**5. Supported SnO2 photocatalysts**

SnO2 is an inorganic compound that is exhibiting high optical transparency, excellent thermal and chemical stability, and strong oxidizing properties [106]. The band gap of SnO2 is quite large, around 3.6 eV, which leads that SnO2 can be used as a photocatalyst at the UV region. This property makes SnO2 becoming an excellent photocatalyst for the degradation of many organic compounds.

Recently, SnO2 played an important role in the photo-oxidation of pollutants and received a lot of attention despite the outstanding properties of this material. However, the vast number of researches used SnO2 in the powder form as a photocatalyst for the degradation of the toxic organic compound, and the experiments are usually performed using SnO2 in the powder form. There are only a few works describing the use of supported SnO2 thin film as a photocatalyst.

In recent times, many methodologies have been applied for the fabrication of SnO2 thin films such as, sol-gel [107], pulsed plasma deposition [108], pulsed laser deposition [109], reactive evaporation [110], and chemical bath deposition [111] methods.

For example, Jana et al. used the galvanic technique to fabricate SnO2 thin film on transparent conducting oxide (TCO) [112].

**Figure 11** shows the nanoporous flake-like structure, which allows more efficient transport of reactant molecules to the active interfaces and results in a higher photocatalytic activity for degrading methyl orange (MO) dye than that of P25 under UV light [112].

However, the SnO2 in the powder form presents low photocatalytic activity comparing with other semiconductors due to its wide-band gap, 3.6 eV, and the rapid recombination of the photo generated electron-hole pairs. Thus, the SnO2 thin film could present lower photocatalytic efficiency comparing with SnO2 in the bulk form. Therefore, the SnO2 thin film is widely combined with other metal ions such as Ni, Co, Fe [113], Cr [114], Zn [115], Sb [116], W [117], or other semiconductors, such as ZnO [118], TiO2 [119], etc.

For example, the W-doped SnO2 thin films are fabricated on glass (ITO) substrate by simple chemical deposition techniques [120]. The result showed that the energy band gap is varied by the doping concentration of W, which is in the range of 3.46–3.35 eV. In addition, the UV-Visible absorption and Photoluminescence characterization results demonstrated that W-dopant SnO2 could narrow the band gap, thus enhancing the photocatalytic efficiency of the W-doped SnO2 in the visible light (**Figure 12**). The author used the fabricated W-doped SnO2 for the degradation of Methylene Blue and Rhodamine (RHB) under the visible region. The W-doped SnO2 thin film presents higher photocatalytic efficiency comparing to the pure SnO2 thin film in the visible light irradiation.

In recent time, Sr-doped metal oxides have great attention in electronic and optoelectronic applications. Besides, when Sr is combined with SnO2, the crystal growth rate of SnO2 is reduced, making the Sr-doped SnO2 to have a higher specific surface area. Thus, the combination of Sr with SnO2 can improve the photocatalytic activity of SnO2. For example, Haya et al. have prepared Sr-doped SnO2 thin film

**167**

SnO2 thin film [127].

substrate.

**Figure 12.**

**Figure 11.**

*Vadivel et al. [120].*

*Supported-Metal Oxide Nanoparticles-Potential Photocatalysts*

on glass substrate by simple sol-gel technique and study its photocatalytic activity under UV-irradiation [121]. The doping of Sr makes the SnO2 thin film to decrease its degree of crystallinity, reducing the particle size and increasing the specific surface area of the thin film. The results show that the Sr-doped (8%) SnO2 film has

*Schematic representation for photocatalytic mechanism of RHB in W-SnO2 thin films. Reproduced by* 

*The SnO2 thin film and the photocatalytic activity of SnO2 thin film. Reproduced by Jana et al. [112].*

In addition, many researchers also combined with other metal elements to improve the photocatalytic activity of SnO2 thin film such as Cu-doped SnO2 [122], Fe-doped SnO2 [123], F- or Sr-doped [124], and Cl-doped SnO2 [125] on glass

Recently, to improve the photocatalytic efficiency of SnO2 thin film, B/Ag/F was doped with the SnO2-ZnO composite film on glass by the sol-gel route. The fabricated composite thin film was used for the degradation of methyl green and formaldehyde under UV irradiation. The result showed that the synergy of ZnO and tri-doping B/Ag/F had improved the photocatalytic activity of SnO2 thin film [126]. In addition, Kong et al. also prepared B/Fe co-doped SnO2-ZnO thin film on glass substrates using the sol-gel technique. The prepared composite thin film improved the lifetime of the photogenerated charge carriers and optical absorption properties. The photocatalytic efficiency of the composite thin film was evaluated through the degradation of organic pollutants such as acid naphthol red and formaldehyde. The B/Fe co-doped SnO2-ZnO film exhibits the highest photocatalytic activity compared with an undoped or only singly doped

higher photocatalytic activity compared to undoped SnO2 thin film.

