# Sol–gel synthesis of TiO₂ and SiO₂

> A metal alkoxide such as titanium isopropoxide (for TiO₂) or tetraethyl orthosilicate (for SiO₂) is mixed with water in alcohol, with an acid or base as catalyst. The alkoxide groups hydrolyse to M–OH, which condense into M–O–M bridges: first a sol of small particles, then a gel whose network spans the whole liquid. Drying gives a dense xerogel or, with supercritical drying, a light aerogel; calcination removes organics and crystallizes the oxide.

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- Updated: 2026-10-14
- Category: Nanomaterial synthesis
- Method: Sol-gel, bottom-up
- Starting materials: Metal alkoxides M(OR)₄: Ti(OCH(CH₃)₂)₄ (TTIP) or Si(OC₂H₅)₄ (TEOS), in alcohol
- Product: TiO₂ or SiO₂ as gels, xerogels, aerogels, films or powders
- Typical size: Primary particles of a few nanometres; pores from micro- to macropores depending on drying
- Key result: Very pure, homogeneous oxides; texture tuned by pH, water ratio, catalyst and drying
- Scalability: High for coatings and powders; slow drying limits monoliths
- Figure: 1920 × 1080 px, 95 editable layers (12 generated objects with settings)

## Steps

1. **Precursor**: Alkoxide dissolved in its alcohol
2. **Hydrolysis**: M–OR + H₂O → M–OH + ROH, catalysed by acid or base
3. **Condensation**: M–OH + HO–M → M–O–M + H₂O (or + ROH): oligomers, then particles
4. **Sol → gel**: Particles link into a network that spans the liquid; the gel no longer flows
5. **Aging, drying**: Evaporative drying shrinks it into a xerogel; supercritical drying keeps the open network (aerogel)
6. **Calcination**: Burns off organics and crystallizes the oxide, e.g. amorphous TiO₂ to anatase

## Strengths

- Low-temperature chemistry, high purity and homogeneity
- Shapes: films, fibres, monoliths, powders, aerogels
- Easy doping and mixed oxides

## Limitations

- Alkoxides are moisture-sensitive (TTIP hydrolyses very fast)
- Large shrinkage and cracking on drying
- Organic residues need calcination

## Uses

- Photocatalytic and self-cleaning TiO₂ coatings
- Optical and protective silica coatings
- Aerogel insulation
- Catalyst supports

## References

1. Hench & West, “The sol-gel process”, Chem. Rev. 1990. https://doi.org/10.1021/cr00099a003 (review)
2. Chen & Mao, “Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications”, Chem. Rev. 2007. https://doi.org/10.1021/cr0500535 (review)
3. Brinker & Scherer, “Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing”, Academic Press 1990. (further reading)

Credit: Redrawn and simplified after Hench & West, Chem. Rev. 1990 (doi:10.1021/cr00099a003); TiO₂ after Chen & Mao, Chem. Rev. 2007 (doi:10.1021/cr0500535).

## Questions

**What does the “Sol–gel synthesis of TiO₂ and SiO₂” template show?** A metal alkoxide such as titanium isopropoxide (for TiO₂) or tetraethyl orthosilicate (for SiO₂) is mixed with water in alcohol, with an acid or base as catalyst. The alkoxide groups hydrolyse to M–OH, which condense into M–O–M bridges: first a sol of small particles, then a gel whose network spans the whole liquid. Drying gives a dense xerogel or, with supercritical drying, a light aerogel; calcination removes organics and crystallizes the oxide.

**What are the steps shown in “Sol–gel synthesis of TiO₂ and SiO₂”?** 1. Precursor: Alkoxide dissolved in its alcohol. 2. Hydrolysis: M–OR + H₂O → M–OH + ROH, catalysed by acid or base. 3. Condensation: M–OH + HO–M → M–O–M + H₂O (or + ROH): oligomers, then particles. 4. Sol → gel: Particles link into a network that spans the liquid; the gel no longer flows. 5. Aging, drying: Evaporative drying shrinks it into a xerogel; supercritical drying keeps the open network (aerogel). 6. Calcination: Burns off organics and crystallizes the oxide, e.g. amorphous TiO₂ to anatase.

**What are the starting materials and the product?** Starting materials: Metal alkoxides M(OR)₄: Ti(OCH(CH₃)₂)₄ (TTIP) or Si(OC₂H₅)₄ (TEOS), in alcohol. Product: TiO₂ or SiO₂ as gels, xerogels, aerogels, films or powders.

**Which papers is “Sol–gel synthesis of TiO₂ and SiO₂” based on?** Hench & West, “The sol-gel process”, Chem. Rev. 1990 (doi:10.1021/cr00099a003); Chen & Mao, “Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications”, Chem. Rev. 2007 (doi:10.1021/cr0500535); Brinker & Scherer, “Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing”, Academic Press 1990.

**Can I edit the “Sol–gel synthesis of TiO₂ and SiO₂” template?** Yes. Open it in the LabCanvas editor: all 95 layers are editable, including 12 generated objects (structures, plots, equipment) with their own settings. Change the text, colours and layout, then export PNG, TIFF, SVG or PDF.

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