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Rekha Dom,Pramod H. Borse,Kyong-Soo Hong,Seyong Choi,Byeong Seob Lee,Myoung Gyu Ha,Jong Pil Kim,Euh Duck Jeong,Hyun Gyu Kim 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.9
Magnesium ferrite (MgFe2O4) exhibiting a spinel phase was synthesized by using the polymerized complex and the solid-state reaction methods, and its physico-chemical properties were studied to explore the water-splitting under visible light photons. The study revealed the potential for using MgFe2O4 particles for photo-catalytic application. The structural study provided information on ferrite nano-crystallites fabricated by using the polymer complex method. The morphological studies demonstrated that, in contrast to the solid-state reaction method, a homogenous, monodispersed ferrite photocatalyst could be formed by using the polymerized complex method. The optical study revealed a larger visible-light absorption capability for the nanosized MgFe2O4 photocatalysts prepared by using the polymer complex methods, and indicated a red-shift of the bandgap by 0.06 eV as compared to the bandgap of the bulk. These nanocrystallites were highly photoactive with respect to the photodegradation and photocatalytic hydrogen evolution applications. The electrochemical analysis showed that they exhibited favorable bandedge positions suitable for photocatalytic H2 evolution. Thus, nanocrystalline MgFe2O4 is an active visible-light photocatalyst, that might be useful for the decomposition of water.
Study on NOx reduction capacity of catalytic coated cordierite monolith
Rekha Durairaj,Neelakrishnan Subramanyan,Divakar Duraiswamy 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.6
Legislation world-wide imposes stringent emission norms, particularly EURO V and beyond. In this regard, extensive research is being conducted for improving the existing filter design, material properties and developing alternative design, materials, testing procedures for more sensitive to reduce NOX values. Cordierite ceramics are having good chemical and electrical properties like high thermal resistance, low dielectric constant, low thermal expansion coefficient, and high chemical and mechanical stability, which makes it for many industrial applications like manufacturing of the thermal insulation materials, optoelectronic devices, plasma display panels, solar panels, catalytic convertors etc. In this work, a pair of cordierite monolith with catalyst coating to NOx storage and reduction was developed. The effectiveness of the catalysis was verified with engine exhaust gas analyser. The testing was carried out with diesel as fuel in a Kirloskar engine with Non-filter, NSR, and combined NSR-SCR system. The investigation was done for five trials with different emission parameters and analysed.
Synthesis of SrFe12O19 and Sr7Fe10O22 systems for visible light photocatalytic studies
Rekha Dom 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.4
Solid state synthesis of two Sr-Fe-O systems viz. Sr7Fe10O22 and SrFe12O19 was attempted and they were investigated for their photocatalytic properties. Although, both the systems exhibited good cystallinity and optical properties, only Sr7Fe10O22 was found to be active for the photocatalytic decomposition of iso-propanol under visible light. It also yielded a significant quantum yield (~1.7%) for photo-reduction of water under visible light irradiation, much better than titanium oxy-nitride samples. The inactiveness of SrFe12O19 was due to its unsuitable band energetics. The Sr7Fe10O22 acted more efficiently than TiO2-xNx due to its suitable band positions and high visible light photon absorptivity.
Rekha, Dasari,Kumar, Jengiti. Dilip,Jayaraj, Bellum,Lingappa, Y.,Chiranjeevi, Pattium Korean Chemical Society 2007 Bulletin of the Korean Chemical Society Vol.28 No.3
A micro organism Agrobacterium tumifacient as an immobilized cell on a solid support was presented as a new biosorbent in a simple and sensitive spectrophotometry determination of Ni(II) in various samples using 4-hydroxy benzaldehyde-4-bromophenyl hydrazone as a color developing agent (λmax 497 nm) at pH 4.0 ± 0.2. Beer's law was obeyed over the range of 0.01-0.1 μg L-1. The molar absorptivity and Sandell's sensitivity were 1.285 × 105 L mol-1cm-1 and 0.007245 μg cm-2 respectively. Under these conditions, the preconcentration factor obtained was 82, and the detection limit achieved was 0.05 μg L-1. The detailed study of various interfering ions made the method more sensitive and selective. The recovery of Ni(II) from various samples range from 97.75 to 99.35%. The present method was successfully applied for the determination of Ni(II) in spiked, natural water and alloy samples. The proposed method was compared with reported methods in terms of Student's ‘t'-test and Variance ratio ‘f'-test which indicates that there is no significant difference between proposed and literature method at 95% confidence level.
Design and Analysis of a Frequency Reconfigurable Penta-Band Antenna for WLAN and 5G Applications
Rekha Shanmugam 한국전자파학회JEES 2021 Journal of Electromagnetic Engineering and Science Vol.21 No.3
This paper presents a discussion on a low-profile, frequency-reconfigurable penta-band antenna. This antenna consists of two asymmetric L-shaped rectangular patches electrically connected by a single PIN diode. The proposed antenna operates at five frequency bands depending upon the switching states of the PIN diode. It operates at 2.4 ㎓ (WLAN) and 5.3 ㎓ (5G) during forward bias of the diode, 3.3 ㎓ (5G) and 5.9 ㎓ (WLAN) during reverse bias of the diode and 4 ㎓ during zero bias condition providing a wide bandwidth (3.6–4.8 ㎓) at this state. The antenna has voltage standing wave ratio (VSWR) ranges from 1 to 2, gain value ranges from 2.6 to 5.0 ㏈i, and a maximum radiation efficiency of 85%. This antenna can be integrated with modern devices such as smart phones, laptops, and other handheld devices due to its simplistic geometry. A prototype of the model is fabricated, and the results are validated.