Continuous Synthesis of Nanominerals in Supercritical Water

Abstract

The synthesis of minerals should play a crucial role in the development of new and advanced materials. Since 2016, a renewal of interest to enlarge the mineral synthesis towards industrial requirements has been observed, especially thanks to three main recent papers. The innovative process exposed combines a continuous process with the use of supercritical water. In addition to curtail synthesis times, this process offers a control on the particle characteristics (size, crystallinity, structure, etc.) and a capacity to be easily transferable at an industrial scale. This innovative concept is demonstrated with the synthesis of three minerals which are the talc (a phyllomineral), the xonotlite and the tobermorite (two inominerals). This article proposes an overview of the possibilities to synthesize nanominerals in continuous processing for the development of advanced materials with promising industrial applications.

Chemical Functionalisation of 2D Materials by Batch and Continuous Hydrothermal Flow Synthesis

“…Moreover, the reaction temperature, when the two flows are mixed, is typically in the range of 300–380 °C, compared to typically less than 250 °C for batch hydrothermal. Thus, CHFS synthesis/functionalisation occurs at supercritical conditions in which the reaction rate increases due to a decrease in the dielectric constant of supercritical water . Fine particles, metal oxides and single crystals can be synthesised in CHFS by processing in near‐ critical or supercritical water conditions by controlling the density, viscosity and dielectric constant of the reaction medium through independent control over reaction parameters, such as flow rates, temperature and pressure .…”

Chemistry in supercritical fluids for the synthesis of metal nanomaterials

“…Indeed, this is particularly interesting to flow chemistry synthesis where the reaction as well as the nucleation and growth of nanomaterials proceed in a continuous stream. 41,[55][56][57][58]121 To this end, mainly two families of designs have been adopted, in both of which the dwelling time of the synthesis process can be finely tuned in the range of seconds to minutes. One is by thermally decomposing a precursor flow in a reactor at controlled temperatures and pressures above the critical points of solvents (type I in Fig.…”

“…For the readers' reference, here are some literature studies on the process with respect to its fundamentals, 149 state-of-the-art progress, 41,54,55,150 environmental impacts, [151][152][153][154] and endeavours in upscaling. 56,155,156 Among others, the interest in using supercritical H2O has also been extended to the controlled synthesis of monodispersed metal nanomaterials that are studied in both a conventional hydrothermal autoclave and flow environments. However, H2O cannot act as a reducing agent and thus the participation of additional reducing agents is indispensable.…”

“…Further, the time can be substantially reduced to only tens of seconds by conducting the mineral synthesis in supercritical water in continuous flow-type setups. [56][57][58][59] The second is 'supercritical fluid reactive/chemical deposition (SFRD/SFCD)' which takes advantage of the good capabilities of supercritical fluids in diffusion and mass transport. It is particularly suitable to achieve homogeneous and conformal deposition of nanomaterials on substrates with complex topographies and ultrafine microstructures.…”

Facile sub-/supercritical water synthesis of nanoflake MoVTeNbOx-mixed metal oxides without post-heat treatment and their catalytic performance

“…Nowadays, sub-/supercritical water is widely used in the preparation of metal-and non-metal-based nano/micro materials, due to the unique and adjustable physicochemical properties around its critical point. [11][12][13][14][15][16] For instance, the low dielectric constant of sub-/supercritical water is conducive to the formation of nanoparticles of metal-based materials [17][18][19][20][21][22][23] and the hybridization of nanoparticles. 24 More importantly, under sub-and supercritical systems, the crystallization of metalbased products can be achieved in a very short time.…”