Homogeneous-dispersed Bi-Ag bimetals over mesoporous TiO2 for enhanced photocatalytic reduction of nitrate

Abstract

Mesoporous TiO₂ with a homogeneous Bi-Ag bimetallic distribution (Bi@Ag@MTs) can be obtained by calcination of a titanium-based metal organic framework (MOF, MIL-125) with Bi and Ag loading and applied to the photocatalytic reduction of nitrate using formic acid as a hole scavenger. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and energy dispersive spectrometer (EDS) analyses show that Ag(I) and Bi(III) are present in MTs as fine clusters and Bi@Ag@MTs have a specific pancake structure, which provides a good carrier for photocatalytic reaction. The contents of Ag and Bi in Bi@Ag@MTs can be up to 2.28 wt% and 0.54 wt% analysed by Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). Under UV irradiation, Bi@Ag@MTs(0.2,0.4) showed a high reduction rate (3.28 h⁻¹, 4.2 times that of P25), high conversion (100 %, 1.3 times that of P25) and high N₂ selectivity (89.2 %, 2.1 times that of P25) for nitrate reduction. In addition, Bi@Ag@MTs(0.2,0.4) showed good reusability, with the respective NO₃⁻ conversion and N₂ selectivity still reaching 82.2 % and 78.0 % after four cycles. X-ray photoelectron spectroscopy (XPS) analysis showed that under UV irradiation, part of Ag(I) would be reduced to Ag⁰, and the formed Ag-Ag₂O structure helped to improve the photocatalytic activity of the catalyst. This preparation strategy provides assistance in the design of photocatalytic materials with significant activity and durability for nitrate reduction.