TY - JOUR

T1 - UV-induced formation of color centers in dispersed TiO2 particles

T2 - Effect of thermal treatment, metal (Al) doping, and adsorption of molecules

AU - Shaitanov, Leonid

AU - Murashkina, Anna

AU - Rudakova, Aida

AU - Ryabchuk, Vladimir

AU - Emeline, Alexei

AU - Artemev, Yurii

AU - Kataeva, Galina

AU - Serpone, Nick

PY - 2018/3/1

Y1 - 2018/3/1

N2 - Titanium dioxide is one of the most popular photoactive solids used as a photocatalyst, and as a self-cleaning, bactericidal, superhydrophilic (hydrophobic) and photochromic material when exposed to UV light. The primary steps of titania's response to UV light are responsible for its photoactivity that involve generation of photocarriers subsequent to photoexcitation in its intrinsic (band-to-band transitions) and extrinsic absorption regions (defects-to-conduction band transitions). Photoexcitation into extrinsic absorption bands related mainly to extrinsic defects introduced deliberately through doping and to pre-existing intrinsic defects is an important step in the creation of visible-light-active (VLA) photocatalysts and other VLA titania-based materials. Despite the useful effects of doping, doping can also be detrimental because it can enhance the loss of otherwise active photocarriers through recombination with increasing dopant concentration. This article reports on AlxTi(1-x)O2 materials at different levels of Al doping that preliminary testing revealed significant photoinduced coloration. Materials were characterized by X-ray diffraction, Raman spectroscopy, XPS spectroscopy, SEM/EDX spectroscopic microanalyses, diffuse reflectance spectroscopy, and by the BET method for specific surface area determination. The principal objectives were to examine the effect(s) of thermal treatment of pristine titania (up to 1000 degrees C) and Al-doped titania that led to the formation of intrinsic and extrinsic (Al in Ti positions) defects in the subsurface region and in the bulk lattice, together with the effect(s) that adsorbed and photoadsorbed oxygen and hydrogen molecules impart on the UV-induced coloration of dispersed titania particles. Results confirm that both thermal treatment and Al doping of titania caused noticeable UV coloration of the titania particles. The ultimate level of coloration of TiO2 under illumination in air was an order of magnitude greater than in vacuum. Results also demonstrate that UV-induced photocoloration of titania could delineate between the subsurface and bulk areas in titania particles, and could assess the depth of the subsurface region from the depth of the space charge region. The relevance of using the photocoloration of titania and other metal oxides as a simple tool to determine whether or not a so-called photocatalyzed reaction is truly catalytic has also been inferred. (C) 2017 Elsevier B.V. All rights reserved.

AB - Titanium dioxide is one of the most popular photoactive solids used as a photocatalyst, and as a self-cleaning, bactericidal, superhydrophilic (hydrophobic) and photochromic material when exposed to UV light. The primary steps of titania's response to UV light are responsible for its photoactivity that involve generation of photocarriers subsequent to photoexcitation in its intrinsic (band-to-band transitions) and extrinsic absorption regions (defects-to-conduction band transitions). Photoexcitation into extrinsic absorption bands related mainly to extrinsic defects introduced deliberately through doping and to pre-existing intrinsic defects is an important step in the creation of visible-light-active (VLA) photocatalysts and other VLA titania-based materials. Despite the useful effects of doping, doping can also be detrimental because it can enhance the loss of otherwise active photocarriers through recombination with increasing dopant concentration. This article reports on AlxTi(1-x)O2 materials at different levels of Al doping that preliminary testing revealed significant photoinduced coloration. Materials were characterized by X-ray diffraction, Raman spectroscopy, XPS spectroscopy, SEM/EDX spectroscopic microanalyses, diffuse reflectance spectroscopy, and by the BET method for specific surface area determination. The principal objectives were to examine the effect(s) of thermal treatment of pristine titania (up to 1000 degrees C) and Al-doped titania that led to the formation of intrinsic and extrinsic (Al in Ti positions) defects in the subsurface region and in the bulk lattice, together with the effect(s) that adsorbed and photoadsorbed oxygen and hydrogen molecules impart on the UV-induced coloration of dispersed titania particles. Results confirm that both thermal treatment and Al doping of titania caused noticeable UV coloration of the titania particles. The ultimate level of coloration of TiO2 under illumination in air was an order of magnitude greater than in vacuum. Results also demonstrate that UV-induced photocoloration of titania could delineate between the subsurface and bulk areas in titania particles, and could assess the depth of the subsurface region from the depth of the space charge region. The relevance of using the photocoloration of titania and other metal oxides as a simple tool to determine whether or not a so-called photocatalyzed reaction is truly catalytic has also been inferred. (C) 2017 Elsevier B.V. All rights reserved.

KW - Adsorption of molecules

KW - Al-doped TiO

KW - Color enters

KW - Electron traps

KW - Electron-hole recombination

KW - Hole traps

KW - Photocatalytic determination using photocoloration

KW - Photocoloration

KW - Recombination centers

KW - Thermal treatment

KW - UV-induced coloration

KW - SPECTRAL DEPENDENCIES

KW - SURFACE-REACTIONS

KW - HETEROGENEOUS PHOTOCATALYSIS

KW - PHOTOCHEMICAL PROCESSES

KW - CHARGE-CARRIER DYNAMICS

KW - DOPED TIO2

KW - ELECTRON-PARAMAGNETIC-RESONANCE

KW - LIGHT-ACTIVE TIO2

KW - Al-doped TiO2

KW - OPTICAL-ABSORPTION

KW - TITANIUM-DIOXIDE

UR - http://www.scopus.com/inward/record.url?scp=85028344868&partnerID=8YFLogxK

U2 - 10.1016/j.jphotochem.2017.07.038

DO - 10.1016/j.jphotochem.2017.07.038

M3 - Article

AN - SCOPUS:85028344868

VL - 354

SP - 33

EP - 46

JO - Journal of Photochemistry and Photobiology A: Chemistry

JF - Journal of Photochemistry and Photobiology A: Chemistry

SN - 1010-6030

ER -