Efficient photodecomposition of 2,4-dichlorophenol on recyclable phase-mixed hierarchically structured Bi2O3 coupled with phosphate-bridged nano-SnO2

Abstract

In this work, phase-mixed hierarchically structured Bi₂O₃ as an efficient visible-light photocatalyst for degrading 2,4-dichlorophenol (2,4-DCP) has been successfully fabricated using (BiO)₂CO₃ as the precursor. Its exceptional photocatalytic activity is mainly attributed to the high charge separation due to the phase-mixed composition and the large surface area due to the hierarchical structure. Moreover, the photogenerated charge separation of the resulting Bi₂O₃ could be further enhanced by coupling with nanocrystalline SnO₂, especially the phosphate-bridged one, mainly based on the surface photovoltage responses and the fluorescence spectra related to the formed hydroxyl radical amounts. This leads to the more obviously improved visible-light activities. It is confirmed that the enhanced charge separation is attributed to the effective transfer of excited high-energy-level electrons from Bi₂O₃ to SnO₂ by means of electrochemical impedance spectroscopy and photocurrent action spectroscopy. Interestingly, it is shown that the as-prepared Bi₂O₃, especially that coupled with the phosphate-bridged nano-SnO₂, exhibits much higher photocatalytic activities under UV-vis irradiation than P25 TiO₂, along with superior mineralization and recovery features. The resulting degradation reaction constant is about 6 times higher than that on P25 TiO₂, and even 50 times higher if the surface area is considered. Furthermore, it is demonstrated through the radical-trapping experiments, detected main intermediates and mineralized chloride amounts that the photogenerated holes and the formed ˙O₂⁻ could respectively dominate the photocatalytic decomposition of 2,4-DCP on Bi₂O₃-based nanocomposites and P25 TiO₂, with different possible decomposition paths suggested.