Remarkable Enhancement of Photocatalytic Water Oxidation in N2/Ar Plasma Treated, Mesoporous TiO2 Films

Syed Z. Islam; Allen Reed; Namal Wanninayake; Doo Young Kim; Stephen E. Rankin

doi:10.1021/acs.jpcc.6b02622

Remarkable Enhancement of Photocatalytic Water Oxidation in N₂/Ar Plasma Treated, Mesoporous TiO₂ Films

Syed Z. Islam, Allen Reed, Namal Wanninayake, Doo Young Kim, Stephen E. Rankin

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52 Scopus citations

Abstract

Mesoporous TiO₂ films treated with N₂/argon plasma were studied for ultraviolet and visible-light-induced photocatalytic water oxidation activity. Compared to pristine TiO₂ films, plasma-treated TiO₂ films showed remarkable enhancement of photocurrents (up to 80-240 times) in both ultraviolet light and visible light, greatly surpassing enhancements previously reported in the literature. The cubic-ordered mesoporous TiO₂ thin films were prepared by a surfactant-templated sol-gel method and were treated with N₂/argon plasma, an approach hypothesized to capitalize on the high degree of disorder in the material and the high energy of the plasma species to achieve efficient nitrogen doping. The effects of reaction gas pressure and N₂ gas flow rate on photoelectrochemical (PEC) response were investigated. UV-vis absorbance spectra indicated that the incorporated N atoms significantly reduced the band gap of TiO₂ with the enhancement of visible-light absorption, and XPS analysis showed primarily substitutional N atom incorporation rather than interstitial. The photocatalytic activity of nitrogen-doped TiO₂ (N-TiO₂) films was evaluated by chronoamperometry and linear sweep voltammetry. The effect of light sources on PEC performance was explored using UV (365 nm), blue (455 nm), and green (530 nm) LEDs. N-TiO₂ films showed 242× and 240× enhancement of photocurrent, compared to undoped TiO₂ films under UV and blue LED irradiation, respectively. The N-doped films also showed overall enhancement of up to 70× and 92× with a broad spectrum Xe arc lamp and halogen bulb, respectively, and photocatalytic activity even with green LED illumination, compared to no measurable activity without doping. The present study shows that plasma-induced doping of sol-gel materials enables the efficient incorporation of heteroatoms into disordered metal oxide nanostructures, thereby leading to remarkable enhancement in visible-light-driven photoelectrochemical water oxidation.

Original language	English
Pages (from-to)	14069-14081
Number of pages	13
Journal	Journal of Physical Chemistry C
Volume	120
Issue number	26
DOIs	https://doi.org/10.1021/acs.jpcc.6b02622
State	Published - Jul 7 2016
Externally published	Yes

Funding

The authors acknowledge financial support from University of Kentucky faculty start-up funds (DYK). Experiments to develop the mesoporous titania film synthesis approach were performed as part of a U.S. Department of Energy EPSCoR Implementation award supported by grant no. DE-FG02-07-ER46375. The detailed study as a function of plasma parameters, further analysis of the spectroscopic and structural characteristics of the doped films, and water oxidation experiments were performed as part of a National Science Foundation EPSCoR Researc Infrastructure Initiative award supported by grant no. IIA-1355438. Finally, the authors thank Prof. Y.T. Cheng, Prof. Dibakar Bhattacharyya and Andrew Colburn, and Prof. Brad Berron and Ishan Fursule, Prof. Anne- Frances Miller and Dr. Rupam Sarma, and Prof. Vijay Singh and Sai Guduru for access and assistance with the XPS, zeta potential, contact angle measurements, oxygen measurement, and water oxidation using the Xe arc lamp, respectively.

Funders	Funder number
U.S. Department of Energy EPSCoR	DE-FG02-07-ER46375
National Science Foundation	IIA-1355438
University of Kentucky

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10.1021/acs.jpcc.6b02622

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title = "Remarkable Enhancement of Photocatalytic Water Oxidation in N2/Ar Plasma Treated, Mesoporous TiO2 Films",

abstract = "Mesoporous TiO2 films treated with N2/argon plasma were studied for ultraviolet and visible-light-induced photocatalytic water oxidation activity. Compared to pristine TiO2 films, plasma-treated TiO2 films showed remarkable enhancement of photocurrents (up to 80-240 times) in both ultraviolet light and visible light, greatly surpassing enhancements previously reported in the literature. The cubic-ordered mesoporous TiO2 thin films were prepared by a surfactant-templated sol-gel method and were treated with N2/argon plasma, an approach hypothesized to capitalize on the high degree of disorder in the material and the high energy of the plasma species to achieve efficient nitrogen doping. The effects of reaction gas pressure and N2 gas flow rate on photoelectrochemical (PEC) response were investigated. UV-vis absorbance spectra indicated that the incorporated N atoms significantly reduced the band gap of TiO2 with the enhancement of visible-light absorption, and XPS analysis showed primarily substitutional N atom incorporation rather than interstitial. The photocatalytic activity of nitrogen-doped TiO2 (N-TiO2) films was evaluated by chronoamperometry and linear sweep voltammetry. The effect of light sources on PEC performance was explored using UV (365 nm), blue (455 nm), and green (530 nm) LEDs. N-TiO2 films showed 242× and 240× enhancement of photocurrent, compared to undoped TiO2 films under UV and blue LED irradiation, respectively. The N-doped films also showed overall enhancement of up to 70× and 92× with a broad spectrum Xe arc lamp and halogen bulb, respectively, and photocatalytic activity even with green LED illumination, compared to no measurable activity without doping. The present study shows that plasma-induced doping of sol-gel materials enables the efficient incorporation of heteroatoms into disordered metal oxide nanostructures, thereby leading to remarkable enhancement in visible-light-driven photoelectrochemical water oxidation.",

