Anions In Seawater Research Articles

Stable Seawater Electrolysis Over 10000H via Chemical Fixation of Sulfate on NiFeBa-LDH.

Although hydrogen production through seawater electrolysis combined with offshore renewable energy can significantly reduce the cost, the corrosive anions in seawater strictly limit the commercialization of direct seawater electrolysis technology. Here, it is discovered that electrolytic anode can be uniformly protected in a seawater environment by constructing NiFeBa-LDH catalyst assisted with additional SO4 2- in the electrolyte. In experiments, the NiFeBa-LDH achieves unprecedented stability over 10000h at 400mAcm-2 in both alkaline saline electrolyte and alkaline seawater. Characterizations and simulations reveal that the atomically dispersed Ba2+ enables the chemical fixation of free SO4 2- on the surface, which generates a dense SO4 2- layer to repel Cl- along with the preferentially adsorbed SO4 2- in the presence of an applied electric field. In terms of the simplicity and effectiveness of catalyst design, it is confident that it can be a beacon for the commercialization of seawater electrolysis technology.

Employing shielding effect of intercalated cinnamate anion in NiFe LDH for stable and efficient seawater oxidation

Seawater electrolysis is a valuable and promising method for clean hydrogen generation. The corrosion induced from active anions in seawater and the competition between oxygen evolution reaction (OER) and chloride evolution reaction (CER) limit the overall efficiency of seawater electrolysis. Herein, shielding strategy was introduced with cinnamate anion (CNA) intercalated in NiFe LDHs (NiFe LDHCNAs) for efficient alkaline seawater oxidation. It displays an outstanding OER performance with 247 mV and 258 mV to achieve the current density of 50 mA/cm2 in 1 M KOH electrolyte and alkaline seawater (1 M KOH + real seawater), respectively. Meanwhile, CNA-NiFe LDH presents excellent durability (over 72 h at 100 mA/cm2) in 1 M KOH electrolyte and alkaline seawater. The enhanced catalytic performance and durability can ascribe to the enlarged interlayer spacing by CNA intercalation and shielding effect of CNA against chlorine corrosion. This research offers a novel approach to the design of efficient electrocatalysts for hydrogen production from seawater electrolysis.

Ultrafast Construction of Interfacial Akaganéite FeOOH Phase to Enable the Long‐Term Stability of Nickel‐Iron Hydroxides for Seawater Splitting at Ampere‐Level Current Density

AbstractNiFe‐based hydroxides are well‐established as efficient electrocatalysts for the oxygen evolution reaction (OER) in alkaline purified water. However, they usually degrade rapidly in seawater electrolysis because of concentrated Cl− anions in seawater. In this work, a facile approach utilizing an ultrafast dipping method is presented to fabricate durable and scalable NiFe hydroxides, enhanced by interfacial akaganéite FeOOH for seawater splitting. This study reveals significantly improved electrocatalytic stability of NiFe hydroxides at an ampere‐level current density of 1000 mA cm−2 for 100 h in alkaline seawater. It is realized by the formed FeOOH in a specific akaganéite phase whose lattice tunnels are well filled by intrinsic Cl− anions, that serve to electrostatically repel corrosive chlorides in electrolyte. This anionic design also provides superior corrosion protection for other active metal‐based OER electrocatalysts when deployed in alkaline purified water and allows for facile scaling up of the anode, facilitating the practical utilization for seawater electrolysis.

Development of a deep-sea in-situ anion analyzer for marine biogeochemical cycle observation

