Nanoporous thin films have emerged as promising gas separation and purification materials due to their high surface area-to-volume ratio and nanoscale pore structure.
Image Credit: vchal/Shutterstock.com
Applying Nanoporous Thin Films to Gas Separation
One of the most important applications of nanoporous thin films is in gas separation, where they are used to selectively filter out different gases from a mixture based on their molecular size, shape, and polarity. This is achieved through the use of nanoporous membranes, which allow gas molecules to pass through while preventing larger or less polar molecules from passing through. Materials such as Zeolite membranes, Metal-organic frameworks (MOFs), and nanoporous carbon membranes are the types of nanoporous thin films that have been extensively studied for gas separation applications.
For example, zeolite membranes composed of a crystalline aluminosilicate framework with a regular pore structure, have been used to separate carbon dioxide from methane, hydrogen and oxygen from nitrogen. Similarly, nanoporous carbon membranes are composed of highly ordered carbon nanotubes or graphene sheets with a regular pore structure that can be tailored to selectively separate gases.
In recent years, there has been a significant amount of research conducted on nanoporous graphene-based membranes for gas separation and purification. In 2021, Dandan Hou et. al developed an easy method for creating large nanoporous atomically thin membranes (NATMs) that are around 15 ×10 cm2 in size. This was achieved by directly casting a porous polymer substrate onto a graphene sheet produced using the chemical vapor deposition (CVD) method.
The researchers found that a skin-free polymer substrate with a uniform sponge-like structure and proper pore size could offer sufficient mechanical support without reducing permeance of NATMs. In fact, NATMs exhibited 3-5 times higher gas (CO2) permeance compared to the current best-performing commercial polymeric membranes. This work demonstrated the significant potential of these membranes in practical applications such as total organic carbon (TOC) detection in the pharmaceutical and semiconductor industries, and in other gas-liquid separation systems.
Additionally, nanoporous thin films can be engineered to have specific surface chemistries, enhancing their selectivity for particular gases. For example, surface functionalization with specific chemical groups can promote the adsorption of certain gases while repelling others. Furthermore, nanoporous thin films can be easily integrated into membrane-based separation systems, which can offer several advantages over traditional separation techniques such as distillation or adsorption.
Membrane-based separation systems can be more energy-efficient, cost-effective, and environmentally friendly, making them an attractive option for gas separation and purification applications. Overall, the unique properties of nanoporous thin films make them an excellent candidate for gas separation and purification, and ongoing research is focused on developing new materials and methods to enhance their performance in these applications further.
How Are Nanoporous Thin Films Manufactured and Analyzed?
Nanoporous thin films can be manufactured using a variety of techniques, including vapor deposition, self-assembly, and electrochemical deposition. The choice of manufacturing method depends on the specific properties desired for the nanoporous thin film and the intended application.
Vapor deposition is a common method used for manufacturing nanoporous thin films. This method involves depositing a thin film of material onto a substrate using a vapor phase precursor. The precursor is typically heated to generate a vapor, condensing onto the substrate to form a thin film. This process can be done using a variety of techniques, including chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD).
Self-assembly is another technique used for manufacturing nanoporous thin films. This method involves the spontaneous formation of a thin film from a solution or suspension of precursor molecules. The precursor molecules are designed to self-assemble into a nanoporous structure under specific conditions, such as temperature, pH, and solvent composition.
Electrochemical deposition is a third method used for manufacturing nanoporous thin films. This method involves depositing a thin film of material onto a substrate using an electrochemical reaction. The reaction is typically carried out in a solution containing the precursor material and an electrolyte. The substrate is used as an electrode, and an electric current is passed through the solution to drive the deposition process.
Once a nanoporous thin film has been manufactured, it can be analyzed using a variety of techniques to characterize its structure and properties. Some common techniques used for analyzing nanoporous thin films include scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). SEM and TEM are imaging techniques used to visualize the nanoporous structure of the thin film.
SEM uses an electron beam to scan the film's surface and create an image, while TEM uses a beam of electrons transmitted through the film to create an image of the internal structure. XRD is a technique used to analyze the crystal structure of the nanoporous thin film.
This technique involves directing a beam of X-rays at the film and analyzing the diffraction pattern produced. The diffraction pattern can be used to determine the crystal structure and orientation of the film. FTIR is a spectroscopic technique used to analyze the chemical composition of the nanoporous thin film. This technique involves directing infrared radiation at the film and analyzing the absorption spectra produced. The absorption spectra can be used to identify the functional groups present in the film and their chemical environment.
Overall, the manufacturing and analysis of nanoporous thin films is a complex process that requires a multidisciplinary approach. Advances in fabrication and characterization techniques are driving the development of new and innovative nanoporous thin films with improved properties and performance for gas separation and purification applications.
References and Further Reading
Ayesha Kausar, Nanoporous graphene in polymeric nanocomposite membranes for gas separation and water purification-standings and headways, Journal of Macromolecular Science, Part A, 2023, 60:2, 81-9. Available at: 10.1080/10601325.2023.2177170
Luis Francisco Villalobos, Deepu J. Babu, Kuang-Jung Hsu, Cédric Van Goethem, and Kumar Varoon Agrawal, Gas Separation Membranes with Atom-Thick Nanopores: The Potential of Nanoporous Single-Layer Graphene, Accounts of Materials Research, 2022, 3 (10), 1073-1087. Available at: 10.1021/accountsmr.2c0014Top of Form
Chengzhen Sun, Boyao Wen, Bofeng Bai, Recent advances in nanoporous graphene membrane for gas separation and water purification, Sci. Bull., 2015, 60(21),1807-1823. Available at: https://doi.org/10.1007/s11434-015-0914-9.
Dandan Hou, Shengping Zhang, Xiaobo Chen, Ruiyang Song, Dongxu Zhang, Ayan Yao, Jiayue Sun, Wenxuan Wang, Luzhao Sun, Buhang Chen, Zhongfan Liu, and Luda Wang, Decimeter-Scale Atomically Thin Graphene Membranes for Gas–Liquid Separation, ACS Applied Materials & Interfaces 2021 13 (8), 10328-10335. Available at: 10.1021/acsami.0c23013