Preparation and characterization of ZnO clusters inside mesoporous silica

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.