Temperature-controlled synthesis and photocatalytic performance of ZnO nanoplatelets

Zinc oxide nanoplatelets are successfully grown on Si(100) by CVD starting from a second-generation ZnII precursor, Zn(hfa)2*TMEDA (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; TMEDA=N,N,N′,N′-tetramethylethylenediamine). The synthesis is performed in a nitrogen + wet oxygen atmosphere under optimized conditions, at temperatures between 250 and 500 °C. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and glancing incidence X-ray diffraction (GIXRD) analyses indicate a direct correlation between morphology and microstructure. The formation of ZnO nanoplatelets, whose characteristics depend on the deposition temperature, is proposed to result from the synergistic combination of a vapor/solid (VS) mechanism and a preferential direction-conducting growth. The chemical composition is analyzed by means of X-ray photoelectron and energy dispersive X-ray spectroscopies (XPS, EDXS). Finally, the photocatalytic performances of ZnO nanoplatelets in the decomposition of the azo-dye Orange II are investigated and compared to those of uniform ZnO coatings synthesized in the absence of water vapor. The obtained results show a higher activity in the case of nanoplatelets due to their peculiar morphology.