Membranas mesoporosas de TiO2, soportadas sobre apatita natural y metacaolín, rentables para aplicaciones de eliminación de colorantes

[EN] The synthesis of a TiO2-tight ultrafiltration membrane supported on a low-cost ceramic substrate based on metakaolin and natural apatite was proposed in this study. To optimize the substrate composition, three samples were prepared by combining metakaolin and natural apatite with weight ratios of 25:75 (MK25), 50:50 (MK50), and 75:25 (MK75), and then sintered for 2 h at 850, 900, 950, and 1000 °C. The effect of sintering temperature and metakaolin content on the final properties of the prepared samples was studied in terms of microstructure, porosity, and mechanical strength. According to the results, the mechanical strength increased with increasing temperature and metakaolin content, but at the same time, the porosity decreased. MK50 composition and the temperature of 950 °C were chosen as optimal conditions, and the support was prepared by extrusion. The prepared substrate presented a compressive strength of 4.4 MPa, porosity of 33%, and an average pore size of 2.2 μm. To prepare a crack-free ultrafiltration membrane, the deposition of the TiO2 top layer was favoured over an alumina intermediate layer. The obtained membrane has a pore size of 6.8 nm and water permeability of 5.6 L h−1 m−2 bar−1. The membrane performance was tested for the removal of cationic and anionic dyes. The ultrafiltration experiments have shown a high removal rate for anionic and cationic dyes. Specifically, it was found that the removal rates of these dyes exceeded 75% without adjusting the pH of the solution. © 2023 The Authors[ES] En este estudio se propone la síntesis de una membrana de ultrafiltración de TiO2 soportada sobre un soporte cerámico de bajo coste basado en metacaolín y apatita natural. Para optimizar la composición del soporte se prepararon tres formulaciones combinando metacaolín y apatita natural en proporciones de peso de 25:75 (MK25), 50:50 (MK50) y 75:25 (MK75), y luego se sinterizaron durante 2 horas a 850, 900, 950 y 1000 °C. Se estudió el efecto de la temperatura de sinterización y el contenido de metacaolín en las propiedades finales de las muestras preparadas en términos de microestructura, porosidad y resistencia mecánica. De acuerdo con los resultados, la resistencia mecánica aumentó con el aumento de la temperatura y el contenido de metacaolín, pero, al mismo tiempo, la porosidad disminuyó. La composición MK50 y la temperatura de 950 °C se eligieron como condiciones óptimas, siendo el soporte preparado por extrusión. El sustrato presentó una resistencia a la compresión de 4.4 MPa, una porosidad del 33% en volumen y un tamaño medio de poro de 2.2 μm. Para preparar una membrana de ultrafiltración libre de defectos, la capa superior de TiO2 se depositó sobre una capa intermedia de alúmina. La membrana obtenida tiene un tamaño de poro de 6.8 nm y una permeabilidad al agua de 5,6 L.h.−1m.−2bar−1. Se evaluó el rendimiento de la membrana para la eliminación de colorantes catiónicos y aniónicos. Los experimentos de ultrafiltración han mostrado una alta tasa de eliminación de colorantes aniónicos y catiónicos. Específicamente, se encontró que las tasas de eliminación de estos colorantes superaban el 75% sin ajustar el pH de la solución.Peer reviewe

Study of the formation of acid‐based geopolymer networks and their resistance to water by time/temperature treatments

International audienceAcid-based geopolymers are known for their high temperature resistance and good mechanical performances. Some compositions also exhibit water resistance, which make them suitable for outdoor applications. This work aims to understand accurately the steps occurring during the geopolymerization process, and focuses on the type of networks forming at early stages of the reaction. The sample, prepared from metakaolin and phosphoric acid, has been analyzed at different durations and temperatures during its solidification, in order to identify which compounds would crystallize. The structural characterizations have been performed using Fourier Transform InfraRed spectroscopy and X-Ray diffraction. Several Al-O-P compounds and especially AlPO4 polymorphs crystallize in these conditions. They belong to three families of aluminophosphates, and are a reliable indication of the amorphous organization of the original sample. The first one is similar to the phases that appear in the phase transition sequences of silica, the second one is composed of AlPO4-based zeolites, and the last one is characterized by the presence of aluminum in an octahedral network. The transitions between the different phases are also discussed. Finally, the water resistance of the calcined samples is improved, and the release of acidic species in the water is limited even after a calcination at low temperature