Mass spectrometric imaging reveals photocatalytic degradation intermediates of aromatic organochlorines resulting from interfacial photoelectron transfer and hydroxyl radical abstraction on semiconductor nanoparticles

• Published in: Analytica chimica acta 2019-04, Vol.1054, p.104-113
• Main Authors: Tang, Xuemei, Qi, Yinghua, Zhang, Wenyang, Zhang, Juan, Jiang, Ruowei, Zhong, Hongying
• Format: Article
• Language: English
• Subjects: Aquatic environment; Atomic properties; Biodegradation; Chemical bonds; Chlorine; Chlorobenzene; Chlorobenzenes; Chlorothalonil; Contaminants; Dechlorination; Electron density; Environmental degradation; Food chains; Free radicals; Hexachlorobenzene; Hydroxyl radical; Hydroxyl radicals; Interfacial photoelectron transfer; Intermediates; Mass spectrometry; Nanoparticles; Organic chemistry; Organochlorine compounds; Photocatalysis; Photodegradation; Photoelectron capture dissociation; Photoelectrons; Pollutants; Purification; Quantum dots; Selectivity; Soil contamination; Spectrometry; Steric effects
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2018.12.032

Organochlorines are highly persistent and toxic contaminants that are widely distributed and accumulated in various aquatic or soil environments as well as food chains. Heterogeneous photocatalytic degradation of such pollutants by using semiconductor nanoparticles has been recognized as one of the effective purification ways. Understanding of degradation mechanisms and designing of highly efficient semiconductor nanoparticles require structural identification of various degradation intermediates that are difficult to achieve with current spectroscopic techniques. Herein a mass spectrometric approach was developed to tackle interfacial photoelectron transfer and hydroxyl radical abstraction on different semiconductor nanoparticles. Chlorobenzenes (including hexachlorobenzene and chlorothalonil) adsorbed on the surfaces of nanoparticles were found to instantly undergo dechlorination and ring dissociation through photoelectron capture dissociation and abstraction of a chlorine atom from aromatic C-Cl bond by hydroxyl radicals. Different intermediates have been unambiguously identified with experimental evidences provided by a Q-TOF mass spectrometer. It has been demonstrated that both electron density around atoms and steric effects of side chains contribute to the site selectivity for photoelectron capture and hydroxyl radical abstraction. But the energies needed for chemical bond cleavages and the stabilization of acquired charges play important roles in degradation efficiency. By using mass spectrometric imaging, photocatalytic differences of different semiconductor nanoparticles have been revealed. [Display omitted] •Photo-generated electron-hole pairs are important for dissociation of aromatic organochlorines (AOCs).•Interfacial photoelectrons initiate dissociation of adsorbed AOCs on semiconductor nanoparticles.•Hole oxidization of adsorbed OH groups results in the formation of hydroxyl radicals.•Chlorines of AOCs can be substituted with hydroxyl radicals followed by photoelectron capture dissociation.