In situ energy-dispersive X-ray diffraction for the synthesis optimization and scale-up of the porous zirconium terephthalate UiO-66.

The synthesis optimization and scale-up of the benchmarked microporous zirconium terephthalate UiO-66(Zr) were investigated by evaluating the impact of several parameters (zirconium precursors, acidic conditions, addition of water, and temperature) over the kinetics of crystallization by time-resolved in situ energy-dispersive X-ray diffraction. Both the addition of hydrochloric acid and water were found to speed up the reaction. The use of the less acidic ZrOCl2·8H2O as the precursor seemed to be a suitable alternative to ZrCl4·xH2O, avoiding possible reproducibility issues as a consequence of the high hygroscopic character of ZrCl4. ZrOCl2·8H2O allowed the formation of smaller good quality UiO-66(Zr) submicronic particles, paving the way for their use within the nanotechnology domain, in addition to higher reaction yields, which makes this synthesis route suitable for the preparation of UiO-66(Zr) at a larger scale. In a final step, UiO-66(Zr) was prepared using conventional reflux conditions at the 0.5 kg scale, leading to a rather high space-time yield of 490 kg m(-3) day(-1), while keeping physicochemical properties similar to those obtained from smaller scale solvothermally prepared batches.

High-speed detector for time-resolved diffraction studies.

There are a growing number of high brightness synchrotron sources that require high-frame-rate detectors to provide the time-scales required for performing time-resolved diffraction experiments. We report on the development of a very high frame rate CMOS X-ray detector for time-resolved muscle diffraction and time-resolved solution scattering experiments. The detector is based on a low-afterglow scintillator, provides a megapixel resolution with frame rates of up to 120,000 frames per second, an effective pixel size of 64 µm, and can be adapted for various X-ray energies. The paper describes the detector design and initial results of time-resolved diffraction experiments on a synchrotron beamline.

Structural chemistry, monoclinic-to-orthorhombic phase transition, and CO2 adsorption behavior of the small pore scandium terephthalate, Sc2(O2CC6H4)CO2)3, and its nitro- and amino-functionalized derivatives.

The crystal structure of the small pore scandium terephthalate Sc(2)(O(2)CC(6)H(4)CO(2))(3) (hereafter Sc(2)BDC(3), BDC = 1,4-benzenedicarboxylate) has been investigated as a function of temperature and of functionalization, and its performance as an adsorbent for CO(2) has been examined. The structure of Sc(2)BDC(3) has been followed in vacuo over the temperature range 140 to 523 K by high resolution synchrotron X-ray powder diffraction, revealing a phase change at 225 K from monoclinic C2/c (low temperature) to Fddd (high temperature). The orthorhombic form shows negative thermal expansivity of 2.4 × 10(-5) K(-1): Rietveld analysis shows that this results largely from a decrease in the c axis, which is caused by carboxylate group rotation. (2)H wide-line and MAS NMR of deuterated Sc(2)BDC(3) indicates reorientation of phenyl groups via π flips at temperatures above 298 K. The same framework solid has also been prepared using monofunctionalized terephthalate linkers containing -NH(2) and -NO(2) groups. The structure of Sc(2)(NH(2)-BDC)(3) has been determined by Rietveld analysis of synchrotron powder diffraction at 100 and 298 K and found to be orthorhombic at both temperatures, whereas the structure of Sc(2)(NO(2)-BDC)(3) has been determined by single crystal diffraction at 298 K and Rietveld analysis of synchrotron powder diffraction at 100, 298, 373, and 473 K and is found to be monoclinic at all temperatures. Partial ordering of functional groups is observed in each structure. CO(2) adsorption at 196 and 273 K indicates that whereas Sc(2)BDC(3) has the largest capacity, Sc(2)(NH(2)-BDC)(3) shows the highest uptake at low partial pressure because of strong -NH(2)···CO(2) interactions. Remarkably, Sc(2)(NO(2)-BDC)(3) adsorbs 2.6 mmol CO(2) g(-1) at 196 K (P/P(0) = 0.5), suggesting that the -NO(2) groups are able to rotate to allow CO(2) molecules to diffuse along the narrow channels.

Effect of Microstructure on the Radioluminescence and Transparency of Ce-Doped Strontium Hafnate Ceramics.

