Yoseb Song

Room-Temperature H2 Gas Sensing Characterization of Graphene-Doped Porous Silicon via a Facile Solution Dropping Method

In this study, a graphene-doped porous silicon (G-doped/p-Si) substrate for low ppm H2 gas detection by an inexpensive synthesis route was proposed as a potential noble graphene-based gas sensor material, and to understand the sensing mechanism. The G-doped/p-Si gas sensor was synthesized by a simple capillary force-assisted solution dropping method on p-Si substrates, whose porosity was generated through an electrochemical etching process. G-doped/p-Si was fabricated with various graphene concentrations and exploited as a H2 sensor that was operated at room temperature. The sensing mechanism of the sensor with/without graphene decoration on p-Si was proposed to elucidate the synergetic gas sensing effect that is generated from the interface between the graphene and p-type silicon.

A noble gas sensor platform: linear dense assemblies of single-walled carbon nanotubes (LACNTs) in a multi-layered ceramic/metal electrode system (MLES)

Monodispersed Pt nanocatalyst-doped and undoped assemblies of single-walled carbon nanotubes (SWCNTs) were aligned with high anisotropy on a multi-layered ceramic/metal electrode system (MLES), which was used as a cheap and cost-effective electrode system, by dielectrophoretic orientation to form linear dense assemblies of SWCNTs (LACNTs). It is envisaged that they can be used as a potentially inexpensive platform for multi-gas sensing nano-devices. To form homogeneously dispersed Pt nanocatalysts (NCs), an aqueous chloroplatinic acid solution (H2PtCl6) was deposited on the surface of acid-treated SWCNTs. This was followed by alignment under the application of alternative currents ranging from 5 kHz to 50 MHz to create electrically conducting LACNT bundles on the MLES platform and reduction under hydrogen plasma. The analysis showed that the Pt nanocatalysts (2 nmav, deviation: ±1 nm) are monodispersed on the SWCNTs, which contributed to a noticeable enhancement in the gas sensing properties towards H2, NO2, H2S and NH3 gases. In addition, the principal component analysis results showed fairly good discrimination of the gases by employing a sensor array composed of Pt/LACNTs and SWCNTs, and the hydrogen sensing performance was high in terms of sensitivity compared to other literature studies. This gas sensing device based on an MLES may pave the way for extended applications of new multi-gas sensing devices as a low-cost and life-long gas sensing platform.

Ultrasensitive detection of low-ppm H2S gases based on palladium-doped porous silicon sensors

In this study, the sensing properties of palladium-doped porous silicon (Pd/p-Si) substrates for low-ppm level detection of toxic H2S gas are investigated. A Si substrate with dead-end pores ranging from nano- to macroscale was generated by a combined process of metal-assisted chemical etching (MacE) and electrochemical etching with tuned reaction time, in which nano-Pd catalysts were decorated by E-beam sputtering deposition. The sensing properties of the Pd/p-Si were enhanced as the thickness of the substrate layer increased; along with the resulting variation in surface area, this resulted in superior H2S sensing performances in the low-ppm range (less than 3 ppm), with a detection limit of 300 ppb (sensitivity 30%) at room temperature. Furthermore, the sensor displayed excellent selectivity toward the hazardous H2S molecules in comparison with various other reducing gases, including NO2, CO2, NH3, and H2, showing its potential for application in workplaces or environments affected by other toxic gases. The enhancement in sensing performance was possibly due to the increased dispersion and surface area of Pd nano-catalysts, which led to an increase in chemisorption sites of adsorbate molecules.

