Synthesis Procedures

*Always use gloves in the hood and centrifuge. Do not use gloves for the cabinet and clean tools.*

Tip: fold weighting paper as an "airplane" for easy use. 

Room Temperature Synthesis

Clean the silver spoon or its end with a chem wipe with methanol.

Measure 170mg of AgNO3 and put it into a small glass vial with a small magnet in it. Clean the spoon.

Measure 160mg of  Se powder and put it into a separate vial/test tube. Clean the spoon. 

Use a 1mL syringe and add 1mL of TOP into Se and mix by sonicating until the solution is transparent yellow. 

Use a 10mL syringe and put 15mL of oleylamine into the vial with AgNO3. Add 0.25 mL of TOP-Se solution by using the same into the vial with AgNO3 and mix on the heat-plate (room-temperature) at about 600 rpm for a couple of days. Can increase the stirring rate to 1000rpm over some time.

Once the dots are synthesized, divide the dots between two or so test tubes using the pipet, diluted with chloroform and ample of methanol (until it turns turdy), and put them in the centrifuge at 3 k for 5 minutes. In order to dry them off, add methanol carefully and dispose of the extra liquid. The QDs should stay attached to the walls. Turn the test tubes around and air dry on the rack for a day or so. 

After a day, use pipet to pour and dissolve with little hexane and pour into a new, non-contaminated vial.  

140° Celcius Synthesis (OUR QD HOOD)

170 mg of AgNO3 and 15 mL of oleylamine are placed in a 50 mL three-neck flask with a stirring magnet. Put on stoppers on the sides, use a syringe to make a hole for the thermocouple, and place it into the solution. connect the flask to the Schlenk line. 

Meanwhile, the TOP-Se solution is prepared by dissolving 39.5 mg of Se powder in 0.25 mL of TOP and sonicating until clean yellow.

Raise the temperature of the solution in the three-neck flask to 140 °C.

The solution should turn from clear to a slightly yellowish color as the temperature is increased to 140 °C.

 When the temperature reaches 140 °C, quickly inject 0.25 mL of the TOP-Se solution (2 M concentration) through the stoppers.

Let it stir for 4 mins at 140 °C and then quench in a water bath.

Divide into test tubes and add a bit of chloroform to dilute the viscous crude solution, add methanol until the solution gets brownish turbid (separates the products from the residual organic molecules.) Mix and divide into equal amounts.

• aside  For short reaction time like less than 5 min, not for every 140 C reaction, add chloroform because the size and the number of the QDs is very small, so the crude solution seems already diluted.

The centrifugation of the solution is then performed at 3000 rpm for 5 min. The precipitates are dried for a couple of hours/overnight and redispersed in hexane into a vial.

Far-IR Synthesis (Polar Synthesis) 

Clean the silver spoon or its end with a chem wipe with methanol.

Measure 59.5 mg of AgNO3 and pour it into a flask with a small stirring magnet in it. Clean the spoon.  

Measure 130 mg of tetrabutylammonium chloride for surface passivation (therefore, does not have to be very exact.) Pour into flask. 

Put rubber stoppers on two sides of the flask. 

Clean the thermocouple with hexane if needed. 

Place the flask into the heating mantle. 

Pour, with a syringe, 4mL of oleylamine into the flask (pierce through the stopper.) 

Stir at 750 rpm. 

Mix TOP and Selenium in a small vial. Use a 1mL syringe, add 0.2 mL of TOP into 32 mg of Se  - need 0.25 mmol of Se, will use 0,125mL of solution, see math below - and mix by sonicating until the solution is transparent yellow. 

Lower stirring to 400rpm and add 0.125mL of TOP-Se solution into the stirring flask. 

Open N2 (using Schlenk line) for 30 mins - waiting for inert conditions. after 30 mins, slowly raise the temperature to 170° Celcius. (Will take a while with our PID.) Increase slowly, about 10°C/10 mins. 

After 170°C temperature is reached and relatively stable (+/- 5°C), keep stirring at 400 rpm for 2 hours, allowing the thermodynamic reaction to take place.

After 2 hours, use a syringe/pipet and divide the solution from the flask into two test tubes. 

Add chloroform until turdy (if does not turn brownish - add a tiny bit of methanol), and put into the centrifuge for 5 mins at 3k rpm. 

Once the centrifuge is complete, pour the waste liquid out and wash the test tubes with methanol (residue quantum dots should be left inside the test tubes). Pro tip: pour methanol into the top of the walls so as to not use liquid pressure to displace the dots.)

Dry for 2-3 hours or overnight. 

Dissolve with chloroform and put into a clean vial with a pipet. 

Tellurium Nanocrystals (Te NCs) Synthesis

Clean the flask and the condenser. 

With a clean spoon, weigh 99mg of Sodium Telluride. Put into the flask with a stirrer magnet. 

