Solid-state 31P Magic Angle Spinning Research Articles

Cs absorption capacity and selectivity of crystalline and amorphous Hf and Zr phosphates

Removal of radioactive Cs from sodium-rich solutions is a technical challenge that goes back to post World War II nuclear waste storage and treatment; and interest in this topic was reinvigorated by the Fukushima-Daiichi nuclear power plant disaster, 10 years ago. Since the 1960′s there has been considerable focus on layered Zr phosphates as robust inorganic sorbents for separation of radionuclides such as Cs. Here we present synthesis and characterization, and direct comparison of Cs sorption capacity and selectivity of four related materials: 1) crystalline α-Zr phosphate and α-Hf phosphate, and 2) amorphous analogues of these. Powder X-ray diffraction, thermogravimetry, solid-state 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and compositional analysis (inductively coupled plasma optical emission spectroscopy and mass spectroscopy, ICP OES and ICP MS) provided formulae; respectively M(HPO4)2⋅1H2O and M(HPO4)2⋅4H2O (M = Hf, Zr) for crystalline and amorphous analogues. Maximum Cs loading, competitive Cs-Na selectivity and maximum Cs-Na loading followed by the above characterizations plus 133Cs MAS-NMR spectroscopy revealed that amorphous analogues are considerably better Cs-sorbents (based on maximum Cs-loading and selectivity over Na) than the well-studied crystalline Zr-analogue. Additionally, crystalline α-Hf phosphate is better Cs-sorbent than crystalline α-Zr phosphate. All these studies consistently show that Hf phosphate is less crystallize than Zr phosphate, when obtained under similar or identical synthesis conditions. We attribute this to lower solubility of Hf phosphate compared to Zr phosphate, preventing ‘defect healing’ during the synthesis process.

Separation of cobalt, neodymium and dysprosium using amorphous zirconium phosphate

The purpose of this study was to investigate the separation of Co, Nd and Dy from a ternary Co-Nd-Dy solution using amorphous zirconium phosphate (am-ZrP). Am-ZrP was synthesized by a precipitation method at room temperature and subsequently characterized by Fourier transform-infrared spectrometry, thermogravimetry, scanning electron microscopy, X-ray diffraction, solid-state 31P magic angle spinning nuclear magnetic resonance spectrometry and sodium hydroxide titration (with and without background salt). The ion exchange kinetics of am-ZrP that were determined in ternary 1mM equimolar solutions at equilibrium pH2.5. The effect of pH on the adsorption was studied in ternary 1mM equimolar solutions and the uptakes of the metals increased with increasing pH until approximately pH3.5. The adsorption isotherms of Co, Nd and Dy were tested in a series of ternary equimolar solution, the total uptake amounted to 4.13meq/g at pH ~3.0. The preference of am-ZrP for these metals occurred in decreasing order Dy>Nd≫Co. The separation of Co, Nd and Dy from their 1mM equimolar ternary mixture was investigated on an am-ZrP column. Effects of loading (7.8%, 62% and 100%) on the separation were compared by measuring the corresponding HNO3 elution fractions. It was found that with a lower metal loading of 7.8%, three clear elution bands were obtained. Am-ZrP exhibited selective separation properties towards the ternary Co-Nd-Dy system, which contribute to the future scale-up studies for the recycling of NdFeB magnets.

The effect of P modification on the acidity of HZSM-5 and P-HZSM-5/CuO-ZnO-Al2O3 mixed catalysts for hydrogen production by dimethyl ether steam reforming

Dimethyl ether steam reforming (DME SR) was catalyzed by a CuO-ZnO-Al2O3 (CuZnAlO) catalyst mixed with P-modified HZSM-5 for the production of H2. The effect of P modification on the acidity and activity of the P-HZSM-5/CuZnAlO mixed catalyst for DME SR was investigated. P-HZSM-5/CuZnAlO gave a higher CO2 selectivity and also higher stability during DME SR compared to the mixed catalyst with HZSM-5. N2 desorption, X-ray diffraction, temperature-programmed oxidation (TPO), NH3 temperature-programmed desorption (NH3-TPD), Fourier transform infrared spectroscopy (FT-IR), and solid-state 31P magic angle spinning nuclear magnetic resonance (31P MAS NMR) were used for catalyst characterization. NH3-TPD results showed that both the acid quantity and strength of HZSM-5 were significantly changed after P modification. With increased P content, the density of strong acid sites decreased, while the weak acid sites changed little. TPO results indicated that catalyst deactivation was mainly caused by the deposition of coke. The catalyst with 5% P exhibited much better stability than the parent HZSM-5 due to the disappearance of strong acid sites after P modification. The FT-IR spectra of pyridine adsorption clearly revealed that with increased P content, there was an obvious decrease of Lewis acid sites and slight decrease of Brönsted acid sites. From the results of 31P MAS NMR, NH3-TPD and FT-IR of adsorbed pyridine, a description of the effect of phosphorus modification on HZSM-5 was proposed.

