Ag- and Sr-enriched nanofibrous titanium phosphate phases as potential antimicrobial cement and coating for a biomedical alloy.

Biomaterials and their surfaces regulate the biological response and ultimately the quality of healing at a possible site of implantation. The physical, chemical and topographical properties of implants' surfaces play a decisive role in the biological integration process for their immediate loading and long-term success. Since at this level of biological interaction nano-dimensionality is basically entailed, bio-functional nanostructured composites either as filling/cement or coating to metallic implants are required. This study shows the possibility of synthesizing two phases of nanostructured titanium phosphate (π and ρ polymorphs) and enriching them with silver nanoparticles and strontium. More importantly, Ag-Sr-enriched nanostructured π­titanium phosphate is induced to grow on a commercially available titanium alloy (Ti-6Al-4V), widely used in orthopedic and dental implants, under highly controlled conditions. Structural and microscopic studies, using XRD, HRTEM and SEM altogether confirm the resultant phases and their enrichment with strontium and silver nanoparticles with an average particle size around 6 nm. Using confocal laser scanning microscopy, the surface roughness was measured and is found to lay at the interface between the nanosized and microsized topologies. Ion release assessments showed that the presence of strontium controlled the release rate of silver ions and this could be beneficial in terms of decreasing the accompanied cytotoxicity that is usually encountered at high concentrations of silver release. Antimicrobial and cell proliferation assays have proved that enriching titanium phosphate with strontium and silver nanoparticles has improved their antimicrobial properties, while the cytotoxicity could be controlled.

Structural and proton conductivity studies of fibrous π-Ti2O(PO4)2·2H2O: application in chitosan-based composite membranes.

Although the fibrous polymorphic modification of titanium phosphate, π-Ti2O(PO4)2·2H2O (π-TiP) has been known for decades, its crystal structure has remained unsolved. Herewith, we report the crystal structure of π-TiP at room temperature, as determined from synchrotron radiation powder X-ray diffraction, and corroborated by 31P solid state NMR and accurate density functional theory calculations. In contrast to the previously reported ρ-TiP polymorph, the as-synthesized hydrated phase crystallizes in the monoclinic system (P21/c, a = 5.1121(2) Å, b = 14.4921(9) Å, c = 12.0450(11), ß = 115.31(1)°, Z = 4), and is composed of corner-sharing titanium octahedra and phosphate units arranged in a pattern that is unique to the ρ-TiP polymorph. The unit cell was confirmed by electron diffraction, while the formation of planar packing imperfections and stacking faults along the [101] plane was revealed by HRTEM analysis. An in situ dehydration study of π-TiP, monitored by high-temperature powder X-ray diffraction, led to a new anhydrous monoclinic (P21/c, a = 5.1187(13) Å, b = 11.0600(21) Å, c = 14.4556(26), ß = 107.65(2)°, Z = 4) phase that crystallizes at 500 °C. The latter resembles the packing fashion of the parental π-TiP, albeit titanium atoms are present in both distorted tetrahedral and octahedral coordination environments. Anhydrous π-TiP was found to partially rehydrate at room temperature, reversibly adopting the structure of the initial phase. The studies carried out under different conditions of leaching and impregnation with H3PO4 showed that π-TiP exhibits an extrinsic proton conductivity (1.3 × 10-3 S cm-1 at 90 °C and 95% RH) due to the presence of the protonated phosphate species bound on the particles surface, as revealed by 31P MAS-NMR spectroscopy data. The composite membranes of Chitosan (CS) matrices filled with H3PO4-impregnated π-TiP solid show an increment of proton conductivity up to 4.5 × 10-3 S cm-1, at 80 °C and 95% RH, which is 1.8-fold higher than those of the bare CS membranes.

Nanolayered Metal Phosphates as Biocompatible Reservoirs for Antimicrobial Silver Nanoparticles.

There is an increasing demand on synthesizing pharmaceuticals and biomaterials that possess antimicrobial and/or antiviral activities. In this respective silver nanoparticles are known for their excellent antimicrobial activity. Nevertheless, their uncontrolled release in a biological medium can induce a cytotoxic effect. For this, we explored the use of nanolayered metal phosphates based on titanium and zirconium as materials that can be enriched with silver nanoparticles. Employing the hydrothermal route, crystalline α-phases of zirconium and titanium phosphates (α-ZrP, α-TiP) were synthesized and there after surface-enriched with silver nanoparticles. The structural assessment confirmed the stability of the structures and their sizes are in the nanoscale at least in one dimension. The cytocompatibility assays confirmed the biocompatibility of the pristine phases and the antimicrobial assay confirmed that both silver-enriched nanolayered structures maintain an antibacterial effect at reasonably low concentrations.

