Correction to: Cluster identification, selection, and description in Cluster randomized crossover trials: the PREP-IT trials

An amendment to this paper has been published and can be accessed via the original article

Maintaining the Structure of Templated Porous Materials for Reactive and High-Temperature Applications

Nanoporous and nanostructured materials are becoming increasingly important for advanced applications involving, for example, bioactive materials, catalytic materials, energy storage and conversion materials, photonic crystals, membranes, and more. As such, they are exposed to a variety of harsh environments and often experience detrimental morphological changes as a result. This article highlights material limitations and recent advances in porous materialsthree-dimensionally ordered macroporous (3DOM) materials in particularunder reactive or high-temperature conditions. Examples include systems where morphological changes are desired and systems that require an increased retention of structure, surface area, and overall material integrity during synthesis and processing. Structural modifications, changes in composition, and alternate synthesis routes are explored and discussed. Improvements in thermal or structural stability have been achieved by the isolation of nanoparticles in porous structures through spatial separation, by confinement in a more thermally stable host, by the application of a protective surface or an adhesive interlayer, by alloy or solid solution formation, and by doping to induce solute drag

Controlling Microstructural Evolution in Pechini Gels through the Interplay between Precursor Complexation, Step-Growth Polymerization, and Template Confinement

The mechanisms driving microstructure formation in template-confined Pechini-type gel systems involving solid solutions of cerium oxide with alkaline earth metals are investigated. Three-dimensionally ordered macroporous microspheres and more extended bicontinuous networks with hierarchical porosity are synthesized directly from a Pechini sol–gel precursor within a colloidal crystal template. The type of morphology generated is related to the mechanisms of phase separation in the precursor, namely, nucleation and growth vs spinodal decomposition. These mechanisms are, in turn, determined by the citric acid concentration in the initial precursor solution and by electrostatic interactions of the precursor with the polymeric template. Microspheres generated by the nucleation-and-growth pathway can be produced between 1–3 μm in size, with polydispersities below 15%. They retain the ordered porous network left by removal of the template. The number of nucleation sites (i.e., oligomers and longer chains of complexed metal) is dependent on the reactant imbalance between metal–citrate complexes and ethylene glycol, as predicted by step-growth polymerization statistics. This method expands existing phase-separation techniques currently exploited in metal alkoxide systems to the production of microstructure in ceramic oxides

Titania–Carbon Nanocomposite Anodes for Lithium Ion Batteries Effects of Confined Growth and Phase Synergism

As lithium-ion batteries (LIB) see increasing use in areas beyond consumer electronics, such as the transportation sector, research has been directed at improving LIBs to better suit these applications. Of particular interest are materials and methods to increase Li⁺ capacity at various charge/discharge rates, to improve retention of Li⁺ capacity from cycle-to-cycle, and to enhance various safety aspects of electrode synthesis, cell construction, and end use. This work focuses on the synthesis and testing of three-dimensionally ordered macroporous (3DOM) TiO₂/C LIB anode materials prepared using low toxicity precursors, including ammonium citratoperoxotitanate­(IV) and sucrose, which provide high capacities for reversible Li⁺ insertion/extraction. When the composites are pyrolyzed at 700 °C, the carbon phase restricts sintering of TiO₂ crystallites and keeps the size of these crystallites below 5 nm. Slightly larger crystallites are produced at higher temperatures, alongside a titanium oxycarbide phase. The composites exhibit excellent capacities as LIB anodes at low to moderate charge/discharge rates (in the window from 1 to 3 V vs Li/Li⁺). Composites pyrolyzed at 700 °C retain over 200 mAh/g TiO₂ of capacity after 100 cycles at a C/2 rate (C = 335 mA/g), and do not suffer from extensive cycle-to-cycle capacity fading. A substantial improvement of overall capacities, especially at high rates, is attained by cycling the composite anodes in a wider voltage window (0.05 to 3 V vs Li/Li⁺), which allows for Li⁺ intercalation into carbon. At currents of 1500 mA/g of active material, over 200 mAh/g of capacity is retained. Other structural aspects of the composites are discussed, including how rutile TiO₂ is found in these composites at sizes below the thermodynamic stability limit in the pure phase

Control of TiO₂ Grain Size and Positioning in Three-Dimensionally Ordered Macroporous TiO₂/C Composite Anodes for Lithium Ion Batteries

