Preparation and Characterization of ZnO Clusters inside Mesoporous Silica

Abstract

Wide band-gap semiconductorzinc oxide nanoclusters have been prepared in the channels of MCM-41 materials by functionalizing the MCM-41 with ethylenediamine groups, absorbing zinc cations, and calcinating at high temperatures. The products have been characterized by XRD, TEM, EDS, nitrogen adsorption and desorption, and UV−vis and PL spectroscopies. ZnO clusters were mostly confined and dispersed in the pores of mesoporous hosts. No large ZnO particles on the external surfaces have been detected. A massive blue-shift in UV−vis absorption spectra has been observed and large band increase can be expected. The nature of the PL spectrum has been attributed to the defects related to oxygen vacancies. In addition, the assembly of cobalt, nickel, and copper oxides inside MCM-41 materials has also been tried by this scheme, but at the moment, only the cobalt oxide can be prepared with good results. Unfortunately, noble metals have usually grown into large particles on the outside surface of MCM-41 by this scheme, e.g., a lot of silver particles with sizes much larger than the pore diameter of MCM-41 host have been obtained. However, the explanation is not yet clear.

Role of zinc interstitials and oxygen vacancies of ZnO in photocatalysis: a bottom-up approach to control defect density

“…It is notable that blue emissions are quite infrequent 15 for the as-prepared samples when compared with the literature. 16,17,[28][29][30][31][32] Note that Zn i is 0.22 eV below the CB, 57 V Zn is 0.30 eV above the VB 58-60 and ex-Zn i s are 0.54 to 0.635 eV below the CB 15 in ZnO for a typical band gap of 3.36 eV. 16 As mentioned earlier, the another set of major defects are V O s, which have been extensively addressed in the literature (see the discussion and cross-references in ref.…”

“…Note that studies based on Zn i s are less frequent than V O s because the former defects are difficult to achieve and control in the as-prepared samples. 16,17,[28][29][30][31][32] In contrast, typically synthesized ZnO is predominant with V O s. 4,8,16,17,27,31,32 Consequently, photocatalysis studies involving V O s dominate the literature. 1,4,6,[8][9][10]13,21 In this context, it is very useful and important to study the effect of Zn i s in PCA and their efficiency against V O s. In addition to the fundamental interest, the results of such a study enable an efficient and cost effective design of novel photocatalysts.…”

ZnO Clusters Encapsulated inside Micropores of Zeolites Studied by UV Raman and Laser-Induced Luminescence Spectroscopies

“…[1][2][3] As we know, when the particle sizes of many semiconductors, ZnO included, decrease to nanometer or sub-nanometer scales, these materials usually exhibit quantum size effects, presenting different electric and optical properties from bulk materials. [4][5][6] The study on subnanometric ZnO clusters as a medium between single molecules and nanocrystals is an active area now days, [7][8][9][10][11] but their luminescent properties are rarely reported. Since ZnO clusters are so small and unstable, many materials, such as glass, polymers and zeolites, are used as supports or stabilizers in the various preparation methods.…”

H2S Removal Using ZnO/SBA-3: New Synthesis Route and Optimization of Process Parameters

“…In the former case, the most usual method is doping of reaction m elange with metal salts [15]. In post-synthetic approach, the most common synthesis routes are: I) incipient wetness impregnation [16]; II) ion exchange [17]; III) equilibrium adsorption [18]; IV) metal complex immobilization [19]; V) vapor phase deposition [20]; and VI) sonication [21][22][23][24]. One of the interesting applications of mesoporous materials is adsorption of hazardous gases.…”