Shield against deadly chemicals

On April 4, 2017, in the war-torn Syria, a chemical bomb was detonated in the town of Khan Shaykhun. This bomb killed 74 people and injured more than 500 people. The bomb contained a deadly and banned chemical called sarin. Inhaling a few milligrams is enough to kill a healthy person within minutes. What’s more, the nerve gas can even be soaked in by the skin. As a result, it is one of the deadliest chemicals. 

However, several deadly chemicals, thought not as powerful as sarin, are routinely used as pesticides in agriculture. In fact, there has been many reports of farmers succumbing to the exposure. While spraying pesticides, even if their mouth and nose are covered, farmers face the risks of skin exposure to the harmful chemicals. There is an estimated 3,00,000 deaths globally due to pesticide poisoning, of which a majority are due to contact with skin.

Absorber of gases

In this light, a novel clothing that can protect one from deadly gas attacks has been developed, reveals a recent report in Chemical Materials. Gregory Parsons, a professor of Chemical and Biomedical Engineering in North Carolina State University, USA, and his team have developed a metal–organic framework (MOF) compound that can stick to a fabric that can destroy deadly poisons like sarin within minutes. This has been called as the ‘MOF Cloth’. “The MOF-Cloth we describe could be used in clothing or face masks, or in protective fabric sheets for ground covers or tarps, or in other formats depending on the threat,” details Gregory. The threat could be from sarin in a war or a mist of pesticides in the field.

Gregory’s team used intricate chemistry to merge UiO-66NH2 with polyethylene fibres. UiO-66NH2 is a type of MOF made from Zircon oxide and terepthalate. The latter is the chemical used in the common PET bottles. UiO-66 compounds, especially the UiO-66NH2, has been in the news lately for its ability to absorb a large amount of gases. The molecule gets assembled into an intricate, highly porous cage-like structure which can attract and retain large amount of gases. It is being touted to be the proverbial carbon sink, that is being able to absorb green house gases like carbon dioxide better than any other absorbers. It is also a fast-acting catalyst splitting up complex organic molecules like pesticides into manageable compounds. 

But UiO-66NH2 does not bind to fibres on its own because the polypropylene fibres have neutral surfaces with methyl groups jutting out.  UiO-66NH2 cannot bind to methyl groups. Gregory’s team deposited a thin layer of a metal oxide such as aluminium oxide to the polypropylene. Using another compound (Beta-cyclodextrin and Cetryltrimethylammonium bromide complex) which on one side can attach to the metal oxide and on the other to the polypropylene, they attached the MOFs to the fabric. 

Securing worker safety

Gregory’s team used woven fabrics directly to deposit MOFs and found the catalyst attach itself firmly to the fibres. The procedure involved simple dipping of the fabric into a solution of UiO-66NH2, rinsing and drying (as in a dyeing vat) giving hopes of producing the special fabric in  large quantities. The team also tested the efficacy of the fabric by exposing it to a pesticide, dimethyl-4-nitrophenyl phosphate (DMNP or Paraoxon).

While ordinary polypropylene fabric pieces retained almost the entire pesticide sprayed on them even after 24 hours, on the UiO-66NH2 coated fabric almost half the amount was reduced by hydrolysis in five to six minutes. Hydrolysis takes the sting out of sarin and such poisons.

“Our work provides a step toward protective clothing and other equipment to secure worker safety exposed to the risks of chemical weapons,” says Gregory. However, wearing this novel shield is a little away in time. “The decontamination test is done at a favourable pH.  Therefore, before the as-formed MOF-cloth can work effectively in the field, more research is needed for ways to maintain correct pH,” cautions Gregory.

If that can be tweaked, which Gregory hopes is not impossible, we will have a wearable shield that can protect us from accidental, deliberate or even occupational exposure to chemical warfare agents.