Absorption Fine Structure Spectroscopy for the Elaboration of Chemistry in Lignocellulosics

Transcription

1 2006 International Conference on Nanotechnology, April 26-28, 2006 Atlanta, GA The Use of C-Near C Edge X-Ray X Absorption Fine Structure Spectroscopy for the Elaboration of Chemistry in Lignocellulosics Presented by: Lucian A. Lucia Associate Professor North Carolina State University

2 Purpose of Presentation Describe a powerful new spectroscopic technique: X-ray fluorescence microscopy Correlate technique with our study of the oxidative activity of hydrogen peroxide during the bleaching of kraft pulps

3 Radicals in H 2 O 2 bleaching M +2 + H 2 O 2 M +3 + OH + - OH M = Cu, Fe, Mn HO + HOO - O 2 - +H 2 O O 2 - +H 2 O 2- O 2 + OH + - OH M + OH M OH OH + H 2 O 2 HO 2 + H 2 O HO 2 H + + O 2 - O 2 - +H 2 O 2 O 2 + OH - + OH M +1 + O 2 - M + O 2 OOH + - OH O 2 - +H 2 O H 2 O 2 + HOO - O OH ROOH RO + HO HO + H-R HOH + R R + O 2 ROO ROO + H-R ROOH + R J. Gierer, Holzforschung, vol. 44, no. 5, (1990).

4 Physical mechanism of degradation Meyer proposed a few potential degradation events to consider: 1.Local ph Fe +3/+2 Mn +3/+2 O 2 /O 2 -. H 2 O 2 /. OH 2.Radical travel 3.In situ production Meyer, U., Kokot, S., Weber, R., Zürcher-Vogt, J., Wie entstehen katalytschäden?, Textilveredlung, 22:5, pp , 1987.

5 Peeling and stopping reactions Key = formation of ketone at C2 Loss of carbohydrate group CHO HCOH HOCH HCOR HCOH CH 2 OH C HOCH CH 2 OH O HCOR HC OR (A) (B) (C) HCOH HCOH CH 2 OH CH 2 OH - H + C O - HOC - RO - CH 2 OH CHO HCOH HOCH HCOR HCOH CH 2 OH HC O (-) CHO CHO (A) (B) (C) (D) COH COH C O -HO - HO CH CH CH + H 2 2 O HCOR HCOH CH 2 OH HCOR HCOH CH 2 OH HCOR HCOH CH 2 OH CO 2 H HCOH CH 2 HCOR HCOH CH 2 OH glucometasaccharinic acid Carboxylic acid A. 1,2 Enediol formation B. β-hydroxy elimination C. Tautomerization D. Benzylic acid rearrangement (will not peel ) depts.washington.edu/pse406/ppt/ ppt

6 What is our focus? Understand oxidative processes in pulp bleaching Understand role of metals in hydrogen peroxide bleaching Determine these events at an atomic scale (nanoscale)

7 X-Ray Synchrotron Giant x-ray ring located at Brookhaven National Laboratory in Long Island New York. Utilized soft x-ray microscopy to visualize chemical groups in paper ESCA (XPS) with pictures

8 Scanning Transmission X- ray Microscope (STXM) Operates between the K edges carbon and oxygen with good penetration in samples slightly less than 1μm, therefore well suited for the study of specimens like single biological cells. Can operate under standard conditions or cryo conditions. The Microscope

9 Soft x-ray microscopy uses X rays with an energy of ev, or a wavelength of about 1-10 nm. X-ray energy (ev). 30nm resolution Only about 1 dozen sychrotron STXMs available worldwide. The Microscope (2)

10 Absorption edges Lambert-Beer law: linear absorption coefficient µ This coefficient makes a jump at specific elemental absorption edges! This example: 0.1 µm protein, silica [ ( E) t] = I D( )] I = I0 exp μ 0exp[ E Absorption Continuum (fully ionized) n=3 n=2 n=1 (ground state) Photon energy

11 Near-edge absorption fine structure (NEXAFS) or X-ray absorption near-edge structure (XANES) Fine-tuning of the x-ray energy near an atom s edge gives sensitivity to the chemical bonding state of atoms of that type First use in microscopy: Ade et al., Science 258, 972 (1992)

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13 Immunogold labeling H. Chapman, C. Jacobsen, and S. Williams, Ultramicroscopy 62, 191 (1996). Fibroblast, antibody labeled for tubulin. More recent work: C. Larabell et al., LBL/UCSF S. Vogt et al., then at Göttingen Labels must be comparable in size to optical resolution. Vogt and Jacobsen, Ultramicroscopy 87, 25 (2001) Challenge: how to label without altering cell?

14 Spectromicroscopy by image stacks Acquire sequence of images over XANES spectral region; automatically align using Fourier cross-correlations or laser interferometer; extract spectra. C. Jacobsen et al., J. Microscopy 197, 173 (2000). Images at N=150 energies are common.

15 Our Work Radicals are formed by the interaction of peroxide and metal that can damage cellulose Damage results in carboxylic acid groups Visualize the damage physical and chemical testing show Severe pulp strength losses Large increases in pulp carbohydrate acid groups (deconvoluted from lignin) Unbleached Mg Bleached Mg

16 Experimental 30 year old Northern black spruce Hydrogen peroxide bleached sampels Embedded in epoxy resin Microtomed Installed in TEM grids BNL studies

17 Working hypothesis Peeling reaction radical induced Propagated by metals to result in severe oxidized pulp carbohydrates Results in generation of acid functionalities Metals cluster there

18 Sample Prep Peroxide bleached and unbleached handsheets Cut ~1cm by 2cm samples Soaked in water Dehydrated in ethanol Used 50/50 mixture of epoxy resin (Epon 812) and propylene oxide 100% epoxy and vacuum Cured in oven between plastic sheets Sectioned to 200nm thick (transverse) and placed on TEM grids

19 Locating Carboxylic Acids (unbleached) TEM grid hole = ~125 μm

20 Locating Carboxylic Acids (2) (bleached) TEM grid hole = ~125 μm

21 Locating Carboxylic Acids (3) (bleached) TEM grid hole = ~125 μm

22 High Resolution (bleached) Stepper scan (.5 μm) vs. piezo scan (30 nm). High resolution images of damaged regions. Perhaps evidence of hollow center Top = 20 μm Bottom = 8 μm

23 Conclusions Resolution is nm now; pushing towards 10 nm Tomography lets you look at whole cells up to 10 µm thick Radiation damage is less than with electrons, but is still a consideration STXM is a viable tool for the investigation of paper chemistry Peroxide bleached samples undergo a heterogeneous enrichment of carboxylic acid groups due to radical damage Results confirm trends previously seen in ToF-SIMS as well as other physical and chemical testing

24 Acknowledgements Chris Jacobsen and Janos Kirz (BNL) Doug Mancosky (Hydro Dynamics) Alan Rudie (Forest Products Laboratory) Hiroki Nanko (Georgia Institute of Technology)

25 Thank You PRESENTED BY Lucian A. Lucia Associate Professor North Carolina State Univerity