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Subject: search.filters.subject.Electrochemical oxidation

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    Role of inorganic anions on the performance of landfill leachate treatment by electrochemical oxidation using graphite/PbO2 electrode
    (Elsevier, 2020-02) Mandal, Pubali
    The influences of sulfate, chloride, nitrate, and bicarbonate ions on the electrochemical treatment performances of landfill leachate have been investigated. The concentrations of SO42−, Cl−, NO3− ions, and bicarbonate alkalinity of landfill leachate were 252 mg L-1, 1244 ± 22.3 mg L-1, 12 mg L-1, and 1750 ± 40.8 mg L-1 as CaCO3 without any external salt addition. The concentrations of anions were analyzed after 2 h of electrochemical oxidation to understand any conversion of externally added anions. Chemical oxygen demand (COD), dissolved organic carbon (DOC), and ammonia-nitrogen removal efficiencies after 2 h of electrolysis were 35.1 ± 2.3 %, 25.6 ± 2.9 %, and 97.6 ± 0.7 % respectively. Although no effect was observed for COD and DOC removal, increasing sulfate ion adversely affected NH3-N removal efficiency; the removal percentage decreased to 87.7 ± 0.5 % for 6082 mg L-1 of SO42− containing leachate. Addition of chloride improved the overall system performance. Obtained COD and DOC removal efficiencies were 67.2 ± 1.5 % and 55.8 ± 2.1 % for Cl− concentration of 4361 mg L-1 in leachate. Very low NH3-N removal (60 ± 2.1 %) for 1483 mg L-1 of nitrate containing leachate was obtained in this study due to the regeneration of ammonia by cathodic reduction of nitrate. Nitrate formation was observed as part of reactions for ammonia removal; for instance, the nitrate concentration increased from 12 mg L-1 to 39.3 ± 4 mg L-1 after electrolysis. For the leachate treatment containing 6000 mg L-1 of externally added HCO3−, the COD and DOC removal efficiencies decreased to 19.6 ± 0.6 % and 17.8 ± 1.1 %, but the more adverse effect was observed for NH3-N removal efficiency which was only 7.4 ± 1.8 %.
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    A novel approach towards multivariate optimization of graphite/PbO2 anode synthesis conditions: Insight into its enhanced oxidation ability and physicochemical characteristics
    (Elsevier, 2018-08) Mandal, Pubali
    Electrochemical oxidation has drawn great interest for its potential application in degrading persistent organic pollutants (POPs) through electrogenerated hydroxyl radical at the surface of anode. This study aims at the preparation of an inexpensive graphite/PbO2 anode. For enhancing oxidation performance, preparation process parameters viz. Pb(NO3)2 concentration, potential, and time of electrodeposition of a graphite/PbO2 anode, electrodeposited from acidic electrolyte bath, were optimized targeting a POP, 2,4-dinitrophenol removal. The changes in morphological properties of the developed oxide films were analyzed using scanning electron microscopy (SEM) which manifested significant impacts of selected anode preparation process parameters. Furthermore, PbO2 film prepared at optimum conditions were characterized using SEM, atomic force microscopy (AFM), energy dispersive X-ray spectroscope (ESD) elemental mapping, and X-ray diffraction (XRD) for thorough investigation of crystal structures, elemental distribution over surface, and phase of PbO2. Angular structures in both SEM and AFM analysis and appearance of β-PbO2 characteristic peaks in XRD analysis confirmed formation of electrocatalytically active phase of PbO2. For further enhancing the oxidation ability, influencing experimental parameters viz. current intensity, pH, and NaCl concentration were optimized. After 2 h of electrolysis at optimum experimental conditions, COD and total organic carbon removal efficiency of 93.6 ± 0.63% and 71.7 ± 1.52% were obtained respectively.
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    Studies on Hydrogen Sensing by Anodized Nanoporous Titania Thin Film Using Soft Drink Electrolyte
    (SEI Publisher, 2013-04) Hazra, Arnab
    Nano-porous titanium dioxide (TiO2) thin films were developed by UV assisted potentiostatic anodization of 99.7% pure titanium foil. The internationally popular soft drink 􀈁Coca-Cola􀈂 was used as the electrolyte in this anodization process. Electrochemical oxidation and photoetching were carried out at room temperature and at 10 V potentiostatic bias without and with 400 W UV light illumination respectively. The prepared TiO2 thin film was annealed at 150ᴼC for 3 hours. The surface of the prepared TiO2 film was characterized with Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) to confirm the crystallinity, porous structure and surface roughness. The Optical study revealed a band gap of 3.898 eV. Hot probe method exhibited n-type conductivity of the electrochemically grown TiO2 thin films. Palladium-Silver alloy (Pd-Ag) contacts were deposited laterally on the oxide surface as catalytic metal electrodes to fabricate a planar sensor configuration. The hydrogen sensor study was carried out at different temperatures (100 to 200ᴼC) and in different hydrogen gas concentrations (1000 to 10000 ppm). Nanocrystalline and nano-porous TiO2 sensor was promising to sense hydrogen in air ambient with relatively fast response and recovery times (e.g. ~2.9 s and ~75 s) at the optimum temperature of 1500C. Brief mechanism behind the sensing performance has been also discussed.
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    Anodically grown nanocrystalline titania thin film for hydrogen gas sensors – a comparative study of planar and MAIM configuration
    (Elsevier, 2013-11) Hazra, Arnab
    Nanocrystalline titanium dioxide (TiO2) thin film was grown by UV assisted anodization of 0.25 mm thick titanium foil (99.7% pure). Room temperature electrochemical oxidation and photo etching were carried out in 0.1 M dilute H2SO4 electrolyte and at 10 V potentiostatic bias without and with 400 W UV light illumination respectively. While 2D-XRD confirmed the anatase crystalline feature AFM study revealed a rough morphology. A band gap of 3.35 eV was determined by optical study. Palladium (Pd) contacts were deposited laterally on the oxide surface as catalytic metal electrodes to fabricate a planar sensor configuration and a vertical metal-active insulator-metal (MAIM) structure was configured using palladium and titanium-silver alloy as top and bottom electrode respectively. The hydrogen sensor study was carried out at different temperatures (100–175 °C) and with different gas concentrations (0.1–1%) for both planar and MAIM structures in nitrogen as well as in air. A detailed hydrogen gas response characteristic was studied for these two types of sensor structures. Both the sensor structures were found suitable to sense 1% hydrogen in nitrogen ambient and at the optimum temperature of 150 °C with a pretty fast response time of 1.1 s for planar sensor and 1.4 s for MAIM sensor. However, the corresponding recovery time of 102.5 s and 92.3 s were quite long. The subsequent studies in air in the identical conditions recorded the response time and recovery time of 0.49 s and 28.8 s for planar and 1.5 s and 44.6 s for MAIM configurations respectively. The selectivity and the long term stability were investigated. A comparative sensor study with the two devices was performed and the results have been explained.