Observation of the ammonium salt of 12-molybdophosphoric acid by in situ Raman spectroscopy during solid-state synthesis: spectral analysis and reconstruction using the band-target entropy minimization (BTEM) algorithm.
The solid-state reaction between ammonium heptamolybdate (AHM) and zirconium phosphate (ZrP) to give the ammonium salt of 12-molybdophosphoric acid (AMPA) was performed at 25-400 degrees C and monitored using in situ Raman spectroscopy. Spectral analysis of the Raman data using the band-target entropy minimization (BTEM) algorithm resulted in spectral estimates for the starting materials and product, AHM, ZrP, and AMPA, as well as the byproduct MoO3 and an intermediate 11(NH4)2O.4(MoO3)7. The time-dependent relative concentration profiles were obtained, and the contributions of the individual signal intensities of each constituent to the total measured signal intensity were determined (range: 8.4-27.2%). The present results are important since the synthesis of AMPA is normally performed in buffered aqueous solution and not in the solid state. The present study also indicates that a maximum yield of the desired ammonium salt of 12-molybdophosphoric acid is achieved by stopping the solid-state reaction at ca. 350 degrees C. The combined spectroscopic and chemometric approach used in this contribution appears applicable to other solid-state synthetic studies in order to reveal more detailed time-dependent information on the species present.
Srilakshmi
Chilukoti
C
Institute of Chemical and Engineering Sciences (ICES), 1, Pesek Road, Jurong Island, Singapore. c_srilakshmi@ices.a-star.edu.sg
Chew
Wee
W
Ramesh
Kanaparthi
K
Garland
Marc
M