Defect-Rich Brown TiO_2–x Porous Flower Aggregates: Selective Photocatalytic Reversibility for Organic Dye Degradation

Abstract

A low-temperature, Mn(II)-assisted sol-solvothermal strategy has been developed for the synthesis of positively surface-charged defective brown TiO 2−x flower aggregates with porous nature. The porous structure possessed enormous surface defect states such as trivalent titanium ion (Ti 3+ ) and oxygen vacancy (V o ) sites. The defect states present in the brown TiO 2−x facilitated enhanced absorption even in the NIR region of the solar spectrum, whereas for the negatively surface-charged TiO 2 sample, synthesized in the absence of Mn(II), the absorption was limited to the visible region. Obviously, band-gap narrowing occurred for brown TiO 2−x as compared to the yellow TiO 2 synthesized in the absence of Mn(II). Interestingly, studying the photocatalytic efficiency of these materials using a methyl orange−methylene blue (MO-MB) dye mixture model system under solar illumination revealed selective photocatalytic reversibility, with MB and MO photodegradation performed by yellow TiO 2 and brown TiO 2−x , respectively. This is the first report on the use of surface-charged brown TiO 2−x with porous flower aggregate morphology for selective photocatalysis.

Plasma-Synthesized Nitrogen-Doped Titanium Dioxide Nanoparticles With Tunable Visible Light Absorption and Photocatalytic Activity

“…8 Schematic "phase diagram" that illustrates the visual color of the synthesized TiO 2 powders, the predominant form of nitrogen doping, and the TiO 2 particle microstructure as a function of the electrode position relative to the oxygen inlet and of the plasma power commercial P25 powder. Both MO and MB dyes are common for benchmarking the photocatalytic of TiO 2 [2,45,48,51,56,60,[78][79][80]. While we do not expect our materials to outperform P25, which is widely seen as gold standard for photocatalytic activity, the intent of this study is to understand how the tunable properties of our materials translate into tunable photocatalytic performance.…”

“…Prior research on photocatalytic degradation of MB and MO of similar concentration (10 −4 M) revealed that typically a catalyst concentration of around 0.5 g/L is required to reach an efficient degradation of 70-90% within 120-240 min [45,79]. Furthermore, additional supplements such as the addition of H 2 O 2 or metal ion doping are usually used to enhance radical production or adjust surface charges in order to degrade different types of organic dyes [45,46].…”

“…Ultraviolet-visible (UV-Vis) absorbance measurements were carried out on a Cary 7000 UV-Vis spectrometer. UV-Vis spectra were collected from particles deposited on glass and normalized to 1; glass was used as a background [45].…”

“…The influences of reactor geometry and plasma power on the synthesized powder are analyzed for multiple reactor configurations. The nanoparticles' photocatalytic behavior is tested under solar irradiation with methyl orange and methylene blue without the use of metal ion dopants or hydrogen peroxide that is often used in other studies and compared against P25 white TiO 2 [45,46].…”

Nanocomposites containing titanium dioxide for environmental remediation

“…Followed by that, blue [ 151 ], brown [ 152 ], and red titania [ 153 ] were reported. Ullattil et al reported low-temperature synthesis of defective brown titania porous flower aggregates using Mn(II) as reducing agent and template for broad and longer wavelength absorbing material via sol-solvothermal process [ 154 ]. The synthesized brown titania had flower like aggregates that contains ample defects states where titania was found as trivalent ion and oxygen vacancies.…”