• Ch Subrahmanyam

      Articles written in Journal of Chemical Sciences

    • Nonthermal plasma assisted photocatalytic oxidation of dilute benzene

      J Karuppiah E Linga Reddy L Sivachandiran R Karvembu Ch Subrahmanyam

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      Oxidative decomposition of low concentrations (50-1000 ppm) of diluted benzene in air was carried out in a nonthermal plasma (NTP) dielectric barrier discharge (DBD) reactor with the inner electrode made up of stainless steel fibres (SMF) modified with transition metal oxides in such a way to integrate the catalyst in discharge zone. Typical results indicate the better performance of MnO$_x$ and TiO2/MnO$_x$ modified systems, which may be attributed to the in situ decomposition of ozone on the surface of MnO$_x$ that may lead to the formation of atomic oxygen; whereas ultraviolet light induced photocatalytic oxidation may be taking place with TiO2 modified systems. Water vapour improved the selectivity to total oxidation.

    • Catalytic non-thermal plasma reactor for the decomposition of a mixture of volatile organic compounds

      B Rama Raju E Linga Reddy J Karuppiah P Manoj Kumar Reddy Ch Subrahmanyam

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      The decomposition of mixture of selected volatile organic compounds (VOCs) has been studied in a catalytic non-thermal plasma dielectric barrier discharge reactor. The VOCs mixture consisting n-hexane, cyclo-hexane and 𝑝-xylene was chosen for the present study. The decomposition characteristics of mixture of VOCs by the DBD reactor with inner electrode modified with metal oxides of Mn and Co was studied. The results indicated that the order of the removal efficiency of VOCs followed as 𝑝-xylene > cyclo-hexane > 𝑛-hexane. Among the catalytic study, MnOx/SMF (manganese oxide on sintered metal fibres electrode) shows better performance, probably due to the formation of active oxygen species by in situ decomposition of ozone on the catalyst surface. Water vapour further enhanced the performance due to the in situ formation of OH radicals.

    • Catalytic decomposition of N₂O over CeO₂ supported Co₃O₄ catalysts


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      This work was aimed to design efficient catalysts for N₂O decomposition at low temperatures. Cobalt oxide (Co₃O₄) was prepared by hydrothermal, precipitation and combustion methods and tested for N₂O decomposition. It was found that the catalysts prepared by solution combustion synthesis were most active for this reaction. Subsequently, a series of ceria (CeO₂) supported Co₃O₄ catalysts (xCeCo) were prepared by solution combustion method and used them for N₂O decomposition. All the catalysts were characterized by analytical methods like XRD, TEM, BET, XPS, UV-Vis, Raman and H2-TPR. It was found that 10 and 20 wt..% loading of CeO₂ on Co₃O₄ promoted the activity of Co₃O₄ towards N₂O decomposition, whereas, higher loading of CeO₂ reduced the activity. Typical results indicated that addition of CeO₂ increases the surface area of Co₃O₄ , and improves the reduction of Co³⁺ to Co²⁺ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step for the N₂O decomposition over Co₃O₄ spinel catalysts. Optimal CeO₂ loading can increase both dispersion and surface area of Co₃O₄ catalysts and weaken the Co–O bond strength to promote N₂O decomposition.

    • Organic transformations catalyzed by palladium nanoparticles on carbon nanomaterials


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      An efficient C–C bond coupling reactions (Suzuki–Miyaura and Glaser) catalyzed by PdO/GO nano-catalyst is presented. In addition, PdO/MWCNT nano-catalyst-mediated domino one-pot synthesis of 2-alkyl/2-aryl benzofurans has been accomplished from 2-iodophenols and terminal alkynes. The formationof benzofurans proceeds through intermolecular Sonogashira reaction followed by intramolecular nucleophilic addition of internal hydroxyl group onto the acetylenic bond. The catalyst PdO/GO has been reused successfully,with nearly no loss of activity up to 5 cycles.

    • Construction of metal oxide decorated g-C3N3 materials with enhanced photocatalytic performance under visible light irradiation


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      Herein we report the synthesis and photocatalytic evaluation of heterostructure WO3/g-C3N4 (WMCN) and CeO2/g-C3N4(CMCN) materials for RhB degradation and photoelectrochemical studies. These materials were synthesized by varying the dosages of WO3 and CeO2 on g-C3N4 individually and were characterized with state-of-the-art techniques like XRD, BET surface area, FT-IR, UV–Vis DRS, TGA, SEM, TEM and XPS. A collection of combined structural and morphological studies manifested the formation of bare g-C3N4, WO3, CeO2, WO3/g-C3N4 and CeO2/g-C3N4 materials. From the degradation results, we found that the materialwith 10 wt% WO3 and 15 wt% CeO2 content on g-C3N4 showed the highest visible light activity. The first order rate constant for the photodegradation performance of WMCN10 and CMCN15 is found to be 5.5 and 2.5times, respectively, greater than that of g-C3N4. Photoelectrochemical studies were also carried out on the above materials. Interestingly, the photocurrent density of WMCN10 photoanode achieved 1.45 mA cm − 2 at 1.23 V (vs.) RHE and this is much larger than all the prepared materials. This enhanced photoactivity of WMCN10 is mainly due to the cooperative synergy of WO3 with g-C3N4, which enhanced the visible light absorption and suppresses the electron–hole recombination

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