Titanium Alkoxide Research Articles

The Central Role of Oxo Clusters in Zirconium‐Based Esterification Catalysis

Oxo clusters are a unique link between oxide nanocrystals and Metal‐Organic Frameworks (MOFs), representing the limit of downscaling each of the respective crystals. Herein, the superior catalytic activity of clusters, compared to zirconium MOF UiO‐66 and nanocrystals is shown. Focus is on esterification reactions given their general importance in consumer products and the challenge of converting large substrates. Oxo clusters have a higher surface‐to‐volume ratio than nanocrystals, rendering them more active. For large substrates, for example, oleic acid, MOF UiO‐66 has negligible catalytic activity while clusters provide almost quantitative conversion, a fact we ascribe to limited diffusion of large substrates through the MOF pores. Clusters do not suffer from limited mass transfer and we also obtain high conversion in solvent‐free reactions with sterically hindered alcohols (hexanol, 2‐ethyl hexanol, benzyl alcohol, and neopentyl alcohol). The cluster catalyst can be recovered and shows identical activity when reused. The structural integrity of the cluster is confirmed using X‐ray total scattering and pair distribution function analysis. Moreover, when homogeneous zirconium alkoxides are used as catalysts, the same oxo cluster is retrieved, showing that oxo clusters are the active catalytic species, even in previously assumed homogeneously catalyzed reactions.

Intermetallic TiFe particles generation within porous monolithic carbon materials arising from paper mill waste and their cooperative hydrogen storage properties

A new materials composed of TiFe particles stabilized onto a carbon support is described. The carbon support is derived from a waste from the paper industry called Kraft Black liquor. The particles are generated through an impregnation/reduction process of a mixture of titanium ethoxide and iron nitrate followed by a thermal treatment. The generated particles have been investigated through XPS, XRD and SEM analysis as well as tested for hydrogen storage. The hydrogen storage at 25 °C leads to a capacity of up to 0.5 wt% while at 150 °C, free of the carbon absorption, leads to a capacity of 0.2 wt% without any prior activation process.

Minimizing surface adhesion of Sylgard 184 for medical applications

Silicones such Sylgard 184 are widely employed in biological applications due to their versatile properties. However, their inherently adhesive surfaces can restrict their application, especially in direct contact with damaged biological tissues, potentially compromising patient comfort. To enhance the surface properties of Sylgard 184 while maintaining its transparency in the visible spectrum, a novel low-temperature method (70 °C) has been developed. This method involves immersing PDMS in a solution of titanium (IV) ethoxide in THF, thus inducing swelling of the silicone's polymer network, followed by the diffusion and condensation of titanium (IV) ethoxide within the polymer matrix. The resulting hybrid material, incorporating amorphous titanium oxide within the silicone network, exhibits significantly increased surface hardness compared to unmodified Sylgard 184, while retaining transparency and improving biological behaviour. The elaborated method holds promising potential for enhancing the performance of silicone-based materials in diverse biomedical applications.

Fabrication of luminescent disc-shaped microstructures via wet-chemical etching of hybrid sol–gel layers for potential photonic applications

Sol–gel materials based on SiO2 and TiO2 precursors are attractive as a new platform for planar photonics. Particularly interesting are those based on organically modified silica (ORMOSIL), which may improve the luminescent properties of organic dyes. However, their microstructurization remains a challenge as it requires optimization of various technological stages. Here, we report the structurization of thin layers based on ORMOSIL precursor and titanium(IV) ethoxide (TET) containing luminescent rhodamine B (RhB) dye. Films were fabricated using sol–gel synthesis and dip-coating method. Depending on the time of annealing performed at 200 °C, layers with different thicknesses (300–760 nm) and refractive indices (RI) (1.51–1.68) were obtained. Combining photolithography and wet-chemical etching processes made it possible to fabricate well-separated sol–gel waveguides and discs of different diameters. The etching time in buffered hydrofluoric acid (BHF) affected the depth of the etched luminescent microstructures. Additionally, it was found that a longer layer’s annealing time increased the etching selectivity of the substrate over the sol–gel layer. This enabled the obtaining of under-etched sol–gel goblet microstructures. Selected samples were investigated using scanning electron microscopy (SEM). UV–Vis photoluminescence measurements showed that long heat treatment also influenced the emission spectrum’s shape. The stability of the films under ambient conditions was established using spectroscopic ellipsometry. It was proven that films heat-treated at 200 °C did not change their properties during storage time of around 2 months. Relatively high RI, luminescent properties, and structurization potential make these microstructures interesting for application in integrated photonic devices, e.g., light amplifiers or sensing systems.

