Desorption of Ammonia Adsorbed on Prussian Blue Analogs by Washing with Saturated Ammonium Hydrogen Carbonate Solution.

Prussian blue analogs (PBAs) have been reported as promising ammonia (NH3) adsorbents with a high capacity compared to activated carbon, zeolite, and ion exchange resins. The adsorbed NH3 was desorbed by heating and washing with water or acid. Recently, we demonstrated that desorption was also possible by washing with a saturated ammonium hydrogen carbonate solution (sat. NH4HCO3aq) and recovered NH3 as an NH4HCO3 solid by introducing CO2 into the washing liquid after desorption. However, this has only been proven for copper ferrocyanide and the relationship between the adsorption/desorption behavior and metal ions in PBAs has not been identified. In this study, we investigated the adsorption/desorption behavior of PBAs that are complexes of first row transition metals with hexacyanometalate anions. Six types of PBAs were tested in this study and copper ferricyanide exhibited the highest desorption/adsorption ratio. X-ray diffraction results revealed high structural stability for cobalt hexacyanocobaltate (CoHCC) and nickel ferricyanide (NiHCF). The Fourier transform infrared spectroscopy results showed that the NH3 adsorbed on the vacancy sites tended to desorb compared to the NH3 adsorbed on the interstitial sites as ammonium ions. Interestingly, the desorption/adsorption ratio exhibited the Irving-Williams order.

Ammonium removal and recovery from sewage water using column-system packed highly selective ammonium adsorbent.

One of the strategies to realize a nitrogen cycle society, we attempted to recover ammonium ions from industrial wastewater, especially sewage water with adsorbent materials. We have developed an adsorbent with high ammonium selectivity based on copper hexacyanoferrate and granulated it as pellets. Using a compact column system filled with this granule adsorbent, ammonium ions were recovered from sewage containing 1000-1500 mg-NH4+/L ammonium ions. Despite the coexistence of many metal ions, the adsorbent selectively and stably adsorbed ammonium ions. Furthermore, it was shown that the saturated adsorbent can be regenerated by flowing a potassium ion solution through a column adsorbent to desorb ammonium ions. In other words, the column can be used repeatedly, and there was almost little deterioration in adsorption even after 250 cycles. In addition, it was shown that by increasing the number of stages of this column, it is possible to sufficiently reduce the ammonium in the adsorbent solution and recover the concentrated ammonium solution.

Ammonium salt production in NH3-CO2-H2O system using a highly selective adsorbent, copper hexacyanoferrate.

Ammonia is a beneficial material that is widely used in agriculture, but its emission into the atmosphere causes air pollution. Recently, Prussian blue (PB) and its analogs (PBA) were found to be ammonia adsorbents with high selectivity and capacity. In this study, we utilized a highly potent PBA adsorbent, copper hexacyanoferrate (CuHCF), to desorb ammonia and turn it into a reusable form. Because the reported NH3-CO2-H2O system phase diagram suggests the possibility of the recovery of solid NH4HCO3, we examined whether adsorbed ammonia desorbs into the saturated ammonium hydrogencarbonate solution (sat. NH4HCO3aq). We demonstrated that 40% of adsorbed ammonia desorbed into sat. NH4HCO3aq. After the desorption, CO2 was blown into the washing liquid, and NH4HCO3 precipitated, which was confirmed by Fourier transform infrared spectroscopy. The molar amount of solid NH4HCO3 was almost equal to that of desorbed ammonia. Our findings pave the way for recovery of ammonia as a valuable product from waste gas.

Trace Ammonia Removal from Air by Selective Adsorbents Reusable with Water.

Ammonia adsorbents effective even in trace concentrations are key to the countermeasure for air pollution of particulate matter caused by ammonia emission from agriculture sectors. We revealed that Prussian blue (PB) and its analogues (PBAs), one of the porous coordination polymers, have higher ammonia adsorption capacity in 10 ppmv of ammonia (parts per million in volume, 10 ppmv = 0.0001 volume percent), ≥8 times that of conventional adsorbents. Moreover, these compounds can be recycled only through water flushing. The adsorption capacity of PBA was restricted to 10 cycles of adsorption/desorption, and the air sample for the experiment was collected from the composting equipment present in a swine farm. Despite the presence of saturated water vapor in the exhaust gas, the adsorbents showed excellent selectivity in the removal of ammonia from the sample.

