A brief overview of photocatalytic mechanisms and pathways in water

2007 ◽  
Vol 55 (12) ◽  
pp. 167-173 ◽  
Author(s):  
P. Pichat
Keyword(s):  
Charge Transfer ◽  
Organic Pollutants ◽  
Liquid Water ◽  
Bound Water ◽  
Near Surface ◽  
Low Concentrations ◽  
Water Layers

This paper outlines the basic events that occur when a semiconductor, in contact with aerated liquid water containing low concentrations of pollutants, is photoexcited. First, the factors favouring this recombination of photoproduced charges are recalled, and the difficulties in decreasing the recombination are underlined. Second, the formation and identification of the species resulting from charge transfer with O2, H2O and pollutants are presented. Third, the reactions involving these species are considered, and methods for assessing their respective importance are critically reviewed. Fourth, on the basis of the view that the photocatalyst surface is covered by tightly bound water layers which hinder the adsorption of many organic pollutants, the hypothesis according to which primary photocatalytic events can take place within the near-surface solution layers is discussed.

Nanostructural Evolution of Au on Silica Surfaces Exposed to Low Energy Ions

2006 ◽  
Vol 929 ◽  
Author(s):  
Volha Abidzina ◽  
I. Tereshko ◽  
I. Elkin ◽  
R.L. Zimmerman ◽  
S. Budak ◽  
...  
Keyword(s):  
Glow Discharge ◽  
Discharge Plasma ◽  
Ion Irradiation ◽  
Absorption Spectrometry ◽  
Low Energy ◽  
Glow Discharge Plasma ◽  
Near Surface ◽  
Silica Surfaces ◽  
Low Concentrations ◽  
Low Energy Ions

ABSTRACTWe studied the effects of the low energy ions to induce nucleation of nanoscale crystals on and near surface of silica nano-layer containing low concentrations of Au. Suprasil substrates were coated with thin layer of gold followed by low-energy ion irradiation in a glow discharge plasma. The formation of nanoscale crystals due to low energy ion irradiation were then studied using RBS and optical absorption spectrometry.

scholarly journals Determining Partial Atomic Charges for Liquid Water: Assessing Electronic Structure and Charge Models

2020 ◽  
Author(s):  
Bowen Han ◽  
Christine Isborn ◽  
Liang Shi
Keyword(s):  
Electronic Structure ◽  
Dipole Moment ◽  
Charge Transfer ◽  
Liquid Water ◽  
Quantum Chemical ◽  
Water Dimer ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Molecular Dipole Moment ◽  
Partial Atomic Charges

Partial atomic charges provide an intuitive and efficient way to describe the charge distribution and the resulting intermolecular electrostatic interactions in liquid water. Many charge models exist and it is unclear which model provides the best assignment of partial atomic charges in response to the local molecular environment. In this work, we systematically scrutinize various electronic structure methods and charge models (Mulliken, Natural Population Analysis, CHelpG, RESP, Hirshfeld, Iterative Hirshfeld, and Bader) by evaluating their performance in predicting the dipole moments of isolated water, water clusters, and liquid water as well as charge transfer in the water dimer and liquid water. Although none of the seven charge models is capable of fully capturing the dipole moment increase from isolated water (1.85 D) to liquid water (about 2.9 D), the Iterative Hirshfeld method performs best for liquid water, reproducing its experimental average molecular dipole moment, yielding a reasonable amount of intermolecular charge transfer, and showing modest sensitivity to the local water environment. The performance of the charge model is dependent on the choice of the density functional and the quantum treatment of the environment. The computed molecular dipole moment of water generally increases with the percentage of the exact Hartree-Fock exchange in the functional, whereas the amount of charge transfer between molecules decreases. For liquid water, including two full solvation shells of surrounding water molecules (within about 5.5 A of the central water) in the quantum-chemical calculation converges the charges of the central water molecule. Our final pragmatic quantum-chemical charge assigning protocol for liquid water is the Iterative Hirshfeld method with M06-HF/aug-cc-pVDZ and a quantum region cutoff radius of 5.5 A.<br>

scholarly journals Main sources of unintentional production of persistent organic pollutants (the case of Odessa)

