Abstract
The fabrication of hierarchical anatase microspheres with potential photocatalytic properties eventually comprises a consolidation step in which a high degree of crystalline order is typically achieved through conventional electric heating treatments. This however entails a substantial reduction in the specific surface area and porosity of the powders, with the consequent deterioration in their photocatalytic response. Here, we have tested the employ of microwave heating as an alternative energy-saving sintering method to promote fast crystallization. The results obtained suggest that under the microwave radiation, the TiO2 hierarchical structures can effectively crystallize in a drastically reduced heating time, allowing the specific surface area and the porosity to be kept in the high values required for an improved photocatalytic performance.
Highlights
The unique physicochemical properties of TiO2 nanoparticles have lately attracted a tremendous interest in a wide range of scientific and technological fields [1-5]
Of particular interest for its potential photocatalytic applications to environmental purification, hydrogen generation and/or solar energy conversion is the preparation of hierarchical structures in which TiO2 anatase nanoparticles are assembled into organized configurations at a microscopic level [6-11]
* Correspondence: dgcalatayud@icv.csic.es 1Instituto de Cerámica y Vidrio, contract of the Spanish National Research Council (CSIC), c/Kelsen 5, Campus de Cantoblanco, Madrid 28049, Spain Full list of author information is available at the end of the article main problem with all these methods is the subsequent thermal treatment at mild/high temperatures, which, being necessary to increase the crystallinity of the samples, reduces their porosity and specific surface area. This provokes a severe devaluation of their photocatalytic performance which hampers the practical application of these powders. In this contribution, we propose to replace the conventional thermal treatment by a microwave heating process, an alternative and energysaving sintering technique which has been successfully employed for the consolidation of some ceramic systems [16-19]
Summary
The unique physicochemical properties of TiO2 nanoparticles have lately attracted a tremendous interest in a wide range of scientific and technological fields [1-5]. Of particular interest for its potential photocatalytic applications to environmental purification, hydrogen generation and/or solar energy conversion is the preparation of hierarchical structures in which TiO2 anatase nanoparticles are assembled into organized configurations at a microscopic level [6-11]. The micrometric size of the organized assemblies will allow an easy recovery of the photocatalyst from the working suspension after use. In this context, different synthesis strategies have been recently tested to prepare TiO2 hierarchical structures. Using templates and/or applying hydro(solvo)thermal conditions, anatase nanostructures assembled onto micronsized spherical units have been synthesized initially showing a high stability and a monodisperse nature that can satisfy the abovementioned characteristics [12-15].
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