Effect of titanium alkoxide on structure, morphology, and biocompatible properties of sol-gel synthesized TiO2 films

The purpose of this work was to study the influence of the nature of titanium alkoxide, used as a precursor for the synthesis of TiO2 films by the sol-gel method, on the crystal structure and morphology of coatings, as well as their biological compatibility. TiO2 coatings were synthesized on silicon substrates using the dip-coating method. Titanium alkoxides with different molecular weights were used as precursors: titanium tetraethoxide, titanium tetraisopropoxide, and titanium tetrabutoxide. The influence of the nature of the titanium precursor on the morphology and thickness of TiO2 films was determined using scanning electron microscopy. The structural properties of the coatings were studied by X-ray diffraction and Raman spectroscopy. Cell viability assay was performed on TiO2/Cu-Si(111) structures to evaluate the ability of TiO2 coatings synthesized from different precursors to prevent the release of toxic ions from the substrate. The biological compatibility of TiO2 films with various surface morphologies and structures was assessed based on the chorioallantoic membrane assay. It has been demonstrated that the type of titanium alkoxide utilized has a substantial influence on the morphology and crystal structure of TiO2 films produced through the sol-gel method. Furthermore, the structural properties of the coatings consequently impact their biological compatibility. Coatings synthesized from titanium tetrabutoxide exhibited the highest protective properties and biological compatibility.

Nickel-Catalyzed Enantioselective Reductive Arylation of Common Ketones.

A nickel complex of chiral bisoxazolines catalyzed the stereoselective reductive arylation of ketones in high enantioselectivity. A range of common acyclic and cyclic ketones reacted without the aid of directing groups. Mechanistic studies using isolated complex of a chiral bis(oxazoline) (L)Ni(Ar)Br revealed that Mn reduction was not needed, while Lewis acidic titanium alkoxides were critical to ketone insertion.

Optimization of the ETL titanium dioxide layer for inorganic perovskite solar cells

Titanium dioxide layers are the most popular electron transport layer (ETL) in perovskite solar cells. However most studies focuses on mesoporous structure and application with organic–inorganic hybrid perovskite. In this study, the topic of ETL in planar structure of inorganic CsPbBr3 perovskite solar cells was tackled, the presented approach will reduce production costs and improve cell stability, which is the greatest drawback of perovskite cells especially organic–inorganic perovskite. The potential application of these technology are greenhouses and building integrated PV sector. Here, the two TiO2 precursors titanium(IV) ethoxide in ethanol and titanium(IV) bis(acetylacetonate) diisopropoxide (Tiacac) were investigated, optimized and compared. TiO2 layers were deposited on high roughness FTO, without the use of a mesoporous layer, by spin coating method. The correlation between stock solution concentration and thickness of manufactured layers was tracked for both precursors as well as their difference in morphology of the final films and other properties. In particular, conformality and optical properties are better for Tiacac. Slightly lower refractive index of Tiacac-based titania reduced the reflective losses from 7.3 to 6.9% effectively. The obtained layers were used for inorganic solar cells of CsPbBr3 perovskite to finally settle the issue of optimal thickness and precursor. It is interesting that despite the supremacy in investigated properties of commonly used of the precursor Tiacac, the results of the cells pointed to the Tieth. The efficiency of the champion cell is 6.08% for Tieth, while 5.62% is noted for Tiacac. Trying to figure out this riddle, we shed a new light on the phenomena going on the ETL/inorganic perovskite interface investigating nanoroughness.

