3. Bismuth oxychloride (BiOCl)

immobilization of ZnO into organics tends to solve both the difficulty of photocatalyst dispersion and recuperation for a cyclic usage together with an improvement of the photostability [30]. The organics that have been reported for immobilization of TiO2 comprise polyaniline [31, 32] and polypyrrole [33] that are hydrophobic and opaque, then it is incompatible for aqueous applications. Hydrogels, based on acrylic polymers, allow effective transport of water and other dissolved molecules due to their hydrophilicity and high swelling capacity. This kind of polymers shows stimuli-responsive properties to pH, temperature, solvent composition, and ionic strengths. Hydrogels come to be an ideal choice for Ag/ZnO photocatalyst immobilization since they are colorless and visually transparent, which permits penetration of light (Figure 7e).

68 Photocatalysts - Applications and Attributes

Figure 7. FTIR (a) and E-SEM image (b) of the as-synthesized Ag/ZnO-PAA. Schematic representation of the ligands between photocatalyst pending from the PAA chain and its photocatalytic role (c). Semi-swell Ag/ZnO-PAA composite (d) and reaction vessel containing photocatalyst dissolved in the pollutant solution (e).Home made photocatalytic reactor

operated at room temperature and pressure (f). Photocatalytic degradation of bisphenol-A (g).

Bismuth oxyhalides BiOCl (X:Cl, Br, and I) are a new class of semiconductors that have recently attracted attentions in the photocatalytic process due to their relatively slow electronhole recombination process. BiOXs are conformed by Bi3+, O2, and halide (X) ions stacked in [X-Bi-O-Bi-X]n layers, giving a tetragonal structure with no linkers interactions with halide

3.1. Experimental section for BiOCl

3.1.1. Modification of BiOCl samples

3.1.2. Characterization

mental scanning electron microscope.

3.1.3. Photocatalytic activity

3.2. Results and discussion

irradiated using a Q200 reactor (λ = 250 nm, 304 mW/cm2

λ = 0.15418 nm over the 2θ range of 10–80 in a step of 0.02s

sample.

The photocatalytic activity was evaluated using two commercial BiOCl samples, which were modified with silver (Ag), graphene oxide (OG), and TiO2. The BiOCl samples were named as P2600 and SB. The P2600 sample is a hydrophobic sample while SB sample is hydrophilic

The modification of BiOCl with Ag and OG was carried out by photodeposition method, which consisted in disperse 500 mg of BiOCl (P2600 and SB) in deionized water during 30 minutes, then the particles of the Ag or OG were added in different percentages; in the case of Ag were 2.0, 0.5, and 0.1% w/w and for OG were 0.5 and 0.1% w/w. Then, the sample was

Later, the samples were centrifuged and thoroughly water washed for several cycles, and finally, they were dried at 70C for 24 h. The composites with TiO2 were prepared by solvothermal method with different weight percentages of TiO2 (25, 50, and 75% w/w).

The crystal structure of the synthesized photocatalysts was analyzed by X-ray diffraction (XRD) using a DX8 advance diffractometer (Bruker) with: Cu Kα radiation, 35 kV, 25 mA,

morphology and microstructure of the samples was carried out by a QUANTA 200 environ-

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>

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

) for 3 h with continuous stirring.

Modified Metallic Oxides for Efficient Photocatalysis http://dx.doi.org/10.5772/intechopen.80834 71

. The analysis of surface

.

1

Figure 8. Scheme of unit cell (a), crystal structure BiOCl with {001} facet (b) and growing of articles of BiOCl in the photocatalytic process in later years (c).

along the C axis as showed in Figure 8a, b. The photocatalytic activity is due to [Bi2O2] layers intercalated of double halogen atoms that allow a better separation of the electron-hole pairs. The bismuth oxychloride (BiOCl) is a solid inorganic compound, not toxic, of pearlescent white color and due its brightness has been used in the cosmetic industry. There is a record not greater than 500 articles reported in the Scopus database concerning the use of BiOCl, as photocatalyst; this review was realized in June 2018 (Figure 8c) and the first publications appeared in 2007 with a growing interest during the last years.

The BiOCl has a bandgap of 3.2–3.5 eV and the valence band is constituted of O2p and Cl3p; while the conduction band has Bi6p according to density functional theory (DFT), whereby when excited, the electrons from Cl atoms are displaced at bismuth orbital [34].

Most studies of BiOCl photocatalyst are focused on enhancing the photocatalytic activity for environmental remediation, especially for dyes degradation during water treatment. Due to the bandgap, its photocatalytic activity, under UV irradiation, has shown a similar or better photocatalytic activity than TiO2 [35]. Some "model" dyes used to evaluate the photocatalytic activity with BiOCl are methylene blue, methyl orange [36], and Rh B [37]. In spite of the bandgap of BiOCl, there are reports wherein demonstrate an excellent degradation of RhB under visible light [38].

However, some challenges remain for BiOCl as most photocatalysts also face; one challenge is its activation under visible light due to the limited absorption of such radiation. A variety of strategies have been employed to get better light absorption and to decrease the charge carrier recombination, such as the heterojunction, doping impurity, and metallization of the surface. Modifications consider the presence of metal elements or compounds like Ag [39, 40], AgCl [41], Fe [42], and Bi [43], also with materials carbon-based as graphene [44], graphene oxide [45], and with other semiconductors as Co3O4 [46], BiOI [47], and TiO2 [48–50]. However, most researches evaluated the photocatalytic activity for degradation of dyes, considering the RhB in many cases. Other pollutant photodegradation studies are bisphenol A using Fe-BiOCl under visible light [42], sulfanilamide with BiOCl-RGO [51], and phenol under visible light with BiOCl-TiO2 composite [50]. Nowadays, the BiOCl is being investigated to reduce of carbon dioxide (CO2) [52].
