The continuous solid solution series based on the ion exchangeable Dion-Jacobson layered perovskites, A1−xA′xLaNb2O7 (A/A′ = Li, Na, K, Rb, Cs; 0 ≤ x ≤ 1), has been investigated to illuminate the relationship between composition and structure. Topochemical synthesis of the solid solutions from combinations of various alkali metal cations has been achieved by reacting pure end members (ALaNb2O7) at appropriate ratios and temperatures. All adjacent sets of alkali metals (Li/Na, Na/K, K/Rb, and Rb/Cs) readily formed solid solutions, while only the one non-adjacent solid solution, K1−xCsxLaNb2O7 (K/Cs), could be obtained. Local cation coordination and the corresponding layer alignments vary as a function of composition where the relative concentration of the larger cation dictates structure. Thermal analysis of the solid solutions, A1−xA′xLaNb2O7 (A/A′ = Li, Na, K) showed that the lithium- and sodium-containing compositions were thermally unstable. This study demonstrates that the systematic variation in average cation sizes in the solid solution series allows for structural control in these important perovskite hosts.

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A new series of inorganic–organic hybrid perovskite materials were prepared by microwave-assisted grafting reactions. Simple carboxylic acids, acetic acid, and propionic acid, as well as hydroxyaromatic carboxylic acids, 3,5-dihydroxy benzoic acid (DBA), 5-hydroxyisophthalic acid (HPA), 4-hydroxybenzoic acid (HBA), and 4-hydroxy-4-biphenyl carboxylic acid (HBCA), were reacted with the Dion–Jacobson double-layered perovskite, HLaNb2O7, and its alcoxy derivatives. Grafting was found to not occur with simple carboxylic acids, while those molecules with hydroxyls were all attached to the perovskite interlayers. Reactivity of the hydroxyaromatic carboxylic acids varied with the different layered perovskite hosts where reactions with HLaNb2O7 did not occur, and those with n-propoxy-LaNb2O7 were limited; the greatest extent of reactivity was seen with n-decoxy-LaNb2O7. This is attributed to the larger interlayer spacing available for the insertion of the various hydroxyaromatic carboxylic acid compounds. The loading exhibited by the grafting species was less than that seen with well-known long-chain alkoxy grafting groups. It is expected that the width of the molecules contributes to this where, due to the benzyl groups, the interlayer volume of the grafted moieties occupies a larger horizontal fraction, therefore minimizing the loading to the below half. X-ray powder diffraction and transmission electron microscopy studies found that grafting of the n-decoxy-LaNb2O7 intermediates with the series of hydroxyaromatics resulted in a reduction in crystallinity along with a disruption of the layer structure. Raman data on the series show little variation in local structure except for HBCA, where there appears to be a lengthening of the Nb-O apical linkage and a possible reduction in the distortion of inner-layer NbO6 octahedra. The optical properties of the hydroxyaromatic carboxylic acid grafted perovskites were also investigated using diffuse-reflectance UV-Vis spectroscopy. The band gaps of DBA, HPA, and HBA were found to be similar to the parent (Eg ≈ 3.4 eV), while the HBCA was significantly less by ca. 0.6 eV. This difference is attributed to electron withdrawal from the perovskite block to the HBCA ligand, leading to a lower band gap for the HBCA compound. The methods described herein allow for the formation of a new series of inorganic–organic hybrid materials where the products are of interest as precursors to more complex architectures as well as models for band gap modification of metal oxide photocatalysts.

