Hydrogen storage in M(BDC)(TED)0.5 metal-organic framework: physical insights and capacities

Finding renewable energy sources to replace fossil energy has been an essential demand in recent years. Hydrogen gas has been becoming a research hotspot for its clean and free-carbon energy. However, hydrogen storage technology is challenging for mobile and automotive applications. Metal-organic frameworks (MOFs) have emerged as one of the most advanced materials for hydrogen storage due to their exceptionally high surface area, ultra-large and tuneable pore size. Recently, computer simulations allowed the designing of new MOF structures with significant hydrogen storage capacity. However, no studies are available to elucidate the hydrogen storage in M(BDC)(TED)0.5, where M = metal, BDC = 1,4-benzene dicarboxylate, and TED = triethylenediamine. In this report, we used van der Waals-dispersion corrected density functional theory and grand canonical Monte Carlo methods to explore the electronic structure properties, adsorption energies, and gravimetric and volumetric hydrogen loadings in M(BDC)(TED)0.5 (M = Mg, V, Co, Ni, and Cu). Our results showed that the most favourable adsorption site of H2 in M(BDC)(TED)0.5 is the metal cluster-TED intersection region, in which Ni offers the strongest binding strength with the adsorption energy of -16.9 kJ mol-1. Besides, the H2@M(BDC)(TED)0.5 interaction is physisorption, which mainly stems from the contribution of the d orbitals of the metal atoms for M = Ni, V, Cu, and Co and the p orbitals of the O, C, N atoms for M = Mg interacting with the σ* state of the adsorbed hydrogen molecule. Noticeably, the alkaline-earth metal Mg strongly enhanced the specific surface area and pore size of the M(BDC)(TED)0.5 MOF, leading to an enormous increase in hydrogen storage with the highest absolute (excess) gravimetric and volumetric uptakes of 1.05 (0.36) wt% and 7.47 (2.59) g L-1 at 298 K and 7.42 (5.80) wt% and 52.77 (41.26) g L-1 at 77 K, respectively. The results are comparable to the other MOFs found in the literature.

Theoretical investigation of CO2 capture in the MIL-88 series: effects of organic linker modification

CO2 capture is a crucial strategy to mitigate global warming and protect a sustainable environment. Metal-organic frameworks with large surface area, high flexibility, and reversible adsorption and desorption of gases are good candidates for CO2 capture. Among the synthesized metal-organic frameworks, the MIL-88 series has attracted our attention due to their excellent stability. However, a systematic investigation of CO2 capture in the MIL-88 series with different organic linkers is not available. Therefore, we clarified the topic via two sections: (1) elucidate physical insights into the CO2@MIL-88 interaction by van der Waals-dispersion correction density functional theory calculations, and (2) quantitatively study the CO2 capture capacity by grand canonical Monte Carlo simulations. We found that the 1πg, 2σu/1πu, and 2σg peaks of the CO2 molecule and the C and O p orbitals of the MIL-88 series are the predominant contributors to the CO2@MIL-88 interaction. The MIL-88 series, i.e., MIL-88A, B, C, and D, has the same metal oxide node but different organic linkers: fumarate (MIL-88A), 1,4-benzene-dicarboxylate (MIL-88B), 2,6-naphthalene-dicarboxylate (MIL-88C), and 4,4'-biphenyl-dicarboxylate (MIL-88D). The results exhibited that fumarate should be the best replacement for both the gravimetric and volumetric CO2 uptakes. We also pointed out a proportional relationship between the capture capacities with electronic properties and other parameters.

Hydrogen gas as a central on-off functional switch of reversible metabolic arrest - New perspectives for biotechnological applications

Metabolism is the sum of all chemical reactions that sustain life. There is an ongoing effort to control metabolic rate, which correlates with the maximum lifespan potential and constitutes one of the oldest scientific questions. Herein, we report on the complete reversible arrest of cellular metabolism and cell growth in a series of organisms, from microalgae to yeast upon exposure to a 100 % hydrogen atmosphere. We also report a tolerance of the microalgae under these conditions against extreme stress conditions, like high salt concentrations. The addition of oxygen or air almost completely restores the metabolic rate and cell growth. Molecular dynamics simulations are employed to decipher this phenomenon at atomic scale. Various proteins, including photosynthetic and respiratory complexes (LHCII, cytochrome c5) are probed in the interaction with hydrogen. Exposure to hydrogen, as opposed to oxygen, decreases the fluctuations of protein residues indicating thermostability. According to the above mechanism, an absolute hydrogen atmosphere can preserve biological products (e.g. fruits) for a long time without consuming any energy. By combining biological, chemical and computational methods, in this research we provide the basis for future innovative studies and advances in the field of biotechnology.

Simultaneous adsorption of SO2 and CO2 in an Ni(bdc)(ted)0.5 metal-organic framework

The metal–organic framework Ni(bdc)(ted)_0.5 is a promising material for simultaneous capture of harmful gases such as SO₂ and CO₂. We found that SO₂ performs much better than CO₂ during adsorption, and the lack of physical insight was clarified through detailed analyses of the electronic structures obtained from density functional theory calculations. Our results showed that strong interactions of the d band of Ni atoms with the valence states (2n, 3n, and 4n) of SO₂ but almost not with those of CO₂ are the main reasons. Our finding is useful for the rational design of new metal–organic frameworks with suitable interactions for the simultaneous capture of not only SO₂ and CO₂ but also other gases.

SO₂ performs much better than CO₂ during co-adsorption due to the d-band of Ni atoms.