Preparation of mesoporous titania by surfactant-assisted sol–gel processing of acetaldoxime-modified titanium alkoxides

doi:10.1016/j.jnoncrysol.2010.04.035

Journal of Non-Crystalline Solids

Volume 356, Issues 25–27, 1 June 2010, Pages 1217-1227

https://doi.org/10.1016/j.jnoncrysol.2010.04.035 Get rights and content

Abstract

Sol–gel processing of acetaldoximate-modified titanium alkoxides in the presence of the non-ionic surfactants Pluronic F127 or Brij56 was investigated. Phase-purity, nanocrystal sizes, specific surface areas and pore diameters were compared with materials prepared under the same conditions with either oxime or surfactant. Concomitant use of both organic compounds turned out to give anatase with superior properties. Influence of surfactant proportion, calcination temperature and heating rate on the materials properties was investigated. X-ray diffraction experiments and small-angle scattering investigations allowed developing a clear understanding on how the structure develops during calcination and how the organic components influence the growth process.

Introduction

The performance of nanocrystalline titania (anatase) films as photocatalytic materials not only depends on the intrinsic properties of the crystal phase and the nanocrystal's size and shape, but also on film properties such as surface area, porosity, pore sizes or pore size distributions. Sol–gel processing of Ti(OR)₄ precursors is often used for the preparation of such films, and addition of surfactants has turned out beneficial to control their structural and thus physicochemical properties. The surfactants stabilize titania nanoparticles formed upon sol–gel processing and thus inhibit crystal growth and reduction of the surface area. Furthermore, mesoporosity is created upon post-synthesis thermal degradation of the surfactants (selected references [1], [2], [3], [4]).

Ligands used to control the reactivity of Ti(OR)₄ precursors also have an important influence on the obtained crystal phase of the particle sizes [5]. Organically modified metal alkoxide precursors are obtained by reaction with protic compounds such as carboxylic, sulfonic or phosphonic acids, β-diketones, β-ketoesters, amino alcohols, etc [6]. The bi- or multidentate anions of these compounds are able to substitute one or more alkoxo groups due to their higher bond strength. Organically modified titanium alkoxide precursors were occasionally employed in surfactant-assisted sol–gel processing [2], but no attention was paid to the question as to how the modifying ligands and the surfactant interact or cooperate with regard to the desired properties of titania films.

We found recently [7] that oximes are particularly well suited to modify transition metal alkoxides for their use in sol–gel processes. Oximates have several advantages compared to other modifying ligands. They are easily synthesized from hydroxylamine and aldehydes or ketones and can be substituted by a wide variety of functional or non-functional organic groups, which render them attractive for many applications of inorganic–organic hybrid materials.

The goal of the present work was to investigate sol–gel processing of oximate-modified precursors in surfactant-assisted processes. We used acetaldoxime (CH₃CHNOH) as a representative oxime and Pluronic F127, a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer, or the ethylene oxide based surfactant Brij56 [C₁₆H₃₃(OCH₂CH₂)₁₀OH] as non-ionic surfactants. Major focus was put on the question to what extent the oximate ligands and the surfactants influence the properties of the obtained titania. For this reason, no other sol–gel parameter was varied, and a standard protocol for sol–gel processing of Ti(OR)₄ (HCl catalysis) was employed.

Section snippets

TiO₂ syntheses

All chemicals were used as received. In a typical experiment, CH₃CH═NOH was dissolved in ethanol and stirred for 30 min. Ti(OⁱPr)₄ was then added dropwise, and the solution stirred for 30 min, followed by addition of the surfactant under mild stirring. After 30 min, aqueous HCl was added under vigorous stirring, and the sol was aged under mild stirring at room temperature for 2 h. The molar ratio of the precursors was Ti(OⁱPr)₄:CH₃CHNOH:EtOH:HCl (4 M):surfactant = 1:3:40:15:x. The x proportion was

Results

The samples investigated in this work were prepared as follows: Ti(OⁱPr)₄ was added dropwise to an ethanolic solution of three molar equivalents of acetaldoxime, CH₃CHNOH. We know from previous work [7] that complexes of the composition [Ti(OⁱPr)₂(ONCHR)₂]₂ are formed under the applied conditions, although the complexes were not isolated in the present work. After addition of the surfactant (Brij56 or F127), hydrolytic polycondensation was initiated by addition of aqueous HCl. The sols were

Discussion

Previous work had shown that part of the alkoxo ligands is replaced by oximate ligands, and [Ti(OⁱPr)₂(oximate)₂]₂ derivatives are formed, when Ti(OⁱPr)₄ is reacted with oximes under the conditions used in this work [7]. The IR spectra in Fig. 1, Fig. 11 clearly showed that the typical C═N bending vibration of oximate ligands at 1640 cm^− 1 is retained in the gels obtained upon acid-catalyzed, surfactant-assisted sol–gel processing of the oximate-substituted derivatives. When the gels were

Conclusions

Surfactant-assisted sol–gel processing of Ti(OR)₄ is an interesting route for the synthesis of mesoporous, nanoparticulate titania and for controlling the structural and physical properties of the obtained materials. We have shown in this article that concomitant use of organically modified titanium alkoxide precursors (instead of unmodified Ti(OR)₄), specifically oximate-modified titanium alkoxides (i.e. in situ-formed [Ti(OⁱPr)₂(ONCHMe)₂]₂), has distinct advantages and offers additional

Acknowledgements

J.Y. thanks the China Scholarship Council for providing a scholarship to stay at Vienna University of Technology. Part of the work was supported by the Austrian Forschungsförderungsgesellschaft (FFG) in the framework of the Austrian Space Application Programme (ASAP).

References (17)

N. Alexaki et al.
Microporous Mesoporous Mater.
(2009)
E.G.A.S. Attar et al.
J. Mater. Sci.
(2008)
J. Livage et al.
Prog. Solid State Chem.
(1988)
U. Schubert
Acc. Chem. Res.
(2007)
U. Schubert et al.
Chem. Mater.
(1995)
S.O. Baumann et al.
Eur. J. Inorg. Chem.
(2009)
D.H.E.K.S.W. Sing et al.
Pure Appl. Chem.
(1985)
U. Cernigoj et al.
Thin Solid Films
(2005)
H. Choi et al.
Topics Catal.
(2007)
G.Q. Liu et al.
J. Sol–Gel Sci. Technol.
(2007)
E. Beyers et al.
J. Phys. Chem. B
(2005)
H. Choi et al.
Thin Solid Films
(2006)
J. Jiu et al.
J. Photochem. Photobiol. A
(2007)

There are more references available in the full text version of this article.

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¹: Permanent address: School of Material Science and Technology, Tianjin University, Tianjin, 300072, China.

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Preparation of mesoporous titania by surfactant-assisted sol–gel processing of acetaldoxime-modified titanium alkoxides

Abstract

Introduction

Section snippets

TiO2 syntheses

Results

Discussion

Conclusions

Acknowledgements

Microporous Mesoporous Mater.

J. Mater. Sci.

Prog. Solid State Chem.

Acc. Chem. Res.

Chem. Mater.

Eur. J. Inorg. Chem.

Pure Appl. Chem.

Thin Solid Films

Topics Catal.

J. Sol–Gel Sci. Technol.

J. Phys. Chem. B

Thin Solid Films

J. Photochem. Photobiol. A

TiO₂ syntheses