A Synthetic Methodology for Preparing Impregnated and Grafted Amine-Based Silica Composites for Carbon Capture

Scientists here at NIST are developing critical measurement science and benchmark materials to accelerate innovation and explore timely, effective, and scalable direct air capture, or DAC, for carbon dioxide removal from the atmosphere. This work focuses on promoting best practices for preparation, measurement, and reporting of a mean functionalized silica composites for DAC applications. This protocol addresses outstanding research challenges and reproducible synthetic procedures for DAC materials by providing clear guidelines and conditions while identifying critical steps.

In addition, we aim to enable a meaningful comparison of carbon dioxide capabilities of these materials through clear documentation of specific absorption experimental parameters. We are turning our efforts towards characterizing benchmark materials and developing standard techniques to foster greater comparability and confidence in reported results. To begin, place all required glassware in an oven at 140 degrees Celsius for at least one hour prior to use.

For the impregnation of silica with PEI 800, first calculate the mass fraction of the amine required. Then take the desired amount of MCM 41 silica in a glass Petri dish and cover it with punctured aluminum foil. After placing the covered dish in a vacuum oven, apply the vacuum.

Then set the oven to a temperature of 110 degrees Celsius and leave it for a minimum of two hours to ensure complete drying of the silica. To prepare for the synthesis, using a clean, dry laboratory spatula, transfer the desired amount of PEI into the reaction vessel. After capping the vessel, transfer it to a chemical fume hood and place it over a stir plate while clamping it securely.

Once set, remove the lid of the reaction vessel and place a clean, dry stir bar into it. Using a pipette, transfer the desired amount of anhydrous methanol to the vessel from a graduated cylinder. Stir the reaction mixture for 15 minutes to ensure the PEI is dissolved and dispersed in the solvent homogeneously.

Next, using a clean, dry laboratory spatula, transfer the desired amount of silica that was dried in the oven onto weighing paper and add it to the PEI solution in the reaction vessel inside the fume hood. If needed, add additional methanol to rinse any residual silica from the vessel wall into the PEI solution. Place the vessel in a heating block at 40 to 50 degrees Celsius to load the amine into the porous silica.

Let the solution undergo stirring for about one hour while ensuring the stir bar is evenly mixing the solution. After that, remove the reaction vessel from the heat source, and while still stirring, allow it to cool to room temperature. When fully cooled, stop the stirring to remove the stir bar.

Connect the vessel containing the sample to the vacuum on a Schlenk line. Let the reaction vessel remain on the Schlenk line until all solvent is visibly removed. Then transfer the sample to a different storage container of choice, such as a glass Petri dish.

After placing the sample in a vacuum oven, turn on the vacuum. Allow the sample to dry under the vacuum at 70 degrees Celsius for at least 18 hours. Store the resultant white powdery material in a moisture-free, air-free environment until needed for further use.

To begin, dry all glassware in the oven for at least two hours before use to ensure a moisture-free surface. Store the aminosilane DAS within a septum-capped lid bottle. Consider the appropriate DAS loading to increase the probability of the aminosilane, locating the silanol groups on the silica for covalent bonding.

Add the desired amount of silica support in a round bottom Schlenk flask equipped with a magnetic stir bar and insert a rubber septum into the reaction vessel before removing air and moisture from the vessel connected to the Schlenk line. First, open the reaction vessel's stopcock to connect it to the vacuum for about 30 seconds. Then close the stopcock, switching to an inert gas supply for another 30 seconds.

Insert a line of inert gas into the septum-capped lid bottle containing anhydrous toluene. Use a gas-tight syringe to draw the desired amount of toluene and purge the syringe with inert gas before removing the solvent from the bottle. Ensure the magnetic stir bar inside the reaction vessel is stirring smoothly and puncture the septum on the reaction vessel with the gas-tight syringe containing the anhydrous toluene and transfer the toluene into the vessel.

After removing the inert gas needle from the toluene, change the needle head. Then, as demonstrated previously, transfer the desired amount of DAS to the reaction vessel. Use an adapter to attach a line from the Schlenk apparatus to a water condenser with the help of vacuum grease.

Wrap the bottom of the condenser apparatus with polytetrafluoroethylene, or PTFE tape, and attach a septum to the bottom of the condenser. After subjecting the line to vacuum and inert gas cycle three times, attach the condenser apparatus to the round bottom Schlenk flask. Then attach the cold water lines to the water condenser and turn on the water circulation.

Lower the reaction vessel into a silicone oil bath at a temperature of 80 to 100 degrees Celsius. Close the stopcock to the inert gas on the round bottom Schlenk flask and leave the stopcock on the condenser open. Stir the reaction while heating for six hours.

After that, cool the reaction vessel to room temperature. Next, connect the Erlenmeyer filer flask to the vacuum via a hose. Place a rubber bung at the opening before placing a Buchner funnel on top of the rubber bung.

After placing a filter within the Buchner funnel, wet the filter with anhydrous toluene Switch on the vacuum before quickly dispensing the solution onto the filter to collect the solid grafted amine silica on filter paper. Rinse the collected material three times with about 10 milliliters of anhydrous toluene. Using a clean, dry laboratory spatula, transfer the white grafted silane material from the filter paper to a vial.

After covering the vial with punctured aluminum foil, place it in a vacuum oven and turn on the vacuum. Set the oven to about 100 degrees Celsius and allow to dry for approximately 18 hours to remove excess toluene.