Alex Silva de Moraes

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.

Ionic liquids have attracted the attention of researchers as possible electrolytes for electrochemical energy storage devices. However, their properties, such as the electrochemical stability window (ESW), ionic conductivity, and diffusivity, are influenced both by the chemical structures of cations and anions and by their combinations. Most studies in the literature focus on the understanding of common ionic liquids, and little effort has been made to find ways to improve our atomistic understanding of those systems. The goal of this paper is to explore the structural characteristics of cations and anions that form ionic liquids that can expand the HOMO/LUMO gap, a property directly linked to the ESW of the electrolyte. For that, we design a framework for randomly generating new ions by combining their fragments. Within this framework, we generate about 10⁴ cations and 10⁴ anions and fully optimize their structures using density functional theory. Our calculations show that aromatic cations are less stable ionic liquids than aliphatic ones, an expected result if chemical rationale is used. More importantly, we can improve the gap by adding electron-donating and electron-withdrawing functional groups to the cations and anions, respectively. The increase can be about 2 V, depending on the case. This improvement is reflected in a wider ESW.