120 research outputs found
Electronic chemical potentials of porous metal-organic frameworks
The binding energy of an electron in a material is a fundamental
characteristic, which determines a wealth of important chemical and physical
properties. For metal-organic frameworks this quantity is hitherto unknown. We
present a general approach for determining the vacuum level of porous
metal-organic frameworks and apply it to obtain the first ionisation energy for
six prototype materials including zeolitic, covalent and ionic frameworks. This
approach for valence band alignment can explain observations relating to the
electrochemical, optical and electrical properties of porous frameworks
Chemical strategies to mitigate electrostatic charging during coffee grinding
The process of grinding coffee generates particles with high levels of
electrostatic charge, causing a number of detrimental effects including
clumping, particle dispersal, and spark discharge. At the brewing level,
electrostatic aggregation between particles affects liquid-solid accessibility,
leading to variable extraction quality. In this study, we quantify the
effectiveness of four charge mitigation strategies. Our data suggests that
adding small amounts of water to whole beans pre-grinding, or bombarding the
grounds with ions produced from a high-voltage ionizer, are capable of
de-electrifying the granular flows. While these techniques helped reduce
visible mess, only the static reduction through water inclusion was found to
impact the brewing parameters in espresso format coffee. There, wetting coffee
with less than 0.05 mL / g resulted in a marked shift in particle size
distribution, in part due to preventing clump formation and also liberating
fine particles from sticking to the grinder. With all other variables kept
constant, this shift resulted in at least 15% higher coffee concentration for
espresso extracts prepared from darker roasts. These findings pose financial
and sustainability implications, and encourage the widespread implementation of
water use to de-electrify coffee during grinding.Comment: 13 pages, 5 figure
Chemical principles underpinning the performance of the metal–organic framework HKUST-1
A common feature of multi-functional metal–organic frameworks is a metal dimer in the form of a paddlewheel, as found in the structure of Cu3(btc)2 (HKUST-1). The HKUST-1 framework demonstrates exceptional gas storage, sensing and separation, catalytic activity and, in recent studies, unprecedented ionic and electrical conductivity. These results are a promising step towards the real-world application of metal–organic materials. In this perspective, we discuss progress in the understanding of the electronic, magnetic and physical properties of HKUST-1, representative of the larger family of Cu⋯Cu containing metal–organic frameworks. We highlight the chemical interactions that give rise to its favourable properties, and which make this material well suited to a range of technological applications. From this analysis, we postulate key design principles for tailoring novel high-performance hybrid frameworks
Ligand design for long-range magnetic order in metal-organic frameworks
We report a class of ligands that are candidates to construct metal-organic frameworks with long-range magnetic order between transition metal centres. Direct quantum chemical calculations predict Neel temperatures exceeding 100 K for the case of Mn
Ligand design for long-range magnetic order in metal-organic frameworks
We report a class of ligands that are candidates to construct metal–organic frameworks with long-range magnetic order between transition metal centres. Direct quantum chemical calculations predict Néel temperatures exceeding 100 K for the case of Mn
Electronic structure design for nanoporous, electrically conductive zeolitic imidazolate frameworks
Electronic structure calculations are used to develop design rules for enhanced electrical conductivity in zeolitic imidazolate frameworks. The electrical resistivity of Co2+ based zeolitic imidazolate frameworks has previously been found to be ∼1000 times lower than that of Zn2+ based materials. The electrical conductivity of the frameworks can also be tuned by ligand molecule selection. Using density functional theory calculations, this controllable electrical conductivity is explained in terms of tuneable conduction band edge character, with calculations revealing the improved hybridisation and extended band character of the Co2+ frameworks. The improvements in the methylimidazolate frameworks are understood in terms of improved frontier orbital matching between metal and ligand. The modular tuneability and previously demonstrated facile synthesis provides a route to rational design of stable framework materials for electronic applications. By outlining these design principles we provide a route to the future development of stable, electrically conductive zeolitic imidazolate frameworks
Cyclopropenium as an Aromatic Alternative A-Site Cation for Hybrid Halide Perovskite Architectures
Hybrid halide perovskites are an emerging class of photovoltaic materials, boasting high solar efficiencies from relatively simple preparations. However, the chemical diversity of the A-site organic cation is limited, generally due to steric constraints of the (PbI3)− cage. Herein we describe the use of a non-benzenoid Hückel aromatic, , as a viable alternative to the readily employed methylammonium, formamidinium, and guanidinium A-site cations. may lead to greater moisture stability due to the lack of an acidic proton relative to the current -based systems while still boasting a narrow electronic band gap and mobile holes and electrons and , respectively)
Computational screening of structural and compositional factors for electrically conductive coordination polymers
The combination of organic and inorganic chemical building blocks to form metal–organic frameworks (MOFs) offers opportunities for producing functional materials suitable for energy generation, storage and conversion. However, such applications rely on robust electron transport and the design of conductive hybrid materials is still in its infancy. Here we apply density functional theory to assess the important structural and compositional factors for forming conducting MOFs. We focus on 1D metal–organic polymers as a model system and assess the choice of organic, inorganic and linking units. The results demonstrate that electronic communication is sensitive to the energy and symmetry of the frontier orbitals associated with the organic and inorganic building blocks and offers guidance on how to optimise electrical conduction in hybrid materials
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