Metal phosphides are promising catalysts for hydrocarbon transformations, but computational screening is complicated by their diverse structures and compositions. To disentangle structural from compositional contributions, here we explore the metal-rich M 2 P (M = Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, Ag, Pt) series in hexagonal and orthorhombic structures that are common to a subset of these materials, using supercell density functional theory (DFT). To understand the contribution of metal choice to utility for catalytic ethane dehydrogenation (EDH), we compute and compare the adsorption of key EDH intermediates across low-index surface terminations. These materials expose both metal and phosphide sites. Calculations show that binding energies at metal sites correlate with the bulk metals, with P incorporation either enhancing or suppressing binding. Phosphide sites compete with metal sites for adsorbates and tend to suppress overactivation by destabilizing highly dehydrogenated species engaging in C–H bond breaking. Results are generally insensitive to bulk structure and surface facet. Results suggest metal-rich Pd phosphides to have favorable adsorption characteristics for catalytic dehydrogenation, consistent with recent observations.
more »
« less
Understanding and controlling the metal-directed assembly of terpyridine-functionalized coiled-coil peptides
Metal-binding peptides are versatile building blocks in supramolecular chemistry. We recently reported a class of crystalline materials formed through a combination of coiled-coil peptide self-association and metal coordination. Here, we probe the serendipitously discovered metal binding motif that drives the assembly and apply these insights to exert rational control over structure and morphology in the materials.
more »
« less
- NSF-PAR ID:
- 10098388
- Date Published:
- Journal Name:
- Chemical Communications
- ISSN:
- 1359-7345
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
High-valent metal oxides such as LiCoO2 and related materials are of increasing environmental concern due to the large-scale use in lithium-ion batteries and potential for metal ion release into aqueous systems. A key aspect of the environmental chemistry of these materials is the potential role redox chemistry plays in their transformations as well as their influence on the surrounding environment (i.e., biomolecules, organisms etc.). In recent work, we showed that LiCoO2(a common lithium-ion battery cathode material) oxidizes nicotinamide adenine dinucleotide (NADH), an essential molecule for electron transport, and enhances Co release from LiCoO2. In the present work, we investigated the mechanism of interaction by examining the role of the ribose, phosphate, adenosine, and the nicotinamide components of NADH in the transformation of LiCoO2 nanoparticles. To build an understanding of the interaction mechanism, we used fluorescence spectroscopy to measure the changes in redox state and inductively coupled plasma-mass spectrometry (ICP-MS) to measure the changes in dissolved Co. Our results reveal the importance of surface binding, via the phosphate functionality, in initiating the redox transformation of both the LiCoO2 and the NADH. Observations from X-ray photoelectron spectroscopy (XPS) data show that molecules containing phosphate were bound to the surface of the nanoparticles and those without that functionality were not. We further established the generality of the results with LiCoO2 by examining other high-valent transition metal oxides. This surface binding effect has implications for understanding how other phosphorylated species can be transformed directly in the presence of high-valent metal oxide nanomaterials.more » « less
-
null (Ed.)Computational methods can provide first-principles insights into the thermochemistry and kinetics of reactions at interfaces, but this capability has not been widely leveraged to design soft materials that respond selectively to chemical species. Here we address this opportunity by demonstrating the design of micrometer-thick liquid crystalline films supported on metal-perchlorate surfaces that exhibit selective orientational responses to targeted oxidizing gases. Initial electronic structure calculations predicted Mn 2+ , Co 2+ , and Ni 2+ to be promising candidate surface binding sites that (1) coordinate with nitrile-containing mesogens to orient liquid crystal (LC) phases and (2) undergo redox-triggered reactions upon exposure to humid O 3 leading to a change in the strength of binding of the nitrile group to the surface. These initial predictions were validated by experimental observations of orientational transitions of nitrile-containing LCs upon exposure to air containing parts-per-billion concentrations of O 3 . Additional first-principles calculations of reaction free energies of metal salts and oxidizing gases predicted that the same set of metal cations, if patterned on surfaces at distinct spatial locations, would provide LC responses that allow Cl 2 and O 3 to be distinguished while not responding to environmental oxidants such as O 2 and NO 2 . Experimental results are provided to support this prediction, and X-ray diffraction measurements confirmed that the experimentally observed LC responses can be understood in terms of the relative thermodynamic driving force for formation of MnO 2 , CoOOH, or NiOOH from the corresponding metal cation binding sites in the presence of humid O 3 and Cl 2 .more » « less
-
Capacitive deionization (CDI) technologies have gained intense attention for water purification and desalination in recent years. Inexpensive and widely available porous carbon materials have enabled the fast growth of electrosorption research, highlighting the promise of CDI as a potentially cost-effective technology to remove ions. Whereas the main focus of CDI has been on bulk desalination, there has been a recent shift towards electrosorption for selective ion separations. Heavy metals are pollutants that can have severe health impacts and are present in both industrial wastewater and groundwater leachates. Heavy metal ions, such as chromium, cadmium, or arsenic, are of great concern to traditional treatment technologies, due to their low concentration and the presence of competing species. The modification/functionalization of porous carbon and recent developments of faradaic and redox-active materials have offered a new avenue for selective ion-binding of heavy metal contaminants. Here, we review the progress in electrosorptive technologies for heavy metal separations. We provide an overview of the wide applicability of carbon-based electrodes for heavy metal removal. In parallel, we highlight the trend toward modification of carbon materials, new developments in faradaic interfaces, and the underlying physico-chemical mechanisms that promote selective heavy metal separations.more » « less
-
Sensors are routinely developed for specific applications, but multipurpose sensors are challenging, due to stability and poor functional design. We report organic materials that operate in solution and gas phase. They show a strong response behaviour to at least three types of environmental changes: pH, amine and metal ion binding/detection. We have confirmed and validated our findings using various analytical and computational methods. We found that the changes in polarity of the solvent and pH not only red shift the tail of the absorption spectra, but also extend the peak optical absorption of these structures by up to 100 nm, with consequential effects on the optical gap and colour changes of the materials. Acid–base response has been studied by spectrophotometric titrations with trifluoroacetic acid (TFA) and triethyl amine (TEA). The experiments show excellent reversibility with greater sensitivity to base than acid for all compounds. Analysis into metal sensing using Zn( ii ) and Cu( ii ) ions as analytes show that the materials can successfully bind the cations forming stable complexes. Moreover, a strong suppression of signal with copper gives an operative modality to detect the copper ion as low as 2.5 × 10 −6 M. The formation of the metal complexes was also confirmed by growing crystals using a slow diffusion method; subsequent single crystal X-ray analysis reveals the ratio of ligand to metal to be 2 to 1. To test sensitivity towards various amine vapours, paper-based sensors have been fabricated. The sensors show a detection capability at 1 ppm of amine concentration. We have employed CIE L * a * b * colour space as the evaluation method, this provides numeric comparison of the samples from different series and allows comparison of small colour differences, which are generally undetectable by the human-eye. It shows that the CIE L * a * b * method can assess both sensitivity to a particular class of analytes and a specificity response to individual amines in this subclass offering an inexpensive and versatile methodology.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9CC03496J
