Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

The overall goal of this procedure is to fabricate photo active nano crystals and nano Chrystal films. This is accomplished by first fabricating the zinc selenide electron donor component. The second step is to overgrow zinc selenide with the cadmium sulfide electronic scepter component.

Next, the metal catalyst is deposited onto the groan zinc selenide cadmium sulfide donor acceptor nanoparticle the synthesis of photo active films of semiconductor nano crystals. Comprising lead sulfide nano Krystal arrays embedded into cadmium sulfide matrix is then demonstrated ultimately the photo activity of both isolated zinc selenide, cadmium sulfide, platinum nano crystals and lead sulfide cadmium sulfide films is demonstrated. So the main advantage of this technique over existing methods is that it allows for direct all inorganic coupling of the light absorber and the catalyst.

We believe this method can contribute to the ongoing research in the field of photo catalysis. Though fabricated materials were designed primarily for hydrogen production, they can also be applied for other catalytic functions such as reduction of organic pollutants or water splitting. Our nanoparticles are designed to facilitate fast conversion of absorbed solar light into a usable chemical or electrical energy.

Consequently, the implications of this technique extend toward the development of both photo catalytic and photovoltaic materials. Generally, individuals new this method will struggle because of the difficulty synthesizing these structures. To begin synthesis place ODA into a three neck flask with a magnetic stir bar.

In a separate flask, combine selenium and TOP. Add a magnetic stir bar to the flask. The mixture of TOP and selenium should be Degas under vacuum for 30 minutes.

Then put the mixture under Argonne flow with a wide glass exhaust. After heating the ODA to 300 degrees Celsius, inject the selenium mixture and then quickly inject a 10%solution of dathyl zinc in hexane or toluene. React at 265 degrees Celsius for around four to five minutes or until the excitation absorbance peak shifts to a desired wavelength.

At this point, remove the flask from the heating mantle. Once the temperature of the reaction flask drops to approximately 60 degrees Celsius, add five milliliters of warm chloroform and 12 milliliters of warm methanol. Split the reaction between two 15 milliliter centrifuge tubes topping off with methanol after centrifuging for five minutes, pour off the liquid phase red dissolve the precipitated nano chrystal in chloroform and repeat for growth of cadmium sulfide rods.

Combine premeasured quantities of topo O-D-P-A-H-P-A and cadmium oxide. In a three neck flask. Add a magnetic stir bar to mix in a separate flask containing a magnetic stir bar.

Combine premeasured quantities of sulfur and TOP Degas the cadmium oxide solution for 45 minutes at 150 degrees Celsius. Meanwhile, Degas the TOP solution for 45 minutes at 120 degrees Celsius. After degassing, put both the cadmium oxide solution and the TOP solution.

Under Argonne flow with wide glass exhausts heat the cadmium oxide solution to 380 degrees Celsius until the cadmium oxide is dissolved and the solution is clear and colorless. Heat the sulfur solution to 120 degrees Celsius until the sulfur is dissolved and the mixture is also clear and colorless. Next, add one fifth of the zinc selenide from the previous section to the sulfur solution.

Add 2.0 milliliters of TOP to the cadmium solution and let the temperature recover to 380 degrees Celsius. Then inject the sulfur nano crystal solution into the cadmium solution to grow rods. Ensure the solution stays above 345 degrees Celsius.

Allow the nano rods to grow for six to nine minutes after the injection is initiated. Following nano rod growth, remove the flask from the heating mantle. The longer the solution is left on the heat, the longer the rods will grow.

At this point, the product should be green and highly viscous. Add chloroform to liquefy the product and split into two vials. Next, add ethanol and centrifuge to precipitate the nano crystals Following centrifugation.

Pour off the liquid phase and red dissolve the precipitated nano crystals in chloroform. Proceed to grow a platinum tip onto one end of the nano rod as discussed in the written protocol. Following growth of the platinum tip precipitate and red dissolve the nano crystals as instructed there To complete fabrication of the zinc cell and I cadmium sulfide donor acceptor nanoparticles.

Hydrophobic oleic acid ligands are exchanged for hydrophilic MUA ligands. This allows a structure to be suspended in water, which facilitates its use in hydrogen production. The details of this procedure can also be found in the written manuscript.

Fabrication of photo active films of semiconductor nano crystals begins with synthesis of lead sulfide nano crystals and growth of cadmium sulfide shell. As detailed in the written manuscript accompanying this video, the next step is to hand wash the FTO coded glass with detergent and rinse with deionized water. Sonicate the glass in successive baths of methanol, acetone, and isopropanol for five minutes each following sonication dry under argonne flow.

