Photocatalytic Singlet-Oxygen Generation and Electrocatalytic Alkaline Hydrogen Evolution Reaction Activity of p-Type Bi2Sn2O7/Carbon Dots Nanocomposites.

Abstract

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.