Kanaparthi Ramesh

Zinc Hydroxyapatite Catalyst for Decomposition of 2‐Propanol

The general formula of hexagonal (P6 3 /m ) HAp is [Ca F 4 ][Ca T 6 ] [(PO 4 ) 6 ][(OH) 2 ], where one-dimensional channels are constructed from columns of framework (F) metaprisms (Ca F O 6 ) that are corner-connected to PO 4 tetrahedra, with the tunnels (T) having an ideal stoichiometry Ca T (OH) 2 . [ 2 ] In common with other small transition metal cations, the incorporation of zinc into HAp inhibits crystal growth, and promotes tricalcium phosphate (TCP) formation at higher calcination temperatures (usually > 700 ° C). [ 3 ] Functionality can be manipulated through a metastable amorphous calcium phosphate (ACP) phase that co-exists during the incorporation of Zn 2 + , and promotes surface adsorption and reactivity. The solid solubility limit of Zn 2 + , which will displace Ca 2 + (Ca 2 + → Zn 2 + ) and can potentially partition to either the framework or tunnel, remains low to satisfy the bond valence sum restrictions. Because Zn 2 + (ionic radius = 0.74Å) is smaller than Ca 2 + (ionic radius = 1.00 Å), the apatite framework fl exes by Ca F O 6 metaprism twisting, such that the a metric shrinks more than c to best alleviate stress arising from the shorter Zn-O bond length. To date, the substitutional mechanism and true symmetry of Zn-HAp remain speculative due to the poor crystallinity and limited Zn solubility. [ 4 ]

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.

X-RAY ABSORPTION SPECTROSCOPY STUDY OF Mn2O3 AND Mn3O4 NANOPARTICLES SUPPORTED ON MESOPOROUS SILICA SBA-15

Mn K-edge absorption measurements were carried out on α-Mn2O3 and Mn3O4 nanocrystals supported on a mesoporous silica, SBA-15. The X-ray absorption near edge structure (XANES) spectra demonstrate the existence of the oxidation states of Mn (2+ and 3+) in Mn3O4 and Mn (3+) in Mn2O3, those ions were present in different octahedral environments. Meanwhile, XANES data demonstrate that some Mn atoms that are bonding to the inner wall of the channels as isolated species, may exist as Mn4+ in Mn2O3/SBA-15. In addition, the structure, texture, and electronic properties of nanocomposites were also studied using various characterization techniques including X-ray diffraction (XRD) and laser Raman spectroscopy (LRS). The formation of the hausmannite Mn3O4 and bixbyite Mn2O3 structures has been confirmed clearly by XRD. The prepared nanocomposites of MnOx showed significant catalytic activity towards CO oxidation below 523 K.