Place the glass in a bath of 75 millimolar titanium tetrachloride in deionized water and heat for 30 minutes at 70 degrees Celsius. After rinsing with deionized water, dry the glass with argonne flow. Then heat the glass to 450 degrees Celsius in air for one hour.

Once the glass has cooled to room temperature, place three drops of titanium dioxide that has been dissolved in terpal on the center of the FTO side of the pretreated Slides following a spin for six seconds at 700 RPM and then one minute. At 2000 RPM ane the slide in air at 450 degrees Celsius until the film turns brown and then clears. All spin coating steps are performed in an Argonne glove box with the titanium dioxide prepared in the previous steps and glass slide spinning at 3000 RPM to begin, place one drop at a time of the previously prepared lead sulfide cadmium sulfide nano crystals onto the rotating slide, and let dry next place 10 drops of a MPA methanol solution on the slide and let it spin for a few seconds.

The surface will not fully dry. Wash the surface with methanol by placing 10 drops on the slide. Then wash it again with octane by the same method.

Repeat these steps for each subsequent layer of the film. A kneeling the film after every third layer at 150 degrees Celsius for 15 minutes until the film reaches the desired thickness. Prepare a solution of cadmium acetate in methanol in a beaker large enough, completely submerge the sample.

Then prepare a solution of sodium sulfide non hydrate in methanol, also in a beaker large enough to completely submerge the sample. Submerge the sample for one minute in the cadmium bath and rinse with methanol. Then submerge the sample for one minute in the sulfur bath and rinse with methanol.

Repeat this process until the pores are filled, generally four to eight times. Then a kneel the sample at 150 degrees Celsius for 15 minutes under argon. Upon completion of the nanoparticle film fabrication, the photovoltaic effect is prominent with the voltage of around 500 millivolts at an exposure of one sun at 1.5.

Air masses. The evolution of the absorption and emission spectra corresponding to zinc, selenide, cadmium sulfide, and platinum nano crystals. During each step of the synthesis is shown here.

Absorbent peaks are expressed at approximately 350 nanometers and 450 nanometers characteristic of cadmium sulfide, ex cyonic transitions. At this point, the nano crystal most notably displays the onset of a fluorescence peak at about 550 nanometers. This fluorescence feature is a result of admissive ex cyonic decay across the zinc selenide cadmium sulfide interface.

This type two inter domain fluorescence is then quenched by the growth of the platinum tip due to the rapid injection of the delocalized electron into the metal moiety. This ultra fast charge separation enables the utilization of the electron for the photo catalytic reduction of water. Hydrophilic MUA ligands are then added to facilitate the removal of the hole from the zinc selenide domain.

Increasing stability by inhibiting oxidation of the semiconductor core, allowing for the sustained production of solar hydrogen. As a result of hole scavenging, the organic ligands become susceptible to photo degradation, but this can be simply mitigated by the addition of fresh ligands. Thus, the introduction of hydrophilic ligands not only renders the nano crystal's water soluble, but also adjusts the energetics of the system to protect the nano structure at the cost of the inexpensive easy to replace organic surfactants.

Shown here is a transmission electron microscope image of the core and shell of lead sulfide, cadmium sulfide nano crystals showing that the cadmium sulfide infiltrates evenly around the lead sulfide core. The nano crystals solid is shown to be relatively free of pores. In this scanning electron microscope image showing the cross section of a device, one result of the shell growth that is observable is a blue shift in both the absorbance and emission peaks.

This shift is attributed to the lead sulfide core shrinking as the cadmium ions infiltrate further into the core. A large increase in the emission can also be seen due to the enhanced quantum confinement provided by the cadmium sulfide shell. The cadmium sulfide layer not only increases the emission, it also protects the core.

The cadmium sulfide layer increases the thermal stability of the solid up to almost 200 degrees Celsius, about 50 degrees Celsius higher than a lead sulfide. Nano crystals solid alone. While attempting this procedure, it is important to remember to closely monitor the growth of the crystals in the zinc selenide core synthesis.

Also, make sure the temperature does not fall below 345 degrees Celsius in the zinc Selenide CAD sulfide rod synthesis. After watching this video, you should have an understanding of how to create photo active materials, both in solution and in the form of thin films. Don't forget that working with chemicals such as TMS and heavy metals can be extremely hazardous and precautions such as proper ventilation and the use of protective equipment should always be taken while performing this procedure.