Study of the decomposition pathway of 12-molybdophosphoric acid in aqueous solutions by micro Raman spectroscopy
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2016
Authors
Bajuk-Bogdanović, Danica
Uskoković-Marković, Snežana

Hercigonja, R.
Popa, Alexandru

Holclajtner-Antunović, Ivanka
Article (Published version)

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Micro Raman spectroscopy was applied to investigate the speciation of heteropoly and isopoly molybdates in 0.05 and 0.005 M aqueous solutions of 12-molybdophosphoric acid at pH values between 1 and 6. For comparative purposes, P-31 NMR spectroscopy was applied too. It is shown that stability of Keggin anion is influenced both by pH and concentration of solution. The Keggin structure is stable in acidic solutions (pH lt 1.6) while defective Keggin structures are formed with further alkalization (up to pH lt 5.6). Monolacunary anion PMo11O397- is the main component in the pH region from 1.6 to 3.4. Further removal of molybdenyl species causes the appearance of other vacant Keggin structures such as PMo9O31(OH)(3)(6-) and PMo6O259- at about pH 4. At pH 5.0, anion PMo6O259- is the main species. In solutions with pH greater than 5.0, heteropolymolybdates disappear completely and isopolymolybdates Mo7O246- and MoO42- are formed in higher amounts. In more diluted solution of 0.005 M, the ...decomposition scheme of 12-molybdophosphoric acid solution with increasing of pH takes place without observation of significant amounts of Mo7O246- species. If alkalinization is performed with 0.5 M instead of 5 M NaOH, there are no significant changes in the Raman spectra of solutions. It is shown that the spectra of evaporated samples may be used for the identification of molecular species in corresponding concentrated solutions. However, Raman spectra of dry residues of more diluted solutions differ from spectra of corresponding solutions due to the reactions performed during the process of drying and cannot be used for unambiguous identification of species in solution. Acidification of 0.05 M solution of Na2MoO4 shows that at pH >5.6, molybdate anion MoO42- dominates, while in the pH range between 5.6 and 1, heptamolybdate anion Mo7O246- is preferentially formed.
Source:
Spectroscopy Letters, 2016, 153, 152-159Publisher:
- Pergamon-Elsevier Science Ltd, Oxford
Funding / projects:
- Electroconducting and redox-active polymers and oligomers: synthesis, structure, properties and applications (RS-172043)
DOI: 10.1016/j.saa.2015.08.029
ISSN: 1386-1425
PubMed: 26301540
WoS: 000365360700020
Scopus: 2-s2.0-84939824912
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PharmacyTY - JOUR AU - Bajuk-Bogdanović, Danica AU - Uskoković-Marković, Snežana AU - Hercigonja, R. AU - Popa, Alexandru AU - Holclajtner-Antunović, Ivanka PY - 2016 UR - https://farfar.pharmacy.bg.ac.rs/handle/123456789/2581 AB - Micro Raman spectroscopy was applied to investigate the speciation of heteropoly and isopoly molybdates in 0.05 and 0.005 M aqueous solutions of 12-molybdophosphoric acid at pH values between 1 and 6. For comparative purposes, P-31 NMR spectroscopy was applied too. It is shown that stability of Keggin anion is influenced both by pH and concentration of solution. The Keggin structure is stable in acidic solutions (pH lt 1.6) while defective Keggin structures are formed with further alkalization (up to pH lt 5.6). Monolacunary anion PMo11O397- is the main component in the pH region from 1.6 to 3.4. Further removal of molybdenyl species causes the appearance of other vacant Keggin structures such as PMo9O31(OH)(3)(6-) and PMo6O259- at about pH 4. At pH 5.0, anion PMo6O259- is the main species. In solutions with pH greater than 5.0, heteropolymolybdates disappear completely and isopolymolybdates Mo7O246- and MoO42- are formed in higher amounts. In more diluted solution of 0.005 M, the decomposition scheme of 12-molybdophosphoric acid solution with increasing of pH takes place without observation of significant amounts of Mo7O246- species. If alkalinization is performed with 0.5 M instead of 5 M NaOH, there are no significant changes in the