Double-vacancy-induced polarization and intensified built-in electric field in S-Scheme heterojunction for removal of antibiotics and Cr (VI)

doi:10.1016/S1872-2067(25)64754-1

Abstract

Abstract:

Antibiotics and heavy metals usually co-exist in wastewater and pose serious environmental hazards. Herein, a series of V_Mo-BMO/O_v-BOB S-scheme heterojunctions with double vacancy (Mo vacancy and photoexcited O vacancy) were constructed via an electrostatic assembly method. The removal efficiency of Cr (VI) and tetracycline (TC) over V_Mo-BMO/O_v-BOB-0.3 was 2.47 and 1.13 times than that of a single system, respectively. In-situ EPR demonstrated that the surface O vacancies could be generated under LED light irradiation. These photoexcited O vacancies (P-O_v) enabled V_Mo-BMO/O_v-BOB composites still exhibit satisfactory activity after five successive cycles and an amplified Fermi level gap. The enhancement could be attributed to the enhanced internal electric field and double-vacancy-induced polarization. Additionally, the density functional theory calculation results suggested that double vacancy induced polarization electric field increases the dipole moment, which was conducive to rapid electron transport. Photoluminescence and time-resolved photoluminescence analysis demonstrated that the introduction of S-scheme heterojunction and double vacancy promoted charge transfer and prolonged the lifetime of carriers. Degradation intermediates and toxicity of products were evaluated. In conclusion, a possible mechanism based on V_Mo-BMO/O_v-BOB S-scheme heterojunction in the simultaneous removal of Cr (VI) and TC was proposed.

Key words: Photocatalysis, S-scheme heterojunction, Double vacancy, Polarization, Fermi level

Xiangyang Zheng, Jinwang Wu, Haifeng Shi. Double-vacancy-induced polarization and intensified built-in electric field in S-Scheme heterojunction for removal of antibiotics and Cr (VI)[J]. Chinese Journal of Catalysis, 2025, 76: 50-64.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(25)64754-1

https://www.cjcatal.com/EN/Y2025/V76/I9/50

Figures/Tables 11

Fig. 1. (a) Schematic of the procedure for the preparation of VMo-BMO/Ov-BOB samples. XRD patterns (b) and FTIR spectra (c) of Ov-BOB, VMo-BMO, and VMo-BMO/Ov-BOB-X (X = 0.2, 0.3, 0.4).

Fig. 2. SEM images of Ov-BOB (a), VMo-BMO (b), and VMo-BMO/Ov-BOB-0.3 (c). TEM (d) and HRTEM (e) images of VMo-BMO/Ov-BOB-0.3. In-situ Bi 4f (f), O 1s (g), Br 3d (h), and Mo 3d (i) XPS spectra of Ov-BOB, VMo-BMO, and VMo-BMO/Ov-BOB-0.3.

Fig. 3. (a) UV-vis DRS of Ov-BOB, VMo-BMO, and VMo-BMO/Ov-BOB-X (X = 0.2, 0.3, 0.4). (b) Tauc’s plots of Ov-BOB and VMo-BMO. (c) UV-vis DRS of VMo-BMO and BMO. (d) VB-XPS spectra of Ov-BOB and VMo-BMO.

Fig. 4. (a) EPR signals of VMo-BMO/Ov-BOB-0.3 upon visible light illumination and maintaining at ambient air with different time. (b) UV-vis DRS spectra of VMo-BMO/Ov-BOB-0.3 under dark and visible light irradiation conditions. (c) Schematic of the Ov looping on VMo-BMO/Ov-BOB-0.3. (d) Digital photographs of as-prepared samples in the initial and colored states.

Fig. 5. (a) The photocatalytic performance of VMo-BMO, Ov-BOB, BMO/Ov-BOB-0.3, VMo-BMO/Ov-BOB-0.3(MM), and VMo-BMO/Ov-BOB-X (X = 0.2, 0.3, 0.4) in TC degradation. (b) The photocatalytic performance of VMo-BMO, Ov-BOB, BMO/Ov-BOB-0.3, VMo-BMO/Ov-BOB-0.3(MM), and VMo-BMO/Ov-BOB-X (X = 0.2, 0.3, 0.4) in Cr (VI) reduction. (c) The simultaneous removal of TC and Cr (VI) over VMo-BMO/Ov-BOB-0.3. The corresponding reaction kinetics constants of TC degradation (d), Cr (VI) reduction (e), and the simultaneous removal of TC and Cr (VI) (f). Conditions: [TC] = 15 mg·L-1, [Cr (VI)] = 10 mg·L-1, [catalyst] = 0.03 g, [pH] = 7.

Fig. 6. The photocatalytic performance of simultaneous removal of TC and Cr (VI) under solar light irradiation over VMo-BMO/Ov-BOB-0.3 (a) and the corresponding reaction kinetics constants (b). (c) Recycling performance of VMo-BMO/Ov-BOB-0.3. (d) XRD patterns for fresh and used VMo-BMO/Ov-BOB-0.3. (e,f) Free radical trap experiments of VMo-BMO/Ov-BOB-0.3. EPR spectra of DMPO-·O2− (g) and DMPO-·OH (h) of VMo-BMO/Ov-BOB-0.3. Conditions: [TC] = 15 mg·L-1, [Cr (Ⅵ)] = 10 mg·L-1, [EDTA] = 1.0 mmol L-1, [IPA] = 1.0 mmol L-1, [BQ] = 0.33 mmol L-1, [Catalyst] = 0.03 g, pH = 7.

Fig. 7. (a) Proposed pathways of TC degradation over VMo-BMO/Ov-BOB-0.3. Toxicity assessment of TC and its intermediate substance: acute toxicity (b), developmental toxicity (c), and mutagenicity (d). (e) Digital photograph of mung bean seed cultured in different solutions.

Table 1 The τavg of the samples were obtained by double exponential fitting.

Sample	τ₁ (ns)	A₁ (%)	τ₂ (ns)	A₂ (%)	τ_avg (ns)
V_Mo-BMO	2.46	0.68	2.67	0.32	2.53
O_v-BOB	1.93	0.51	1.59	0.49	1.65
BMO/O_v-BOB-0.3	2.03	0.44	2.64	0.56	2.41
V_Mo-BMO/O_v-BOB-0.3 (dark)	2.71	0.64	3.04	0.36	2.84
V_Mo-BMO/O_v-BOB-0.3 (light)	2.75	0.32	3.12	0.78	3.02

Fig. 8. PL spectra (a), TR-PL decay spectra (b), EIS (c), and transient photocurrent response spectra (d) of the Ov-BOB, VMo-BMO, BMO/Ov-BOB-0.3, and VMo-BMO/Ov-BOB-0.3 samples.

Fig. 9. The crystal structures of Ov-BOB (a), VMo-BMO (b), and VMo-BMO/Ov-BOB heterojunction (c). Work function of VMo-BMO (d), BMO (e), Ov-BOB (f), and BOB (g). Modulation of Fermi level between VMo-BMO, Ov-BOB, BMO and BOB. The band structures of VMo-BMO and Ov-BOB: before contact (h), after contact (i), and the photoinduced carriers transfer mechanism (j). (k) Modulation of Fermi level between VMo-BMO, Ov-BOB, BMO and BOB.

Fig. 10. Diagram of the electrostatic potential of Ov-BOB (a), VMo-BMO (b), VMo-BMO/Ov-BOB-0.3 (c), and the value of dipole moment fitted by the electrostatic potential diagram (d). (e) The possible simultaneous removal mechanism of Cr (VI) and TC over the VMo-BMO/Ov-BOB-0.3 composite.

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