Nitrogen-Doped Graphene Quantum Dot-Passivated δ-Phase CsPbI 3 : A Water-Stable Photocatalytic Adjuvant to Degrade Rhodamine B.

Inorganic halide perovskite CsPbI 3 is highly promising in the photocatalytic field for its strong absorption of UV and visible light. Among the crystal phases of CsPbI 3 , the δ-phase as the most aqueous stability; however, directly using it in water is still not applicable, thus limiting its dye photodegradation applications in aqueous solutions. Via adopting nitrogen-doped graphene quantum dots (NGQDs) as surfactants to prepare δ-phase CsPbI 3 nanocrystals, we obtained a water-stable material, NGQDs-CsPbI 3 . Such a material can be well dispersed in water for a month without obvious deterioration. High-resolution transmission electron microscopy and X-ray diffractometer characterizations showed that NGQDs-CsPbI 3 is also a δ-phase CsPbI 3 after NGQD coating. The ultraviolet-visible absorption spectra indicated that compared to δ-CsPbI 3 , NGQDs-CsPbI 3 has an obvious absorption enhancement of visible light, especially near the wavelength around 521 nm. The good dispersity and improved visible-light absorption of NGQDs-CsPbI 3 benefit their aqueous photocatalytic applications. NGQDs-CsPbI 3 alone can photodegrade 67% rhodamine B (RhB) in water, while after compositing with TiO 2 , NGQDs-CsPbI 3 /TiO 2 exhibits excellent visible-light photocatalytic ability, namely, it photodegraded 96% RhB in 4 h. The strong absorption of NGQDs-CsPbI 3 in the visible region and effective transfer of photogenerated carriers from NGQDs-CsPbI 3 to TiO 2 play the key roles in dye photodegradation. We highlight NGQDs-CsPbI 3 as a water-stable halide perovskite material and effective photocatalytic adjuvant.