State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology , Harbin 150090, P. R. China.
Environ Sci Technol. 2016 Oct 18;50(20):11218-11225. doi: 10.1021/acs.est.6b03455. Epub 2016 Sep 28.
Removal of nitrate from water has been receiving growing attention in water treatment. In this study, we report the photocatalytic denitrification (PCDN) by nonlinear optical (NLO) material, i.e. lithium niobate (LiNbO). The hydrothermally synthesized LiNbO powder could achieve efficient denitrification in water, evidenced by 98.4% nitrate removal and 95.8% nitrogen selectivity at reaction time of 120 min and pH-neutral condition. Based on the first-order kinetics of PCDN, the kinetic constant for LiNbO is almost three times as that of conventional TiO (P25) under the same conditions. As suggested by the hole scavenger experiments, the LiNbO should proceed with photocatalytic reduction of nitrate through direct heterogeneous interaction with electrons at the conduction band of LiNbO. This may represent a different mechanism from P25, where nitrate is mainly reduced by CO radicals generated by the holes at the valence band. The unique second harmonic generation (SHG) effects of NLO materials enable them to produce more electrons and minimize the electron-hole recombination, which improves the efficiency and stability of the PCDN process. The current study provides a proof-of-concept demonstration of NLO photocatalytic material for more effective nitrate removal in water treatment.
从水中去除硝酸盐在水处理中受到越来越多的关注。在这项研究中，我们报告了非线性光学（NLO）材料，即铌酸锂（LiNbO）的光催化脱硝（PCDN）。水热合成的 LiNbO 粉末在中性 pH 值条件下，在 120 分钟的反应时间内可实现高效脱硝，硝酸盐去除率达 98.4%，氮选择性达 95.8%。根据 PCDN 的一级动力学，在相同条件下，LiNbO 的动力学常数几乎是传统 TiO（P25）的三倍。根据空穴捕获剂实验的结果，LiNbO 应该通过与 LiNbO 导带中的电子的直接非均相相互作用进行光催化还原硝酸盐。这可能代表了与 P25 不同的机制，在 P25 中，硝酸盐主要是通过价带中的空穴生成的 CO 自由基还原的。NLO 材料独特的二次谐波产生（SHG）效应使它们能够产生更多的电子，并最小化电子-空穴复合，从而提高 PCDN 过程的效率和稳定性。本研究为 NLO 光催化材料在水处理中更有效地去除硝酸盐提供了概念验证。