Influence of dissolved organic carbon on the efficiency of P sequestration by a lanthanum modified clay

A laboratory scale experiment was set up to test the effect of dissolved organic carbon (DOC) as well as ageing of the La–P complex formed during phosphorus (P) sequestration by a La modified clay (Phoslock®). Short term (7 days) P adsorption studies revealed a significant negative effect of added DOC on the P sequestration of Phoslock®, whereas a long-term P adsorption experiment revealed that the negative effect of added DOC was reduced with time. The reduced P binding efficiency is kinetic, as evident from solid-state 31P magic-angle spinning (MAS) NMR spectroscopy, who showed that the P binding did not change in the presence of DOC. 31P MAS NMR also reveals that up to 26% of the sequestered phosphate is as loosely bound redox-sensitive P species on the surface of rhabdophane (LaPO4 · nH2O, n ≤ 3). The ratio between the loosely bound P and lanthanum phosphate did not change with time, however both NMR and La LIII-extended x-ray absorption fine structure (EXAFS) spectroscopy shows a transformation of lanthanum phosphate from the initially formed rhabdophane towards the more stable monazite (LaPO4). Furthermore, the effect of natural DOC on the P binding capacity was tested using water and pore water from 16 Danish lakes. Whilst DOC has an immediate negative impact on P binding in the lake water, with time this effect is reduced.

Acidity characterization of rare-earth-exchanged Y zeolite using 31P MAS NMR

Detailed qualitative and quantitative information on the effects of rare-earth (RE) cations on the types (Brönsted and Lewis), strengths, and distributions of acid sites on Y zeolite was studied by solid-state 31P magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, using adsorbed trimethylphosphine oxide (TMPO) and tributylphosphine oxide (TBPO) as probe molecules. A total of seven 31P resonance peaks, with 31P NMR/TMPO chemical shifts at δ = 78, 70, 65, 62, 58, 55, and 53, corresponding to sites with different acid strengths, were identified. The peaks at δ = 78 and 70 arose from external and internal acid sites, the peaks at δ = 65, 62, 58, and 53 were from internal Brönsted acid sites, and the peak at δ = 55 was from internal Lewis acid sites. With increasing RE content, the number of medium strength Brönsted acid sites (δ = 62 and 58) increased significantly, whereas those of strong Brönsted acid sites (δ = 65) and weak Lewis acid sites (δ = 55) decreased. These experimental results were explained in terms of the influence of framework Al, extra-framework Al, and RE cations on the Y zeolite acidity.

Novel Cu(I)-selective chelators based on a bis(phosphorothioyl)amide scaffold.

Bis(dialkyl/aryl-phosphorothioyl)amide (BPA) derivatives are versatile ligands known by their high metal-ion affinity and selectivity. Here, we synthesized related chelators based on bis(1,3,2-dithia/dioxaphospholane-2-sulfide)amide (BTPA/BOPA) scaffolds targeting the chelation of soft metal ions. Crystal structures of BTPA compounds 6 (N(-)R3NH(+)) and 8 (NEt) revealed a gauche geometry, while BOPA compound 7 (N(-)R3NH(+)) exhibited an anti-geometry. Solid-state (31)P magic-angle spinning NMR spectra of BTPA 6-Hg(II) and 6-Zn(II) complexes imply a square planar or tetrahedral geometry of the former and a distorted tetrahedral geometry of the latter, while both BTPA 6-Ni(II) and BOPA 7-Ni(II) complexes possibly form a polymeric structure. In Cu(I)-H2O2 system (Fenton reaction conditions) BTPA compounds 6, 8, and 10 (NCH2Ph) were identified as most potent antioxidants (IC50 32, 56, and 29 μM, respectively), whereas BOPA analogues 7, 9 (NEt), and 11 (NCH2Ph) were found to be poor antioxidants. In Fe(II)-H2O2 system, IC50 values for both BTPA and BOPA compounds exceeded 500 μM indicating high selectivity to Cu(I) versus the borderline Fe(II)-ion. Neither BTPA nor BOPA derivatives showed radical scavenging properties in H2O2 photolysis, implying that inhibition of the Cu(I)-induced Fenton reaction by both BTPA and BOPA analogues occurred predominantly through Cu(I)-chelation. In addition, NMR-monitored Cu(I)- and Zn(II)-titration of BTPA compounds 8 and 10 showed their high selectivity to a soft metal ion, Cu(I), as compared to a borderline metal ion, Zn(II). In summary, lipophilic BTPA analogues are promising highly selective Cu(I) ion chelators.