Large-scale synthesis of size-controlled amorphous and anatase TiO2 via a benzoic acid-assisted sol-gel-hydrothermal process

The ability to control the particle size of titanium dioxide nanoparticles (TNPs) is crucial for their practical use. This study presents a method for preparing monodisperse amorphous and anatase TNPs with high surface areas and tunable grain sizes. The method combines a sol-gel process with a hydrothermal process, using benzoic acid (BA) as a structure-directing agent. By adjusting the hydrolysis and condensation rates of the titanium alkoxide, we can synthesize monodisperse amorphous TNPs with a controllable size range of 200–800 nm. Additionally, the amorphous TNPs synthesized through this method serve as raw material, enabling the morphology of anatase TNPs to be inherited from amorphous TNPs with a hydrothermal reaction time of 1 h. When the hydrothermal reaction time is extended to 10 h, the closely linked primary titanium dioxide is fully separated and replaced by ultra-fine anatase TNPs. This optimal scheme show promise for self-assembly and large-scale synthesis of monodisperse amorphous and anatase TNPs.

Bendable and Chemically Stable Metal-Organic Hybrid Membranes for Molecular Separation.

Crystalline porous metal-organic materials are ideal building blocks for separation membranes because of their molecular-sized pores and highly ordered pore structure. However, creating ultrathin, defect-free crystalline membranes is challenging due to inevitable grain boundaries. Herein, we reported an amorphous metal-organic hybrid (MOH) membrane with controlled microporosity. The synthesis of the MOH membrane entails the use of titanium alkoxide and organic linkers containing di/multicarboxyl groups as monomers in the polymerization reaction. The resultant membranes exhibit similar microporosity to existing molecular sieve materials and high chemical stability against harsh chemical environments owing to the formation of stable Ti-O bonds between metal centers and organic linkers. An interfacial polymerization is developed to fabricate an ultrathin MOH membrane (thickness of the membrane down to 80 nm), which exhibits excellent rejections (>98% for dyes with molecular weights larger than 690 Da) and high water permeance (55 L m-2 h-1 bar-1). The membranes also demonstrate good flexibility, which greatly improves the processability of the membrane materials.

Effect of silica addition on the photocatalytic activity of MO2@SiO2 (M=Ti, Zr, Sn, Ce) nanocomposites prepared by sol-gel

AbstractPhotocatalysis uses wide band gap ceramic semiconductors (anatase, zirconia, ceria, cassiterite…) that have the ability to promote electron-hole pairs by UV light irradiation producing both reducing and oxidants ions and radicals. In general, oxidizing species are more efficient, using photocatalysis as an advanced oxidation process (AOP) for the biodegradation of organic substances refractory to conventional treatments, such as azo dyes, or atmospheric pollutants as NOx. In this communication, the photocatalytic activity of xSiO2@(1-x)MO2 (M = TiO2, ZrO2, SnO2, CeO2, x = 0, 0.1, 0.3 and 0.5) composites on the Orange II azo dye in solution, as well as on NOx in air, was analysed. The composites were obtained by Sol-Gel methods based on the hydrolysis-condensation of alcoholic solutions of silicon tetraethoxide (TEOS) and titanium n-butoxide, zirconium iso-propoxide, SnCl2.2H2O and Ce(NO3)3.6H2O as precursors of MO2 oxides. The resulting xerogels were studied by XRD, bandgap measurements from UV-Vis-NIR diffuse reflectance spectroscopy, photocatalytic activity against Orange II in dissolution and NOx in air (efficiency in nitrate abatement), and SEM-EDX microstructural analysis. In the case of non-stabilized samples, charring samples at 300 °C/1 h and fired samples at 500 °C/1 h were also studied. The cassiterite-silica composite stands out for its photocatalytic activity against Orange II in solution and the cerianite-silica composite against NOx in air. Silica increases the photocatalytic activity on NOx in zirconia, tin oxide and ceria composites and also on Orange II in zirconia and tin oxide. Graphical Abstract

Preparation, X-ray Characterization, and Reactivity of the Rod-like and Angular Germanium- and Titanium(IV)-Capped Iron(II) Bis-Clathrochelates and Their Mono- and Bis-Capped (Semi)clathrochelate Precursors.

