Sc and Ti-functionalized 4-tert-butylcalix[4]areneas reversible hydrogen storage material

Abstract

Using the idea of metal functionalized material for H2storage, 4-tert-butylcalix[4]arene(CA) functionalized with Sc and Ti atoms are explored. The first principles density func-tional theory (DFT) with M06 functional and 6-311G(d,p) basis set is used to explore thehydrogen storage properties of metal functionalized CA. Sc and Ti strongly binds with CAby Dewar coordination with high binding energy. It is found that maximum four hydrogenmolecules are adsorbed on each metal site in Sc and Ti functionalized CA. Hydrogenmolecules are adsorbed on metals by Kubas and Niu-Rao-Jena mechanism. In Sc func-tionalized CA system all 4 hydrogen molecules on each Sc bind in molecular fashion whileon each Ti in Ti functionalized CA, the first hydrogen molecule binds in dissociativefashion and remaining three hydrogen molecules bind in a molecular form. The stability ofSc and Ti functionalized CA is studied by computing conceptual DFT parameters, whichobeys maximum hardness and minimum electrophilicity principle. Hirshfeld chargeanalysis and electrostatic potential map explore the charge transfer mechanism during thehydrogen adsorption. Born-Oppenheimer molecular dynamics simulations are performedat temperature range 200e473 K to study the stability of the system and the reversibility ofadsorbed hydrogen from the system. The calculated H wt% is found to be 10.3 and 10.1,respectively for Sc and Ti functionalized CA systems on complete H2saturation. This studyexplores that Sc and Ti functionalized CA systems are efficient reversible hydrogen storagematerial.