Surface functionalized N-C-TiO2/C nanocomposites derived from metal-organic framework in water vapour for enhanced photocatalytic H2 generation

Surface-functionalized nitrogen/carbon co-doped polymorphic TiO2 phase junction nanoparticles uniformly distributed in porous carbon matrix were synthesized by a simple one-step pyrolysis of titanium based metal-organic framework (MOF), NH2-MIL-125(Ti) at 700 degrees C under water vapour atmosphere. Introducing water vapour during the pyrolysis of NH2-MIL-125(Ti) not only functionalizes the derived porous carbon matrix with carboxyl groups but also forms additional oxygen-rich N like interstitial/intraband states lying above the valence band of TiO2 along with the self-doped carbon, which further narrows the energy band gaps of polymorphic TiO2 nanoparticles that enhance photocatalytic charge transfer efficiency. Without co-catalyst, sample N-C-TiO2/C-ArW demonstrates H-2 evolution activity of 426 mu mol g(cat)(-1) h(-1), which remarkably outperforms commercial TiO2 (P-25) and N-C-TiO2/C-Ar with a 5-fold and 3-fold H-2 generation, respectively. This study clearly shows that water vapour atmosphere during the pyrolysis increases the hydrophilicity of the Ti-MOF derived composites by functionalizing porous carbon matrix with carboxylic groups, as well as enhancing the electrical conductivity and charge transfer efficiency due to the formation of additional localized oxygen-rich N like interstitial/intraband states. This work also demonstrates that by optimizing the anatase-rutile phase composition of the TiO2 polymorphs, tuning the energy band gaps by N/C co-doping and functionalizing the porous carbon matrix in the N-C-TiO2/C nanocomposites, the photocatalytic H-2 generation activity can be further enhanced. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

In this study, surface-functionalized nitrogen/carbon co-doped polymorphic TiO2 nanoparticles uniformly distributed in porous carbon matrix were synthesized by pyrolysis of titanium based metal-organic framework NH2-MIL-125(Ti) under water vapour atmosphere. The introduction of water vapour not only functionalizes the porous carbon matrix but also enhances charge transfer efficiency, resulting in significantly improved photocatalytic H-2 generation activity.