With a clean spoon, weigh 340 mg of polyvinylpyrrolidone. Put it into the same flask with a stirrer magnet. 

Clean the scale and spoon with methanol.  Put rubber stoppers on the two ends of the flask and use cable ties to tighten the rubber stoppers for the vacuum. 

Use vacuum grease on the condenser. 

Using a syringe, add 10 ml of ethylene glycol into the flask. Dispose of the syringe. Put in thermocouple and stir at 500 to 900 rpm. If the magnet is stuck, can try taking the flask out of the heating mantle and lowering the speed of the stir. 

Turn on the pump. Ideally, we'd want a pressure of about 150mTorr, but usually, we get around 300mTorr. If have LN2 dewar, submerge the solution trap into it. 

You can turn on N2. Apply vacuum grease where the thermocouple is.  Open the Schlenk line to vacuum, and wait 30 mins at low pressure (at 300mTorr). (What we are doing is vacuum inserting = purging before filling with inert N2.) 

 * the following steps need to be executed very carefully *

After 30 mins, turn off the pump. Very quickly open and close to N2 a couple of times. Makes sure oil does not get into the Schlenk line!!! (Oil will want to flow to the areas of low pressure, aka vacuum, hence need to open/close the N2 very quickly to help pressurize the flask and condenser gradually.)

Take out and pour 0.5mL of hydrazine hydrate into the flask. Important Put the bottle of hydrazine hydrate back into the desiccator immediately! It is very explosive and should never be used under a vacuum. 

Gradually (usually quickly, but our PID controller is sad) increase the temperature to 180°C.  You will see the solution turns black. After it reaches 180°C, leave stirring for 4 hours. (Check on it every now and then though.) 

Once done, quench with water/ice bath, and put into two test tubes using the pipets. 

Add chloroform and ethanol. About 1/3 of the solution volume of chloroform and more ethanol. Mix well with a pipet. (Will be hard to see when well mixed as the solution is always turbid.) 

Centrifuge for 5 mins at 3krpm. If no dry residue after the first centrifuge run, can add/dissolve with more chloroform and ethanol and do another centrifuge run. 

* If do more work-ups, with ethanol in between, see if there is aggregations left (clumps of Te NCs coming together on walls), and if no aggregations - then don't need ethanol for the dilution. 

Wash Te NCs with ethanol and dry them for a couple of hours. (Put a cloth underneath. Reminder: dispose of waste solution into the waste bottle.) 

Dilute in ethanol and chloroform, and pour into a clean vial.  (Refer to *) 

•  aside Can change the recipe by injecting more hydrazine hydrate (1.2mL) and leaving to stir for more time (5 hours 30 mins) = shorter NCs

                                                              ^^recipes still need calibration^^

Clean the flask with ethanol and chloroform. Clean condenser with hexane. 

How to calculate concentrations (aside)

Ag2Se are 2:1 concentration (2 mols of Ag to 1 mol of Se)

We do experiments in mmol/mg (hence divide everything by 1000:

1mmol of AgNO3 (170mg) and thus, 0.5mmol of Se is needed.

We get Se from solution with TOP - 0.25mL of TOP-Se solution needed. (We make a solution with 2 Molar concentration, so we need to use half of that solution. 0.5mL solution = 2 mmol of Se (2mmol/mL concentration)) 
Since the solution is viscose, we make a bit more of the solution (say 0.4mL) 

To make 2 Molar (mmol/mL) concentration TOP-Se solution:
0.4mL × 2 mmol/mL = 0.8 mmol of Se present (we need 0.5mmol to have correct ratio with Ag)
0.8 mmol ×79mg = how much of Se you add to TOP of 0.4mL 

Then, using a syringe would still add only 0.25mL of TOP-Se solution to 170mg of AgNO3.

140 degrees Celcius Synthesis

The oleylamine passivated-Ag2Se CQDs were synthesized with the scale-up method as detailed from a previous report.

Generally, 170 mg of AgNO3 and 15 mL of oleylamine were placed in a 50 mL three-neck flask.

The flask was stirred vigorously and purged with argon. Meanwhile, the TOP-Se solution was prepared by dissolving 39.5 mg of Se powder in 0.25 mL of TOP.

The preparation of the TOP-Se solution proceeded in a glovebox to prevent oxygen exposure.

The temperature of the solution in the three-neck flask was raised to 140 °C.

The solution turned clear to a slightly yellowish color as the temperature was increased to 140 °C.

 When the temperature was reached, 0.25 mL of the TOP-Se solution (2 M) was quickly injected, and the solution immediately turned to black.

Aliquots of the solution were taken according to the desired reaction time and quenched in an ice bath.

The products were precipitated by adding chloroform and ethanol to separate the products from the residual organic molecules.

The centrifugation of the solution was performed at 4000 rpm for 10 min. The precipitates were dried and redispersed in hexane.

(by Prof. Jeong)