Scientists at Tomsk Polytechnic University (TPU) in Russia, working in collaboration with international researchers, have developed a method to convert PET plastic waste into porous materials for use in water and gas purification.
The technology allows discarded plastic to be used as a raw material for producing metal-organic frameworks — known by the acronym MOF — which can be applied, among other uses, in substance separation and catalysis processes.
MOFs are highly porous crystalline materials capable of functioning as a kind of ‘molecular sponge’. Thanks to this structure, they can selectively capture certain molecules present in water or air, giving them potential for use in purification and treatment processes.
To produce the new materials, the researchers ground PET waste into particles smaller than one millimetre and subjected them to a chemical process that yields 2-nitroterephthalic acid and 2-iodoterephthalic acid. These compounds are subsequently used in the synthesis of the metal-organic frameworks.
According to the researchers, the key innovation lies in combining steps that, in conventional methods, are carried out separately. Rather than first decomposing the PET, isolating and purifying the intermediate products and only then proceeding with chemical modification, the new method integrates these operations into a single process.
‘Electrophilic modification of the aromatic portion of PET is considered an extremely complex process. That is why the processing and chemical modification of the resulting terephthalic acid are normally carried out sequentially. First, the polymer is decomposed, then the intermediate product is isolated and purified, and only then is the desired functional group introduced into its structure,’ said Olga Guselnikova, a researcher at the TPU International Research Laboratory ‘Non-Covalent Interactions in Materials Chemistry’.
According to the researchers, the principal innovation lies in combining two steps that are normally performed separately.
According to Guselnikova, integrating the different steps reduces the number of operations required, as well as the amount of equipment and materials needed.
‘We combined these two steps into a single reaction process. This allowed us to reduce the number of stages, eliminate the need to isolate and purify various intermediate compounds, and decrease the amount of equipment required, thereby reducing the cost of the technology,’ she added.
The team tested the method using different PET sources, including food containers, plastic bottles, industrial waste, polyester fabrics, and mixtures containing the polymer. Temperature, reaction time, and reagent quantities were adjusted to increase the yield of the compounds subsequently used in MOF production.
Results indicated that materials produced from the waste displayed crystallinity, microporosity, and thermal stability characteristics comparable to those of reference materials. Calculations carried out by the team also point to a significant reduction in the production costs of the compounds used in MOF synthesis.
For compounds containing nitro groups, the estimated cost is five to seven times lower than that of commercial equivalents. For iodine-containing compounds, the researchers estimate a reduction of between 75 and 80 times.
‘Using low-cost components derived from PET waste could make MOFs more accessible for water purification and chemical production. For example, iodine-containing MOF materials show greater capacity to capture chlorinated organic pollutants, while structures containing nitro groups can act as effective catalysts,’ said Guselnikova.
In addition to enabling the reuse of plastic waste, the method could help reduce the production cost of materials destined for water treatment and other chemical processes. The researchers now intend to scale up the process and evaluate the full production cycle, from the collection and grinding of PET through to the use of the materials produced.
Source: TV Brics
Source: Diário Económico
Original article: https://www.diarioeconomico.co.mz/?p=548311
