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Decadal Pattern of Spatial and Temporal Variability of Nitrate Along the Southwest Bay of Bengal Using Remote Sensing Techniques
摘要： The seasonal and interannual variability of sea surface nitrate was studied in the southwest Bay of Bengal. MODIS-Aqua-derived SST and chlorophyll data are used to develop seasonal nitrate maps for the period of 2002–2017. Seasonally developed nitrate images were validated for the year 2013 with corresponding in situ datasets, and the validation of this nitrate model provides the statistically signi?cant relationship for postmonsoon (R2 = 0.612), summer (R2 = 0.535), premonsoon (R2 = 0.554) and monsoon (R2 = 0.533) seasons. The seasonal SST, chlorophyll a, nitrate and wind speed images depict the clear seasonal pattern between the seasons without any abrupt increase or decrease in trend observed during all these years. This was also con?rmed by the Kruskal–Wallis one-way analysis of variance on ranks with a statistical signi?cance (P = \ 0.001) between the seasons. From the results, this is a clear indication that the nitrate concentration is under the natural control without any anthropogenic contaminations.
关键词： Paraboloid,Nitrate,Seasons,MODIS,Chlorophyll,SST
更新于2025-09-10 09:29:36
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Nitrate Removal via Formate Radical-induced Photochemical Process
摘要： Removal of excess nitrate is critical to balance the nitrogen cycle in aquatic systems. This study investigated a novel denitrification process by tailoring photochemistry of nitrate with formate. Under UV light irradiation, short-lived radicals (i.e., HO·, NO2· and CO3·-) generated from nitrate photolysis partially oxidized formate to highly reductive formate radical (CO2·-). CO2·- further reduced nitrogen intermediates generated during photochemical denitrification (mainly NO·, HNO, and N2O) to gas-phase nitrogen (i.e., N2O and N2). The degradation kinetics of total dissolved nitrogen was mainly controlled by the photolysis rates of nitrate and nitrite. The distribution of final products was controlled by the reaction between CO2·- and N2O. To achieve a simultaneous and complete removal of dissolved nitrogen (i.e., nitrate, nitrite, and ammonia) and organic carbon, the formate-to-nitrate stoichiometry was determined as 3.1 ± 0.2 at neutral pH in deionized water. Solution pH impacted the removal rates of nitrate and nitrite, but not that of total dissolved nitrogen or formate. The presence of dissolved organic matter at levels similar to groundwater had a negligible impact on the photochemical denitrification process. A high denitrification efficiency was also achieved in a synthetic groundwater matrix. Outcome from this study provides a potential denitrification technology for decentralized water treatment and reuse facilities to abate nitrate in local water resources.
关键词： denitrification,water treatment,nitrate removal,photochemical process,formate radical
更新于2025-09-10 09:29:36
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Selective reduction of nitrate to nitrogen gas by novel Cu2O-Cu0@Fe0 composite combined with HCOOH under UV radiation
摘要： The nitrate reduction by Fe-based materials has been extensively studied, however, the selectivity of nitrate reduction to nitrogen gas is very low, which hinders the application of this technology. In this study, a novel Cu2O-Cu0@Fe0 composite was synthesized and a strategy of Cu2O-Cu0@Fe0 composite combined with HCOOH under UV radiation as reducers for the nitrate reduction was established to improve the selective reduction of nitrate (NO3?) to nitrogen gas (N2). The Cu2O-Cu0@Fe0 composite was synthesized by simple chemical replacement and O2 oxidation process and characterized by SEM, EDS, XRD and XPS. The nitrate removal efficiency of 100% and the N2 selectivity of 95.4% were achieved in Cu2O-Cu0@Fe0/HCOOH/UV system when the initial nitrate concentration was 50 mg N/L and the reduction time was 60 min. The nitrate reduction efficiency was low by the role of alone or combinations of Cu2O-Cu0@Fe0 composite, HCOOH or UV radiation. The quick reduction of nitrate to nitrite was due to the synergistic effect of electrons from the galvanic-type cell consisting of Fe0 as anode and Cu0 as cathode, photoelectrons from Cu2O under UV radiation and CO2?? produced mainly via photochemical reaction between HCOOH and UV radiation. The subsequent conversion of nitrite to N2 was caused by CO2??, which was responsible for the high efficient reduction of nitrate to nitrogen gas in the Cu2O-Cu0@Fe0/HCOOH/UV system. Finally, the denitrification mechanism of the Cu2O-Cu0@Fe0/HCOOH/UV system was tentatively proposed.
关键词： Denitrification,Galvanic-type cell,Cuprous oxide,Nitrate reduction
更新于2025-09-10 09:29:36
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Relationship between structure/properties of vapour deposited PEDOT and sensitivity to passive nitrate doping
摘要： The ability to sense and monitor aspects of a process or environment is becoming of utmost importance as digital technology integrates into our daily lives. This is true for agriculture where knowledge of real time levels of fertiliser in soil is empowering farmers. Such sensing and monitoring requires understanding of the structure-property-performance relationships of specific materials. In this study this relationship for the conducting polymer poly(3,4-ethylenedioxythiophene), PEDOT, and its passive doping with nitrate (NO3) is explored. The highly ordered structure of vapour deposited PEDOT doped with tosylate (Tos) is commensurate with high doping levels. In turn this correlates with the nitrate doping level in PEDOT-Tos/NO3 being sensitive to NO3 concentration in the surrounding solution. Such an understanding has impact for potentially designing other conducting polymers for ion sensing applications.
