Solid State Phenomena Vol. 302

Abstract: In this research, low carbon steel surface was modified using electrophoretic deposition (EPD) technique from a graphene oxide (GO) water suspension. The electrophoretic deposition (EPD) is the technique used for manipulation and deposition of nanomaterials. The GO coating was used as a layer to increase the hardness of low carbon steel. GO was successfully synthesized using the modified Hummers method. EPD technique was performed by applying voltage at 9 volts and the deposition time of 15 mins. The working distance between the cathode and anode was fixed at 15 mm. The GO film had been deposited by EPD technique where it was carburized at 900, 950, 1000 and 1050°C, for 60 mins. The microstructure of the carbide film was investigated using scanning electron microscopy (SEM). As the carburization temperature raised (1050°C), more volume carbon atoms reacted with iron atoms to form iron carbon (Fe₃C) layer on to the substrate surface. The carbide films are columnar crystal growth with a particle size of approximately 50 μm. The growth rate of the carbide films at 1050°C is about 8 µm/min. Energy dispersive X-ray spectrometer (EDS) was studied for chemical elements analysis. Fe, C and O elements were then detected. At carburization temperature of 1050°C, it showed that C element distribution is higher than others’ temperatures. Moreover, the hardness on the carbide films was investigated using a Vickers hardness tester under an applied load of 500 grams for 10 seconds. It was found that the hardness increased with the increasing carburization temperatures. The hardness of low carbon steel is 172.99 ± 2.28 HV. After the carburization processing via GO at temperature of 1050°C, the highest hardness of 821.42 ± 35.33 HV was obtained. It was observed that the mechanical properties of low carbon steel surface were found to be strongly influenced by the process of carburization temperature.

Abstract: To handle persistent toxic organic contaminants in water, advanced oxidation process (AOP) by titanium dioxide (TiO₂) and its composites has been extensively utilized. A smart combination of composite materials was synthesized to improve photocatalytic activity of TiO₂ via engineering effective charge transfer. In this study, synthesis of Ag/Graphite Oxide (GO)/TiO₂ was investigated. Degussa P25 TiO₂ (Rutile:Anatase of 85:15, 99.9%, 20nm) nanopowder was purchased. Graphite oxide was prepared using modified Hummer’s method. Photoreduction and ultrasonication were conducted to prepare Ag nanoparticles (AgNPs). XRD was used to confirm formation of Ag- GO- TiO₂, i.e., peaks of GO, AgNPs and phases of anatase and rutile of TiO₂ P25. Backscattered SEM was used to identify the AgNPs in different compositions of the AgNPs/GO/TiO₂ composites. TEM was used for high resolution images to observe sizes and shapes of nanomaterials involved. X-ray absorption near edge structure (XANES) spectra of the Ag L₃-edge were used to confirm zero-valence AgNPs. The best performed photocatalyst from this study was 5Ag0.5GOTiO₂ with 78.86 % degradation of RhB after 2 hours. The AgNPs were found to be spherical with sizes of around 2-10 nanometers and evenly distributed within the GO/TiO₂ matrix.

Abstract: Si and Mg are good candidates for anode lithium-ion batteries because Si and Mg have high theoretical capacity of 4200 mAh g^-1 and 994 mAh g^-1, respectively. However, these elements generate high-volume expansion during the charge-discharge process, which can cause the electrode to crack after being used for a few cycles. To solve this problem, the active materials are prepared in a nanosize and composited with a 2D-sheet of nitrogen-doped graphene, as the high mechanical stability and flexibility of nitrogen-doped graphene can support the volume expansion. Preparation of Si-Mg and nitrogen-doped graphene includes two steps. First, the reduction of Mg²⁺ ions with NaBH₄ in ethylene glycol solution and reflux at 350 - 400 °C for 3 hr and Si nanoparticles, which were prepared by magnesiothermic reduction, was conducted. Second, Si and Mg nanoparticles and nitrogen-doped graphene were mixed in ethylene glycol solution and then collected by centrifugation. The obtained Si-Mg nanocomposite particles were well distributed on the nitrogen-doped graphene. The phases were indexed as Si, Mg and nitrogen-doped graphene. The particle sizes were small (approx 21 - 56 nm) with good dispersion on the nitrogen-doped graphene which observed by transmission electron microscopy and scanning electron microscopy techniques. Energy dispersive spectrometry results confirmed the existence of Si-Mg. Therefore, Si-Mg and nitrogen-doped graphene nanocomposite materials are expected to contain promising properties that can be used as high-performance anode materials in lithium-ion batteries in the future.