A novel deep-sea in-situ anion analyzer (DIAA) is proposed and developed for long-term and continuous observation of marine biogeochemistry and ecology. The DIAA is designed to analyze the concentrations of various anions in seawater, such as F−, Cl−, Br−, NO3−, SO42−, and PO43−, based on ion chromatography (IC) technology. The DIAA consists of a control circuit module, a conductivity signal acquisition module, and a flow analysis module. The control circuit module is installed in a sealed pressure-resistant vessel, while the conductivity signal acquisition module and the flow analysis module are housed in a sealed pressure-balanced vessel. The two vessels are capable of functioning at a water depth of up to 4000 m. A seawater in-situ dilution device is designed to solve the issue that the concentrations of Cl− and SO42− in seawater exceeds the IC detection limit. Moreover, an in-situ calibration device enables the DIAA to operate subsea for a long time without recovery. In addition, the DIAA can diagnose and isolate faults automatically. The operation status can be monitored remotely on the shore, and the scientific data can be acquired in real-time. During the sea trial, the DIAA was connected to Monterey Accelerated Research System (MARS) seafloor observatory at a water depth of approximately 900m and operated for six months successfully. The measurement accuracy and the long-term stability of the instrumentation have been verified.

A deep-sea in-situ chemical laboratory for cabled seafloor observatories

A deep-sea in-situ chemical laboratory (DICL) is proposed for new insight into ocean chemical evolution. The DICL integrates a deep-sea in-situ anion analyzer (DIAA) and several chemical sensors connected to cabled seafloor observatories via a science instrument interface module (SIIM). It can measure the concentrations of seawater anions (e.g., Fˉ, Clˉ, Brˉ, NO3ˉ, SO4 2ˉ, PO4 3ˉ), chlorophyll-a, dissolved oxygen, and methane, as well as pH value. The system operation status can be monitored remotely on the shore, and the science data can be acquired in real-time. After water pressure tests and shallow sea trials, the DICL was tested in the Monterey Accelerated Research System (MARS) deep-sea observatory and collected high-resolution time-series chemical parameters. The experimental results demonstrated that the DICL's mechatronics integration design is reasonable and feasible.

Halogen Cycling in the Solid Earth

Each of the halogens constrains a different aspect of volatile cycling in the solid Earth. F is moderately incompatible in the mantle and has a low mobility at Earth's surface, meaning that it is preferentially retained in the mantle and continental crust. In contrast, Cl, Br, and I are strongly incompatible and highly soluble. Chloride is the dominant anion in seawater and many geofluids and a major component of evaporite minerals. Br and I are essential for life and significantly incorporated into organic matter that accumulates in marine sediments. Surficial fluids circulated into continental and oceanic crust incorporate surface-derived halogens into alteration minerals. As a result, subducting slabs and arc lavas are weakly enriched in F and strongly enriched in Cl, Br, and I. Subduction has maintained mantle Cl and Br concentrations at relatively constant levels since Earth's early differentiation, but mantle I/Cl has decreased over time. ▪Halogen abundances on the early Earth were affected by I partitioning into Earth's core and possible loss of hydrophilic Cl, Br, and I in an early formed ocean.▪Halogens are powerful tracers of subduction zone processes on the modern Earth, with Cl, Br, and I having a dominantly subducted origin in Earth's mantle.▪The deep subduction cycles of Cl, Br, and I are more similar to that of H2O than they are to F, but the geochemical cycle of each halogen differs in detail.▪Halogen abundance ratios and stable isotope ratios vary systematically in Earth's surface reservoirs, meaning that halogens are powerful tracers of geological fluids and melts.

CCQM-K161 "Anions in Seawater"

