Stimulating the Visible-Light catalytic activity of Bi2MoO6 nanoplates by embedding carbon dots for the efficient oxidation, cascade reaction, and photoelectrochemical O2 evolution

Abstract

The present work demonstrates the facile synthesis and applications of carbon dots (CD)-embedded Bi2MoO6 nanoplates photocatalyst in the oxidative coupling of amines and oxidation of toluene and ethylbenzene. The synthetic protocol is applied to afford good yields of benzimidazole/benzothiazole via the cascade reaction between benzylamine and o-aminothiophenol/o-phenylenediamine. These photocatalytic reactions are performed under very mild conditions using the household light-emitting diode bulb as a light source and O2 (1 atm). The CD-embedded, 2.4 wt % CD/Bi2MoO6 exhibits the best photocatalytic activity. Impressive visible-light absorbance coefficient, quantum confinement, photoluminescence up-conversion, and stable photoelectrochemical properties of CD are contemplating the excellent photocatalytic activity of CD/Bi2MoO6 than the pristine Bi2MoO6. Generation and influence of various reactive species in these catalytic reactions are investigated by radical scavenging, fluorescence spectroscopy, and cyclic voltammetric (CV) analysis. Both qualitative and quantitative estimation of the in situ generated H2O2 in the photocatalytic oxidative coupling of amines was ascertained using CV and redox titration, respectively. Further, the influence of substitution in the benzylamine and involvement of the carbocations are confirmed using Hammett plot. The developed catalysts are also used as photoanode for O2 evolution from water oxidation in a photoelectrochemical (PEC) cell. Several PEC techniques evaluate the PEC activity of the photoanodes. The reactivity order for various substituted benzylamine and the involvement of reactive oxygen species (O2· −) in the oxidation reaction was obtained and confirmed from the band edge potentials of the best photocatalyst using Mott−Schottky analysis. Efficient catalytic recyclability and photostability are additional important features of the present investigation. This study provides a feasible alternative to the development of non-noble metal (CD)-based nanocomposite photocatalysts that can manifest important photocatalytic and photoelectrocatalytic applications in chemical synthesis and solar fuel production.