Pre-enrichment of radioactive cesium in muddy water separated into suspended and dissolved substances for trace analysis.

A new in-situ pre-enrichment system was developed for trace analysis of radioactive Cs in environmental water such as rivers, ponds, and seas, where the radioactive Cs is separated into suspended substances (SS) and dissolved substances (DS). The SS component was collected as the enrichment slurry by cross-flow filtration, thereby compact systems were realized. The DS component was collected in a small cartridge filled with a non-woven fiber with immobilized adsorbent nanoparticles. The recovery rate was estimated at around 95%. The size distribution of the SS and the concentration of radioactive Cs after enrichment were the same as that of the raw water before enrichment. The condensed SS can be used for other evaluations such as ignition loss. From the field test at a pond in the Fukushima-area, the Cs concentration of the SS was found to be 4-5 times higher than that of the sediment in the same pond. The organic content estimated by ignition loss was also three times higher.

Unveiling Cs-adsorption mechanism of Prussian blue analogs: Cs+-percolation via vacancies to complete dehydrated state.

Metal hexacyanoferrates (MHCF) or Prussian blue analogs are excellent Cs+-adsorbents used for radioactive Cs-decontamination. However, the adsorption mechanism is controversial. To clarify the issue, we quantitatively investigated the Cs-adsorption behaviors of potassium copper hexacyanoferrate (KCuHCF) and A y Cu[Fe(CN)6]1-x ·zH2O. To obtain samples having homogeneous chemical composition and particle size, flow systems were used for both synthesis and purification. After sufficient rinsing with water, the range of x stable in aqueous solution in time appropriate for Cs-adsorption was 0.25 < x < 0.50. The relations y = 4 - 2x and z = 10x were also found independent of x, indicating complete dehydration of K+ in the crystal. We concluded that the excellent Cs-selectivity of MHCF was not due to difference in free energy of the adsorbed state between K+ and Cs+ but because of the hydrated state in aqueous solution. We also found that the guiding principle for determining the maximum capacity depended on the chemical composition. In particular, for the range 0.25 < x < 0.35, we propose a new model to understand the suppression of the maximum capacity. In our model, we hypothesize that Cs+ could migrate in the crystal only through [Fe(CN)6]4- vacancies. The model reproduced the observed maximum capacity without fitting parameters. The model would also be applicable to other MHCFs, e.g. a little adsorption by soluble Prussian blue. The ion exchange between Cs+ and H+ occurred only when the implemented K+ was small.

High-capacity and selective ammonium removal from water using sodium cobalt hexacyanoferrate.

A new NH4 + adsorbent with high capacity and selectivity, sodium cobalt(ii) hexacyanoferrate(ii) (NaCoHCF, Na y Co(ii) [Fe2+(CN)6] x ·zH2O), was prepared. The adsorption performance was investigated by varying the mixing ratio of [Fe(CN)6]4- to Co2+ during synthesis, R mix. The ammonia capacity was found to be proportional to R mix, indicating that the NH4 + capacity can be increased by increasing the Na+-ion content in NaCoHCF. To conduct a detailed study, we prepared homogeneous nanoparticles by flow synthesis using a micromixer with R mix = 1.00. Even on the addition of a saline solution (NaCl) with an Na+-ion concentration of 9350 mg L-1, the capacity was maintained: q max = 4.28 mol kg-1. Using Markham-Benton analysis, the selectivity factor, defined by the ratio of equilibrium constants for NH4 + to that for Na+, was calculated to be α = 96.2, and 4.36 mol kg-1 was found to be the maximum capacity. The high selectivity of NaCoHCF results in good NH4 +-adsorption performance, even from seawater. In comparison with other adsorbents under the same conditions and even for a NH4Cl solution, NaCoHCF showed the highest capacity. Moreover, the coexisting Na+ caused no interference with the adsorption of ammonium by NaCoHCF, whereas the other adsorbents adsorbed ammonia only slightly from the saline solution. We also found that the pores for NH4 + adsorption changed their sizes and shapes after adsorption.

Inversion analysis on vertical radiocesium distribution in pond sediment from γ-ray count measurement.

