Raman- and infrared-spectroscopic investigations of dilute aqueous phosphoric acid solutions

Rudolph, Wolfram W.

doi:10.1039/c0dt00417k

Cited by 107 publications

(98 citation statements)

References 36 publications

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“…The peaks at around 2340 and 2930 cm -1 are characteristic of PA and arise from symmetric and anti-symmetric ν-OH modes. [44][45][46] The high frequency broad peak at around 3560 cm -1 is also characteristic of the free (non-hydrogen bonding) OH moiety of H 3 PO 4 .…”

Section: Resultsmentioning

confidence: 97%

“…The evaporation of both water and nitric acid enhances the formation of the calcium phosphate type species. [44][45][46] Because we could identify the presence CaHPO 4 ·2H 2 O or Ca(H 2 PO 4 ) 2 ·H 2 O in the PXRD pattern, these spectral changes can be attributed to the formation of those phosphates in the freshly prepared samples. [45] The FTIR spectral changes also confirm that these species re-dissolve over time and many sharp peaks disappear from the spectra (compare spectra III and IV in Figure 3, b).…”

Section: Resultsmentioning

confidence: 98%

“…[ [44][45][46] The other broad features at around 3200-3500 cm -1 are due to the free and coordinated water molecules around the ions. The peak at around , and its high frequency shoulder in the pure PA, shifts to 956 cm -1 .…”

Section: Resultsmentioning

confidence: 99%

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Salt‐Acid‐Surfactant Lyotropic Liquid Crystalline Mesophases: Synthesis of Highly Transparent Mesoporous Calcium Hydroxyapatite Thin Films

Tunkara

Dag

2015

Eur J Inorg Chem

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 98%

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Salt‐Acid‐Surfactant Lyotropic Liquid Crystalline Mesophases: Synthesis of Highly Transparent Mesoporous Calcium Hydroxyapatite Thin Films

Tunkara

Dag

2015

Eur J Inorg Chem

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“…An analogous signal is evident in the Raman spectrum of bulk aqueous phosphoric acid [46][47][48]. The most intense Raman band of bulk aqueous phosphoric acid is located between 840 and 960 cm À1 and is caused by stretching vibrations mðPðÀOHÞ 3 Þ of H 3 PO 4 molecules and mðPðÀOHÞ 2 Þ of H 2 PO À 4 ions.…”

Section: Raman Spectramentioning

confidence: 91%

Uptake of protic electrolytes by polybenzimidazole-type polymers: absorption isotherms and electrolyte/polymer interactions

Korte¹,

Conti

Wackerl³

et al. 2015

J Appl Electrochem

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Polybenzimidazole (PBI) membranes doped with phosphoric acid are used as proton-conducting membrane in high-temperature polymer electrolyte fuel cells. There is no general model for the thermodynamics of the absorption process over the whole accessible doping range for all published data. The interactions between H 3 PO 4 and polymer chains, the polycondensation equilibria of H 3 PO 4 and the implications on proton conductivity are still largely unknown. In this study, we demonstrate that the uptake of a protic electrolyte by a polymer with basic moieties, i.e. a PBI-type polymer, can be described satisfactorily with a BET-like absorption isotherm. The absorption equilibria of the uptake process are analysed using literature data on the H 3 PO 4 , H 2 SO 4 and HClO 4 uptake of non-crosslinked m-PBI and AB-PBI as well as using our own investigations on the H 3 PO 4 uptake of a commercial crosslinked PBI derivative, Fumapem AM-55. In addition to the thermodynamic data of the absorption process, Raman data on m-PBI taken from the literature and our own Raman investigations on Fumapem AM-55 are taken into account. It is possible to correlate domains in the absorption isotherms with specific features in the Raman spectra. Two stages for the uptake of a protic electrolyte can be distinguished: (i) the protonation of the polymer chains and thus coulombic interactions with the electrolyte anions, (ii) the formation of H bonds directly with the chains and with electrolyte molecules that are still absorbed.

