3.1.3. Photocatalytic activity

The photocatalytic activity was evaluated with two pollutants. The samples modified with Ag and OG were evaluated for RhB degradation under visible light, the RhB degradation was followed by UV-Vis spectrophotometer at 552 nm. The composites with TiO2 were evaluated for Phenol degradation under visible light (Xenon lamp; Oriel 300 W; λ = 450 nm). Monitoring of phenol degradation was carried out by high performance liquid chromatography (HPLC) using a C18 column with a mobile phase of acetonitrile-water (27–75%) with a flow of 0.5 mL min<sup>1</sup> .

### 3.2. Results and discussion

Both pure BiOCl samples (P2600 and SB) showed overlapping flakes forming flower-like morphology, the size of flakes were of 10–60 microns approximately in P2600 samples (Figure 9a), while SB samples displayed a size of flakes about 9–34 microns (Figure 9b).

In the Ag-modified samples, small BiOCl-impregnated particles on the flakes were observed, in the case of the modified SB samples, a major impregnation of Ag particles was noticed (Figure 9c) in comparison with Ag-P2600 sample (Figure 9d); probably due to hydrophobic character of P2600 sample avoiding that Ag particles could have contact with the photocatalyst. Regarding OG-BiOCl samples, in both modified photocatalysts, it was observed

Figure 9. SEM images of BiOCl pure samples; SB (b) and P2600 (a). BiOCl modified with silver; Ag-SB (c) and Ag-P2600 (d). BiOCl modified with graphene oxide; OG-SB (e) and OG-P2600 (f). BiOCl modified with titanium dioxide; TiO2-SB (g) and TiO2-P2600 (h).

that small sheet of OG was deposited in the flakes of BiOCl, mainly in the edges of flakes as it is observed in Figure 9e-f. While in the composites of TiO2-BiOCl, the generated TiO2 was incrusted as small agglomerated particles on the BiOCl flakes (Figure 9c-d). Both photocatalysts could promote a better separation of photocharges generated during the reaction and therefore a better photocatalytic activity (Figure 9g-h).

The RhB degradation under visible light with Ag-BiOCl is shown in Figure 10a, b, the maximum degradation of RhB was obtained with pure BiOCl; and 30 and 40% of RhB degradation with P2600 and SB were obtained, respectively. In the case of Ag-SB, as the percentage of Ag increased, the photocatalytic activity decreased, while with Ag-P2600 was observed a greater degradation with 0.5% Ag than with 0.1%Ag. The presence of Ag in the BiOCl generates a decrease of photocatalytic activity, this result may be due to the presence of Ag in two oxidation states (Ag<sup>0</sup> and Ag1+) observed in the XRD specter (Figure 10c, d), which may be acting as recombination sites. The modification with Ag incites a displacement of the [001] peak in the XRD specter probably due to the change of atoms of Bi by atoms of Ag because both elements have a similar ionic radius. Likewise, change of intensity in the [002] and [101] peaks in the spectra may be associated with a modification of the crystalline phase. This change in the Ag-BiOCl may affect the photocatalytic activity.

phenol degradation and TiO2-SB (50–50%) giving 36% of phenol degradation during 6 h of reaction (Figure 12a, b). For the composite TiO2-P2600 conforming the percentage of TiO2 decreased, the photocatalytic activity also decreased. Such results confirm that there is a good interaction between both photocatalysts (BiOCl and TiO2), in the TiO2-P2600 composites, the size and hydrophobicity of P2600 played an important role in the adsorption of phenol on the surface, and therefore, gave a higher photocatalytic activity. In addition, higher TiO2 percentage generated the appropriate heterojunction. In the XRD spectrum of TiO2-BiOCl, the presence of peaks from both photocatalysts was observed (Figure 12c, d), also an overlap of the peaks [002] and [101] of BiOCl with the peak of [001] of TiO2. In TiO2-SB composites, it observed a lower intensity for [001] peak corresponding to BiOCl. Regarding TiO2-SB composites, the SB exhibited a smaller size and hydrophilic character; then it was necessary that less amount of TiO2 is active under visible light, and an increment of TiO2 could generate the

Figure 10. RhB degradation under visible irradiation with BiOCl pure and modified with silver; Ag-SB (a) and Ag-P2600

Modified Metallic Oxides for Efficient Photocatalysis http://dx.doi.org/10.5772/intechopen.80834 73

The results obtained in our study offer a promising direction for the design of more practical and efficient photocatalysts to be used under visible light. In addition, the photocatalysis using BiOCl is becoming a promising research topic due to its fascinating characteristics, and it is necessary to study and understand the synthesis methods, morphology, predominant facets that improve the photocatalytic activity in all visible irradiations in order to achieve the mineralization of pollutants. Currently, our research group is working with the generation of

recombination of electron-hole pairs decreasing the photocatalytic activity.

biofuels by photocatalysis using BiOCl.

(b). XRD spectra of BiOCl samples; Ag-SB (c) and Ag-P2600 (d).

With the OG-BiOCl sample, the photocatalytic activity was different, since with low percentage of OG, the photocatalytic activity increased. The OG-SB sample (0.1% of OG) gave the greater degradation of RhB, while the OG-P2600 (0.1% of OG) and pure P2600 had the same degradation percentage (Figure 11a, b). In the XRD spectra of OG-BiOCl was observed, a decrement in intensities of [001], [102], and [112] peaks, and an intensity increment for [002] peak as the OG percentage increased. This result indicates that OG induces a better orientation of {001} facet in both BiOCls (Figure 11c, d).

