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

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.

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

Positron Lifetime Spectroscopy 16 ns delay Calibration: 0.0125 ns/ch Time calibration using 60Co source More porous Less porous

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 0.169 ns to 0.191 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.

* 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