Grinding induced the formation of the heterojunction Bi6O5(OH)3(NO3)5•3H2O/BiOI with improved visible-light photoreactivity

Considering that basic bismuth nitrate Bi6O5(OH)(3)(NO3)(5)center dot 3H(2)O (BBN) with a wide band gap energy (E-g = similar to 3.40 eV) could only respond to UV light, herein, BiOI-coupled BBN (BBN/BiOI) heterojunction at the size of several microns was synthesized by a grinding-assistant ion-exchange strategy. BiOI nanoparticles with relatively uniform diameters in the range of 0.22-0.71 mu m attached on the surface of BBN at the size of around 10 mu m. BBN/BiOI exhibited significantly enhanced visible-light photocatalytic activity for malachite green (MG, 20 mg/L) degradation at the premium BiOI content with initial I-/Bi3+ molar ratio of 0.8, and the degradation efficiency was increased to 90% from 4% of bare BBN and 44% of BiOI. Especially, the as-prepared BBN/BiOI possessed higher photocatalytic activity than that obtained by solution reaction, which should result from more intimate contact between BiOI and BBN due to mechanical force from grinding, as well as electrostatic attraction between positively charged surface of BBN and oxygen-terminated surface of BiOI. All these are beneficial to transfer and separation of photogenerated carriers, thus improving photo-quantum efficiency. Dissolution behavior of BBN in several dyes' solution was clarified.