Structural aspects of heteropolyacid microemulsions

Abstract

Metrical insights from X-ray scattering studies of dense fluid phases (known as "third" phases) in the Keggin heteropolyacid-tri-n-butyl phosphate (TBP)-n-alkane system are provided. Small-angle X-ray scattering (SAXS) experiments reveal inter-acid correlation peaks corresponding to average centre-of-mass to centre-of-mass separations of 18-23 Å between P···P, Si···Si, and Al···Al of H3PW12O40, H4SiW12O40, and H5AlW12O40, respectively, consistent with the presence of TBP solvates that form by hydrogen bonding between the acids and the phosphoryl group of TBP. The Baxter sticky sphere model analyses of the SAXS data reveal identical structures for all the dense phases with inter-cluster interaction energies of ∼5kBT. We demonstrate that the sticky sphere model is an essential paradigm for interpreting SAXS and predicting mesoscale assembly in heteropolyacid microemulsions. The model parameters for the ternary polyoxometalate-amphiphile-oil systems reveal, in rigorous clarity, how the interactions between heteropolyacid solvates underpin their condensation to produce the observed scattering data. Aside from aiding researchers in predicting the physical origins of SAXS in strongly-interacting micellar systems found in natural and engineered settings, such as chemical separations, our study provides mesostructural information that complements previously observed electrochemical behaviours for third phases formed by solvent extraction involving the contact of aqueous electrolytes of dodecatungsto-phosphoric, -silicic, and -aluminic acids with organic solutions (e.g. n-dodecane and n-octane) of TBP, and by simple dissolution of the acid salts of the polyoxometalate hydrates in the same organic solutions.

Solution Speciation and Stability of Cobalt‐Polyoxometalate Water Oxidation Catalysts by X‐ray Scattering

“…[31] Moreover, shape, size and electron density contrast of particles can be identified and characterized in the solution state with much higher sensitivity and precision towards small radii and low concentrations than dynamic light scattering (DLS). [32][33][34][35][36][37][38][39][40] In this context, [Co 9 (H 2 O) 6 (OH) 3 (HPO 4 ) 2 (PW 9 O 34 ) 3 ] 16-(Co 9 ) (Figure 1, left), reported in 2012 as a WOC, [7,8] is particularly fascinating. Regarding metal-oxo clusters, SAXS is growing in popularity in the inorganic community and several publications reveal the potential of SAXS as a direct method for determining the form, structuring, and related function of POMs and polyoxocations in solution.…”

Lanthanum Exchanged Keggin Structured Heteropoly Compounds for Biodiesel Production

“…The La exchanged HPA samples showed XPS peaks at around 836.6 eV, 839.7 eV, 853.3 eV, and 856.3 eV related to La 3d 5/2 and La 3d 3/2 components, respectively. And the two peaks in each line could be assigned to main and satellite peaks due to 3d 0 4f 0 and 3d 0 4f 1 L configurations [24]. It was observed that different types of La compounds exhibit satellite peaks at different binding energies [25].…”

Direct Synthesis of Controlled‐Size Nanospheres inside Nanocavities of Self‐Organized Photopolymerizing Soft Oxometalates [PW12O40]n (n=1100–7500)

“…Similarly, extensive studies on heterogenized POMs have aimed to exploit the versatile catalytic properties of POMs even including those in the making of fuel cells . Recently, POMs have been self‐assembled into their superstructures with soft‐matter properties (SOMs) . It may also be mentioned that very recently “a self‐organizing chemical assembly line” and a light‐driven POM shuttle in homogeneous catalysis have been reported .…”

“…[4][5][6] Secondly,t oa chieve functionality, catalytically active structures based on polyoxometalates (POMs) were synthesized. [7][8][9][10][11][12][13][14][15][16][17][18][19] Moreover,t he self-assembly of complex supramolecular POM structures to soft-oxometalate (SOM) macroions was also achieved. [20][21][22][23] However,t he synthesis of self-assembled functionally active soft oxometalates (SOMs) still remains ac hallenge.H ere we address this challenge.…”

“…[28] Recently,P OMs have been self-assembledi nto their superstructures with soft-matter properties (SOMs). [16][17][18][19] It may also be mentioned that very recently "a self-organizing chemical assembly line" and al ight-drivenP OM shuttlei nh omogeneous catalysis have been reported. [29,30] SOM macroions based on paddle-wheel POMs [31] have extended the coordination chemistry of POMs to soft matter and presentn ew opportunities.…”