Seawater Oxidation Research Articles

Sulfonated Polystyrene-Block-(Ethylene-Ran-Butylene)-Block-Polystyrene (SPSEBS) Membrane for Sea Water Electrolysis to Generate Hydrogen

Sea water oxidation is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis poisonous chlorine evolution is the most favored reaction over oxygen evolution at the anode. In this work, study has been focused on the development of electrode materials with high selectivity for oxygen evolution reaction over chlorine evolution. We employed perm selective membrane i.e. sulfonated polystyrene-block-(ethylene-ran-butylene)-block-polystyrene (SPSEBS) which electrostaticlly repels the chloride ion (Cl-) to the electrode surface and thereby enhances the oxygen evolution and reduces the chlorine evolution at the anode. The electrochemical behavior of both modified and bare IrO2 electrodes were characterized using polarization studies and the gas evolution efficiencies are calculated based on bulk electrolysis method. The surface morphology of the electrode was analyzed before and after electrolysis using scanning electron microscope (SEM). The results suggest that the nearly 95% oxygen evolution efficiency could be achieved when the surface of IrO2/Ti electrode was modified with perm selective membrane.

A seafloor microbial biome hosted within incipient ferromanganese crusts

Exposed rocks on underwater mountains and ridges host abundant and diverse microbial communities. X-ray and microscopic analyses of volcanic rocks associated with Loihi seamount in Hawaii suggest that seafloor microbes may commonly be sustained by energy inputs from the water column. Exposed rocks at underwater volcanoes and ridges host complex, abundant and diverse microbial communities1,2,3. The volcanic glasses associated with these features constitute one of the most geochemically reactive components of the Earth’s crust. The most commonly held hypothesis is that their oxidation in sea water provides the energy necessary to establish a seafloor biosphere4,5,6,7. However, this hypothesis has yet to be directly tested. Here we used synchrotron-based X-ray microprobe mapping, X-ray absorption spectroscopy and high-resolution scanning and transmission electron microscopy techniques to examine the initial chemical changes that occur as the glassy rims of young pillow basalts are colonized by microbial organisms at Loihi seamount, Hawaii. We found little evidence of basalt dissolution. Instead, microbial biofilms were intimately associated with Fe(III)- and Mn(IV)-oxides that had precipitated from sea water onto the fresh basalt surfaces. These accumulations of secondary minerals probably represent the earliest stages of ferromanganese crust formation. We suggest that fluid-derived energy sources, such as dissolved and particulate Fe(II), Mn(II) and organic matter, may support the microbial communities colonizing seafloor rocks to a greater degree than local rock dissolution.

Fate of incorporated metals during mackinawite oxidation in sea water

Oxidation of mackinawite can occur at the water-sediment interface when anoxic sediment is disrupted into the oxic water column. During this process, pollutant metals and As that have become incorporated into the pyrite precursor could change oxidation states and become mobile in the water column. Mackinawite oxidation in aerated sea water was measured in laboratory experiments. Synthesized mackinawite oxidized readily with most sulfide reacting within 5 h when exposed to light and 8 h when kept in the dark. A batch of the synthetic mackinawite doped with several metals and As was then placed in filtered sea water and aerated. The filtrates and particulates were collected at various times to analyze both for trace metals and As. Most metals and As were found to remain in the particulate phase. But Cd was found to be unique as a measurable portion did partition into the filtrate.

Uptake of arsenate, trimethylarsine oxide, and arsenobetaine by the shrimp Crangon crangon

Common shrimp, Crangon crangon (L.), were exposed to inorganic arsenic (arsenate), trimethylarsine oxide, or arsenobetaine in sea water (100 l gA s l )1 ) or in food (1 mg As g )1 wet wt) for up to 24 d, followed by 16 d depuration in clean sea water with undosed food, in order to determine the eAciency of uptake and retention of the compounds. Accumulation of arsenic in the tail muscle, gills, midgut gland, exoskeleton, and remaining tissues was found to depend on the chemical form of the arsenic and the route of exposure. No arsenic was accumulated by C. crangon exposed to arse- nate or trimethylarsine oxide in sea water. Shrimps ex- posed to waterborne arsenobetaine initially accumulated a small amount of arsenic in their tail muscle and gills. After 16 d, C. crangon fed arsenate, trimethylarsine ox- ide, or arsenobetaine had accumulated arsenic in their tail muscle to levels 2-, 2-, or 40-times, respectively, that of the control group. A roughly linear rate of ac- cumulation was shown by shrimps fed trimethylarsine oxide or arsenobetaine, but C. crangon fed arsenate ac- cumulated arsenic for 16 d, then lost arsenic such that their concentration on Day 24 was not significantly diAerent from that of the control group. Patterns of arsenic accumulation in the gills of shrimps fed the compounds were similar to those seen in the tail muscle. On a whole animal basis, C. crangon retained1.2% of the arsenate, 1.6% of the trimethylarsine oxide, and 42% of the arsenobetaine consumed over the first 16 d of exposure, with roughly half present in the tail muscle in each case. Data obtained support the view that the direct uptake of arsenobetaine from sea water does not make a significant contribution to the relatively high concentrations of this compound in marine crustaceans, and that food is the primary source. Naturally occurring arsenic compounds in C. crangon and possible trans- formations of the administered arsenic compounds were examined by high performance liquid chromatography using an inductively coupled plasma mass spectrometer as the arsenic-specific detector. Control C. crangon contained arsenobetaine as the major arsenic compound (>95% of total arsenic); tetramethylarsonium ion (0.7%) and an unknown arsenic compound (1.7%) were also present as minor constituents. Shrimp ingesting arsenobetaine accumulated it unchanged. Shrimp in- gesting arsenate did not form methylated arsenic com- pounds; they appeared to contain their accumulated arsenic as unchanged arsenate only, although the pos- sibility that some of the arsenic was reduced to arsenite could not be excluded. C. crangon ingesting trimethyl- arsine oxide biotransformed the compound predomi- nantly to dimethylarsinate.

