Complete debromination of 2,2′,4,4′-tetrabromodiphenyl ether by visible-light photocatalysis on g-C3N4 supported Pd

• Published in: Applied catalysis. B, Environmental Environmental, 2020-02, Vol.261, p.118236, Article 118236
• Main Authors: Lei, Ming, Wang, Zhiying, Zhu, Lihua, Nie, Wenshan, Tang, Heqing
• Format: Article
• Language: English
• Subjects: Bromine; Carbon nitride; Chemical attack; Chemical reduction; Debromination; Electrons; Ethers; g-C3N4; Hydrogen; Intermediates; Irradiation; Light irradiation; Methanol; Nanoparticles; Organic chemistry; Palladium chloride; Pd nanoparticle; Photocatalysis; Pollutants; Pollution control; Polybrominated diphenyl ethers; Radiation; Visible light photocatalysis
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2019.118236

[Display omitted] •Complete debromination of BDE47 is achieved by illuminating visible light on Pd/g-C3N4 in 120 min.•The content of noble metal Pd in Pd/g-C3N4 is as low as 0.5%.•g-C3N4 is used as both photocatalyst and support of Pd nanoparticles.•Pd nanoparticles provide a high affinity interaction with Br for assisting the C-Br cleavage.•Pd nanoparticles promote charge separation and subsequent formation of active H atom species. Deep debromination of polybrominated diphenyl ethers (PBDEs) by visible light photocatalysis is still a challenge in the field of halogenated pollutants control. Here, an efficient photocatalyst (Pd/g-C3N4) was prepared by a simple impregnation-chemical reduction method with bulk g-C3N4 and PdCl2 as precursors. Under preferred reaction conditions (visible light irradiation for 120 min), the use of the 0.5% Pd/g-C3N4 composites (0.4 g L−1) yielded an almost complete debromination of BDE47 (10 μmol L−1) in methanol-water mixture, while the debromination of BDE47 did not occur on pure g-C3N4. A “Pd-promoted active H atom species attack and C-Br bond cleavage” route was proposed according to the identified degradation intermediates. A catalytic mechanism was further clarified: Pd nanoparticles exerted affinity interaction with bromine atoms, and the storing of electrons on Pd would increase the binding interaction. In the debromination process, methanol acts as both a hole scavenger and a hydrogen donor to provide active H atom species through the reaction of H+ and photogenerated electrons on Pd nanoparticles. The initiation of BDE47 debromination on Pd nanoparticles required an induction period to enrich a critical amount of electrons for stretching the C-Br bond and its subsequent being attacked by active H atoms. The generated 2,2′-dibromodiphenyl ether (BDE4) would be further reduced to bromine-free products by hydro-debromination process or coupling reaction.