A cheap method to remove microplastics from water

Nov. 13. () –

Researchers from the University of São Paulo (USP) publish a low-cost solution based on nanotechnology in Micron magazine for the removal of micro and nanoplastics from water.

Tiny plastic particles are ubiquitous in today’s world and may be one of the biggest environmental problems, after the climate emergency and the accelerated extinction of species and ecosystems.

Microplastics are in soil, water and air, and in the bodies of animals and humans. They come from everyday consumer goods and the wear and tear of larger materials. They are found everywhere and in all types of environments. An important source is the water used to wash clothes made of synthetic fibers. Microplastics currently cannot be filtered from wastewater and end up penetrating the soil, the water table, rivers, oceans and the atmosphere.

Defined as fragments up to 1 millimeter, microplastics themselves are a well-identified and visible problem. Nanoplastics, however, are a thousand times smaller and are proving to be an even more insidious danger, as they can pass through key biological barriers and reach vital organs. A recent study, for example, detected its presence in the human brain.

“Nanoparticles are neither visible to the naked eye nor detectable with conventional microscopes, so they are very difficult to identify and remove from water treatment systems,” said Henrique Eisi Toma, professor at the Institute of Chemistry (IQ-USP) and author of the study, cited by the FAPESP agency.

The procedure developed at USP uses magnetic nanoparticles functionalized with polydopamine, a polymer derived from dopamine, a neurotransmitter present in the human body. These nanoparticles can bind to micro- and nanoplastic waste, and the combined particles can then be removed from the water. by applying a magnetic field.

“Polydopamine is a substance that mimics the adhesive properties of mussels, which adhere with great tenacity to many surfaces. It adheres firmly to plastic fragments in water and allows magnetic nanoparticles to capture them. This undesirable material can be removed from the water with a magnet” explains Toma.

The process has already proven to be effective in removing micro- and nanoplastics from water, especially in treatment systems. However, the research group also aims to degrade them using specific enzymes such as lipase, which can break down polyethylene terephthalate (PET) into its basic components. The use of enzymes breaks down PET and other widely used plastics into smaller molecules, that can be reused to produce plastic materials.

“Our goal is not only to eliminate plastic from water, but also to contribute to its recycling in a sustainable way,” explains Toma.

PET is a raw material for plastic bottles and other items. It is an important pollutant, especially because its degradation produces terephthalic acid (C6H4(COOH)2) and ethylene glycol (C2H4(OH)2), both toxic.

“Lipase breaks down PET into these initial monomeric forms, which can be reused to synthesize new PET. Our study focused on PET, but other researchers may include other specific enzymes for processing different plastics, such as polyamide or nylon, for example“he says.

In the study led by Toma, magnetic nanoparticles of iron oxide (II, III), or black iron oxide (Fe3O4), were synthesized by coprecipitation and then coated with polydopamine (PDA) by partially oxidizing the dopamine in a slightly alkaline solution. to form Fe3O4@PDA. The lipase was immobilized on this substrate. Hyperspectral Raman microscopy was used to monitor plastic sequestration and degradation in real time.

The term “plastics” refers to a wide range of synthetic or semi-synthetic polymers, most of which are derived from fossil fuels. Its malleability, flexibility, light weight, durability and low cost have ensured its presence in countless products used in everyday life. Concern about the waste and waste produced by this intensive use has led to the search for alternatives, such as bioplastics. Instead of non-renewable petrochemicals, bioplastics are derived from renewable and biodegradable sources.

“It’s a good idea, but before completely degrading, bioplastics also fragment and form micro- or nanoplastics. Being biocompatible, they are even more insidious because they can interact more directly with our organisms and trigger biological reactions,” Toma said.