Three major stages in the synthesis of SBA-15 materials proceeding according to the cooperative self-assembly mechanism have been identified, and the structures of the intermediates species have been established.
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Heterogeneous photo-catalysis is an advanced oxidation process (PAO), which has been the subject of numerous studies and applications, particularly using the commercial oxide of TiO2 (P25, Evonik). Zinc oxide (ZnO) has often been considered a valid alternative to TiO2 due to its good opto-electronic, catalytic and photochemical characteristics along with its low cost. In order to improve the photocatalytic performance of ZnO for practical applications, various types of synthetic approaches have been developed, including, among others, the hydrothermal / solvothermal growth method, sol-gel method, ultrasonic assisted method, deposition chemistry in vapor phase, etc. with the aim of preparing ZnO particles with different sizes and morphologies. However, all of these methods require relatively severe reaction conditions such as high temperature, sophisticated techniques, high purity of gases, adjustable gas flow, expensive raw materials, etc. Therefore, it is important to find a simple and cost-effective method for the synthesis of crystalline nano-particles of ZnO. For this reason, in the present work, the ZnO has been synthesized by three different procedures: conventional aqueous precipitation method, hydrothermal method (H) and microwave assisted method (MW). In all three processes, the same material is obtained, hydrocincite [Zn5(CO3) 2(OH)6], which evolves to crystalline ZnO after calcination thermal treatments. We investigated the effect of the calcination temperature, at the same time (2 h), on the optical, textural and structural properties. Photo-catalytic studies were performed using two selected substrates, Methyl Orange and Phenol, as toxic model substrates (one colorant and the other transparent). The catalysts prepared were characterized by several techniques: DRX, SBET, FE-SEM, TEM and UV-Vis (in diffuse reflectance mode).From the results of XRD, it has been possible to establish that a minimum difference between the relative intensities of exposed faces (I100 and I002) is a crucial factor to obtain good photocatalytic properties. This minimum difference is achieved, in our cases by thermal treatments of calcination at 400ºC, 2 h. When this temperature is chosen, there is no appreciable variation between the photocatalytic activities of the oxides of zinc obtained by the three processes, and there are small differences depending on the nature of the substrate chosen, which can be attributed to the textural differences between the oxides. In any case, the obtained zinc oxides show, for each substrate, photo-catalytic activities in the UV that are superior to those presented by the widely used commercial oxide TiO2 (P25) used as reference.
was studied and it is found that the synthesis of NiSb/SBA-15 …
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As the synthesis proceeds, the voids between the cylinders are filled with the silicate species which undergo condensation reactions resulting in cross-linking and covalent bonding, leading to the formation of highly ordered SBA-15 mesostructure.