Kaolinite nanoscrolls (NScs) are halloysite-like nanotubular structures of great interest due to their ability to superimpose halloysite's properties and applicability. Especially attractive is the ability of these NScs to serve as reaction vessels for the uptake and conversion of different chemical species. The synthesis of kaolinite NScs, however, is demanding due to the various processing steps that lead to extended reaction times. Generally, three intercalation stages are involved in the synthesis, where the second step of methylation dominates others in terms of duration. The present research shows that introducing microwave processing throughout the various steps can simplify the procedure overall and reduce the synthesis period to less than a day (14 h). The kaolinite nanoscrolls were obtained using two final intercalating agents, aminopropyl trimethoxy silane (APTMS) and cetyltrimethylammonium chloride (CTAC). Both produce abundant NScs, as corroborated by microscopy measurements as well as the surface area of the final products; APTMS intercalated NScs were 63.34 m2/g, and CTAC intercalated NScs were 73.14 m2/g. The nanoscrolls averaged about 1 μm in length with outer diameters of APTMS and CTAC intercalated samples of 37.3 ± 8.8 nm and 24.9 ± 6.1 nm, respectively. The availability of methods for the rapid production of kaolinite nanoscrolls will lead to greater utility of these materials in technologically significant applications.

Compounds that exhibit spin-crossover (SCO) type behavior have been extensively investigated due to their ability to act as molecular switches. Depending on the coordinating ligand, in this case 1H-1,2,4-triazole, and the crystallite size of the SCO compound produced, the energy requirement for the spin state transition can vary. Here, SCO [Fe(Htrz)2(trz)](BF4)] nanoparticles were synthesized using modified reverse micelle methods. Reaction conditions and reagent ratios are strictly controlled to produce nanocubes of 40–50 nm in size. Decreases in energy requirements are seen in both thermal and magnetic transitions for the smaller sized crystallites, where, compared to bulk materials, a decrease of as much as 20 °C can be seen in low to high spin state transitions.

Platinum@hexaniobate nanopeapods (Pt@HNB NPPs) are a nanocomposite photocatalyst that was selectively engineered to increase the efficiency of hydrogen production from visible light photolysis. Pt@HNB NPPs consist of linear arrays of high surface area Pt nanocubes encapsulated within scrolled sheets of the semiconductor H x K4-x Nb6O17 and were synthesized in high yield via a facile one-pot microwave heating method that is fast, reproducible, and more easily scalable than multi-step approaches required by many other state-of-the-art catalysts. The Pt@HNB NPPs' unique 3D architecture enables physical separation of the Pt catalysts from competing surface reactions, promoting electron efficient delivery to the isolated reduction environment along directed charge transport pathways that kinetically prohibit recombination reactions. Pt@HNB NPPs' catalytic activity was assessed in direct comparison to representative state-of-the-art Pt/semiconductor nanocomposites (extPt-HNB NScs) and unsupported Pt nanocubes. Photolysis under similar conditions exhibited superior H2 production by the Pt@HNB NPPs, which exceeded other catalyst H2 yields (μmol) by a factor of 10. Turnover number and apparent quantum yield values showed similar dramatic increases over the other catalysts. Overall, the results clearly demonstrate that Pt@HNB NPPs represent a unique, intricate nanoarchitecture among state-of-the-art heterogeneous catalysts, offering obvious benefits as a new architectural pathway toward efficient, versatile, and scalable hydrogen energy production. Potential factors behind the Pt@HNB NPPs' superior performance are discussed below, as are the impacts of systematic variation of photolysis parameters and the use of a non-aqueous reductive quenching photosystem.

Barium titanate (BaTiO3) peapod nanocomposites were prepared by the controlled capture of nanoparticles (NPs) in scrolling hexaniobate (HNB) nanosheets. BaTiO3 NPs and proton-exchanged potassium hexaniobate were treated solvothermally at 220 °C for 6 h in toluene to produce linear NP chains confined within multiwalled HNB nanoscrolls. This method consistently produced nanopeapods with average filling fractions greater than 70%. The controlled introduction of nanocomponents along with a combination of oleylamine and oleic acid surfactants was critical to the success of these reactions. The ability to form BaTiO3@HNB significantly expands the number of important peapod composites accessible by the controlled NP capture.

