Environmentally friendly synthesis of catalyst based on chitosan for the degradation of phenolic contaminants

POSSETTO, DAVID; NATERA, JOSÉ; SACCHETTO, JULIETA; PRAMPARO, JULIETA; MISKOSKI, SANDRA; REYNOSO, AGUSTINA; GATICA, EDUARDO; MASSAD, WALTER A.

Conferencia; Catalysis Virtual 2020; 2020

The main degradation pathways for pollutants are chemical ones, which include those transformations thattake place in the presence of solar radiation, known as direct or indirect photoreactions. In this work, the focus will beon sensitized photolysis reaction, it requires the presence of another molecule, a dye, which will absorb light radiationand produce excited states with the ability to initiate a cascade of photoprocesses in which highly reactive species aregenerated. The main problem with these processes lies in removing the dye once the reaction is complete. With the useof polymeric dyes (PD) whose water solubility varies with the solution's pH this issue can be minimized or completelyresolved since it allow its extraction, after being used in the removal of contaminant, with a simple change of pH in themedium.The polymeric dye is composing by two naturals reactive, principally the sensitizer flavin mononucleotide(FMN) and the chitosan (CH). Among other relevant characteristics, we can mention: they are biomolecules, non-toxic,biocompatible, food and cosmetic additives, which makes CP completely friendly to aquatic environments.For CP synthesis, 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) was used to crosslinker, toproduce a phosphoramidate bond through EDC, which is formed from the phosphate group of FMN and the aminogroup of CH. A polymer of the same colour and similar photophysical properties of FMN was obtained.Another relevant characteristic of this PD is that it is more photostable than the free dye and is easily extractedfrom the medium by pH change, since it is soluble in acetic acid solution and precipitates in pH solution > 5.9.To evaluate the photocatalytic activity of the synthesized polymer, trihydroxybenzenes (THB) compoundswere chosen. THB are recognized pollutants and in homogeneous media are reactive towards singlet oxygen (1O2). Thephotosensitised degradation of THBs by CP was monitored by oxygen consumption and UV-Vis spectroscopy. In allcases, the presence of THB increases the rate of oxygen consumption when irradiating the CP solution alone. On theother hand, spectral changes were recorded in the irradiated solutions. To determine the reactive oxygen species in thedegradation mechanism different specific inhibitors was used. These experiments show the participation of 1O2, H2O2and hydroxyperoxil radicals in the THBs degradation. Furthermore, laser flash photolysis experiments showed that theelectronically excited states of CP also participate in THB degradation.The use of a photosensitized heterogeneous system represents a great advantage over homogeneous systems.On the hand, the CP has a greater photostability, which allows it to be used for longer times, and on the other hand, itis the most promising of these CP, is that it can be extracted after photosensitized reaction, leaving the aquaticenvironments without contaminants or dyes.