Synthesis of Nanosized TiO₂ by Cationic Polymerization of (µ₄‐oxido)‐hexakis(µ‐furfuryloxo)‐octakis(furfuryloxo)‐tetra‐titanium

Abstract

Nanosized titanium dioxide is of importance as a photocatalyst, as pigment, and, for example for photovoltaic applications because of its electronic, optoelectronic, and catalytic properties.[1] The most convenient synthetic route is the hydrolytic sol-gel process which allows titanium oxides and/or its precursors to be produced in a straightforward way from titanium alkoxides by hydrolysis and condensation at low temperature. [2][3][4][5] This synthetic methodology has a widespread applicability and is well documented. [2][3][4][5] The sol-gel approach requires water addition for the hydrolysis process and hence, the formation of by-products (e.g., alcohols) and the associated formation of a gel, which undergoes substantial shrinkage on drying, is observed. However, nonaqueous synthetic routes allow the control of the shape, size, and crystallinity of metal oxides and in addition, are readily to handle, compared to convenient sol-gel processes. [6][7][8][9] The main limitation of this concept is the insufficient solubility of some metal halides in nonaqueous solvents. In this work we present a new concept for the synthesis of titanium dioxide starting from cationically polymerizable titanium monomers. The so called ''Twin-Polymerization'' strategy [10] allows the reaction of hybrid monomers in organic solvents or in melt without admitting water. The formation of the polymer is associated with that of the inorganic compound. Thus, it is possible to synthesize interpenetrating inorganic/ polymer composite materials. We report here on the synthesis and cationic polymerization of a titanium hybrid monomer which undergoes polymerization to a poly(furfuryl alcohol)/ titanium oxide nanocomposite material. The titanium oxide component can be obtained after removing of the organic polymer out of the composite.(m 4 -Oxido)-hexakis(m-furfuryloxo)-octakis(furfuryloxo)-tetra-titanium (I) is readily accessible by the transesterification of tetraethyl orthotitanate with furfuryl alcohol (Scheme 1). Madaliev et al. described a similar reaction of tetra-tert-butyl orthotitanate and furfuryl alcohol, in order to obtain tetra-furfuryl orthotitanate.[11] The product was characterized by quantitative elemental analysis, bromine number, and saponification value.[11]Excess of furfuryl alcohol and ethanol (formed during the reaction) were removed by distillation from the reaction mixture containing one equivalent of tetraethyl orthotitanate and 4.05 equiv. of furfuryl alcohol, whereby the resulting brown liquid solidified at room temperature. Moisturesensitive crystals of I suitable for single crystal X-ray structure analysis were obtained from a mixture of toluene/n-hexane (1:1 v v À1) at room temperature. The structural analysis reveals that I exists in the solid state as a novel tetrameric titaniumoxo-cluster containing a Ti 4 (m 4 -O) core, cf. Figure 1. Oxoclusters containing the Ti 4 (m 4 -O) core are very rare, so far only two related clusters have been described, [12,13] possessing;however, a further m-bridging oxido (O 2À ) li...

Nanostructured Organic–Inorganic Composite Materials by Twin Polymerization of Hybrid Monomers

“…It can be obtained from salicyl alcohol and Si(OC 2 H 5 ) 4 by transesterification using fluoride as catalyst and toluene as the solvent. [14] The net equation given above has been confirmed by means of 13 C and 29 Si solid-state NMR spectroscopy of the phenolic-resin/SiO 2 nanocomposite obtained, just as in the polymerization of TFOS. From 2,2 0 -spirobis [4H-1,3,2-benzodioxasiline], a nanostructured phenolic-resin/SiO 2 Type-I hybrid material is formed in only one step by cationic polymerization initiated by a Brønsted acid (CF 3 COOH or CH 3 SO 3 H).…”

“…Four titanium atoms are arranged around one oxygen atom, and the 14 furfuryloxy units are found in the periphery of the Ti 4 O structural unit. [13] Obviously, FA acts as the oxygen-bridging compound during synthesis. [13] On cationic polymerization, these monomers react smoothly to produce a PFA/TiO x (OH) y nanocomposite, which can be converted into monophasic anatase by subsequent treatment with water and oxidation of the organic polymer (Fig.…”

The Power of Non-Hydrolytic Sol-Gel Chemistry: A Review

“…This technique was developed by Spange et al as a method for the preparation of high-surface-area metal oxides and nanoparticles [167], such as SiO 2 [168,169] and TiO 2 [170]. The concept underlying this synthetic route is based on the reaction of a well-defined metal-containing monomer leading to interpenetrating composite networks consisting, for example, of a metal oxide and a polymer (Scheme 9).…”

Nanokomposite mit 0.5 bis 3 nm großen Strukturdomänen durch Polymerisation von Silicium‐Spiroverbindungen

“…B. ausgehend von Tetrafurfuryloxysilan oder verschiedenen Titan-Monomeren, können anorganische und organische Polymere simultan in einem einzigen Prozess erzeugt werden, jedoch unter begleitender Bildung von Wasser. [15][16][17] [14] Dazu kommt, dass der Polymerisationsmechanismus unseres Verfahrens völlig neu ist.…”