Impact of Co2+ Substitution on Microstructure and Magnetic Properties of CoxZn1-xFe2O4 Nanoparticles.

In the present work, we synthesized CoxZn1-xFe2O4 spinel ferrite nanoparticles (x= 0, 0.1, 0.2, 0.3 and 0.4) via the precipitation and hydrothermal-joint method. Structural parameters were cross-verified using X-ray powder diffraction (XRPD) and electron microscopy-based techniques. The magnetic parameters were determined by means of vibrating sample magnetometry. The as-synthesized CoxZn1-xFe2O4 nanoparticles exhibit high phase purity with a single-phase cubic spinel-type structure of Zn-ferrite. The microstructural parameters of the samples were estimated by XRD line profile analysis using the Williamson-Hall approach. The calculated grain sizes from XRPD analysis for the synthesized samples ranged from 8.3 to 11.4 nm. The electron microscopy analysis revealed that the constituents of all powder samples are spherical nanoparticles with proportions highly dependent on the Co doping ratio. The CoxZn1-xFe2O4 spinel ferrite system exhibits paramagnetic, superparamagnetic and weak ferromagnetic behavior at room temperature depending on the Co2+ doping ratio, while ferromagnetic ordering with a clear hysteresis loop is observed at low temperatures (5K). We concluded that replacing Zn2+ ions with Co2+ ions changes both the structural and magnetic properties of ZnFe2O4 nanoparticles.

Nanosheets of Nonlayered Aluminum Metal-Organic Frameworks through a Surfactant-Assisted Method.

During the last decade, the synthesis and application of metal-organic framework (MOF) nanosheets has received growing interest, showing unique performances for different technological applications. Despite the potential of this type of nanolamellar materials, the synthetic routes developed so far are restricted to MOFs possessing layered structures, limiting further development in this field. Here, a bottom-up surfactant-assisted synthetic approach is presented for the fabrication of nanosheets of various nonlayered MOFs, broadening the scope of MOF nanosheets application. Surfactant-assisted preorganization of the metallic precursor prior to MOF synthesis enables the manufacture of nonlayered Al-containing MOF lamellae. These MOF nanosheets are shown to exhibit a superior performance over other crystal morphologies for both chemical sensing and gas separation. As revealed by electron microscopy and diffraction, this superior performance arises from the shorter diffusion pathway in the MOF nanosheets, whose 1D channels are oriented along the shortest particle dimension.

Sub-Micron Polymeric Stomatocytes as Promising Templates for Confined Crystallization and Diffraction Experiments.

The possibility of using sub-micrometer polymeric stomatocytes is investigated to effectuate confined crystallization of inorganic compounds. These bowl-shaped polymeric compartments facilitate confined crystallization while their glassy surfaces provide their crystalline cargos with convenient shielding from the electron beam's harsh effects during transmission electron microscopy experiments. Stomatocytes host the growth of a single nanocrystal per nanocavity, and the electron diffraction experiments reveal that their glassy membranes do not interfere with the diffraction patterns obtained from their crystalline cargos. Therefore, it is expected that the encapsulation and crystallization within these compartments can be considered as a promising template (nanovials) that hold and protect nanocrystals and protein clusters from the direct radiation damage before data acquisition, while they are examined by modern crystallography methodologies such as serial femtosecond crystallography.

Photocatalytic degradation of 2-(4-methylphenoxy)ethanol over TiO2 spheres.

The photocatalytic TiO2-assisted decomposition of 2-(4-methylphenoxy)ethanol (MPET) in aqueous solution has been studied for the first time. The intermediate compounds of MPET photodegradation have been also determined. A toxic p-cresol is formed in significant quantities during the photocatalytic reaction. A solvent-exchange approach for a template-free preparation of spherical TiO2 particles has been described, which is based solely on precipitation of hydrous titania from aqueous titanium peroxo complex by using organic solvents. The proposed method favours the formation of spherical titania particles with a mean size varying from 50 to 260nm depending on the choice of solvent. The procedure for converting nonporous titania spheres into mesoporous material maintaining the same spherical morphology has been developed. The synthesized TiO2 spheres demonstrate a degree of MPET photo-degradation close to that of the commercial titania Aeroxide P25, besides being successfully recovered and reused for four reaction cycles without loss of photocatalytic activity. The effectiveness of the commercial Aeroxide P25 in MPET photodegradation, on the other hand, suffers 10-time drop during the third reaction cycle, which is attributed to its poor recoverability because the photocatalyst is composed of small particles of 20nm size.

The ability of a fibrous titanium oxophosphate for nitrogen-adsorption above room temperature.

