Highly Sensitive and Exceptionally Wide Dynamic Range Detection of Ammonia Gas by Indium Hexacyanoferrate Nanoparticles Using FTIR Spectroscopy.

Ammonia gas is useful but caustic; thus, its concentration is monitored depending on applications. We prepared indium hexacyanoferrate nanoparticles (InHCF-NPs, HCF = [FeII(CN)6]4-) with average diameter around 8 nm by simple reaction at room temperature between In cations and HCF anions, and we found the unique functionality of InHCF-NPs which were capable of highly sensitive (16 ppb) and exceptionally wide range (190000, 16 ppb -0.3%) detection of ammonia gas within 6 min by IR measurements. Slope changes of the IR peak ratio of adsorbed ammonium over CN moieties in the InHCF framework indicated a good log-log linear correlation along gas concentrations, in which a wide dynamic range over 105 was realized for the first time in the field of ammonia gas detection.

Vesicles exhibit high-performance removal of per-and polyfluoroalkyl substances (PFAS) depending on their hydrophobic groups.

The removal of per- and polyfluoroalkyl substances (PFAS) from drinking water is urgently needed. Here, we demonstrated high performance of vesicles on PFAS adsorption. Vesicles used in this study were enclosed amphiphile bilayers keeping their hydrophobic groups inside and their hydrophilic groups outside in water. The distribution coefficient Kd of perfluorooctane sulfonic acid (PFOS) for vesicles was 5.3 × 105 L/kg, which is higher than that for granulated activated carbon (GAC), and Kd of perfluorooctanoic acid (PFOA) for vesicles was 103-104 L/kg. The removal efficiencies of PFOA and PFOS adsorption on DMPC vesicles were 97.1 ± 0.1% and 99.4 ± 0.2%, respectively. The adsorption behaviors of PFOA and PFOS on vesicles were investigated by changing the number of cis-double bonds in the hydrophobic chains of the vesicle constituents. Moreover, vesicles formed by membranes in the different phases were also tested. The results revealed that, when vesicles are formed of a membrane in the liquid-crystalline (liquid-like) phase, the adsorption amounts of both PFOA and PFOS increased as the cis-double bond in the hydrocarbon chains decreased, which is considered due to molecular shape similarity. When vesicles are formed of a membrane in the gel (solid-like) phase, they do not adsorb PFAS as much as in the liquid-crystalline phase, even though the hydrocarbon chains do not have any cis-double bond. Our findings demonstrate that vesicles can be utilized as PFAS adsorbents by optimizing the structure of vesicle constituents and their thermodynamical phase. Indeed, the vesicles (DMPC) were demonstrated that they can adsorb PFOA and PFOS, and be coagulated by a coagulant even in environmental water. The coagulation will enable the removal of PFOA and PFOS from the water after adsorption.

Surface modification enhances the bulk proton conductivity of Prussian blue.

Surface-modified Prussian blue shows 102 times higher bulk proton conductivity (0.018 S cm-1) than that of unmodified Prussian blue. This enhancement is attributed to the monolayer adsorption of Na4[Fe(CN)6] on the nanoparticle surface, which reduces the surface resistance. Surface modification is an effective strategy for improving bulk proton conductivity.

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.

One million cyclable blue/colourless electrochromic device using K2Zn3[Fe(CN)6]2 nanoparticles synthesized with a micromixer.

Well-defined K2Zn3[Fe(CN)6]2-nanoparticles (NPs) synthesized with a micromixer showed robust redox reaction cyclability. Crystal structure analysis revealed that the robustness results from the maintenance of the original rhombohedral crystal structure in the oxidation state. The blue/colourless electrochromic device with the K2Zn3[Fe(CN)6]2-NPs and Prussian blue NPs showed recyclability over 1 million redox reactions.

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.