Background and motivation

What lies beyond photocatalysis? Light-driven chemical reactions prompted by photogenerated carriers on semiconductors’ surfaces are extensively studied,[1,2] yet the role of photons in directly reshaping materials remains largely untapped. Therefore, increasing attention has been recently paid to understanding how photoinduced redox processes can lead to structural and compositional modifications of materials themselves. Such investigations not only open new pathways for mitigating photodegradation but also offer promising strategies for the light-triggered synthesis of composite materials under conditions “orthogonal” to their functional application. In this context, bismuth oxides have emerged as ideal candidates due to their tunable properties and rich redox chemistry, which favour the formation of diverse Bi-based composites.[3]

Here, we demonstrate that light can be harnessed to directly modify bismuth oxide (Bi₂O₃), yielding a complex composite that integrates (BiO)₂CO₃ nanosheets alongside PbO₂ nanoparticles. Furthermore, light also plays a pivotal role in triggering the composite’s reactivity, yielding intermediate non-hydroxyl radicals which can effectively degrade phenol.

Materials and methods

Bi₂O₃ microrods were obtained according to literature protocols.[3] These microrods were dispersed in bidistilled water, and the suspension was placed in a quartz reactor hosting a jacketed 450 W medium-pressure Hg lamp. The illumination in the presence of a continuous flow of 10 mL min^–1 of CO₂ yielded the composite Bi₂O₃/(BiO)₂CO₃ (“BBc”). PbO₂ was, in turn, photodeposited on the materials with or without (BiO)₂CO₃ by adding Pb(NO₃)₂ as precursor (yielding respectively the composites “BBcPb” and “BPb”) and keeping the suspension under oxygen-reduced conditions by Ar bubbling (20 mL min^–1). The sample “BBcBx” has also been synthesized for comparison by irradiating BBc under an inert atmosphere in the absence of Pb(NO₃)₂.
 

Results and discussion

A wide set of composite semiconductors was obtained through this light-mediated route. The formation of (BiO)₂CO₃ nanosheets was observed as a consequence of the intercalation of CO₂ into the photogenerated defective (BiO)₂²⁺ surface states. On the contrary, the presence of PbO₂ stimulated the epitaxial formation of Bi₂O_4–x nanoprisms, which contributed to increasing the surface area. These features have been confirmed through ex-situ high-resolution SEM and TEM images on the material sampled at precise time intervals.

Moreover, the Bi₂O₃ microrods functionalized with (BiO)₂CO₃ nanosheets and PbO₂ (“BBcPb”) exhibited the highest activity in the photocatalytic generation of ethanol-based radicals, which, in turn, attack and degrade phenol. Mechanistic investigations have been carried out to prove the importance of the presence of ethanol as radical mediator.

Thus, our findings highlight the transformative power of photons – not just as catalysts’ activators but as architects of functional materials.