Hydrothermal formation of N-doped (BiO)2CO3 honeycomb-like microspheres photocatalysts with bismuth citrate and dicyandiamide as precursors.

In order to develop efficient visible light driven photocatalysts for environmental application, novel N-doped (BiO)2CO3 honeycomb-like hierarchical microspheres were fabricated by an one-pot and template-free hydrothermal method, firstly using bismuth citrate and dicyandiamide as precursors. The as-prepared samples were characterized by XRD, SEM, FT-IR, PL, XPS, and UV-vis DRS in detail. The results indicated that the crystal structure and morphology of the samples can be tuned by hydrothermal reaction temperature. The source of nitrogen doping was from dicyandiamide, which also played a key role in hydrolyzing bismuth citrate to produce bismuth ions and citrate ions. The ammonium ions from the decomposition of dicyandiamide reacted with bismuth ions and carbonate ions from decomposition of citrate ions, producing in situ N-doped (BiO)2CO3 microspheres. The doped nitrogen substituted for oxygen in (BiO)2CO3 and was responsible for the band gap reduction of N-doped (BiO)2CO3. The as-prepared N-doped (BiO)2CO3 microspheres were applied for removal of NO in air and exhibited excellent visible light activity, exceeding that of N-doped TiO2 and C-doped TiO2. Time-dependent evolutions of crystal structure, morphology, chemical composition, and optical property were investigated systematically to reveal the growth mechanism of the honeycomb-like (BiO)2CO3 microspheres. The growth process involved multiple steps, including reaction, nucleation, crystallization, aggregation, and recrystallization. The proposed growth mechanism could provide new insights into the design and fabrication of hierarchical materials with advanced properties.