Evaluation of vertical distribution of radiocesium in bottom sediment by measuring vertical γ-ray count profile was discussed. A stable inversion formula was derived based on the maximum entropy method. Efficiency of the formula was confirmed by using a low-cost apparatus composed of an array of PIN photodiodes and a single board computer with real-time inversion code. In-door experiment by using five model sediment disks showed good reproducibility of vertical radiocesium profile. On-site experiment was also carried out at a pond in Fukushima to confirm the efficiency. It was suggested that combination of the simple apparatus and MEM inversion formula gave reasonable estimates on vertical radiocesium distribution in bottom sediment of 1 kBq/kg-wet level within about 10 min.

Radiocesium removal system for environmental water and drainage.

With the development of the nuclear power generation, it is expected that severe pollution of environmental water by radiocesium (r-Cs) may occur. We developed a r-Cs removal system with a continuous stirring tank reactor (CSTR) and r-Cs adsorbent of non-woven fiber immobilizing Prussian blue nanoparticles (PBN). Results confirmed that this system can remove r-Cs from environmental water with a removal rate higher than 80% at processing speed of 2 m3/h. In this study, the processing speed and processing capacity of this system were confirmed using kinetic and equilibrium analyses of Cs adsorption behavior on PBN. The equilibrium of Cs adsorption was analyzed using a Langmuir equation. Results show that the maximum adsorption capacity was 160 mg/g (PBN). The kinetic data were well fitted using a pseudo-first order kinetic model. This rate constant was correlated to the PBN/liquid ratio in the system.

Historical Pigment Exhibiting Ammonia Gas Capture beyond Standard Adsorbents with Adsorption Sites of Two Kinds.

Prussian blue is a historical pigment synthesized for the first time at the beginning of 18th century. Here we demonstrate that the historical pigment exhibits surprising adsorption properties of gaseous ammonia. Prussian blue shows 12.5 mmol/g of ammonia capacity at 0.1 MPa, whereas standard ammonia adsorbents show only 5.08-11.3 mmol/g. Dense adsorption was also observed for trace contamination in atmosphere. Results also show higher adsorption by Prussian blue analogues with the optimization of chemical composition. The respective capacities of cobalt hexacyanocobaltate (CoHCC) and copper hexacyanoferrate (CuHCF) were raised to 21.9 and 20.2 mmol/g, the highest value among the recyclable adsorbents. Also, CoHCC showed repeated adsorption in vacuum. CuHCF showed regeneration by acid washing. The chemical state of the adsorbed ammonia depends on the presence of the water in atmosphere: NH3, which was stored as in the dehydrated case, was converted into NH4(+) in the hydrated case.

Thermal dewetting behavior of polystyrene composite thin films with organic-modified inorganic nanoparticles.

The thermal dewetting of polystyrene composite thin films with oleic acid-modified CeO2 nanoparticles prepared by the supercritical hydrothermal synthesis method was investigated, varying the nanoparticle concentration (0-30 wt %), film thickness (approximately 50 and 100 nm), and surface energy of silanized silicon substrates on which the composite films were coated. The dewetting behavior of the composite thin films during thermal annealing was observed by an optical microscope. The presence of nanoparticles in the films affected the morphology of dewetting holes, and moreover suppressed the dewetting itself when the concentration was relatively high. It was revealed that there was a critical value of the surface energy of the substrate at which the dewetting occurred. In addition, the spatial distributions of nanoparticles in the composite thin films before thermal annealing were investigated using AFM and TEM. As a result, we found that most of nanoparticles segregated to the surface of the film, and that such distributions of nanoparticles contribute to the stabilization of the films, by calculating the interfacial potential of the films with nanoparticles.

Dealing with the aftermath of Fukushima Daiichi nuclear accident: decontamination of radioactive cesium enriched ash.

Environmental radioactivity, mainly in the Tohoku and Kanto areas, due to the long living radioisotopes of cesium is an obstacle to speedy recovery from the impacts of the Fukushima Daiichi Nuclear Power Plant accident. Although incineration of the contaminated wastes is encouraged, safe disposal of the Cs enriched ash is the big challenge. To address this issue, safe incineration of contaminated wastes while restricting the release of volatile Cs to the atmosphere was studied. Detailed study on effective removal of Cs from ash samples generated from wood bark, household garbage, and municipal sewage sludge was performed. For wood ash and garbage ash, washing only with water at ambient conditions removed radioactivity due to (134)Cs and (137)Cs, retaining most of the components other than the alkali metals with the residue. However, removing Cs from sludge ash needed acid treatment at high temperature. This difference in Cs solubility is due to the presence of soil particle originated clay minerals in the sludge ash. Because only removing the contaminated vegetation is found to sharply decrease the environmental radioactivity, volume reduction of contaminated biomass by incineration makes great sense. In addition, need for a long-term leachate monitoring system in the landfill can be avoided by washing the ash with water. Once the Cs in solids is extracted to the solution, it can be loaded to Cs selective adsorbents such as Prussian blue and safely stored in a small volume.

