X-ray XRD SAXS Study of amorphous, extraordinary absorbing, high-surface area magnesium carbonate using a laboratory diffractometer PDF Olga Narygina 1, Marco Sommariva 1, Sara Frykstrand 2, Johan Forsgren 2 1 PANalytical B.V., Almelo, The Netherlands 2 Division for Nanotechnology and Functional Materials, Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, Uppsala, Sweden.
Nano-porous Upsalite Upsalite is a nano-porous amorphous magnesium carbonate synthesized without the use of surfactants as pore forming agents: Pore size < 6 nm Surface area ~ 800 m 2 /g Synthesis: MgO+CO 2 in the presence of CH 3 OH (P,T) MicroNano 2015 2
Multi-technique investigation of nanomaterials using X-rays Wide-angle X-ray scattering (X-ray diffraction) Phase composition Lattice parameters Crystallite size Atomic positions Pair distribution function Short range order Lattice parameter Crystallite size WAXS (XRD) PDF XRF SAXS T, P, rh... Small-angle X-ray scattering Nano-particle/pore size distribution Shape Inner structure Surface area Degree of dispersion Orientation... In situ X-ray fluorescence analysis Chemical composition MicroNano 2015 3
Intensity Intensity Int. What is SAXS (small-angle X-ray scattering)? nano-particle formed by several crystallites 3000 WAXS (XRD) 5-100 Atomic scale X-rays 2000 1000 WAXS (XRD) 1-100 nm (SAXS) Up to 700 nm (USAXS) SAXS 10 0 10-1 10-2 10-3 10-4 10-5 SAXS 0.05-5 Nano scale 0.05 0 0.2 0.42Theta 0.6 0.8 5 1.0 0 10 20 30 40 50 5 2 Theta 100 2 Theta Providing information about nanomaterials For both crystalline and amorphous materials Experiments are performed with Cu radiation Only transmission geometry 4
What is PDF (Pair Distribution Function) analysis? PDF A pair distribution function provides the probability of finding a distance r between two atoms in a material. 4.5 Å 4.5 Å 2.8 Å 4 Å 2 Å 2.8 Å 4 Å 2 Å MicroNano 2015 5
What is PDF (Pair Distribution Function) analysis? PDF Correction and normalization Inter atomic distances Providing information about the inter-atomic distances For both crystalline and amorphous materials Experiments are performed with Mo and Ag radiation Transmission geometry or reflection geometry* * highly absorbing materials MicroNano 2015 6
Study of nano-porous Upsalite Experimental details SAXS and WAXS at ambient conditions in air SAXS at variable temperature (T) and relative humidity (rh) and vacuum PDF at ambient conditions MicroNano 2015 7
Study of nano-porous Upsalite Experimental details WAXS at ambient conditions in air MicroNano 2015 8
Nano-porous Upsalite WAXS (XRD) results Counts Crystalline MgO + amorphous MgCO 3 Foil used for sample preparation 0 30 40 50 60 70 80 90 100 110 Position [ 2q (Copper (Cu)) WAXS (XRD) In addition to amorphous phase, Upsalite sample contains 43 % of remaining crystalline MgO MicroNano 2015 9
Study of nano-porous Upsalite Experimental details PDF at ambient conditions MicroNano 2015 10
Atomic PDF G(r) [Å -2 ] Nano-porous Upsalite PDF results Fit of the PDF (red line) with cubic MgO structure -- Upsalite -- pure non-porous MgCO 3 Radial distance [Å] PDF of Upsalite is dominated by the signal from crystalline MgO. Sample with significantly lower amount of crystalline phase would be more suitable for PDF analysis MicroNano 2015 11
Study of nano-porous Upsalite Experimental details SAXS at ambient conditions in air and vacuum MicroNano 2015 12
Intensity (counts) DvR (1/Å) Nano-porous Upsalite SAXS in air Raw SAXS curves Volume-weighted pore-size distribution 6.4 nm 7.8 nm 9.6 nm 0 1 2 3 4 5 6 2Theta ( ) 0 200 400 600 800 Radius (Å) SAXS SAXS signal of Upsalite is changing with time. Does it only happen it air? MicroNano 2015 13
Intensity (counts) DvR (1/A) Nano-porous Upsalite SAXS in vacuum Raw SAXS curves Volume-weighted pore-size distribution 41 repeated scans in vacuum over 24 h Upsalite after 5.5days exposure to air Upsalite after 2.5days exposure to air Same sample loading remeasured after being exposed to air for 2.5days Same sample loading remeasured after being exposed to air for 5.5days 0 1 2 3 4 5 6 2Theta ( ) Upsalite after 24h in vacuum Upsalite in vacuum, 1 st measurement 0 100 200 300 400 500 600 700 Radius (A) SAXS SAXS signal of Upsalite does not change whilst sample is under vacuum MicroNano 2015 14
Study of nano-porous Upsalite Experimental details SAXS at variable temperature (T) and relative humidity (rh) MicroNano 2015 15
Intensity (counts) Nano-porous Upsalite SAXS at variable T-rH Raw SAXS curves @ 25 C Increasing rh Decreasing rh 1 1 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 2Theta ( ) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 2Theta ( ) MicroNano 2015 16
Pore diameter (nm) Intensity (counts) Nano-porous Upsalite SAXS at variable T-rH Pore diameter as function of T and rh (in situ SAXS) Upsalite SAXS curves before and after rh ramp 30 25 at 25 ºC at 50 ºC 20 15 10 5 0 10 20 30 40 50 60 70 80 90 100 Relative humidity (%rh) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 2Theta ( ) SAXS T, rh In humid atmosphere Upsalite demonstrates pore growth, followed by shuttering of the porous structure MicroNano 2015 17
What is happening to the pore structure of Upsalite? Upsalite pore formation mechanism Upsalite (porous MgCO 3 ) humid air ( ~ 2 weeks) MgO+CO 2 in the presence of CH 3 OH non-porous Mg(HCO 3 )(OH) 2 H 2 O) Nesquehonite S. Frykstrand et al., Micropor. Mesopor. Mat. 190 (2014) 99 104 MicroNano 2015 18
Summary Combining a number of X-ray diffraction and scattering techniques we showed that: Upsalite is amorphous, however, it is difficult to obtain pure phase without traces of crystalline MgO, which complicates structural analysis; In humid atmosphere Upsalite pore structure is changing; WAXS (XRD) PDF SAXS T, P, rh... This is most likely related to early stages of the formation of Nesquehonite. MicroNano 2015 19
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