preparation of wet grafted silica with n’-(3-trimethylsilyl propyl) diethyleneamine (das)

Impregnation and Grafting of Aminated Compounds onto Silica Substrates

The anthropogenic CO2 emissions over the past several decades have been widely implicated as the main factor driving the greenhouse gas effect and consequently, related climate change1,2,3,4. There are two general methods for CO2 capture, point source and direct air capture. For more than 50 years, wet-scrubbing CO2 capture technologies have been utilized for point source capture within the industry to mitigate CO2 emissions5,6. These technologies are based on liquid-phase amines that react with CO2 to form carbamates under dry conditions and hydrogen carbonates in the presence of water7,8, see Figure 1. The main reason that carbon capture and storage is utilized at large point (industrial) sources is to prevent the further release of large quantities of CO2, thus having a neutral effect on total CO2 concentration in the atmosphere. However, point-source carbon capture systems suffer from several drawbacks, such as equipment corrosion, solvent degradation, and high energy requirements for regeneration9. Direct air capture (DAC) goes beyond emission reduction and can facilitate the removal of CO2 from the atmosphere. The removal of this existing CO2 is necessary to limit continued climate change. DAC is an emerging methodology and must address the difficulties of removing low concentrations of CO2 in atmospheric conditions (400 to 420 ppm), operate in a variety of different environmental conditions, and address the need for cost-effective materials that can be reused many times1,2,3. Significant work is needed to identify materials that meet these requirements, which will accelerate the adoption of DAC and improve its economic feasibility. Most importantly, community consensus on critical parameters of measurement needs to be established, which is essential for benchmark materials to be developed.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65845/65845fig01.jpg" /> 
Figure 1: Schematic of the expected liquid amine adsorbent CO2 capture mechanism. The top reaction is in dry conditions, and the bottom reaction is in the presence of moisture. <a href="https://www.jove.com/files/ftp_upload/65845/65845fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In an effort to remedy these drawbacks, considerable research and development of novel porous material technology have resulted in a wide array of promising materials that have the potential to be utilized as either capture materials or substrates for DAC. Some examples of such materials include mesoporous silica species10,11,12,13, zeolites14,15, activated carbon16,17, and metal-organic frameworks18. Many solid-supported amine adsorbents also show a higher tolerance to water, which is a vital consideration in CO2 removal through DAC approaches. For DAC applications, researchers must consider wet/dry environmental conditions, hot/cold temperatures, and an overall dilute atmospheric CO2 concentration. Amongst the various substrate materials, silica is commonly used because of its adjustable pore sizes, ability to surface functionalize, and large surface area1,2,3. Typical synthetic procedures and primary features of both impregnated and grafted amine-silica composites are described within this work (Figure 2). Direct synthesis, where the material is made in situ with both components, substrate and amine, is another commonly used methodology2.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/65845/65845fig02.jpg" /> 
Figure 2: Schematic representations of impregnation. Mixing of PEI and silica substrate in methanol through diffusion (top) and grafted amine-silica composites through covalent tethering (bottom). <a href="https://www.jove.com/files/ftp_upload/65845/65845fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Impregnation&#160;is a method in which an amine is physically adsorbed onto a surface, in this case, a porous silica medium, through van der Waals forces and hydrogen bonding between the amine and silica surface19,&#160;see Figure 2. Solvents such as ethanol and methanol are commonly used to promote the diffusion of the molecules into the porous structure of the substrate material. The solution can also be heated to increase the solubility of the high molar mass polyamines, thereby increasing the homogeneity of amine penetration within the pores. In the case of impregnated materials, the amount of amine introduced to a silica substrate is determined by the initial quantity of the amine and the surface area of the substrate. If the amount of amine introduced exceeds the available surface area of the silica substrate, the amine species will agglomerate on its surface. This agglomeration is readily apparent, as the impregnated material will appear to have a gel-like coating, often yellow, rather than the expected white and powdery appearance1. Among the many types of amine-base solid adsorbents, polyethyleneimine (PEI) and tetraethylene pentamine (TEPA) are the most widely used due to their high stability and high nitrogen content20. For physically impregnated systems, the theoretical loading quantity of amine can be calculated from the pre-weighted amounts of the substrate and the density of the amine. The obvious advantage of physical impregnation lies in the straightforward synthesis procedure to prepare it, as well as the potential for a large amine content due to the high porosity of the silica substrate. Conversely, the stability of the amine within the silica is limited because there is no covalent bonding between the amine and silica support. Therefore, after multiple cycles of CO2 uptake and regeneration through heat or steam, the amine can leach out of the pores. Despite these drawbacks, the implementation of such materials for DAC holds great promise for removing CO2 from the atmosphere.
