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. 2022 Dec 7;27(24):8642.
doi: 10.3390/molecules27248642.

Efficient Degradation of Congo Red in Water by UV-Vis Driven CoMoO4/PDS Photo-Fenton System

Huimin Zhou  1 , Yang Qiu  1 , Chuanxi Yang  2 , Jinqiu Zang  2 , Zihan Song  2 , Tingzheng Yang  2 , Jinzhi Li  3 , Yuqi Fan  1 , Feng Dang  4 , Weiliang Wang  2
Affiliations

Efficient Degradation of Congo Red in Water by UV-Vis Driven CoMoO4/PDS Photo-Fenton System

Huimin Zhou et al. Molecules. .

Abstract

In order to improve the catalytic activity of cobalt molybdate (CoMoO4), a PDS-activated and UV-vis assisted system was constructed. CoMoO4 was prepared by coprecipitation and calcination, and characterized by XRD, FTIR, Raman, SEM, TEM, XPS, TGA Zeta potential, BET, and UV-Vis DRS. The results showed that the morphology of the CoMoO4 nanolumps consisted of stacked nanosheets. XRD indicated the monoclinic structures with C2/m (C32h, #12) space group, which belong to α-CoMoO4, and both Co2+ and Mo6+ ions occupy distorted octahedral sites. The pH of the isoelectric point (pHIEP) of CMO-8 at pH = 4.88 and the band gap of CoMoO4 was 1.92 eV. The catalytic activity of CoMoO4 was evaluated by photo-Fenton degradation of Congo red (CR). The catalytic performance was affected by calcination temperature, catalyst dosage, PDS dosage, and pH. Under the best conditions (0.8 g/L CMO-8, PDS 1 mL), the degradation efficiency of CR was 96.972%. The excellent catalytic activity of CoMoO4 was attributed to the synergistic effect of photo catalysis and CoMoO4-activated PDS degradation. The capture experiments and the ESR showed that superoxide radical (·O2-), singlet oxygen (1O2), hole (h+), sulfate (SO4-·), and hydroxyl (·OH-) were the main free radicals leading to the degradation of CR. The results can provide valuable information and support for the design and application of high-efficiency transition metal oxide catalysts.

Keywords: CoMoO4; Congo red; PDS; photo-Fenton.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Molecular structure of CR.
Figure 2
Figure 2
(a) Determined unit crystal illustration (cyan represents Mo, jacinth represents Co, and red represents O); (b) XRD; (c) Raman; (d) FTIR spectra of CMO-8, CMO-9, and CMO-1.
Figure 3
Figure 3
SEM images of CMO-8 (a,b); CMO-9 (c,d); CMO-1 (e,f).
Figure 4
Figure 4
TEM images of CMO-8 (a,b); CMO-9 (c,d); CMO-1 (e,f).
Figure 5
Figure 5
XPS spectra of (a) Co 2p; (b) Mo 3d; (c) O 1s; (d) C 1s of CMO-8.
Figure 6
Figure 6
(a) TGA; (b) DTG; (c) Zeta potential of various pH with 2, 4, 6, and 8; (d) The variation curve for zeta potential as a function of pH value of CMO-8.
Figure 7
Figure 7
BET of (a) CMO-8; (b) CMO-9; (c) CMO-1; UV-visible diffuse reflectance spectra of (d) CMO-8; (e) CMO-9; (f) CMO-1.
Figure 8
Figure 8
Degradation of CR of (a) CMO-8, CMO-9, CMO-1; (b) CMO-8, CMO-9, CMO-1 + PDS; (c) Effect of catalyst loading; (d) Effect of PDS concentration; (e) Effect of pH; (f) Degradation of CR in different conditions. The error bars represent the standard deviation (n = 3).
Figure 9
Figure 9
Effect of radical scavengers on the removal of CR in the CMO-8/PDS system (conditions: 100 mg·L−1 CR, 1 g·L−1 catalyst, 0.5 mM PMS and pH of 7). The error bars represent the standard deviation (n = 3).
Figure 10
Figure 10
ESR analysis for the CMO-8/PDS system in aqueous dispersion by spin trapping with DMPO (a) SO4−·, OH·; (b) ·O2−; (c) TEMP-1O2; (d) TEMPO-h+ at different time intervals.
Figure 11
Figure 11
Photo-Fenton mechanism of CoMoO4/PDS system.
Figure 12
Figure 12
(a) Cyclic degradation performance, the error bars represent the standard deviation (n = 3); (b) the XRD of reused CMO-8 and after reuse CMO-8; the ratio of Co2+, Co3+, Olatt, Ovac (c,d).
Figure 13
Figure 13
(a) MS spectra of Congo red dye solution after treatment with catalyst; (b) Product formation from the degradation of CR dye.
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