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Title: The role of titanium-oxo clusters in the sulfate process for TiO 2 production

Abstract

TiO 2 is manufactured for white pigments, solar cells, self-cleaning surfaces and devices, and other photocatalytic applications. The industrial synthesis of TiO 2 entails: (1) the dissolution of ilmenite ore (FeTiO 3) in aqueous sulfuric acid which precipitates the Fe while retaining the Ti in solution, followed by (2) dilution or heating the Ti sulfate solution to precipitate the pure form of TiO 2. The underlying chemistry of these processing steps remains poorly understood. Here we show that the dissolution of a simple Ti IV-sulfate salt, representative of the industrial sulfate process for the production of TiO 2, immediately self-assembles into a soluble Ti-octadecameric cluster, denoted as {Ti 18}. We observed {Ti 18} in solution by small-angle X-ray scattering and Ti extended X-ray absorption fine structure (Ti-EXAFS) analysis, and ultimately crystallized it for absolute identification. The {Ti 18} metal-oxo cluster was previously reported as a polycation; but shown here, it can also be a polyanion, dependent on the number of sulfate ligands it carries. After immediate self-assembly, the {Ti 18}-cluster persists until TiO 2 precipitates, with no easily identified structural intermediates in the solution or solid state, despite the fact that the atomic arrangement of {Ti 18} differs vastly frommore » that of titania. The evolution from solution phase {Ti 18} to precipitated TiO 2 nanoparticles was detailed by X-ray scattering and Ti-EXAFS. Here, we offer a hypothesis for the key mechanism of complete separation of Fe from Ti in the industrial sulfate process. These findings also highlight the emerging importance of the unusual Ti(Ti) 5 pentagonal building unit, featured in {Ti 18} as well as other early d 0 transition metal-oxo clusters including Nb, Mo and W. Finally, this study presents an example of crystal growth mechanisms in which the observed “pre-nucleation cluster” does not necessarily predicate the structure of the precipitated solid.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Oregon State Univ., Corvallis, OR (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
OSTI Identifier:
1547405
Alternate Identifier(s):
OSTI ID: 1530467
Grant/Contract Number:  
SC0010802
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Dalton Transactions
Additional Journal Information:
Journal Volume: 48; Journal Issue: 29; Journal ID: ISSN 1477-9226
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
ENGLISH
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Kozma, Karoly, Wang, Maoyu, Molina, Pedro I., Martin, Nicolas P., Feng, Zhenxing, and Nyman, May. The role of titanium-oxo clusters in the sulfate process for TiO2 production. United States: N. p., 2019. Web. doi:10.1039/c9dt01337g.
Kozma, Karoly, Wang, Maoyu, Molina, Pedro I., Martin, Nicolas P., Feng, Zhenxing, & Nyman, May. The role of titanium-oxo clusters in the sulfate process for TiO2 production. United States. https://doi.org/10.1039/c9dt01337g
Kozma, Karoly, Wang, Maoyu, Molina, Pedro I., Martin, Nicolas P., Feng, Zhenxing, and Nyman, May. Thu . "The role of titanium-oxo clusters in the sulfate process for TiO2 production". United States. https://doi.org/10.1039/c9dt01337g. https://www.osti.gov/servlets/purl/1547405.
@article{osti_1547405,
title = {The role of titanium-oxo clusters in the sulfate process for TiO2 production},
author = {Kozma, Karoly and Wang, Maoyu and Molina, Pedro I. and Martin, Nicolas P. and Feng, Zhenxing and Nyman, May},
abstractNote = {TiO2 is manufactured for white pigments, solar cells, self-cleaning surfaces and devices, and other photocatalytic applications. The industrial synthesis of TiO2 entails: (1) the dissolution of ilmenite ore (FeTiO3) in aqueous sulfuric acid which precipitates the Fe while retaining the Ti in solution, followed by (2) dilution or heating the Ti sulfate solution to precipitate the pure form of TiO2. The underlying chemistry of these processing steps remains poorly understood. Here we show that the dissolution of a simple TiIV-sulfate salt, representative of the industrial sulfate process for the production of TiO2, immediately self-assembles into a soluble Ti-octadecameric cluster, denoted as {Ti18}. We observed {Ti18} in solution by small-angle X-ray scattering and Ti extended X-ray absorption fine structure (Ti-EXAFS) analysis, and ultimately crystallized it for absolute identification. The {Ti18} metal-oxo cluster was previously reported as a polycation; but shown here, it can also be a polyanion, dependent on the number of sulfate ligands it carries. After immediate self-assembly, the {Ti18}-cluster persists until TiO2 precipitates, with no easily identified structural intermediates in the solution or solid state, despite the fact that the atomic arrangement of {Ti18} differs vastly from that of titania. The evolution from solution phase {Ti18} to precipitated TiO2 nanoparticles was detailed by X-ray scattering and Ti-EXAFS. Here, we offer a hypothesis for the key mechanism of complete separation of Fe from Ti in the industrial sulfate process. These findings also highlight the emerging importance of the unusual Ti(Ti)5 pentagonal building unit, featured in {Ti18} as well as other early d0 transition metal-oxo clusters including Nb, Mo and W. Finally, this study presents an example of crystal growth mechanisms in which the observed “pre-nucleation cluster” does not necessarily predicate the structure of the precipitated solid.},
doi = {10.1039/c9dt01337g},
url = {https://www.osti.gov/biblio/1547405}, journal = {Dalton Transactions},
issn = {1477-9226},
number = 29,
volume = 48,
place = {United States},
year = {2019},
month = {6}
}

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