Within the past decade, there has been an emergence of reports regarding the synthetic isolation of multinary metal chalcogenide nanocrystals that persist under ambient conditions with metastable crystal structures; however, many of the direct syntheses remain largely serendipitous with respect to the conditions needed to achieve the metastable product. Toward the development of more rational design principles that enable the predictable isolation of metastable nanocrystals, we demonstrate a molecular programming approach for the synthesis of CuInSe 2 nanocrystals utilizing diorganyl diselenide precursors of the structure R-Se-Se-R. Specifically, we show that the kinetics of diselenide precursor conversion are dependent upon C−Se and Se−Se bond dissociation energies and that the strength of the C−Se bond is the phase-directing variable. When dibenzyl and dimethyl diselenide precursors with relatively weaker C−Se bonds are employed, the resulting nanocrystals form in the thermodynamically stable chalcopyrite phase of CuInSe 2 . However, precursors like diphenyl diselenide that possess stronger C− Se bonds alter the reaction kinetics so as to steer the reaction toward formation of the metastable wurtzite-like phase. These two phases form via distinct copper selenide intermediates, with chalcopyrite forming through Cu 2−x Se and the wurtzite-like phase forming through Cu 3 Se 2 intermediates, and it was found that the ultimate wurtzite-like phase displays remarkable resistance to relaxation to the chalcopyrite phase. This molecular programming approach should be applicable toward the isolation of other metastable phases of metal chalcogenide nanocrystals.

Anti-NASICON Fe2(MoO4)3 (P21/c) shows significant structural and electrochemical differences in the intercalation of Li + and Na + ions. To understand the origin of this behavior, we have used a combination of in-situ X-ray and high-resolution neutron diffraction, total scattering, electrochemical measurements, density functional theory calculations, and symmetry-mode analysis. We find that for Li +-intercalation, which proceeds via a two-phase monoclinic-to-orthorhombic (Pbcn) phase transition, the host lattice undergoes a concerted rotation of rigid polyhedral subunits driven by strong interactions with the Li + ions, leading to an ordered lithium arrangement. Na +intercalation, which proceeds via a two-stage solid solution insertion into the monoclinic structure, similarly produces rotations of the lattice polyhedral subunits. However, using a combination of total neutron scattering data and density-functional theory calculations, we find that while these rotational distortions upon Na + intercalation are fundamentally the same as for Li + intercalation, they result in a far less coherent final structure, with this difference attributed to the substantial difference between the ionic radii of the two alkali metals.

It is known that alkali, transition metal and lanthanide salts can form lyotropic liquid crystalline (LLC) mesophases with non-ionic surfactants (such as CiH2i+1(OCH2CH2)jOH, denoted as CiEj). Here we combine several salt systems and show that the percent deliquescence relative humidity (%DRH) value of a salt is the determining parameter in the formation and stability of the mesophases and that the other parameters are secondary and less significant. Accordingly, salts can be divided into 3 categories: Type I salts (such as LiCl, LiBr, LiI, LiNO3, LiClO4, CaCl2, Ca(NO3)2, MgCl2, and some transition metal nitrates) have low %DRH and form stable salt-surfactant LLC mesophases in the presence of a small amount of water, type II salts (such as some sodium and potassium salts) that are moderately hygroscopic form disordered stable mesophases, and type III salts that have high %DRH values, do not form stable LLC mesophases and leach out salt crystals. To illustrate this effect, a large group of salts from alkali and alkaline earth metals were investigated using XRD, POM, FTIR, and Raman techniques. Among the different salts investigated in this study, the LiX (where X is Cl(-), Br(-), I(-), NO3(-), and ClO4(-)) and CaX2 (X is Cl(-), and NO3(-)) salts were more prone to establish LLC mesophases because of their lower %DRH values. The phase behavior with respect to concentration, stability, and thermal behavior of Li(I) systems were investigated further. It is seen that the phase transitions among different anions in the Li(I) systems follow the Hofmeister series.