Transmetalation of the bis{triethylantimony(V)}-capped iron(II) tris-α-dioximate with n-butylboronic acid afforded the mixed antimony, boron cross-linked clathrochelate with single reactive antimony(V)-based apical fragment. This macrobicyclic precursor easily underwent the transmetalation reactions with germanium and titanium(IV) alkoxides to give the rod-like and angular FeII2MIV-trinuclear bis-clathrochelates. Those of the aforementioned diantimony(V)-capped complex with 3- and 4-carboxyphenylboronic acids afforded the monoboron-capped iron(II) semiclathrochelates, undergoing a double-cyclization (macrobicyclization) with germanium- and titanium(IV)-based capping agents. The reactions in the low-temperature range unexpectedly gave the stable 2:1 associates, formed by the bridging of two carboxyl-terminated macrobicyclic molecules of the mixed carboxylboron, triethylantimony-capped iron(II) clathrochelate with a triethylantimony(V)-based linker fragment. The obtained complexes were characterized using elemental analysis, MALDI-TOF, 1H and 13C{1H} NMR and UV-vis spectra, and single-crystal XRD experiments. The encapsulated iron(II) ion in their 3D-molecules is situated almost in the center of its FeN6-coordination polyhedron possessing a truncated trigonal-pyramidal geometry. Fe-N distances fall in the range 1.887(7)-1.945(4) Å characteristic of the low-spin iron(II) complexes. The cross-linking titanium and germanium(IV) ions in the corresponding bis-clathrochelate molecules form the octahedral MIVO6-coordination polyhedra, the MIV-O distances of which vary from 1.946(2) to 1.964(2) Å and from 1.879(7) to 1.907(6) Å, respectively.

Synthesis of zirconium(IV) and hafnium(IV) isopropoxide, sec-butoxide and tert-butoxide.

We revisited the synthesis of zirconium(IV) and hafnium(IV) alkoxides, namely the metal isopropoxide isopropanol complex (M(OiPr)4·iPrOH, M = Zr, Hf) and the metal sec- and tert-butoxide (M(OsBu)4 and M(OtBu)4, M = Zr, Hf). We optimized the most convenient synthesis methods and compared the products with commercial sources. En route to the metal sec- and tert-butoxides, we synthesized the metal diethylamido complex (M(NEt2)4, M = Zr, Hf).

Controllable and facile one-pot synthesis of high surface area amorphous, crystalline, and triphasic TiO2: catalytic and photocatalytic applications

A simple and controllable synthesis led to both amorphous and crystalline porous TiO2with remarkably high surface area and pore volume. Their distinctive characteristics influenced their effectiveness in photocatalytic and catalytic processes.

Zirconium complexes of an aminophenolate-etherphenolate ONO'O ligand: Synthesis, characterization and catalytic properties

A synthetic protocol to access new aminophenolate-etherphenolate ONO'O ligands is presented. Zirconium iso-propoxide and benzyl complexes of a prototypical tert-butyl substituted ONO'O ligand can be synthesized in high yields as single conformational isomers. Combined NMR spectroscopy and single-crystal X-ray diffraction studies on (ONO'O)Zr(OiPr)2 show that the ligand binds to the metal center in a fac-fac coordination mode, like the well-known bis(aminophenolate) ONNO analogue. The iso-propoxide complex (ONO'O)Zr(OiPr)2 proved to be a competent catalyst for L- and rac-lactide polymerization, exhibiting a productivity similar to that of the benchmark (ONNO)Zr(OiPr)2 in solution and in neat monomer. The benzyl complex (ONO'O)ZrBn2 is inactive in ethylene polymerization under the reaction conditions explored, unlike the benchmark (ONNO)ZrBn2. DFT studies suggest that a larger range of geometries is accessible for cationic active species with ONO'O ligands compared to ONNO or OO'O'O ligands.

Transient photocatalytic oxidation of toluene vapor via nanostructured layers prepared by sol-gel on anatase particles

Gas-phase photocatalytic degradation of toluene mixed with wet oxygen was performed in a continuous reactor using anatase nanoparticles, home-prepared by the sol-gel method combined with peptization treatments. Titanium (IV) isopropoxide was used to synthesize amorphous titania precursor, partially transformed into crystalline nanoparticles by hydrothermal or thermal treatments. The main oxidation product was carbon dioxide, but traces of benzene and benzoic acid were also detected. In order to characterize the catalysts, the evolution of titanium (IV) alkoxide to form anatase nanoparticles was studied using 1H-MAS NMR, EPR, TPD, and FTIR techniques. The results indicate that the four coordinated Ti4+ cations of the alkoxide induce the formation of amorphous aggregates of polymeric layers. The organics removal by peptization originates thin nanostructured titania layers that cover anatase particles, forming TiO2 homojunction. Photoactivity runs showed that both toluene retention and mineralization occurred at the start of irradiation, both processes exhibiting a long transient. After different times, retention stopped while mineralization reached steady-state conditions. Hydrated proton structures are considered to be the origin of both processes. Under irradiation, water photodesorption from these structures favors both the interaction of nanostructured layers with anatase particles, determining hole transfer to external surfaces and the generation of hydrated hydronium cations which, depending on the water loss, are centers able to carry out toluene mineralization or retention. After the mineralization step, photocatalytic centers must be reconstituted by recovering water, a process whose rate becomes the rate-determining one.

