Emerging pollutants are compounds — microplastics, oils, dyes, pharmaceuticals, plasticizers, etc. — that end up in aquatic ecosystems and can pose an environmental and health risk. These pollutants, which are related to human activities, can be found in wastewater, and removing them represents a scientific, technological and societal challenge.
Now, a study led by the University of Barcelona presents an innovative strategy based on using particles of a superhydrophobic nature to degrade pollutants that are difficult to remove from water. The paper by UB researchers Oriol Rius-Ayra and Núria Llorca-Isern, from the Characterization and Processes in Materials Science Research Group (CPCM), is published in the Journal of Environmental Chemical Engineering.
The results of the study open up new possibilities for the design of new superhydrophobic materials with multifunctional properties to remove persistent pollutants, a scientific objective that is one of the research group's lines of research.
Clean water and sanitation for all humanity
Ensuring water availability and a sustainable management of water resources and sanitation is one of the Sustainable Development Goals (SDGs) adopted by the United Nations for the period 2015–2030. However, most of the wastewater related to human activity is still discharged into rivers or the sea without removing the pollutants.
This study describes the multifunctional properties of particles of a superhydrophobic nature to remove and degrade various pollutants in water. Specifically, superhydrophobicity is a characteristic naturally present in some animals and plants to reduce or eliminate surface contact with water molecules.
"The use of superhydrophobic materials is an effective strategy to fight environmental pollution. A few years ago, attempts were made to mimic the superhydrophobicity present in nature, as in the case of the lotus flower (an emblematic example of this property).
"Recently, however, research has progressed to design new materials with various applications," says Rius-Ayra, Serra Húnter lecturer at the UB's Department of Materials Science and Physical Chemistry. "Superhydrophobic materials stand out for their great versatility, with uses such as the self-cleaning of surfaces or the removal of oils and organic solvents."
Superhydrophobic particles with dual functionality
As part of the study, the team prepared a set of particles with two faces, i.e., two regions with different chemical compositions: these are the superhydrophobic Janus-type FeNi3/Al2O3 particles, named after the Roman god with the same name, a classical deity depicted with two faces.
"The fact that the particle has two clearly differentiated domains gives it multifunctional properties that allow it to eliminate three different types of pollutants: organic solvents, stable dyes and microplastics," says professor Llorca-Isern. "Since these materials have two different sides, this makes it possible for each one to act differently.
"Specifically, one side has a greater affinity with organic solvents and microplastics, as it is functionalized with a compound called lauric acid. In contrast, the other side does not contain this compound, but allows for the fast and effective degradation of a fairly stable dye. These two characteristics make the system capable of eliminating different types of pollutants."
To obtain these superhydrophobic materials, first, an alloy is formed, in an energy-intensive process, to finally obtain chemically active materials that are often difficult to obtain under other conditions. The second stage involves functionalization of the surface to impart the new superhydrophobic properties.
"The most complex stage in the processing of these materials is functionalization, as it requires a chemical reaction on the surface with a structure of micro- and nano-sized dimensions. One of the methodological challenges is not to use fluorinated compounds, which are often toxic, and therefore research must be directed towards the use of more sustainable compounds of natural origin," Llorca-Isern says.
"In the future, the possibility of combining different chemical compositions in a single material could broaden the field of application of these materials with superhydrophobic properties," the team concludes.
