1. Positron Lifetime Studies of Cu-Core/ Mn3O4-Shell Nanoparticles
Damilola S. Fasheru
Department of Engineering and Technology
Advisor
Naidu V. Seetala
Department of Mathematics and Physics
Grambling State University
Other Investigators
Nachal D. Subramanian and James J. Spivey
Department of Chemical Engineering
LSU - Baton Rouge

2. Introduction
The objective of the project is to understand the role of microstructure in activation and stability of catalysts for fuel conversion.
CO +H2  Alkenes/Hydrocarbons + H2O
Core–shell nanoparticles exhibit chemical and physical properties that are distinct from the bulk material.
We studied the effect of oxidation on the nano-porosity of Cu/Mn3O4 core/shell nanoparticles using positron lifetime spectroscopy.

3. Cu/Mn3O4 core/shell Nanoparticles
Nanoparticles are prepared at LSU using a wet-chemical method.
Core/shell structure - using synchrotron radiation-based small-angle X-ray scattering (SAXS) and X-ray absorption near edge structure (XANES):
Cu core (d = 6.1 nm)–porous Mn3O4 shell (3.4 nm thick) nanoparticles.
Oxidation of nanoparticles is performed at 400 oC for 10 h in O2/He2 atmosphere.
J. Phys. Chem. C, 2011, 115 (30), pp 14500–14506; June 23, 2011

4. Positron Lifetime Spectroscopy
16 ns delay
Calibration:
ns/ch
Time calibration using 60Co source
More porous
Less porous

5. Positron Lifetime Results – Cu/Mn3O4 core/shell nanoparticles
Sample
τ1 (ns)
τ2 (ns)
τ3 (ns)
I1 (%)
I2 (%)
I3 (%)
As-made
Cu/Mn3O4
0.169 ±0.005
0.367 ±0.006
1.978 ±0.020
24.1 ±2
71.3
4.6
±0.1
Oxidized
0.191 ±0.005
0.399 ±0.006
1.912 ±0.020
46.8
48.9
4.3
Pore size R estimation:
t3-1 = 2[1-R/Ro + {1/2p}sin(2pR/Ro)]; Where Ro = R + dR and dR = 1.66 Á
The estimated pore diameter is about 6 Á. No significant change in t3 and I3 between as-made and oxidized Cu/Mn3O4 core/shell nanoparticles, indicates that the pore structure (pore size and concentration) did not change due to oxidation. However, t1 increased from ns to ns due to oxidation and its intensity increased from 24% to 47%, which clearly indicates that the Cu-core is oxidized and its trapping rate for positrons has increased. As a result, fewer positrons are trapped in Mn3O4 shell, indicated by relative decrease in I2 due to oxidation.

6. * Work supported by DOE-EFRC grant
Conclusions
As-made and oxidized Cu-core/Mn3O4 nanoparticles were studied by positron lifetime spectrometer.
Lifetime spectra gave three lifetimes: related to positron annihilation in Cu-core, in Mn3O4 shell, Positronium annihilation in the pores of Mn3O4 shell.
The results indicates that Cu-core is oxidized and these is no change in the pore structure of Mn3O4shell due to oxidation.
* Work supported by DOE-EFRC grant