Crystal-phase engineering of BiVO₄ induced by N-doped carbon quantum dots for photocatalytic application

Crystal phase engineering was applied for BiVO₄ via the introduction of N-doped CQDs (NCDs), in which the phase of BiVO₄ was converted from monoclinic phase to tetragonal phase, generating a self-heterostructure. The intense heterostructure between NCDs and BiVO₄ via strong electronic interaction, confirmed by the conversion of crystal phase and XPS results, led to the promoted separation and migration ability of photoinduced carriers. Moreover, the varied band structure (more negative Fermi level) of BiVO₄ after the introduction of NCDs and the up-conversion luminescent property of CQDs led to the vast generation of O₂⁻, which was confirmed to play a significant role during RhB photodegradation. However, there existed an optimal introducing amount of NCDs, confirmed to be 30 mg, which revealed 100% photodegradation efficiency after 180 min illumination. The decrease of photocatalytic activity in the condition of excessive NCDs introducing amount was ascribed to the aggregation of these quantum dots or the cover of the active plane of BiVO₄ by NCDs. In addition, the photodegradation mechanism exploration revealed that both O₂⁻ and photoinduced holes acted as radical species during the photoreduction process, and O₂⁻ played more significant role.