The use of microwave irradiation for the synthesis of inorganic nanomaterials has recently become a widespread area of research that continues to expand in scope and specialization. The growing demand for nanoscale materials with composition and morphology tailored to specific applications requires the development of facile, repeatable, and scalable synthetic routes that offer a high degree of control over the reaction environment. Microwave irradiation provides unique advantages for developing such routes through its direct interaction with active reaction species, which promotes homogeneous heat distribution, increased reaction rates, greater product quality and yield, and use of mild reaction conditions. Many catalytic nanomaterials such as noble metal nanoparticles and intricate nanocomposites have very limited synthetic routes due to their extreme temperature sensitivity and difficulty achieving homogeneous growth. This work presents recent advances in the use of MW irradiation methods to produce high-quality nanoscale composites with controlled size, morphology, and architecture.

The new mixed-metal Dion-Jacobson layered perovskite RbLaNaNb3O10 has been prepared by direct reaction. Rietveld refinement of X-ray diffraction data shows this compound to be tetragonal (a = 3.88703(7) angstrom, c = 15.1349(5) angstrom; S.G. P4/mmm) and isostructural to RbCa2Nb3O10 with La and Na statistically distributed over the Asite within the perovskite block. The compound can be topochemically manipulated, readily undergoing ion exchange reactions to produce the series A'LaNaNb3O10 (A' = H, Li, Na, K, CuCI). Thermal studies show that, with the exception of KLaNaNb3O10, the exchange products are all low temperature phases, decomposing below 800 degrees C with a decomposition pathway varying with the nature of the interlayer species. Significant to this study is the observation that the rare combination of site sharing trivalent and monovalent cations (La/Na) imparts an increased stability for the A'LaNaNb3O10 compounds relative to the corresponding A'Ca2Nb3O10 analogues - the thermal stability in LiLaNaNb3O10 for example is over 50 degrees C higher than that of LiCa2Nb3O10.

A reliable method for encapsulation of palladium nanoparticles (6-8 nm particles) in halloysite (Pd@Hal) has been developed. The Pd@Hal was found to be a highly efficient room-temperature catalyst for Suzuki-Miyaura cross-coupling reactions that gave high yields of a diverse array of coupling products in 5:2 n-PrOH/H2O within 1 h. The catalytic system was remarkably effective with a broad substrate scope. In addition, the catalyst was easily recovered and recycled without a significant loss of catalytic activity.

Mechanistic studies were carried out on the formation of scrolled nanopeapod structures. Linear size-selective self-assembly of nanoparticles initially occurs along surface edges of hexaniobate sheets. Individual nanosheets then scroll and capture the particle arrays to produce peapod nanocomposites. Subsequently, the nanopeapods detach from the oxide sheets. Understanding and controlling this behavior will lead to development of more intricate multicomponent particle assemblies of interest to a variety of areas including catalysis, magnetics, and optical materials. More information can be found in the Full Paper by John B. Wiley et al. on page 1373 in Issue 11, 2019 (DOI: 10.1002/cnma.201900316).

Ceria hexaniobate nanopeapods have been prepared and their formation and assembly studied. Various sized ceria nanocubes (5 to 40 nm) were synthesized via a solvothermal approach with oleic acid and oleylamine capping agents. Utilizing a second solvothermal treatment, the nanoparticles were then captured within scrolling hexaniobate nanosheets to produce ceria@hexaniobate nanopeapods. In some instances, peapods were partially filled with ceria so that in a subsequent step, open sites could be filled with Au nanoparticles via in situ growth methods leading to arrangements of gold and ceria NPs within nanoscrolls. Studies on nanoparticle assembly and encapsulation were also carried out. Size-selective preassembly of nanoparticles on hexaniobate nanosheet surfaces is observed prior to scrolling, after which smaller ceria NPs (ca. <= 10 nm) are efficiently captured inside scrolled nanosheets. Improved understanding and control of this behavior is important for further development of more intricate multicomponent particles assemblies and formations within varieties of tubular structures with different morphological and structural features.

Support from the National Science Foundation (CHE-1412670) is gratefully acknowledged. Also, C. D.-W. C. would like to thank the Louisiana Board of Regents for her Graduate Fellowship.