Electronic properties of heterometallic zeolitic imidazolate framework and its encapsulation with Ni, Pd and Pt

Abstract

The electronic properties of heterometallic zeolitic imidazolate frameworks (ZIF-8) containing Cd and Zn metal centres have been examined using density functional theory to reveal the nature of metal to ligand interaction, band gap, density of states and charge distribution. The band gap energy of mixed-metal ZIF-8(Zn/Cd) has been calculated for each ratio of Cd and Zn in the mixed-metals showing a small window of possible alternating the electronic states of this material. The band gap energy shifts from 4.84 eV in pristine ZIF-8(Zn) to 4.33 eV when all the Zn2+ metal centres were replaced by Cd2+ ions. Increasing the ratio of Cd to Zn decreases the band gap energy due to the shifting of the electronic states of Cd at the edge of the conductance band. Modification of the electronic structure was also examined when several metals of Ni, Pd, and Pt were dopped in the mixed-metal ZIF-8(Zn/Cd) to give band gap energies of 2.19, 3.35, and 3.41 eV, respectively. The presence of mixed-metal seems to fine tune the band gap energy than doping the metals in ZIF-8(Zn) only. Density of states have been evaluated to reveal the coordination nature in the mixed-metal ZIF-8(Zn/Cd) as well as after doping with the metals. Additional electronic parameter of the net atomic charge distribution based on the repeating electrostatic potential extracted atomic method was also determined in a range of van der Waals (vdW) radius to see the effect of mixed metals in ZIF-8(Zn/Cd). The net atomic charge of each metal centre is observed to be convergence when the vdW radius scale was set to 0.8, 0.9 and 1.0.