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Special Issue "Sol-Gel Technique"

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A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Material Sciences and Nanotechnology".

Deadline for manuscript submissions: closed (15 December 2010)

Special Issue Editor

Guest Editor
Prof. Dr. Jay B. Benziger

Department of Chemical Engineering, Princeton University, Engineering Quad., Room A-407, Princeton, NJ 08544-5263, USA
Website | E-Mail
Phone: 01-609-258-5416
Fax: +1 609 2580211
Interests: reaction engineering of organic vapor phase deposition; dynamics of polymer electrolyte membrane fuel cells; recovery of thiols for hydrocarbon streams; developing a large-scale liquid scintillation detector

Special Issue Information

Dear Colleagues,

Sol-gels are versatile materials made by condensing a solution (sol) of metal oxide precursors into three dimensional networks. The gels are bi-phasic systems in which a continuous fluid phase fills the space inside a polymerized network. The gels can be dried in controlled fashion to produce porous solids with unique thermal, mechanical, optical and chemical properties. Sol-gel materials have grown in importance over the past 30 years as chemists and engineers have learned how to vary the reactants and processing conditions to tailor material properties for specific applications.

The early work with sol-gels focused on those made of silica, derived by condensation of silanols groups (Si-OH), as illustrated in by reaction (1).

Reaction 1

Reaction 1. Condensation of silanols into a gel. The silanols condense by forming water leading to a network of Si-O-Si bonds. The quaternary functionality of the Si results in a three dimensional network.

The silanols groups may be on the surface of nanometer sized silica particles or could be formed by hydrolysis of silicone alkoxides as illustrated in reaction (2).

Reaction 2

Reaction 2. Hydrolysis of silicon alkoxides to produce silanols. The silanols subsequently undergo condensation reactions to produce silica gels.

Silicon has four functional groups that can undergo condensation. By altering the reaction conditions (temperature, concentration, pH, solvent and reactant), the degree and nature of the condensation reactions can be controlled. At low pH conditions the rate of condensation slows down with degree of branching resulting in low cross-link density and very porous gels. In contrast high pH will accompany rapid condensation that can produce dense particles that precipitate from the solution. The gels are filled with liquid, generally a water alcohol solution. Controlled drying of the gel is employed to tailor the porosity and composition for specific applications. Highly porous materials can be produced that are exceptional thermal insulators. Alternatively dense gels may be employed as thin film protective coatings for lenses.

Advances in chemistry and the chemical precursors available for sol-gel processing have made it an extremely flexible process for materials synthesis. We are no longer limited to silica gels or even to metals oxides. It is now possible to make sol gels materials from almost any transition metal, as well as make composite materials. The applications of sol-gel materials have grown as the synthesis and processing methods have opened new vistas of material properties. A list of some of major applications of sol-gels is given in Table 1.

Table 1. Applications of Sol-gel materials.

 

Application
Sol-Gel Material
Optical fibers
High purity doped silica gel films for optical fiber precursors
Protective optical coatings
Abrasion resistance silica gel coatings on plastic substrates
Anti-reflective optical coatings
Laser windows, smart windows
Thermal insulation for windows
Aerogel window spacers, solar collector coatings
High Temperature Refractory Insulation
Ceramic foams
Chemical Sensors
Thin film NOx sensors, sol-gel coated crystal oscillators
Catalysts and Adsorbents
Silica alumina solid acid catalysts, high surface area catalyst supports, Silica gel desiccant
Ceramic membranes
Sol-gel molecular sieves, antibacterial filters
Abrasives
Alumina abrasives
Dental sealants and fillers
Hydroxyapatite

 

Sol-gel technology offers many important advantages in materials processing. The nanometer structure of the gels permits low temperature processing of ceramic materials so that ceramics and plastics can be combined in hybrid materials. The introduction of metal alkoxides precursors for sol-gels made possible the production of high purity materials that dramatically improved the quality of optical fibers. The pore structure and large surface areas associated with sol-gel materials has been essential to the development of catalysts and adsorbents making possible improved production of gasoline and removing impurities for automobile exhausts and new photocatalysts for splitting water. We now have a tool box of chemical and processing methods to tailor sol-gels to tackle new materials technologies. In this special issue we present reviews of the synthesis and processing techniques to produce sol-gel materials.

