Observing the Role of Graphene in Boosting the Two-Electron Reduction of Oxygen in Graphene–WO₃ Nanorod Photocatalysts

Abstract

The new role of graphene (GR) in boosting the two-electron reduction of O2 to H2O2 has been first identified in the GR-WO3 nanorod (NR) nanocomposite photocatalysts, which are fabricated by a facile, solid electrostatic self-assembly strategy to integrate the positively charged branched poly(ethylenimine) (BPEI)-GR (BGR) and negatively charged WO3 NRs at room temperature. Photoactivity test shows that, as compared to WO3 NRs, BGR-WO3 NRs with an appropriate addition ratio of GR exhibit remarkably enhanced and stable visible-light photoactivity toward the degradation of Rhodamine B. Besides the common roles of GR observed in the GR-based composite photocatalysts in the literature, including enhancing the visible-light absorption intensity, improving the lifetime and transfer of photogenerated charge carriers, and increasing the adsorption capacity for reactants, we have observed the new role of GR in boosting the two-electron reduction of O2 to H2O2 in this specific BGR-WO3 NR photocatalyst system. Importantly, this new role of GR does contribute to the overall photoactivity enhancement of BGR-WO3 NR nanocomposites. The synergistic contribution of GR on improving the photoactivity of WO3 NRs and the underlying reaction mechanism have been analyzed by the structure-photoactivity correlation analysis and controlled experiments using radicals scavengers.

Graphene based metal and metal oxide nanocomposites: synthesis, properties and their applications

“…281 The intrinsic conductivity of WO 3 plays an important role in its sensing performance; however, it is expected to be improved greatly by the effect of graphene sheets in the composite materials. 482 Qin et al reported the synthesis of HRG/WO 3 nanocomposites by a multi-step process via UV-assisted photoreduction in water at room temperature. 483 In the as-prepared nanocomposites graphene sheets are decorated with a dispersion of WO 3 nanoplatelets with lengths of 50-200 nm, where some of the WO 3 nanoplatelets were oriented perpendicular to the graphene sheets.…”

Tungsten-based nanomaterials (WO 3 & Bi 2 WO 6 ): Modifications related to charge carrier transfer mechanisms and photocatalytic applications

“…The modification of WO 3 with CNTs, graphene or RGO enhances the photocatalytic activity in many ways [34,38,[174][175][176][177][178][179][180]: (i) large surface area of carbon nanostructures promotes the adsorption of pollutant on the composite surface; (ii) improves the light absorption properties and range; (iii) they serve as excellent conductive pathways to trap the electron from WO 3 CB and detraps them to adsorbed oxygen; (iv) prevents the WO 3 from agglomeration thus exposing more active surface for photocatalytic reactions; (v) chemical bonding formed between WO 3 and carbon eliminate the interface defects and accelerates the interfacial charge transfer pathways.…”

“…This indicates that the Page 32 of 72 A c c e p t e d M a n u s c r i p t 32 charge carrier trapping and detrapping from carbon nanostructures is more effective to generate active species, rather than the generation of hydroxyl radicals from VB holes [175]. The graphene initiated two step reduction of oxygen to produce H 2 O 2 [178] and also elevated the CBM of WO 3 that can favor thermodynamic reduction of CO 2 in TiO 2 -graphene composite [179]. Interestingly, RGO-WO 3 promoted oxygen evolution [180a], while failed towards hydrogen evolution owing to the positive CB potential of WO 3 -RGO, which is below H + /H 2 potential.…”

Hybrid nanocomposites with enhanced visible light photocatalytic ability for next generation of clean energy systems

“…[90] Further, the increased catalytic ability of the r-GO-based hybrids when compared with pure WO3 is presumably due to the chemical coupling between WO3 nanoparticles and specific sites of C onto r-GO's, which could thus enhance the hybrid's ability for organic dye degradation by increasing dye's adsorptivity at the hybrid interface [91] and improving photogenerated charge carrier lifetime, or by boosting a two-electron reduction of O2 to H2O2 in solution. [92] The enhanced photocatalytic ability of the r-GO-based hybrids could also derive from the strong coupling between the r-GOdecorated surfaces, which can promote interfacial electron transfers to effectively reduce electron-hole pair recombination rates [93] and thus increase the amount of radical components with strong oxidation capability (for instance hydroxyl radicals; Scheme S1) and lifetime of charge carriers upon their formation. [94] Previous results support our studies and show that carrier motility, the ability to photogenerate electron-hole pairs, as well as the efficiency of recombination could affect nanoparticle photocatalytic performance.…”