DIY Quantum Dots(Nanotech in Your Kitchen)

I'm an undergrad researcher in material science and nanomaterials. For years I've wanted a simple science experiment that a child could do with parental or adult supervision for nanoscience outreach. I'm tired of simple baking soda volcanoes. You are better than that.... So lets make nanomaterials in the kitchen! Today, you're gonna make the tiniest Instructable ever.

Specifically, we are making Carbon Quantum Dots. Quantum dots are nanometer scale particles, typically of semiconductor. They are so small that when high energy light hits them, the photons will be absorbed then emitted at a lower energy state. QD's are usually made from toxic chemicals but today I'll show you how to make non-toxic quantum dots in your home. Also, they can be used as fluorescent dyes, inks, and possibly paints. I will probably be making things glow around my apartment in the coming days.

The original paper at the bottom used baking soda and fructose over the course of an hour. I modified it to use sucrose and take 10 minutes.

Disclaimer: This is as dangerous as making candy. This is simply cooking, be safe and use common sense, molten sugar is the worst thing to burn yourself with.

Equipment Needed

Microwave

Tempored Glass bowl(I prefer Borosilicate but we aren't rapidly changing temperatures)

Heat resistant gloves(perhaps with silicone for grip)

A few containers for you samples

Plastic Pipettes

Glass vials to store

UV or Blacklight

Supplies

Water(I used tap water)

Baking soda(Sodium Bicarbonate)

Cane sugar(Sucrose)

White Vinegar(Acetic Acid)

Step 1: Prep the Saccharide

Add to the glass bowl

1 cup of water

1/4th cup of vinegar

6 tablespoons of sugar(80 grams)

Microwave for 5 minutes

The sucrose must be broken down in a process called inversion, the sucrose is broken into fructose and glucose. Sucrose inversion is heavily used candy making because it makes the sugar less grainy in sweets. The acid decreases the time needed to do this from hours to minutes, especially with the application of heat.

Step 2: Neutralize the Acid

Allow the bowl to cool to be safely handled

Slowly add 20 grams of baking soda to the solution.(See video to see what happens when you do it all at once.)

The solution must be basic for the synthesis to occur so we add enough baking soda to neutralize the acid and make raise the pH.

Step 3: Synthesize the Quantum Dots

Microwave the basic solution for 5 minutes. The liquid will yellow then darken.

As the concentration of QD's increase, the liquid will get darker and darker. I was able to get formation within 3 minutes but I wanted to minimize any chance of failure for anyone reproducing this experiment.

Step 4: Dilute the Quantum Dots

Allow the bowl to cool then pipette small amounts to a half filled vial of water. The Quantum Dots/sugar mixture will disburse and glow Green when exposed to an ultraviolet light.

If the QD's are too concentrated then they wont glow as well, you have most likely made several cups or a liters worth of Quantum Dots in 10 minutes, Congratulations.

Step 5: Discussion

This project was originally much more difficult but made an additional color. It originally took significantly longer to make the QDs.

Photo 1:I Took a sample at 1 minute, 20 minutes, 30 minutes, 40 minutes, and an hour.

The sucrose(a disaccharide) is not as easily converted to Quantum Dots as simple sugars(monosaccharides). I spent an hour and a half to get QD's just using baking soda. The sucrose would only decompose to Glucose and Fructose at high temperatures for extended periods of time. When simple sugars are in a basic solution, they can form the quantum dots. So using the acid and heat, I made lots of free fructose and glucose, but then I had to make the solution basic again.

So we added baking soda to neutralize the acid, but that isn't enough, when acetic acid and baking soda mix, they form sodium acetate which acts as a weakly acidic buffer solution. So i added plenty of sodium bicarbonate to the instructions to overcome the sodium acetate's buffering properties.

All in all, it was a fascinating challenge and I hope I've satisfied everyone's curiosity today.

Additional Reading and references

https://pubs.rsc.org/en/content/articlelanding/201...

https://www.tandfonline.com/doi/full/10.1080/21691...

