[ Un article de The Conversation écrit par Marco Daturi – Professeur de chimie, Université de Caen Normandie – et Christian Serre – Directeur de recherches spécialiste en chimie des matériaux, Université Paris Dauphine – PSL ]
Currently, solutions to reduce its impact on our health remain insufficient. Indeed, traditional filters based on active coals have notable limits: their effectiveness decreases over time and environmental conditions, especially when ambient temperature and humidity vary. These filters can even become sources of formaldehyde at the end of life. They are therefore very limited in terms of safety.
Other solutions could be envisaged, such as the use of zeolith filters. However, these porous materials are sensitive to the presence of water and are penalized by considerable energy requests during their regeneration. The mineralization of formaldehyde (and other pollutants) at room temperature requires, on the other hand, catalysts based on noble metals, therefore very expensive.
Obviously, it would be more judicious to decrease this type of pollutants at the source, but they are present in a diffuse manner in most building materials, as well as in furniture and clothing, because formaldehyde is a preservative widely used to avoid the formation of mosses and fungi, especially when consumer goods are transported by boat from their production centers. While waiting to change our economic model, we should therefore find a solution to this pollution.
To look for more effective solutions than those that exist, we have looked into porous materials on a very small scale (size of “pores” of the order of the molecule or the hundred molecules) called “MOF” (for Metal-Organic Frameworks), and have added particular chemical functions within pores, the pyrazoles.
These hybrid materials, real molecular sponges, have shown exceptional potential for the capture of formaldehyde. They make it possible to selectively capture tiny traces of formaldehyde in the presence of humidity, offering a new route to improve the quality of indoor air.
Why does the formaldehyde are a problem?
In closed spaces, indoor air can be up to five times more polluted than outside air. The formaldehyde, present in almost all interior environments, frequently exceeds the thresholds recommended by the WHO. For example, in new houses, its concentrations can reach between 20 and 60 micrograms per cubic meter of air, or even more than 100 micrograms per cubic meter of air in poorly ventilated rooms (for a threshold at 100 micrograms per cubic meter of air for thirty minutes).
Many people do not even realize that the air they breathe at home can be as, even more, polluted than that in a big city. Under these conditions, it is not easy to reduce this invisible and unknown risk.
MOF: an innovative solution
THE Metal-Organic Frameworks or MOF are extremely modular porous materials. The discovery of these crystallized hybrid porous solid porous began over twenty-five years ago. Like LEGO, they are made up of constructions that can be assembled to the way depending on the physico-chemical properties sought. Their production on an industrial scale, as well as the first industrial applications, were postponed a few years ago and mainly concern the capture of the CO2degradation of pollutants or gas storage.
These bricks are of two types: on the one hand inorganic entities, made up of metals in their cationic form, and on the other hand organic molecules mainly made up of carbon and oxygen or nitrogen, called ligands.
The assembly of these two types of bricks leads to the formation of a network of pores or cavities of nanometric size (one billionth of meters). Like sponges that can store water in their pores, MOFs are capable of capturing a wide diversity of pollutants, for example toluene with efficiency much higher than conventional filters.
We have made and tested a family of MOF with a very specific organic brick, containing pyrazoles groups, which form very strong links with formaldehyde molecules and thus allow them to be captured in a very effective way.
Thus, one of our MOF has an adsorption capacity around 20 % in mass, almost 2 to 3 times more than commercial filters, and retains its efficiency even in strong humidity conditions, typical of our homes or when the room temperature increases.
We can also synthesize it in water, at ambient pressure and a temperature below that of boiling water, which facilitates its large -scale production. The first production tests show the possibility of easily manufacturing tens of kilograms of this material and everything suggests that a very large-scale production (1-100 tonnes) is feasible.
A sustainable and regenerable performance
One of the challenges of air filters is their saturation, that is to say the moment when the filter is no longer effective because all the pores are full.
Current filters should most of the time be changed and the cremated filter. On the contrary, the MOF that we have developed perhaps regenerated, that is to say that its pores will be emptied, by plunging the filter into water at room temperature for a few hours, the formaldehyde being then evacuated in the sink.
In addition, our MOF does not release formaldehyde below a temperature of 75 ° C – while others relaar all the polluting molecules accumulated at lower temperatures, which can result in a “pollution peak” than in the initial conditions where the pollutant is diffuse. To give an idea, in a car in the middle of summer, temperatures can vary drastically between its use with air conditioning (20 ° C) and stopping in full sun, where temperature can be closer to 50 ° C.
Finally, this new MOF is very “selective”, that is to say that its efficiency of capture of formaldehyde is very little impacted by the presence of other pollutants of indoor air.
In terms of perspectives, tests are underway with industrialists or specialists recognized in the field of indoor air quality in order to integrate these new adsorbents into systems, active or passive, air purification. The large -scale production of these MOFs should also reduce the manufacturing cost of the MOF.
In the longer term, it will be interesting to couple the capture of formaldehyde to a process of catalytic regeneration allowing to extend the duration of use of these MOFs to purify the indoor air. Other potential applications are later envisaged for the capture of other harmful pollutants of indoor air such as acids for the protection of works of art or for the detection of organovolutile compounds.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
