Photocatalytic singlet oxygen generation and electrocatalytic alkaline HER activity of p-type Bi2Sn2O7/carbon dots nanocomposites.

We present here a scheme for production of singlet oxygen in aqueous medium by pyrochlore based nanocomposite of p-type bismuth stannate (Bi2Sn2O7) and carbon dots (Bi2Sn2O7/CD), and demonstrate its applications as photocatalysts for tetracycline degradation, and as electrocatalyst for alkaline hydrogen evolution reaction via water splitting. The batches of Bi2Sn2O7/CD are synthesized by hydrothermal method with varying carbon dot contents and they are thoroughly characterized to obtain their structural, morphological, textural and compositional information. The carbon dots in the nanocomposite offered photosensitizing behaviour. About 96% photocatalytic degradation of tetracycline hydrochloride is achieved in 40 min (k = 0.072 min-1), which is 3.6 times higher than pristine Bi2Sn2O7. The rate of singlet oxygen production in the reaction medium has been studied with respect to sunlight exposure time by EPR, which is described as a key for enhanced photocatalytic degradation. In addition, the batch of Bi2Sn2O7/(CD)3.0 as an electrocatalyst for alkaline hydrogen evolution reaction (HER) is revealed from low overpotential 136 mV at 10 mA cm-2 and Tafel slope of 41 mV dec-1 in 1M KOH, corresponding to high mass activity of 22.2 A g-1 and high specific activity 0.018 mA cm-2 at η=350 mV. The mechanism of alkaline HER is discussed.