Ab initio studies for characterization and identification of nanocrystalline copper pyrophosphate confined in mesoporous silica

Abstract

Here we employ a novel method for preparing the homogeneous copper pyrophosphate nanocrystals inside silica mesopores. In order to characterize and identify synthesized nanocrystals we performed the ab initio studies of the α phase of Cu2P2O7. The electronic and crystal structure were optimized within the density functional theory with the strong electron interactions in the states on copper atoms and van der Waals corrections included in calculations. The relaxed lattice parameters and atomic positions agree very well with the results of the diffraction measurements for nanocrystalline copper pyrophosphates embedded inside SBA-15 silica pores. The obtained Mott insulating state with the energy gap of 3.17 eV exhibits the antiferromagnetic order with magnetic moments on copper atoms (0.8 ) that is compatible with the experimental studies. The phonon dispersion relations were obtained to study the dynamical properties of the Cu2P2O7 lattice and the element-specific atomic vibrations were analyzed using the partial phonon density of states. The calculated Raman spectrum revealed the consistency of typical bands of Cu2P2O7 with the experimental data. The investigation that combines a new synthesis of nanomaterials with the first-principles calculations is important for better characterization and understanding of the physical properties relevant for nanotechnological applications.

Synthesis, thermal evolution and magnetic investigations of SBA-15 silica functionalized with anchored iron phosphonate molecules

“…In the second region, weight loss was at a level of 11% (from 95% to 84%) and was connected with the chemically-bonded water abruption, thermal decomposition of methyl (trimethylsilane-) groups and anchored iron propilphosphonate chains. The last ones were decomposed with the formation of various phosphates, pyrophosphates and oxides, the formation of which was observed in similar systems [24,50,51]. Since, according to electron diffraction, at this region, no crystalline products were noticed, one can assume that those products were in a complex amorphous form spread on the inner surface of the silica mesopores.…”

“…Hence, SBA-15 is, on the one hand, a matrix for metal ion immobilization and, further, the remediation of pollutants. However, on the other hand, mesoporous SBA-15 is a slurry nanoreactor in which metal ions immobilized inside the pore walls may recrystallize at suitable conditions (temperature, pH, humidity, and oxygen fugacity) and form nanometric-size particles [22][23][24]. It seems that environmental factors create a new structure with novel individual features.…”

Mechanism of Negative Thermal Expansion in Monoclinic Cu2P2O7 from First Principles

“…The anisotropic atomic displacement parameters and thermal ellipsoids were calculated using PHONOPY. , The chemical bonding analyses through crystal orbital Hamilton populations (COHPs) were performed using LOBSTER. , Projected electronic DOSs were extracted using VASPKIT . Moreover, the colinear antiferromagnetic configuration (see Figure S1) in Cu 2 P 2 O 7 was used, which was also mentioned in the previous studies. , Note that we did not adopt the + U correction to the d electrons in the Cu 2+ ions (see section 4 of the Supporting Information for the discussion of the + U correction).…”

“…The crystal structures in Figures 1, 4, 7, and 9–11 were visualized with VESTA and the TSS Physics webpage. Supporting Information includes refs , , , , and − .…”

“… 25 Moreover, the colinear antiferromagnetic configuration (see Figure S1 ) in Cu 2 P 2 O 7 was used, which was also mentioned in the previous studies. 26 , 27 Note that we did not adopt the + U correction to the d electrons in the Cu 2+ ions (see section 4 of the Supporting Information for the discussion of the + U correction).…”