After several high-profile incidents that raised concerns about the hazards posed by lithium ion batteries, research has accelerated in the development of safer electrodes and electrolytes. One anode material, titanium dioxide (TiO₂), offers a distinct safety advantage in comparison to commercialized graphite anodes, since TiO₂ has a higher potential for lithium intercalation. In this article, we present two routes for the facile, robust synthesis of nanostructured TiO₂/carbon composites for use as lithium ion battery anodes. These materials are made using a combination of colloidal crystal templating and surfactant templating, leading to the first report of a three-dimensionally ordered macroporous TiO₂/C composite with mesoporous walls. Control over the size and location of the TiO₂ crystallites in the composite (an often difficult task) has been achieved by changing the chelating agent in the precursor. Adjustment of the pyrolysis temperature has also allowed us to strike a balance between the size of the TiO₂ crystallites and the degree of carbonization. Using these pathways to optimize electrochemical performance, the primarily macroporous TiO₂/C composites can attain a capacity of 171 mAh/g at a rate of 1 C. Additionally, the carbon in these composites can function as a secondary template for high-surface-area, macroporous TiO₂ with disordered mesoporous voids. Combining the advantages of a nanocrystalline framework and significant open porosity, the macroporous TiO₂ delivers a stable capacity (>170 mAh/g at a rate of C/2) over 100 cycles

Generalized Approach to the Microstructure Direction in Metal Oxide Ceramics via Polymerization-Induced Phase Separation

When three-dimensionally ordered macroporous (3DOM) materials are synthesized in polymeric colloidal crystal templates using a Pechini-type approach, polymerization-induced phase separation (PIPS) can occur. Depending on the reaction conditions, the porous products have a variety of morphologies, including an extended inverse opal structure, bicontinuous networks of 3DOM materials interrupted by extended voids, uniform 3DOM microspheres, sheet structures of templated macroporous oxides, and hollow particles obtained by structural disassembly. In this study, the mechanism underpinning morphology control of 3DOM metal oxides through PIPS is elucidated for Ce_0.5Mg_0.5O_1.5 and CeO₂ systems. The mechanistic information is then applied to synthesize target morphologies for Mn₃O₄ and Fe₂O₃/Fe₃O₄ systems, demonstrating the more general nature of the synthetic approach for aqueous metal precursors that can be complexed with citric acid. The effects of reactant balance, complexation behavior, processing temperature, and template sphere size are related directly to the microstructures obtained. The predominant controlling factor of microstructural evolution in PIPS Pechini precursors is found to be the degree of polymerization of the polyester, which can be controlled through tailoring the reagent imbalance. 3DOM microspheres produced by the method are between 0.5 and 3 μm in size, with polydispersities below 25%

Enhanced Oxidation Kinetics in Thermochemical Cycling of CeO₂ through Templated Porosity

Two-step thermochemical cycling was achieved using CeO₂ with sub-micrometer sized macropores, allowing for substantially improved CO production at fast cycle rates when compared to nonporous CeO₂. The effects of porosity, pore order, and packing density were probed by synthesizing ceria materials with different morphologies. Polymeric colloidal spheres were used as templates for the synthesis of three-dimensionally ordered macroporous (3DOM) CeO₂ and nonordered macroporous (NOM) CeO₂. Aggregated CeO₂ nanoparticles with feature sizes similar to those in 3DOM CeO₂ were prepared by fragmenting 3DOM CeO₂ into its building blocks using ultrasonication. The three templated materials and nonporous, commercial CeO₂ were tested in thermochemical cycles using an infrared furnace. CeO₂ was reduced at ∼1200 °C, and the reduced CeO_2−δ materials were reoxidized under CO₂ at ∼850 °C. The high temperatures required for cycling induced changes in the morphology of the porous materials, which were characterized by electron microscopy, X-ray diffraction, and nitrogen sorption measurements. In spite of sintering, the macroporous materials retained an interconnected pore network during 55 cycles, providing a 10-fold enhancement in CO productivity and production rate when compared to nonporous CeO₂. Additionally, 3DOM CeO₂ provided the fastest rate of CO production of all tested materials and also retained the smallest solid feature sizes. This boost in reaction kinetics allowed for extremely rapid cycling with less than a minute required for complete reduction or oxidation. Characterization of the porous materials also provided some insight into thermal gradients that developed in the sample bed as a result of rapid heating and cooling

Optimal protection against Salmonella infection requires noncirculating memory

While CD4 Th1 cells are required for resistance to intramacrophage infections, adoptive transfer of Th1 cells is insufficient to protect against Salmonella infection. Using an epitope-tagged vaccine strain of Salmonella, we found that effective protection correlated with expanded Salmonella-specific memory CD4 T cells in circulation and nonlymphoid tissues. However, naive mice that previously shared a blood supply with vaccinated partners lacked T cell memory with characteristics of tissue residence and did not acquire robust protective immunity. Using a YFP-IFN-γ reporter system, we identified Th1 cells in the liver of immunized mice that displayed markers of tissue residence, including P2X7, ARTC2, LFA-1, and CD101. Adoptive transfer of liver memory cells after ARTC2 blockade increased protection against highly virulent bacteria. Taken together, these data demonstrate that noncirculating memory Th1 cells are a vital component of immunity to Salmonella infection and should be the focus of vaccine strategies