The triclinic form of AlPO 4 -34, a microporous aluminophosphate with the chabazite (CHA) topology, adopts a rhombohedral symmetry upon calcination. The framework structure of this phase remains intact under ambient conditions, but it distorts dramatically, though reversibly, in the presence of water. Following these structural changes in situ by X-ray diffraction revealed that there are actually two stable rehydrated phases, which differ from each other by one water molecule in the channel. Both of these phases have triclinic unit cells that are closely related to that of the calcined rhombohedral phase. The structure of the low-temperature (10 °C), fully rehydrated phase (phase B) was elucidated by combining high-resolution synchrotron powder diffraction with solid-state NMR techniques. Coordination of three of the six Al atoms to water molecules causes the deformation of the framework and the reduction of the symmetry. Rietveld refinement of the structure of phase B in the triclinic space group P1 (a ) 9.026, b ) 9.338, c ) 9.508 Å, R ) 95.1°, β ) 104.1°, and γ ) 96.6°) converged with R F ) 0.079 and R WP ) 0.176 (R exp ) 0.087). Framework connectivities derived from the structure were used to assign 31 P NMR lines as well as part of the 27 Al NMR signal.

Wet hydrogen peroxide catalytic oxidation (WHPCO) is one of the most important industrially applicable advanced oxidation processes (AOPs) for the decomposition of organic pollutants in water. It is demonstrated that manganese functionalized silicate nanoparticles with interparticle porosity act as a superior Fenton‐type nanocatalyst in WHPCO as they can decompose 80% of a test organic compound in 30 minutes at neutral pH and room temperature. By using X‐ray absorption spectroscopic techniques it is also shown that the superior activity of the nanocatalyst can be attributed uniquely to framework manganese, which decomposes H2O2 to reactive hydroxyls and, unlike manganese in Mn3O4 or Mn2O3 nanoparticles, does not promote the simultaneous decomposition of hydrogen peroxide. The presented material thus introduces a new family of Fenton nanocatalysts, which are environmentally friendly, cost‐effective, and possess superior efficiency for the decomposition of H2O2 to reactive hydroxyls (AOP), which in turn readily decompose organic pollutants dissolved in water.

Structural dynamics of Ca(BDC)(DMF)(H 2 O) with rhombic-shaped channels and 4 4 net topology upon heating and hydration were elucidated by using complementary methods of diffraction (XRD) and spectroscopy (FT-IR, MAS NMR, EXAFS, XANES). During heating the Ca(BDC)-(DMF)(H 2 O) framework underwent structural changes in two steps. The first change at 150 °C includes breaking of Ca−O bonds with H 2 O and DMF molecules. In this step, DMF is removed from the surface or near the surface of the crystals. The affected parts of the crystals are transformed to a new nonporous Ca-BDC(400) phase that prevents the diffusion of DMF from the cores of the crystals. Second transition at 400 °C led to the complete transformation to Ca-BDC(400). This phase is reversibly transformed to a pseudo-3-D framework Ca(BDC)(H 2 O) 3 upon exposure to humid environment. We proposed mechanisms of Ca-BDC(RT) → Ca-BDC(400) and Ca-BDC(400) → Ca(BDC)(H 2 O) 3 transformations, which include breaking of the bonds between Ca 2+ and carboxylate groups, rotating of BDC ligand, and recoordination of COO − groups to Ca 2+ centers. The crystal-to-crystal transformations are driven by the tendencies to change the bonding modes between COO − and Ca 2+ with the change of Ca 2+ coordination number. Thus the decrease in Ca 2+ coordination number, which is usually a consequence of activation, does not lead to the expansion or contraction of the pores, but it leads to pronounced structural rearrangement. Such behavior can explain the lack of porosity in Ca-MOF systems.