Removal of Nitrate by Photocatalytic Denitrification Using Nonlinear Optical Material

摘要

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_3). The hydrothermally synthesized LiNbO_3 powder could achieve efficient denitrification in water, evidenced by 98.4% nitrate removal and 95.896 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_3 is almost three times as that of conventional TiO_2 (P25) under the same conditions. As suggested by the hole scavenger experiments, the LiNbO_3 should proceed with photocatalytic reduction of nitrate through direct heterogeneous interaction with electrons at the conduction band of LiNbO_3. This may represent a different mechanism from P25, where nitrate is mainly reduced by CO_2~(·-) 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.