Temperature‐Controlled Synthesis and Photocatalytic Performance of ZnO Nanoplatelets

Abstract

Zinc oxide nanoplatelets are successfully grown on Si(100) by CVD starting from a second-generation Zn II precursor, Zn(hfa) 2 ÁTMEDA (Hhfa = 1,1, 1,5,5, TMEDA= N,N,N′,. 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.

MOCVD of ZnO Films from Bis(Ketoiminato)Zn(II) Precursors: Structure, Morphology and Optical Properties

“…The spontaneous polarization along this direction triggers the (001) orientation, due to the tendency to satisfy the decrease in the overall free energy. [6,10,12] Irrespective of the precursor used, the highest raw intensity of the (002) diffraction peak was observed at 600 8C, the temperature corresponding to the highest film thickness (see above). Nevertheless, a positive influence of thermal energy supply on the above-mentioned orientation, with a maximum effect at 600 8C, cannot be completely ruled out.…”

“…3a) and the corresponding rms roughness, as high as 42 nm. [1,[31][32][33][34][35] Since the effective surface area is typically larger for a rough surface, [10][11] the obtainment of such morphology might be an interesting starting point in view of possible photocatalytic or gas sensing applications. In the case of precursor 1, a further increase in the substrate temperature to 700 8C led to the formation of a film composed of interconnected aggregates (average size % 100 nm), resulting in a more compact crosssectional assembly and an appreciably lower overall thickness.…”

“…Irrespective of the process conditions and the used precursor, the Zn2p 3/2 and Zn3p 3/2 spin-orbit components were centered at binding energies (BE) ¼ 1021.8 and 88.9 eV, as expected for ZnO. [10,13,[36][37] The fingerprint for the presence of zinc(II) oxide, free from other phases, was provided by the evaluation of the Auger a parameter, which was 2010.2 eV for all films grown from precursors 1 and 2. This value is in excellent agreement with literature data for ZnO.…”

“…[1][2][3][4][5][6][7][8][9][10][11] There have been several reports on the fabrication of ZnO thin films or nanostructures, including thermal evaporation, sputtering, pulsed laser deposition, molecular beam epitaxy (MBE), sol-gel, atomic layer deposition (ALD), and MOCVD. [1,6,10,[12][13][14] Among them, the latter is by far the most promising technique for large scale production, and more importantly, by varying the CVD process parameters and nature of the precursors, it is possible to regulate the morphology and structure of the films. The precursor chemistry for ZnO-based materials has focused on various compounds, typically Zn II acetate, [15] zinc alkyls (both methyl and ethyl), [4,[16][17][18][19][20][21][22][23] and b-diketonates (mainly Zn (acac) 2 , with acac ¼ 2, 4-pentanedionate).…”

Synthesis, Properties and Applications of Nanostructured Zinc Oxide

“…O comportamento fotocatalítico de ZnO com diversas morfologias vem sendo estudado. Como exemplo, nanofios 57 , nanodisco 58 , nanoplaca 59 , nanotubo 60 , entre outras nanoestruturas hierárquicas. 61,62 Algumas características desejáveis destes materiais são estabilidades físicas e químicas, alta capacidade oxidativa, largura de banda proibida na região do UV ou do visível do espectro eletromagnético, baixo custo, alta disponibilidade e baixa toxicidade.…”