Electrical conduction and thermodynamic properties of K2NiP2O7

The pyrophosphate K2NiP2O7 has been synthesized by the classic ceramic method and characterized by X-ray diffraction, solid-state 31P magic angle spinning (MAS) NMR, and IR and electrical impedance spectroscopy. The solid-state 31P MAS NMR, performed at 121.49 MHz, shows two isotropic resonances at −17.66 and −19.94 ppm, revealing the existence of two phosphorus environments in the structure. The electrical conductivity and dielectric properties have been investigated in the frequency and the temperature range of 200 Hz–1 MHz and 603–728 K, respectively. The frequency dependence of the conductivity is interpreted using the augmented Jonscher relation. The close values of activation energies obtained from the analysis of hopping frequency and dc conductivity imply that the transport is through ion hopping mechanism. The charge carrier concentration in the investigated sample has been evaluated using the Almond–West formalism and shown to be independent of temperature. Thermodynamic parameters such as the free energy of activation ΔF, the enthalpy ΔH, and the change in entropy ΔS have been calculated.

One‐Dimensional Polymers Based on Silver(I) Cations and Organometallic cyclo‐P3 Ligand Complexes

The synthesis and characterization of the first supramolecular aggregates incorporating the organometallic cyclo-P3 ligand complexes [CpRMo(CO)2(eta3-P3)] (CpR=Cp (C5H5; 1a), Cp* (C5(CH3)5; 1b)) as linking units is described. The reaction of the Cp derivative 1a with AgX (X=CF3SO3, Al{OC(CF3)3}4) yields the one-dimensional (1D) coordination polymers [Ag{CpMo(CO)2(mu,eta3:eta1:eta1-P3)}2]n[Al{OC(CF3)3}4]n (2) and [Ag{CpMo(CO)2(mu,eta3:eta1:eta1-P3)}3]n[X]n (X=CF3SO3 (3a), Al{OC(CF3)3}4 (3b)). The solid-state structures of these polymers were revealed by X-ray crystallography and shown to comprise polycationic chains well-separated from the weakly coordinating anions. If AgCF3SO3 is used, polymer 3a is obtained regardless of reactant stoichiometry whereas in the case of Ag[Al{OC(CF3)3}4], reactant stoichiometry plays a decisive role in determining the structure and composition of the resulting product. Moreover, polymers 3a, b are the first examples of homoleptic silver complexes in which Ag(I) centers are found octahedrally coordinated to six phosphorus atoms. The Cp* derivative 1b reacts with Ag[Al{OC(CF3)3}4] to yield the 1D polymer [Ag{Cp*Mo(CO)2(mu,eta3:eta2:eta1-P3)}2]n[Al{OC(CF3)3}4]n (4), the crystal structure of which differs from that of polymer 2 in the coordination mode of the cyclo-P3 ligands: in 2, the Ag+ cations are bridged by the cyclo-P3 ligands in a eta1:eta1 (edge bridging) fashion whereas in 4, they are bridged exclusively in a eta2:eta1 mode (face bridging). Thus, one third of the phosphorus atoms in 2 are not coordinated to silver while in 4, all phosphorus atoms are engaged in coordination with silver. Comprehensive spectroscopic and analytical measurements revealed that the polymers 2, 3a, b, and 4 depolymerize extensively upon dissolution and display dynamic behavior in solution, as evidenced in particular by variable temperature 31P NMR spectroscopy. Solid-state 31P magic angle spinning (MAS) NMR measurements, performed on the polymers 2, 3b, and 4, demonstrated that the polymers 2 and 3b also display dynamic behavior in the solid state at room temperature. The X-ray crystallographic characterisation of 1b is also reported.

SOLID-STATE FOURIER TRANSFORM INFRARED AND 31P NUCLEAR MAGNETIC RESONANCE SPECTRAL FEATURES OF PHOSPHATE COMPOUNDS

Solid-state spectroscopic techniques, including Fourier transform infrared (FT-IR) and solid-state 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies, are powerful tools for evaluating metal speciation and transformation mechanisms of P compounds in soil, animal manure, and

Employment of 31P MAS NMR for the Identification of Amorphous Precipitation Products Obtained from the MAP Process

Abstract In order to recover aqueous ammonium (NH4+) and phosphate (PO43−) from wastewater, these ions were immobilized with MgO and MgCl2 into an insoluble solid. Analysis by X-ray diffraction (XRD) showed that the insoluble solid was a single phase of ammonium magnesium phosphate (Mg(NH4)PO4·6H2O: MAP). Therefore, the present process has been commonly known as the MAP process. However, analysis by the solid-state 31P magic-angle spinning nuclear magnetic resonance (31P MAS NMR) of the insoluble solid revealed that the solid contained various phosphate compounds together with crystalline MAP. The results indicated that the solids obtained from the MAP process should be carefully identified, since they are considered to be utilized as a slow-acting fertilizer.