Supercritical hydrothermal synthesis and in situ organic modification of indium tin oxide nanoparticles using continuous-flow reaction system.

ITO nanoparticles were synthesized hydrothermally and surface modified in supercritical water using a continuous flow reaction system. The organic modification of the nanoparticles converted the surface from hydrophilic to hydrophobic, making the modified nanoparticles easily dispersible in organic solvent. The addition of a surface modifier into the reaction system impacted the crystal growth and particle size as well as dispersion. The particle size was 18 nm. Highly crystalline cubic ITO with a narrow particle size distribution was obtained. The advantages of short reaction time and the use of a continuous reaction system make this method suitable for industrial scale synthesis.

Estimation of local density augmentation and hydrogen bonding between pyridazine and water under sub- and supercritical conditions using UV-vis spectroscopy.

The local density around pyridazine was evaluated by examining the UV-vis spectral shift of pyridazine in a high-pressure liquid state and supercritical water from 25 to 450 degrees C and from 20 to 45 MPa. Augmentation of the local density was observed from 380 to 420 degrees C, and showed the maximum at a lower density than the critical density of water. The degree of hydrogen bonding was estimated in consideration of the local density augmentation. The estimated degree of hydrogen bonding under subcritical conditions without any difference between the local density and the bulk density corresponded to the previously reported results with a UV-vis absorbance spectral shift of quinoline and an NMR proton chemical shift. However, the degree of hydrogen bonding near the critical point of water was larger than that in the case that the local density augmentation was not taken into account. At 380 degrees C and 0.2 g cm(-3) of the bulk density there are 30% as many hydrogen bonds as those under the ambient condition, and it was around 1.5-times that without considering local-density augmentation.

Determination of Kamlet-Taft solvent parameters pi* of high pressure and supercritical water by the UV-Vis absorption spectral shift of 4-nitroanisole.

Kamlet-Taft solvent parameters, pi*, of high pressure and supercritical water were determined from 16-420 degrees C based on solvatochromic measurements of 4-nitroanisole. For the measurements, an optical cell that could be used at high temperatures and pressures was developed with the specification of minimal dead space. The low dead space cell allowed us to measure the absorption spectra of 4-nitroanisole at high temperature conditions before appreciable decomposition occurred. The behavior of pi* in terms of water density (pi* = 1.77rho- 0.71) was found to be linear, except in the near critical region, in which deviations were observed that could be attributed to local density augmentation. Excess density, which was defined as the difference between local density and bulk density, showed a maximum near the critical density of water. The frequencies of UV-Vis spectra of 4-(dimethylamino)benzonitrile and N,N-dimethyl-4-nitroaniline were correlated with pi* based on a linear solvation energy relationship (LSER) theory. Local density augmentation around 4-nitroanisole and that around 4-(dimethylamino)benzonitrile were similar but the augmentation observed around N,N-dimethyl-4-nitroaniline was larger.

Melting point depression of ionic liquids confined in nanospaces.

A new physical method was proposed to control the liquid properties of room temperature ionic liquids (RT-ILs) in combination with nanoporous materials; the melting point of ILs confined in nanopores remarkably decreases in proportion to the inverse of the pore size.

Amination of n-hexanol in supercritical water.

The amination of 1-n-hexanol followed by amidation was carried out in supercritical water at 380, 400, and 420 degrees C and water densities of 0.1, 0.3, and 0.5 g/cm3. The replacement of the hydroxyl group with the amino group was found to occur in 1-n-hexanol using ammonium acetate in supercritical water without the addition of a metal or an acid catalyst. The yield of the final product, N-n-hexylacetamide, increased by increasing the reaction temperature, water density, and the amount of ammonium acetate. The yield and the selectivity of N-n-hexylacetamide were 78.5% and 87.5%, respectively, in supercritical water at 400 degrees C, 0.5 g/cm3, for 10 min.