Synthesis and Reaction Chemistry of Nanosize Monosodium Titanate

The surfactant mediated sol-gel synthesis of nanosized monosodium titanate is described, along with preparation of the corresponding peroxide modified material. An ion-exchange reaction with Au(III) is also presented.

Transcript

The overall goal of the following experiment is to prepare nanosized sodium titanate materials including peroxide-modified and gold(III)loaded materials. This is achieved by first performing a surfactant-mediated sol-gel synthesis to prepare nanosized monosodium titanate particles in the range of 100 to 150 nanometers. As a second step, the nanosized monosodium titanate can be treated with hydrogen peroxide which converts a portion of the material to a peroxotitanate form.

Next, an ion-exchange reaction can be performed to prepare metal-loaded titanates for various applications. An example is the addition of a solution of gold(III)chloride to the nanotitanate to produce the corresponding gold(III)exchanged titanate. Results are obtained that show spherical particles in the range of 100 to 150 nanometers can be prepared using the method, based on electron microscopy imaging and dynamic light scattering measurements.

We first had the idea for this method when we began looking at the application of titanates in the biomedical field where particle size becomes more important. This method can be extended to materials normally synthesized using sol-gel techniques, allowing materials with a range of different particle sizes to be prepared. Nanosized particles, monosodium titanate, provide the opportunity to improve ion exchange performance due to their higher surface area to volume ratio.

Use of metal exchange titanates as bactericides can be enhanced with nanosized materials. To begin the synthesis of nano monosodium titanate, or nMST, first add 0.58 milliliters of 25 weight percent sodium methoxide solution to 7.62 milliliters of isopropanol followed by 1.8 milliliters of titanium isopropoxide. Label the solution number one.

Next, add 0.24 milliliters of ultra-pure water to 9.76 milliliters of isopropanol to make solution number two. Add 0.44 milliliters of Triton X-100 to 280 milliliters of isopropanol in a three-neck flask and stir well with a magnetic stirrer. Fit the syringe ends with tubing of sufficient length to deliver the solutions below the level of the liquid in the flask and load solutions one and two into two separate syringes.

Next, place the syringes into a dual-channel syringe pump and deliver the solutions at a rate of 0.333 milliliters per minute to the flask. After addition, cap the flask and continue stirring for 24 hours at room temperature. Afterwards, uncap the flask and heat the mixture to reflux for 45 to 90 minutes.

Purge the flask with nitrogen and add ultra-pure water in portions to replace evaporated isopropanol as heating is continued. After most of the isopropanol has evaporated and the volume of water added has reached approximately 50 milliliters, remove the heat from the flask and allow the mixture to cool. Filter the product through a 0.1 micron nylon filter paper and wash it several times with water.

Finally, transfer the slurry from the filter into a pre-weighed bottle and store it at ambient temperature. To determine the yield, weigh an aliquot of the aqueous slurry before and after drying. To perform the exchange with gold(III)ions, first transfer 6.50 grams of the 4.23 weight percent slurry of nMST to a 50 milliliter centrifuge tube.

Next, add about one milliliter of water to 0659 grams of hydrogen tetrachloro gold(III)trihydrate in a one dram glass vial. Transfer the solution to the centrifuge tube. Continue by rinsing the glass vial with water and adding it to the tube.

Repeat this several times to ensure that all of the gold reagent is transferred. Add water to the tube to bring the total volume up to 11 milliliters. Wrap the tube in foil and then tumble it on a shaker for a minimum of four days.

After tumbling the mixture, centrifuge the tube for 15 minutes. Discard the supernatant and re-suspend the solids in distilled water. Centrifuge the sample again and repeat the washing procedure twice more.

Finally, re-suspend the solids in water and store in the dark at room temperature. To prepare peroxotitanate, begin by adding five grams of a 9.8 weight percent slurry of nMST to a flask and stir the slurry magnetically. Continue by adding dropwise 0.154 grams of a 30 weight percent hydrogen peroxide solution to the flask, which induces a color change from white to yellow.

Continue stirring the mixture at ambient temperature for 24 hours. Next, filter the product through a 0.1 micron nylon filter paper and was the product several times with water to remove any un-reacted hydrogen peroxide. Finally, transfer the slurry from the filter into a pre-weighed bottle and store the aqueous slurry of peroxotitanate at ambient temperature.

Shown here is a typical particle size distribution as measured by dynamic light scattering using the established sol-gel method. Note that this synthesis produces a multimodal distribution of particles with the majority around one micrometer. When reaction conditions that aimed to reduce the particle size of the monosodium titanate were employed, which involved removing the seeding step and using more dilute reagents, this resulted in a bimodal distribution of particle sizes centered at 50 to 100 nanometers and 500 nanometers after 24 hours.

After 48 hours, a trimodal distribution of particles measuring up to 1000 nanometers was observed, as demonstrated in this graph. Importantly, the addition of Triton X-100 during the synthesis of nMST is critical for producing an almost uniform particle size distribution as measured by dynamic light scattering. Transmission and scanning electron microscopy showed that the Triton X-100 produced nMST particles at a more uniform size and morphology when compared to those of monosodium titanate.

The surface modification of nMST particles by hydrogen peroxide was confirmed by the appearance of an absorption band at 883 wave numbers in its Fourier transform infrared spectrum. After its development, this technique paved the way for researchers in the field of biological applications of inorganic materials to explore the use of nanotitanates to deliver therapeutic metals and the metal exchange titanates to service bactericides. After watching this video, you should have good understanding of how to prepare nanoscale particles of monosodium titanate along with the peroxide-modified and metal-loaded forms.

Remember that working with flammable solvents and reagents can be extremely hazardous. Precautions should be taken to prevent the buildup of flammable vapors. It is recommended that sol-gel synthesis be carried out in a chemical fume hood.

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Synthesis and Reaction Chemistry of Nanosize Monosodium Titanate

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