TiO2 doping by hydroxyurea at the nucleation stage: towards a new photocatalyst in the visible spectral range

Abstract

We report an original method of preparation of OCN-doped TiO 2 for photocatalysis in the visible spectral range. The preparation is achieved by a sol-gel route using titanium tetraisopropoxide precursor. Special attention was paid to fluid micromixing, which enables homogeneous reaction conditions in the reactor bulk and monodispersity of the produced clusters/nanoparticles. The dopant hydroxyurea (HyU, CH 4 N 2 O 2 ) is injected into the reactive fluid at the nucleation stage, which lasts tens of milliseconds. The doping results in a strong yellow coloration of the nanocolloids due to the absorption band in the spectral range 380-550 nm and accelerates the aggregation kinetics of both nuclei at the induction stage and sub-nuclei units (clusters) at the nucleation stage. FTIR, Raman and UV-visible absorption analyses show the formation of a stable HyU-TiO 2 complex. EXAFS spectra indicate no appreciable changes of the first-shell Ti atom environment. The doping agent takes available surface sites of TiO 2 clusters/ nanoparticles attaining B10% molar loading. The reaction kinetics then accelerates due to a longer collisional lifetime between nanoparticles induced by the formation of a weak QOÁ Á ÁTi bond. The OCN-group bonding to titanium atoms produces a weakening of the CQO double bond and a strengthening of the C-N and N-O bonds.

Highly Efficient Low-Temperature N-Doped TiO2 Catalysts for Visible Light Photocatalytic Applications

“…No differences between samples are noticeable in the Ti 2 p area. Indeed, the shift to a slightly lower binding energy induced by a change in the titanium chemical environment (as in the case of Ti–O–N bonding) would be too small to be distinguished from the main peak [ 47 ]. On the other hand, the systematic absence of a peak around 455–456 eV excludes the presence of Ti–N species.…”

“…For each sample, the O 1 s (530 eV)/Ti 2p ratio is close to 2, corresponding to stoichiometric TiO 2 . The two other components at higher binding energy are complicated to attribute, as they correspond to oxygen bonded to carbon due to carbon contamination and/or nitrogen bonding (N–O–Ti, N=O) [ 47 ].…”

“…This contribution was not taken into account in the latter quantification. In the literature, a N 1 s peak around 400 eV may correspond to many contributions such as NH x , NO x , NHOH potentially due to impurities but also interstitial Ti–O–N [ 47 , 48 ]. Substitutional Ti–N–O can be excluded in our case, since the specific corresponding peak around 395 eV is never observed.…”

“…Concerning the N-doped samples, an increase in the activity is observed for all samples compared to the corresponding pure TiO 2 materials. All samples present a peak at 400 eV, which may correspond to Ti–O–N bonds [ 47 , 48 , 55 , 56 ].…”

New Preparation Method of Visible Light Responsive Titanium Dioxide Photocatalytic Films

“…In addition, the dried gels prepared with urea have included nitrogen as shown in Tables 3(a) and (c). According to the literatures [48]- [50], it has been reported that urea coordinates to titanium through weak C=O → Ti coordination bonding with remaining the carbonyl groups. Therefore, it was expected that the sites coordinated by urea are easy to be hydrolyzed by H 2 O.…”