Abstract: In this study, nitrogen-doped graphene (NrGO)/ titanium dioxide (B) (TiO₂(B))/ silicon composites were synthesized by dispersion method. Weight ratios of NrGO:TiO₂(B):Si were varied as 9:1:0, 8:2:0, 7:1:2 and 6:2:2. NrGO was prepared from graphite by the Modified Hummers method, followed by heat treatment under nitrogen atmosphere and N-added by annealing with melamine. TiO₂(B) was prepared by hydrothermal method and its phase was confirmed by X-Ray powder diffraction pattern (XRD), transmission electron microscopy (TEM) and electron diffraction pattern. Silicon was synthesized from bamboo leaves by combustion followed by magnesiothermic reduction process. The results from XRD could confirm components of the composites and the unchanged phase of TiO₂(B). From scanning electron microscopy (SEM) images of the composites, together with energy dispersive spectroscopy (EDS) data, silicon particles were distributed on the surface of NrGO, and TiO₂(B) nanorods which are between 0.5-5 µm in length were distributed on the surface and spaces between layers of NrGO, and NrGO/TiO₂ 8:2 had the most thoroughly distribution of particles.

Abstract: Platinum (Pt) is widely used as anode catalyst for direct ethanol fuel cell (DEFC) but toxic CO gas was produced in the system. Pt bimetallic catalysts can increase the reaction rate, current density and reduce CO gas production. However, some bimetallic catalysts are still expensive and give the low reaction rate. Trimetallic catalysts on carbon supporter were represented instead due to their better catalytic activities, long life time of operation and higher current density. In this study, we synthesized trimetallic alloy on N-doped reduced graphene oxide (NrGO) catalysts using as DEFC anode. The percentage of metals composition in the synthesized catalysts was varied. NrGO was prepared by Modified Hummers Method, then reduced by annealing under Nitrogen gas atmosphere and N-added by annealing with melamine. The preparation method for trimetallic alloy catalysts on NrGO was NaBH₄ reduction. The X-ray diffraction (XRD) patterns displayed their alloy phase of PtMRu (M = Au, Sn) which compose of Pt main structure and NrGO supporter. Scanning Electron Microscopy (SEM) images showed the dispersion of alloy metal particles on NrGO surface. The composition of catalysts could be confirmed by Energy dispersive spectroscopy (EDS) data and the phase of alloy particles were verified by electron diffraction (SAD) patterns. Transmission Electron Microscopy (TEM) images showed the particle size of PtAuRu and PtSnRu in various specific percentage on NrGO. The approximate particle size for 10Pt2Au8Ru = 4.88±1.02 nm, 10Pt5Au5Ru = 58.45±42.16 nm, 10Pt8Au2Ru = 11.05±2.29 nm, 10Pt2Sn8Ru = 3.31±1.44 nm, 10Pt5Sn5Ru = 3.50±0.73 nm and 10Pt8Sn2Ru = 4.09±0.97 nm. Catalytic activity of these materials related to their particle size.

Abstract: Herein, we report a facile synthesis of zinc oxide-reduced graphene oxide (ZnO-rGO) hybrid materials by two-step method. Firstly, rGO was synthesized by using graphite powder mixed with sodium nitrate, sulfuric acid and potassium permanganate via Hummers method. Synthesized rGO were dispersed in ethanol by ultra-sonication for a designated time period. Then, zinc oxide (ZnO) powder was added into rGO-ethanol solution and transferred into Teflon-lined stainless steel autoclave. The ZnO-rGO was produced by hydrothermal method at 180 °C for 120 and 180 min (here after referred to as ZnO(120)-rGO and ZnO(180)-rGO, respectively). The morphological and crystalline structures of synthesized rGO and ZnO-rGO were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Synthesized ZnO-rGO was exposed to 100 parts per million (ppm) nitrogen dioxide (NO₂) gas at room temperature, 50 °C and 75 °C for testing its sensing performance. The results show that ZnO(180)-rGO hybrid materials exhibit high response to NO₂ gas at 50 °C and 75 °C. The electrical resistance of ZnO-rGO sensors decreased when the sensors responded to NO₂ gas, indicating a p-type behavior. Moreover, the ZnO-rGO hybrid materials can detect 100 ppm NO₂ gas with an operating temperature limit at 50 °C. The results imply that synthesized ZnO-rGO hybrid materials could be used as gas sensing device for ppm-level NO₂ detection at low temperature and consume low power.