Mixed-mode chromatographic performance using nicotinic acid-functionalized chito-oligosaccharide-bonded Ti/Si hybrid monolithic capillary columns.

This article describes the fabrication of porous nicotinic acid-functionalized chito-oligosaccharide-bonded titania/silica hybrid monoliths (TiO2/SiO2@ChO-N) through a co-gelation sol-gel process. A capillary monolith with a well-defined and homogeneous structure was obtained by controlling the hydrolysis speed of titanium alkoxides in a sol mixture by using glycerol and acetylacetone. As a result of the functionalization with chito-oligosaccharides (ChO)-modified nicotinic acid, the obtained stationary phase provides superior physiochemical properties, such as a cationic hydrophilic surface, porosity, and mechanical strength. Scanning electron microscope and attenuated total reflectance-infrared spectroscopy were used to characterize the functionalized monolithic columns. The produced capillary columns showed high chromatographic performance with acceptable selectivity for charged analytes as well as organic polar compounds such as nucleic bases, nucleosides, carbamate pesticides, and strobilurinfungicides. The obtained results also indicated that the functionalized ChO's amino, amide, hydroxyl, and pyridinium ring moieties served as hydrophilic electrostatic traps for charged substances, in addition tostroing π-π interaction with the carbamate pesticides and strobilurin fungicides analytes via hydrogen bonding.

Deep-UV sensitivity of xerogel thin films prepared from solutions of modified titanium alkoxides

Deep-UV sensitivity of xerogel thin films prepared from solutions of modified titanium alkoxides

(Invited) Solid State Hybrid Inorganic Organic Polymer Electrolytes for Advanced Sodium Secondary Batteries

The large-scale rollout of electric vehicles, smart grids and portable electronics is expected to require an amount of energy storage devices that the Li-ion technology alone will not be able to satisfy. In this concern, a quest for novel electrochemical energy storage technologies has started [1]. Sodium secondary batteries appear to be a good choice due to: (i) the high availability of raw materials; (ii) the low cost of sodium; (iii) the low sodium standard reduction potential; and (iv) the similarity between the chemistries of sodium and lithium, which facilitates the transition between the two technologies. Up to date, the best-performing electrolytes for the reversible deposition of sodium are based on organic solvents, which suffer from safety concerns and a poor stability towards sodium metal. Thus, research activities in this field are devoted to the development of safe and stable solid state electrolytes able to efficiently transport Na+ ions.Inspired by the pioneering work done by Di Noto and co-workers [2-4], herein we present a family of hybrid inorganic-organic polymer electrolytes (HIOPEs) for advanced solid state sodium secondary batteries. The initial HIOPE is obtained by means of a reaction between zirconium ethoxide and polyethylene glycol (PEG400). The resulting material is doped with sodium perchlorate as source of Na+ ions. In this system a 3D network is obtained, where inorganic zirconium metal nodes are interconnected by means of organic PEO chains. The latter ensure flexibility to the overall structure. Na+ ions are coordinated by and exchanged between the oxygen atoms of the ethereal functionalities of PEO chains. In addition, to guarantee a good structural stability, positively charged Zr nodes partially coordinate perchlorate anions, thus raising the sodium transference number. After doping with the poly(ethylene glycol) dimethyl ether (PEGDME250) plasticizer, a room temperature conductivity higher than 10-4 S cm-1 is demonstrated. An advanced study of the thermal and structural properties of the proposed materials is presented, with a particular focus on the interactions established between the different chemical species and complexes composing the HIOPEs. The conduction mechanism is elucidated starting from the results obtained in a wide range of temperatures from broadband electrical spectroscopy studies. Taking all together, this study offers insights on the application of non-traditional solid state electrochemical functional components as replacements for conventional solvents in the emerging field of sodium secondary batteries. Acknowledgments The project “Interplay between structure, properties, relaxations and conductivity mechanism in new electrolytes for secondary Magnesium batteries” (Grant Agreement W911NF-21-1-0347-(78622-CH-INT)) of the U.S. Army Research Office. The project “ACHILLES” (prot. BIRD219831) of the University of Padua. The project “VIDICAT” (Grant Agreement 829145) of the FET-Open call of Horizion 2020. The project TRUST (protocol 2017MCEEY4) of the Italian MIUR funded in the framework of “PRIN 2017” call.

