Preethi L K, Antony Rajini P, Mathews Tom, Walczak Lukasz, Gopinath Chinnakonda S
Surface and Nanoscience Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Homi Bhabha National Institute, Kalpakkam, 603 102, India.
Chemistry Division, Chemistry Group, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
Sci Rep. 2017 Oct 30;7(1):14314. doi: 10.1038/s41598-017-14463-0.
The two important factors that affect sunlight assisted water splitting ability of TiO are its charge recombination and large band gap. We report the first demonstration of nitrogen doped triphase (anatase-rutile-brookite) TiO nanotubes as sun light active photocatalyst for water splitting with high quantum efficiency. Nitrogen doped triphase TiO nanotubes, corresponding to different nitrogen concentrations, are synthesized electrochemically. Increase in nitrogen concentration in triphase TiO nanotubes is found to induce brookite to anatase phase transformation. The variation in density of intra-band states (Ti and N 2p states) with increase in nitrogen doping are found to be critical in tuning the photocatalytic activity of TiO nanotubes. The presence of bulk heterojunctions in single nanotube of different nitrogen doped TiO samples is confirmed from HRTEM analysis. The most active nitrogen doped triphase TiO nanotubes are found to be 12 times efficient compared to pristine triphase TiO, for solar hydrogen generation. The band alignment and charge transfer pathways in nitrogen doped TiO with triphase heterojunctions are delineated. Bulk heterojunctions among the three phases present in the nanotubes with intra-band defect states is shown to enhance the photocatalytic activity tremendously. Our study also confirms the theory that three phase system is efficient in photocatalysis compared to two phase system.
影响TiO光催化分解水能力的两个重要因素是其电荷复合和较大的带隙。我们首次展示了氮掺杂的三相（锐钛矿-金红石-板钛矿）TiO纳米管作为太阳光活性光催化剂用于高效量子效率的水分解。通过电化学方法合成了对应不同氮浓度的氮掺杂三相TiO纳米管。发现三相TiO纳米管中氮浓度的增加会诱导板钛矿相向锐钛矿相转变。发现随着氮掺杂量增加，带内态（Ti和N 2p态）密度的变化对于调节TiO纳米管的光催化活性至关重要。通过高分辨率透射电子显微镜（HRTEM）分析证实了不同氮掺杂TiO样品的单个纳米管中存在体相异质结。发现最具活性的氮掺杂三相TiO纳米管在太阳能制氢方面的效率是原始三相TiO的12倍。描绘了具有三相异质结的氮掺杂TiO中的能带排列和电荷转移途径。具有带内缺陷态的纳米管中三相之间的体相异质结被证明极大地提高了光催化活性。我们的研究还证实了三相体系在光催化方面比两相体系更有效的理论。
