Effects of Substitutional Dopants on the Photoresponse of a Polyoxotitanate Cluster

Abstract

In this paper, using a simple method, 17 isostructural polyoxotitanates (POTs) were synthesized, including the pristine [Ti12O16(O(i)Pr)16], the monodefected [Ti11O13(O(i)Pr)18], and the heterometal-doped [Ti11O14(O(i)Pr)17(ML)] (M = Mg, Ca, Zn, Cd, Co, or Ni; L = Cl, Br, I, or NO3). The electronic structures of these POTs were determined by UV-vis spectroscopy and DFT calculations. Upon UV irradiation of the POTs, electron spin resonance showed the formation of Ti(III) under anaerobic conditions and superoxide (O2(•-)) in the presence of O2. The photoactivities of the POTs were then probed with Ti(III) production and short-circuit photocurrent experiments. The photophysical processes were studied using steady-state and transient photoluminescence. The results show that within the very similar structures, the deexcitation processes of the photoexcited POTs can be greatly affected by the dopants, which result in enhanced or decreased photoactivities. Co and Ni doping enhances the absorption of the visible light accompanied by serious loss of UV photoactivities. On the other hand, a Ti vacancy (in [Ti11O13(O(i)Pr)18]) does not reduce the band gap of a POT but improves the UV photoactivities by serving as surface reaction site. The POTs were then used as molecular models of titanium oxide nanoparticles to understand some important issues relevant to doped titanate, i.e., coordination environment of the dopant metal, electronic structure, photoactivities, and photophysical processes. Our present findings suggest that for solar energy harvesting applications of titanium oxides like photocatalysis and solar cells substitution of titanium atoms by transition metal ions (like Co and Ni) to extend the absorption edges may not be an efficient way, while loading of Ti vacancies is very effective.

Binding Modes of Salicylic Acids to Titanium Oxide Molecular Surfaces

“…For TiO 2 NPs functionalized with 2,4,6‐trichlorophenol, they observed a g ≈2.0 ESR signal and assigned it as a phenoxyl radical . For catechol‐functionalized TiO 2 NPs, they also observed the g ≈2.0 ESR signals and assigned them as carbon‐centered radicals at the benzene ring . In the present study, solid‐state ESR of the SSA‐functionalized TOCs show signals centered at g ≈2.0 (Figure ).…”

“…X‐ray crystallographic data for all compounds were recorded with a Bruker SMART APEX II instrument equipped with a Mo Kα source ( λ =0.71073 Å) or Cu Kα radiation ( λ =1.54184 Å). Data were collected in the cryogenic mode (173 K) as described previously . Crystallographic data are provided in the Supporting Information.…”

Structural, optical, and magnetic study of Ni-doped TiO2 nanoparticles synthesized by sol–gel method

“…This shift is associated with the doping as well as the formation of stable phase (rutile) of TiO 2 (Table 1). This can be attributed to the introduction of new electron states in the band structure of TiO 2 upon Ni doping [45]. With further increase in dopant concentration, the bandgap decreases.…”

Engineering new defective phases of UiO family metal–organic frameworks with water

“…The modulated hydrothermal methodology proposed by Ref. 43 provides a green and scalable approach to synthesising several frameworks isoreticular to fcu UiO-66(Zr). However, we noted that the material assigned as the cubic fcu UiO-66(Zr) (F 4 BDC) 43,60 displays a characteristic splitting of the reflection indexed to the fcu (111) reflection into two peaks at 0.49 Å −1 and 0.52 Å −1 , and an additional reflection is present at 0.35 Å −1 .…”

“…Previously reported syntheses of UiO-66 (F 4 BDC) (UiO-66 with tetrafluoroterephthalate linkers) with and without water produce diffraction patterns indicative of different phases, but this has until now not been explained. [42][43][44] Additionally, although the hcp topology has been reported for UiO MOFs formed from other ligands, such as 2,2'-bipyridinedicarboxylate and (nitro)triphenyldicarboxylate 45 since our synthesis of hcp UiO-67(Hf), the archetypal hcp UiO-66 material was until recently unknown, and has only been synthesised using ionic liquids rather than a more standard solvothermal synthesis. 46 In this work we systematically investigate the role of water in the formation of defect phases of UiO family MOFs, using a combination of synthesis, powder X-ray diffraction, thermogravimetric analysis and quantum chemical calculations.…”