Effect of the P/Ti Ratio on the Visible-Light Photocatalytic Activity of P-Doped TiO₂

Abstract

P-doped TiO 2 nanoparticles were synthesized by the sol-gel method with various H 3 PO 4 amounts. The samples were calcinated at different temperature and charactered by XPS, ICP, XRD, SEM, Raman, FTIR, and UV-vis methods, so that the formation process of phosphate species could be inspected. The XRD results show that P species hinder the particle growth of anatase and increase the anatase-to-rutile phase transformation temperature to more than 900 °C, and a new titanyl phosphate, Ti 5 O 4 (PO 4 ) 4 , was observed in P-doped TiO 2 when calcined at 1000 °C. The UV-vis results indicate that the P species is likely to have two different states, leading to the variety of visible-light photocatalytic activity and band gap energy of P-doped TiO 2 . One state is the "separated phase". In this state, the P/Ti ratio is very low so that the P species is surrounded by TiO 2 . The "separated phase" of P species introduces oxygen into TiO 2 lattice and hence causes a red-shift of the adsorption band edge of anatase, leading to the increased visible-light photocatalytic activity of P-doped TiO 2 . The other state is the "congregated phase". It appears at the micro region where the ratio of P/Ti is high enough to make the TiO 2 clusters isolated by P species. The "congregated phase" of P species acts as the interface phase between TiO 2 clusters and strongly retards the crystal growth of anatase, resulting in the widened band gap of P-doped TiO 2 . Furthermore, a possible mechanism was also proposed to explain the formation of the two phases during the sol-gel process. The results indicate that in order to improve the visible-light photocatalytic activity of P-doped TiO 2 the percentage of "separated phase" in P species needs to be enhanced.

Surface free energy and surface stress as elastic components of the surface tension of condensed matter

“…The latter is close to the recent DFT calculations [59] of oxygen adsorption on Pb(111) resulted in notable changes in the interlayer distance of the substrate, in the strong influence of the O adsorbate on the neighboring Pb atoms, and in important redistribution of the electronic structure. The similar results were reported for DFT calculations of hydrogen adsorption on Mg(0001) [60].…”

Phenyl Hypophosphorous Acid‐Assisted Synthesis of Carbon‐Modified Anatase‐Brookite Bicrystal TiO2 Nanoparticles with Enhanced Visible‐Light Photocatalytic Performance

“…After the addition of PA, the XRD pattern and TEM results of 0.005 C/TiO 2 reveal the anatase (101) phase and emerging peak of brookite (121), which indicates that the 0.005 C/TiO 2 is a mixture of anatase and brookite. Moreover, with the increasing contents of PA up to 0.01 g, only pure anatase TiO 2 is observed, suggesting that the anatase→brookite→rutile transformation reaction is inhibited by PA . On the other hand, compared to 0.01 C/TiO 2 , 0.015 C/TiO 2 and 0.02 C/TiO 2 samples, 0.005 C/TiO 2 exhibits a weak intensity of anatase (101), which shows the amorphous brookite and small particle size in 0.005 C/TiO 2 .…”

Steam-induced changes in surface characteristics and corrosion resistance of spark-anodized titanium

“…The thin water layer became saturated with [Ti(OH) 6 ] 2− and phosphate anions gradually and then these ions precipitated back to the sample surface. During the precipitation, [Ti(OH) 6 ] 2− aggregated with [Ti(OH) 6 ] 2− or phosphate anions to form Ti-O-Ti or Ti-O-P bonds through dehydration reaction [17], leading to the formation of crystalline anatase and Ti(OH)PO 4 on the surface of spark-anodized titanium. In addition, it was observed that some wire-like products were distributed in low places around the microprojection or in the crater (Fig.…”