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

Nanocomposite of pyrochlore-based p-type Bi2Sn2O7/carbon dot (Bi2Sn2O7/CD) has been developed as a multifunctional material for photocatalytic generation of singlet oxygen (1O2) in aqueous medium and for alkaline hydrogen evolution reaction (HER) via water splitting. Compared to pristine Bi2Sn2O7, the light-exposed electron paramagnetic resonance (EPR) studies of hydrothermally synthesized Bi2Sn2O7/CD treated with 2,2,6,6-tetramethylpiperidine (TEMP) reveal a progressively increasing rate of 1O2 production. Higher photocatalytic 1O2 generation is corroborated by highly efficient (i.e., 96%) nonradical photocatalytic degradation of tetracycline hydrochloride solution in 40 min (k = 0.072 min-1), which is 3.6 times higher than that exhibited by pristine Bi2Sn2O7. The light-exposed EPR of Bi2Sn2O7/CD treated with 2,2,6,6,-tetramethylpiperidine-N-oxide radical (TEMPO) suggests the generation of holes and reveals its role in the photocatalytic degradation of tetracycline. The EPR studies confirm that hydroxyl radicals and superoxide radicals are not generated. Furthermore, compared to pristine Bi2Sn2O7, the Bi2Sn2O7/CD exhibits drastically lower overpotential (136 mV) at 10 mA cm-2 and lesser Tafel slope (41 mV dec-1) in 1M KOH for electrocatalytic alkaline HER via water splitting. The enhanced photocatalytic and electrocatalytic activity of Bi2Sn2O7/CD is attributed to higher absorptivity, suitable band structure, higher electron mobility, lower charge transfer resistance, higher active sites, and improved wettability.