Ti2O(PO4)2·2H2O (1), a three-dimensional titanium oxophosphate, thermally transforms to Ti2O(PO4)2 (2), a fibrous novel compound. The crystal structure of 2 was solved ab initio using powder X-ray diffraction data (triclinic, P1[combining macron], a = 5.0843(1) Å, b = 8.6121(2) Å, c = 9.6766(2) Å, α = 74.501(2)°, ß = 76.146(2)°, γ = 74.488(3)°, Z = 2). Compound 2, containing both 4- and 6-fold coordinated titanium atoms, shows measurable thermally activated nitrogen-adsorption. To our knowledge, the process described here constitutes the first example of nitrogen-fixation by an inorganic material at above-ambient temperature.

Synthesis, Structures and Luminescence Properties of Metal-Organic Frameworks Based on Lithium-Lanthanide and Terephthalate.

Metal-organic frameworks assembled from Ln(III), Li(I) and rigid dicarboxylate ligand, formulated as [LiLn(BDC)2(H2O)·2(H2O)] (MS1-6,7a) and [LiTb(BDC)2] (MS7b) (Ln = Tb, Dy, Ho, Er, Yb, Y0.96Eu0.04, Y0.93Tb0.07, and H2BDC = terephthalic acid), were obtained under hydrothermal conditions. The isostructural MS1-6 crystallize in monoclinic P21/c space group. While, in the case of Tb3+ a mixture of at least two phases was obtained, the former one (MS7a) and a new monoclinic C2/c phase (MS7b). All compounds have been studied by single-crystal and powder X-ray diffraction, thermal analyses (TGA), vibrational spectroscopy (FTIR), and scanning electron microscopy (SEM-EDX). The structures of MS1-6 and MS7a are built up of inorganic-organic hybrid chains. These chains constructed from unusual four-membered rings, are formed by edge- and vertex-shared {LnO8} and {LiO4} polyhedra through oxygen atoms O3 (vertex) and O6-O7 (edge). Each chain is cross-linked to six neighboring chains through six terephthalate bridges. While, the structure of MS7b is constructed from double inorganic chains, and each chain is, in turn, related symmetrically to the adjacent one through the c glide plane. These chains are formed by infinitely alternating {LiO4} and {TbO8} polyhedra through (O2-O3) edges to create Tb⁻O⁻Li connectivity along the c-axis. Both MS1-6,7a and MS7b structures possess a 3D framework with 1D trigonal channels running along the a and c axes, containing water molecules and anhydrous, respectively. Topological studies revealed that MS1-6 and MS7a have a new 2-nodal 3,10-c net, while MS7b generates a 3D net with unusual ß-Sn topology. The photoluminescence properties Eu- and Tb-doped compounds (MS5-6) are also investigated, exhibiting strong red and green light emissions, respectively, which are attributed to the efficient energy transfer process from the BDC ligand to Eu3+ and Tb3+.

Surface-confined atomic silver centers catalyzing formaldehyde oxidation.

Formaldehyde (HCHO) is a prior pollutant in both indoor and outdoor air, and catalytic oxidation proves the most promising technology for HCHO abatement. For this purpose, supported metal catalysts with single silver atoms confined at 4-fold O4-terminated surface hollow sites of a hollandite manganese oxide (HMO) as catalytic centers were synthesized and investigated in the complete oxidation of HCHO. Synchrotron X-ray diffraction patterns, X-ray absorption spectra, and electron diffraction tomography revealed that geometric structures and electronic states of the catalytic centers were tuned by the changes of HMO structures via controllable metal-support interactions. The catalytic tests demonstrated that the catalytically active centers with high electronic density of states and strong redox ability are favorable for enhancement of the catalytic efficiency in the HCHO oxidation. This work provides a strategy for designing efficient oxidation catalysts for controlling air pollution.

Dimensionality changes in the solid phase at room temperature: 2D → 1D → 3D evolution induced by ammonia sorption-desorption on zinc phosphates.

Two-dimensional zinc phosphate NH4Zn2(PO4)(HPO4) (), via ammonia vapor interaction at room temperature, transforms to a one-dimensional novel compound NH4Zn(NH3)PO4 (). By ammonia desorption (in air at room temperature) transforms to NH4ZnPO4 () with a well-known ABW-zeolitic topology. The crystal structure of was solved ab initio using synchrotron powder X-ray diffraction data (monoclinic, P21/a, a = 16.5227(2) Å, b = 6.21780(8) Å, c = 5.24317(6) Å, ß = 91.000(2)°, Z = 4). The structures of three compounds include extra-framework ammonium cations to the 4-fold coordinated zinc (ZnO4 tetrahedra for and , and ZnO3N tetrahedra for ) and phosphorus (PO4 tetrahedra) with bi-, mono- or three-dimensional linkages, respectively for , or . To our knowledge, the process described here constitutes the first example of dimensionality change in the solid phase promoted by a solid-gas interaction at room temperature in metal phosphates.

