Supercritically exfoliated Bi2Se3 nanosheets for enhanced photocatalytic hydrogen production by topological surface states over TiO2.

ABSTRACT

Owing to the unique electronic properties of layered materials, topological insulators have interestingly grabbed much attention in the field of photocatalytic water splitting. Nowadays, 2D layered materials were composited with semiconductor photocatalysts, encourage much as it provides enormous active sites and also significantly prevent photogenerated charge recombination. Especially, Bi2Se3 possesses exceptional properties like topologically preserved conducting surface states with bulk insulating behavior and high surface area, which provides unconventional electron dynamics, resulting in facile electron transport and effective charge separation to photocatalyst. So far, several methods have been attempted to synthesize few-layered Bi2Se3 nanosheets from its bulk crystals. Here, a unique attempt is made and succeeded to exfoliate bulk Bi2Se3 to few layered nanosheets via surfactant free supercritical fluid processing using N-Methyl-2-pyrrolidone (NMP) as an exfoliating agent, with a short reaction time of 15 min. The exfoliation of Bi2Se3 crystal was confirmed by several characterization techniques, such as XRD, SEM, Raman, and HR-TEM. Furthermore, different weight percentages of exfoliated Bi2Se3 sheets/anatase TiO2 nanoparticles were prepared and examined the photocatalytic activity using glycerol as a hole scavenger. Among them, 15 wt.% Bi2Se3 coupled TiO2 nanocomposite showed enormous hydrogen evolution rate of 84.9 mmol h-1g-1cat, which is 80 times higher than that of TiO2 nanoparticles. In addition, the photostability of the nanocomposite was also verified, where it retains 94% of activity even after 4 cycles of continuous experiments. The improved rate of H2 production was understood by theoretical calculations that topologically preserved conducting surface states of co-catalyst, Bi2Se3 nanosheets is supported to high mobile and scatter free electrons. It mediates the transport of electrons with TiO2 nanoparticles that helped the effective charge separation. Thus, it proves a promising candidate for photocatalytic hydrogen production.