Environmental pollution due to chemical and other toxic substances is currently a major global challenge that requires efficient and urgent solution. Currently, emerging pollutants from various personal care and pharmaceutical products have been on the rise. These substances are mainly found in water at various concentration that poses a great threat to the environment and human health. An example of a pharmaceutical product is the ibuprofen drug used for treating different inflammatory conditions. However, part of the drug is normally excreted by patients in their original forms thus causing surface water pollution due to their high annual output.
Presently available water and sewerage treatment strategies are not effective for drug elimination. This has led to the development of advanced treatment processes with high removal rates for treatment of the emergent pollutants. These processes are however costly in terms of energy and resources demands. Recently, solar energy and TiO2 nanoparticles have been identified as a promising efficient alternative energy source for wastewater treatment through degradation by photocatalysis. Unfortunately, TiO2 nanoparticles cause several environmental impacts such as interference with the redox cycles of microorganisms and micro molecule degradation due to their highly toxic nature. Therefore, effective approaches for addressing the aforementioned challenge are highly desirable. Recently, preparation and optimization of nanostructured self-assembled thin films using the layer-by-layer technique for TiO2 immobilization have been studied to prevent the leaching of the photocatalysts into the environment. This requires understanding the effects of incorporating different materials in the polyelectrolyte multilayers.
Mário César Vebber (PhD candidate), Dr. Janaina da Silva Crespo and Dr. Marcelo Giovanela from University of Caxias do Sul in Brazil used response surface methodology to evaluate various deposition conditions that results in favorable and best properties for the application of nanostructured self-assembled thin films in the photodegradation of ibuprofen from an aqueous medium. Fundamentally, the authors prepared a combination of poly (acrylic acid), poly (allylamine hydrochloride) and TiO2 to evaluate the deposition parameters and photocatalytic properties. The work is currently published in the journal, Chemical Engineering Journal.
The photoactivity of the self-assembled thin films was significantly affected by the TiO2 concentration and the pH of the cation solution. They were capable of reducing the ibuprofen concentration by 95% and degrading their aromatic centers by 50%. This was effectively achieved at a pH of 6.5 after only 150min. While the authors chose to focus their study on ibuprofen, it is important to notice that photooxidation with TiO2 is effective towards a wide range of emergent pollutants and most pharmaceuticals. The high degradation efficiencies were ascribed to the large active surface area due to the nanostructured topology. Furthermore, the film roughness was noted to be directly proportional to the TiO2 concentration.
In summary, the Brazilian scientists are the first to mathematically model the thickness and photoactivity of the self-assembled thin films using both designs of experiments and response surface methodology methods. They obtained suitable deposition parameters and properties for photolytic applications. This method is environment friendly as it uses sunlight energy, does not requires the addition of, nor it releases any chemicals during the water treatment, and thus it is a promising alternative to conventional effluent treatment methods.
Vebber, M., da Silva Crespo, J., & Giovanela, M. (2019). Self-assembled thin films of PAA/PAH/TiO2 for the photooxidation of ibuprofen. Part I: Optimization of photoactivity using design of experiments and surface response methodology. Chemical Engineering Journal, 360, 1447-1458.Go To Chemical Engineering Journal