Bromide and iodide selectivity in membrane capacitive deionisation, and its potential application to reduce the formation of disinfection by-products in water treatment.

The formation of toxic disinfection by-products during water disinfection due to the presence of bromide and iodide is a major concern. Current treatment technologies such as membrane, adsorption and electrochemical processes have been known to have limitations such as high energy demand and excessive chemical use. In this study, the selectivity between bromide and iodide, and their removal in membrane capacitive deionisation (MCDI) was evaluated. The results showed that iodide was more selectively removed over bromide from several binary feed waters containing bromide and iodide under various initial concentrations and applied voltages. Even in the presence of significant background concentration of sodium chloride, definite selectivity of iodide over bromide was observed. The high partial-charge transfer coefficient of iodide compared to bromide could be a feasible explanation for high iodide selectivity since both bromide and iodide have similar ionic charge and hydrated radius. The result also shows that MCDI can be a potential alternative for the removal of bromide and iodide during water treatment.

Influence of physicochemical properties of various soil types on iodide and iodate sorption.

Studies that deal with iodine mobility in uncontaminated agricultural soils are scarce and unique. Therefore, in this article, we have evaluated the sorption behavior of two most abundant naturally occurring inorganic iodine species - iodide and iodate - in several soil types. Our results showed that the sorption process is extremely slow with equilibrium achieved after ten days. The sorption of both iodine species is well described by Freundlich isotherm. The affinity of iodine for all investigated soils in the observed concentration range is relatively low. Our results showed that besides iodine speciation, sorption efficiency is highly dependent on soil types and their characteristics. While in mineral soils with low organic carbon content iodide sorption is dominant, organic rich soils are more favorable for iodate sorption. Organic carbon, clay content, pH and the abundance of iron, aluminum and manganese oxides and hydroxides showed to be the most important soil properties controlling iodine sorption. Our results provide new insight into the complex iodine behavior and retention in soils. This is crucial for better understanding of iodine mobility and the ability to enter the food chain.

Enhanced uptake of iodide on Ag@Cu2O nanoparticles.

In order to improve the uptake capacity of Cu2O for I- anions from water, Ag loaded Cu2O composites have been synthesized through a facile method, characterized using SEM, XRD, XPS and applied to remove I- anions under different experimental environments. The results show that the uptake capacity of Ag@Cu2O increased with the increasing Ag doped amount. Meanwhile, the uptake capacity (0.20 mmol g-1) of 1.0%-Ag@Cu2O for the removal of I- anions is ten times higher than that of pure Cu2O (0.02 mmol g-1). Furthermore, a mechanism explaining the highly efficient removal of I- anions has been proposed according to characterization analyses of the composites after adsorption and subsequently been verified by adsorption under visible light experiments. 1.0%-Ag@Cu2O (0.5%-Ag@Cu2O, 0.2%-Ag@Cu2O) shows a high iodide uptake efficiency of 98.5% (77.6%, 37.8%) in the visible light, much higher than that under the darkness (86.3%, 69.7% and 30.8%). In addition, the adsorbent showed excellent selectivity for I- anions in the presence of large concentrations of competitive anions, eg. uptake efficiencies are 78.2%, 62.8%, 70.2% and 77.9% in the presence of the Cl-, CO32-, SO42- and NO3- competitive anions, respectively, and could work in a wide pH range of 3-11. This study is hopefully to prompt Cu2O to become a new and highly efficient adsorbent for iodide adsorb from solutions.

Spatial distribution of perchlorate, iodide and thiocyanate in the aquatic environment of Tianjin, China: environmental source analysis.

Although China is the largest producer of fireworks (perchlorate-containing products) in the world, the pathways through which perchlorate enters the environment have not been characterized completely in this country. In this study, perchlorate, iodide and thiocyanate were measured in 101 water samples, including waste water, surface water, sea water and paired samples of rain water and surface runoff collected in Tianjin, China. The concentrations of the target anions were generally on the order of rain>surface water≈waste water treatment plant (WWTP) influent>WWTP effluent. High concentrations of perchlorate, iodide and thiocyanate were detected in rain samples, ranging from 0.35 to 27.3 (median: 4.05), 0.51 to 8.33 (2.92), and 1.31 to 107 (5.62) ngmL(-)(1), respectively. Furthermore, the concentrations of the target anions in rain samples were significantly (r=0.596-0.750, p<0.01) positively correlated with the concentrations obtained in the paired surface runoff samples. The anions tested showed a clear spatial distribution, and higher concentrations were observed in the upper reaches of rivers, sea waters near the coast, and rain-surface runoff pairs sampled in urban areas. Our results revealed that precipitation may act as an important source of perchlorate, iodide and thiocyanate in surface water. Moreover, iodide concentrations in the Haihe River and Dagu Drainage Canal showed a good correlation with an ideal marker (acesulfame) of domestic waste water, indicating that input from domestic waste water was an important source of iodide in the surface waters of Tianjin.