Main textAnions or nutrients in seawater are very important targets for oceanographic research and environmental monitoring of contaminations. Quantification of minor and trace anions in seawater has always been a challenge for the extremely high salinity, disparate levels of analyte and matrix ions, and even need to be measured at levels close to the detection limits of the method performance. Evidence of successful participation in formal, relevant international comparisons is needed to support calibration and measurement capability claims (CMCs) made by the national metrology institutes (NMIs) and designated institutes (DIs).The CCQM-K161 Anions in Seawater was organized by the Inorganic Analysis Working Group (IAWG) of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) to assess the abilities of the NMIs and DIs for the accurate determination of minor and trace anions in seawater. The measurands covered chloride (16 mg/g-25 mg/g), sulfate (1 mg/g-4 mg/g), bromide (30 mg/kg-100 mg/kg), nitrate (1 mg/kg-5 mg/kg) and phosphate (60 µg/kg-300 µg/kg). Twelve national metrology institutes and designated institutes participated in this key comparison. Participants were requested to evaluate the mass fractions, expressed in mg/g for chloride and sulfate, mg/kg for bromide and nitrate, and µg/kg for phosphate (as phosphorus) in a mixed natural seawater that was spiked with the phosphate. A variety of techniques including isotope dilution inductively coupled plasma mass spectrometry (IDMS), isotope dilution gas chromatography-mass spectrometry (ID-GC-MS), ion chromatography (IC), UV visible spectrophotometry (UV-Vis), flow injection analysis (FIA) was used by the participants for the determination.The NIST Decision Tree was used to assign the KCRV estimate and to calculate the degrees of equivalence of each participants following the IAWG Guidance on Using NIST Decision Tree for Comparison Reporting from 30 June 2023.Successful participation in CCQM-K161 demonstrates measurement capabilities for determination of anions in seawater. Considering the IAWG Core Capability Matrix, this material falls into the matrix challenge called 'High salts content', which corresponds to the CCQM amount-of-substance category sea water, and so will support CMCs for the anions in a mass fraction range from 60 µg/kg to 25 mg/g.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

(Invited) High Productivity Electrocatalytic Water Splitting Using Diverse Water Sources

Water electrolysis is a commercially established process. However, significant cost reductions are desired for the large scale applications anticipated in the future. Electrolysis is typically performed under extreme pH conditions due to the high reaction rate of the electrocatalyst and low solution resistance. On the other hand, energy conversion using electricity generated from renewable energy requires a water splitting electrocatalyst that is versatile, safe, and durable. Recent water splitting research has focused on the development of catalyst materials and elucidation of their efficient action under non-extreme pH conditions. However, there are several problems associated with water splitting in the mild pH range. The first problem is the lack of protons and hydroxide ions at mild pH, which leads to large concentration overpotentials. To solve these problems, concentrated buffered electrolytes are used to suppress local pH shifts and to compensate for the steady-state proton or hydroxyide ion. To maximize the buffering effect, concentrated buffer electrolyte solutions should be applied near the pKa values where protonated and deprotonated species coexist. A second problem at near-neutral pH levels is the inherently lower conductivity of the electrolyte solution compared to strongly acidic or strongly alkaline solutions. The ohmic potential (iR) drop between the anode and cathode is critical to the cell voltage of water splitting devices, especially at the high current densities that are industrially important. The conductivity at pH 7.0 of phosphate buffer can be maximized by varying the molar ratio and selecting the appropriate counter cation (K among Li, Na, K, and Cs). The choice of conditions essentially reduces viscosity and maximizes solubility, which strongly affects the conductivity of the solution. The conductivity of saturated K phosphate reaches a maximum of ~20 S m−1, but this value is still not as high as the alkaline one (~130 S m−1). Viscosity and solution resistance can be adjusted by mixing different electrolytes and fine-tuning the position of pKa within the target pH range. In water containing Mg2+ and Ca2+, precipitation of these ionic salts can be a problem. Keeping the pH between 8 and 10 prevents such precipitation. We are also attempting to intentionally use chloride ions, which have the highest concentration anion in seawater. In this way, solution resistance is further improved. Thus, it is emphasized that electrolyte engineering is an important technology for cost-effective water electrolysis by finding new reaction environments to efficiently electrolyze water under more moderate conditions.

Hydroxyl radical production by abiotic oxidation of pyrite under estuarine conditions: The effects of aging, seawater anions and illumination

Pyrite is widely distributed in estuarine sediments as an inexpensive natural Fenton-like reagent, however, the mechanism on the hydroxyl radical (HO·) production by pyrite under estuarine environmental conditions is still poorly understood. The batch experiments were performed to investigate the effects of estuarine conditions including aging (in air, in water), seawater anions (Cl−, Br− and HCO3−) and light on the HO· production by pyrite oxidation. The one-electron transfer dominated the process from O2 to HO· induced by oxidation of pyrite. The Fe (oxyhydr)oxide coatings on the surface of pyrite aged in air and water consumed hydrogen peroxide while mediating the electron transfer, and the combined effect of the two resulted in a suppression of HO· production in the early stage of aging and a promotion of HO· production in the later stage of aging. Corrosion of the surface oxide layers by aggressive anions was the main reason for the inhibition of HO· production by Cl− and Br−, and the generation of Cl· and Br· may also play a role in the scavenging of HO·. HCO3− increased the average rate of HO· production through surface-CO2 complexes formed by adsorption on the surface of pyrite. The significant enhancement of HO· production under light was attributed to the formation of photoelectrons induced by photochemical reactions on pyrite and its surface oxide layers. These findings provide new insights into the environmental chemical behavior of pyrite in the estuary and enrich the understanding of natural remediation of estuarine environments.

