Polymorphic phase transformation of Degussa P25 TiO2 by the chelation of diaminopyridine on TiO62− octahedron: Correlation of anatase to rutile phase ratio on the photocatalytic activity

Abstract

a b s t r a c tA series of nitrogen-doped Degussa P25 photocatalysts were synthesized successfully by grinding and calcination method using 2,6-diaminopyridine (DAP) as a nitrogen precursor. The prepared samples were characterized by various analytical methods. The phase contents of anatase and rutile in the Degussa P25 powders have been altered by simply changing the proportion of DAP. A mechanism involving chelated DAP molecule on TiO 6 2− octahedron is discussed. The enhanced activity is attributed to synergistic effect in the two phase solid material. Due to the low activation barrier, the effective inter particle electron transfer between the two polymorphs is quite efficient only when they are in close proximity with similar crystallite sizes. The transfer of electrons from the rutile phase to lattice/electron trapping sites of anatase and also to the Ti 3+ -V o defect level created by the dopant favors effective charge separation and enhance the photocatalytic activity under solar illumination.

Heating rate dependence of anatase to rutile transformation

“…In fact, the presence of nanopar-ticles with high surface area contributes non-negligibly to the chemical potential by changing the activation energy for the phase transformation. For example, in the phase diagrams taken into consideration, there is a significant difference from the value reported by Dachille et al [28], which plotted the extrapolations to atmospheric pressure of the anatase-rutile boundaries intersecting the temperature axis at 605°C, in comparison to the anatase-rutile phase transition temperature reported more recently by Sun et al [25] and fixed at 780°C. Further, the phase stability, that, at room temperature and for macro-crystalline powders, is higher for rutile than for anatase, reverses when particle size becomes less than 10-15 nm [29][30][31].…”

“…Moreover there are many researches that have demonstrated rutile's photocatalytic activity similar to anatase when the crystal size of both phases was comparable [24]. This goal was achieved when the rutile was not prepared as thermally stable phase as reported by Eraiah et al [25].…”

“…Thus, by varying the initial size of TiO 2 nanoparticles the phase transformation reaction path changes, both in terms of transition onset point and growth rate. The significant change of transformation rate and activation energy (about 165.6 kJ/mol and over 330 kJ/mol, respectively, for rutile nucleation, within nanocrystalline anatase particles and coarse ones [32,33]) result into a transition temperature that can vary from 400°C to 1200°C [25,34,35].…”

Melamine modified P25 with heating method and enhanced the photocatalytic activity on degradation of ciprofloxacin

“…Furthermore, the photocatalyst is limited itself properties. For instance, TiO 2 , as the most attention photocatalyst, is low cost, nontoxic and long term stability, especially P25 is a well known commercial material containing anatase and rutile phases which is best for photocatalytic process, and it is widely used in degradation of pollutants, as one kind of bacteriostat, catalytic synthesis area, et al However, it possesses shortcoming of wide band gap and narrow optical absorption range which limited the low quantum efficiency and have hindered its practical application for removal pollutants [4][5][6][7]. Therefore, there are many approaches for modified P25 (TiO 2 ), such as doping with metal and/or nonmetal elements, compound other semiconductors, surfaced sensitization, et al Aiming to reduce the photo-generated charge recombination during the photocatalytic processes, and/or extend the responded light range in the solar [8][9][10].…”

Enhancement of Photoelectrocatalysis Efficiency by Using Nanostructured Electrodes

“…The most efficient powder reported in the literature is the Degussa P25, which is a combination of rutile and anatase allotropic phases in the ratio 3:1. There are many advantages of using this powder: it provides high surface area showing excellent photocatalytic activity because of the adsorptive affinity of organic compounds on the surface of anatase [45]. However, a post-treatment filtration step is required to separate it from the solution, which limits practical application as this is a time-consuming and costly process.…”