Abstract:
Using the idea of metal functionalized material for H2 storage, 4-tert-butylcalix[4]arene
(CA) functionalized with Sc and Ti atoms are explored. The first principles density functional theory (DFT) with M06 functional and 6-311G(d,p) basis set is used to explore the
hydrogen storage properties of metal functionalized CA. Sc and Ti strongly binds with CA
by Dewar coordination with high binding energy. It is found that maximum four hydrogen
molecules are adsorbed on each metal site in Sc and Ti functionalized CA. Hydrogen
molecules are adsorbed on metals by Kubas and Niu-Rao-Jena mechanism. In Sc functionalized CA system all 4 hydrogen molecules on each Sc bind in molecular fashion while
on each Ti in Ti functionalized CA, the first hydrogen molecule binds in dissociative
fashion and remaining three hydrogen molecules bind in a molecular form. The stability of
Sc and Ti functionalized CA is studied by computing conceptual DFT parameters, which
obeys maximum hardness and minimum electrophilicity principle. Hirshfeld charge
analysis and electrostatic potential map explore the charge transfer mechanism during the
hydrogen adsorption. Born-Oppenheimer molecular dynamics simulations are performed
at temperature range 200e473 K to study the stability of the system and the reversibility of
adsorbed 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 H2 saturation. This study
explores that Sc and Ti functionalized CA systems are efficient reversible hydrogen storage
material