Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

The overall goal of the following experiment is to demonstrate the seeded synthesis of rod and tetrapod shaped multi-component nanostructures consisting of cadmium, sulfide and cadmium selenide. This is achieved by first preparing molecular reactive precursors. As a second step, the molecular precursors are reacted to form cadmium selenide seeds of tite and zinc blend crystal structures.

Next, the Tite and zinc blend seeds are used as a template for the growth of rod and tetrapod shaped nano crystals respectively. The results demonstrate that choice of the crystal structure of the cadmium selenide seed affords precise control over the final morphology of the cadmium selenide cadmium sulfide hetero structure. Today, it is possible to make multi-component nano crystals with independent control over the composition phase size, shape, even the connectivity of every component within the nano crystal.

To achieve this, we need to separate the nucleation from the growth, and this is done by performing nucleation and growth in independent and distinct synthetic steps. Visual demonstration of this method is useful since small differences in technique can have a large impact on the final product obtained with identification of the specific factors to which the nano Chrystal synthesis is very sensitive. The reproducibility of these methods continues to improve.

Several of the chemicals used in these synthesis are acutely toxic and carcinogenic. Additionally, nanomaterials may pose other hazards beyond their bulk counterparts. Please use all appropriate safety measures including engineering controls and proper protective equipment.

Also, consult the relevant material safety data sheet before performing the synthesis. Prior to starting this procedure, prepare the molecular precursors including cadmium mirror, state octal, phosphine, selenide, and tri Tal Phosphine sulfide as described in the text protocol following this combines 60 milligrams of cadmium oxide, 3.0 grams of tri octal phosphine oxide, and 280 milligrams of N Octa desal phospho acid. In a 25 milliliter, three neck, round bottom flask equipped with a stir bar, a thermocouple, a reflux condenser, and a rubber septum.

Degas the mixture at 150 degrees Celsius under vacuum for one hour while stirring at 800 RPM. After Degassing, place the solution under Argonne atmosphere and heat it to 300 degrees Celsius until it becomes an optically clear solution. Remove the flask from the heating mantle and carefully swirl the solution to remove excess cadmium oxide from the sidewalls of the flask.

Following this, heat the solution again until it becomes optically clear. Add 1.5 grams of tri anal phosphine dropwise to the solution and raise the temperature to 370 degrees Celsius. Using a syringe with a 14 gauge needle rapidly, add the octal phosphine selenide solution to the reaction mixture.

Let the reaction proceed for the desired duration as the size of the wite cadmium selenide. Nano Chrystal can be tuned by adjusting the reaction time. Once the reaction is complete, remove the heating mantle and rapidly cool the flask using a stream of compressed air.

Next, add 10 milliliters of anhydrous methanol to the solution. When the temperature falls below 60 degrees Celsius to F floate, the nano crystals transfer the solution to a vial under argon and centrifuge for 10 minutes. At 2, 600 G following centrifugation, decant the supernatant and re disperse the precipitate.

In anhydrous toluene. Add anhydrous methanol until the solution becomes turbid and centrifuge for 10 minutes at 2, 600 G, decant the supernatant and repeat the cleaning procedure using hexane and isopropanol after centrifugation disperse the cleaned precipitate in a few milliliters of anhydrous toluene. Next, confirm the word site crystal structure of the cadmium selenide nano crystals by x-ray diffraction.

Then determine the concentration of the wite cadmium selenide solution. Using UV vis absorption spectroscopy combine 0.17 grams of cadmium mirror state and 37 milliliters of one Octa deene. In a 50 milliliter, three neck, round bottom flask equipped with a stir bar, a thermocouple, a reflux condenser, and a rubber septum.

Degas the solution under vacuum at 90 degrees Celsius for one hour while stirring at 800 RPM. Subsequently, cool the solution to room temperature under Argonne. Next, briefly remove the rubber septum and add 33 milligrams of selenium dioxide powder to the flask.

After replacing the septum, Degas the solution under vacuum at 50 degrees Celsius for 15 minutes while stirring at 800 RPM. After placing the solution under Argonne atmosphere, heat it to 240 degrees Celsius at a ramp rate of approximately 10 degrees Celsius per minute. When the solution reaches 240 degrees Celsius, add dropwise a previously Degas one Octa Deene solution.

After 30 minutes, remove the heating mantle and allow the solution to cool to room temperature. Once the particles have been cleaned, confirm the zinc blend crystal structure of the cadmium selenide nano crystals by x-ray diffraction. Then determine the concentration of the zinc blend.

