Ammonia interactions and competition with water at the interface of nanoporous metal organic framework thin films of HKUST-1 (Cu3Btc2, Btc = 1,3,5-benzenedicarboxylate) are investigated with ambient pressure X-ray photoelectron spectroscopy (APXPS). In the absence of water, ammonia adsorption at the Cu2+ metal center weakens the metal-linker bond of the framework. In the presence of water, due to the higher binding energy (adsorption strength) of ammonia compared to water, ammonia replaces water at the unsaturated Cu2+ metal centers. The water molecules remaining in the pores are stabilized by hydrogen bonding to ammonia. Hydrogen bonding between the water and ammonia strengthens the metal-ammonia interaction due to cooperative interactions. Cooperative interactions result in a reduction in the metal center oxidation state facilitating linker replacement by other species explaining the previously reported structure degradation.

The combination of block copolymer templating with electrostatic self-assembly provides a simple and robust method for creating nano-patterned polyelectrolyte multilayers over large areas. The deposition of the first polyelectrolyte layer provides important insights on the initial stages of multilayer buildup. Here, we focus on two-dimensionally confined “dots” patterns afforded by block copolymer films featuring hexagonally-packed cylinders that are oriented normal to the substrate. Rendering the cylinder caps positively charged enables the selective deposition of negatively charged polyelectrolytes on them under salt-free conditions. The initially formed polyelectrolyte nanostructures adopt a toroidal (“doughnut”) shape, which results from retraction of dangling polyelectrolyte segments into the “dots” upon drying. With increasing exposure time to the polyelectrolyte solution, the final shape of the deposited polyelectrolyte transitions from a doughnut to a hemisphere. These insights would enable the creation of patterned polyelectrolyte multilayers with increased control over adsorption selectivity of the additional incoming polyelectrolytes.

This article presents an overview of recent advances in field and laboratory studies of atmospheric particles formed in processes of environmental air-surface interactions. The overarching goal of these studies is to advance predictive understanding of atmospheric particle composition, particle chemistry during aging, and their environmental impacts. The diversity between chemical constituents and lateral heterogeneity within individual particles adds to the chemical complexity of particles and their surfaces. Once emitted, particles undergo transformation via atmospheric aging processes that further modify their complex composition. We highlight a range of modern analytical approaches that enable multimodal chemical characterization of particles with both molecular and lateral specificity. When combined, these approaches provide a comprehensive arsenal of tools for understanding the nature of particles at air-surface interactions and their reactivity and transformations with atmospheric aging. We discuss applications of these novel approaches in recent studies and highlight additional research areas to explore the environmental effects of air-surface interactions.

The layer-by-layer epitaxial growth of HKUST-1 (Cu3(btc)2 where btc = 1,3,5-benzenetricarboxylate) thin films is measured by quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray diffraction (XRD), and scanning electron microscopy (SEM) as a function of the number of layers (20-80 layers) for OH and COOH functionalized surfaces. Up to approximately 40 layers, the film growth proceeds by a layer-by-layer mode controlled by the chemical functionalization of the surface. For example, on hydroxylated SiO2, film growth is in the preferred [222] direction. Beyond 40 layers, for both COOH and OH functionalized surfaces, the crystallite grain size increases and 50-100 nm octahedral crystals are formed. Independent of the surface functional groups (COOH and OH), the octahedral crystals form with the {200} planes oriented parallel to the surface. By monitoring changes in mass and dissipation, the QCM data provides evidence for the change in growth behavior. The stability of the films, determined by measuring CO2 adsorption isotherms, depends on film properties (morphology and grain size) as well as film age. For films deposited on hydroxylated SiO2 surfaces, CO2 uptake decreases rapidly within a few days after film synthesis with the 40 layer films ({222} planes) exhibiting a more pronounced decrease than the 80 layer films ({200} planes, octahedral crystals). The decrease in CO2 uptake is attributed to the differing propensities for water uptake in thin films of different morphologies as evidenced by water vapor adsorption isotherms and Raman spectral changes.

Nano-patterned materials are beneficial for applications such as solar cells, opto-electronics, and sensing owing to their periodic structure and high interfacial area. Here, we present a non-lithographic approach for assembling polyelectrolytes into periodic nanoscale patterns over cm(2)-scale areas. Chemically modified block copolymer thin films featuring alternating charged and neutral domains are used as patterned substrates for electrostatic self-assembly. In-depth characterization of the deposition process using spectroscopy and microscopy techniques, including the state-of-the-art scanning transmission X-ray microscopy (STXM), reveals both the selective deposition of the polyelectrolyte on the charged copolymer domains as well as gradual changes in the film topography that arise from further penetration of the solvent molecules and possibly also the polyelectrolyte into these domains. Our results demonstrate the feasibility of creating nano-patterned polyelectrolyte layers, which opens up new opportunities for structured functional coating fabrication.