Optimizing the sol–gel parameters on the synthesis of mesostructure nanocrystalline γ-Al 2O 3

Abstract

The sol–gel procedure was applied for the synthesis of nanocrystalline γ-alumina by means of the aluminum isopropoxide (AIP) precursor and a cationic surfactant in acidic medium. In this study, the response surface method (RSM) was applied for optimizing the most significant sol–gel parameters to achieve the largest pore diameter and the highest pore volume. The effects of three variables, pH of the solution, water/AIP molar ratio and template/AIP molar ratio, at three levels were investigated using the Box–Behnken design. The results obtained in this work showed that with the variation of the pH of the solution while holding constant the other two parameters, the changing of the pore diameter and pore volume are more evident in comparison with the variations of the other two parameters, water/AIP molar ratio and template/AIP molar ratio. The highest pH value, which is equal to 6.5, is critical to obtain a large pore diameter and high pore volume gamma alumina support. Validation of the model was obtained by performing one experiment at the optimum conditions predicted by the model. The predicted optimum conditions were 6.5, 0.8 and 90 for the pH value, template/AIP molar ratio and water/AIP molar ratio, respectively. The obtained pore diameter and pore volume for the sample prepared under the optimum conditions were 17.03 nm and 1.76 cm 3 g −1, respectively, which were the highest values among all the samples prepared.