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“…The first dissociation step of phosphoric acid has been determined by conductivity measurements from 25-200°C and up to 2000 bar pressure [21]. A recent Raman study on dilute aqueous phosphoric acid solutions and deuterated phosphoric acid in D 2 O included the Raman spectroscopic determination of the first dissociation constant in a moderate temperature interval below 100°C [22].…”

Section: Introductionmentioning

confidence: 99%

Raman-Spectroscopic Measurements of the First Dissociation Constant of Aqueous Phosphoric Acid Solution from 5 to 301 °C

Rudolph

2012

J Solution Chem

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Dilute aqueous phosphoric acid solutions have been studied by Raman spectroscopy at room temperature and over a broad temperature range from 5 to 301°C. R-normalized spectra (Bose-Einstein correction) have been constructed and used for quantitative analysis. The vibrational modes of H 3 PO 4 (aq) (pseudo C 3v symmetry) have been assigned. The band with the highest intensity, the symmetric stretch ν s {P(OH) 3 }(ν 1 (a 1 )) is strongly polarized while ν 4 (e), the antisymmetric stretch ν as P(OH) 3 ) is depolarized. The stretching mode of the phosphoryl group (-P=O), ν 2 (a 1 ) occurs at 1178 cm −1 and is polarized. In the range between 300 and 600 cm −1 , the deformation modes are observed. The deformation mode, δ{PO-H}, involving the O-H group has been detected at 1250 cm −1 as a very weak and broad mode.In addition to the modes of phosphoric acid, modes of the dissociation product H 2 PO − 4 (aq) have been observed. The mode at 1077 cm −1 has been assigned to ν s {PO 2 }, and the mode at 877 cm −1 to ν s {P(OH) 2 } which is overlapped by ν s {P(OH) 3 } of H 3 PO 4 (aq). The modes of H 2 PO − 4 (aq) have been measured in dilute solution and were assigned and presented as well. H 3 PO 4 is hydrated in aqueous solution, which can be verified with Raman spectroscopy by following the modes ν 2 (a 1 ) and ν 1 (a 1 ) as a function of temperature. These modes show a strong temperature dependency. The mode ν 1 (a 1 ) broadens and shifts to lower wavenumbers. The mode ν 2 (a 1 ) on the other hand, shifts to higher wavenumbers and broadens considerably with increases in temperature. At 301°C the phosphoric acid is almost molecular in nature. In very dilute H 3 PO 4 solutions at room temperature, however, the dissociation product, H 2 PO − 4 (aq) is the dominant species. In these dilute H 3 PO 4 (aq) solutions no spectroscopic features could be detected for a hydrogen bonded dimeric species of the formula H 5 P 2 O − 8 (or the neutral dimeric acid H 6 P 2 O 8 ). Pyrophosphate formation, although favored at high temperatures, could not be detected in dilute solution even at 301°C due to the high water activity. In highly concentrated solutions, however, pyrophosphate formation is observable and in hydrate melts the formation of pyrophosphate is already noticeable at room temperature.

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Raman- and infrared-spectroscopic investigations of dilute aqueous phosphoric acid solutions

Cited by 107 publications

References 36 publications

Salt‐Acid‐Surfactant Lyotropic Liquid Crystalline Mesophases: Synthesis of Highly Transparent Mesoporous Calcium Hydroxyapatite Thin Films

Salt‐Acid‐Surfactant Lyotropic Liquid Crystalline Mesophases: Synthesis of Highly Transparent Mesoporous Calcium Hydroxyapatite Thin Films

Uptake of protic electrolytes by polybenzimidazole-type polymers: absorption isotherms and electrolyte/polymer interactions

Raman-Spectroscopic Measurements of the First Dissociation Constant of Aqueous Phosphoric Acid Solution from 5 to 301 °C

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