pubmed.ncbi.nlm.nih.gov

Photocatalytic Reduction of Cr(VI) in the Presence of Humic Acid Using Immobilized Ce-ZrO2 under Visible Light - PubMed

  • ️Wed Jan 01 2020

Photocatalytic Reduction of Cr(VI) in the Presence of Humic Acid Using Immobilized Ce-ZrO2 under Visible Light

Fabrício Eduardo Bortot Coelho et al. Nanomaterials (Basel). 2020.

Abstract

Cr(VI) has several industrial applications but it is one of the most dangerous pollutants because of its carcinogenicity and high toxicity. Thus, the removal of Cr(VI) by photocatalytic reduction was investigated. The catalyst applied, Ce-ZrO2, was immobilized, through a sol-gel process on a silicon carbide (SiC) support, to increase the efficiency and avoid using suspended nanoparticles. The influence of initial pH, humic acid (HA), and catalyst dosage was investigated for Cr(VI) containing solutions. Then, a real galvanizing industry effluent (Cr(VI) = 77 mg L-1mg.L-1, Zn = 1789 mg L-1) was treated. It was observed that Cr(VI) adsorption and photoreduction are greatly favored at low pH values. HA can decrease Cr(VI) adsorption but also acts as holes scavenger, reducing the electron-hole recombination, favoring then the photoreduction. With the immobilized Ce-ZrO2, more than 97% of Cr(VI) was removed from the diluted effluent. These results indicate the feasibility to treat Cr(VI) effluents even in the presence of other metals and natural organic matter. The developed material has great chemical and mechanical resistances and avoids the use of nanoparticles, dangerous for the environment and hard to recover. Moreover, solar light can be used to drive the process, which contributes to the development of more sustainable, cleaner, and cost-effective wastewater treatments.

Keywords: catalyst immobilization; hexavalent chromium; humic acid; natural organic matter; photocatalysis; photoreduction; zinc; zirconia.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1

Experimental setup for Cr(VI) photocatalytic reduction with immobilized Ce–ZrO2.

Figure 2
Figure 2

Percentage of Cr(VI) adsorbed for different pH values and catalyst dosages for the systems: (a) without humic acid and (b) with 10 mg L−1 of humic acid.

Figure 3
Figure 3

(a) Cr(VI) species distribution diagram for a total Cr(VI) concentration of 10 mg L−1 in water; (b) ζ-potential for Ce-doped zirconia.

Figure 4
Figure 4

Cr(VI) removed at an initial pH of 4, without humic acid (HA) and with 10 mg L−1 of HA, in the experiments using: (a) 0.5 g L−1 of Ce–ZrO2 and (b) 1.0 g L−1 of Ce–ZrO2.

Figure 5
Figure 5

(a,b) Total Cr(VI) removed and (c,d) Cr(VI) removed by photoreduction for different pH values and catalyst dosages for the systems: (a,c) without humic acid and (b,d) with 10 mg L−1 of humic acid.

Figure 6
Figure 6

Potential in respect to the standard hydrogen electrode (Eh) versus pH diagram of Cr–H2O system at 25 °C for a total chromium concentration of 10 mg L−1.

Figure 7
Figure 7

Proposed mechanism for the photocatalytic reduction of Cr(VI) in the presence of HA using Ce–ZrO2 under visible light irradiation.

Figure 8
Figure 8

(a) Photo, (b) FE-–EM image, and (c) X-ray diffractogram of the immobilized Ce–ZrO2 on the silicon carbide (SiC) support. (d) Absorbance spectra of the samples obtained by applying the Kubelka–Munk function, F(R), to the diffuse reflectance spectra. The inset is the Tauc plot of the SiC support + ZrO2 intermediate layer and the immobilized Ce–ZrO2.

Figure 9
Figure 9

Percentages of Cr(VI) removed using immobilized Ce–ZrO2 in the tests with: (a) model solution containing 10 mg L−1 of Cr(VI); (b) model solutions containing different initial Cr(VI) concentrations; (c) diluted galvanizing industry effluent.

Similar articles

Cited by

References

    1. Yang J.K., Lee S.M. Removal of Cr(VI) and humic acid by using TiO2 photocatalysis. Chemosphere. 2006;63:1677–1684. doi: 10.1016/j.chemosphere.2005.10.005. - DOI - PubMed
    1. Khalil L.B., Mourad W.E., Rophael M.W. Photocatalytic reduction of environmental pollutant Cr(VI) over some semiconductors under UV/visible light illumination. Appl. Catal. B Environ. 1998;17:267–273. doi: 10.1016/S0926-3373(98)00020-4. - DOI
    1. Gheju M., Iovi A., Balcu I. Hexavalent chromium reduction with scrap iron in continuous-flow system. J. Hazard. Mater. 2008;153:655–662. doi: 10.1016/j.jhazmat.2007.09.009. - DOI - PubMed
    1. Sane P., Chaudhari S., Nemade P., Sontakke S. Photocatalytic reduction of chromium (VI) using combustion synthesized TiO2. J. Environ. Chem. Eng. 2018;6:68–73. doi: 10.1016/j.jece.2017.11.060. - DOI
    1. Gupta V.K., Rastogi A. Biosorption of hexavalent chromium by raw and acid-treated green alga Oedogonium hatei from aqueous solutions. J. Hazard. Mater. 2009;163:396–402. doi: 10.1016/j.jhazmat.2008.06.104. - DOI - PubMed