Differential effects of chloride salts on seed germination and seedling growth of Cistus monspeliensis: Towards revegetation of the Mediterranean salt-contaminated soils

Soil salinity is seriously threatening the Mediterranean basin, negatively affecting crops, and degrading natural habitats. However, limited information is available about chloride (Cl−) toxicity, the most common anion in seawater, on seed germination and seedling growth. In addition, seed emergence under individual and combined chloride salts has seldom been studied. In this research, the individual and combined effects of four chloride salts (KCl, CaCl2, MgCl2, and NaCl) on seed germination and seedling growth of Cistus monspeliensis, a Mediterranean shrub that regenerates through seeds, were investigated. Four concentrations of chloride salts (0, 40, 80, and 120 mM) were used. Germination rate (1/t50) was utilized in a halotime model to quantify the maximum concentration of Cl− (Cl−max) for germination at 20 °C under light. Germination decreased with increasing salt concentrations. The reduction in germination at 120 mM was higher in seeds treated with KCl and MgCl2, compared to the other salts, in both light and dark periods. In addition, the germination reduction at 120 mM was greater in dark periods than in light periods for seeds treated with CaCl2 and mixed salts. Germination velocity (GV) was maintained in all salts and concentrations except CaCl2, which decreased it. The lowest synchrony (0.13 ± 0.03) and the highest uncertainty (2.6 ± 0.25) were found in seeds stressed with 80 mM CaCl2. The mixed salts and NaCl improved GV and germination synchronization indicating that these salts have priming effects in enhancing germination speed in salty soils. The Cl−max value of ca. 491 mM for germination, obtained by treating seeds with different chloride salts, shows that C. monspeliensis can be a useful species for restoring chloride-dominated salty soils.

Inactivation of ciliate Uronema marinum under UV/peroxydisulfate advanced disinfection system in marine water

Protozoa in mariculture water will cause the outbreak of seafood diseases, and there are also discharge regulations about protozoa in the ballast water of ocean ships. However, the inactivation of protozoa has not attracted attention. This study investigated the inactivation of ciliate Uronema marinum (U. marinum) as surrogate for protozoa by ultraviolet (UV)/peroxydisulfate (PDS) system. Results showed that the addition of 1 mM PDS significantly enhanced the inactivation from 0.73 log to 1.47 log by UV exposure at 3.6 mJ·cm−2. Reactive species responsible for the inactivation were identified to be •SO4− and •OH. The anions in seawater inhibited the inactivation of U. marinum in UV/PDS system. UV/PDS inactivated U. marinum by damaging the cell membrane and releasing of intracellular materials. The activities change of the antioxidant enzymes showed that oxidative species destroyed the defense function. Moreover, omics analysis proved that the radicals affected the expression of genes, proteins and metabolites of U.marinum. In authentic marine water, the inactivation of U. marinum was 1.38 log in 120 s. There was no generation of chlorate (ClO3−), bromate (BrO3−) and adsorbable organic halogens (AOX). The economic cost of UV/PDS for inactivation of U. marinum was preliminarily calculated to be 0.062 $ m−3. The results suggest that it will be beneficial to upgrade UV disinfection to •SO4− based advanced oxidation technology for inactivation of protozoa in marine water.

