Exfoliation of zirconium aminophosphonates: investigation on the electronic structure by ab initio calculations
Recently new zirconium aminophosphonates structures are being proposed by modifications of its synthesis for different applications. In this work, we report a theoretical study of the structural and electronic properties of bulk materials and their 2D forms for three layered zirconium phosphonates: α−Zr(HPO4)2 · H2O, Zr2H2[(C2O4)3(O3PCH2NH2)2] · 2 H2O (ZAMPAOX) and Zr(O3PCH2CH2NH3)2Cl2 (ZAEPACl). Moreover, the 13C and 31P NMR chemical shifts and infrared absorption spectra were also calculated and constructed to assist the characterization of future experimental analysis. For the 2D forms, the exfoliation energies were lower than 30 meVÅ -2 and the energetic order was: α-ZrP and ZAMPAOX > ZAEPACl. This trend could be confirmed by the nature of the intra and interlayer hydrogen bonds, which was analyzed by charge density difference plots. In the case of the band structures, all materials presented indirect band gaps, though some differences related to band gap values were found after being exfoliated. The influence of the hydration on the band structure was also evaluated. Structural modifications could be detected for the 2D forms of α-ZrP and ZAMPAOX after the removal of water molecules. The density of states suggested that the partial substitution of ions is a promising way to tune the band gap, as in the case of ZAEPACl with the substitution of chloride by other anions in the interlayer region.