Tailoring photocatalytic performance through EDTA-2Na coordination: Competition of electron transfer to conduction band and valence band in bismuth-based compounds

The effect of EDTA-2Na on the photocatalytic performance of bismuth-based compounds varied with their chemical compositions and EDTA dosage. For Bi 2 O 3 and Bi 5 O 7 I with high Bi/anions ratios, coordinating with EDTA-2Na at molar ratios of 1.5:1 for Bi 2 O 3 and 5:1 for Bi 5 O 7 I significantly improved photocatalytic activity of methyl violet (MV, 50 mg·L -1 ) degradation under visible irradiation, with apparent rate constants ( k ) of 0.0715 min −1 and 0.0261 min −1 , which were 102 and 44 times of those for pure Bi 2 O 3 and Bi 5 O 7 I, respectively. Besides, these samples also exhibited enhanced adsorption performance to cation dye MV due to decreased zero zeta potential. However, If the molar ratio of EDTA to Bi 2 O 3 exceeded 4:1 and the molar ratio of EDTA to Bi 5 O 7 I exceeded 5:1, the samples possessed the poor photocatalytic performance for the degradation of MV, even inferior to pure Bi 2 O 3 and Bi 5 O 7 I. Conversely, BiOX (X = Br, I) and Bi 2 O 2 CO 3 with low Bi/anion ratios didn’t show significant improvement in photocatalytic activity, and BiVO 4 and Bi 2 MoO 6 with lower Bi/anion ratios exhibited even worse photocatalytic performance after coordinating with EDTA-2Na. Photocatalytic mechanism suggests that EDTA-2Na’s electron transfer capabilities to the conduction band of high Bi/anion ratio compounds promote reactive oxygen species generation, enhancing their photocatalytic performance. For the low Bi/anion ratio compounds, the electrons of EDTA would transit to VB and trap the holes, hindering the hole-dominant photo catalysis process.