A Novel Approach for the Biological Desalination of Major Anions in Seawater Using Three Microalgal Species: A Kinetic Study

The global water shortage alert has been upgraded to a higher risk level. Consequently, a sustainable approach for ecofriendly, energy efficient water desalination is required for agricultural and municipal water reuse. In this study, an energy-efficient biological desalination process was used to treat chloride anions, which are the most abundant anion salt in seawater. Three algal species were studied: Scenedismus arcuatusa (S. arcuatusa), Chlorella vulgaris (C. vulgaris), and Spirulina maxima (Sp. maxima), under different operating conditions (saline concentrations, contact time, high light intensity, and CO2 supply), and two kinetic models were used. It was identified that under a high light intensity and CO2 supply, S. arcuatusa enhanced chloride removal from 32.42 to 48.93%; the daily bioaccumulation capacity (Qe), according to the kinetic models, was enhanced from 124 to 210 mg/g/day; and the net biomass production was enhanced from 0.02 to 0.740 g/L. The EDX analysis proved that salt bioaccumulation may be attributed to the replacement of Ca2+ and Mg2+ with Na+ and K+ through algal cells. The study’s findings provide promising data that can be used in the search for novel energy-efficient alternative ecofriendly desalination technologies based on algae biological systems with biomass byproducts that can be reused in a variety of ways.

Combined LIBS and Raman spectroscopy: an approach for salinity detection in the field of seawater investigation.

As salinity is an important indicator in marine geology, ecology, breeding, and other fields, accurate, rapid, and continuous measurement of salinity is of great significance in marine investigations. At present, the seawater salinity detection methods used in practice are mainly based on the principle that the conductivity and refractive index parameters of the water change with the concentration of elements, which are composed of salinity change. However, these methods quantitatively analyze salinity values by measuring other parameters (electrical or optical parameters) that may change depending on the salinity of the water, rather than the mass fraction of the components that make up the salinity. Moreover, when the salinity value of seawater water changes substantially or the proportion of various common components composing salinity changes significantly, the detection accuracy of the above methods is difficult to guarantee. Therefore, a spectral approach, LIBS, and the Raman spectroscopy combination method for salinity analyzation, LRSS, were proposed to provide a new option. The main idea of this approach is to use the two spectral detection methods, LIBS and Raman, to determine the mole values of cations and non-monatomic anions in per unit quality (1 kg) of water, respectively. Then the mole value of the chloride ion, which is the main monatomic anion in seawater, can be determined according to the electrically neutral principle. Based on all the obtained molar values and the molar mass of each ion, the salinity of the water sample can be determined. To demonstrate the performance of this new method, we compared it with LIBS under laboratory conditions and found that, when non-monatomic anions are present in the water, the accuracy of LRSS is significantly improved compared to using the LIBS method alone. Moreover, we also compared the LRSS with the other two traditional methods through the 11 water samples configured and found that the absolute value relative error of the LRSS is only 2.63% when the salinity and components concentration change is in the possible range, which is better than the conductivity method 0.53 times and better than the refractive index method 1.52 times.

Kinetics and mechanisms of flumequine degradation by sulfate radical based AOP in different water samples containing inorganic anions.

Many studies have reported that hydroxyl radical (HO˙) driven advanced oxidation processes (AOPs) could degrade fluoroquinolones (FQs) antibiotics effectively. Compared with HO˙, sulfate radical (SO4˙−) shows a similar oxidation capacity but a longer half-life. SO4˙− could cause chain reactions and resulted in the generation of halogen radicals and carbonate radicals from the main anions in sea water including Cl−, Br− and HCO3−. However, few studies were focused on the degradation of FQs in marine aquaculture water and seawater, as well as the bioaccumulation of transformation products. As a typical member of FQs, flumequine (FLU) was degraded by UV/peroxodisulfate (PDS) AOPs in synthetic fresh water, marine aquaculture water and seawater. The reaction rate constants in the three water samples were 0.0348 min−1, 0.0179 min−1 and 0.0098 min−1, respectively. The reason was attributed to the inhibition of the anions as they could consume SO4˙− and initiate the quenching reaction of free radicals. When the pH value increased from 5 to 9, the reaction rate decreased from 0.0197 min−1 to 0.0066 min−1. The energy difference between HOMO and LUMO of FLU was calculated to be 8.07 eV indicating that FLU was a stable compound. The atoms on quinolone ring of FLU with high negative charge would be more vulnerable to attack by free radicals through electrophilic reactions. Two possible degradation pathways of FLU were inferred according to the degradation products. Preliminary bioaccumulation analysis of transformation products by the EPI suite software proved that the values of log Kow and log BCF of the final product P100 were less than those of FLU and the intermediates.

