Modification Strategies for Semiconductor Photocatalyst Based on Energy Band Structure Theory

doi:10.15541/jim20140648

Abstract

Abstract:

Design and controllable synthesis of catalyst and its property tuning are an interesting subject for physical chemistry, materials chemistry and catalytic chemistry. As a new environmental-purifying technology, semiconductor photocatalytic oxidation technology has arosen worldwide attention. However, conventional photocatalyst exhibits poor utilization of solar energy and low efficient of photogenerated charge separation, which restricts the practical application of the technology. Therefore, it is still a challenging topic to design and synthesize visible-light-response photocatalytic materials with higher utilization efficiency of solar energy. Besides tuning synthesis method (by controlling particle size, morphology, crystallinity and other microstructures, etc), modification is a crucial strategy for the activity enhancement of photocatalyst. In this paper, we reviewed the basic mechanism for the photocatalyst modification from the view of semiconductor energy structure. Taking consideration of the basic mechanism and process of photocatalysis, there are two key modification strategies: chemical structure modification (energy band modification) to broaden the light absorption and surface modification (surface sensitization, semiconductor combinations and noble metal deposition) to increase life-time of carrier. Suitable band structure is responsible for the visible-light harvesting and effective separation of carrier of semiconductor photocatalyst.

Key words: catalyst, photocatalysis, energy band structure, modification, strategies, review

CLC Number:

O614

WANG Dan-Jun, ZHANG Jie, GUO Li, SHEN Hui-Dong, FU Feng, XUE Gang-Lin, FANG Yi-Fan. Modification Strategies for Semiconductor Photocatalyst Based on Energy Band Structure Theory[J]. Journal of Inorganic Materials, 2015, 30(7): 683-693.

Figures/Tables 14

Fig. 1 Band-edge position of semiconductor photocatalyst and various redox couples in water (pH=7)

Fig. 2 Schematic illustration of basic mechanism of a semiconductor photocatalytic process[4]

Fig. 3 Elementary ideology to improve photocatalytic activity of semiconductor

Fig. 4 Three strategies to narrow the band gap of semiconductor photocatalysts to match the solar spectrum

Fig. 5 (A) Bonding diagram of TiO2 and (B) DOS of metal-doped TiO2-xAxO2 (A=V、Cr、Mn、Fe、Co, or Ni)[9]

Fig. 6 (A) Total DOSs of doped TiO2 and (B) DOSs of the dopants anion located at a substitutional site for O atom in the anatase TiO2 crystal[10] Ni-doped stands for N doping at an interstitial sites, and Ni-s-doped stands for doping at both substitutional and interstitial sites

Fig. 7 (A) Total DOS of S-doped TiO2 and (B) total DOS of F-doped TiO2[18] Eg indicates the band gap energy. The impurity states are labeled (I) and (II)

Fig. 8 Serial electronic structures of α-AgMO2(M=A1, Ga, In) and comparation of their photo catalytic activity (A) Electronic structures of α-AgMO2 (M=Al, Ga, In), (B) Photocatalytic degradation of isopropanol using α-AgGaO2 and α-AgInO2 under visible light irradiation (400 nm<λ<520 nm) and (C) Apparent photonic efﬁciency of acetone evolution using α-AgGaO2 for various wavelength ranges within the UV-visible absorption spectrum[28]

Fig. 9 Energy band structures for (A) Ag3PO4 and (B) Ag2O

Fig. 10 Schematic illustration of band structures of GaN and ZnO, and their solid solution[31]

Fig. 11 (A)Schematic electronic structures of AgAlO2, AgGaO2 and AgAl1-xGaxO2 solid solutions; (B) UV-visible absorption spectra of β-AgAl1-xGaxO2 solid solutions; (C) Rate of acetone evolution, band-gap, and color of β-AgAl1-xGaxO2 as a function of x; (D) Apparent quantum efﬁciency of IPA photodegradation over β-AgAl0.6Ga0.4O2 in various wavelength ranges within the V-visible absorption spectrum[32]

Fig. 12 Excitation process of dye molecule sensitizer

Fig. 13 Energy band structure aof AgBr/Bi2WO6 heterojunction[39]

Fig. 14 Photocatalytic activity enhancement of Ag-loaded Bi2WO6[48] (Left: room temperature photoluminescence (PL) spectra of Bi2WO6 (a), and Ag-loaded Bi2WO6 nanoarchitecture, λexcitation=300 nm; Right: Energy band diagram and photocatalytic scheme of the Ag-loaded Bi2WO6)

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