Using Nanomaterials to Decontaminate Water

Molybdenum Disulfide can be of great use in water filtration, but difficulties in producing large amounts of the substance have hindered its use. Now, an international team of researchers has found that the production of the substance in nanoribbons could allow the scaling up of fabrication. 

Molybdenum Disulfide (MoS₂) is a compound that is widely used in the decontamination and filtration of water. It also has uses in other fields such as energy storage, and chemical and light-sensing thanks to its superior electronic properties. But, thus far high costs and the relative complexity of fabrication have prevented the scaling up of MoS₂-based techniques and thus, have impeded its wider adoption.

Now an international team of researchers believes that they have found a solution to these challenges. In a paper published in the journal Advanced Materials, the team layout a way to better refine and produce this unpredictable and hard-to-control inorganic compound composed of molybdenum and sulfur. Thus, they provide a road map that could have significant benefits in the diverse fields of environmental conservation, energy, and consumer electronics.

There are many different ways to fabricate this material, but no one has yet been able to make it in a controlled and tunable dimension in large quantities, in a low-cost, reproducible fashion.

Donglei (Emma) Fan, corresponding author of the paper and associate professor, Cockrell School of Engineering’s Walker Department of Mechanical Engineering and Texas Materials Institute

Nanoribbons — The Key to Large-scale Molybdenum Disulfide Fabrication

Previous methods of fabrication of MoS₂ have only allowed scientists to synthesize the silvery black solid in very small amounts. This small quantity of the substance is attached to a substrate, making it challenging to use. The team tackled this challenge by producing MoS₂ in the form of thin nanoribbons.

By cutting the cost of producing a gram of MoS₂ by 3,000 times, Fan and her team’s breakthrough method allows the fabrication of thin nanoribbons of MoS₂ in large volumes with a single synthesis producing a ‘spoonful’ of the material.

This may not initially sound like ‘scaling up,’ but it has to be contrasted with previous production methods that have managed to produce only a microscopic amount of the substance.

The team also says that there is technically no limit to the amount of MoS₂ that the new method of fabrication can produce with further development and improvement. 

The MoS₂ that the team was able to synthesize was freestanding and in a powder form consisting of longitudinal MoS₂ nanostructures — nanoribbons, — and their oxide hybrids with tunable dimensions. 

During fabrication, the team’s method allows the collection of nanoribbons of MoS₂ at different reaction stages, meaning that the production method presented in the paper is high yield and particularly robust. 

The MoS₂ nanoribbons can readily be removed from their substrate and dispersed in a solution. From there, the team demonstrated that these nanoribbons can be manipulated, and even assembled in controlled patterns, and directly onto microelectrodes with UV‐click‐chemistry — a way of using light to join molecules that replicate natural examples. 

Real World Applications 

The easy dispersal of the nanoribbons in a solution is the element of the team’s work that makes it of particular use in water treatment. One of the most important functions of MoS2 in filtration is the removal of mercury — a dangerous element that can cause brain and kidney damage, especially in the young. This damage can occur by direct exposure to contaminated water, or by the introduction of mercury to the food chain via the consumption of exposed organisms by fish. 

The fact that the team’s research could lead to the scaling up of MoS₂ nanoribbon production makes the material a competitive alternative to other mercury-reducing modalities in terms of both cost-effectiveness and efficiency. Thus, this lab-based breakthrough could promise a significant and positive ‘real-world’ effect.

This is an attractive material because it has unique properties for various applications with potential to change people’s lives. Being able to make the material with controlled dimensions and in a large quantity, assemble it and integrate it with pre-made devices brings MoS2 a step closer to practical applications, not just staying in the lab.

Donglei (Emma) Fan

Sources and Further Reading

Huang. Y., Yu. K., Li. H., Fan. D., et al, [2020], ‘Scalable Fabrication of Molybdenum Disulfide Nanostructures and their Assembly,’ Advanced Materials. [https://doi.org/10.1002/adma.202003439]