In this paper we report on the fabrication and characterization of SrHfO(3):Ce ceramics. Powders were prepared by solid-state synthesis using metal oxides and carbonates. X-ray diffraction measurements showed that phase-pure SrHfO(3) is formed at 1200°C. Inductively coupled plasma spectroscopy confirmed the purity and composition of each batch. SrHfO(3) exhibits several phase changes in the solid, but this does not appear to be detrimental to the ceramics. Microprobe experiments showed uniform elemental grain composition, whereas aluminum added as charge compensation for trivalent cerium congregated at grain boundaries and triple points. Radioluminescence spectra revealed that the light yield decreases when the concentration of excess Sr increases. The decrease in the light yield may be related to the change of Ce(3+) into Ce(4+) ions. For stoichiometric SrHfO(3):Ce, the light yield is about four times that of bismuth germanate (BGO), the conventional benchmark, indicating great potential for many scintillator applications.

Suppression of Afterglow in Microcolumnar CsI:Tl by Codoping With Sm: Recent Advances.

Microcolumnar CsI:Tl remains a highly desirable sensor for digital X-ray imaging due to its superior spatial resolution, bright emission, high absorption efficiency, and ready availability. Despite such obvious advantages, two characteristic properties of CsI:Tl undermine their use in clinical and high speed imaging: a persistent afterglow in its scintillation decay, and a hysteresis effect that distorts the scintillation yield after exposure to high radiation doses.In our earlier work we have discovered that the addition of 0.05 to 0.5 mol percent of Sm(2+) to crystals of CsI:Tl suppresses their afterglow by a factor of up to 50, even when subjected to a very high exposure of 120 R. This additive also diminishes hysteresis by an order of magnitude, which is a major accomplishment. Consequent- ly, our work is now focused on developing codoped microcolumnar CsI:Tl, Sm films that can potentially combine excellent properties of the current state-of-the-art CsI:Tl films with the reduced afterglow and hysteresis observed in codoped crystals. While our earlier attempts in CsI:Tl, Sm film fabrication, reported at the previous IEEE meeting, demonstrated obvious advantages of the approach, the recent work has succeeded in producing films that show improvement by at least a factor of 7 in afterglow and 150% in brightness compared to the standard CsI:Tl films. We report these important results in this paper, along with other recent advances in film growth and new imaging results.

Structural Transformations and adsorption of fuel-related gases of a structurally responsive nickel phosphonate metal-organic framework, Ni-STA-12.

The structure of the nickel N,N'-piperazinebismethylenephosphonate, Ni-STA-12 (St. Andrews porous material-12), has been determined in the hydrated (Ni2L x 8 H2O, L = O3PCH2NC4H8NCH2PO3), partially dehydrated (Ni2L x 2 H2O), and fully dehydrated (Ni2L) forms from high-resolution synchrotron X-ray powder diffraction. The framework structures of Ni2L x 8 H2O and Ni2L x 2 H2O are almost identical (R, a = 27.8342(1) A, c = 6.2421(2) A; R, a = 27.9144(1) A, c = 6.1655(2) A) with additional physisorbed water of the as-prepared Ni-STA-12 present in an ordered hydrogen-bonded network in the channels. Ab initio structure solution of the fully dehydrated solid indicates it has changed symmetry to triclinic (P1, a = 6.03475(5) A, b = 14.9157(2) A, c = 16.1572(2) A, alpha = 112.5721(7) degrees, beta = 95.7025(11) degrees, gamma = 96.4950(11) degrees) as a result of a topotactic structural rearrangement. The fully dehydrated solid possesses permanent porosity with elliptical channels 8 A x 9 A in free diameter. The structural change results from the loss of water coordinated to the nickel cations, so that the nickel coordination changes from edge-sharing octahedral NiO5N to edge- and corner-sharing five-fold NiO4N. During this change, two out of three phosphonate groups rotate to become fully coordinated to nickel cations, leaving the remainder of the phosphonate groups coordinated to nickel cations by two oxygen atoms and with a P=O bond projecting into the channels. This transformation, which is completely reversible, causes substantial changes in both vibrational and electronic properties as shown by IR, Raman, and UV-visible spectroscopies. Complementary adsorption, calorimetric, and infrared studies of the probe adsorbates H2, CO, and CO2 reveal the presence of several distinct adsorption sites in the solid, which are attributed to their interactions with nickel cations which are weak Lewis acid sites, as well as with P=O groups that project into the pores. At 304 K, the adsorption isotherms and enthalpies of adsorption on dehydrated Ni-STA-12 have been measured for CO2 and CH4: Ni-STA-12 gives adsorption uptakes of CO2 of 2.5 mmol g(-1) at 1 bar, an uptake ca. 10 times that of CH4.

