Molecular mechanisms of the metal oxide sol-gel process and their application in approaches to thermodynamically challenging complex oxide materials

This review presents a brief overview of recent insights into general reaction pathways in sol-gel synthesis of metal oxides. Metal-based sol-gel precursors display kinetically unhindered reactivity, combining high reaction speed with reversibility on a molecular level. The process producing metal oxide sols can thus be described as nucleation of an oxide phase with growth option efficiently precluded by extremely low solubility. The emerging nuclei are essentially Polyoxometalate (POM) species, with sizes in the colloid range starting from about 2 nm. They are stabilized in solution by colloid forces (charge interactions, hydrogen bonding, van der Waals forces), defined by the nature and arrangement of species on their surface, which permits them to be denoted as Micelles Templated by Self-Assembly of Ligands (MTSALs). The sol-gel transition occurs on aggregation of particles resulting in percolation. Exploiting this mechanism, it is possible to produce materials with controlled porosity, biocompatibility, and even to access thermodynamically challenging phases that cannot be produced by conventional synthetic techniques

Modeling metal oxide nanoparticle GABA interactions: Complexation between the Keggin POM and gamma-aminobutyric acid in the solid state and in solution influenced by additional ligands

Phosphotungstic acid (POM) was crystallized together with the neurotransmitter gamma-aminobutyric acid (GABA) in acidic medium to form [(HGABA)3PW12O40], compound 1. The latter would only crystalize in the presence of dopamine, while dopamine itself did not become a part of the complex, but crystallized separately as [(Hdopamine)2HPW12O40], compound 2, as previously reported. GABA interacts with POM via hydrogen bonding between the protonated amino group and a terminal oxygen on POM and also via protonated carboxylic acid group. Based on structural information from the crystal structures of 1 and 2 together with complementary studies using other catechols we attempted to provide molecular insight into the well-known structure-directing effect of dopamine. Strong hydrogen bonding between dopamine and POM, together with formation of "dopamine dimers" in the packed structure by interactions between the aromatic rings and intermolecular hydrogen bonding might be important factors for them in directing the self-assembly of polyoxometalates into complex hierarchal structures. Interaction between dopamine and GABA in solution was investigated by diffusion ordered spectrometry (DOSY) NMR in MilliQ-water and in 0.1 M HCl

Novel solvothermal approach to hydrophilic nanoparticles of late transition elements and its evaluation by nanoparticle tracking analysis

Solvothermal treatment of late transition metal acetylacetonates in a novel medium composed either of pure acetophenone or acetophenone mixtures with amino alcohols offers a general approach to uniform hydrophilic metal nanoparticles with high crystallinity and low degree of aggregation. Both pure metal and mixed-metal particles can be accesses by this approach. The produced materials have been characterized by SEM-EDS, TEM, FTIR in the solid state and by Nanoparticle Tracking Analysis in solutions. The chemical mechanisms of the reactions producing nanoparticles has been followed by NMR. Carrying out the process in pure acetophenone produces palladium metal, copper metal with minor impurity of Cu2O, and NiO. The synthesis starting from the mixtures of Pd and Ni acetylacetonates with up to 20 mol% of Pd, renders in minor yield the palladium-based metal alloy along with nickel oxide as the major phase. Even the synthesis starting from a mixed solution of Cu(acac)2 and Ni(acac)2 produces oxides as major products. The situation is improved when aminoalcohols such as 2-aminoethanol or 2-dimethylamino propanol are added to the synthesis medium. The particles in this case contain metallic elements and pairs of individual metals (not metal alloys) when produced from mixed precursor solutions

Self-Assembly of Asymmetrically Functionalized Titania Nanoparticles into Nanoshells

