Nano-mineral induced nonlinear optical LiNbO 3 with abundant oxygen vacancies for photocatalytic nitrogen fixation: boos
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ORIGINAL ARTICLE
Nano‑mineral induced nonlinear optical LiNbO3 with abundant oxygen vacancies for photocatalytic nitrogen fixation: boosting effect of polarization Xiazhang Li1,2 · Chengli He1 · Da Dai1 · Shixiang Zuo1 · Xiangyu Yan1 · Chao Yao1 · Chaoying Ni2 Received: 10 March 2020 / Accepted: 30 April 2020 © King Abdulaziz City for Science and Technology 2020
Abstract 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 LiNbO3 modulated by natural nano-mineral palygorskite (LiNbO3/Pal) has been synthesized via sol–gel method. The intrinsic polarization of LiNbO3/Pal is investigated by second harmonic generation (SHG) measurements, which indicates an intensity of about 3.1 times that of typical NLO material KH2PO4 (KDP). The strong polarization can facilitate the separation of photogenerated charge carriers in the bulk phase and on the surface of L iNbO3/Pal. The existence of oxygen vacancies in LiNbO3/Pal may originate from doping of metal ions and active groups on the surface of Pal during crystallization of LiNbO3, which shortens the bandgap of L iNbO3 and facilitates the absorption and activation of N 2 molecules. As a result, the polarization effect and rich oxygen vacancies make the LiNbO3/Pal an exceptional photocatalyst for N2 fixation. The 40 wt% LiNbO3/Pal composite achieves an average rate of photocatalytic N H4+ production of 52.57 μmol gcat−1 h−1 under simulated solar light, which is about sixfold higher than that of bulk LiNbO3. This work not only presents a new perspective on mineral modification of NLO material but also offers a cost-effective photocatalyst for nitrogen fixation. Keywords Nonlinear optical material · Polarization · Palygorskite · Oxygen vacancy · Photocatalytic nitrogen fixation
Introduction
Xiazhang Li and Chengli He contributed equally to the paper. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13204-020-01443-6) contains supplementary material, which is available to authorized users. * Xiazhang Li [email protected] * Chaoying Ni [email protected] 1
Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, Changzhou University, Changzhou 213164, People’s Republic of China
Department of Materials Science and Engineering, University of Delaware, Newark, DE 19716, USA
2
Ammonia (NH3) is an essential component for the synthesis of fertilizers and fibers. It has also attracted considerable interest as a potential hydrogen carrier owing to its low liquefying pressure (∼ 8 atm) and high hydrogen density (17.8 wt%) (Medford and Hatzell 2017; Shiraishi et al. 2018). Traditionally, although the Haber–Bosch
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