Titania Inverse Opals: An Innovative Preparation Method with an Improvement in the Mechanical, Optical and Photonic Properties

LOPEZ ROBLEDO G.; CURTI M.; UBOGUI J.; DOS SANTOS CLARO, P.C.; MENDIVE C.

Bariloche

Congreso; Congreso Internacional de Metalurgia y Materiales SAM-CONAMET 2018; 2018

CNEA Bariloche

Inverse opals have attracted considerable interest in the latest yearsdue to their many interesting properties and aplications, especially with theaim of energy generation and photocatalysis. Briefly, their structure can bedescribed as the negative of opal coloidal crystals, face-centered cubicarrangements of sub-micron sized spheres. Many materials are suitable for theirpreparation, but one of the most important ones is titanium dioxide, TiO2,because of its high refractive index, low toxicity, low cost and other desiredproperties.A key step in the preparation of titanium dioxide inverse opals is theinflitration step, which is tipically done using a liquid precursor (LP-IO). However,this method involves the formation of a compact overlayer of TiO2 ontop of the inverse opal structure, which goes in detriment of the photonic andphotocatalytic properties, as it may block the light flow into the structureand impede the reactants difussion. An improved method uses a suspension of TiO2nanoparticles (NP-IO) and shows many advantages. To compare both types of preparations a thorough characterization studywas performed, including the study of the mechanical, optical and photonicproperties. The samples were firstly characterized by scanning electronmicroscopy (SEM) and transmission electron microscopy (TEM). A rough surfacetexture and a thick overlayer were clearly visible in the LP-IO samples, whilethe surface of NP-IO samples was more homogeneous and showed no overlayer. TEMmicrographies showed a distinctive, elongated crystallite shape for NP-IOsamples.X-ray diffraction patterns showed that anatase TiO2 was theonly crystalline phase present in both samples, and a slightly larger averagecrystallite size for LP-IO. Additionally, adherence tests were performedaccording to an ASTM standard test, showing a highly improved mechanicalstability for NP-IO samples.Toassess the photocatalytic activity of both samples the degradation of methyleneblue was evaluated. A remarkable increase in the rate constants was observedfor NP-IO samples, owing to the absence of the blocking overlayer.