Welcome to the Geiger Laboratories

for Nonlinear Optics at Interfaces

at Northwestern University

in Focus Interaction of Cr(III) and Cr(VI) with Hematite Studied by Second Harmonic Generation Julianne M. Troiano, David S. Jordan, Christopher J. Hull, and Franz M. Geiger J. Phys. Chem. C, 2013, 117 (10), pp 5164–5171 Publication Date (Web): February 18, 2013 (Article) DOI: 10.1021/jp3122819 The fate of chromium in the environment relies heavily on its redox chemistry and interaction with iron oxide surfaces. Atomic layer deposition was used to deposit a 10 nm film of polycrystalline α-Fe2O3 (hematite) onto a fused silica substrate which was analyzed using second harmonic generation (SHG), a coherent, surface-specific, nonlinear optical technique. Specifically, the χ(3) technique was used to investigate the adsorption of Cr(III) and Cr(VI) to the hematite/water interface under flow conditions at pH 4 with 10 mM NaCl. We observed partially irreversible adsorption of Cr(III), the extent of which was found to be dependent on the concentration of Cr(III) ions in solution. This result was confirmed using X-ray photoelectron spectroscopy. The interaction of Cr(III) with hematite is compared with the adsorption of Cr(III) to the silica/water interface, which is the substrate for the ALD-prepared hematite films, and found to be fully reversible under the same experimental conditions. The observed binding constant for Cr(III) interacting with the silica surface was found to be 4.0(6) × 103 M–1, which corresponds to an adsorption free energy of −30.5(4) kJ/mol when referenced to 55.5 M water. The surface charge density at maximum metal ion surface coverage was found to be 0.005(1) C/m2, which corresponds to 1.0 × 1012 ions/cm2 assuming a +3 charge for chromium. In contrast, the observed binding constant for Cr(III) interacting reversibly with the hematite surface was calculated to be 2(2) × 104 M–1, corresponding to an adsorption free energy of −35(2) kJ/mol when referenced to 55.5 M water. The surface charge density at maximum metal ion surface coverage was found to be 0.004(5) C/m2 for the reversibly bound chromium species, which corresponds to 8.3 × 1011 reversibly bound ions per cm2, again assuming a +3 charge of chromium. The data also allows us to estimate that about 6.7 × 1012 Cr(III) ions are irreversibly bound per cm2 hematite at saturation coverage. The results of this investigation suggest that the use of hematite in permeable reactive barriers, for cost-effective chromium remediation, allows for Cr(III) remediation at very low concentrations through adsorptive and redox processes but quickly renders the barriers ineffective at high chromium concentrations due to surface saturation.http://pubs.acs.org/doi/abs/10.1021/jp3122819?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/jp3122819?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/jp3122819?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/jp3122819?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/jp3122819?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/jp3122819?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/jp3122819?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/jp302631z?prevSearch=%255BContrib%253A%2Bfranz%2Bgeiger%255D&searchHistoryKey=shapeimage_2_link_0shapeimage_2_link_1shapeimage_2_link_2shapeimage_2_link_3shapeimage_2_link_4shapeimage_2_link_5shapeimage_2_link_6
Free Energy Relationships in the Electrical Double Layer over Single-Layer Graphene Jennifer L. Achtyl, Ivan V. Vlassiouk, Pasquale F. Fulvio, Shannon M. Mahurin, Sheng Dai, and Franz M. Geiger Am. Chem. Soc., 2013, 135, pp 979-981 Publication Date (Web): January 8, 2013  Fluid/solid interfaces containing single-layer graphene are important in the areas of chemistry, physics, biology, and materials science, yet this environment is difficult to access with experimental methods, especially under flow conditions and in a label-free manner. Herein, we demonstrate the use of second harmonic generation to quantify the interfacial free energy at the fused silica/single-layer graphene/water interface at pH 7 and under conditions of flowing aqueous electrolyte solutions ranging in NaCl concentrations from 10–4 to 10–1 M. Our analysis reveals that single-layer graphene reduces the interfacial free energy density of the fused silica/water interface by a factor of up to 7, which is substantial given that many interfacial processes, including those that are electrochemical in nature, are exponentially sensitive to interfacial free energy density.http://pubs.acs.org/doi/abs/10.1021/ja3120899?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/ja3120899?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/ja3120899?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/ja3120899?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/ja3120899?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/ja3120899?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/abs/10.1021/ja3120899?prevSearch=%255BContrib%253A%2BFranz%2BGeiger%255D&searchHistoryKey=http://pubs.acs.org/doi/pdf/10.1021/ja3120899shapeimage_3_link_0shapeimage_3_link_1shapeimage_3_link_2shapeimage_3_link_3shapeimage_3_link_4shapeimage_3_link_5shapeimage_3_link_6

Member of the DOE Fluid Interface Reactions, Structures and Transport (FIRST) EFRC at Oak Ridge and the NSF Center for Chemical Innovation (CCI) for Sustainable Nanotechnology (CSN) at the University of Wisconsin, Madison - check out the CCI CNS blog!

“Happy Spring” from the Geiger group ... Laser Lectures started Friday, May 10 ...