**4.4 Other photocatalysts**

Different photocatalysts such as WO3, PdO, ZrO2, and SnO2 have exhibited distinctive photocatalytic effects against organic dye molecules with various advantageous features such as cost-effectiveness, environmental compatibility, wide applied pH ranges, and flexible nanostructure [26, 53]. WO3, with its bandgap varied from 2.4 to 2.8 eV, an n-type semiconductor photocatalyst, is considered as a potential photocatalyst; however, due to the fast recombination of electron and hole pairs, the photocatalytic activities of WO3 were relatively weak. To intercept the recombination as a result of the short diffusion length of charge carriers and enhance the photocatalysis, Ma et al. introduced the grafting of Cu species by impregnation method for interfacial charge transfer effect applied in RB degradation under visible light irradiation [54]. The p- and n-type heterostructured semiconductors show better charge transfer in accordance with Fermi level equilibrium. The redistribution of charges between n-type and p-type produces inner electric fields, which facilitate the transportation of charge carriers and restrict the recombination, thus enhancing the photocatalysis. CuCrO2-decorated SnO2 composite nanofibers were synthesized by electrospinning, followed by a drop-casting method. The composite nanofibers displayed 41% better rate of constant value in comparison with pure SnO2 [55]. Zr is in the same group IVB of elements as Ti, but ZrO2 can only absorb 4% of solar light because of the high energy bandgap and low specific area. Lots of efforts have been made to dope ZrO2 with other nonmetals, metals, and semiconductors in order to improve light response. The effects of different compositions of TiO2/ ZrO2 nanofibers were reported in the photocatalytic degradation of MB dye; the nanofibers containing 40 wt% ZrO2 displayed the best performance under visible light [56]. **Table 2** lists the photocatalytic degradation of varied metal oxidebased composite nanofibers.

**129**

**5. Conclusion**

**Table 2.**

in real dye effluents.

*Composite Nanofibers: Recent Progress in Adsorptive Removal and Photocatalytic Degradation…*

2. PdO/WO3 NFs MB Visible light 24 86.4 [9]

1 2

MB Visible light 3 79.8 [49]

MB Visible light 3 82.7 [56]

MB UV 3 97.4 [30]

MB UV 18 76.06 [31]

MB Solar light 40 min > 80 [50]

RB UV 1 98.2 [48]

RB Visible light 3 85 [54]

Sunlight 4 94.8

Visible light

**efficiency, %**

0.5 > 95 [46]

95 95

1.5 97 [55]

66.8

**Reference**

[25]

[52]

**No. Photocatalyst Dye Light source Time (h) Degradation** 

MB Simulated solar light

MB UV

MB UV/visible light

Electrospun composite nanofibers are advantageous in adsorbing and degrad-

*Comparison of different photocatalytic materials incorporated into electrospun nanofibers for dye degradation.*

ing dyestuffs with better results than using sole absorbents and promote the convenient regeneration. Many transitional metal oxides have shown efficient dye removal effects by both adsorption and photocatalytic degradation. Zeolite, graphene, GO, and MOFs have also demonstrated the high capability for dye adsorption. The mechanisms were driven by physisorption, chemisorption, and so on, which have been discussed thoroughly in this chapter. Future research should be concentrated on combining different adsorbents in the nanofibrous membranes to overcome drawbacks of each adsorbent and create hybrid nanocomposite materials with novelty and super adsorption performance. Lots of advancements are still needed to overcome the remaining issues of recyclability, secondary pollutants, and the viability in the industrial scale for the application

*DOI: http://dx.doi.org/10.5772/intechopen.91201*

1. C-doped ZnO

3. Ag-ZnO

4. Mo/N-doped TiO2 nanorods@CNFs

5 CuCrO2-decorated SnO2 composite nanofibers

6. TiO2/ZrO2

7. TiO2-decorated

8. TiO2@carbon

9. ZnFe2O4@

10. α-Fe2O3/Bi2MoO6

11. Semi-wrapped

12. WO3/Cu (II)

nanofiber

photocatalyst anchored on carbon nanofibers

> composite nanofibers

carbon nanofibers

flexible fiber

TiO2 composite nanofibers

> composite nanofibers

TiO2@carbon nanofibers

nanofibers

MB RB


*Composite Nanofibers: Recent Progress in Adsorptive Removal and Photocatalytic Degradation… DOI: http://dx.doi.org/10.5772/intechopen.91201*

