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The Photoelectrophoresis of Colloidal Iron Oxides I: Hematite (alpha-Fe2O3)

Research output: Contribution in Book/Report/Proceedings - With ISBN/ISSNChapter (peer-reviewed)

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The Photoelectrophoresis of Colloidal Iron Oxides I: Hematite (alpha-Fe2O3). / Boxall, Colin; Zhang, Zhenhong; KELSALL, G H .

Colloids in the Aquatic Environment. ed. / Tharwat Thadros; John Gregory. Amsterdam : Elsevier Science Ltd., 1993. p. 145-163.

Research output: Contribution in Book/Report/Proceedings - With ISBN/ISSNChapter (peer-reviewed)

Harvard

Boxall, C, Zhang, Z & KELSALL, GH 1993, The Photoelectrophoresis of Colloidal Iron Oxides I: Hematite (alpha-Fe2O3). in T Thadros & J Gregory (eds), Colloids in the Aquatic Environment. Elsevier Science Ltd., Amsterdam, pp. 145-163.

APA

Boxall, C., Zhang, Z., & KELSALL, G. H. (1993). The Photoelectrophoresis of Colloidal Iron Oxides I: Hematite (alpha-Fe2O3). In T. Thadros, & J. Gregory (Eds.), Colloids in the Aquatic Environment (pp. 145-163). Elsevier Science Ltd..

Vancouver

Boxall C, Zhang Z, KELSALL GH. The Photoelectrophoresis of Colloidal Iron Oxides I: Hematite (alpha-Fe2O3). In Thadros T, Gregory J, editors, Colloids in the Aquatic Environment. Amsterdam: Elsevier Science Ltd. 1993. p. 145-163

Author

Boxall, Colin ; Zhang, Zhenhong ; KELSALL, G H . / The Photoelectrophoresis of Colloidal Iron Oxides I: Hematite (alpha-Fe2O3). Colloids in the Aquatic Environment. editor / Tharwat Thadros ; John Gregory. Amsterdam : Elsevier Science Ltd., 1993. pp. 145-163

Bibtex

@inbook{8f2ad2fe7ed040229cb0106cfe58f434,
title = "The Photoelectrophoresis of Colloidal Iron Oxides I: Hematite (alpha-Fe2O3)",
abstract = "Aqueous dispersions of colloidal hematite were prepared by aqueous precipitation and characterised using X-ray diffraction and Fourier transform infrared spectroscopy. Their surface chemistry was studied using (photo-)electrophoresis, in which electrophoretic mobilities were determined by laser Doppler electrophoresis, in the absence and presence of irradiation of photons from a xenon lamp and monochromator. Absorption of ultra-band-gap energy photons in Fe2O3 results in the generation of electron (e-)-hole (h+) pairs, which may then recombine, with the generation of heat/radiation, or react with lattice sites, solvent or solution species. Changing the pH of alpha-Fe2O3 particle preparation from 2 to 1.4 was found to alter the resultant surface from one comprising mostly alpha-Fe2O3, alpha-FeOOH and gamma-FeOOH with an isoelectric point (i.e.p.) of 7.4, to one whose behaviour was dominated by the presence of delta-FeOOH with an i.e.p. of 1.5. The alpha-Fe2O3 particles whose surfaces are found to be mostly ''Fe(OH)3''/Fe2O3.nH2O in character exhibit a continuum of i.e.p.s due to the non-crystalline nature of that phase. Large changes in the electrophoretic mobility of colloidal alpha-Fe2O3 at a pH of less than about 7-8 were observed upon irradiation with photons with ultra-band-gap energies, indicative of the formation of net surface positive charge, due to the hole-driven photo-oxidation of surface >Fe-OH sites to form (>Fe-OH)+ sites. Photogenerated conduction band electrons were removed from the particles via either the reductive dissolution of the alpha-Fe2O3 surface or, possibly, the formation of hydrogen from the reduction of H+ ions. The photoelectrophoretic mobility-illumination wavelength spectrum of colloidal alpha-Fe2O3 exhibits two distinct mobility change onsets, one at 2.2 eV and the other at 3 eV, reflecting the presence of an ''upper'' and ''lower'' valence band on hematite. The oxidation of surface >Fe-OH groups responsible for the change in net surface positive charge is found to proceed ten times more slowly than the corresponding reaction on colloidal TiO2. ",
keywords = "COLLOIDAL SEMICONDUCTORS; HEMATITE; IRON OXIDES AND OXYHYDROXIDES; PHOTOELECTROPHORESIS; SOLAR ENERGY CONVERSION",
author = "Colin Boxall and Zhenhong Zhang and KELSALL, {G H}",
year = "1993",
language = "English",
isbn = "978-1-85861-038-2",
pages = "145--163",
editor = "Tharwat Thadros and John Gregory",
booktitle = "Colloids in the Aquatic Environment",
publisher = "Elsevier Science Ltd.",