The first route to large pore metal phosphonates.

The first large pore (free diameter > 7 A) metal phosphonates have been prepared as divalent metal N,N'-piperazinebis(methylenephosphonate)s that possess pores greater than ca. 10 A in free diameter, are stable up to 400 degrees C and offer a route to chiral adsorbents and catalysts.

Nondestructive method for quantifying thallium dopant concentrations in CsI:Tl crystals.

We report a quantitative method for using X-ray fluorescence (XRF) to nondestructively measure the true content of Tl dopant in CsI:Tl scintillator crystals. The instrument is the handheld LeadTracer™, originally developed at RMD Instruments for measuring Pb concentration in electronic components. We describe both the measurement technique and specific findings on how changes in crystal size and growth parameters affect Tl concentration. This method is also applicable to numerous other activator ions important to scintillators, such as Ce(3+) and Eu(2+).

A rare example of a porous Ca-MOF for the controlled release of biologically active NO.

A 1D-microporous 3D calcium tetracarboxylate MOF has been solvothermally prepared and its structure solved from single crystal data. It exhibits coordinatively unsaturated Ca(2+) Lewis acid sites able to trap and deliver nitric oxide at a biological level.

Biodegradable therapeutic MOFs for the delivery of bioactive molecules.

A new metal organic framework (MOF) built up from non-toxic iron and the therapeutically active linker nicotinic acid, with pellagra-curative, vasodilating, and antilipemic properties, has been isolated and characterised via single crystal methods. The release of the therapeutic agent, which is a constituent of the framework, is achieved through the degradation of the hybrid phase, under simulated physiological conditions, allowing for the delivery of the bioactive molecule.

Yttrium bisphosphonate STA-13: a racemic phosphonate metal organic framework with permanent microporosity.

Crystallisation of yttrium and other trivalent metal cations of similar radius with racemic N,N'-2-methylpiperazinebis(methylene phosphonic acid) gives a small pore bisphosphonate metal-organic framework solid displaying coordinative and hydrogen bonding and permanent porosity.

Synthesis and in situ transformation of PST-1: a potassium gallosilicate natrolite with a high Ga content.

The synthetic details of a novel potassium gallosilicate natrolite with Si/Ga = 1.28, denoted PST-1, are described. The presence of K(+) and Ga with well-defined levels of concentration in the synthesis mixture is essential for directing its crystallisation. PST-1 transforms rapidly into TNU-6 under hydrothermal conditions, behaviour that contrasts sharply with its very high thermal and hydrothermal stability, which is unusual for a material of such a high Ga content. These stability issues are discussed and rationalized based on chemical composition, likely violations of Loewenstein's rule and the temperature of dehydration of as-made K-PST-1. The crystal structure of TNU-6 has been resolved through the combined use of synchrotron X-ray and electron diffraction data; it has the BaFeGaO(4) structure type with an additional radical 3a x radical 3a "GeAlO(4)" superstructure that arises from tilting of some of the tetrahedral units in all of the 6-rings.

Single crystal X-ray diffraction studies of carbon dioxide and fuel-related gases adsorbed on the small pore scandium terephthalate metal organic framework, Sc2(O2CC6H4CO2)3.

The adsorption behavior of the microporous scandium terephthalate Sc2(O2CC6H4CO2)3 for small fuel-related molecules has been measured. The structure shows an adsorption capacity for N2 and CO2 of 6.5 mmol g(-1) and is able to take up straight chain hydrocarbons. The mechanism of adsorption of CO2, CH4, and C2H6 has been determined by single crystal synchrotron X-ray diffraction at approximately 230 K. Adsorption of CO2 at 235 K and 1 bar pressure and H2 at 80 K and 0.25 bar results in each case in a symmetry change from orthorhombic Fddd to monoclinic C2/c through tilts in the terephthalate linkers. CO2 molecules take up different sites in the two symmetrically different channels that result from this symmetry change. The structure remains orthorhombic in 9 bar of CH4 and 5 bar of C2H6, and the adsorption sites are located. CH4 and C2H6 are observed to adopt sites within the channels, and C2H6 is also observed to adopt adsorption sites between phenyl groups in the channel walls, suggesting that the structure is sufficiently flexible to allow diffusion of small molecules between adjacent channels.

