A newly developed composite membrane made from two or more materials has showed remarkable colour change when exposed to vapours of different amines. The Mixed Matrix Membrane (MMM) could thus aide in the detection of ammonia or other amine leaks in laboratories or industrial settings.

Ammonia or other aliphatic amines are extensively used as raw material or intermediate products in many chemical, fertilizer and food industries. They are highly toxic and corrosive and become widely dispersed in the environment. They can quickly oxidize in water to produce several N-nitrosamines, which are very hazardous. Direct contact with amines can cause severe respiratory irritation and skin burns.  Occupational Safety and Health Administration (OSHA) has established a workplace threshold limit of 50 ppm for NH3. Concentrations above this level can lead to severe and potentially fatal health issues. Thus, detecting ammonia and aliphatic amines, whether in vapour or liquid form, at both high and low concentrations is essential for effective environmental and water monitoring and are extremely important for preventing onsite gas leakage and disasters.

Recently, 2D MOF nanosheets have attracted more attention than their 3D bulk counterparts. 2D MOFs provide numerous exposed active sites, an extremely high surface-to-volume atomic ratio, and a larger specific surface area, which enhance their performance in various applications such as catalysis, gas separation and storage.

A team of researchers led by Dr Monika Singh at Institute of Nano Science and Technology, Mohali, have synthesised a highly water-stable, ultrathin Ni-btc nanosheets, with a thickness of approximately 4.15 nm, using the 2D oxide sacrifice approach (2dOSA), says a press release. These MOF nanosheets exhibited exceptional sensitivity in detecting aliphatic amines and ammonia in an aqueous medium through a unique “turn-on” fluorescence process, which is rare.

The researchers used these to fabricate a Mixed matrix membrane of MOF nanosheet that showed a naked-eye colour change in the presence of NH3 and aliphatic amines. The response of colour change differs in each case, enabling MMMs to visually distinguish different types of amine vapours. These membranes are also reusable and can be easily employed for real-time detection of amines.