Design and synthesis of La3+-, Sb3+-doped MOF-In2S3@FcDc-TAPT COFs hybrid materials with enhanced photocatalytic activity
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Based on the synthesis of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and ferrocene-1,1′-dicarbaldehyde (FcDc), a variety of novel La3+-, Sb3+-doped MOF-In2S3@FcDc-TAPT COFs hybrid materials were designed and synthesized with NH2-MIL-68(In) as matrix. A dense cladding layer has formed on the surface of the MOF-In2S3 heterostructure through coating FcDc-TAPT COFs. The detection of C-N bonds confirmed that the hybrid materials were covalently bonded with the ferrocene-1,1′-dicarbaldehyde (FcDc)-modified covalent triazine-based frameworks (FcDc-TAPT). Then, the photocatalytic reduction of Cr(VI) in aqueous phase under visible light was implemented with the hybrid materials as photocatalysts. Doping La3+ or Sb3+ has obviously improved the photocatalytic degradation efficiency of Cr(VI). In particular, Sb3+-doped MOF-In2S3@FcDc-TAPT COFs had the best removal of Cr(VI) with removal rate of 99% within 20 min. By fitting the experimental data with the pseudo-first-order equation, the speed constants were obtained. The kinetics constant of Sb3+-doped MOF-In2S3@FcDc-TAPT COFs for Cr(VI) degradation was 0.4307 min−1, which was more than 19.87 times as much as that of the non-doped MOF-In2S3@FcDc-TAPT COFs hybrid materials. The DRS and PL results verified that the introduction of La3+ or Sb3+ into the hybrid materials could effectively inhibit the photogenic electron and promote the separation of electron–hole pairs. The cyclic and stability results displayed that the removal rate of Cr(VI) by Sb3+-doped MOF-In2S3@FcDc-TAPT COFs after five times of repeated use was still 95.39%; in particular, it was not significantly changed even after 150 d. It confirmed that the Sb3+-doped MOF-In2S3@FcDc-TAPT COFs was a very stable catalyst, due to the carbonyl and Cp ring conjugate of FcDc, which could produce delocalized electrons and stabilize the ions or free radicals.
The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (Grant No: 21607176), the Natural Science Foundation of Hunan Province, China (Grant No. 2017JJ3516), the Research Foundation of Education Bureau of Hunan Province, China (Grant No. 16B274), and The open fund for key discipline of Forestry of Central South University of Forestry and Technology (Grant No. 2016ZD11). The authors also thank the reviewers for their constructive comments and suggestions.
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Conflict of interest
The authors declare no competing financial interest.
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