A Novel Synthetic Method for N Doped TiO2 Nanoparticles Through Plasma-Assisted Electrolysis and Photocatalytic Activity in the Visible Region

Nitrogen doped TiO2 (N-TiO2) nanoparticles were synthesized via a novel plasma enhanced electrolysis method using bulk titanium (Ti) as a source material and nitric acid as the nitrogen dopant. This method possesses remarkable merits with regard to the direct-metal synthesis of nanoparticles with its one-step process, eco-friendliness, and its ability to be mass produced. The nanoparticles were synthesized from bulk Ti metal and dipped in 5–15 mmol of a nitric acid electrolyte under the application of AC 500 V, the minimum range of voltage to generate plasma. By controlling the electrolyte concentration, the nanoparticle size distribution could be tuned between 12.1 and 24.7 nm using repulsion forces via variations in pH. The prepared N-TiO2 nanoparticles were calcined at between 100 and 300°C to determine their photocatalytic efficiency within the visible-light region, which depended on their crystal structure and N doping content. Analysis showed that the temperature treatment yielded an anatase TiO2 crystalline structure when the N doping content was varied from 0.4 to 0.54 at.%. In particular, the 0.4 at.% N doped TiO2 catalyst exhibited the highest catalytic performance with quadruple efficiency compared to the P-25 standard TiO2 nanoparticles, which featured a 91% degradation of methyl orange organic dye within 300 min. This solid-liquid reaction based on plasma enhanced electrolysis could open new pathways with regard to high purity mass producible ceramic nanoparticles with advanced properties.

AB0712 Analysis of Different Manifestations in The Cervical Spine Involvement of Longstanding Ankylosing Spondylitis: Atlantoaxial Ankylosis (AAA) and Atlantoaxial Subluxation (AAS)

Background Atlantoaxial ankylosis (AAA) is another late manifestation of cervical spine involvement in longstanding AS and suggest that higher cervical mSASSS is more related with the development of AAA than atlantoaxial subluxation (AAS). AAA does not cause as much cervical instability as AAS. Objectives To analyze radiologic and clinical findings of atlantoaxial ankylosis and atlantoaxial subluxation in ankylosing spondylitis Methods A total of 150 AS patients (145 men, 5 women, mean age, 36.8 years) who had AAA (60 men and 2 women, mean age, 60 years) or AAS (85 men and 3 women, mean age, 34 years) were randomly gathered and underwent at least two plain radiographs of lateral cervical spine on flexion. The atlantodental interval more than 3mm was considered as AAS. Loss of atlantodental interval was considered as AAA. The plain radiographs of lateral cervical spine were independently analyzed by two radiologists. Interobserver reliability between reader 1 and 2 in scoring mSASSS in AS was analyzed. We compared the results of mSASSS between AAS and AAA to see if it was related to severity or duration of the disease. Results The mean mSASSS of AS patients with AAA and AAS were 40.1 and 16.5 respectively and the mean duration of AS patients with AAA and AAS were 19.3 and 13.7 years each. There was a significantly (p<0.05) higher total mSASSS, especially cervical spine mSASSS, for AS patients with AAA than those with AAS after mSASSS was corrected for age and duration. But, disease duration was not significantly related with the development of AAA compared with that of AAS. Conclusions We found that it has incidence as high as AAS and both are similar in that they are late presentation of AS and occur in patient with long duration. We found that AAA is another manifestation of cervical spine involvement in longstanding AS and is related to severity of the AS reflected by higher cervical mSASSS. References Martel W. The occipito-atlanto-axial joints in rheumatoid arthritis and ankylosing spondylitis. Am J Roentgenol Radium Ther Nucl Med 1961;86:223–240 Meijers KA, van Voss SF, Francois RJ. Radiological changes in the cervical spine in ankylosing spondylitis. Ann Rheum Dis 1968;27:333–338 Lee HS, Kim TH, Yun HR, Park YW, Jung SS, Bae SC, et al. Radiologic changes of cervical spine in ankylosing spondylitis. Clin Rheumatol 2001;20:262–266 Laiho K, Kauppi M. The cervical spine in patients with ankylosing spondylitis. Clin Exp Rheumatol 2002;20:738 n> Disclosure of Interest None declared