Electronic metal-support interactions in single-atom catalysts.

The synthesis of single-atom catalysts and the control of the electronic properties of catalytic sites to arrive at superior catalysts is a major challenge in heterogeneous catalysis. A stable supported single-atom silver catalyst with a controllable electronic state was obtained by anti-Ostwald ripening. An electronic perturbation of the catalytic sites that is induced by a subtle change in the structure of the support has a strong influence on the intrinsic reactivity. The higher depletion of the 4d electronic state of the silver atoms causes stronger electronic metal-support interactions, which leads to easier reducibility and higher catalytic activity. These results may improve our understanding of the nature of electronic metal-support interactions and lead to structure-activity correlations.

A metal-organic framework assembled from Y(III), Li(I), and terephthalate: hydrothermal synthesis, crystal structure, thermal decomposition and topological studies.

A novel metal-organic framework assembled from Y(iii), Li(i), and terephthalate ligand, formulated as [LiY(BDC)2(H2O)·2(H2O)] (1) (H2BDC = terephthalic acid), has been obtained as single phase under hydrothermal conditions. The crystal structure was solved by single-crystal X-ray diffraction and the bulk was characterized by powder X-ray diffraction (PXRD), thermal analyses (TG-MS and DSC), vibrational spectroscopy (FTIR), scanning/transmission electron microscopy (SEM-EDX, TEM, SAED, and BF-STEM-EDX), and powder X-ray thermodiffractometry (HT-XRD). 1 crystallizes in monoclinic space group (P21/c, with a = 11.6415(7) Å, b = 16.0920(4) Å, c = 13.2243(8) Å and ß = 132.23(1)°) and possesses a 3D framework with 1D trigonal channels running along the [101] direction containing water molecules. The structure of 1 is made up of unusual four-membered rings formed by edge- and vertex-shared {YO8} and {LiO4} polyhedra. The four-membered rings are isolated and connected to each other via carboxylate groups. HT-XRD reveals that 1 undergoes phase transformation upon the dehydration process which is a reversible process involving a spontaneous rehydration characterized by fast kinetics. Topological studies were also performed revealing that 1 has a new 2-nodal net.

Series of metal organic frameworks assembled from Ln(III), Na(I), and chiral flexible-achiral rigid dicarboxylates exhibiting tunable UV-vis-IR light emission.

Two series of isoreticular chiral metal-organic frameworks assembled from Ln(III) (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb), Na(I), and chiral flexible-achiral rigid dicarboxylate ligands, formulated as [NaLn(Tart)(BDC)(H(2)O)(2)] (S1) and [NaLn(Tart)(biBDC)(H(2)O)(2)] (S2) (H(2)Tart = tartaric acid; H(2)BDC = terephthalic acid; H(2)biBDC = biphenyl-4,4'-dicarboxylic acid), were obtained as single phases under hydrothermal conditions. The compounds have been studied by single-crystal and powder X-ray diffraction, thermal analyses (TG-MS and DSC), vibrational spectroscopy (FTIR), scanning electron microscopy (SEM-EDX), elemental analysis, and X-ray thermodiffractometry. The catalytic activity has been also investigated. The photoluminescence properties of selected compounds have been investigated, exhibiting room temperature tunable UV-vis-IR light emission.

Metal organic frameworks assembled from Y(III), Na(I), and chiral flexible-achiral rigid dicarboxylates.

New chiral metal organic frameworks, assembled from Y(III), Na(I), and chiral flexible-achiral rigid dicarboxylate ligands, formulated as [NaY(Tart)(BDC)(H(2)O)(2)] (1) and [NaY(Tart)(biBDC)(H(2)O)(2)] (2) (H(2)Tart = Tartaric acid; H(2)BDC = Terephthalic acid; H(2)biBDC = Biphenyl-4,4'-dicarboxylic acid), were obtained as single phases under hydrothermal conditions. Their structures were solved by single-crystal X-ray diffraction (XRD), and characterized by (13)C CPMAS NMR, thermal analyses (thermogravimetry-mass spectrometry (TG-MS) and differential scanning calorimetry (DSC)), and X-ray thermodiffractometry. Both compounds crystallize in the orthorhombic chiral space group C222(1) with a = 6.8854(2) A, b = 30.3859(7) A, c = 7.4741(2) A for 1, and a = 6.8531(2) A, b = 39.0426(8) A, c = 7.4976(2) A for 2. 1 and 2 are layered structures whose three-dimensional stability is ensured by strong hydrogen bond interactions. The dehydration of both compounds is accompanied by phase transformation, while the spontaneous rehydration process is characterized by different kinetics, fast in the case of 1 and slow for 2.