Photocatalytic decolorization of methylene blue over Zn1−xCoxO under visible light irradiation

Xiao, Qi; Zhang, Jiang; Xiao, Chong; Tan, Xiaoke

doi:10.1016/j.mseb.2007.06.021

Cited by 113 publications

(63 citation statements)

References 25 publications

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“…The red shift of the band edge with the incorporation of Co into ZnO has been observed [17] and ascribed to the sp-d exchange interactions between the band electrons and the localized d electrons of the Co 2+ ions which substitute Zn 2+ ions [18]. The s-d and p-d exchange interactions led to a negative and a positive correction to the conduction band and the valence band edges separately, resulting in a band gap narrowing [19]. In addition, the reflection rate of the Co-doped ZnO in visible light range decreases with the increase of the Co 2+ doping concentration.…”

Section: Uv-vis Diffuse Reflectance Analysismentioning

confidence: 99%

Preparation, characterization and photocatalytic activity of Co-doped ZnO powders

Cao

et al. 2010

Journal of Alloys and Compounds

148

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Section: Uv-vis Diffuse Reflectance Analysismentioning

confidence: 99%

Preparation, characterization and photocatalytic activity of Co-doped ZnO powders

Cao

et al. 2010

Journal of Alloys and Compounds

148

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Mid-gap photoactivity is usually associated with donor-or acceptor-type photoionization (or charge-transfer) transitions of the added impurity ions. Such transitions can generate one band-like charge carrier (either a conduction-band electron or a valence-band hole) by formal charge transfer from or to the impurity.…”

Section: Introductionmentioning

confidence: 99%

Visible-light photoconductivity of Zn1−xCoxO and its dependence onCo
Johnson
¹
,
Cohn
²
,
Kaspar
³

et al. 2011
Phys. Rev. B
37
5
39
1
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Abstract. Many metal oxides investigated for solar photocatalysis or photoelectrochemistry have band gaps that are too wide to absorb a sufficient portion of the solar spectrum. Doping with impurity ions has been extensively explored as a strategy to sensitize such oxides to visible light, but the electronic structures of the resulting materials are frequently complex and poorly understood. Here, we report a detailed photoconductivity investigation of the wide-gap II-VI semiconductor ZnO doped with Co 2+ (Zn 1-x Co x O), which responds to visible light in photoelectrochemical and photoconductivity experiments and thus represents a well-defined model system for understanding dopant-sensitized oxides. Variable-temperature scanning photoconductivity measurements have been performed on Zn 1-x Co x O epitaxial films to examine the relationship between dopant concentration (x) and visible-light photoconductivity, with particular focus on mid-gap intra-d-shell (d-d) photoactivity. Excitation into the intense 4 T 1 (P) dd band at ~2.0 eV (620 nm) leads to Co 2+/3+ ionization with a quantum efficiency that increases with decreasing cobalt concentration and increasing sample temperature. Both spontaneous and thermally assisted ionization from the Co 2+ d-d excited state are found to become less effective as x is increased, attributed to an increasing conduction-band-edge potential. These trends counter the increasing light absorption with increasing x, explaining the experimental maximum in external photon-to-current conversion efficiencies at values well below the solid solubility of Co 2+ in ZnO.

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“…Photocatalytic deactivation has been reported whether photocatalyst is used in slurry or fixed-bed configuration which is related to the strong inhibition from the inorganic ions on the surface of the TiO 2 [58]. A number of studies have been conducted on the effect of inorganic ions (anions and cations) on TiO 2 photocatalytic degradation [59]. Some of the cations such as copper, iron and phosphate have been reported to decrease the photodegradation efficiency if they are present at certain concentrations whereas calcium, magnesium and zinc have little effect on the photodegradation of organic compounds which is associated to the fact that these cations have are at their maximum oxidation states that results in their inability to have any inhibitory effect on the degradation process [60].…”

mentioning

confidence: 99%

A Review on the Factors Affecting the Photocatalytic Degradation of Hazardous Materials

