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. 2025 May 21;30(10):2237.
doi: 10.3390/molecules30102237.

Efficiently Degrading RhB Using Bimetallic Co3O4/ZnO Oxides: Ultra-Fast and Persistent Activation of Permonosulfate

Bai Sun  1   2 , Rui Liu  1 , Fengshou Zhao  1 , Shengnan He  1 , Yun Wang  1 , Xiangxiang Wang  1 , Hao Huang  1 , Mingjian Yi  1 , Shuguang Zhu  1
Affiliations

Efficiently Degrading RhB Using Bimetallic Co3O4/ZnO Oxides: Ultra-Fast and Persistent Activation of Permonosulfate

Bai Sun et al. Molecules. .

Abstract

To address the issues of poor Co2+ regeneration and limited interfacial electron transfer in heterogeneous catalytic systems, this study proposes the synthesis of highly efficient and stable Co3O4/ZnO composites through the pyrolysis-oxidation reaction of Co/Zn MOFs for the degradation of rhodamine B (RhB) using activated peroxymonosulfate (PMS). The results confirmed that the catalyst exhibited a high electron transfer capacity, and the synergistic effect between the bimetals enhanced the reversible redox cycle of Co3+/Co2+. Under optimal conditions, complete removal of RhB was achieved in just 6 min using the Co3O4/ZnO composite, which demonstrated excellent stability after five cycles. Furthermore, the catalyst exhibited a high degradation efficiency in real water samples with a total organic carbon (TOC) removal rate of approximately 65% after 60 min. The electrochemical measurements, identification of active species, and X-ray photoelectron spectroscopy (XPS) analysis revealed that non-radicals (1O2 and direct charge transfer) played a major role in the degradation of RhB. Finally, the potential mechanisms and degradation pathways for RhB degradation using this catalyst were systematically investigated. This study opens new avenues for the development of efficient and stable PMS catalysts, and provides insights into the preparation of other emerging metal oxides.

Keywords: Co3O4/ZnO composite; RhB degradation; bimetallic synergy; persulfate activation.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
(a) Illustration for preparation route of Co3O4/ZnO composite. (b–d) SEM images of Co3O4/ZnO composite. (e) Corresponding element mappings and (f) energy-dispersive X-ray spectrum.
Figure 2
Figure 2
(a) XRD and (b) FTIR spectra of Co3O4, ZnO, and Co3O4/ZnO composite. (c) Specific XPS analysis: (d) Co 2p, (e) Zn 2p, and (f) O 1s.
Figure 3
Figure 3
(a) N2 adsorption/desorption isotherms of Co3O4/ZnO and (b) pore size distribution of Co3O4/ZnO.
Figure 4
Figure 4
Effects of (a) catalyst dosage, (b) PMS concentration, (c) reaction temperature, (d) pH, (e) different oxidants catalyzed, and (f) different water samples on Co3O4ZnO composite to activate PMS for RhB degradation. Experimental conditions: [RhB] = 20 mg/L, [PMS] = 0.08 mM, [catalyst] = 0.1 g/L, and pH = 5.7.
Figure 5
Figure 5
(a) CV curves of Co3O4, ZnO, Co3O4/ZnO composite, respectively; (b) EIS spectrum of Co3O4, ZnO, and Co3O4/ZnO composite, respectively.
Figure 6
Figure 6
(a) EPR spectra of DMPO-·OH, DMPO- SO4·−, and TEMP-1O2 in Co3O4/ZnO/PMS system. (b) UV-Visible absorption spectra of the variation of monoformazan. (c,d) Removal efficiency of RhB with the addition of different scavengers in Co3O4/ZnO/PMS system. (e,f) Effect of dissolved oxygen on degradation of RhB in Co3O4/ZnO/PMS system. Reaction conditions: [RhB] = 20 mg/L, [PMS] = 0.08 mM, [catalyst] = 0.1 g/L, [DMPO] = 5 mM, [EtOH] = [TBA] = [L-his] = 80 mM, and pH = 5.7.
Figure 7
Figure 7
(a) Survey spectrum, (b) Co 2p, (c) Zn 2p, and (d) O 1s in XPS spectra of Co3O4/ZnO composite catalyst before and after reaction (Reaction conditions: [RhB] = 20 mg/L, [PMS] = 0.08 mM, [catalyst] = 0.1 g/L, [DMPO] = 5 mM, and pH = 5.7).
Figure 8
Figure 8
Illustration of possible mechanism of pollutant degradation in Co3O4/ZnO/PMS reaction process.
Figure 9
Figure 9
Possible degradation pathways of RhB in Co3O4/ZnO/PMS system.
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