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. 2022 Oct 29;23(21):13162.
doi: 10.3390/ijms232113162.

Monitoring the Simultaneous Implantation of Ti and Tb Cations to a Sacrificial Template and the Sol-Gel Synthesis of Tb-Doped TiO2 (Anatase) Hollow Spheres and Their Transition to Rutile Phase

María Teresa Colomer  1 , Florencia Vattier  2
Affiliations

Monitoring the Simultaneous Implantation of Ti and Tb Cations to a Sacrificial Template and the Sol-Gel Synthesis of Tb-Doped TiO2 (Anatase) Hollow Spheres and Their Transition to Rutile Phase

María Teresa Colomer et al. Int J Mol Sci. .

Abstract

Tb-doped TiO2 (anatase) micro-hollow spheres (HSs) with nano-shells, in the range 0.00-3.00 at.% Tb, were successfully synthesized by a simultaneous chemical implantation route of both Ti and Tb cations from chlorides to a poly-styrene (PST)-co-poly-divinyl benzene (PDVB) sacrificial template, followed by controlled hydrolysis and polycondensation reactions. After water addition to the mixture of the precursors with the template, a decrease in the intensity and a shift to lower wavenumbers of the C=O absorption band in the IR spectra can indicate not only the anchoring of Ti and Tb ions to the carbonyl group of the template but also the hydrolysis of the implanted precursors. This latter process can involve a proton attack on the Ti-Cl, Tb-Cl and C=O bonds, the occupation of a vacant site by a water molecule, and then the dissociation of the dangling Ti-Cl, Tb-Cl ligands and C=O bonds. It gives rise to Ti1-xTbx[(OH)4-uClv]@PST-PDVB and Ti1-xTbx[(OH)4-y]@PST-PDVB complexes (x = 0.00, 0.0012, 0.0170 and 0.030). Finally, polycondensation of these species leads to Ti1-xTbxO2-w'@PST-PDVB compounds. After subsequent thermal removal at 550 °C of the template, the IR bands of the core (template) totally vanished and new bands were observed in the 400-900 cm-1 region which can be attributed to the metalloxane bondings (M-O, M'-O, M-O-M, M-O-M' and/or M'-O-M', being M and M' = Ti and Tb, respectively, i.e., mainly vibration modes of anatase). Then, micron-sized HSs of TiO2 and Tb-doped-TiO2 (anatase) were obtained with nano-shells according to field emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM) observations. Furthermore, X-ray photoelectron spectroscopy (XPS) measurements confirmed the presence of Tb4+ (38.5 and 41.2% for 1.70 and 3.00 at.% Tb, respectively) in addition to Tb3+ in the resulting HSs, with increasing Tb4+ content with both Tb doping and higher calcination temperatures. Then, these HSs can be considered as rare earth (RE) co-doped systems, at least for 1.70 and 3.00 at.% Tb contents being the transition to rutile phase favored by Tb doping for those compositions. Finally, diffusion of Tb from the inner parts to the surface of the HSs with the calcination treatments was also observed by XPS.

Keywords: Tb; TiO2; X-ray methods; hollow sphere; implantation; sol-gel.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Normalized IR spectra of the template (a), of the template + TiCl4 and TbCl3 mixture + HClaq after 2 h of reaction (b) and after 5 h of reaction (c), i.e., of the Ti1−xTbx[(OH)4−uClv]@PST–PDVB intermediate compound (Tb content in (b) and (c) is 0.12 at.%). Arrows are added in order to follow the evolution of the IR bands being the related reactions explained in the text.
Figure 2
Figure 2
FEG-SEM picture of the mixture of the template + TiCl4 and TbCl3 precursors together with its characteristic XEDS analysis before the water addition, i.e., before hydrolysis and polycondensation reactions (HSs with 0.12 at.% Tb).
Figure 3
Figure 3
Normalized IR spectra of 0.00%_550 and 1.70%_550 (a) and (b), respectively, and 0.00%_1000 and 1.70%_1000 (c) and (d), respectively.
Figure 4
Figure 4
FEG-SEM pictures of the template + TiCl4 and TbCl3 mixture + HClaq after 5 h of reaction (a) (it corresponds to the sample of IR in Figure 1c) and FEG-SEM picture of the 0.12 at.% Tb HSs after 7 h of reaction and calcination at 550 °C (0.12%_550) (b).
Figure 5
Figure 5
TEM picture of a 0.12%_550 HS where the shell thickness of the capsule can be observed (a). SAED pattern corresponding to the HS is shown in (b).
Figure 6
Figure 6
(a) N2 adsorption–desorption isotherm curves of the template and of the Ti0.988Tb0.012 [(OH)4−uClv]@PST–PDVB composite. (b) N2 adsorption–desorption isotherm curves of 0.12%_550 HSs and 1.70%_550.
Figure 6
Figure 6
(a) N2 adsorption–desorption isotherm curves of the template and of the Ti0.988Tb0.012 [(OH)4−uClv]@PST–PDVB composite. (b) N2 adsorption–desorption isotherm curves of 0.12%_550 HSs and 1.70%_550.
Figure 7
Figure 7
Indexed XRD patterns of the template (a), the Ti1−xTbx[(OH)4−uClv]@PST–PDVB (x = 0.012) intermediate product after 5 h of reaction (b) and Ti1−xTbxO2−w′ (x = 0.012) after calcination at 550 °C for 30 min (0.12%_550) (normalized XRD pattern) (c). The peaks at 18.18, 18.74 and 25.26° that can confirm the implantation of TiCl4 and TbCl3 in the PST–PDVB matrix are indicated with arrows.
Figure 8
Figure 8
Thermogravimetric and differential thermal analyses curves of the Ti0.988Tb0.012 [(OH)4−uClv]@PST–PDVB composite (a and a′, respectively) in air (Tb content is 0.12 at.%). The star indicates the exothermic peak related to Cl− removal.
Figure 9
Figure 9
Experimental and fitted Tb 3d5/2 X-ray photoelectron spectral region for selected samples 3.00%_550 (a), 1.70%_800 (b), and 1.70%_1000 (c). Vertical lines are added for easy reading of the peak values on the X-axis.
Figure 10
Figure 10
(a) Normalized and indexed XRD patterns of 0.00%_800 (a), 0.12%_800 (b), 1.70%_800 (c) and 1.70%_1000 (d). HSs. a indicates anatase and r rutile phase, respectively. The peak of the Si holder and SiO2 (contamination of agate mortar after milling: crystoballite quartz) are labeled * and §, respectively.
Figure 11
Figure 11
Representative TEM picture of a 1.70%_1000 HS (a) and SAED pattern corresponding to the HS is shown in (b).
See this image and copyright information in PMC

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