In Situ Characterization of Aluminum-Containing Mineral-Microorganism Aqueous Suspensions Using Scanning Transmission X-ray Microscopy

Authors

Tae Hyun Yoon, Stanford University
Stephen B. Johnson, Stanford University
Karim Benzerara, Stanford University
Colin S. Doyle, Stanford University
Tolek Tyliszczak, Lawrence Berkeley National Laboratory
David K. Shuh, Lawrence Berkeley National Laboratory
Gordon E. Brown, Jr., Stanford University

Date of this Version

2004

Comments

Published in Langmuir, Vol. 20, No. 24, 2004.

Abstract

In situ characterization of colloidal particles under hydrous conditions is one of the key requirements for understanding their state of aggregation and impact on the transport of pollutants in aqueous environments. Scanning transmission X-ray microscopy (STXM) is one of the few techniques that can satisfy this need by providing element- and chemical-state-specific 2-D maps at a spatial resolution better than 50nmusing soft X-rays from synchrotron radiation wiggler or undulator sources tuned to the absorption edges of different elements. X-ray absorption near-edge structure (XANES) spectra can also be collected simultaneously at a similar spatial resolution and can provide phase identification in many cases. In this study, we report STXM images and XANES spectroscopy measurements at or above the Al K-edge (E = 1559.6 eV) of various Al-containing minerals and synthetic oxides [a-Al₂O₃ (corundum), У-Al_2O3, У-AlOOH (boehmite), a-Al(OH)₃ (bayerite), KAl₂(AlSi₃O₁₀)(OH)₂ (muscovite), (Al,Mg)₈(Si₄O₁₀)₄(OH)₈·nH2O (montmorillonite), and Mg₆Al₂(OH)₁₆CO₃·4H₂O (hydrotalcite)] and demonstrate the capability of this spectromicroscopic tool to identify different Al-containing mineral colloids in multiphase mixtures in aqueous solution. We also demonstrate that STXM imaging at or above the C K-edge (E = 284.2 eV) and Al K-edge can provide unique information on the interactions between bacteria and Al-containing nanoparticles in aqueous suspensions. STXM images of a mixture of Caulobacter crescentus and montmorillonite and corundum particles just above the C and Al K-edges show that the mineral particles and bacteria are closely associated in aggregates, which is likely due to the binding of bacteria to clay and corundum particles by extracellular polysaccharides.