Copolymerization of polyethylene terephthalate and polycaprolactone using catalytic transesterification

A random copolymer between polyethylene terephthalate (PET) and polycaprolactone (PCL) is formed using catalytic transesterification in the melt. The copolymer, poly[(ET)2-co-(CL)2], has a backbone structure similar to that of polybutylene adipate terephthalate (PBAT) and could replace it at a lower cost, while simultaneously managing waste PET. Theoretically, a biodegradable copolymer is achieved when only two consecutive ET blocks remain. This degree of transesterification requires an active catalyst, capable of selective transesterification while limiting undesired chain scission. 1H NMR spectroscopy revealed that titanium alkoxide catalysts were the most effective for rapid transesterification, leading to di-blocks of both ET and CL units. It was found that the random copolymer could only be produced by catalysts containing both highly acidic metal ions and highly basic, small linear ligands. These observations led to the proposal that catalytic transesterification is likely to occur via an insertion-coordination mechanism. Increasing catalyst loading from 0.35 to 1.1 parts per hundred when using Ti(OBu)4 significantly accelerates transesterification, but a plateau is reached at about 0.85. Pleasingly, a reaction time of 2 min was sufficient for the reaction to be complete, suggesting reactive extrusion could be feasible. DSC thermograms of Ti(OEt)4 and Ti(OBu)4 catalysed blends have no observable recrystallization and melting peaks along with a sharp glass transition temperature suggesting the copolymer was highly amorphous with no unreacted homopolymers. Gel permeation chromatography of THF soluble blends revealed that a high extent of transesterification led to a decrease in chain length such that the Mn was reduced from about 68000 (PCL) to 13000–20000 (copolymer), suggesting that there is a need to use a minimum amount of catalyst to avoid excessive chain scission. The results demonstrate a proof-of-concept that transesterification of PET with PCL is possible to a high extent and that the reaction proceeds via an insertion-coordination mechanism. The results will inspire future research towards repurposing waste PET on extrusion scales and the creation of other biodegradable polyester materials using waste polymers.

Long-term stability of silane-passivated zirconia nanoparticles with low surface energy

The performance of zirconia nanoparticles (ZrO2 NPs) is critically dependent on their dispersion and stability. Effective control of NP dispersion is crucial for achieving a high refractive index, transparency, and exceptional mechanical properties in organic-inorganic hybrid films that incorporate ZrO2 NPs. In this study, we compared the crystalline properties and stability of ZrO2 NPs synthesized via two distinct methodologies: solvothermal synthesis using a zirconium isopropoxide isopropanol complex (ZII, Zr(OCH(CH3)2)4·(CH3)2CHOH) and sol-gel synthesis using zirconyl chloride octahydrate (ZC, ZrOCl2·8H2O). Both solutions exhibited precipitation, and the particles showed aggregation behavior. Despite being in a suspended state, the particles synthesized using the ZII precursor (T-ZrO2) exhibited hard-sphere behavior, distinct interparticle boundaries, and a tetragonal crystalline phase. However, the particles produced using the ZC precursor (A-ZrO2) were nearly amorphous without well-defined sizes and morphologies. Further, the hydroxyl end groups of both particle types were exchanged using a silane coupling agent (3-(trimethoxysilyl)propyl methacrylate, TMSPM) via hydrolysis and condensation reactions. The presence of the TMSPM groups on the surface of ZrO2 NPs afforded surface-modified TMSPM-T-ZrO2 with enhanced stability and prevented particle aggregation, thus maintaining the dispersion stability for up to one year under ambient conditions. The low surface energy and stabilization of the TMSPM-T-ZrO2 NPs were influenced by the tetragonal crystalline phase, which was conducive to surface modification using a silane coupling agent.