Highly efficient visible-light-assisted photocatalytic reduction of Cr(VI) to Cr(III) from water using multifunctional Zr(IV)-porphyrin MOFs, Zr6(μ3-OH)8(OH)8(MTCPP)2, (PCN-222(M)) (M = H2, ZnII, CuII, NiII, CoII, FeIIICl, and MnIIICl) is presented. The...

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We present the detailed comparative study of dihydrogen adsorption in Li, Mg, Ca, and Sc decorated γ-graphyne (Gγ) performed with density functional theory calculations. Hydrogen molecules are sequentially loaded onto metal decorated Gγ. Maximum hydrogen weight percentage for Li, Mg, Ca, and Sc decorated Gγ is found to be 8.69, 7.73, 8.10, and 6.83, respectively, with maximum 8 H2 on Li, Mg, and Sc while 10 on Ca decorated Gγ. All hydrogen molecules are physisorbed over all the complexes except that the first one on each Sc of Gγ-2Sc is chemisorbed. Orbital hybridization involved in Dewar coordination of metal decoration and the Kubas mechanism of hydrogen adsorption has been explained with the partial density of states. Lower values of adsorption and desorption energies in these complexes indicate the reversibility of adsorption. These complexes obey high hardness and low electrophilicity principles and contain no imaginary frequencies which specify their stability. In Born-Oppenheimer molecular dynamics, reversibility of adsorption is proven at various temperatures. Based on the comparative studies of hydrogen weight percentage, energetics, stability, and reversibility, Gγ-2Ca is proven to be a better hydrogen storage candidate. This comprehensive study confirms the potential of metal decorated γ-graphyne as a suitable hydrogen storage material.

Hydrogen is the most convenient recourse to shift from fossil fuels to an efficient and sustainable source of energy in automobiles. Achieving a high hydrogen weight percentage while storing hydrogen is the prime challenge in using hydrogen fuel. In the current study, a nanoporous metal−organic framework of 2.069 nm pore size having R-graphyne as a linker (G R −MOF) is reported for the first time. Employing density functional theory, the hydrogen sorption characteristics of G R −MOF functionalized with Li and its mechanism are investigated. A Kubas-like mechanism is observed in the process of hydrogen adsorption with sorption energies in the 0.25−0.27 eV range, with the highest hydrogen weight percentage of 11.95%. It is observed during the van 't Hoff desorption and Born−Oppenheimer molecular dynamics study that G R −MOF reversibly stores hydrogen under operable thermodynamic conditions (100−300 K, 1−3 atm). G R −MOF stands out to be a prospective material for reversible hydrogen storage under the norms set by the Department of Energy, USA.

Hydrogen is the most potential substitute for fossil fuels in automobiles and shifting to a sustainable energy source. The lack of high-density hydrogen storage materials impedes the use of hydrogen as a fuel. In this study, a porous metal cluster framework (MCF) with Ti cluster as a linker has been reported for the first time. This framework has a pore size of 2.204 nm and a vertical length of 2.597 nm. Using density functional theory, the hydrogen storage capacity and the mechanism of adsorption have been investigated. The Kubas interaction is observed during the hydrogen adsorption process with adsorption energy in the range of 0.22− 0.25 eV, and the maximum hydrogen weight percentage is found to be 9.6%. Our findings from Born−Oppenheimer molecular dynamics, van 't Hoff desorption study, and occupation number reveal that MCF reversibly adsorbs hydrogen with high gravimetric density under ambient thermodynamic conditions. MCF fulfills the targets of the U.S. Department of Energy, which makes it a promising reversible hydrogen storage candidate.