2018 ◽  
pp. 110-119 ◽  
Author(s):  
V. I. Mykhailenko ◽  
T. P. Shanina ◽  
T. A. Safranov
Keyword(s):  
Organic Pollutants ◽  
Persistent Organic Pollutants ◽  
Building Materials ◽  
The Body ◽  
Household Waste ◽  
Mobile Sources ◽  
Low Concentrations ◽  
Organic Fuels ◽  
One Year ◽  
Global Threat

Persistent organic pollutants represent a serious global threat to human health and the environment. They have certain properties: resistance to decomposition, bioaccumulation, extreme toxicity, even at ultra-low concentrations, ability to transboundary transfer and deposition. Unfortunately, there is no separate normative and legislative base regulating production of persistent organic pollutants in Ukraine. All norms and rules regulating such pollutants formation are included in a large number of various legislative acts and this does not allow systematization and specification of the actions associated with treatment of POPs. The purpose of this work is to evaluate the main sources of unintentional formation of persistent organic pollutants (using Odessa as an example). As part of the study it was established that the main sources of unintentional formation of POPs in Odessa are: combustion of organic fuels by stationary and mobile sources; production of building materials; open landfills of solid household waste; smoking of meat and fish products; functioning of crematoria; tobacco smoking; functioning of the city sewage system. The analysis of the legislative base of Ukraine is carried out which resulted in making a conclusion that there is no separate normative and legislative base regulating production of persistent organic pollutants in Ukraine. For the first time the list of the main sources of unintentional formation of these pollutants was established for Odessa with estimation, using the most advanced European methods, of the mass of persistent organic pollutants formed from each type of above-stated production facilities, and estimation of the total mass of their generation over the territory of Odessa. Since different techniques give results in different units of measurement, a transition to one unit of measurement was performed. Based on the concept of maximum permissible concentration (MPC), the permissible number of molecules of POPs equivalent to 2,3,7,8- tetrachlorodibenzodioxin (TCDD) which can enter the body of one person through respiratory organs was calculated. A comparison with the number of molecules of 2,3,7,8-TCDD entering the atmosphere in a permissible quantity per 1 citizen of was carried out and corresponding conclusions based on calculations of unintentional formation of POPs in Odessa during one year were made. Also, based on the obtained results, priority sources of unintentional production of persistent organic pollutants were established which allows correct and timely implementation of appropriate measures to reduce formation of these polluting substances.

scholarly journals Water budget and partial melting in an Archean crustal column: example from the Dharwar Craton, India

2019 ◽  
Vol 489 (1) ◽  
pp. 115-133 ◽  
Author(s):  
Gautier Nicoli
Keyword(s):  
Partial Melting ◽  
Water Budget ◽  
Critical Parameter ◽  
Bound Water ◽  
Dharwar Craton ◽  
Bulk Rock ◽  
Near Surface ◽  
Surface Conditions ◽  
Magma Compositions ◽  
Water Saturated

AbstractThe fluid budget of a composite crustal column is a critical parameter that influences many lithospheric processes. The amount of water introduced into the middle and lower crust can be quantified using phase equilibrium modelling. The Dharwar Craton, India, displays a now-exposed continuous crustal section from near-surface conditions to c. 30 km depth. This section records the different steps of a c. 15 myr-long high-temperature metamorphic event (60°C kbar−1) responsible for the formation of syn- to post-tectonic anatectic intrusions. The global water budget is assessed using thermodynamic modelling on bulk-rock compositions of an average early Proterozoic supracrustal unit and c. 3.0 Ga felsic basement, the Peninsular gneisses. Results show the fast burial of a water-saturated supracrustal package (1.6 wt%) will release c. 50% of its mineral-bound water, triggering water-fluxed partial melting of the basement. Modelled anatectic magma compositions match the observed granitoid chemistries, and distinction can be made between water-fluxed melting and water-absent melting in the origin of syn- to post-tectonic anatectic granites. Findings from this study show the importance of crustal pile heterogeneity in controlling the nature of partial melting reactions, the composition of the magmas and the rheology of the crust.

