TiO2-catalyzed photodegradation of aromatic compounds: relevance of susceptibility to oxidation and electrophilic attack by hydroxyl radical

  • Fabiola Cristina Ricci Spazzini
  • Thomaz Pol Ximenes
  • Valdecir Farias XimenesEmail author
Research Paper


The application of nanostructured titanium dioxide (TiO2) as catalyst for the photodegradation of drugs and dyes is well established. We aimed to evaluate the importance of the reactivity of aromatic compounds submitted to photodegradation. Specifically, we were interested in the correlation between susceptibility to oxidation and/or to electrophilic attack and the efficiency of degradation. We demonstrated that hydroxyl radical (HO˙) is the most relevant species generated in the photodegradation process. Considering that HO˙ has both oxidizing and electrophilic features, the efficiency of degradation of selected aromatic compounds was performed. The choice was based on their susceptibility to oxidation and/or to electrophilic attack. Benzoic acid (C1), salicylic acid (C2), and protocatechuic acid (C3) were compared regarding their oxidability using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and were ranked as follows: C3 ≫ C2~C1. These compounds were efficiently photodegraded and no significant difference was observed among them. To assess the importance of susceptibility to electrophilic attack, anisole (C4), acetophenone (C5), and nitrobenzene (C6) were selected. Compared to C5 and C6, the higher susceptibility of C4 to electrophilic attack was demonstrated using hypochlorous acid, an electrophilic reagent. The photodegradation showed that C4 was also more susceptible to degradation compared to C5 and C6. In summary, we found that by acting as a powerful oxidant/electrophile agent, HO˙ was able to promote the degradation of aromatic moieties. Considering that the majority of drugs and dyes bear aromatic moieties, our findings explain the great success of photodegradation using metal oxides as catalysts.


Titanium dioxide Photodegradation Aromatic compounds Pharmaceutical drugs Electrophilic susceptibility Nanostructured catalysts 


Funding information

This work was supported by grants from the São Paulo Research Foundation (FAPESP, #2016/20549-5), National Council for Scientific and Technological Development (CNPq #302793/2016-0), and Coordination for the improvement of higher education (CAPES).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

11051_2018_4433_MOESM1_ESM.docx (219 kb)
ESM 1 (DOCX 219 kb)


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Copyright information

© Springer Nature B.V. 2018

Authors and Affiliations

  1. 1.Department of Chemistry, Faculty of SciencesUNESP - São Paulo State UniversitySão PauloBrazil

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