#### **Table 2.**

*Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

netism (saturation magnetization is less than 1 emu g<sup>−</sup><sup>1</sup>

contrast to γ-Fe2O3 and Fe3O4 (up to 92 emu g<sup>−</sup><sup>1</sup>

influences over the magnetic properties of iron oxide nanoparticles due to the changes in magnetic anisotropy. Among magnetic materials, FeO (wustite), Fe3O4 (magnetite), α-Fe2O3 (hematite), β-Fe2O3 (beta phase), γ-Fe2O3 (magnetite), and spinel ferrites (MFe2O4) have been focused on for the multiple applications including catalysis, sensors, and magnetic data storage. α-Fe2O3 presents weak ferromag-

employed extensively to regenerate photocatalysts owing to good magnetic separation [51]. The convenience of separation by using an external magnetic field helps replace the tedious task of filtration and centrifugation for photocatalyst recovery. One prominent advantage of iron oxides is the relative narrow bandgap for the use of visible light activity, which is between 1.9 and 2.5 eV. In comparison to anatase TiO2 (3.03–3.2 eV), which can only harvest light at a wavelength of 387 nm or below in the UV region, iron oxide-based photocatalysts prove to be superior in visible light range. The use of heterogeneous photocatalysts can accelerate the photocatalytic performance of iron oxides as a result of the enhanced visible light activation, better separation of electron-hole pair, and interfacial charge transfer. Bi2MoO6, which possesses a small bandgap (2.5–2.8 eV), was prepared by electrospinning; then the solvothermal method was followed to prepare 1D α-Fe2O3/Bi2MoO6 composite nanofibers [52]. The composite was demonstrated to exhibit enhanced photocatalysis in MB and RB degradation under sunlight irradiation because of the charge separation character of heterogeneous α-Fe2O3 and Bi2MoO6 composite

Different photocatalysts such as WO3, PdO, ZrO2, and SnO2 have exhibited distinctive photocatalytic effects against organic dye molecules with various advantageous features such as cost-effectiveness, environmental compatibility, wide applied pH ranges, and flexible nanostructure [26, 53]. WO3, with its bandgap varied from 2.4 to 2.8 eV, an n-type semiconductor photocatalyst, is considered as a potential photocatalyst; however, due to the fast recombination of electron and hole pairs, the photocatalytic activities of WO3 were relatively weak. To intercept the recombination as a result of the short diffusion length of charge carriers and enhance the photocatalysis, Ma et al. introduced the grafting of Cu species by impregnation method for interfacial charge transfer effect applied in RB degradation under visible light irradiation [54]. The p- and n-type heterostructured semiconductors show better charge transfer in accordance with Fermi level equilibrium. The redistribution of charges between n-type and p-type produces inner electric fields, which facilitate the transportation of charge carriers and restrict the recombination, thus enhancing the photocatalysis. CuCrO2-decorated SnO2 composite nanofibers were synthesized by electrospinning, followed by a drop-casting method. The composite nanofibers displayed 41% better rate of constant value in comparison with pure SnO2 [55]. Zr is in the same group IVB of elements as Ti, but ZrO2 can only absorb 4% of solar light because of the high energy bandgap and low specific area. Lots of efforts have been made to dope ZrO2 with other nonmetals, metals, and semiconductors in order to improve light response. The effects of different compositions of TiO2/ ZrO2 nanofibers were reported in the photocatalytic degradation of MB dye; the nanofibers containing 40 wt% ZrO2 displayed the best performance under visible light [56]. **Table 2** lists the photocatalytic degradation of varied metal oxide-

) at room temperature in

). Thus, Fe3O4 and γ-Fe2O3 have been

**128**

based composite nanofibers.

nanomaterials.

**4.4 Other photocatalysts**

*Comparison of different photocatalytic materials incorporated into electrospun nanofibers for dye degradation.*