scholarly journals Morphological evidence for geologically young thaw of ice on Mars: A review of recent studies using high-resolution imaging data

2013 ◽  
Vol 37 (3) ◽  
pp. 289-324 ◽  
Author(s):  
M.R. Balme ◽  
C.J. Gallagher ◽  
E. Hauber
Keyword(s):  
Liquid Water ◽  
Morphological Evidence ◽  
Polar Regions ◽  
Imaging Data ◽  
Patterned Ground ◽  
Large Lakes ◽  
Near Surface ◽  
Crater Lakes ◽  
Recent Climate ◽  
Liquid Flows

Liquid water is generally only meta-stable on Mars today; it quickly freezes, evaporates or boils in the cold, dry, thin atmosphere (surface pressure is about 200 times lower than on Earth). Nevertheless, there is morphological evidence that surface water was extensive in more ancient times, including the Noachian Epoch (∼4.1 Ga to ∼3.7 Ga bp), when large lakes existed and river-like channel networks were incised, and early in the Hesperian Epoch (∼3.7 Ga to ∼2.9 Ga bp), when megafloods carved enormous channels and smaller fluvial networks developed in association with crater-lakes. However, by the Amazonian Epoch (∼3.0 Ga to present), most surface morphogenesis associated with liquid water had ceased, with long periods of water sequestration as ice in the near-surface and polar regions. However, inferences from observations using imaging data with sub-metre pixel sizes indicate that periglacial landscapes, involving morphogenesis associated with ground-ice and/or surface-ice thaw and liquid flows, has been active within the last few million years. In this paper, three such landform assemblages are described: a high-latitude assemblage comprising features interpreted to be sorted clastic stripes, circles and polygons, non-sorted polygonally patterned ground, fluvial gullies, and solifluction lobes; a mid-latitude assemblage comprising gullies, patterned ground, debris-covered glaciers and hillslope stripes; and an equatorial assemblage of linked basins, patterned ground, possible pingos, and channel-and-scarp features interpreted to be retrogressive thaw-slumps. Hypotheses to explain these observations are explored, including recent climate change, and hydrated minerals in the regolith ‘thawing’ to form liquid brines at very low temperatures. The use of terrestrial analogue field sites is also discussed.

Effects of Intermolecular Charge Transfer in Liquid Water on Raman Spectra

2016 ◽  
Vol 7 (20) ◽  
pp. 4147-4151 ◽  
Author(s):  
Hironobu Ito ◽  
Taisuke Hasegawa ◽  
Yoshitaka Tanimura
Keyword(s):  
Charge Transfer ◽  
Raman Spectra ◽  
Liquid Water ◽  
Intermolecular Charge Transfer

scholarly journals Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling

2018 ◽  
Author(s):  
Achim Heilig ◽  
Olaf Eisen ◽  
Michael MacFerrin ◽  
Marco Tedesco ◽  
Xavier Fettweis
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Pore Space ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Liquid Water Content ◽  
Water Infiltration ◽  
Near Surface ◽  
Percolation Zone

Abstract. Increasing melt over the Greenland ice sheet (GrIS) recorded over the past years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness are observable in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779° N/46.2856° W) at 2120 m a.s.l. The radar is capable to monitor quasi-continuously changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well, for both, timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg/m2 into firn beneath the summer surface of 2015. We find that continuous observations of liquid water content, percolation depths and rates for the seasonal mass fluxes are sufficiently accurate to provide valuable information for validation of model approaches and help to develop a better understanding of liquid water retention and percolation in perennial firn.

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