Nano-mineral induced nonlinear optical LiNbO3 with abundant oxygen vacancies for photocatalytic nitrogen fixation: boosting effect of polarization

• Published in: Applied nanoscience 2020-09, Vol.10 (9), p.3477-3490
• Main Authors: Li, Xiazhang, He, Chengli, Dai, Da, Zuo, Shixiang, Yan, Xiangyu, Yao, Chao, Ni, Chaoying
• Format: Article
• Language: English
• Subjects: Chemistry and Materials Science; Crystal defects; Crystal structure; Crystallinity; Crystallization; Current carriers; Lattice vacancies; Lithium niobates; Materials Science; Membrane Biology; Nanochemistry; Nanotechnology; Nanotechnology and Microengineering; Nitrogen; Nitrogenation; Nonlinear optics; Original Article; Oxygen; Photocatalysis; Photocatalysts; Polarization; Potassium phosphates; Second harmonic generation; Sol-gel processes; Vacancies
• ISSN: 2190-5509; 2190-5517
• DOI: 10.1007/s13204-020-01443-6

Defective crystalline semiconductor plays a significant role in photocatalytic nitrogen fixation, however the rapid recombination of photoexcited electron/hole pairs largely reduces the efficiency. Spontaneous polarization of the nonlinear optical (NLO) material has emerged as a promising strategy for addressing the problem. Herein, a defects-rich NLO crystalline LiNbO 3 modulated by natural nano-mineral palygorskite (LiNbO 3 /Pal) has been synthesized via sol–gel method. The intrinsic polarization of LiNbO 3 /Pal is investigated by second harmonic generation (SHG) measurements, which indicates an intensity of about 3.1 times that of typical NLO material KH 2 PO 4 (KDP). The strong polarization can facilitate the separation of photogenerated charge carriers in the bulk phase and on the surface of LiNbO 3 /Pal. The existence of oxygen vacancies in LiNbO 3 /Pal may originate from doping of metal ions and active groups on the surface of Pal during crystallization of LiNbO 3 , which shortens the bandgap of LiNbO 3 and facilitates the absorption and activation of N 2 molecules. As a result, the polarization effect and rich oxygen vacancies make the LiNbO 3 /Pal an exceptional photocatalyst for N 2 fixation. The 40 wt% LiNbO 3 /Pal composite achieves an average rate of photocatalytic NH 4 + production of 52.57 μmol g cat −1  h −1 under simulated solar light, which is about sixfold higher than that of bulk LiNbO 3 . This work not only presents a new perspective on mineral modification of NLO material but also offers a cost-effective photocatalyst for nitrogen fixation.