Thermal and plasma synthesis of metal oxide nanoparticles from MOFs with SERS characterization

Aluminum oxide (Al2O3) and chromium oxide (Cr2O3) nanoparticles were synthesized by thermolysis of metal-organic frameworks (MOFs). Further O2 plasma treatment is required to obtain high crystalline quality metal oxides. The composition and morphology of metal oxide nanoparticles were confirmed by powder X-ray diffraction and scanning electron microscopy characterization, respectively. The quality of synthesized metal oxides was also examined by observing the surface-enhanced Raman scattering (SERS) spectra of methyl orange adsorbed on Al2O3 and Cr2O3. The observed SERS effect can be ascribed to charge-transfer (CT) resonance effect between methyl orange and metal oxide surfaces. UV-vis absorption spectra and DFT calculations of metal oxide- methyl orange complexes have confirmed that the observed SRS effect is due to CT resonance between the metal oxide nanoparticles and the adsorbed methyl orange molecules.