Advanced oxidation processes are technologies currently being developed and applied to degrade many emerging contaminants that require special attention due to the risks associated with health and the environment. However, the transformation products (TPs) produced by the degradation of these contaminants have attracted little attention from the community regarding their effects on degradation processes, persistence, and environmental toxicity. To present this concern to the scientific community, this article provides data and information that allows us to identify that TPs cannot be pushed to the background or completely ignored in environmental decontamination studies. To this end, heterogeneous photocatalysis was chosen as the primary data collection mechanism due to its interdisciplinary nature. Computational simulation tools, such as Density Functional Theory (DFT), which are widely used to study the properties of materials and contaminants, are very useful and should be applied more frequently to understand the properties of TP. These compounds can interact with photocatalysts and impact the degradation performance of the primary contaminant. Monitoring TPs in degradation reactions is also a challenge due to the lack of analytical standards, the variability of the compounds formed, and the low concentrations produced. The results presented here allow us to conclude that these TPs can affect photocatalytic performance, induce questionable conclusions about their performance, be more toxic than the contaminant of origin, and, above all, contribute relevant information to conclude about the degradation mechanisms.

In this work, we report on the development of single-phase ceramic powders with excellent thermal and colorimetric stability using the sol-gel combustion method for the production of 2+ zinc oxide doped with Co (Zn1-xCoxO; x= 0.0, 0.04, 0.1, and 0.2 mol). The techniques of Xray diffraction (XRD), high-resolution scanning electron microscopy (SEM-FEG), X-ray dispersive spectroscopy (EDS), and UV-Vis spectroscopy (UV-Vis) were used to characterize the pigments produced. The XRD patterns of the samples heat-treated at 1000 ºC/2h indicated obtaining single-phase powders, confirmed by the Rietveld refinement. The pigments showed agglomerated particles with an almost spherical shape. CIELab measurements showed that pigments modified with 10 and 20% cobalt, subjected to heat treatment up to 1000 ºC, showed better values of the a* coordinate, thus indicating the formation of a green pigment with better tonality.