Photosensitized degradation of paracetamol by rose bengal-modified clays and alginate materials/rose-bengal

MAYER, YANET; WAIMAN, CAROLINA; MASSAD, WALTER A.; NATERA, JOSÉ; ZANINI, GRACIELA

Congreso; The 11th Interfaces Against Pollution; 2021

The presence of contaminants in natural waters (ground and surface waters) and their accumulation in plants and animals is a worldwide major concern. Among the large variety of substances that human activity introduces into the environment are organic pollutants. Within this group, pharmaceuticals are the ones that have given rise to most concern and studies in recent years. Just in the EU, the use of some pharmaceutical products, such as paracetamol, is estimated to be similar to the pesticides amount. Paracetamol is a widespread painkiller and antipyretic drug which is widely consumed throughout the world. Nowadays, it is one of the most frequently found drugs in hospital effluents, water treatment plants, rivers and sludge. Therefore, removing and/or degrading this contaminant in aqueous media is of great interest since clean water is essential for life. In this context, photosensitized degradation is an environmentally friendly option for organic pollutant removal. These processes are mostly based on the use of a photosensitizer that absorbs ultraviolet or visible radiation and reacts with water-dissolved molecular oxygen generating reactive oxygen species (ROS). Subsequently, ROS are responsible for degrading organic compounds dissolved in water. Rose bengal (RB) is a non-toxic dye that can be used as photosensitizer. It is known that RB dissolved in water photogenerates singlet oxygen (O2(1Δg)), a type of ROS [1]. Probably, the main challenge of photosensitized degradation processes is to remove the photosensitizer from water at the end of the photo oxidative cycle. This inconvenience can be solved by incorporating this substance in an easy-to-handle green support without losing its photochemical properties and allowing easy separation. This work aims to synthesize materials composed by RB, montmorillonite clay (MMT) modified with aminopropyltriethoxysilane (APTES) and alginate biopolymer for the formation of MMT-APTES-RB beads in order to generate O2(1Δg) and then photodegrade paracetamol in water.The ability of the synthesized beads to photogenerate ROS was studied by oxygen uptake experiments. For this purpose, ground-state oxygen consumption (O2(3Σg-)) was determined using a specific electrode and a furfuryl alcohol solution (1×10-4M) as substrate for O2(3Σg-) variation recording. After determining that the beads are capable of photochemically generating O2(1Δg), photodegradation assays of paracetamol were performed. These experiments were carried out with irradiation at a wavelength between 500 and 550 nm (green LED) in the presence and absence of MMT-APTES-RB beads under constant stirring. In addition, the adsorption of the contaminant on the beads was studied in the dark. The assays were performed with a paracetamol solution (1×10-4M) at a pH above its pKa so that the phenolic group is deprotonated and reactive towards O2(1Δg). UV-Vis spectra of paracetamol were recorded every 10 min for 90 min. The spectra of the studies in the presence of beads in the dark and those of direct photolysis (irradiation in the absence of beads) showed no variation over time. On the other hand, spectra collected during experiment of irradiation in presence of beads showed spectral changes (decrease in absorbance and appearance of new bands) indicating that paracetamol is degrading and new species are being formed.Results in the present study demonstrate that the synthesized material can photogenerate O2(1Δg) in aqueous solution and this ROS is capable to photodegrade paracetamol dissolved in water. In addition, no quantifiable adsorption of the pharmaceutical was observed on the bead. Photodegradation of this contaminant by direct irradiation was not observed.In addition to the ability to generate O2(1Δg) and degrade organic contaminants dissolved in water, these materials are economical and environmentally friendly because their components are non-toxic and because their synthesis does not involve toxic solvents and does not generate waste. Finally, it is also important to point out that these beads are easy to handle, so they can be effortless removed from aqueous media. These features enable MMT-APTES-RB beads to be proposed as water decontamination materials from emerging contaminants such as paracetamol.References[1] C. R. Lambert and I. E. Kochevar, ?Does rose bengal triplet generate superoxide anion?? J. Am. Chem. Soc., vol. 118, no. 13, pp. 3297?3298, Apr. 1996.