author = "Islam, {Syed Z.} and Allen Reed and Namal Wanninayake and Kim, {Doo Young} and Rankin, {Stephen E.}",

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T1 - Remarkable Enhancement of Photocatalytic Water Oxidation in N2/Ar Plasma Treated, Mesoporous TiO2 Films

AU - Islam, Syed Z.

AU - Reed, Allen

AU - Wanninayake, Namal

AU - Kim, Doo Young

AU - Rankin, Stephen E.

PY - 2016/7/7

Y1 - 2016/7/7

N2 - Mesoporous TiO2 films treated with N2/argon plasma were studied for ultraviolet and visible-light-induced photocatalytic water oxidation activity. Compared to pristine TiO2 films, plasma-treated TiO2 films showed remarkable enhancement of photocurrents (up to 80-240 times) in both ultraviolet light and visible light, greatly surpassing enhancements previously reported in the literature. The cubic-ordered mesoporous TiO2 thin films were prepared by a surfactant-templated sol-gel method and were treated with N2/argon plasma, an approach hypothesized to capitalize on the high degree of disorder in the material and the high energy of the plasma species to achieve efficient nitrogen doping. The effects of reaction gas pressure and N2 gas flow rate on photoelectrochemical (PEC) response were investigated. UV-vis absorbance spectra indicated that the incorporated N atoms significantly reduced the band gap of TiO2 with the enhancement of visible-light absorption, and XPS analysis showed primarily substitutional N atom incorporation rather than interstitial. The photocatalytic activity of nitrogen-doped TiO2 (N-TiO2) films was evaluated by chronoamperometry and linear sweep voltammetry. The effect of light sources on PEC performance was explored using UV (365 nm), blue (455 nm), and green (530 nm) LEDs. N-TiO2 films showed 242× and 240× enhancement of photocurrent, compared to undoped TiO2 films under UV and blue LED irradiation, respectively. The N-doped films also showed overall enhancement of up to 70× and 92× with a broad spectrum Xe arc lamp and halogen bulb, respectively, and photocatalytic activity even with green LED illumination, compared to no measurable activity without doping. The present study shows that plasma-induced doping of sol-gel materials enables the efficient incorporation of heteroatoms into disordered metal oxide nanostructures, thereby leading to remarkable enhancement in visible-light-driven photoelectrochemical water oxidation.

AB - Mesoporous TiO2 films treated with N2/argon plasma were studied for ultraviolet and visible-light-induced photocatalytic water oxidation activity. Compared to pristine TiO2 films, plasma-treated TiO2 films showed remarkable enhancement of photocurrents (up to 80-240 times) in both ultraviolet light and visible light, greatly surpassing enhancements previously reported in the literature. The cubic-ordered mesoporous TiO2 thin films were prepared by a surfactant-templated sol-gel method and were treated with N2/argon plasma, an approach hypothesized to capitalize on the high degree of disorder in the material and the high energy of the plasma species to achieve efficient nitrogen doping. The effects of reaction gas pressure and N2 gas flow rate on photoelectrochemical (PEC) response were investigated. UV-vis absorbance spectra indicated that the incorporated N atoms significantly reduced the band gap of TiO2 with the enhancement of visible-light absorption, and XPS analysis showed primarily substitutional N atom incorporation rather than interstitial. The photocatalytic activity of nitrogen-doped TiO2 (N-TiO2) films was evaluated by chronoamperometry and linear sweep voltammetry. The effect of light sources on PEC performance was explored using UV (365 nm), blue (455 nm), and green (530 nm) LEDs. N-TiO2 films showed 242× and 240× enhancement of photocurrent, compared to undoped TiO2 films under UV and blue LED irradiation, respectively. The N-doped films also showed overall enhancement of up to 70× and 92× with a broad spectrum Xe arc lamp and halogen bulb, respectively, and photocatalytic activity even with green LED illumination, compared to no measurable activity without doping. The present study shows that plasma-induced doping of sol-gel materials enables the efficient incorporation of heteroatoms into disordered metal oxide nanostructures, thereby leading to remarkable enhancement in visible-light-driven photoelectrochemical water oxidation.

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ER -

Remarkable Enhancement of Photocatalytic Water Oxidation in N₂/Ar Plasma Treated, Mesoporous TiO₂ Films

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