A Crystalline Mesoporous Germanate with 48‐Ring Channels for CO2 Separation
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Abstract One of the challenges in materials science has been to prepare crystalline inorganic compounds with mesopores. Although several design strategies have been developed to address the challenge, expansion of pore sizes in inorganic materials is more difficult compared to that for metal–organic frameworks. Herein, we designed a novel mesoporous germanate PKU‐17 with 3D 48×16×16‐ring channels by introducing two large building units (Ge 10 and Ge 7 clusters) into the same framework. The key for this design strategy is the selection of 2‐propanolamine (MIPA), which serves as the terminal species to promote the crystallization of Ge 7 clusters. Moreover, it is responsible for the coexistence of Ge 10 and Ge 7 clusters. To our knowledge, the discovery of PKU‐17 sets a new record in pore sizes among germanates. It is also the first germanate that exhibits a good selectivity toward CO 2 over N 2 and CH 4 .Keywords:
Germanate
Germanate
Laser diode
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Glasses of the system xGd2O3 · (100 − x)[7GeO2 · 3PbO] with 0 ≤ x ≤ 40 mol% were prepared using the melt quenching method. Lead germanate glasses are particularly interesting in the context of the germanate anomaly. In this paper, we investigate changes in the coordination number of germanium in gadolinium–lead germanate glasses using molar volume analysis, density measurements, FTIR and UV–VIS spectroscopy, and density functional theory (DFT). Despite some inconsistencies, the coordination change model remains the currently accepted model for the anomalous behaviour of lead germanate glasses. Based on these experimental results, we propose the following mechanism for the germanate anomaly. (i) The low thermodynamic stability of the [GeO6] structural unit and the occupation of interstices of larger dimensions (the six-coordinated interstices of the [PbO6] structural units) in the lead germanate network yield [GeO5] structural units with higher thermodynamic stability and larger ionic radii. (ii) Not linked to the terminal oxygens of the [GeO5] structural units and with the formation of smaller network cavities of the lead germanate glass, links are required with [GeO4] tetrahedra for stabilization, generating the formation of three-membered rings of [GeO4] tetrahedral structural units.
Germanate
Tetrahedron
Chemical Stability
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Differential scanning calorimetry, Raman scattering, optical absorption, and upconversion of infrared to green luminescence have been studied for Er3+-doped lead-germanate glass 55GeO2⋅20PbO⋅10BaO⋅10ZnO⋅5K2O (GPBZK) and lead-tellurium-germanate glass 30GeO2⋅30PbO⋅30TeO2⋅10CaO (GPTC). Judd–Ofelt intensity parameters of Er3+ in the two host glasses were determined and used to calculate radiative transition rates and lifetimes. Values of the radiative quantum yield of the 4S3/2→4I15/2 transition and the infrared (797 nm) to green (547 nm) upconversion efficiency of Er3+ were obtained. It has been found that the 4S3/2→4I15/2 radiative transition rate of Er3+ in GPTC glass is about twice that in the GPBZK glass and the upconversion efficiency in the GPTC glass is about four times larger than that in the GPBZK glass. These host-dependent properties are mainly attributed to the enhanced local field and the reduced multiphonon rate in lead-tellurium-germanate glass compared to lead-germanate glass.
Germanate
Photon Upconversion
Tellurium
Chalcogenide glass
Bismuth germanate
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Abstract The crystal-chemical classification of Li-germanates was performed. Depending on the types of Ge-polyhedra and their interconnections, the Li-gennanates ace divided into 3 groups: the framework MT-structures; the MT condensed structures and T-structures. The structure invariant M2T4 is established in the framework germanates and in Li4Ge3 VI Ge3 VIO12 germanate with M, T condensed structure. The crystals synthesized is in hydrothermal GeO2—LiOH—H2O system are analyzed on the basis of crystal-chemical classification suggested. The representatives of all groups mentioned above are formed in aqua solutions at high temperatures and pressures. The most stable germanate is characterized b the direct condensation of the dimmers M2T4. Germanates with a prevalence of Ge in the structure (M3T2 and MT3) exist in a very small region at low kmperatures and low LiOH concentration, then they are replaced by the framework germanate MT2.
Germanate
Polyhedron
Crystal Chemistry
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Germanate
Quantum yield
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Germanate
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The prominent problem in archetypal germanate glasses is the germanate anomaly where the density exhibits maxima at 15−20 mol % of the alkali oxide content. Here we report 17O two-dimensional NMR spectra for GeO2 and Na-germanate glasses where the presence of both bridging oxygen linking [4]Ge and highly coordinated Ge ([5,6]Ge−O−[4]Ge) and nonbridging oxygen, and an increase in topological disorder are demonstrated at the density maximum, manifesting atomic origins of the anomaly. These densification mechanisms in germanate glasses with Na content are remarkably similar to densification in v-B2O3 with pressure.
Germanate
Anomaly (physics)
Quantum chemical
Maxima
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Germanate
Anomaly (physics)
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For unit cubes the half-wave voltages of lithium germanate at 632·8 nm range from 300 to 3000 kV for the four configurations measured. For lead germanate the corresponding values for the two configurations studied are 20 and 15 kV; one of these two configurations is attractive for device use.
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