Role of Hydroxyl, Superoxide, and Nitrate Radicals on the Fate of Bromide Ions in Photocatalytic TiO2 Suspensions

F Parrino,S Livraghi,E Giamello,R Ceccato,L Palmisano

doi:10.1021/acscatal.0c02010

F Parrino, S Livraghi + Show 3 more

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https://doi.org/10.1021/acscatal.0c02010

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Abstract

The influence of bromide ions on systems containing highly reactive radical species is of great interest for environmental remediation, atmospheric chemistry, and the synthesis of high-added-value ...

Highlights

Bromide ion is a ubiquitous species in natural aqueous systems
The latter has been classified by the International Agency for the Research on Cancer (IARC) as a potentially carcinogenic species, and the World Health Organization (WHO)[16] guidelines reported in 2011 that a concentration of bromate of 3 μg L−1 is associated with an upper-bound excess lifetime cancer risk of 10−5
The results presented above on the role of hydroxyl and superoxide radicals allow a clarification of some mechanistic aspects related to the recently reported photocatalytic production of elemental bromine,[21,22] as briefly summarized below for the benefit of the reader

Summary

INTRODUCTION

Bromide ion is a ubiquitous species in natural aqueous systems. Its concentration is quite low in rainwater, ranging from 0 to 110 μg L−1,1 but reaches considerable values in groundwater, between 0.01 and 2 mg L−1,2 and in seawater, typically about 70 mg L−1. As far as human activities are concerned, it has been shown that the ozonation of bromide-containing water, in addition to the desired effects of water pollutant degradation, quantitatively induces the oxidation of bromide to the bromate ion The latter has been classified by the International Agency for the Research on Cancer (IARC) as a potentially carcinogenic species, and the World Health Organization (WHO)[16] guidelines reported in 2011 that a concentration of bromate of 3 μg L−1 is associated with an upper-bound excess lifetime cancer risk of 10−5. The spin-trapping technique is based on the detection, by electron paramagnetic resonance (EPR), of stable radical adducts formed by the reaction of a short-lived radical species (e.g., OH, HO2) with a suitable trapping molecule This was done both in the presence and in the absence of bromide and nitrate ions and at different pH values. These mechanisms could help to tackle the problem of brominated oxidation intermediates, hazardous compounds formed when advanced oxidation processes are used for environmental remediation of bromide-containing effluents

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS

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