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Sol-Gel Processes in Micro-Environments of Black Shale: Learning from the Industrial Production of Nanometer-Sized TiO2 Polymorphs

Helmholtz Centre Potsdam GFZ—German Research Centre for Geosciences, Section 3.2 Organic Geochemistry, D-14473 Potsdam, Germany
ChemEngineering 2019, 3(1), 28; https://doi.org/10.3390/chemengineering3010028
Received: 15 February 2019 / Revised: 1 March 2019 / Accepted: 4 March 2019 / Published: 8 March 2019
(This article belongs to the Special Issue TiO2 Nanoparticles: Synthesis and Applications)
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Abstract

Micro-environments in black shale are reactors for geochemical reactions that differ from the bulk scale. They occur in small isolated pores of several 10 s to 100 s of nanometers without or with limited ionic exchange by diffusion to the surrounding matrix. The example of the formation of titania polymorphs brookite (and anatase) in black shale demonstrates that pH < 4 of the pore waters or lower must prevail to enable dissolution of Ti-bearing precursors followed by the precipitation of these metastable solids. Comparably low pH is applied during the industrial production of nanometer-sized brookite or anatase by sol-gel methods. The process parameters during industrial production such as low pH, negative Eh, or low ionic strength (to promote agglomeration) allow a comparison with parameters during geochemical processes leading to titania formation in black shale. Sol-gel processes are suggested herein as key geochemical processes in micro-environments of black shale in order to understand the formation of single brookite crystals or agglomerates on a nanometer scale. View Full-Text
Keywords: black shale; brookite; micro-environment; sol-gel process black shale; brookite; micro-environment; sol-gel process
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Schulz, H.-M. Sol-Gel Processes in Micro-Environments of Black Shale: Learning from the Industrial Production of Nanometer-Sized TiO2 Polymorphs. ChemEngineering 2019, 3, 28.

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