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Discrimination of infrared fingerprints of bulk and surface POH and OH of hydroxyapatites

Paper ID Volume ID Publish Year Pages File Format Full-Text
54511 47012 2014 8 PDF Available
Title
Discrimination of infrared fingerprints of bulk and surface POH and OH of hydroxyapatites
Abstract

•The bulk and surface νOH infrared fingerprints of hydroxyapatite were discriminated.•Isotopic labeling of the lone surface or of the bulk was monitored by infrared.•Five acidic surface νPO-H contributions are perturbated upon CO adsorption.•The 3572 cm−1 band involves both bulk and surface emerging OH from the channels.•Basic surface OH leads to the formation of hydrogenocarbonate upon CO2 adsorption.

The identification of the nature of the surface acid base pairs present on hydroxyapatites surface is a key point to rationalize their catalytic properties. To investigate the possible involvement of acidic protonated phosphate (POH) and/or of basic OH emerging from the channels, the spectroscopic fingerprints of the surface sites have to be discriminated from bulk HPO42− and OH− groups. This was monitored by infrared spectroscopy (i) using isotopic H–D exchanges, either implemented in mild conditions (353–373 K) or at higher temperature (573 K) to selectively label the lone surface or to achieve deep deuteration, respectively (ii) following then the perturbation induced upon adsorption probe molecules. Two bulk contributions are observed in the νOH region, one at 3572 cm−1 that is associated to OH− from the channels, and one at 3657 cm−1 that was assigned to HPO42−. Five surface contributions perturbated upon CO adsorption at 77 K can be ascribed to protonated forms of the various terminated phosphates. The formation of hydrogenocarbonate species upon CO2 adsorption evidences the presence of basic surface OH−. However, due to complex material restructuring occurring upon CO2 adsorption that greatly modifies the H-bonding interactions, the related νOH fingerprint could not be formally identified. Whatever, from the formation of low intense band at 2633 or 3572 cm−1 under soft deuteration or protonation conditions respectively, it is inferred that the related bands could be ascribed to both surface and bulk OD or OH.

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Keywords
Infrared; Deuteration; Isotopic labeling; Surface; Hydroxypatite; Acidic and basic probe molecule
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Discrimination of infrared fingerprints of bulk and surface POH and OH of hydroxyapatites
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 226, 1 May 2014, Pages 81–88
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us