Electrochemical nitrite and ammonia oxidation in sea water

Nitrite and ammonia destruction from sea water by an electrochemical oxidation was investigated to determine nitrite and ammonia oxidation efficiencies. Operating conditions considered in the experimental studies included the electric current, pH, initial nitrite and ammonium concentrations and salinity. Both nitrite and ammonia oxidation processes were found to obey a zero‐order kinetics and reaction rate coefficients were a linear function of electric current and a nonlinear function of salinity. Nitrite removal was found to be significantly faster than the ammonia removal. In the presence of an electrolyte (chloride), the indirect oxidations of both nitrite and ammonia by a strong oxidant (hypochlorite) were faster than direct anodic oxidation of the pure component.

Microbially mediated cerium oxidation in sea water

REDOX processes influence the geochemistry of many elements in the ocean, but attributing the distribution of these elements in the water column and sediments to specific redox processes is difficult because they are also influenced by non-redox processes and by other inputs that are poorly constrained. Cerium provides an opportunity to study redox processes in the ocean1–5 because its redox chemistry leads to its enrichment or depletion ('cerium anomalies') with respect to its lanthanide neighbours. A detailed understanding of Ce geochemistry is lacking, however, because of the paucity of knowledge of the redox rates and mechanisms in natural waters. Here I report measurements of Ce(III) oxidation rates using radiotracers in seawater samples collected in the Sargasso Sea and in Vineyard Sound, Massachussetts, which are much faster than previous, indirect estimates1. The data indicate that the negative Ce anomaly in sea water is the result of microbial oxidation followed by preferential scavenging of Ce(IV); no abiotic oxidation was detectable. This suggests that inhibition by sunlight of microbial oxidation and scavenging of Ce and Mn contribute to the pronounced surface maxima observed for these elements.

Oxidation of copper(I) in seawater

The oxidation of Cu(I) in air-saturated solutions of sea water has been measured as a function of pH (5.3-8.6), temperature (5-45 /sup 0/C), and salinity (5-44). The overall rate constant k (kg mol/sup -1/ min/sup -1/) d(Cu(I))/dt = -k(Cu(I))(O/sub 2/) has been fitted to log k = 10.73 + 0.23 pH - 2373/T - 3.33I/sup 1/2/ + 1.45I with a standard error of 0.08 in log k. The energy of activation was found to be 45.6 +/- in 1.7 kJ mol/sup -1/. The strong chloride dependence of the rates has been attributed to the effect of temperature and ionic strength on the oxidation of Cu/sup +/ and CuCl/sup 0/ species. At a given Cl/sup -/ concentration, the rates of oxidation in sea water are lower than in NaCl or NaCl-NaClO/sub 4/ mixtures. These differences in sea water are due to a decrease in the rates due to Mg/sup 2 +/ and Ca/sup 2 +/ and the increase in the rates due to HCO/sub 3//sup -/. Possible causes of these effects are discussed.

Quantitative measurement of tributyltin oxide in sea water by differential pulse anodic stripping voltammetry

Bis(tri-n-butyltin) oxide (TBTO) was measured directly in sea water at μg l −1 levels at a hanging drop mercury electrode (HDME) and at a mercury-film rotating-disc glassy carbon electrode (MFE) by differential pulse anodic stripping voltammetry. The HDME responded to TBTO additions in sea water purged either with nitrogen (pH 8.2) or carbon dioxide (pH 4.8) with two distinct stripping peaks. The MFE produced stripping peaks for TBTO at pH 8.2 and no response at pH 4.8. Peak potentials and peak heights varied depending upon the history of the water sample, suggesting an influence by dissolved organic materials. The limit of detection for TBTO in sea water on the HMDE was approximately 5 μg l −1. The HMDE responded to additions of inorganic tin in sea water at both pH 4.8 and 8.2, whereas the MFE did not respond at either pH.

Shipboard measurement of dissolved nitrous oxide in sea water by electron capture gas chromatography

Shipboard measurement of dissolved nitrous oxide in sea water by electron capture gas chromatography

Calculation of organic matter formation and oxidation in sea water : Skopintsev B.A., 1965. (In Russian; English abstract). Okeanolog. Issled., Rez. Issled. po Programme Geofiz. Goda, Mezhd. Geofiz. Komitet, Prezidiume Akad. Nauk. SSSR, No. 13: 96–107

Calculation of organic matter formation and oxidation in sea water : Skopintsev B.A., 1965. (In Russian; English abstract). Okeanolog. Issled., Rez. Issled. po Programme Geofiz. Goda, Mezhd. Geofiz. Komitet, Prezidiume Akad. Nauk. SSSR, No. 13: 96–107

Oxidation in Sea Water

1. Putrefaction in sea-water sets free compounds toxic to Calanus. A portion of these compounds withstands oxidation to non-toxic forms in air saturated water for considerable periods.2. “Deep water” from the English Channel contains a catalyst, probably an iron compound, which increases the rate of oxidation of a number of easily oxidisable organic compounds. Its action is inhibited in surface and inshore waters by dissolved organic matter.3. Hydrogen peroxide decomposes relatively quickly in “deep water” from the English Channel, at a velocity corresponding to that of a monomolecular reaction. A catalyst, probably an iron compound, active towards hydrogen peroxide, occurs in sea-water. The action of the catalyst is inhibited by dissolved organic substances in surface and inshore water, until such substances are oxidised by the hydrogen peroxide.