Water crisis has been documented as an important global risk by the World Economic Forum and rightly so. Fresh water supplies are subjected to constant contamination owing to increasing industrialisation and urbanisation. Studies have identified metal-based oxoanions, such as arsenate, as one of the most toxic contaminants of water. The emerging effects of such oxoanions have made them the center of research interests around the globe.
An often-used strategy of sequestering oxoanions involves adsorbing them onto a material and then exchanging the harmful ions with harmless ones using an ion exchange based purification. However, this method is not specific towards oxoanions, which are usually present at low levels in water, while other potentially desirable anions such as chlorine, which need not be removed, are lost in the process.
To overcome this challenge, Prof. Sujit Ghosh’s group at IISER Pune has developed a specialised material which they like to call ‘IP-comp6’. The team developed this new material in such a way that apart from anion exchange, certain specialised binding sites in the material can interact with specific oxoanions like arsenate.
To develop this material, the team employed what is referred to as a bottle-around-ship strategy in the field of materials science. This resulted in a new composite material with properties of both its components, that of a metal-organic cage and a porous aerogel material.
The ‘bottle’ here corresponds to a metal-organic gel that forms the framework for this material. This framework has an infinite network structure; thus, it does not dissolve in any solvent. This facilitates the sequestration process. The ‘ship’ corresponds to metal-organic polyhedra cages, which are trapped inside the gel, and together they form a system that the team likes to call ‘IP-comp6’, which can selectively trap oxoanions.
This material is inherently cationic in nature. This material can also be modified for sequestering different kinds of oxoanions and is a promising tool for overcoming the oxoanion challenge.
In order to explore the practical utility of the material, the team collected samples of natural drinking water from two different locations in West Bengal’s Malda district, which are widely known as highly arsenic affected areas in India. The new hybrid material was found to reduce the arsenic levels dramatically to well below the WHO permitted level (>10 ppb) of drinking water.
These findings present a new pathway for the development of a variety of advanced sorbent materials for real-world water purification.
Sahel Fajal, Writakshi Mandal, Samraj Mollick, Yogeshwer D. More, Arun Torris, Satyam Saurabh, Mandar M. Shirolkar, Sujit K. Ghosh (2022). Trap inlaid cationic hybrid composite material for efficient segregation of toxic chemicals from water. Angewandte Chemie 61(32) e202203385.
- By Srushti Chipde, with inputs from Fajal Sahel and Writakshi Mandal