Synthesis and characterization of mesoporous cadmium titanate thin films

Abstract

This thesis work focuses on the synthesis and characterization of mesoporous CdTiO3 thin films by using a salt-surfactant assembly, which is defined as molten salt assisted self-assembly (MASA) method. The MASA method is a proper process to fabricate mesoporous transparent thin films. The characterization of the calcined powder and fresh gel samples was made by using XRD, SEM, TEM, ATR-IR, N2 sorption and POM techniques. The preparation of a clear solution containing ethanol as solvent, [Cd(H2O)4](NO3)2, two different surfactants ((C16H33N(CH3)3)Br and EO20PO70EO20), titanium(IV)butoxide (Ti(OC4H9)4) as titania source and concentrated HNO3 as acid to prevent quick polymerization of titanium alkoxide is the first step for the synthesis of the desired material. The prepared clear solution is coated on the glass substrates to form a liquid crystalline mesophase by the hydrolyzed titania species and the molten salt by the guidance of surfactant domains. Upon the calcination of the fresh gel samples, mesoporous CdTiO3 material is formed. In scope of this thesis work, several parameters were changed to determine the optimum the salt uptake, acid amount, surfactant ratio, coating method and calcination path for the synthesis. Among dip coating, spin coating and drop casting methods, dip coating method gave better results to produce a material with less side products, which was mainly CdO. The amount of HNO3 added to the solution affects the homogeneity and stability of the prepared fresh films. Although changing the amount of HNO3 did not affect the surface area significantly, it was observed that addition of excess amount of acid resulted in an uneven surface on calcined films. CdTiO3 is nanocrystalline at 350oC and stable up to 550oC. The initial calcination temperature is an important parameter to synthesize a material with less side product. Mesoporous CdTiO3 displays 44 to 79 m2/g surface area and pore volume of 0.11 to 0.18 cm3/g depending on the synthesis conditions.