A review of the removal of anions and oxyanions of the halogen elements from aqueous solution by layered double hydroxides.

The application of layered double hydroxides (LDHs) and thermally activated LDHs for the removal of various fluorine (F(-),BF4(-)), chlorine (Cl(-),ClO4(-)), bromine (Br(-),BrO3(-)) and iodine (I(-),IO3(-)) species from aqueous solutions has been reviewed in this article. LDHs and thermally activated LDHs were able to significantly reduce the concentration of selected anions in laboratory scale experiments. The M(2+):M(3+) cation ratio of the LDH adsorbent was an important factor which influenced anion uptake. Though LDHs were able to remove some target anion species through anion exchange and surface adsorption thermal activation and reformation generally produced better results. The presence of competing anions including carbonate, phosphate and sulphate had a significant impact on uptake of the target anion as LDHs typically exhibit lower affinity towards monovalent anions compared to anions with multiple charges. The removal of fluoride and perchlorate from aqueous solution by a continuous flow system utilising fixed bed columns packed with LDH adsorbents has also been investigated. The adsorption capacity of the columns at breakpoint was heavily dependent on the flow rate and lower than result reported for the corresponding batch methods. There is still considerable scope for future research on numerous topics summarised in this article.

Physicochemical properties of silica gel coated with a thin layer of polyaniline (PANI) and its application in non-suppressed ion chromatography.

Physicochemical properties of a new sorbent and its potential application in non-suppressed ion chromatography (IC) have been investigated. The sorbent was obtained in a process of covering silica gel particles with a film of polyaniline (PANI). The properties of silica modified with polyaniline such as particle size, porosity, average quantity of polyaniline covering carrier and density of sorbent were determined. In our study the following methods were used: microscopic analysis, laser diffraction technique, combustion analysis, mercury porosimetry and helium pycnometry. Column with the newly obtained packing was used for the separation of inorganic anions. Optimized chromatographic system was successfully employed for analysis of iodide and bromide in selected pharmaceutical products (Bochnia salt and Iwonicz salt) applied in chronic respiratory disease. Analysis was carried out using 0.1M solution of HCl in mixture of methanol/water (50:50v/v) as a mobile phase; the flow rate was 0.3 mL min(-1), temperature was 24°C and λ=210 nm. Validation parameters such as correlation coefficient, RSD values, recovery, detection and quantification limits were found to be satisfactory.

Graphene sheet-starch platform based on the groove recognition for the sensitive and highly selective determination of iodide in seafood samples.

The functionalization of graphene nanosheets was realized using a simple starch mixture to achieve a highly selective recognition of iodide, thereby surmounting the complicated reactions possibly leading to low yield during functionalization. The groove recognition for starch to iodide, a novel recognition model, was established. The starch-to-graphene nanosheet mass ratio of 3:2 produced an optimal current signal. The recognition and measurement procedures were conducted in different cells, respectively. These procedures improved the selectivity and sensitivity, and overcame the possibility of interference from coexisting ions. Under optimal conditions, the graphene sheet-starch electrode was immersed in a recognition cell at pH 2.0 for 10min, afterward, in a measurement cell at pH 1.0 for quantitative analysis, resulting in the highest current signals obtained. The quantitative electrochemical measurements yielded a mean value of 214.6mg/kg in actual samples of commercially available seafood sample, whereas the spectrophotometric measurements produced a mean value of 226.7mg/kg. If the spectrophotometric value for the seafood sample is accurate, the percentage error for the electrochemical method is only 5.3%. Therefore, the electrochemical method is reliable for qualitative iodide measurements. The groove recognition was highlighted to elucidate the specific selectivity.

Determination of iodide in seawater by capillary ion chromatography using hexadimethrine bromide modified C30 stationary phases.

