The project PolyCeraMem consists to apply the «Polymer-Derived Ceramics« route to prepare silicon carbide-based hollow fibers and capillaries. The general aim is to apply these materials as H2 permselective membranes ( hollow fiber ) or for the treatment of water (capillaries) after their surface modification by (photo)catalysts.
The main objective is to prepare non-oxide ceramic hollow fibers with (photo)catalytic properties for the treatment of fluids (H2 separation and purification and water treatment) for a «membrane« application. The first objective is to develop the SiC-based hollow fibers through a detailed investigation of the synthesis of polycarbosilazanes as ceramic precursor, their melt-spinning and their conversion into hollow fibers that are known to be robust and durable. These materials are then used for gas permeation after surface modification with metals. The second objective is to synthesize SiC-based powders from polycarbosilazanes, then to mix these powders with other compunds forming a paste which displays the rheological properties to be extruded into raw capillaries. The capillaries are then sintered at high temperature to generate SiC-based capillaries to be modified by photocatalysts for the treatment of water (desalination, decontamination) . The third objective is to modify the surface of these materials by a coating based on palladium alloys for separation and purification of H2 and by a titanium oxide coating doped with nitrogen ant/or silver for the treatment of pollutants in water under irradiation. Taking into account the originality of the field of research, the fundamental aspects will be particularly studied. There are several challenges. The PolyCeraMem project aims to correct problems that occur with carbon and/or oxide materials which do not have sufficient stability in aggressive environment and who have a different surface chemistry. Furthermore, research on hollow fibers and capillaries is poorly explored; one challenge is to understand the behavior of these materials in the intended applications.
This project aims to implement the so-called PDCs route associated with shaping or sintering processes. Our approach firstly consists in the synthesis of polycarbosilazanes possibly modified. The polymers are characterized by infrared spectroscopy, molecular weight measurement and chemical analysis. These polymers are synthesized to form during spinning a viscous liquid at a reasonable temperature which is forced through a capillary to form a continuous filament which solidifies during its mechanical stretching by means of a spool. In this project, these polymers must be synthesized to obtain solid and preferably soluble (synthesis) and fusible (spinning). Their structure is studied by solid state NMR. Then, we investigate the spinnability of polymers in relation with their structure and their rheological properties as well as the conversion of polymer hollow fibers, but also polymers in powder form. The steps related to the conversion process and the chemical and structural changes of the polymer during thermal treatments are studied in detail by combining several characterization tools. The identification of the reactional mechanisms allows to fix the crosslinking and pyrolysis parameters for processing into SiC-based powders and hollow fibers without loss of fiber cohesion. The powders are then transformed into a paste to perform extrusion and generate capillaries which are then sintered. The surface modification of hollow fibers and capillaries by metals (H2 permselectivity) and photocatalysts (water treatment under irradiation) will allow application of these materials into membranes.
The polymers have been characterized by infrared spectroscopy, solid-state NMR and chemical analysis. The first two types of polymers obtained by hydroboration of a dichloromethylvinylsilane followed by addition of methylamine and a controlled addition of ammonia are adapted to melt-spinning and form at a reasonable temperature a liquid polymer with appropriate rheological properties to form a continuous filament. Their spinnability is studied in connection with their structure identified by NMR. Spinning has been carried out using a single hole annular die to produce hollow fibers of small diameter (10-20 microns) whose walls are microporous in order to satisfy an application for separation and purification H2 (1st objective of this project). These fibers are now mechanically tested and palladium deposition tests are in progress. The third type of polymer is obtained by hydroboration of a commercially-available polycarbosilazane. Based on the solid-state NMR, it emerged that during the addition of the boron source (borane dimethylsulfide), the hydroboration reaction, theoretically expected, is associated with a dehydrocoupling reaction involving BH units and NH functions present in the main chain of polysilazane. These polymers were then converted into ceramic powder at 1000 ° C under nitrogen and this transformation was followed by infrared spectroscopy and solid-state NMR.
Futur prospects will be to optimize the preparation of hollow fibers and capillaries to be surface-modified for membrane application (hydrogen permselectivity and water treatment)
F. Sandra, O. Majoulet, M. Depardieu, Z. Mouline, A. Viard, G. Vignoles, Y. Iwamoto, P. Miele, R. Backov, S. Bernard, accepté dans Chem. Eur. J., 2016. DOI: 10.1002/chem.201600060
A. Viard, P. Miele, S. Bernard, submitted to J. Ceram. Soc. Jp., April 2016
Motivated by the increasing demand in technical membranes for the treatment of fluids, the present proposal is concerned with the design, processing, properties and surface modification of polymer-derived silicon-based non-oxide ceramic hollow fibers (PDCHFs) with controlled diameters for membrane applications. The materials proposed here are prepared in the silicon-containing carbonitride (Si-(B/Al)-C-N) systems to maintain durability in aggressive and adverse environments while achieving permeability, selectivity and (photo)catalytic properties through the modification of their surface by Pd-based metal alloy layers (Pd-M) and silver/titanium dioxide coatings (Ag/TiO2). The proposed materials are expected to be used for H2 permselectivity and water treatment. Within this project which is located at the frontiers of materials chemistry, processing, ceramic science and physics, we focus on the synthesis, spinning and pyrolysis of preceramic polymers into hollow non-oxide ceramic fibers with controlled composition, nanostructure and diameters which are decorated on their surface by impregnation processes. To reach our objectives, the project is shared into six interconnected scientific tasks (Ta1?Ta6) The first task (Ta1) is focused on the synthesis and characterization of preceramic polymers (polycarbosilazanes which can be modified by boron and/or aluminum). Detailed investigation of their molecular chemistry will be achieved through routine characterization, while their structure will be investigated by NMR and molecular weight measurements. The second task (Ta2) consists in the polymer spinning and investigation of thermomechanical and rheological phenomena that take place during the spinning process. Rheology of preceramic polymers in shear and extension will be studied based on the structural information obtained in Ta1 in order to optimize the melt-spinning process to produce hollow green fibers. The task 3 (Ta3) is focused on the ceramic conversion of hollow green fibers prepared in Ta2 into the desired final nanostructures and compositions. Detailed investigation of polymer-to-ceramic conversion will be achieved through FTIR, GC/MS and solid-state NMR in particular to propose our targeted materials without loss of fiber cohesion. The task 4 (Ta4) is dedicated to the surface modification of as-obtained PDCHFs to render them (photo)catalytic for fluid separation/treatment. The task 5 (Ta5) is focused on the characterization of PDCHFs before and after surface decoration with a particular attention on the mechanical properties. The task 6 (Ta6) concerns the evaluation of the potentialities of final materials (as-obtained and (photo)catalytic) as H2 permselective membranes and membranes for water treatment (water permeation, desalination, photodegradation of water pollutants). These materials are expected to lead to benefits for the advancement of science, industry and society.
Monsieur Samuel Bernard (Institut Européen des Membranes de Montpellier)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
LARMAUR Laboratoire de Recherche en Mécanique Appliquée
LCMCP Laboratoire de Chimie et de la Matière Condensée de Paris
IEMM Institut Européen des Membranes de Montpellier
Help of the ANR 484,486 euros
Beginning and duration of the scientific project: October 2013 - 48 Months