Hello,
I´ve been trying to synthesize TiO2 nano-particles via sol-gel by the hydrolysis of titanium isopropoxide without success. Every time I end up with a white suspension that tends to sediment. I´ve tried both acid and basic pH, as well as both heating and cooling.
My synthesis consists in dissolving TTIP in isopropanol and then dropwise adding a solution of isopropanol under either stirring or ultrasound.
Any tips would be appreciated.
Jose Nicolas Cardenas Espana Good question and one that's been asked for many years. First thing - TiO2 in all its 3 major forms has a high density (~ 4.2 g/cm3) and this means it will settle pretty easily. Carry out a Stokes' Law calculation to determine what size of particles could remain in free Brownian motion (the ASTM standard for DLS - ASTM E2490-09 (2021) Standard Guide for Measurement of Particle Size Distribution of Nanomaterials in Suspension by Photon Correlation Spectroscopy (PCS) has a table with a material of density 4.2 g/cm3 in it together with predicted settling times. This is to mimic TiO2). The fact you have a white precipitate tells you that the size of the particles is >> 100 nm (and thus they'll settle - a true nano colloidal suspension won't settle and will be close to transparent). So, what does that tell me about your preparation conditions? It's the fact that your concentrations of the TiO2 precurosor (the usual isopropoxide) is way too high. Small sizes are favored by low concentrations so that the formed particles have less chance of rapid recombination. Dilute your TTIP in IPA by a factor of 10 or 100, or maybe even 1000, as a starting point. You should end up with a clear, or faintly blue opalescent, liquid. You may also need a stabilizer. In aqueous media the optimum concentration of phosphate is used for charge/electrostatic stabilization. In organic media you may need to look for a steric stabilizer such as 50 kDa PEG or PEI.
The is more on TiO2 in this webinar (free registration required):
Dispersion and nanotechnology
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat
Keep the colloidal suspension in the liquid form. Do not attempt to dry or filter or you'll lose the 'nano-ness' of the system. Good luck with your research.
I´ve synthesized anatase-TiO2 nano-particles via hydrolysis of titanium isopropoxide by reaction medium of DI water and peptization by IP. Every time I end up with a white suspension that is centrifuged at 12000rpm get the particle.
At acidic hydrolysis conditions and a digestion time of up to 18 hours, you get a ppt of TiO2.
Md. Ashraful Alam A precipitate cannot be nano (100% < 100 nm). Consider Stokes’ Law…
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