Chemical Vapor Deposition Approach Developed As Scalable Method for Making Covalent Organic Framework Thin Films

Over recent years, covalent organic frameworks have gained significant attention due to their unique properties and potential uses in different fields. However, there is a challenge in finding a reliable method to create these films with controlled thickness and high quality.

What are COFs?

Covalent organic frameworks (COFs) are a type of crystalline polymer network useful for their versatile functionality, high porosity, and tunable architecture. They are useful in filtration systems, energy generation, drug delivery, and making sensors and semiconductor devices.

COFs have the potential to be useful in different catalytic processes, such as breaking down carbon dioxide into useful compounds like formic acid and ethylene. They are also useful in controlling pore size, serving as membranes for desalination and helping replace energy intensive processes like desalination. In the electronics industry, these crystalline networks can be used as battery separators and organic transistors.

COFs are special because they are polymers but arrange themselves in repeating, ordered structures, making them crystalline. These structures resemble chicken wire, where hexagonal arrangements repeat themselves on a two-dimensional plane. As they stack on top of each other, a layered 2D material is created.

Traditional solution-based approaches to creating COFs are known for their slow reactions, which produce powders that are difficult to process into adaptable form factors for functional uses. There is also a need for easy and fast synthesis methods for producing crystalline and ordered COF thin films.

All-in-One Synthesis Technique

The production methods are a challenge preventing COFs from being used more widely. They typically involve lengthy solution processing, which is more difficult to accommodate in industrial settings.

Led by Rice doctoral student Jeremy Daum, the research team developed a synthesis technique that makes it possible to produce ordered 2D crystalline covalent organic frameworks in record time. Producing the powders for the solutions required to generate COFs usually takes 3 to 5 days, but the method developed by the researchers takes only 20 minutes or less.

COFs are typically produced through solution processing, which does not create alignment on the film. The synthesis technique developed by the researchers allowed them to control the sheet orientation and ensured that pores were aligned. They analyzed their samples using the Advanced Photon Source at the Argonne National Laboratory to ensure that the films they developed had the right molecular structure.

Microscopy studies suggest synthesizing organic molecules requires temperatures up to 644 degrees Fahrenheit (340 degrees Celsius). It is believed that heating organic molecules up to such high temperatures will prevent the right reactions from happening. However, the experts discovered that chemical vapor deposition is a viable way to create organic materials.

To create the COFs, Daum and his colleagues built an ad-hoc reactor using discarded equipment parts in the laboratory and other inexpensive materials. The entire process was very cheap to assemble. The researchers hope that establishing a scalable, robust approach to producing various COF films will enable better applications of COFs in energy storage, catalysis, and other uses.