Résumé
Originally dedicated to the treatment of aqueous wastes, the simultaneous coupling of low ultrasonic frequency irradiation and hydrothermal conditions has emerged as an innovative and efficient technique for the synthesis of nanomaterials [1-4]. After more than a decade, this presentation will give a glance at both the fundamental aspects of the sonohydrothermal (SHT) treatment and its application for the synthesis of materials developed in our laboratory [2-4].First, it appears of prime importance to state if acoustic cavitation under such conditions could eventually occurred. Based on gas phase analyses, revealing the accumulation of hydrogen with the atmosphere of our SHT reactor (Figure 1), we actually reported for the first time the existence of the sonochemical activity, and thus acoustic cavitation occurrence, within water under 20 kHz ultrasonic irradiation at 200 °C with an autogenous pressure of 13 bars [2]. In order to assess in what extend acoustic cavitation under hydrothermal conditions could influence the synthesis of materials, this innovative approach was then dedicated to the preparation of mesoporous (Ce,Zr)O2 for catalytic oxidation applications and Ti@TiO2 core-shell photocatalysts for hydrogen production [2-4]. More recently, SHT conditions were also considered for the study of the metastable zeolite A formation and its phase conversion into sodalite. Structural and morphological analyses were carried out on final products using various techniques such as SEM/EDX, TEM and XRD, µ-Raman, XPS, BET surface area techniques. Obtained results showed that SHT treatment could lead to morphological changes of the synthesized materials and to kinetic increase up to two orders of magnitude compared to classical hydrothermal treatment. The origin of such drastic effects and underneath mechanisms are still under investigations but we will discuss, in the light of our results, that observed effects can be related to oriented aggregation mechanisms, sonofragmentation and enhanced mass transfer due to acoustic cavitation phenomenon.