关键词： Structure-property relationship,Agriculture,Ion selective material,Nitrate,Conducting polymer
更新于2025-09-10 09:29:36
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Enhanced Photocatalytic Activity of B, N-Codoped TiO <sub/>2</sub> by a New Molten Nitrate Process
摘要： B, N-codoped titania mesoporous crystals were prepared by the sol–gel method followed by a molten nitrate process to modify the sample morphology. The composition, morphology and microstructure of the obtained samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), Brunauer Emmett Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). Fourier Transform Infrared spectroscopy (FTIR) revealed weak complex vibrations between the Ti–O oxide species and the unsaturated sites (Ti3+) through the incorporation of hydroxyl groups, which was not observed in the bulk titania (B–N–TiO2). The photocatalytic reactivity of boron-nitrogen codoped TiO2 was examined for the removal of methylene blue (MB) under visible light irradiation. The nitrates treated B-doped TiO2 exhibited better photocatalytic activity for dye degradation than that of B-doped TiO2 and nitrates treated TiO2. The best performance was obtained in the sample treated at a calcination temperature of 550 °C.
关键词： Photocatalysis,Visible Light,Nitrate,Boron Doped Titanium Dioxide
更新于2025-09-09 09:28:46
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Revisiting structural and photocatalytic properties of g-C3N4/TiO2: Is surface modification of TiO2 by calcination with urea an effective route to “solar” photocatalyst?
摘要： g-C3N4/TiO2 derived from the surface modification of TiO2 by calcination with urea has been widely studied as a “visible-light-active” photocatalyst for environmental purification applications. However, few attentions have been paid to the structure characterization and the photocatalytic properties of the resultant nanocomposite photocatalysts under a practical sunlight irradiation. Here we employ various characterization techniques, including TGA, XRD, TEM, XPS, UV-Vis spectrum, and N2-sorption analysis to characterize the evolutions in phase crystal structure, microstructure and optical properties of g-C3N4/TiO2 nanohybrids synthesized through calcining a mechanical mixture of urea and Evonik Aeroxide P-25 TiO2 (P25) at 350-500 oC. The thermal pyrolysis of urea leads to the surface decoration of TiO2 with graphitic carbon nitrate (g-C3N4) at temperatures above 400 oC. The photocatalytic properties of the resultant g-C3N4/TiO2 nanoparticles are evaluated through photocatalytic decoloration of methylene blue (MB) and reduction of Cr(VI) to Cr(III) under visible (420 nm), UV (365 nm), and simulated solar light irradiations. The nanohybrid photocatalysts, as most previous studies reported, show much higher photocatalytic activity under visible light irradiation than the single-component counterparts, i.e. P25 or g-C3N4. However, under solar and UV irradiation, no considerable improvements are found, which is caused by the decrease in redox potential upon interfacial charge carrier transfer between g-C3N4 and TiO2. Moreover, g-C3N4/TiO2 shows an ultralow photocatalytic activity in Cr(VI) reduction. The surface modification with organic g-C3N4 is assumed to tune the surface properties (e.g. hydrophilicity) of TiO2. Our results demonstrate that photocatalytic activity in UV range is as important as that in visible range, and developing efficient “solar” photocatalysts should balance both since they might be incompatible with each other.
关键词： graphitic carbon nitrate,dye degradation,TiO2 nanoparticles,Cr (VI) reduction,semiconductor photocatalysis,Aeroxide P25,charge carrier transfer
更新于2025-09-04 15:30:14
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Generating highly specific spectra and identifying thermal decomposition products via Gas Chromatography / Vacuum Ultraviolet Spectroscopy (GC/VUV): Application to nitrate ester explosives
摘要： Gas chromatography/mass spectrometry (GC/MS) is a "workhorse" instrument for chemical analysis, but it can be limited in its ability to differentiate structurally similar compounds. The coupling of GC to vacuum ultraviolet (VUV) spectroscopy is a recently developed technique with the potential for increased detection specificity. To date, GC/VUV has been demonstrated in the analysis of volatile organic compounds, petroleum products, aroma compounds, pharmaceuticals, illegal drugs, and lipids. This paper is the first to report on the utility of GC/VUV for explosives analysis in general, and the first to report on thermal degradation within the VUV cell and its analytical utility. The general figures of merit and performance of GC/VUV were evaluated with authentic standards of nitrate ester explosives (e.g., nitroglycerine (NG), ethylene glycol dinitrate (EGDN), pentaerythritol tetranitrate (PETN), and erythritol tetranitrate (ETN)). In addition, the explosive analytes were thermally degraded in the VUV cell, yielding reproducible, complex and characteristic mixtures of gas phase products (e.g., nitric oxide, carbon monoxide, and formaldehyde). The relative amounts of the degradation products were estimated via spectral subtraction of library spectra. Lastly, GC/VUV was used to analyze milligram quantities of intact and burned samples of double-base smokeless powders containing nitroglycerine, diphenylamine, ethyl centralite, and dibutylphthalate.
关键词： Thermal degradation,Nitrate ester explosives,Vacuum ultraviolet spectroscopy,Gas chromatography
更新于2025-09-04 15:30:14