ZnxFe3-xO4–ZnO heterojunction interfaced with poly(L-DOPA) electron transfer mediator layer for enhanced visible light photocatalytic activity
Ovidiu Pană, Anca Petran, Adriana Popa, Maria Ştefan, Teofil Dănuţ Silipaş, Cristian Leoștean, Bogdan Ştefan Vasile, Florina Pogăcean, Dana Toloman
Abstract
Z-scheme heterojunctions comprising Zn x Fe 3-x O 4 @poly(L-DOPA)@ZnO (ZF@PD@ZnO) were synthesized using solvothermal and precipitation techniques. The study aimed to investigate the impact of the poly(L-DOPA) electron transfer mediator on the photocatalytic performance of Zn x Fe 3-x O 4 @ZnO (ZF@ZnO) nanocomposites under visible light irradiation. X-ray diffraction (XRD) and HRTEM analysis confirmed the formation of heterostructures, identifying the crystalline phases of both ZnO and zinc ferrite . BFTEM images revealed a polyhedral shape for all samples, with a tendency toward mild agglomeration. The partial inversion of the zinc ferrite cubic spinel structure was evidenced by FT-IR, XPS , and VSM analyses. Zinc ferrite was found to be ferromagnetic, with cation distributions between tetrahedral (A) and octahedral (B) positions as [ Zn 0.6 2 + Fe 0.4 3 + ] A [ Fe 0.4 2 + Fe 1.6 3 + ] B O 4 . The samples exhibited notable photocatalytic activity against Rhodamine B, serving as a model contaminant. Furthermore, the stability and reusability of the samples were examined. Additionally, the study elucidated the photocatalytic mechanism produced by the ternary Z-scheme ZF@PD@ZnO, involving spin-polarized charge carriers. Energy band alignment was evaluated by combining ultraviolet photoelectron spectroscopy (UPS) with UV-Vis spectroscopy. The interplay between band alignment and reactive oxygen species (ROS) generation was discussed in correlation with EPR results. Enhanced ROS generation under visible light illumination, observed in the ZF@PD@ZnO nanocomposite, is mainly due to the addition of the conductive poly(L-DOPA) layer, acting as an electron transfer mediator in the Z-scheme heterojunction, ensuring enhanced charge separation. • Novel Z-scheme Zn x Fe 3-x O 4 @poly(L-DOPA)@ZnO heterojunctions were prepared. • Poly(L-DOPA) represents an electron transfer mediator. • The samples have superparamagnetic behavior at room temperature. • All samples show photocatalytic activity against RhB under visible irradiation. • The mechanism of photodegradation process was elucidated.