Another option for the preparation of DAC materials is grafting. Grafting is a method through which amines are immobilized onto a porous silica substrate through a chemical reaction, as shown in Figure 2. This reaction proceeds by reacting an aminosilane with the surface&#39;s silanol functional group, resulting in a covalent bond. Therefore, the number of functional groups on the surface of the silica substrate impacts the grafted amine density21,22. Compared to amine-impregnated adsorbents, chemical grafting methods have had lower CO2 adsorption capacity mainly due to the low amine loading21. Conversely, chemically-grafted amines have increased thermal stability due to their covalently bound structure. This stability can be useful in the regeneration of the material as adsorbents (such as grafted silica) are heated and pressurized to remove the captured CO2 for reuse to save material and cost. In a typical synthesis procedure, the mesoporous silica substrate is dispersed in a solvent (e.g., anhydrous toluene), which is then followed by the addition of aminosilanes. The resulting sample is then washed to remove unreacted aminosilanes. Improvements in aminosilane density are reported to have been achieved through water addition, specifically with SBA-15, to expand pore size23. The procedure for grafting that will be described herein uses moisture-sensitive techniques. Therefore, additional water will not be used. Implementation of grafted aminosilane materials for DAC is promising due to their expected stability during CO2 adsorption and desorption processes. However, the major drawbacks of this methodology include the complex reactions/preparation of these materials, leading to increased cost, and their overall low CO2 adsorption capacity, meaning larger quantities are required.
Overall, results of many previous studies indicate that the structure of the substrate and amine-related modification has a significant impact on the adsorption performance with specific studies utilizing techniques such as transmission electron microscopy (TEM) and quasi-elastic neutron scattering (QENS) to fully characterize these materials24,25. In other words, the structural properties (e.g., porosity and surface area) of the substrate material determine the amine loading, so increasing these parameters can improve CO2 capacity24,25. Continued research into the optimization and design of substrate materials and preparation processes is critical to the development of high-performance adsorbents for DAC. The goal of this work is to provide guidance on impregnation and grafted amine synthesis in hopes of facilitating better transparency of synthetic techniques. Within the literature, specific details on the amounts of solvent, substrate, and amines are not always described, making it difficult to understand the correlation between experimental loading amounts and quantitative measurements of amine-silica composites. The exact loading amounts and a detailed description of the experimental procedures will be provided herein to better facilitate these types of comparisons.

Author Spotlight: Standardizing the Development of Amine-Based Silica Composites as CO2 Adsorbents for Direct Air Capture 

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 amine-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 adsorption experimental parameters. We are turning our efforts towards characterizing benchmark materials and developing standard techniques to foster greater comparability and confidence in reported results.

Watch this Scientific Journal Video about Preparation of Wet Grafted Silica with N'-3-Trimethylsilyl Propyl Diethyleneamine DAS at JoVE.com

Preparation of Wet Grafted Silica with N&#8217;-(3-Trimethylsilyl Propyl) Diethyleneamine (DAS)  

Preparation of Wet Grafted Silica with N’-(3-Trimethylsilyl Propyl) Diethyleneamine (DAS)

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.

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268 visualizações.  National Institute of Standards and Technology (NIST). Para começar a secar todos os copos no forno por pelo menos duas horas antes de usar. Para garantir uma superfície livre de umidade. Armazenar o aminosilano DAS dentro de um frasco tampado de septo.Considerar a carga apropriada de DAS para aumentar a probabilidade do aminosilano. Localização dos grupos silanol na sílica para colagem covalente. Adicione a quantidade desejada de suporte de sílica em um balão Schlenk de fundo redondo equipado com uma barra de agitação magnética....