Hydrophobic coatings on cotton fabrics were successfully prepared via solution deposition of a “flat” nanoscale aluminum hydroxo cluster and a photo-assisted anneal using ultraviolet light. The coatings have a low...

The structural attributes and structure-dependent properties of metal oxide nanocrystals are often defined during the earliest stages of nanocrystal growth. The species formed early in the growth process are notoriously difficult to study due to their small size and rapidly changing structures. Thus, despite many studies on the formation and initial growth of nanocrystals, little is known about how to control these steps during synthesis. Here, we investigate how the choice of reagentoleyl alcohol or oleylamineinfluences the earliest stages of indium oxide nanocrystal growth in a reagent-driven, continuous addition synthesis. The metal oxide precursor is activated through reaction with the reagent (through amidation or esterification) as opposed to thermal decomposition. Amidation proceeds faster than esterification, and this difference has a significant influence on the early steps of nanocrystal formation and growth. Fewer, larger nanocrystals are formed in the presence of oleylamine whereas more, but smaller, nanocrystals are formed in oleyl alcohol. Our studies suggest that differences in surface reactivity in the presence of the two reagents influence the transition from nanocrystal formation to growth. In the case of oleylamine, the reagent activates the surface of the nanocrystal through amidation reactions that expose more reactive metal hydroxyl species. Due to the higher concentration of these species, the rate of attachment of activated precursor to existing nanocrystals outpaces the rate of condensation of precursors to form new nanocrystals. As a result, the formation of new particles ends earlier in oleylamine than it does in oleyl alcohol, resulting in fewer particles being formed in the presence of amine. When mixtures of the amine and alcohol are used, the reactions also proceed through reagent-driven, rather than thermally driven, growth, and the ratio of reagents can be used to control the number of nanocrystals formed.

Cerium oxide nanocrystals have size-and shape-dependent properties that are potentially useful in a variety of applications if these structural attributes can be controlled through synthesis. Various syntheses have been developed in attempts to access different sizes and shapes, but little is known about selecting reaction conditions to predictably control the growth, and therefore properties, of the nanocrystals. Here, we investigate the role of cerium precursor oxidation states, reaction atmospheres, and acetic acid ligation on the size and shape of cerium oxide nanocrystals. A continuous addition synthesis allowed us to vary individual reaction parameters to better understand how each affects growth and morphology. Under N 2 , the synthesis leads to either irregular shapes or nanoribbons, whereas the same synthesis under air leads to size-tunable nanocubes. To determine whether air might be oxidizing the cerium precursor and changing its reactivity, we synthesized Ce(IV)-rich and Ce(III) oleate precursors and found that the oxidation state of the precursor has little effect on the resulting nanocrystals. In fact, we found that Ce(IV) oleate is readily reduced to Ce(III) at at temperatures above 100 °C in the reaction medium. The significant role of air during synthesis therefore suggests that oxygen is altering the surface reactivity of the nanocrystals, as opposed to the precursor. We investigated the origin of nanoribbon formation and found that the presence of acetate ligands is responsible for nanoribbon formation in syntheses under N 2 , with more acetate leading to longer nanoribbons. These insights were used to identify conditions to predictably grow various sizes and shapes of nanocubes and nanoribbons. The findings elucidate the effects that various synthetic parameters can have on cerium oxide nanocrystal synthesis and suggest that redox reactivity may influence growth and properties in other syntheses where changes in the oxidation state occur for the precursor or the nanocrystal surface.

Plasmonic band-stop filters with tunable optical absorbance in the near-and mid-IR are important for wireless communications, bioimaging, and filtering applications. However, their design is constrained by the limited tunability of individual components and complex fabrication techniques. Here, we demonstrate a method to overcome these limitations that employs mixtures of nanocrystals to predictably sculpt the combined localized surface plasmon resonance (LSPR) for band-stop filters. The additive nature of the LSPR optical absorbances of tin-doped In 2 O 3 (ITO) nanocrystals was used to control the combined absorbance in a nanocrystal thin film. The optical properties of the nanocrystals were modulated via a low-temperature esterification synthesis and an inexpensive solution-processing fabrication method, spin-coating, was used to produce the films. Because of the additive nature of the LSPR absorbance of the nanocrystals, the absorbance of the films can be easily predicted and designed by summing the spectra of the individual components over the range of 6000−1000 cm −1 . By design and synthesis of individual nanocrystals with tailored optical properties, and selecting the right combinations of nanocrystals to incorporate into films, both wide and narrow band-stop filters were easily constructed.

The electrochemical reduction of CO2 into fuels using renewable electricity presents an opportunity to utilize captured CO2. Electrocatalyst development has been the primary focus of research in this area. This is especially true at the nanoscale, where researchers have focused on understanding nanostructure-property relationships. However, electrocatalyst structure may evolve during operation. Indium- and tin-based oxides have been widely studied as electrocatalysts for CO2 reduction to formate, but evolution of these catalysts during operation is not well-characterized. Here, we report the evolution of nanoscale structure of tin-doped indium oxide nanocrystals under CO2 reduction conditions. We show that sparse monolayer nanocrystal films desorb from the electrode upon charging, but thicker nanocrystal films remain, likely due to increased number of physical contacts. Upon applying a cathodic voltage of -1.0 V vs RHE or greater, the original 10-nm diameter nanocrystals are no longer visible, and instead form a larger microstructural network. Elemental analysis suggests the network is an oxygen-deficient indium-tin metal alloy. We hypothesize that this morphological evolution is the result of nanocrystal sintering due to oxide reduction. These data provide insights into the morphological evolution tin-doped indium oxide nanocrystal electrocatalysts under reducing conditions and highlight the importance of post-electrochemical structural characterization of electrocatalysts.