Titania (anatase) nanoparticles were anisotropically functionalized in water-toluene Pickering emulsions to self-assemble into nanoshells with diameters from 500 nm to 3 mu m as candidates for encapsulation of drugs and other compounds. The water-phase contained a hydrophilic ligand, glucose-6-phosphate, while the toluene-phase contained a hydrophobic ligand, n-dodecylphosphonic acid. The addition of a dilute sodium alginate suspension that provided electrostatic charge was essential for the self-limited assembly of the nanoshells. The self-assembled spheres were characterized by scanning electron microscopy, elemental mapping, and atomic force microscopy. Drug release studies using tetracycline suggest a rapid release dominated by surface desorption

Adinkras From Ordered Quartets of BC4{}_4 Coxeter Group Elements and Regarding 1,358,954,496 Matrix Elements of the Gadget

We examine values of the Adinkra Holoraumy-induced Gadget representation space metric over all possible four-color, four-open node, and four-closed node adinkras. Of the 1,358,954,496 gadget matrix elements, only 226,492,416 are non-vanishing and take on one of three values: $-1/3$, $1/3$, or $1$ and thus a subspace isomorphic to a description of a body-centered tetrahedral molecule emerges.Comment: LaTeX twice, 56pp, 30 tables, 5 figures, latest version includes link to updated code, minor corrections, and additional support about inequivalent representations and tetrahedral geometry comments added along with observations about similarity with results previously found by Nekraso

Tailoring a bio-based adsorbent for sequestration of late transition and rare earth elements

The demand for new renewable energy sources, improved energy storage and exhaust-free transportation requires the use of large quantities of rare earth (REE) and late transition (LTM, group 8-12) elements. In order to achieve sustainability in their use, an efficient green recycling technology is required. Here, an approach, a synthetic route and an evaluation of the designed bio-based material are reported. Cotton-derived nano cellulose particles were functionalized with a polyamino ligand, tris(2-aminoethyl) amine (TAEA), achieving ligand content of up to ca. 0.8 mmol g(-1). The morphology and structure of the produced adsorbent were revealed by PXRD, SEM-EDS, AFM and FTIR techniques. The adsorption capacity and kinetics of REE and LTM were investigated by conductometric photometric titrations, revealing quick uptake, high adsorption capacity and pronounced selectivity for LTM compared to REE. Molecular insights into the mode of action of the adsorbent were obtained via the investigation of the molecular structure of the Ni(ii)-TAEA complex by an X-ray single crystal study. The bio-based adsorbent nanomaterial demonstrated in this work opens up a perspective for tailoring specific adsorbents in the sequestration of REE and LTM for their sustainable recycling

Bismuth(III) Forms Exceptionally Strong Complexes with Natural Organic Matter

The use of bismuth in the society has steadily increased during the last decades, both as a substitute for lead in hunting ammunition and various metallurgical applications, as well as in a range of consumer products. At the same time, the environmental behavior of bismuth is largely unknown. Here, the binding of bismuth(III) to organic soil material was investigated using extended X-ray absorption spectroscopy (EXAFS) and batch experiments. Moreover, the capacity of suwannee river fulvic acid (SRFA) to enhance the solubility of metallic bismuth was studied in a long-term (2 years) equilibration experiment. Bismuth(III) formed exceptionally strong complexes with the organic soil material, where >99% of the added bismuth(III) was bound by the solid phase, even at pH 1.2. EXAFS data suggest that bismuth(III) was bound to soil organic matter as a dimeric Bi3+ complex where one carboxylate bridges two Bi3+ ions, resulting in a unique structural stability. The strong binding to natural organic matter was verified for SRFA, dissolving 16.5 mmol Bi per gram carbon, which largely exceeds the carboxylic acid group density of this compound. Our study shows that bismuth(III) will most likely be associated with natural organic matter in soils, sediments, and waters

Factors influencing stoichiometry and stability of polyoxometalate - peptide complexes