*DOI: http://dx.doi.org/10.5772/intechopen.93238*

**Figure 11.** *The SnO2 thin film and the photocatalytic activity of SnO2 thin film. Reproduced by Jana et al. [112].*

#### **Figure 12.**

*Photophysics, Photochemical and Substitution Reactions - Recent Advances*

degradation of MB and Cr6+ in wastewater under UV illumination.

photocatalyst for the degradation of many organic compounds.

describing the use of supported SnO2 thin film as a photocatalyst.

on transparent conducting oxide (TCO) [112].

catalytic activity of WO3 thin film.

**5. Supported SnO2 photocatalysts**

fabricated composite was deposited don fluorine-doped tin oxide (FTO) substrate [105]. The photocatalytic activity of the composite was tested by photocatalytic

The supported WO3/C3N4 composite present higher photocatalytic activity on the decoloration of MB and the reduction of Cr6+ to Cr3+, compared to the photo-

SnO2 is an inorganic compound that is exhibiting high optical transparency, excellent thermal and chemical stability, and strong oxidizing properties [106]. The band gap of SnO2 is quite large, around 3.6 eV, which leads that SnO2 can be used as a photocatalyst at the UV region. This property makes SnO2 becoming an excellent

Recently, SnO2 played an important role in the photo-oxidation of pollutants and received a lot of attention despite the outstanding properties of this material. However, the vast number of researches used SnO2 in the powder form as a photocatalyst for the degradation of the toxic organic compound, and the experiments are usually performed using SnO2 in the powder form. There are only a few works

In recent times, many methodologies have been applied for the fabrication of SnO2 thin films such as, sol-gel [107], pulsed plasma deposition [108], pulsed laser deposition [109], reactive evaporation [110], and chemical bath deposition [111]

For example, Jana et al. used the galvanic technique to fabricate SnO2 thin film

**Figure 11** shows the nanoporous flake-like structure, which allows more efficient transport of reactant molecules to the active interfaces and results in a higher photocatalytic activity for degrading methyl orange (MO) dye than that of P25

However, the SnO2 in the powder form presents low photocatalytic activity comparing with other semiconductors due to its wide-band gap, 3.6 eV, and the rapid recombination of the photo generated electron-hole pairs. Thus, the SnO2 thin film could present lower photocatalytic efficiency comparing with SnO2 in the bulk form. Therefore, the SnO2 thin film is widely combined with other metal ions such as Ni, Co, Fe [113], Cr [114], Zn [115], Sb [116], W [117], or other semiconductors,

For example, the W-doped SnO2 thin films are fabricated on glass (ITO) substrate by simple chemical deposition techniques [120]. The result showed that the energy band gap is varied by the doping concentration of W, which is in the range of 3.46–3.35 eV. In addition, the UV-Visible absorption and Photoluminescence characterization results demonstrated that W-dopant SnO2 could narrow the band gap, thus enhancing the photocatalytic efficiency of the W-doped SnO2 in the visible light (**Figure 12**). The author used the fabricated W-doped SnO2 for the degradation of Methylene Blue and Rhodamine (RHB) under the visible region. The W-doped SnO2 thin film presents higher photocatalytic efficiency comparing

In recent time, Sr-doped metal oxides have great attention in electronic and optoelectronic applications. Besides, when Sr is combined with SnO2, the crystal growth rate of SnO2 is reduced, making the Sr-doped SnO2 to have a higher specific surface area. Thus, the combination of Sr with SnO2 can improve the photocatalytic activity of SnO2. For example, Haya et al. have prepared Sr-doped SnO2 thin film

**166**

methods.

under UV light [112].

such as ZnO [118], TiO2 [119], etc.

to the pure SnO2 thin film in the visible light irradiation.

*Schematic representation for photocatalytic mechanism of RHB in W-SnO2 thin films. Reproduced by Vadivel et al. [120].*

on glass substrate by simple sol-gel technique and study its photocatalytic activity under UV-irradiation [121]. The doping of Sr makes the SnO2 thin film to decrease its degree of crystallinity, reducing the particle size and increasing the specific surface area of the thin film. The results show that the Sr-doped (8%) SnO2 film has higher photocatalytic activity compared to undoped SnO2 thin film.

In addition, many researchers also combined with other metal elements to improve the photocatalytic activity of SnO2 thin film such as Cu-doped SnO2 [122], Fe-doped SnO2 [123], F- or Sr-doped [124], and Cl-doped SnO2 [125] on glass substrate.

Recently, to improve the photocatalytic efficiency of SnO2 thin film, B/Ag/F was doped with the SnO2-ZnO composite film on glass by the sol-gel route. The fabricated composite thin film was used for the degradation of methyl green and formaldehyde under UV irradiation. The result showed that the synergy of ZnO and tri-doping B/Ag/F had improved the photocatalytic activity of SnO2 thin film [126]. In addition, Kong et al. also prepared B/Fe co-doped SnO2-ZnO thin film on glass substrates using the sol-gel technique. The prepared composite thin film improved the lifetime of the photogenerated charge carriers and optical absorption properties. The photocatalytic efficiency of the composite thin film was evaluated through the degradation of organic pollutants such as acid naphthol red and formaldehyde. The B/Fe co-doped SnO2-ZnO film exhibits the highest photocatalytic activity compared with an undoped or only singly doped SnO2 thin film [127].