Prof. Dr. Jay B. Benziger
Guest Editor

Keywords

  • silica gels
  • aerogels
  • xerogels
  • optical fiber cladding
  • sol gel derived waveguides
  • abrasive resistant coatings or hybrid glass coatings
  • antireflective coatings
  • titania sol gel photocatalysts
  • aerogel windows
  • sol gel catalysts
  • adsorbents
  • ceramic foams
  • sol gel membranes
  • sol gel NOx sensors
  • colloidal gels
  • sol gel transition
  • self cleaning coatings
  • ceramic spin coating
  • ceramic dip coating
  • sol gel composite

Related Special Issue

Published Papers (5 papers)

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Research

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Open AccessArticle Whole Cell Imprinting in Sol-Gel Thin Films for Bacterial Recognition in Liquids: Macromolecular Fingerprinting
Int. J. Mol. Sci. 2010, 11(4), 1236-1252; doi:10.3390/ijms11041236
Received: 28 January 2010 / Revised: 26 February 2010 / Accepted: 22 March 2010 / Published: 24 March 2010
Cited by 25 | PDF Full-text (1920 KB) | HTML Full-text | XML Full-text
Abstract
Thin films of organically modified silica (ORMOSILS) produced by a sol-gel method were imprinted with whole cells of a variety of microorganisms in order to develop an easy and specific probe to concentrate and specifically identify these microorganisms in liquids (e.g., water). Microorganisms
[...] Read more.
Thin films of organically modified silica (ORMOSILS) produced by a sol-gel method were imprinted with whole cells of a variety of microorganisms in order to develop an easy and specific probe to concentrate and specifically identify these microorganisms in liquids (e.g., water). Microorganisms with various morphology and outer surface components were imprinted into thin sol-gel films. Adsorption of target microorganism onto imprinted films was facilitated by these macromolecular fingerprints as revealed by various microscopical examinations (SEM, AFM, HSEM and CLSM). The imprinted films showed high selectivity toward each of test microorganisms with high adsorption affinity making them excellent candidates for rapid detection of microorganisms from liquids. Full article
(This article belongs to the Special Issue Sol-Gel Technique)
Open AccessArticle Modification of Different Zirconium Propoxide Precursors by Diethanolamine. Is There a Shelf Stability Issue for Sol-Gel Applications?
Int. J. Mol. Sci. 2009, 10(11), 4977-4989; doi:10.3390/ijms10114977
Received: 12 October 2009 / Revised: 28 October 2009 / Accepted: 9 November 2009 / Published: 13 November 2009
Cited by 6 | PDF Full-text (943 KB) | HTML Full-text | XML Full-text
Abstract
Modification of different zirconium propoxide precursors with H2dea was investigated by characterization of the isolated modified species. Upon modification of zirconium n-propoxide and [Zr(OnPr)(OiPr)3(iPrOH)]2 with ½ a mol equivalent of H
[...] Read more.
Modification of different zirconium propoxide precursors with H2dea was investigated by characterization of the isolated modified species. Upon modification of zirconium n-propoxide and [Zr(OnPr)(OiPr)3(iPrOH)]2 with ½ a mol equivalent of H2dea the complexes [Zr2(OnPr)6(OCH2CH2)2NH]2 (1) and [Zr2(OnPr)2(OiPr)4(OCH2CH2)2NH]2 (2) were obtained. However, 1H-NMR studies of these tetranuclear compounds showed that these are not time-stable either in solution or solid form. The effect of this time instability on material properties is demonstrated by light scattering and TEM experiments. Modification of zirconium isopropoxide with either ½ or 1 equivalent mol of H2dea results in formation of the trinuclear complex, Zr{η3μ2-NH(C2H4O)2}3[Zr(OiPr)3]2(iPrOH)2 (3) countering a unique nona-coordinated central zirconium atom. This complex 3 is one of the first modified zirconium propoxide precursors shown to be stable in solution for long periods of time. The particle size and morphology of the products of sol-gel synthesis are strongly dependent on the time factor and eventual heat treatment of the precursor solution. Reproducible sol-gel synthesis requires the use of solution stable precursors. Full article
(This article belongs to the Special Issue Sol-Gel Technique)
Open AccessArticle Eu-Doped BaTiO3 Powder and Film from Sol-Gel Process with Polyvinylpyrrolidone Additive
Int. J. Mol. Sci. 2009, 10(9), 4088-4101; doi:10.3390/ijms10094088
Received: 16 July 2009 / Revised: 13 August 2009 / Accepted: 3 September 2009 / Published: 17 September 2009
Cited by 18 | PDF Full-text (758 KB) | HTML Full-text | XML Full-text
Abstract
Transparent BaTiO3:Eu3+ films were prepared via a sol-gel method and dip-coating technique, using barium acetate, titanium butoxide, and polyvinylpyrrolidone (PVP) as modifier viscosity. BaTiO3:Eu3+ films ~500 nm thick, crystallized after thermal treatment at 700 ºC. The powders
[...] Read more.
Transparent BaTiO3:Eu3+ films were prepared via a sol-gel method and dip-coating technique, using barium acetate, titanium butoxide, and polyvinylpyrrolidone (PVP) as modifier viscosity. BaTiO3:Eu3+ films ~500 nm thick, crystallized after thermal treatment at 700 ºC. The powders revealed spherical and rod shape morphology. The optical quality of films showed a predominant band at 615 nm under 250 nm excitation. A preliminary luminescent test provided the properties of the Eu3+ doped BaTiO3. Full article
(This article belongs to the Special Issue Sol-Gel Technique)

