High efficient photocatalytic reduction of nitrate to N2 by Core-shell Ag/SiO2@cTiO2 with synergistic effect of light scattering and surface plasmon resonance

Abstract

Photocatalytic denitrification has attracted great attention owing to its high efficiency and environmentally friendly features. However, selectively photocatalytic reduction of high concentration nitrate to N2 is still a challenging problem due to the competition of photons between nitrate and photocatalysts. Herein, the Ag/SiO2 core encapsulated in the crystalline TiO2 shell (Ag/SiO2@cTiO2) was constructed for improvement of photocatalytic denitrification. Finite difference time domain (FDTD) simulation demonstrated that strong light scattering improved light harvesting via optical confinement. Meanwhile, surface plasmon resonance and electron sink effect of Ag not only enhanced the photogenerated electrons density but also promoted charge carriers separation of Ag/SiO2@cTiO2. More importantly, ecb− of TiO2-shell could be immediately transferred to Ag to keep the balance between Ag0 and Ag+, which contributed to the good stability of Ag/SiO2@cTiO2. 95.8% nitrate (C0 = 2000 mg/L) was removed by 5 wt%Ag/SiO2@cTiO2 with N2 selectivity of 93.6% within 4 h. Even after five cycles, 5 wt%Ag/SiO2@cTiO2 still remained high photocatalytic denitrification efficiency (92.2%). Notably, since TiO2-shell prevented the reaction between Ag and Cl−, more than 92% nitrate could be removed within 5.3 h in the presence of high concentration Cl−.