Local structure and connectivity in lithium phosphate glasses: a solid-state 31P MAS NMR and 2D exchange investigation

High resolution solid-state 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the local structure and connectivity for three xLi 2O·(1 - x)P 2O 5 glasses. The principal components of the 31P chemical shift anisotropy (CSA) tensors for the different phosphate tetrahedron sites (Q n ) and the relative populations of each Q n species were determined from simulation of the MAS spectra. The medium range structure and connectivity between similar or different Q n units in these lithium phosphate glasses were probed using novel two-dimensional (2D) MAS exchange experiments. Radio-frequency dipolar recoupling (RFDR) techniques allowed the reintroduction of the through space 31P- 31P dipolar-dipolar interaction even in the presence of fast MAS. For these binary phosphate glasses the connectivity and medium range structure for different Q n species is described well by a statistical distribution, and is consistent with a model of random depolymerization.

Synthesis, X-ray diffraction and solid-state 31P magic angle spinning NMR study of ?-tricalcium orthophosphate

The effects of synthesis conditions on the quantitative preparation of α-tricalcium phosphate (α-TCP) have been investigated. The following parameters of the synthesis were considered: nature of the starting material-Ca-deficient hydroxyapatite, DAP, versus hydroxyapatite-anhydrous dicalcium phosphate mixtures (HAP-DCPA); Ca/P atomic ratio of the mixture, calcination temperature and time, and cooling rate. The yield and crystallinity of the final product have been estimated using X-ray diffraction (XRD) and solid state 31P magic angle spinning NMR (MAS-NMR) techniques. The results show that pure, well-crystallized α-TCP powders exhibiting nearly ideal MAS-NMR spectra, can be obtained by reactive sintering of HAP-DCPA (Ca/P=1.50...1.52) mixtures, at 1400°C for 8 h. The broadening of MAS-NMR spectra can be used as an indicator of structural order in the final product. The α-TCP yield with DAP was always less than 50%.

Nuclear Magnetic Resonance Spectroscopic Study on the Grafting of Ethylene Oxide onto the Interlayer Surface of γ-Zirconium Phosphate

Abstract The reaction products of γ-zirconium phosphate with ethylene oxide were analyzed by solid-state 31P magic-angle spinning (MAS) NMR, and 31P and 13C solution NMR spectroscopy. γ-Zirconium phosphate can be formulated as Zr(PO4)(H2PO4)·2H2O. Ethylene oxide molecules react with the interlayer H2PO4 groups, forming diester derivatives of ethylene and/or diethylene glycols.

Iminophosphorane-substituted proton sponges. Part 5. Structures in the solid state. Correlation between solid state31P MAS NMR spectra and crystal structures

The 31P NMR spectra of protonated Iminophosphorane-substituted proton sponges of known crystal structure have been recorded in the solid state under the conditions of magic angle spinning (MAS) and 1H-decoupling. Variable temperature experiments and a comparison with the averaged 31P chemical shifts in solution show that no proton transfer occurs in the crystal, even when strong intramolecular hydrogen bonds are present. Good agreement between the NMR results and the X-ray structures gives weight to structural predictions based on solid state 31P MAS NMR spectroscopy, for compounds which do not yield suitable monocrystals.

Solid-state 31P magic-angle spinning NMR relaxation study of silica-supported polyoxoanions of the Keggin and Dawson structures

Solid-state 31P magic-angle spinning NMR investigations performed on silica-supported phosphopolyoxoanions [PMo 11Vo 40] 4−, [PW 12O 40] 3− and [P 2W 18O 62] 6− reveal a similar trend as already observed with [PMo 12O 40] 3− — the 31P spin-lattice relaxation rate increases with decreasing concentration of the polyanions at the silica surface. However the relaxation time T 1 decreases with increasing the age of the samples, especially for the tungstic compounds. More generally T 1 depends on the history of the sample after having been supported on silica; a vacuum treatment increases T 1 whereas exposure to water vapour has an opposite effect, showing the influence of water molecules assisting the relaxation. In addition the chemical shift anisotropy for the less symmetrical anions ([PMo 11Vo 40] 4− and [P 2W 18O 62] 6−) is partially averaged after water exposure, which could be explained by a “pseudoliquid phase”, already invoked for the interpretation of the “spillover” effect at the silica surface.

Solid-state nuclear magnetic resonance spectroscopic study of γ-zirconium phosphate

An idealised model for the structure of γ-Zr(HPO4)2·2H2O is proposed on the basis of solid-state 31P magic-angle spinning (m.a.s.) n.m.r. spectroscopy. Two types of phosphate environment are seen of which only one undergoes phosphate exchange with phosphate and phosphonate esters. 13C Cross-polarisation m.a.s. n.m.r. confirms the phenyl phosphate exchange and indicates that the phenyl rings are rigid between the layers.