Cadmium selenide solution using UV vis absorption spectroscopy to a 25 milliliter, three neck, round bottom flask equipped with a stir bar, a thermocouple, a reflux condenser, and a rubber septum. Add 207 milligrams of cadmium oxide, 1.08 grams of N Okta desal phospho acid, 3.35 grams of tri octal, phosphine oxide, and 15 milligrams of propyl phospho acid. After degassing and complexing the reaction solution, place it under Argonne atmosphere and heat it to 340 degrees Celsius.

Then inject 1.5 grams of tri octal phosphine dropwise, and let the temperature recover to 340 degrees Celsius. Using a syringe with a 14 gauge needle rapidly add 0.65 grams of the tri Tal Phosphine sulfide solution to the reaction mixture. After 20 seconds rapidly, add a Tite cadmium selenide solution in a similar manner.

Adjust the reaction temperature to 320 degrees Celsius. After 10 minutes at 320 degrees Celsius, remove the heating mantle to cool the solution. Following this at approximately 10 milliliters of anhydrous toluene to the flask, when the temperature is around 100 degrees Celsius to prevent solidification of the tri octal phosphine oxide.

After transferring the crude solution to a vial, purify the seated rods. See the text protocol for details on the purification procedure com Combine 207 milligrams of cadmium oxide, 1.08 grams of N Octa desal phospho acid, 3.35 grams of tri octal, phosphine oxide, and 50 milligrams of propyl phospho acid. In a 25 liter, three neck, round bottom flask equipped with a stir bar, a thermocouple, a reflux condenser, and a rubber septum.

After the reaction mixture has been degas and placed under an argon atmosphere, heat it to 300 degrees Celsius. When the temperature reaches 300 degrees Celsius, add 1.5 grams of tri tal phosphine dropwise and allow the temperature to recover to its initial value. Next rapidly, add 0.65 grams of octal phosphine sulfide to the reaction mixture using a syringe with a 14 gauge needle.

After 40 seconds rapidly, add a zinc blend, cadmium selenide solution in a similar manner, raise the reaction temperature to 315 degrees Celsius at a rate of one degree per minute. After 20 minutes at 315 degrees Celsius, remove the heating mantle to cool the reaction. Then add anhydrous toluene to the flask when the temperature is around 100 degrees Celsius to prevent solidification of the tri octal phosphine oxide.

After transferring the crude solution to a centrifuge vial, purify the seeded tetrapods. See the text protocol for details on the purification procedure when finished, store the tetrapods toluene. Finally separate the tetrapods from the undesired nano rod byproducts by centrifuging the toluene solution at 12, 000 G.For 30 minutes.

Following centrifugation, discard the upper nano rod layer and dissolve the lower tetrapod layer. Hoene shown. Here are the absorption and photo luminescence spectra of the word site and zinc blend cadmium selenide, nano crystals respectively.

These spectra can be used to calculate the extinction coefficient and quantum yield of the nano structures. The insets are transmission electron microscopy, images of the cadmium selenide, nano Chrystal seeds, the x-ray of fraction patterns of the tite and zinc blend cadmium selenide. Nano crystals are pictured here with the line patterns of corresponding bulk materials provided for reference X-ray of fraction and transmission electron microscopy can be used to determine the phase and morphology of the nanostructures.

The transmission electron microscopy, images of the cadmium selenide, cadmium sulfide, nano rods and cadmium selenide cadmium sulfide tetrapods are shown here. The x-ray diffraction patterns of the nano rods and tetrapods are pictured here, and only reflections from wite cadmium sulfide are apparent. Shown here are the absorption and photo luminescence spectra of the cadmium selenide, cadmium sulfide, nano rods and tetrapods respectively.

The green line shows the magnified absorption spectra to highlight the absorption. Due to the cadmium selenide seed, We've demonstrated a method of adjusting the final morphology of a nano hetero structure. By controlling the crystal structure of the seed Nanostructures of the cadmium ides have served as a useful model system for the development of new synthetic techniques.

While this video protocol has demonstrated the synthesis of a particular nanostructure, the same techniques are applicable to a variety of other structures. The synthesis of nanocrystals has now advanced to the point where it is possible to design intricate structures for particular purposes and applications. If you embark on a new nano krysttal synthesis, remember to take account all of the hazards you may encounter and to perform the synthesis safely.