Abstract: Nowadays, there is an increasing of the demanding in high energy density lithium-ion batteries (LIBs) due to the growing of energy storage needs for electronic vehicles and portable devices. Silicon (Si) and Tin (Sn) are the promising anode materials for LIBs due to their high theoretical capacity of 4200 mAh/g and 994 mAh/g. Moreover, Si can be derived from rice husk which is the main agricultural product in Thailand. However, the using of Si and Sn encounters with the huge volume expansion during lithiation and delithiation process. To alleviate this problem, Nitrogen-doped graphene (NrGO), carbon supporter, is used as composite with these metals to buffer the volume change and increase the electrical conductivity of composites. This work aims to synthesis Si/NrGO and SiSn/NrGO nanocomposites and Si used in these composites is derived from rice husk. All products were characterized by X-rays diffraction (XRD), Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. XRD results showed that the composites contained phases of Si, Sn and carbon. The electron microscopy techniques were the main part to clarify the morphology and distribution of Si and Sn particles on NrGO. SEM and TEM results confirm that there were small sized particles of Si and Sn dispersed and covered on NrGO surface. Furthermore, the electrochemical properties of prepared composites were measured to confirm their efficiency as anode materials in lithium-ion batteries by coin cell assembly. The composite with 10 percent Si and 10 percent Sn on NrGO could deliver a high capacity around 480 mAh/g over 100 cycles and expected to use as anode materials in the next generation lithium-ion batteries.

Abstract: Sugarcane leaves (SLs) are a bio-waste from sugar production industry. To explore the value-added SLs, the SLs were used raw materials of activated carbons (ACs) by steam activation and their electrochemial properties were investigated for supercapacitor applications. The synthesis of ACs from the SLs consisted of two steps; carbonization at 500oC and steam activation. The synthesis condition was optimized by varying activation temperature (800 and 850oC) The porous structures were thoroughly formed on the surface after steam activation and the surface areas were reached to 630 and 639 m² g^-1 at the activation temperature of 800 and 850oC, respectively. The SLs-derived ACs activated at 800oC assembled in coin cell using organic electrolyte showed the highest specific capacitance of approximately 16 F g^-1 with a capacitance retention of 62% when the current density increased to 1.5 A g^-1. Even though there is a room to improve the electrochemical properties such as optimization of porosity and removal of inorganic component, the SLs show a potential use as raw materials of ACs for supercapacitor applications.

Abstract: Carbon nanotubes (CNTs) are considered as the most promising materials to solve the electromagnetic interference (EMI) issue. Various forms of CNTs including CNTs/polymer composites, metal nanoparticles-decorated CNTs and freestanding CNT buckypapers (CNT BPs) have been proposed to enhance shielding effectiveness. In this study, the synergistic effect of nickel nanoparticles (NPs) and relatively short CNTs for the enhancement of microwave shielding properties was investigated. CNT BPs were prepared by vacuum filtration of well-dispersed multi-walled CNTs and subsequently nickel was decorated on the CNT BPs (Ni/CNT) by pulsed DC sputtering technique with different deposition times of 0, 5, 10 and 15 min (hereinafter referred to as CNi0, CNi05, CNi10 and CNi15, respectively). The diameter of Ni/CNT increased from 8.74±0.53 to 72.5±3.2 nm and the conductivity improved from 9.57±0.87 to 12.57±0.59 S/cm when the nickel deposition time was 15 min. Nickel NPs were the mixed phases of nickel and nickel oxide with a dominant nickel phase. The shielding effectiveness at the frequency of 9.5 GHz achieved to -34.1 dB for CNi15. The enhancement of shielding effectiveness of CNi15 is attributed to the synergistic effect of CNTs and nickel NPs on wave dissipation