Referring to TiO2-BiOCl composite, its photocatalytic activity was evaluated for phenol degradation under visible light. The better composites were TiO2-P2600 (75–25%) giving 45% of

Figure 10. RhB degradation under visible irradiation with BiOCl pure and modified with silver; Ag-SB (a) and Ag-P2600 (b). XRD spectra of BiOCl samples; Ag-SB (c) and Ag-P2600 (d).

that small sheet of OG was deposited in the flakes of BiOCl, mainly in the edges of flakes as it is observed in Figure 9e-f. While in the composites of TiO2-BiOCl, the generated TiO2 was incrusted as small agglomerated particles on the BiOCl flakes (Figure 9c-d). Both photocatalysts could promote a better separation of photocharges generated during the reaction and therefore a

Figure 9. SEM images of BiOCl pure samples; SB (b) and P2600 (a). BiOCl modified with silver; Ag-SB (c) and Ag-P2600 (d). BiOCl modified with graphene oxide; OG-SB (e) and OG-P2600 (f). BiOCl modified with titanium dioxide; TiO2-SB (g)

The RhB degradation under visible light with Ag-BiOCl is shown in Figure 10a, b, the maximum degradation of RhB was obtained with pure BiOCl; and 30 and 40% of RhB degradation with P2600 and SB were obtained, respectively. In the case of Ag-SB, as the percentage of Ag increased, the photocatalytic activity decreased, while with Ag-P2600 was observed a greater degradation with 0.5% Ag than with 0.1%Ag. The presence of Ag in the BiOCl generates a decrease of photocatalytic activity, this result may be due to the presence of Ag in two oxidation states (Ag<sup>0</sup> and Ag1+) observed in the XRD specter (Figure 10c, d), which may be acting as recombination sites. The modification with Ag incites a displacement of the [001] peak in the XRD specter probably due to the change of atoms of Bi by atoms of Ag because both elements have a similar ionic radius. Likewise, change of intensity in the [002] and [101] peaks in the spectra may be associated with a modification of the crystalline phase. This

With the OG-BiOCl sample, the photocatalytic activity was different, since with low percentage of OG, the photocatalytic activity increased. The OG-SB sample (0.1% of OG) gave the greater degradation of RhB, while the OG-P2600 (0.1% of OG) and pure P2600 had the same degradation percentage (Figure 11a, b). In the XRD spectra of OG-BiOCl was observed, a decrement in intensities of [001], [102], and [112] peaks, and an intensity increment for [002] peak as the OG percentage increased. This result indicates that OG induces a better orientation

Referring to TiO2-BiOCl composite, its photocatalytic activity was evaluated for phenol degradation under visible light. The better composites were TiO2-P2600 (75–25%) giving 45% of

better photocatalytic activity (Figure 9g-h).

and TiO2-P2600 (h).

72 Photocatalysts - Applications and Attributes

of {001} facet in both BiOCls (Figure 11c, d).

change in the Ag-BiOCl may affect the photocatalytic activity.

phenol degradation and TiO2-SB (50–50%) giving 36% of phenol degradation during 6 h of reaction (Figure 12a, b). For the composite TiO2-P2600 conforming the percentage of TiO2 decreased, the photocatalytic activity also decreased. Such results confirm that there is a good interaction between both photocatalysts (BiOCl and TiO2), in the TiO2-P2600 composites, the size and hydrophobicity of P2600 played an important role in the adsorption of phenol on the surface, and therefore, gave a higher photocatalytic activity. In addition, higher TiO2 percentage generated the appropriate heterojunction. In the XRD spectrum of TiO2-BiOCl, the presence of peaks from both photocatalysts was observed (Figure 12c, d), also an overlap of the peaks [002] and [101] of BiOCl with the peak of [001] of TiO2. In TiO2-SB composites, it observed a lower intensity for [001] peak corresponding to BiOCl. Regarding TiO2-SB composites, the SB exhibited a smaller size and hydrophilic character; then it was necessary that less amount of TiO2 is active under visible light, and an increment of TiO2 could generate the recombination of electron-hole pairs decreasing the photocatalytic activity.

The results obtained in our study offer a promising direction for the design of more practical and efficient photocatalysts to be used under visible light. In addition, the photocatalysis using BiOCl is becoming a promising research topic due to its fascinating characteristics, and it is necessary to study and understand the synthesis methods, morphology, predominant facets that improve the photocatalytic activity in all visible irradiations in order to achieve the mineralization of pollutants. Currently, our research group is working with the generation of biofuels by photocatalysis using BiOCl.

Author details

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References

1040-8

jlumin.2016.12.046

Vladimir A. Escobar Barrios1

Materials Division, San Luis Potosí, México

Sciences Division, San Luis Potosí, México

\*, Dalia Verónica Sánchez Rodríguez<sup>1</sup>

1 Instituto Potosino de Investigación Científica y Tecnólogica, A.C. (IPICYT), Advanced

2 Instituto Potosino de Investigación Científica y Tecnólogica, A.C. (IPICYT), Environmental

3 Department of Materials and Environmental Chemistry, Stockholm University, Stockholm,

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\*Address all correspondence to: vladimir.escobar@ipicyt.edu.mx

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Modified Metallic Oxides for Efficient Photocatalysis http://dx.doi.org/10.5772/intechopen.80834 75

Figure 11. RhB degradation under visible irradiation with BiOCl pure and modified with graphene oxide; OG-SB (a) and OG-P2600 (b). XRD spectra of BiOCl samples; OG-SB (c) and OG-P2600 (d).

Figure 12. Phenol degradation under visible irradiation with BiOCl pure and modified with titanium dioxide; TiO2-SB (a) and TiO2-P2600 (b). XRD spectra of BiOCl samples; TiO2-SB (c) and TiO2-P2600 (d).
