Simple and fast synthesis of BiOBr/[Bi6O5(OH)3](NO3)5·3H2O composites for efficient photocatalytic degradation of RhB under visible light

Abstract

In this study, a heterostructure photocatalyst consisting of Bi6O5(OH)3](NO3)5·3H2O (was denoted as BiOOHN) and BiOBr was fabricated via a simple and economic co-precipitation method. In this method, the amount of Br in the composition was controlled by changing the volume of hydrobromic acid (HBr) during the manufacturing process. The photocatalytic performance of the prepared samples by photodegradation of rhodamine B (RhB) solution under visible light radiation was investigated and the optimum amount of HBr was obtained. The results showed that BiOBr/BiOOHN composite has higher photocatalytic efficiency compared to pure BiOOHN and BiOBr, so that almost 100 % of RhB solution was degraded in the presence of BiOBr/BiOOHN composite photocatalyst during 100 min, while this value was equal to 0 % and 21 % for pure BiOOHN and BiOBr, respectively. Results indicated that the BiOOHN band gap is in the ultraviolet region (3.45 eV) and not possible to activate this sample to generate electron-hole pairs under visible radiation. While the energy gap of the samples synthesized in the presence of HBr was around 2.90 eV, which enables the activation of these compounds under visible radiation to generate electron-hole pairs for photocatalytic reactions. Therefore, the weak BiOOHN photocatalytic performance is attributed to the its wide band gap energy in comparison with other samples. Also, the better performance of composite samples compared to pure BiOBr is owing to the formation of a heterostructure between BiOOHN and BiOBr. It leads to better separation of electron-hole pairs at the interface of two semiconductors and hinders their recombination, which improves photocatalytic performance. Also, a mechanism for the photocatalytic reactions of RhB degradation was proposed based on experimental data and the experiment of trapping active species. According to this mechanism, the holes and free hydroxyl radicals (•OH) play a key role in the photocatalytic degradation reactions of RhB.