A BaTiO3/WS2 composite for piezo-photocatalytic persulfate activation and ofloxacin degradation

Abstract

Piezoelectric fields can decrease the recombination rate of photogenerated electrons and holes in semiconductors and therewith increase their photocatalytic activities. Here, a BaTiO₃/WS₂ composite is synthesized and characterized, which combines piezoelectric BaTiO₃ nanofibers and WS₂ nanosheets. The piezo-photocatalytic effect of the composite on the persulfate activation is studied by monitoring Ofloxacin (OFL) degradation efficiency. Under mechanical forces, LED lamp irradiation, and the addition of 10 mM persulfate, the OFL degradation efficiency reaches ~90% within 75 min, which is higher than efficiencies obtained for individual BaTiO₃, WS₂, or TiO₃, widely used photocatalysts in the field of water treatment. The boosted degradation efficiency can be ascribed to the promotion of charge carrier separation, resulting from the synergetic effect of the heterostructure and the piezoelectric field induced by the vibration. Moreover, the prepared composite displays good stability over five successive cycles of the degradation process. GC-MS analysis is used to survey the degradation pathway of OFL during the degradation process. Our results offer insight into strategies for preparing highly effective piezo-photocatalysts in the field of water purification.

Fig. 1. Structural characterization of the so-synthesized materials.

a The XRD and b FT-IR spectra of the pure BaTiO₃, WS₂, and BaTiO₃/WS₂. High-resolution XPS spectra of c Ba 3d, d Ti 2p, and e W 4 f of BaTiO₃/WS₂ composite.

Fig. 2. Morphological analysis of the materials.

a–c SEM, and d–f TEM images of WS₂, BaTiO₃, and the BaTiO₃/WS₂ composite, respectively. g HR-TEM image of the BaTiO₃/WS₂ composite and d-spacing calculated for h BaTiO₃ and i WS₂ using the selected areas on HR-TEM.

Fig. 3. Elemental mapping graphs of the BaTiO₃/WS₂ composite.

a The SEM image and b–g SEM elemental mapping of the BaTiO₃/WS₂ composite. h The EDX spectra correspond to the composite (inserted Table: quantitative results obtained for W, S, O, Ba, and Ti).

Fig. 4. The efficiency of the BaTiO₃/WS₂ composite in the piezo-photocatalytic activation of persulfate.

a Synergistic effect of the piezo-photocatalytic assisted activation of persulfate. b Comparison of the piezo-photocatalytic activity of the BaTiO₃/WS₂ composite with the pure TiO₂, BaTiO₃, and WS₂ and. Experimental conditions: Catalyst concentration = 1.0 g L⁻¹, [OFL] = 20 mg L⁻¹, [PS] = 10 mM, pH = 6.5. The error bars were not shown, as they were smaller than the data points.

Fig. 5. Effect of different operating parameters on the degradation efficiency of OFL.

a Effect of catalyst concentration, c the effect of initiate pH, d various OFL concentrations, e bath ultrasonic power, and f persulfate concentration on the piezo-photocatalytic degradation of OFL. b pH_pzc of BaTiO₃/WS₂ nanocomposite. Experimental conditions: Catalyst concentration = 1.0 g L⁻¹, [OFL] = 20 mg L⁻¹, [PS] = 10 mM, pH = 6.5. The error bars were not shown, as they were smaller than the data points.

Fig. 6. The reusability and stability of the BaTiO₃/WS₂ composite.

a The piezo-photocatalytic degradation efficiency of OFL and b XRD patterns of the BaTiO₃/WS₂ composite before and after five successive cycles. Experimental conditions: Catalyst concentration = 1.0 g L⁻¹, [OFL] = 20 mg L⁻¹, [PS] = 10 mM, pH = 6.5.

Fig. 7. Evaluating the produced ROSs and piezo-photocatalytic mechanism.

a The effect of diverse scavengers on the piezo-photocatalytic degradation of OFL in the presence of PS, b Fluorescence spectra of the materials in the presence of AgNO₃, c–h high-resolution XPS spectra of W, Ba, and Ti before and after contact of WS₂ and BaTiO₃, and i–k the proposed schematic mechanism for the charge-carrier transference of the BaTiO₃/WS₂ composite. Experimental condition: Catalyst concentration = 1.0 g L⁻¹, [OFL] = 20 mg L⁻¹, pH = 6.5, [Scavengers] = 5 mmol L⁻¹. The error bars were not shown, as they were smaller than the data points.

Fig. 8. Degradation mechanism of OFL.

Proposed reaction pathways for OFL based on the determined by-products.