Probing the unusual anion mobility of LiBH_4 confined in highly ordered nanoporous carbon frameworks via solid state NMR and quasielastic neutron scattering

Particle size and particle–framework interactions have profound effects on the kinetics, reaction pathways, and even thermodynamics of complex hydrides incorporated in frameworks possessing nanoscale features. Tuning these properties may hold the key to the utilization of complex hydrides in practical applications for hydrogen storage. Using carefully synthesized, highly-ordered, nanoporous carbons (NPCs), we have previously shown quantitative differences in the kinetics and reaction pathways of LiBH_4 when incorporated into the frameworks. In this paper, we probe the anion mobility of LiBH_4 confined in NPC frameworks by a combination of solid state NMR and quasielastic neutron scattering (QENS) and present some new insights into the nanoconfinement effect. NMR and QENS spectra of LiBH_4 confined in a 4 nm pore NPC suggest that the BH_4− anions nearer the LiBH_4–carbon pore interface exhibit much more rapid translational and reorientational motions compared to those in the LiBH_4 interior. Moreover, an overly broadened BH_4− torsional vibration band reveals a disorder-induced array of BH_4− rotational potentials. XRD results are consistent with a lack of LiBH_4 long-range order in the pores. Consistent with differential scanning calorimetry measurements, neither NMR nor QENS detects a clear solid–solid phase transition as observed in the bulk, indicating that borohydride–framework interactions and/or nanosize effects have large roles in confined LiBH_4

Precursor chemistry for TiO2: titanium complexes with a mixed nitrogen/oxygen ligand sphere

Novel mixed amido-malonato complexes of titanium are reported. The complexes were synthesized by partially replacing the amido groups from the complexes [Ti(NMe2)(4)] and [Ti(NEt2)(4)] via Bronstedt acid/base reactions, using the malonate-ligands di-isopropylmalonate (Hdpml) and di-tert-butylmalonate (Hdbm]). Four representative complexes were synthesized and fully characterised by H-1 NMR, C-13 NMR, CHN analysis and mass spectrometry. The crystal structures of the six-coordinated complexes [Ti(NMe2)(2)(dbml)(2)] (3) and [Ti(NEt2)(2)(dbml)(2)] (4) are presented and discussed. The complexes are solids and the chemical and thermal characteristics of the complexes strongly depend on the substitution at the malonate ligand. While dpml containing complexes show a promising behaviour for classical MOCVD, dbml containing complexes seem to be more suitable for liquid injection-metal-organic chemical vapour deposition (LI-MOCVD). Based on its thermal characteristics, the most promising complex for thermal CVD, [Ti(NEt2)(2)(dpml)(2)] (2) was selected for preliminary MOCVD experiments, which indicate a good suitability for the deposition of TiO2 thin films

Reversible Hydrogen Storage by NaAlH₄ Confined within a Titanium-Functionalized MOF-74(Mg) Nanoreactor

We demonstrate that NaAlH₄ confined within the nanopores of a titanium-functionalized metal–organic framework (MOF) template MOF-74(Mg) can reversibly store hydrogen with minimal loss of capacity. Hydride-infiltrated samples were synthesized by melt infiltration, achieving loadings up to 21 wt %. MOF-74(Mg) possesses one-dimensional, 12 Å channels lined with Mg atoms having open coordination sites, which can serve as sites for Ti catalyst stabilization. MOF-74(Mg) is stable under repeated hydrogen desorption and hydride regeneration cycles, allowing it to serve as a “nanoreactor”. Confining NaAlH₄ within these pores alters the decomposition pathway by eliminating the stable intermediate Na₃AlH₆ phase observed during bulk decomposition and proceeding directly to NaH, Al, and H₂, in agreement with theory. The onset of hydrogen desorption for both Ti-doped and undoped nano-NaAlH₄@MOF-74(Mg) is ∼50 °C, nearly 100 °C lower than bulk NaAlH₄. However, the presence of titanium is not necessary for this increase in desorption kinetics but enables rehydriding to be almost fully reversible. Isothermal kinetic studies indicate that the activation energy for H₂ desorption is reduced from 79.5 kJ mol^–1 in bulk Ti-doped NaAlH₄ to 57.4 kJ mol^–1 for nanoconfined NaAlH₄. The structural properties of nano-NaAlH₄@MOF-74(Mg) were probed using ²³Na and ²⁷Al solid-state MAS NMR, which indicates that the hydride is not decomposed during infiltration and that Al is present as tetrahedral AlH₄^¯ anions prior to desorption and as Al metal after desorption. Because of the highly ordered MOF structure and monodisperse pore dimensions, our results allow key template features to be identified to ensure reversible, low-temperature hydrogen storage

MOCVD of TiO2thin films from a modified titanium alkoxide precursor

A new titanium precursor, [Ti(OPri)2(deacam)2] (deacam\u2009=\u2009N,N-diethylacetoacetamide), was developed by the reaction of the parent Ti alkoxide with the \u3b2-ketoamide. The compound, obtained as a monomeric six-coordinated complex, was used in metal organic chemical vapor deposition (MOCVD) of TiO2 both as a single source precursor (SSP) and in the presence of oxygen. The high thermal stability of [Ti(OPri)2(deacam)2] enabled the fabrication of TiO2 films over a wide temperature range, with steady growth rates between 500 and 800\u2009\ub0C. The microstructure of the obtained systems was analyzed by X-ray diffraction (XRD) and Raman spectroscopy, whereas atomic force microscopy (AFM) and field emission-scanning electron microscopy (FE-SEM) measurements were performed to investigate the surface morphology and nanoorganization. Film composition was investigated by complementary techniques like Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). The electrical properties of the layers were investigated by performing capacitance voltage (C\u2013V) and leakage current measurements