Mixed phosphotungstic acid/titanium oxide gels and thin solid xerogel films with electrochromic-ionic conductive properties

Orel, B.; Lavrenčič‐Štangar, U.; Hutchins, M.G.; Kalcher, Kurt

doi:10.1016/0022-3093(94)90018-3

Cited by 31 publications

(12 citation statements)

References 29 publications

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“…26 On the contrary, the solvothermal preparation of PW 12 /TiO 2 exA and PW 12 /ZrO 2 exA composites gave rise to materials in which the HPA skeletal vibrations are not clearly evident 26 ν as (WO d ) was observed, although red-shifted by ca. 10 cm −1 with respect to the pristine PW 12 , indicating a stronger interaction between the HPA and the support, as previously observed by Orel et al 32 with analogous samples. The structure of the Keggin cluster was also preserved in both the binary PW 12 /SiO 2 exA and PW 12 /ZrO 2 exA samples, with slight widening of the vibration bands that can be attributed to electrostatic interaction with the support.…”

Section: Resultssupporting

confidence: 84%

“…On the contrary, the solvothermal preparation of PW 12 /TiO 2 exA and PW 12 /ZrO 2 exA composites gave rise to materials in which the HPA skeletal vibrations are not clearly evident and only the ν as (WO d ) was observed, although red-shifted by ca. 10 cm –1 with respect to the pristine PW 12 , indicating a stronger interaction between the HPA and the support, as previously observed by Orel et al with analogous samples.…”

Section: Resultssupporting

confidence: 84%

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Local Structure of Supported Keggin and Wells–Dawson Heteropolyacids and Its Influence on the Catalytic Activity

et al. 2019

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Keggin [PW12O40] 3and Wells-Dawson [P2W18O62] 6heteropolyanions are nanosized transition metal-oxygen clusters belonging to the heteropolyacids (HPAs) family. They are widely used as catalysts, due to their strong Brönsted acidity, and their dispersion on solid supports favours the accessibility to their acid sites generally increasing the catalytic activity. A series of binary materials composed of Keggin or Wells-Dawson HPAs and SiO2, TiO2 and ZrO2 has been prepared by impregnation or solvothermal methods. Remarkable differences have been found in the catalytic activities among the unsupported and supported HPAs. These differences have been correlated in the past to the structural changes of the HPAs due to the cluster-support interaction, which is different depending on preparation methodologies of the binary material. In the present work, the modes of interaction between the two types of HPA, Keggin and Wells-Dawson, and various supports have been studied by X-ray absorption spectroscopy. The obtained data have been compared with the characterization of the same materials reported before by using different bulk and surface physicochemical techniques. The characterization results were then used to correlate the interaction modes between the HPAs and the supports with the catalytic performances reported for 2-propanol dehydration to propene and for propene hydration to 2-propanol. The results reveal that the deposition of HPA by impregnation or solvothermal treatment may cause distortions in the H3PW12O40 cluster structure depending on stronger (TiO2 and ZrO2) or weaker (SiO2) basic sites presence in the support, respectively. Moreover, the type of preparation method affects the structure and acidic properties of the supported HPAs. In particular, during the preparation of TiO2 and ZrO2 with HPA by in-situ solvothermal method, the reaction of the HPA with the products of metal alkoxides hydrolysis occurs with consequent destruction of the Keggin structure. Therefore, the catalytic activity of such materials is poor. These modifications, in addition to the bulk and surface features of the supported HPAs, affected the catalytic 2-propanol dehydration to a significant extent. On the contrary, the propylene hydration was less influenced, probably, due to the propene non-polar nature.

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Section: Resultssupporting

confidence: 84%

Section: Resultssupporting

confidence: 84%

Local Structure of Supported Keggin and Wells–Dawson Heteropolyacids and Its Influence on the Catalytic Activity

et al. 2019

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“…However, arguments in favor of this explanation were not offered. Also, it is known [13] that electrochemical protonation of PWA is accompanied by a significant weakening of the ν a (W-O b -W) and ν a (W-O c -W) bands and no intensity change of the ν(W=O d ) band. Therefore, the analogous behavior of these bands upon UV irradiation of PVA/PWA nanocomposite films is connected logically to photo-induced proton transfer from PVA to PWA.…”

mentioning

confidence: 98%

Structure and photochromic properties of poly(vinylalcohol)/phosphotungstic acid nanocomposite films

