Preparation and Enhanced Photocatalytic Activity of Flower Cluster Photocatalyst BiOI/ZnO with Z-Scheme p–n Heterostructure Using Carbon Quantum Dots as Electron Bridges

Abstract

The design and construction of heterojunctions are effective strategies to improve the catalytic performance of photocatalysts. Here, BiOI/ZnO nanoflower-cluster p–n heterostructures were prepared by an in situ synthesis method and modified with carbon quantum dots (CQDs) synthesized via a microwave-assisted hydrothermal method (denoted as CQDs@BiOI/ZnO). This modification leveraged the up-conversion property of CQDs to further improve the photocatalytic performance of the composites. The synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), photoluminescence (PL) and other analytical techniques. Their photocatalytic and recycling performance was evaluated via multimode photocatalytic degradation of methyl orange (MO). The results show that the composite has a nanoflower-cluster morphology, with a degradation efficiency of 90% for MO under ultraviolet light within 120 min. The composite CQDs@BiOI/ZnO exhibited the lowest PL intensity, the smallest impedance arc radius and the highest photocurrent density. A possible photocatalytic mechanism was proposed based on radical-trapping experimental results. The results indicate that the successful construction of p–n heterojunctions and the modification with CQDs are the main reasons for the improved photocatalytic activity.