Review

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Open AccessReview Sol Gel-Derived SBA-16 Mesoporous Material
Int. J. Mol. Sci. 2010, 11(9), 3069-3086; doi:10.3390/ijms11093069
Received: 24 June 2010 / Revised: 29 July 2010 / Accepted: 29 July 2010 / Published: 31 August 2010
Cited by 33 | PDF Full-text (540 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this article is to review current knowledge related to the synthesis and characterization of sol gel-derived SBA-16 mesoporous silicas, as well as a review of the state of the art in this issue, to take stock of knowledge about current
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The aim of this article is to review current knowledge related to the synthesis and characterization of sol gel-derived SBA-16 mesoporous silicas, as well as a review of the state of the art in this issue, to take stock of knowledge about current and future applications. The ease of the method of preparation, the orderly structure, size and shape of their pores and control, all these achievable through simple changes in the method of synthesis, makes SBA-16 a very versatile material, potentially applicable in many areas of science and molecular engineering of materials. Full article
(This article belongs to the Special Issue Sol-Gel Technique)
Figures

Open AccessReview A Review of Photocatalysts Prepared by Sol-Gel Method for VOCs Removal
Int. J. Mol. Sci. 2010, 11(6), 2336-2361; doi:10.3390/ijms11062336
Received: 12 April 2010 / Revised: 11 May 2010 / Accepted: 21 May 2010 / Published: 28 May 2010
Cited by 61 | PDF Full-text (221 KB) | HTML Full-text | XML Full-text
Abstract
The sol-gel process is a wet-chemical technique (chemical solution deposition), which has been widely used in the fields of materials science, ceramic engineering, and especially in the preparation of photocatalysts. Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. Among the
[...] Read more.
The sol-gel process is a wet-chemical technique (chemical solution deposition), which has been widely used in the fields of materials science, ceramic engineering, and especially in the preparation of photocatalysts. Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. Among the approaches to remove VOCs from indoor air, photocatalytic oxidation (PCO) is regarded as a promising method. This paper is a review of the status of research on the sol-gel method for photocatalyst preparation and for the PCO purification of VOCs. The review and discussion will focus on the preparation and coating of various photocatalysts, operational parameters, and will provide an overview of general PCO models described in the literature. Full article
(This article belongs to the Special Issue Sol-Gel Technique)

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