}

RIS

TY - CHAP

T1 - The Photoelectrophoresis of Colloidal Iron Oxides I: Hematite (alpha-Fe2O3)

AU - Boxall, Colin

AU - Zhang, Zhenhong

AU - KELSALL, G H

PY - 1993

Y1 - 1993

N2 - Aqueous dispersions of colloidal hematite were prepared by aqueous precipitation and characterised using X-ray diffraction and Fourier transform infrared spectroscopy. Their surface chemistry was studied using (photo-)electrophoresis, in which electrophoretic mobilities were determined by laser Doppler electrophoresis, in the absence and presence of irradiation of photons from a xenon lamp and monochromator. Absorption of ultra-band-gap energy photons in Fe2O3 results in the generation of electron (e-)-hole (h+) pairs, which may then recombine, with the generation of heat/radiation, or react with lattice sites, solvent or solution species. Changing the pH of alpha-Fe2O3 particle preparation from 2 to 1.4 was found to alter the resultant surface from one comprising mostly alpha-Fe2O3, alpha-FeOOH and gamma-FeOOH with an isoelectric point (i.e.p.) of 7.4, to one whose behaviour was dominated by the presence of delta-FeOOH with an i.e.p. of 1.5. The alpha-Fe2O3 particles whose surfaces are found to be mostly ''Fe(OH)3''/Fe2O3.nH2O in character exhibit a continuum of i.e.p.s due to the non-crystalline nature of that phase. Large changes in the electrophoretic mobility of colloidal alpha-Fe2O3 at a pH of less than about 7-8 were observed upon irradiation with photons with ultra-band-gap energies, indicative of the formation of net surface positive charge, due to the hole-driven photo-oxidation of surface >Fe-OH sites to form (>Fe-OH)+ sites. Photogenerated conduction band electrons were removed from the particles via either the reductive dissolution of the alpha-Fe2O3 surface or, possibly, the formation of hydrogen from the reduction of H+ ions. The photoelectrophoretic mobility-illumination wavelength spectrum of colloidal alpha-Fe2O3 exhibits two distinct mobility change onsets, one at 2.2 eV and the other at 3 eV, reflecting the presence of an ''upper'' and ''lower'' valence band on hematite. The oxidation of surface >Fe-OH groups responsible for the change in net surface positive charge is found to proceed ten times more slowly than the corresponding reaction on colloidal TiO2.

AB - Aqueous dispersions of colloidal hematite were prepared by aqueous precipitation and characterised using X-ray diffraction and Fourier transform infrared spectroscopy. Their surface chemistry was studied using (photo-)electrophoresis, in which electrophoretic mobilities were determined by laser Doppler electrophoresis, in the absence and presence of irradiation of photons from a xenon lamp and monochromator. Absorption of ultra-band-gap energy photons in Fe2O3 results in the generation of electron (e-)-hole (h+) pairs, which may then recombine, with the generation of heat/radiation, or react with lattice sites, solvent or solution species. Changing the pH of alpha-Fe2O3 particle preparation from 2 to 1.4 was found to alter the resultant surface from one comprising mostly alpha-Fe2O3, alpha-FeOOH and gamma-FeOOH with an isoelectric point (i.e.p.) of 7.4, to one whose behaviour was dominated by the presence of delta-FeOOH with an i.e.p. of 1.5. The alpha-Fe2O3 particles whose surfaces are found to be mostly ''Fe(OH)3''/Fe2O3.nH2O in character exhibit a continuum of i.e.p.s due to the non-crystalline nature of that phase. Large changes in the electrophoretic mobility of colloidal alpha-Fe2O3 at a pH of less than about 7-8 were observed upon irradiation with photons with ultra-band-gap energies, indicative of the formation of net surface positive charge, due to the hole-driven photo-oxidation of surface >Fe-OH sites to form (>Fe-OH)+ sites. Photogenerated conduction band electrons were removed from the particles via either the reductive dissolution of the alpha-Fe2O3 surface or, possibly, the formation of hydrogen from the reduction of H+ ions. The photoelectrophoretic mobility-illumination wavelength spectrum of colloidal alpha-Fe2O3 exhibits two distinct mobility change onsets, one at 2.2 eV and the other at 3 eV, reflecting the presence of an ''upper'' and ''lower'' valence band on hematite. The oxidation of surface >Fe-OH groups responsible for the change in net surface positive charge is found to proceed ten times more slowly than the corresponding reaction on colloidal TiO2.

KW - COLLOIDAL SEMICONDUCTORS; HEMATITE; IRON OXIDES AND OXYHYDROXIDES; PHOTOELECTROPHORESIS; SOLAR ENERGY CONVERSION

M3 - Chapter (peer-reviewed)

SN - 978-1-85861-038-2

SP - 145

EP - 163

BT - Colloids in the Aquatic Environment

A2 - Thadros, Tharwat

A2 - Gregory, John

PB - Elsevier Science Ltd.

CY - Amsterdam

ER -