ИЗУЧЕНИЕ СОДЕРЖАНИЯ АГРЕССИВНЫХ ИОНОВ В АТМОСФЕРЕ И МОРСКОЙ ВОДЕ ГЕЛЕНДЖИКСКОЙ БУХТЫ

The method of capillary electrophoresis was used to measure the content of aggressive ions in 7 geographical points of the Gelendzhik bay in the air atmosphere and sea water during the period from September 1, 2019 to January 31, 2020. The results of measurements of the contents of K+, Na+, Mg2+, Ca2+, , Cl-, F- are compared with meteorological indicators at the time of measurement. It is shown that the total concentration of cations and anions in sea water corresponds to its salinity measured by the standard method. A high correlation between the chemical composition of samples in air and sea water was revealed.

Enrichment mechanisms of antimony and arsenic in marine ferromanganese oxides: Insights from the structural similarity

Marine ferromanganese crusts and nodules as potential mineral deposits have received increasing attention. However, much less knowledge is available concerning the incorporation and enrichment mechanisms for antimony (Sb) and arsenic (As) in marine ferromanganese oxides. In this study, the surface complexations of Sb(V) and As(V) on synthetic ferrihydrite and Mn oxides (δ-MnO2 and birnessite) were investigated by a combination of adsorption experiments, extended X-ray absorption fine structure (EXAFS) analyses, and quantum chemical calculations. The speciation, distribution, and local structure of Sb and As in different types of natural marine ferromanganese oxides were determined by X-ray absorption near edge structure (XANES) and EXAFS analyses to reveal the enrichment mechanisms for the two elements in ferromanganese oxides at the molecular level. To the best of our knowledge, the Sb EXAFS analyses for different types of marine ferromanganese oxides are herein reported for the first time. Results showed that Sb(V) is preferentially adsorbed on Mn oxides through energetically favorable bidentate–mononuclear complexation because of the structural similarity between the octahedron SbV(OH)6− and MnO6 unit, although bidentate–binuclear (corner-sharing) and bidentate–mononuclear (edge-sharing) complexes can be formed on ferrihydrite and Mn oxides for the adsorption of Sb(V). By contrast, tetrahedral AsVO43− is mostly adsorbed on ferrihydrite and Mn oxides with the formation of bidentate–binuclear complexes. In natural marine ferromanganese oxides, Sb and As can be retained by Fe and Mn (oxyhydr)oxide components, and the disparate distribution of the two elements to Mn oxides may largely depend on the Mn/Fe ratio and constituent minerals. The larger enrichment factor of Sb than that of As in marine ferromanganese oxides may result from their preferential attachment modes onto the Fe and Mn phases and different inhibition effects from coexisting anions in seawater. Compared with As, a part of Sb may be strongly associated with the lateral sites in Mn oxides via the formation of bidentate edge-sharing complexes, with which anions such as sulfate in seawater do not significantly compete. The findings from this study provide the molecular-scale insights into the enrichment processes and mechanisms of Sb and As in marine ferromanganese oxides. Our study also helps elucidate the incorporation mechanisms and geochemical behaviors of other oxyanions in marine and surface environments.

