Historic Prussian blue (PB) pigment is easily obtained as an insoluble precipitate in quantitative yield from an aqueous mixture of Fe 3+ and [Fe II (CN) 6 ] 4− (Fe 2+ and [Fe III (CN) 6 ] 3−). It has been found that the PB pigment is inherently an agglomerate of 10-20 nm nanoparticles, based on powder x-ray diffraction (XRD) line broadenings and transmission electron microscopy (TEM) images. The PB pigment has been revived as both organic-solvent-soluble and water-soluble nanoparticle inks. Through crystal surface modification with aliphatic amines, the nanoparticles are stably dispersed from the insoluble agglomerate into usual organic solvents to afford a transparent blue solution. Identical modification with [Fe(CN) 6 ] 4− yields water-soluble PB nanoparticles. A similar ink preparation is applicable to Ni-PBA and Co-PBA (nickel and cobalt hexacyanoferrates). The PB (blue), Ni-PBA (yellow), and Co-PBA (red) nanoparticles function as three primary colour inks.

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.

We have revealed the fundamental mechanism of specific Cs(+) adsorption into Prussian blue (PB) in order to develop high-performance PB-based Cs(+) adsorbents in the wake of the Fukushima nuclear accident. We compared two types of PB nanoparticles with formulae of Fe(III)4[Fe(II)(CN)6]3·xH2O (x = 10-15) (PB-1) and (NH4)0.70Fe(III)1.10[Fe(II)(CN)6]·1.7H2O (PB-2) with respect to the Cs(+) adsorption ability. The synthesised PB-1, by a common stoichiometric aqueous reaction between 4Fe(3+) and 3[Fe(II)(CN)6](4-), showed much more efficient Cs(+) adsorption ability than did the commercially available PB-2. A high value of the number of waters of crystallization, x, of PB-1 was caused by a lot of defect sites (vacant sites) of [Fe(II)(CN)6](4-) moieties that were filled with coordination and crystallization water molecules. Hydrated Cs(+) ions were preferably adsorbed via the hydrophilic defect sites and accompanied by proton-elimination from the coordination water. The low number of hydrophilic sites of PB-2 was responsible for its insufficient Cs(+) adsorption ability.

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A novel microscopic mechanism of bi-directional structural changes is proposed for the photoinduced magnetic phase transition in Co-Fe Prussian blue analogues on the basis of ab initio quantum chemical cluster calculations. It is shown that the local potential energies of various spin states of Co are sensitive to the number of nearest neighbor Fe vacancies. As a result, the forward and backward structural changes are most readily initiated by excitation of different local regions by different photons. This mechanism suggests an effective strategy to realize photoinduced reversible phase transitions in a general system consisting of two local components. 78.90.+t,71.35.Lk, Repeatable switching-on and -off of magnetization by external stimuli such as light is one of the most fascinating phenomena with potential applications in next generation's information storage and processing. A bi-directional photo-induced magnetization was first discovered in a cobalt-iron Prussian blue analogue,Illumination of visible light (500 -700 nm) at low temperature induces a bulk magnetization (presumably, ferrimagnetism), which can be eliminated by illumination of near-IR light (∼1300 nm). In spite of various experimental and theoretical efforts [1,2,[4][5][6][7][8], the microscopic mechanism of the reversible magnetization is still not clear. In this Letter we report ab initio quantum chemical cluster calculations for the Co-Fe Prussian blue analogue, unveiling the microscopic mechanism of the bi-directional photo-induced local structural changes that trigger the phase transitions.The crystal of a Prussian blue analogue K 1−2x Co 1+x Fe(CN) 6 is composed of two metallic sites located on vertices of the cubic lattice and each surrounded by six cyano moieties, as shown in Fig. 1. The d-orbitals of transition metals split into t 2g and e g orbitals by the ligand field. In the case of x =0, there are vacancy sites with replacement of CN by H 2 O as shown in Fig. 1(b). Various fascinating phenomena including a room temperature magnet [9], electrochemically tunable magnets [10], transparent and colored magnetic thin films [11], and photo-induced magnetic dipole inversion [12] have been observed in such non-stoichiometric compounds. We will show that this non-stoichiometric aspect is essential for the reversible photo-induced magnetization.The low spin (LS) configuration of the ground nonmagnetic state and the high spin (HS) configuration of the meta-stable magnetic state of K 0.4 Co 1.3 Fe(CN) 6 · 5H 2 O are most likely Co III (dε 6 , S = 0)Fe II (dε 6 , S = 0) and Co II (dε 5 dγ 2 , S = 3/2)Fe III (dε 5 , S = 1/2), respectively [1,2]. These are depicted in Fig.2 as LS0 and HS0 states. Figure 2 schematically represents the most plausible elementary processes in the cycle of the photo-induced structural change. The LH0 and HS0 states are converted to the intermediate states LS1 and HS1, respectively, by photo-induced charge transfer (CT) between iron and cobalt atoms, and then to the final states HS0 and LS0 by intersystem crossing due t...

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Cs+ adsorption selectivity caused by hydration energy and percolation theory to evaluate the ion-exchangeable site ratio.