In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

The overall goal of this experimental protocol is to provide new types of metal nanoparticles and metal oxide semiconductor hybrids that have unique nanostructures. This method can produce new types of nanostructured hybrid materials called metal nanoparticles and radial semiconductors for pigments, dyes, catalysts, and photocatalysts. The main advantage of this technique is that it provides nanostructured hybrids having good transparency and stability of metal nanoparticles.

Demonstrating the procedure will be Shiori Kawamura, a graduate student from Niigata. To begin this procedure, pre-clean a glass substrate through ultrasonic treatments using an ultrasonic cleaner containing one molar aqueous sodium hydroxide for 30 minutes. When finished, rinse the substrate with five to 10 milliliters of ultrapure water.

Dip the glass substrate in 0.1 molar aqueous hydrochloric acid. After three minutes, rinse the substrate with five to 10 milliliters of ultrapure water. Following this, clean the substrate through an ultrasonic treatment in pure water for one hour.

After rinsing with pure water, dry the substrate with a hair dryer for two to three minutes until dry. Now cast a previously prepared colloidal suspension of TNS on the glass substrate in 300 microliter aliquots. Dry the glass substrate at 60 degrees Celsius for two hours in a dry oven to give the TNS cast film.

To achieve thermal fixation of the TNS components on the glass substrate, center the obtained TNS cast film at 500 degrees Celsius for three hours in the oven. After repeating the centering process twice, immerse the centered TNS film in a 0.2 millimolar aqueous solution of methyl viologen dichloride salt for seven hours at room temperature under dark conditions. Rinse the obtained sample with five to 10 milliliters of ultra pure water, and dry in the dark for approximately one hour at 60 degrees Celsius.

Next, immerse the methyl viologen intercalated film in a 25 millimolar aqueous solution of tetrachloroauric acid for three hours at room temperature under dark conditions. Rinse the obtained samples with five to 10 milliliters of ultrapure water and dry in the dark for approximately one hour at 60 degrees Celsius. Following this, immerse the gold intercalated TNS film in a 0.1 molar aqueous solution of sodium borohydride for half an hour at room temperature under dark conditions.

Dry the obtained film in the dark for approximately one hour at 60 degrees Celsius. Now immerse the centered TNS film in a 0.1 molar aqueous solution of 2-AET chloride for 24 hours at room temperature. Rinse the obtained film with five to 10 milliliters of ultrapure water and dry in the dark for approximately one hour at 60 degree Celsius.

Next, immerse the 2-AET contained film in a 25 millimolar aqueous solution of tetrachloroauric acid for three hours at room temperature. Rinse the obtained film with five to 10 milliliters of ultrapure water and dry in the dark for approximately one hour at 60 degrees Celsius. Following this, immerse the 2-AET gold TNS film in a 0.1 molar aqueous solution of sodium borohydride for half an hour at room temperature under dark conditions.

Finally, rinse the obtained film with five to 10 milliliters of ultrapure water and dry in the dark for approximately one hour at 60 degrees Celsius. Adsorption of gold within the TNS film was confirmed by energy dispersive x-ray analysis, which proved clear signals of titanium and gold. When the methyl viologen TNS film was soaked in tetrachloroauric acid, the two characteristic XRD signals were shifted to a higher angle region, suggesting the adsorption of gold.

The sodium borohydride treated film exhibited a broader signal than that of the gold TNS film, suggesting the regular stacking structure became disordered upon treatment. The clear gold intercalated TNS film turned metallic purple through the borohydride treatment, which suggests the formation of reduced gold nanoparticles. The D-002 signal of the centered TNS film became intense and narrow upon 2-AET treatment, indicating that the stacking structures became ordered, and suggesting that the 2-AET molecules were intercalated into the TNS layer.

XRD analysis showed that the D-00 signals became broader after sodium borohydride treatment, suggesting that the regular stacking structures became disordered. The color of the film turned clear to reddish, suggesting the formation of gold nanoparticles. No spectral change was observed after four months for the gold nanoparticles and the TNS layer with 2-AET under ambient atmosphere, indicating that the gold nanoparticles were stable against oxygen.

Once mastered, this technique can be done in three days if it is performed properly. While attempting this procedure, it's important to remember to perform all experiments in the dark to avoid a photoreaction of TNS. Although, we performed under bright conditions for filming.

Moreover, don't move or shake the Petri dish. Following this procedure, other metal nanoparticles like copper and silver can be prepared in order to provide other metal nanoparticles and radial metal oxide semiconductor hybrids. After its development, this technique paved the way for researchers in the field of metal nanoparticles to explore catalysts and photocatalysts in sustainable chemistry.

After watching this video, you should have a good understanding of how to synthesize metal nanoparticles and radial semiconductor hybrids. Don't forget that working with sodium borohydride oxide can be extremely hazardous and precautions, such as wearing glasses and gloves, should always be taken while performing this procedure.