Efficient photocatalytic dye degradation over Er-doped BiOBr hollow microspheres wrapped with graphene nanosheets: enhanced solar energy harvesting and charge separation

Abstract

In this work, Er-doped BiOBr hollow microspheres wrapped with graphene nanosheets, which acted as a photocatalyst with excellent photocatalytic activity and stability, have been successfully synthesized through a simple two-step hydrothermal method. The related properties of the as-prepared photocatalyst were analyzed and a possible reaction mechanism was proposed. Incorporating the rareearth element Er into the BiOBr crystal lattice can greatly expand the optical window, maybe owing to the reduced energy band gap by the impurity energy level introduced below the conduction band and indirect utilization of long-wavelength visible light caused by the up-conversion performance. The wrapping with surface graphene nanosheets can efficiently promote charge separation and transmission over the hybrid photocatalyst. The synergistic effect between efficient solar energy harvesting and charge separation gives rise to a remarkable improvement of photocatalytic activity for RhB degradation under simulated sunlight irradiation. In addition, the as-prepared photocatalyst possesses excellent photocatalytic stability, mainly due to the robust coordination interaction between the graphene and the (001) facets of the BiOBr subunits. The rational design of this highly active and stable photocatalyst provides a promising approach for future applications.

Hydrothermal synthesis of BiOBr and BiOBr/CNT composites, their photocatalytic activity and the importance of early Bi6O6(OH)3(NO3)3·1.5H2O formation

“…Hence, these are now considered as one of the promising materials in environmental cleaning. Other successful tuning of BiOBr's properties has also been reported [41,53,[57][58][59][60][61]. In particular, TiO 2 /MWCNT composite was able to degrade oxalic acid and phenol [62].…”

“…Two major challenges for many photocatalysts, including BiOBr, are the prevention of recombination of electrons and holes [52], and efficient harvesting of solar energy [53], both of which drastically affect the photocatalytic activity. One way to remediate these problems is by doping or preparing composites materials.…”

Synthesis and photocatalytic properties of sunlight‐responsive BiOBr–CoWO4 heterostructured nanocomposites

“…Therefore, BiOBr shows low photocatalytic performance with visible light, thus limiting its use for practical applications in environmental remediation. Researchers have reported that the BiOBr performance can be improved by metal ion doping, noble metal deposition and developing semiconductor composites . These approaches have helped in tailoring band‐edge position and enabling charge separation and ultimately increasing the photoactivity of BiOBr.…”

A review on bismuth oxyhalide based materials for photocatalysis

“…In addition, it has also been reported that Er-doped BiOBr–graphene hollow microspheres exhibited a major improvement in photocatalytic activity for the degradation of RhB under simulated sunlight irradiation, which may be due to the strong synergistic effect between charge separation and solar energy harvesting. 202 In summary, compared with other layered materials, graphene is much more appealing to exactly regulate the behaviors of photogenerated electrons and holes in bismuth oxyhalide-based composite photocatalysis systems, largely due to its flexible atom-thin 2D nature, unique electronic properties and excellent absorptivity, which are promising candidates in photocatalysis. 203 …”