Kumar

Gajanan

ey³

2017

MSEIJ

207

124

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The oxidation rates and efficiency of the photocatalytic system are highly dependent on a number of operational parameters that govern the photodegradation of the organic molecule. Several study have been reported the significance of operational parameter. The photodegradation depends on the some basic parameters which are concentration of substrate, amount of photocatalyst, pH of the solution, temperature of reaction medium, time of irradiation of light, the intensity of light, surface area of photocatalyst, dissolve oxygen in the reaction medium, nature of the photocatalyst, nature of the substrate, doping of metal ions and non metal and structure of photocatalyst and substrate. The photodegradation of organic compound have been studied by the several scientists and conclude the optimum conditions for the photodegradation of organic compound.The photodegradation of organic compounds was found maximum at low concentration of organic substrate with optimum amount of photocatalyst. The pH of the solution is also affect the photodegradation of organic substrate. The Titania show the maximum adsorption at low pH hence the photodegradation also found maximum at low pH. The surface area is the crucial factor for the photodegradation of organic substrate. If we are increasing the surface area of photocatalyst, the photodegradation of organic substrate increase. This is because that the number of active site increased with increasing the surface area. The amount of photocatalyst is the primary requirement of any photocatalysis process. The amount of photocatalyst should be optimum, if we take the high amount of photocatalyst the photodegradation is decreased, if we take the low amount of photocatalyst the photodegradation also decreased. The doping of metal ions and non-metal ions affect the photodegradation of organic substrate. Therefore, we have to use the metal ions which increased the positive charge on the surface of photocatalyst. The temperature and irradiation of light also affect the photodegradation of organic substrate. For the maximum photodegradation, the photocatalytic reaction should perform at room temperature not greater than 80 °C. The light of irradiation should be used which exit the electron easily from valence band to conduction band or equal to band gap energy. Keywords: A Review on the Factors Affecting the Photocatalytic Degradation of Hazardous Materials 2/10Copyright: ©2017 Kumar et al. for the removal of pollutants at high concentrations. The biological treatments are very slow, dispose large amount of sludge and required strict control of proper pH and temperature [21]. In this regard photo catalytic processes have advantages for the removal of pollutants even at low concentration for industrial waste water [22]. Moreover in photo oxidation, complete oxidation of organic pollutants take place within few hours, even at ppb level, without formation of secondary hazardous products using highly active and cheap catalysts which can be used in specially design reactor systems [23].Ti...

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Photocatalytic decolorization of methylene blue over Zn1−xCoxO under visible light irradiation

Cited by 113 publications

References 25 publications

Preparation, characterization and photocatalytic activity of Co-doped ZnO powders

Preparation, characterization and photocatalytic activity of Co-doped ZnO powders

Visible-light photoconductivity of Zn1−xCoxO and its dependence onCo
Johnson
¹
,
Cohn
²
,
Kaspar
³

et al. 2011
Phys. Rev. B
37
5
39
1
View full text Add to dashboard Cite

A Review on the Factors Affecting the Photocatalytic Degradation of Hazardous Materials

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Photocatalytic decolorization of methylene blue over Zn1−xCoxO under visible light irradiation

Cited by 113 publications

References 25 publications

Preparation, characterization and photocatalytic activity of Co-doped ZnO powders

Preparation, characterization and photocatalytic activity of Co-doped ZnO powders

Visible-light photoconductivity of Zn1−xCoxO and its dependence onCoJohnson1, Cohn2, Kaspar3 et al. 2011Phys. Rev. B375391View full textAdd to dashboardCite

A Review on the Factors Affecting the Photocatalytic Degradation of Hazardous Materials

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Visible-light photoconductivity of Zn1−xCoxO and its dependence onCo
Johnson
¹
,
Cohn
²
,
Kaspar
³

et al. 2011
Phys. Rev. B
37
5
39
1
View full text Add to dashboard Cite