Fascinating paper using Smartphones and carbon dots. https://www.nature.com/articles/s41598-017-11572-8

Nitrogen doping CQD's. https://www.nature.com/articles/srep05294

https://www.hindawi.com/journals/jnm/2015/787862/

Comments

[FLIPPER4440]

Im confused as to why this works but wanting to know if I'm understanding it correctly,
Step 2 is sucrose + vinegar = fructose & glucose sitting in vinegary acid
Step 3 is now that you have fructose & glucose, neutralize the acid into base of sodium acetate due to the baking soda which when in the presence of basic sugars like fructose & glucose causes quantum dots
Step 4 is heat the mix simply to speed up the process & i suppose result in a greater yield.
Im guessing sodium acetate, simply because its a base, alters the shape/size of something that somehow makes the quantum dots. Is it a matter of the molecular shape of glucose that after bases have their way with it, it happens to be the correct shape to expand the incoming UV light into green light or is it that the size & material of the resulting particles happen to absorb the UV light & then also are the right size to them radiate that energy into green light?

[weiweiweiwear]

Hi StrangelyAmusing, thanks for the awesome tutorial and the simple access for nano science, I wonder if this dye is sufficient for making luminescent solar concentrator? if not, why?

Thank you!

[nancydo0298]

"When simple sugars are in a basic solution, they can form the quantum dots"
Can someone explain this part to me? I don't see why this is the case. Chemical equations would be helpful

[divinamalpas]

at what temperature in the microwave should I use? thank you!

[ishashafaqat567]

what will be its temp on microwave???will microwave be preheated on some temp or not?????

[glambert17]

My undergrad chem lab group will replicate this for our semester-long experiment. Thanks for posting! We will be adding gelatin too, since that is what we started with in our original experiment.

[jpedrick]

I used distilled water sodium carbonate and continued until I got a ph of approximately 10(measured with ph strips). At this phase, even without additional heating the solution started to yellow and showed some florescence.

[dereks123]

I am curious to know if this is not simply rayleigh scattering as I do not see a significant shift in wavelength from the exciting wavelength. I would need some convincing that nanoparticles have indeed been assembled.

[VanadiumFour]

I agree, without EM nanoparticles are extremely difficult to assert, particularly on color alone, if the author has access EM images would a nice confirmation

[SHOE0007]

Would this work with different dyes (Tonic water) for example and with Lasers 405 nm purple dot laser? I like the Idea of Non-toxic quantum dots tho. Keep up the good work.

[ad1000]

The laser I used in the demo above was a 405nm purple dot laser, so yes, this works.

[ralph.peteranderl]

I looked at the original paper cited here (Which is a free pdf download from the Journal "Green Chemistry", and they show excitation spectra for their quantum dots. According to the paper, excitation at 405 - 470 nm gave rise to emission spectra between 500 - 600 nm (roughly - check out figure 4d in the paper).
I don't think that tonic water/quinine (Sp?) will give you a better result, partially because the quinine will already add its own fluorescence.
A very interesting option, though, is excitation with near IR light. According to the original paper, carbon-based quantum dots are very good at 2 photon excitation, where 2 IR photons at 820 nm do the job of 1 near UV photon at 410 nm. So you could convert IR light into visible green light..

[SHOE0007]

Well, that interesting but I hoped quinine would work. It a lot of work for something that barely glows but cool if an IR diode was used I don't have many applications for IR diodes Laser type Right now and they are sort of expensive! Still very cool.

[ralph.peteranderl]

Quinine fluorescence is a different mechanism - the electrons in the molecule get bumped up into a higher energy level by the UV or blue light, they loose some energy as heat, and then release the remainder as a fluorescence photon.
It seems that people are not quite sure yet how the emission works in carbon quantum dots, but for regular quantum dots the dimensions of the particle determine the wavelength/energy of the photon that can be emitted.

[SHOE0007]

Well, thank you so it is the size of the "Nanoparticles". Looking at it, it does not seem like it fluoresces a lot and why would this be? Is it because it is fairly sensitive to heat, and sugar formation? It is still very cool converting 800 nm IR wavelength into green would be good if it "was bright enough" tho!

[SHOE0007]

Well I have a 405 nm laser I could eventually get a 445 nm blue laser but they are NOT cheap either on Ebay.

[SHOE0007]

Well getting a 445-450 nm blue laser to give a orange color with Quantium dots sounds cool but they are quite expensive too.

[ralph.peteranderl]

I ended up buying a bundle of laser pointers (Red, green, blue) from a Chinese site on Amazon, and the price was not all that bad.

[ad1000]

Awesome post. Couldn't resist making some. They look particularly stunning when illuminated with a purple laser (left glass is plain water, right one has quantum dots in it.

[SHOE0007]

That is very cool I may try this with a 200 mw Purple 405 nm laser or even buy a 808 nm IR laser to get it to glow green (the beam). So far I only have Violet Dot 200 mw, and Red 200 mw Laser line and 50 mw green. I do a lot of projects with Prisms, etc.