A novel and simple capillary ion chromatographic method for the determination of iodide is reported. Separation was achieved on a laboratory-made packed capillary column (100 mm × 0.32 mm i.d.) packed with triacontyl-functionalized silica, followed by a modification with hexadimethrine bromide, where 1 mM sodium chloride-acetonitrile (95:5, v/v) was used as the eluent and UV-absorbing analyte anions were detected at 225 nm. The effects of the eluent composition on the retention behavior of inorganic anions were investigated. The addition of a small amount of an organic substance in an eluent such as acetonitrile increased the retention of iodide, while the addition of methanol decreased its retention. The present analytical method was successfully applied to the rapid and direct determination of iodide in seawater without any preconcentration. Also, this modified column could be used for about two months (6 h operation per day) without hexadimethrine bromide being contained in the eluent.

Synthesis, characterization and application of a new chelating resin for on-line separation, preconcentration and determination of Ag(I) by flame atomic absorption spectrometry.

A simple and reliable on-line separation/preconcentration procedure was developed for the determination of trace levels of Ag(I) by flame atomic absorption spectrometry. Poly[N-(3-methyl-1H-indol-1-yl)-2-methacrylamide-co-2-acrylamido-2-methyl-1-propane sulfonic acid-co-divinylbenzene] was synthesized and characterized as a new chelating resin for the first time. Ag(I) was sorbed on the chelating resin, from which it could be eluted with 3 mol L(-1) HCl and then introduced directly to the nebulizer-burner system for flame atomic absorption spectrometry. The parameters influential on the determination of Ag(I) ions such as the pH of the sample solution, amount of resin, eluent type, interfering ions and flow variables were studied. Under the optimum conditions, the calibration graph obtained was linear over the concentration range of 2-20 µg L(-1). The detection limit of the method (3σ) was 0.3 µg L(-1) while precision was 1.5% (n=25) at the level of 10 µg L(-1) Ag(I). The limit of quantification for the method, based on 20 σ, was 2.0 µg L(-1). The enrichment factor was found to be 65 while the optimized sample volume was 13.6 mL. The accuracy of the method was performed by analyzing certified reference materials. The developed method was applied successfully for the determination of silver in different water samples with satisfactory results.

Properties and applications of zeolites.

Zeolites are aluminosilicate solids bearing a negatively charged honeycomb framework of micropores into which molecules may be adsorbed for environmental decontamination, and to catalyse chemical reactions. They are central to green-chemistry since the necessity for organic solvents is minimised. Proton-exchanged (H) zeolites are extensively employed in the petrochemical industry for cracking crude oil fractions into fuels and chemical feedstocks for other industrial processes. Due to their ability to perform cation-exchange, in which the cations that are originally present to counterbalance the framework negative charge may be exchanged out of the zeolite by cations present in aqueous solution, zeolites are useful as industrial water-softeners, in the removal of radioactive Cs+ and Sr2+ cations from liquid nuclear waste and in the removal of toxic heavy metal cations from groundwaters and run-off waters. Surfactant-modified zeolites (SMZ) find particular application in the co-removal of both toxic anions and organic pollutants. Toxic anions such as arsenite, arsenate, chromate, cyanide and radioactive iodide can also be removed by adsorption into zeolites that have been previously loaded with co-precipitating metal cations such as Ag+ and Pb2+ which form practically insoluble complexes that are contained within the zeolite matrix.

1-Butyl-3-methylimidazolium hexafluorophosphate ionic liquid as a new solvent for the determination of lead(II) and cadmium(II) by anodic stripping voltammetry after extraction of the iodide complexes.

The use of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM x PF(6)) as a solvent for the anodic stripping analysis of Pb(II) and Cd(II) after extraction of the iodide complexes has been investigated. This method is based on the extraction of the metal iodide complexes into BMIM x PF(6), followed by differential-pulse anodic stripping voltammetry with an in-situ plated bismuth film electrode onto an edge-plane type of pyrolytic graphite substrate. When tetra-n-propylammonium iodide at a concentration of 0.20 mol L(-1) was used as an extractant and a supporting electrolyte, the reduced lead and cadmium produced well-defined anodic peaks at -414 and -736 mV vs. Ag/AgCl, respectively. The peak currents for Pb(II) and Cd(II) were directly proportional to the initial metal concentration in the ranges of 0.01-0.50 microg mL(-1) and 0.05-1.0 microg mL(-1) under the optimized conditions. A detection limit (S/N = 3) of 0.001 microg mL(-1) Pb(II) was obtained with a volume ratio (V(aq)/V(BMIM x PF(6))) of 2.0 at 300 s deposition time. The relative standard deviation was 3.2% on replicate runs (n = 10) for the determinations of 0.20 microg mL(-1) Pb(II).