Sushko

Третинников

2010

J Appl Spectrosc

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Poly(vinylalcohol)/phosphotungstic acid (PVA/PWA) nanocomposite films were studied using Fourier-transform infrared and electron absorption spectroscopy. It was found that entrapping PWA into PVA leads to the formation of hydrogen bonds between OH groups of PVA and bridging oxygen atoms of PWA. Terminal oxygen atoms of PWA do not participate in hydrogen-bonding interactions with the polymer. Exposure of the nanocomposite film to UV radiation results both in the photo-induced transfer of protons from PVA to PWA with their attachment to the bridging oxygen atoms of PWA and in the formation of a PVA-PWA complex with the participation of deprotonated oxygen atoms of PVA and the terminal oxygen atoms of PWA. The UV irradiation causes the films to turn blue and a band of d-d transitions of W 5+ ions (480 nm) and two bands of intervalence W 5+ → W 6+ charge-transfer transitions (740 and 1250 nm) to appear in their electronic spectrum.Introduction. Phosphotungstic acid (PWA) is one of many heteropolyacids, which in turn include a variety of polyoxometalates (POM) that are nanoclusters based on transition metal oxides [1]. POM have a broad spectrum of important practical applications including chemical catalysis, membrane and sensor technologies, electrochemical fuel elements, and medicine [2]. These compounds exhibit photochromic properties (reversibly acquire or change color under the action of UV radiation). This enables them to be viewed as promising materials for optical and opto-electronic technologies and information recording and storage media [3]. Lately the number of publications dedicated to studies of hybrid nanomaterials obtained by dispersion of POM nanoclusters in matrices of organic polymers has been increasing rapidly [4-9]. Our goal was to prepare materials combining the advantages of polymers (low specific weight with high mechanical strength, thermal stability, long service life, and ease of fabrication into the required shape) and the photochromic properties of POM incorporated into them. The photochromic additive must be highly dispersed in the polymeric matrix in order to obtain polymer/POM nanocomposites. This is possible only if strong non-bonding interactions occur between the polymer and POM molecules. In practice, this is achieved by using polymers such as polyvinyl alcohol (PVA) [4,5,7], polyvinylpyrrolidone [6], polyacrylamide [8], and dextran [9]. However, strong nonbonding interactions between the polymer and POM can affect the structure of the polymeric matrix and/or the POM nanoclusters and cause substantial changes in the overall properties of the material, including its photochromic properties. Therefore, detailed studies of the molecular structure and non-bonding interactions in these materials with respect to their photochromic properties are needed in order to fabricate polymer/POM hybrid nanocomposites with given and controlled photochromism.The goal of our work was to study the structure and photochromic properties of PVA/PWA nanocomposite films using IR and electronic absorption s...

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“…It was found that the frequencies of the WPAJtitania skeletal bands (1079 cm -1, 979 cm -1, 897 cm -1, 819 cm -1) (Fig. In our previous paper [12] a more detailed IR spectral analysis is reported and the spectral changes upon H + intercalation are discussed for the films made without alkoxide modification. 29H20 by only a few cm -l which indicates that the structure of the Keggin salt was well preserved inside the gel.…”

Section: Resultsmentioning

confidence: 96%

Chromogenic WPA/TiO2 hybrid gels and films

Štangar

Orel

Régis

et al. 1997

J Sol-Gel Sci Technol

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A novel low-temperature electrochromic and photochromic material in the form of gels and thin solid films composed of Ha PW12040 9 nH20 (WPA) incorporated in titanium oxide gel issued of Ti(OPr/)4 with addition of acetic acid were made via the sol-gel route by the dip-coating technique. Gels in bulk and thin film forms have been studied with the help of FT-IR transmission, reflection absorption and Raman spectroscopy. Similarity of the characteristic band frequencies with pure WPA confirmed that entrapped Keggin salt is well preserved inside the gel. Photochromism of WPA/TiO2 gels which appears after short exposure to UV (~. = 366 nm) radiation is related to the excitation effect of branched alcohol leading to formation of carbonyl modes due to the alcohol transformation to aldehyde. Electrochromic properties of WPA/TiO2 gel films were tested in aqueous 0.001M HCIO4 and 0.1M LiC104 electrolytes as well as in the sol-gel electrochromic device (ECD) composed of LiC104 doped ormolyte and Sb : Mo : SnO2 counter electrode film with optically passive response. Slight improvement of the WPA/TiO2 intercalation/deintercalation kinetics was obtained with the films exhibiting one order of magnitude higher electronic conductivity which were made with addition of in situ polymerized pyrrole with Fe(NO3)3.

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Mixed phosphotungstic acid/titanium oxide gels and thin solid xerogel films with electrochromic-ionic conductive properties

Cited by 31 publications

References 29 publications

Local Structure of Supported Keggin and Wells–Dawson Heteropolyacids and Its Influence on the Catalytic Activity

Local Structure of Supported Keggin and Wells–Dawson Heteropolyacids and Its Influence on the Catalytic Activity

Structure and photochromic properties of poly(vinylalcohol)/phosphotungstic acid nanocomposite films

Chromogenic WPA/TiO2 hybrid gels and films

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