Photoassisted Oxidation of the Recalcitrant Cyanuric Acid Substrate in Aqueous ZnO Suspensions

Abstract

The photoassisted oxidative transformation of the highly recalcitrant cyanuric acid was examined in the liquidsolid regime at pH 3 and natural pH 7.5 under UV irradiation in oxygen-and ozone-saturated ZnO suspensions using ZnO as a photomediator. Loss of cyanuric acid was assayed by HPLC UV absorption spectroscopy, whereas intermediates and final products were determined by HPLC ion chromatography (IC), by MS techniques using an electrospray ionization mass spectrometer operated in the negative-ion mode, and by FT-IR spectroscopy. Final reaction products were CO 2 gas and NO 3 -ions. The measure of nitrate in solution quantified the degree of mineralization of the substrate; its concentration in solution was lower than indicated by the loss of cyanuric acid owing to adsorption of the latter to the ZnO surface. Some degree of corrosion of ZnO occurred as evidenced by the quantity of Zn 2+ present in acidic and near-neutral aqueous media before and during the photoassisted process. The possible site(s) and mode(s) of adsorption of cyanuric acid on ZnO have been inferred from theoretical calculations of point charges; the position(s) of attack of the substrate by • OH radicals was inferred from frontier electron density calculations. Mechanistic considerations are based on the possible involvement of Zn 2+ -cyanurate species (chemisorbed cyanuric acid) in the degradation of such a recalcitrant substrate, inasmuch as the use of TiO 2 -photoassisted processes under similar conditions have so far failed to oxidize cyanuric acid.

Comparative study of MnO2 nanoparticle synthesis by marine bacterium Saccharophagus degradans and yeast Saccharomyces cerevisiae

“…The peak at 2922.59 cm −1 signifies CH 2 stretching vibration of fat (Qiu and Wang 2014). The peak at 529.50 cm −1 arises due to the side chain in plane C-N bending vibration (García-López et al 2007). In the FT-IR spectrum of MnO 2 NPs, the peak of 3409 cm −1 from S. cerevisiae cells was shifted to 3351.14 cm −1 .…”

Spectral and Thermal Degradation of Melamine Cyanurate

“…The medium peak at 2825 cm −1 is assigned to N-H deformation. Usually this band appears in the range of 2828 cm −1 -2907 cm −1 in the cyanuric acid spectrum [22]. A medium peak at 2698 cm −1 can be assigned to NH 2 asymmetric stretching of vibration [19].…”

“…This may be due to intermolecular interaction through the NH 2 groups of melamine molecule. This causes the rising of their frequencies for bending type of motion [22]. The triple bond C-N stretching frequency in the IR spectra of cyanurates should be assigned to a strong polarization of the cyanurate anion by melamine cation [4].…”

“…is due to the side chain in plane C-N bending vibration [22]. Figure 3 shows the TG-DTG spectra recorded for the synthesized melamine cyanurate.…”

Perspectives and Advances in Photocatalysis

“…The chemical properties of cyanuric acid may have contributed significantly to its resistance to photocatalytic degradation. Cyanuric acid is a stable substrate, poorly soluble in water, and is a weak acid in aqueous media (pK a1 = 7.0, pK a2 = 11.3, and pK a3 = 14.5), which occurs as enol in a tautomeric mixture with 2,4,6-trioxo-striazine or isocyanuric acid (7) (the keto form) (Jańczyk et al 2006;García-López et al 2007). In alkaline solution, the acid exists in the enolic form, whereas in acidic media (pH < 6), the keto form is the more stable tautomer.…”