In the pursuit of understanding the factors guiding interactions between polyoxometalates (POMs) and biomolecules, several complexes between Keggin phosphomolybdate and diglycine have been produced at different acidity and salinity conditions, leading to difference in stoichiometry and in crystal structure. Principal factors determining how the POM and dipeptide interact appear to be pH, ionic strength of the medium, and the molar ratio of POM to peptide. An important effect turned out to be even the structure-directing role of the sodium cations coordinating carbonyl functions of the peptide bond. Given the interest in applying POMs in biological systems, these factors are highly relevant to consider. In the view of recent interest in using POMs as nano catalysts in peptide hydrolysis also the potential Keggin POM transformation in phosphate buffered saline medium was investigated leading to insight that nanoparticles of zirconium phosphate (ZrP) can be actual catalysts for breakdown of the peptide bond

Synthesis, Structure and Thermal Properties of Volatile Indium and Gallium Triazenides

Indium and gallium nitride are important semi-conductor materials with desirable properties for high-frequency and power electronics. We have previously demonstrated high-quality ALD grown InN and GaN using the hexacoordinated 1,3-diisopropyltriazenide In(III) and Ga(III) precursors. Herein we report the structural and thermal properties their analogues employing combinations of isopropyl, sec-butyl and tert-butyltriazenide alkyl groups on the exocyclic nitrogen of the triazenide ligand. The new triazenide compounds were all found to be volatile (80-120 degrees C, 0.5 mbar) and showed very good thermal stability (200 and 300 degrees C). These new triazenide analogues provide a set of precursors whose thermal properties are determined and can be accordingly tailored by strategic choice of exocyclic nitrogen alkyl substituents

In situ Functionalized Mesoporous Silicas for Sustainable Remediation Strategies in Removal of Inorganic Pollutants from Contaminated Environmental Water

Low-cost mesoporous silicas of the SBA-15 family were prepared, aimed for removal of a broad spectrum of both cationic and anionic forms of hazardous metal pollutants (Cr(III, VI), Mn(II, VII), Pb(II), Cd(II), and Cu(II)) from environmental water. Series of mono-and bifunctional materials with immobilized ethylenediaminetriacetic acid (EDTA), primary amine (NH2), and quaternary ammonium (QAS) groups were prepared in a cost-efficient one-step synthesis using two silica sources, low-cost sodium metasilicate (Na2SiO3 9H(2)O) and the conventional source-tetraethylorthosilicate (TEOS). The functionalized SBA-15 samples obtained from both silica sources were highly ordered, as evidenced by TEM and SAXS data. All obtained materials were mesoporous with high surface area values of up to 745 m(2)/g, pore volumes from 0.99 to 1.44 cm(3)/g, and narrow pore distributions near 7 nm. The adsorption affinity of the EDTA-functionalized samples followed the common order Pb(II)> Cd(II)> Cu(II)> Cr(III)> Mn(II), which could be explained based on the Pearson theory. The highest adsorption capacities were observed for samples functionalized by EDTA groups using TEOS for synthesis (TEOS/EDTA): 195.6 mg/g for Pb(II), 111.2 mg/g for Cd(II), 58.7 mg/ g for Cu(II), 57.7 mg/g for Cr(III), and 49.4 mg/g for Mn(II). Moreover, organic matter (humic acid up to 10 mg/L) and inorganic (Na(I), K(I), Mg(II), Ca(II), etc) macrocomponents present in environmental water had almost negligible effect on the removal of these cations. The NaSi/EDTA/NH2 sample revealed a better selectivity compared to the NaSi/NH2 sample towards such species as Cr(III), Mn(II), Cd(II), and Cu(II). The chromate-ions uptake at pH 7.5 by the TEOS/QAS sample turned practically unaffected by the presence of doubly charged anions (CO32-, SO42-). The content of functional groups on the surface of MS decreased only slightly (similar to 1-5%) after several regeneration cycles. The complete desorption of all heavy metal ions can be achieved using 1 mol/L EDTA solution. Reusability tests demonstrated the complete stability of the adsorbent for at least five to six consecutive adsorption/ desorption cycles with no decrease in its adsorption characteristics compared to those obtained by 0.05 mol/L HNO3 treatments. The synthesized mesoporous materials were evaluated for removal of the heavy metal ions from drinking and different natural water samples, proving their potential as sustainable, effective, and cost-efficient adsorbents