Boric acid and borate incorporation in inorganic calcite inferred from B/Ca, boron isotopes and surface kinetic modeling

The boron concentration (B/Ca ratio) and isotopic composition (δ11B) of biogenic calcite are widely applied to reconstruct past changes in seawater carbonate chemistry. Knowledge of B incorporation pathways into calcite is critical for these applications and for improving the theoretical basis of B proxies. While the canonical interpretation of δ11B holds that B in calcite predominantly derives from dissolved borate anion in seawater, recent studies of the B content, coordination, and isotopic composition in calcite suggest more complex B incorporation pathways. To provide new insights into these pathways, here we present δ11B of inorganic calcite precipitated from saline solutions of varying pH, calcium and dissolved inorganic carbon (DIC) concentration for which B/Ca data were previously reported by Uchikawa et al. (2015). Results show that calcite δ11B significantly increases with increasing pH and decreases with increasing [Ca2+] and [DIC]. In combination, these experiments show that the difference in δ11B between solid calcite and aqueous borate linearly decreases with increasing calcite precipitation rate. To interpret these data, we present the first application of surface kinetic modeling (SKM) to boron incorporation. The SKM can simultaneously explain rate-dependent B/Ca and δ11B patterns observed in our and previously published inorganic calcite precipitation experiments when both aqueous borate and boric acid contribute to boron in inorganic calcite. If the B incorporation mechanism shown here for inorganic calcite is applicable to biogenic calcite, precipitation rate variations could modify δ11B patterns by changing the contributions of aqueous boric acid and borate to boron in calcite. However, better knowledge of biogenic calcite precipitation mechanisms and rates is needed to assess the importance of this effect for applications of B proxies in biogenic carbonates.

β-Hydroxy sulfides and their syntheses.

Sulfur-containing natural products are ubiquitous in nature, their most abundant source being marine organisms since sulfur, in the form of the sulfate ion, is the second most abundant anion in sea water after chloride. As part of natural products, sulfur can appear in a multitude of combinations and oxidation states: thiol, sulfide (acyclic or heterocyclic), disulfide, sulfoxide, sulfonate, thioaminal, hemithioacetal, various thioesters, thiocarbamate and isothiocyanate. This review article focuses on β-hydroxy sulfides and analogs; their presence in natural products, general protocols for their synthesis, and examples of their application in target oriented synthesis.

Selective separation of aqueous sulphate anions via crystallization of sulphate–water clusters

In this study, the potential of oxoanion separation with the ligands N-4-methylbenzyl-4-amino-1,2,4-triazole (L1), N-4-fluorobenzyl-4-amino-1,2,4-triazole (L2), N-4-hydroxy benzyl-4-amino-1,2,4-triazole (L3), and N-3-methoxy-4-hydroxybenzyl-4-amino-1,2,4-triazole (L4) was explored. The salts of sulphate, nitrate, and perchlorate were crystallized in the form of [HL1]+[HSO4]−·H2O, [HL2]+[HSO4]−·H2O, 2[HL3]+[SO4]2−·2(H2O), and 2[HL4]+[SO4]2−·H2O, [HL3]+[NO3]−·H2O and [HL4]+[NO3]−, and [HL3]+[ClO4]− and [HL4]+[ClO4]−, respectively. Competitive crystallization and competitive sulphate-binding experiments demonstrated special recognition of the sulphate–water clusters (in the forms of [HSO4−·H2O]n or [SO42−·H2O]n) via the parallel packed 3-D architectures of HL1+, HL2+, and HL4+ cations, which were far more effective and selective than the non-3-D structure of HL3+ cation. The observed selectivity for sulphate, nitrate, and perchlorate was found to be anti-Hofmeister. In addition, the selective separation of sulphate anions in seawater was investigated, which demonstrated the real-world application of the present strategy.

Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination

Salt removal via formation of gas hydrate was investigated by experimental measurement of the salt concentration in filtered water and water retrieved from hydrate crystals. Gas hydrate formation was carried out at 277.15K, using seawater of 3.4wt% salinity and 3mol% cyclopentane to water-cyclopentane mixture. Single-stage hydrate formation followed by filtration removed 63% of the salt ions. Successive washing treatment with 274.15 and 277.15K freshwater was applied with different amounts of washing water, and several major cations and anions in seawater were analyzed in each treatment step. Ions having larger radii showed less salt removal by hydrate formation, and salt removal decreased as the conversion of water to hydrate progressed. However, salt removal was improved by washing treatment to nearly the same degree regardless of the kind of salt ions and the salt removal efficiency improved up to 42% more than that of filtration only. The results presented in this study can be used as basic design values for the development of a hydrate-based desalination process.