The morphology evolution of nitrogen-doped carbon quantum dots/hollow TiO2 composites and their applications in photocatalysis

Design and controllable synthesis of photocatalysts and tailoring their catalytic property such as degradation performance of organic dyes are an interesting subject. We reported the preparation of nitrogen-doped carbon quantum dots/TiO2 composites (N-CDs/TiO2) by hydrothermal process using urea and tetrabutyl titanate (TBT) as precursors. The morphology and chemical structure of N-CDs/TiO2 (N-CDs/TiO2-X, where X is the mass ratio of urea to TBT) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance. We found that the fine N-CDs have the specific properties that it can tune the growth behavior of TiO2 in micrometer size. With the decrease in the ratio of N-CDs to TBT, the morphology of as-fabricated N-CDs/TiO2 changes from hollow spheres, honeycomb to agglomerations bulks, with changing their crystalline phase accordingly. The degradation testing of rhodamine B (RhB) under visible-light irradiation (λ ≥ 400 nm) shows that the photocatalytic performance of N-CDs/TiO2-X substantially improved relative to pure TiO2, while calcinations process substantially decreased the catalytic activity. The optimal photocatalytic performance of N-CDs/TiO2-1 totally removed the RhB in 120 min, which is 11.42 times over that of TiO2. Radical trapping experiment and EPR spin-trapping study show that the ·O2− radical and h+ were the main active species that account for the photodegradation performance.