Effects of scintillator on the detective quantum efficiency (DQE) of a digital imaging system.

OBJECTIVE: To compare the effects of scintillator on the detective quantum efficiency (DQE) of a charge-coupled device (CCD) digital intraoral radiographic system. STUDY DESIGN: Three screens composed of 3 different scintillator materials, namely europium-doped lutetium oxide (Lu2(O3):Eu3+), transparent optical ceramic (TOC), thallium-doped cesium iodide (CsI:Tl; CsI), and terbium-doped gadolinium oxysulfide (Gd2(O2)S:Tb; GOS) were compared, in turn, in combination with a CCD detector having square pixels with height and width dimensions of 19.5 microm. DQE was investigated using the slanted-slit-derived MTF and surrogate signal-to-noise ratio (SNR) measurements derived from calculations of the mean and standard deviations from the mean pixel values of multiple random patches from various uniform exposures. An Irix x-ray generator operated at 70 kVp and 8 mA, with a nominal focal spot size of 0.7 mm and 2.5 mm Al equivalent filtration, was used in making all exposures. RESULTS: Using TOC, the peak DQE was 62% at 5 cycles/mm. For CsI, the peak DQE was 22% at 2 cycles/mm. With GOS, the peak DQE was 10% at 1 cycle/mm. CONCLUSION: Under identical experimental settings, TOC consistently resulted in higher DQE than CsI and commercially available GOS scintillators combined with the same high-resolution solid-state detector.

Effects of scintillator on the modulation transfer function (MTF) of a digital imaging system.

OBJECTIVE: To investigate the effects of 2 components (scintillator and x-ray generator) in the imaging chain on the modulation transfer function (MTF) of a charge-coupled device (CCD) digital intraoral radiographic system. STUDY DESIGN: Three screens composed of 3 different scintillator materials, namely europium-doped lutetium oxide transparent optical ceramic (TOC), thallium-doped cesium iodide (CsI), and terbium-doped gadolinium oxysulfide (GOS), were compared. Each was used, in turn, in conjunction with a CCD detector having a pixel dimension of 19.5 mum. Two different x-ray generators were also used to evaluate this variable. MTF was investigated using the slanted slit method. RESULTS: The TOC provided a good modulation response for low and middle frequencies, reducing to 0 only at a high cutoff frequency. With CsI and GOS, the system MTF dropped to 0 at a lower cutoff frequency than was the case with TOC. Hence, TOC provided higher spatial resolution than the other 2 scintillators tested under the experimental conditions applied. The differences in MTF attributed to the scintillator type were proportional and consistent. CONCLUSIONS: Despite constant pixel dimensions, MTF was affected to a considerable degree by the scintillator applied and the x-ray generator used in conjunction with the same CCD imaging device. TOC shows potential as a possible replacement for CsI and GOS as a scintillator screen material for intraoral digital x-ray imaging using a solid-state detector, providing higher spatial resolution under the given experimental conditions.

Synthesis and structure of the framework scandium methylphosphonates ScF(H2O)CH3PO3 and NaSc(CH3PO3)2.0.5H2O.

Two framework scandium methylphosphonates have been prepared hydrothermally and their structures solved. ScF(H(2)O)CH(3)PO(3) is a non-porous solid built up from -ScF- chains linked by methylphosphonate groups. The ScO(4)F(2) octahedra are completed by a coordinated water molecule. NaSc(CH(3)PO(3))(2).0.5H(2)O was solved ab initio from high-resolution synchrotron X-ray powder diffraction data. It has a fully connected, negatively charged scandium phosphonate framework where ScO(6) octahedra share vertices with PO(3)CH(3) groups. The solid contains charge balancing sodium cations, coordinated by a water molecule, which may be reversibly removed and adsorbed. The structure of the perdeuterated, dehydrated solid has been refined against neutron powder diffraction data collected at 2.5 K, showing the CD(3) groups in a fully staggered orientation with respect to the phosphonate oxygen atoms.