Understanding the lattice composition directed in situ structural disorder for enhanced visible light photocatalytic activity in Bismuth iron niobate pyrochlore

Abstract

Herein we report the cationic disorder dependent photocatalytic efficiency of pyrochlore type Bi1.33 Fe0.052Nb1.24Fe1.04O7-δ (BFNF) and Bi1.34Fe0.66Nb1.34O7-δ (BFN) nanoparticles (Nps) for the first time. Bi based photocatalytic materials endowed with lone pair of 6s2 electrons is additionally perturbed by nonstoichiometry and studied for its optoelectronic properties. Rietveld refinements show that the crystal structure is cubic and the space group is Fd3¯m. In BFNF Nps, Bi3+ cation on the eight coordinate pyrochlore A-site shows displacive disorder, as a consequence of its lone pair electronic configuration as well as due to higher iron concentration. The lattice vibrational analysis using Raman spectra is consistent with the displacive disorder of the pyrochlore. A quantitative chemical compositional and state analysis has been done using X-ray photoelectron spectroscopy. The band-gap energy (Eg) and band edge offset of BFNF and BFN NPs were estimated to be 2.43 and 2.56eV respectively by using UV–vis spectroscopy and the valence band XPS spectra. Under visible light, the BFNF NPs exhibits a much better visible-light-responsive photocatalytic performance than BFN NPs for the degradation of RhB and commercially available pharmaceutical acetoaminophen (Dolo 650). The mechanism of high photocatalytic activity was suggested on the basis of the photoluminescence spectra, electrochemical impedance spectra (EIS), and active species trapping measurements. Our findings indicated that the synergistic effect of higher degree of cationic disorder in BFNF NPs is responsible for favourable direct transition along with NBE (near bandedge) transition, efficient separation and migration of photoinduced charge carriers, thus resulting in the remarkably improved photocatalytic activity.