Anion exchange silica monolith for capillary liquid chromatography.

An anion exchange monolithic silica capillary column was prepared by surface modification of a hybrid monolithic silica capillary column prepared from a mixture of tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMS). The surface modification was carried out by on-column copolymerization of N-[3-(dimethylamino)propyl]acrylamide methyl chloride-quaternary salt (DMAPAA-Q) with 3-methacryloxypropyl moieties bonded as an anchor to the silica surface to form a strong anion exchange stationary phase. The columns were examined for their performance in liquid chromatography (LC) and capillary electrochromatography (CEC) separations of common anions. The ions were separated using 50 mM phosphate buffer at pH 6.6. Evaluation by LC produced an average of 30,000 theoretical plates (33 cm column length) for the inorganic anions and nucleotides. Evaluation by CEC, using the same buffer, produced enhanced chromatographic performance of up to ca. 90,000 theoretical plates and a theoretical plate height of ca. 4 mum. Although reduced efficiency was observed for inorganic anions that were retained a long time, the results of this study highlight the potential utility of the DMAPAA-Q stationary phase for anion separations.

Treatment of brackish produced water using carbon aerogel-based capacitive deionization technology.

Capacitive deionization (CDI) with carbon-aerogel electrodes represents a novel process in desalination of brackish water and has merit due to its low fouling/scaling potential, ambient operational conditions, electrostatic regeneration, and low voltage requirements. The objective of this study was to investigate the viability of CDI in treating brackish produced water and recovering iodide from the water. Laboratory- and pilot-scale experiments were conducted to identify ion selectivity, key operational parameters, evaluate desalination performance, and assess the challenges for its practical applications. The performance of the CDI technology (CDT) system tested was consistent throughout the laboratory- and field-scale experiments. Deterioration of the carbon-aerogel electrodes was not observed during testing. The degree of ions adsorbed to the carbon aerogel (in mol/g aerogel) during treatment of brackish water was dependent upon initial ion concentrations in the feed water with the following selectivity I>Br>Ca>alkalinity>Mg>Na>Cl. The preferential sorption of iodide revealed merit to efficiently recover iodide from brackish water even in the presence of dominant co-ions. The research findings derived from this study identified parameters that merit further improvements regarding design and operation, including modification of pore-size distribution of aerogel, development of high capacitance and low-cost electrode materials, reducing the dead volume after regeneration and rinsing, minimizing energy consumption, and maximizing system recovery.

Ag-doped carbon aerogels for removing halide ions in water treatment.

The objective of this study was to analyze the efficiency of silver(Ag)-doped carbon aerogels for the removal of bromide (Br(-)) and iodide (I(-)) from drinking waters. Textural characterization of Ag-doped aerogels showed that an increase in the Ag dose added during the preparation process produced: (i) a reduction in the surface area (S(BET)) and (ii) an increase in mesopore (V(2)) and macropore (V(3)) volumes. Chemical characterization of the materials revealed an acidic surface (pH of point of zero charge, pH(PZC)=4.5, O(surface)=20%). The oxidation state of Ag was +1 and the surface concentration of this element ranged from 4% to 10%. The adsorption capacity (X(m)) and affinity of adsorbent (BX(m)) increased with a reduction in the radius of the halogenide. Furthermore, an increase in the adsorption capacity was observed with higher Ag concentrations on the aerogel surface. The high adsorption capacity of the aerogel may be due to the presence of Ag(I) on its surface, with the formation of the corresponding Ag halides. Our observations indicate that the halogenides adsorption on commercial activated carbon (Sorbo-Norit) is much lower than that of the Ag-doped carbon aerogels. The presence of chloride and natural organic matter (NOM) in the medium reduced the adsorption capacity of Br(-) and I(-) on Ag carbon aerogels.

Removal of bromide and iodide anions from drinking water by silver-activated carbon aerogels.

The aim of this study is to analyze the use of Ag-doped activated carbon aerogels for bromide and iodide removal from drinking water and to study how the activation of Ag-doped aerogels affects their behavior. It has been observed that the carbonization treatment and activation process of Ag-doped aerogels increased the surface area value ( [Formula: see text] ), whereas the volume of meso-(V(2)) and macropores (V(3)) decreased slightly. Chemical characterization of the materials revealed that carbonization and especially activation process considerably increased the surface basicity of the sample. Original sample (A) presented acidic surface properties (pH(PZC)=4.5) with 21% surface oxygen, whereas the sample that underwent activation showed mainly basic surface chemical properties (pH(PZC)=9.5) with only 6% of surface oxygen. Carbonization and especially, activation process considerable increased the adsorption capacity of bromide and iodide ions. This would mainly be produced by (i) an increase in the microporosity of the sample, which increases Ag-adsorption sites available to halide anions, and (ii) a rise of the basicity of the sample, which produces an increase in attractive electrostatic interactions between the aerogel surface, positively charged at the working pH (pH(solution)

Preparation and application of organo-modified zeolitic material in the removal of chromates and iodides.