Nanoparticles of nickel phosphide are finding wide ranging utility as catalysts for hydrodesulfurization, hydrogen evolution reaction, and hydrodeoxygenation of bio-oils. Herein, we present a methodology to tailor monodisperse nickel phosphide nanoparticles in terms of size and phase through the use of a statistical response surface methodology. Colloidal nickel phosphide nanoparticles were synthesized by replacing octadecene (ODE), a commonly used organic solvent, by a more sustainable phosphonium-based ionic liquid (IL). The replacement of ODE with the phosphonium-based IL resulted in faster crystallization at lower temperatures to yield phase-pure, monodisperse Ni2P nanoparticles. Using a first-order design, the PPh3/Ni precursor ratio was identified as the most critical factor influencing the resulting size and phase of the nanoparticles. Optimization using a Doehlert matrix for second-order design yielded a second-degree polynomial equation used to predict the mean diameter of the nanoparticles (over a range of 4–12 nm) as a function of the PPh3/Ni precursor ratio and the temperature used during synthesis. The resulting model was validated by performing reactions using randomly chosen sets of conditions; the experimentally determined nanoparticle sizes were in excellent agreement with the theoretical sizes predicted by our model. This demonstrates the utility of a multivariate experimental design as a powerful tool in the development of synthetic strategies toward the preparation of colloidal nanoparticles with highly controlled size, size distribution, and phase.

Lithium salt (LiCl, LiBr, LiI, or LiNO 3 ) and a non-ionic surfactant (such as 10-lauryl ether, C 12 E 10 ) form lyotropic liquid crystalline (LLC) mesophases in the presence of a small amount of water. The mesophases can be prepared as gels by mixing all the ingredients in one pot or in the solution phase that they can be prepared by coating over any substrate where the LLC phase is formed by evaporating excess solvent. The second method is easier and produces the same mesophase as the first method. A typical composition of the LLC phases consists of 2-3 water per salt species depending on the counter anion. The LiI-C 12 E 10 mesophases can also be prepared by adding I 2 to the media to introduce an I À /I 3 À redox couple that may be used as a gel-electrolyte in a dye-sensitized solar cell. Even though the mesophases contain a large amount of water in the media, this does not affect the cell performance.The water molecules in the mesophase are in the hydration sphere of the ions and do not act like bulk water, which is harmful to the anode of the dye-sensitized solar cells (DSSC). There are two major drawbacks of the salt-surfactant LLC mesophases in the DSSCs; one is the diffusion of the gels into the pores of the anode electrode and the other is the low ionic conductivity. The first issue was partially overcome by introducing the gel content as a solution and the gelation was carried in/over the pores of the dye modified titania films. To increase the ionic conductivity of the gels, other salts (such as LiCl, LiBr, and LiNO 3 ) with better ionic conductivity were added to the media, however, those gels behave less effectively than pure LiI/I 2 systems. Overall, the DSSCs constructed using the LLC electrolyte display high short circuit current (I sc of around 10 mA), high open circuit voltage (V oc of 0.81 V) and good fill factor (0.69) and good efficiency (3.3%). There is still room for improvement in addressing the above issues in order to enhance the cell efficiency by developing new methods of introducing the gel-electrolytes into the mesopores of the anode electrode. Lanka † Electronic supplementary information (ESI) available: ATR-FTIR spectra of G2-LiCl-2, G2-LiBr-2, G2-LiI-2, and G2-LiNO 3 -2, ATR-FTIR spectrum and XRD pattern of mesocrystals of G2-LiI-I 2 -4, UV-vis absorption spectra of G2-LiI-I 2 -x (x is 1, 2, 3, 4, and 5) and LiI-I 2 mixture in ethanol, water, acetonitrile and glycol Raman spectra of G2-LiI-2 and G2-LiI-I 2 -2, IPCE and time dependent IV curves. See