Raman spectra of solutions. It is shown that the spectra of evaporated samples may be used for the identification of molecular species in corresponding concentrated solutions. However, Raman spectra of dry residues of more diluted solutions differ from spectra of corresponding solutions due to the reactions performed during the process of drying and cannot be used for unambiguous identification of species in solution. Acidification of 0.05 M solution of Na2MoO4 shows that at pH >5.6, molybdate anion MoO42- dominates, while in the pH range between 5.6 and 1, heptamolybdate anion Mo7O246- is preferentially formed. PB - Pergamon-Elsevier Science Ltd, Oxford T2 - Spectroscopy Letters T1 - Study of the decomposition pathway of 12-molybdophosphoric acid in aqueous solutions by micro Raman spectroscopy VL - 153 SP - 152 EP - 159 DO - 10.1016/j.saa.2015.08.029 ER -
@article{ author = "Bajuk-Bogdanović, Danica and Uskoković-Marković, Snežana and Hercigonja, R. and Popa, Alexandru and Holclajtner-Antunović, Ivanka", year = "2016", abstract = "Micro Raman spectroscopy was applied to investigate the speciation of heteropoly and isopoly molybdates in 0.05 and 0.005 M aqueous solutions of 12-molybdophosphoric acid at pH values between 1 and 6. For comparative purposes, P-31 NMR spectroscopy was applied too. It is shown that stability of Keggin anion is influenced both by pH and concentration of solution. The Keggin structure is stable in acidic solutions (pH lt 1.6) while defective Keggin structures are formed with further alkalization (up to pH lt 5.6). Monolacunary anion PMo11O397- is the main component in the pH region from 1.6 to 3.4. Further removal of molybdenyl species causes the appearance of other vacant Keggin structures such as PMo9O31(OH)(3)(6-) and PMo6O259- at about pH 4. At pH 5.0, anion PMo6O259- is the main species. In solutions with pH greater than 5.0, heteropolymolybdates disappear completely and isopolymolybdates Mo7O246- and MoO42- are formed in higher amounts. In more diluted solution of 0.005 M, the decomposition scheme of 12-molybdophosphoric acid solution with increasing of pH takes place without observation of significant amounts of Mo7O246- species. If alkalinization is performed with 0.5 M instead of 5 M NaOH, there are no significant changes in the Raman spectra of solutions. It is shown that the spectra of evaporated samples may be used for the identification of molecular species in corresponding concentrated solutions. However, Raman spectra of dry residues of more diluted solutions differ from spectra of corresponding solutions due to the reactions performed during the process of drying and cannot be used for unambiguous identification of species in solution. Acidification of 0.05 M solution of Na2MoO4 shows that at pH >5.6, molybdate anion MoO42- dominates, while in the pH range between 5.6 and 1, heptamolybdate anion Mo7O246- is preferentially formed.", publisher = "Pergamon-Elsevier Science Ltd, Oxford", journal = "Spectroscopy Letters", title = "Study of the decomposition pathway of 12-molybdophosphoric acid in aqueous solutions by micro Raman spectroscopy", volume = "153", pages = "152-159", doi = "10.1016/j.saa.2015.08.029" }
Bajuk-Bogdanović, D., Uskoković-Marković, S., Hercigonja, R., Popa, A.,& Holclajtner-Antunović, I.. (2016). Study of the decomposition pathway of 12-molybdophosphoric acid in aqueous solutions by micro Raman spectroscopy. in Spectroscopy Letters Pergamon-Elsevier Science Ltd, Oxford., 153, 152-159. https://doi.org/10.1016/j.saa.2015.08.029
Bajuk-Bogdanović D, Uskoković-Marković S, Hercigonja R, Popa A, Holclajtner-Antunović I. Study of the decomposition pathway of 12-molybdophosphoric acid in aqueous solutions by micro Raman spectroscopy. in Spectroscopy Letters. 2016;153:152-159. doi:10.1016/j.saa.2015.08.029 .
Bajuk-Bogdanović, Danica, Uskoković-Marković, Snežana, Hercigonja, R., Popa, Alexandru, Holclajtner-Antunović, Ivanka, "Study of the decomposition pathway of 12-molybdophosphoric acid in aqueous solutions by micro Raman spectroscopy" in Spectroscopy Letters, 153 (2016):152-159, https://doi.org/10.1016/j.saa.2015.08.029 . .