Chemistry
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Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices
Summary March 27th, 2019
Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the materials.
Transcript
This protocol is significant because porous surface characteristic relating to the confinement effect of liquids in porous matrices is a key problem in energy, medicine, and environment application. A synthesis and characterization of the new materials, carbon and silica nanopores, and determination of the wetting parameters provide new information about properties of the confinement nanophases. In nanotechnology, biology, and medicine, it is crucial to optimize the synthesis methods for new materials in order to obtain a product with desired properties.
Essential synthesis and their characterization methods should be apparent and present in order to obtain product with desired structural and surface properties. The visual demonstration of this procedure is important as it provides a detailed explanation of the applied procedures and ensures a repeatable performance. Demonstrating of the procedure will be Dr.Malgorzata Zienkiewicz-Strzalka, a postdoc from the Faculty of Chemistry of Maria Curie-Sklodowska University, and Dr.Angelina Sterczynska, a postdoc from my laboratory.
To begin, prepare 360 milliliters of 1.6-molar hydrochloric acid in a 500-milliliter round-bottom flask. To the flask, add 10 grams of polyethylene 10500 polymer. Then place the flask in an ultrasonic bath and heat the solution to 35 degrees Celsius.
Stir it until the solid polymer is completely dissolved, making a homogenous mixture. Next add 10 grams of 1, 3, 5-trimethylbenzene to the flask and stir the content while maintaining it at 35 degrees Celsius in the water bath. After stirring for 30 minutes, add 34 grams of tetraethyl orthosilicate to the flask.
Over 10 minutes, add the tetraethyl orthosilicate slowly and dropwise with constant stirring. Then stir the mixture for an additional 20 hours at 35 degrees Celsius. After 20 hours, transfer the contents of the flask into a PTFE cartridge.
Place the cartridge in an autoclave, and bake the solution for 24 hours at 90 degrees Celsius. The next day, use a Buchner funnel to filter the resulting precipitate. Then wash it with distilled water, using at least one liter of water.
Dry the obtained solid at room temperature, and use a muffle furnace in an air atmosphere to apply a thermal treatment to the sample at 500 degrees Celsius for six hours. Start by preparing two impregnation solutions with appropriate proportions of water, three-molar sulfuric acid, and glucose, where glucose plays the role of carbon precursor, and sulfuric acid acts as catalyst. To prepare impregnation solution one, mix five grams of water, 0.14 grams of three-molar sulfuric acid, and 1.25 grams of glucose for each gram of silica.
Then prepare impregnation solution two. For this solution, mix five grams of water, 0.8 grams of three-molar sulfuric acid, and 0.75 grams of glucose for each gram of silica. Place one gram of the silica material, one gram of impregnation solution one, and the catalyst in a 500-milliliter flask.
Heat the mixture in a vacuum dryer at 100 degrees Celsius for six hours. Next add one gram of impregnation solution two to the mixture in the vacuum dryer, and heat the mixture again in the vacuum dryer at 160 degrees Celsius for 12 hours. Transfer the obtained composite to a mortar, and grind the particles to create a homogenous mixture.
Place the obtained product into the flow furnace under nitrogen, and heat it to 700 degrees Celsius at a heating rate of 2.5 degrees Celsius per minute. Hold the material at this temperature for six hours under a nitrogen atmosphere. After six hours, turn off the furnace, and allow the solution to cool before opening the furnace.
First prepare 100 milliliters of etching solution. Mix 50 milliliters of 95%ethyl alcohol and 50 milliliters of water. To this, add seven grams of potassium hydroxide, and stir until it is dissolved.
Place all of the obtained carbonized material in a 250-milliliter round-bottom flask, and add 100 milliliters of etching solution. Supply the system with a reflux condenser and a magnetic stirrer. Heat the mixture to a boil while stirring constantly, and allow it to boil for one hour.
Transfer the obtained material to the Buchner funnel. Wash it with at least four liters of distilled water, and then dry it. If desired, characterize the material using low-temperature nitrogen absorption-desorption measurements, TEM imaging, energy-dispersive X-ray spectroscopy, potentiometric titration measurements, and/or dielectric relaxation spectroscopy as described in the accompanying text protocol.
Nitrogen sorption and TEM methods have shown highly ordered mesoporous structures of synthesized materials. The EDS and potentiometric titration methods have shown the OMC is characterized by decreasing the acid sites and reduction of oxygen content. To determine the contact angle inside the pores of the studied samples, start by applying the modified Washburn's equation, shown here and described in the text protocol, to estimate the values of the advancing contact angles inside the studied pores.
Then prepare the force tensiometer. For powders, prepare a small tube with a diameter of three millimeters. For a liquid, prepare a vessel with a diameter of 22 millimeters and a maximum volume of 10 milliliters.
Next start the computer program connected to the tensiometer. Then put a vessel with a liquid on a motor-driven stage, and suspend the glass tube with the sample on an electric balance. Start the motor and approach the sample at a constant rate of 10 millimeters per minute.
Set the immersion depth of the sample tube into the liquid so that it is equal to one millimeter. Stop the experiment when m squared equals f of t starts to show the characteristic plateau. The wettability inside the pores is strongly dependent on the roughness of the pore, the kind of the wall, and the porosity.
The wettability of liquids in pores is significantly different than that on ideal, flat surface. Here are sample results of the measurements of contact angles inside the nanopores of ordered mesoporous carbon material. Also shown is the referenced wettability of smooth, highly-oriented pyrolytic graphite.
The measured contact angles are shown as a function of the microscopic wetting parameter. The lower the contact angle, the higher the wettability, which means that the interaction of the penetrating liquid molecule with the studied surface is stronger. The measured contact angles have indicated better wettability of the silica walls than the OMC walls and suggests that an influence of pore roughness on the fluid-wall interactions is more pronounced for silica than for carbon nanopores.
In addition to what was shown here, the adsorbent-adsorbate interaction, by means of a dielectric on Fourier-transform infrared spectroscopy or structural analysis by X-ray, can give additional insight into the molecular dynamics of materials. The techniques used for characterization of surface properties of nanomaterials may also be applied to the interactions between the material's surface and biological active substances. Please be caution when impregnating the silica matrix, as this step is hazardous due to the toxic sulfuric acid.
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