrogen sensing

To increase the adhesion of thick film on a substrate, boron oxide (B2O3) was added to titanium dioxide (TiO2), and the change in the morphology, crystallinity and band gap of TiO2 thick film was investigated. TiO2 and TiO2-B2O3 pastes were prepared and deposited on the microscopic glass using screen-printing technique and then annealed under air at different temperatures of 400°C, 450°C and 500°C for 30 min. The morphology, elemental composition, structure and absorption of the thick films were characterized using FESEM, EDX, XRD and UV–visible spectroscopy. The TiO2 and TiO2-B2O3 thick films were fabricated as gas sensors and exposed to 100–1000 ppm of hydrogen at an operating temperature of 300°C. The results revealed that the addition of B2O3 increased the crystallinity of anatase phases and rutile phases in TiO2 as annealing temperature increased. The TiO2-B2O3(T500) gas sensor exhibited the highest response to various concentrations of hydrogen (100–1000 ppm) at an operating temperature of 300°C

Effects of MWCNTs/graphene nanoflakes/MXene addition to TiO2 thick film on hydrogen gas sensing

Various doping materials, such as MWCNTs, graphene nanoflakes and MXene, have been doped into TiO2 and the hydrogen sensing properties investigated. Using a similar volume, MWCNTs (5 wt.%) and graphene nanoflakes (5 wt.%) and MXene (10 wt.%) were added to TiO2 and prepared in a paste form by mixing the sensing material with the organic binder. The sensing film was deposited on an alumina substrate using a screen-printing technique and annealed at 500 °C for 30 min in ambient air. The crystallinity of TiO2 and the doped material in the sensing film after the annealing treatment were verified using FESEM, EDX, XRD and Raman Spectroscopy. By depositing an interdigitated electrode at the bottom of the sensing film, the thick film gas sensors (TiO2/MWCNT, TiO2/Gr, TiO2/MXene) were exposed to 100–1000 ppm of hydrogen at an operating temperature of 100–250 °C. The responses showed that the addition of MWCNTs and MXene to TiO2 reduced the operating temperature of the TiO2 gas sensor from 150 °C to 100 °C, while the addition of graphene nanoflakes did not affect the operating temperature of the TiO2 gas sensor. The TiO2/MWCNT gas sensor showed linear sensitivity as hydrogen concentrations increased for operating temperatures of 100–250 °C. The optimal operating temperature for TiO2/MXene occurred at 100 °C, while the optimal operating temperature for the TiO2/Gr gas sensor occurred at 200 °C. The highest sensitivity for 100–500 ppm hydrogen was generated by the TiO2/MXene gas sensor, and for 600–1000 ppm hydrogen was generated by the TiO2/MWCNT gas sensor at an operating temperature of 250 °C. The TiO2/MWCNT gas sensor produced the highest sensitivity to hydrogen at the operating temperature of 250 °C with sensitivity values of approximately 6.36, 33.61, 67.64, 102.23 and 159.07 for 100, 300, 500, 700 ppm and 1000 ppm of hydrogen, respectively