The removal of chromates and iodides from aqueous solutions by organo-modified tuffs from the Pentolofos area (Thrace, Greece) was investigated using (51)Cr- and (131)I-labelled solutions and gamma-ray spectroscopy. The zeolitic material was modified by hexadecyltrimethyl-ammonium bromide (HDTMA-Br) and octadecyltrimethyl-ammonium bromide (ODTMA-Br) and characterized by scanning electron microscopy, FT-IR spectrometry and zeta potential measurements. Both experimental study and modelling indicated that both organo-zeolitic sorbents have a bigger affinity for iodide than for chromate. The chromium uptake did not seem to be influenced by the type of modifier but showed, as expected, a dependence on the solution pH. The maximum sorption capacity (2.27 mg/g) of Cr(VI) was achieved for the solution of initial pH 4. On the other hand, the HDTMA-modified tuff showed a lower sorption affinity for iodides than did the ODTMA-modified one (3.37 and 4.02 mg/g, respectively).

Optically stimulated luminescence in an imaging plate using BaFi:Eu.

BaFI:Eu phosphors are fabricated using a new method of synthesis: liquid phase synthesis, in which the phosphor particles are formed through the association of Ba2+ ions, F-ions and Eu2+ ions in solution. An intense optically stimulated luminescence (OSL) peak at about 410 nm is observed by stimulating X ray irradiated BaFI:Eu phosphor with about 550-750 nm light. It is found that the peak wavelength of the optically stimulation spectrum is about 690 nm. This result suggests that the semiconductor laser can be used as the stimulating light source. It is also found that the OSL intensity is increased with increasing the X ray dose. The BaFI:Eu phosphor as a photostimulable material for the imaging plate of a computed radiography system provides the following advantages; (1) high X ray absorption coefficient, (2) high monodispersion in size which would contribute to sharp images, (3) high OSL and thus low luminescence mottle and (4) high DQE (detective quantum efficiency).

Retardation capacity of organophilic bentonite for anionic fission products.

Sorption and diffusivity of iodide and pertechnetate (I- and TcO4-) on MX-80 bentonite with different hexadecylpyridinium (HDPy+) loadings were studied using equilibrium solutions of different ionic strengths. In HDPy(+)-modified bentonite, iodide and pertechnetate ions exhibited increasing sorption (characterized by the distribution ratio, Rd), while Cs+ and Sr2+ showed decreasing sorption with increasing organophilicity. In case of medium-loading levels, the simultaneous sorption of anions (I- and TcO4-) and cations (Cs+ and Sr2+) was observed. Sorption of ions was influenced by the composition of the electrolytes employed. It decreased gradually with increasing ionic strength of the electrolyte solutions. The experiments revealed the general tendency that the diffusivity (Da [cm2.s-1]) for iodide and pertechnetate decreases with increasing organophilicity and increases with increasing ionic strength of the equilibrium solutions, confirming the results of the sorption experiments. Additionally, some mineralogical and chemical investigations, like IR spectral analysis of the organo-bentonite samples and exchange behavior of HDPy+, were performed. On the basis of these analyses, it was concluded that the alkylammonium ions are sorbed as (1) HDPy+ cations, (2) HDPyCl molecules and (3) micelles with decreasing binding intensities in this order.

Capillary electrophoresis of anions at high salt concentrations.

It is commonly thought that even a moderately high ionic concentration in the background electrolyte (BGE) would lead to Joule heating and serious peak distortion. However, we obtained very satisfactory separations of both inorganic and organic anions in electrolyte solutions as high as 5 M sodium chloride using direct photometric detection. Samples containing a 0.5 M concentration of a salt can be analyzed directly by making the BGE concentration of the same salt even higher to obtain electrostacking. The temperature in the center of the capillary was calculated to be 49 degrees C when the current is at its maximum of 280 microA. The effect of various salts on electrophoretic and electroosmotic mobility is discussed. Several examples are given of capillary electrophoresis under high-salt conditions.