Francois-Marie Allioux

Electro-catalytic biodiesel production from canola oil in methanolic and ethanolic solutions with low-cost stainless steel and hybrid ion-exchange resin grafted electrodes

Biodiesel is a growing alternative to petroleum fuels and is produced by the catalysed transesterification of fats in presence of an alcohol base. Transesterification processes using homogeneous catalysts are considered to be amongst the most efficient methods but rely on the feedstock quality and low water content in order to avoid undesirable saponification reactions. In this work, the electro-catalytic conversion of canola oil to biodiesel in a 1% aqueous methanolic and ethanolic reaction mixture was performed without the addition of external catalyst or co-solvent. An inexpensive stainless steel electrode and a hybrid stainless steel electrode coated with an ion-exchange resin catalyst were used as cathode materials while the anode was composed of a plain carbon paper. The cell voltages were varied from 10 to 40 V and the reaction temperature maintained at 20 or 40°C. The canola oil conversion rates were found to be superior at 40°C without saponification reactions for cell voltages below 30 V. The conversion rates were as high as 87% for the hybrid electrode and 81% for the plain stainless steel electrode. This work could inspire new process development for the conversion of high water content feedstock for the production of second-generation biodiesel.

Graphene based room temperature flexible nanocomposites from permanently cross-linked networks

Graphene based room temperature flexible nanocomposites were prepared using epoxy thermosets for the first time. Flexible behavior was induced into the epoxy thermosets by introducing charge transfer complexes between functional groups within cross linked epoxy and room temperature ionic liquid ions. The graphene nanoplatelets were found to be highly dispersed in the epoxy matrix due to ionic liquid cation–π interactions. It was observed that incorporation of small amounts of graphene into the epoxy matrix significantly enhanced the mechanical properties of the epoxy. In particular, a 0.6 wt% addition increased the tensile strength and Young’s modulus by 125% and 21% respectively. The electrical resistance of nanocomposites was found to be increased with graphene loading indicating the level of self-organization between the ILs and the graphene sheets in the matrix of the composite. The graphene nanocomposites were flexible and behave like ductile thermoplastics at room temperature. This study demonstrates the use of ionic liquid as a compatible agent to induce flexibility in inherently brittle thermoset materials and improve the dispersion of graphene to create high performance nanocomposite materials.

Preparation of Porous Stainless Steel Hollow-Fibers through Multi-Modal Particle Size Sintering towards Pore Engineering

The sintering of metal powders is an efficient and versatile technique to fabricate porous metal elements such as filters, diffusers, and membranes. Neck formation between particles is, however, critical to tune the porosity and optimize mass transfer in order to minimize the densification process. In this work, macro-porous stainless steel (SS) hollow-fibers (HFs) were fabricated by the extrusion and sintering of a dope comprised, for the first time, of a bimodal mixture of SS powders. The SS particles of different sizes and shapes were mixed to increase the neck formation between the particles and control the densification process of the structure during sintering. The sintered HFs from particles of two different sizes were shown to be more mechanically stable at lower sintering temperature due to the increased neck area of the small particles sintered to the large ones. In addition, the sintered HFs made from particles of 10 and 44 μm showed a smaller average pore size (<1 μm) as compared to the micron-size pores of sintered HFs made from particles of 10 μm only and those of 10 and 20 μm. The novel HFs could be used in a range of applications, from filtration modules to electrochemical membrane reactors.

Insights into Free Volume Variations across Ion-Exchange Membranes upon Mixed Solvents Uptake by Small and Ultrasmall Angle Neutron Scattering

Ion-exchange membranes are composite separation materials increasingly used in a variety of electro-membranes and electrochemical processes. Although promising for solvent reclamation, to date, their main applications are limited to aqueous environments due to physicochemical and microstructural changes of the materials upon exposure to nonaqueous and mixed solvents solutions, affecting long-term stability and separation performance. In the present work, the structural changes of commercial and novel hybrid ion-exchange membranes in mixed methanol/water and ethanol/water solutions are assessed for the first time using ultra- and small-angle neutron scattering techniques. The interface between the ion-exchange functional layer and the mechanical support of the membranes is evaluated in the ultralow-q region, while a broad solvent-dependent peak at the mid-q region was correlated to the microstructural properties which are related to the free volume across the ion-exchange domains and to the materials electrical and nanoscale mechanical properties. The results of this study may offer new opportunities toward the development of an efficient separation process using ion-exchange membranes for the purification of fermentation broths toward biofuel generation.

Ultrasound-assisted fabrication of metal nano-porous shells across polymer beads and their catalytic activity for reduction of 4-nitrophenol

Metal nano-porous architectures are a novel class of nanomaterials which has been applied in the fields of catalysis, sensing and gas storage because of their high surface-to-volume ratio, high mechanical strength and long-range ordered architectures. A commonly-used synthetic strategies to achieve architectures with high precision and diverse porosity design is the seed-and-growth method. In this work, using a dual-frequency sequential sonication approach, we have demonstrated a sonochemical-assisted one-pot seeding with a successive shell growth synthetic strategy for mesoporous metal deposition via a gold (Au) nanoparticle and poly(styrene) beads system. A uniform coating of gold nanoparticle seeds with dense surface coverage was formed by first employing 300 kHz ultrasound irradiation while the nano-porous shell growth was then performed under 1 MHz ultrasonic frequency. The precise control over the process conditions and parameters allowed for the design of well-defined shell thicknesses and surface roughness and area. The catalytic property of the MNMs was evaluated for the degradation of 4-nitrophenol and a high catalytic activity was achieved for the most porous gold structures, suggesting synergistic effects between the architecture of the nanomaterials and their surface reactivity.

Single step synthesis of Janus nano-composite membranes by atmospheric aerosol plasma polymerization for solvents separation

Solvent permeation across membranes is limited due to physical resistance to diffusion from the selective layer within the membrane and to plasticizing effects generated by the solvent molecules onto the polymeric macromolecular matrix. Nano-composite thin film membranes provide promising routes to generate controlled microstructural separation materials with higher selectivities and permeabilities. Here, the fabrication of nano-composite based on octamethyl-polyhedral oligomeric silsesquioxane - hexamethyldisiloxane thin film membranes is demonstrated by aerosol assisted atmospheric plasma deposition onto pre-formed nano-porous membrane supports for the first time. Stable, atomically smooth and continuous solid films with controllable thickness down to 50 nm were achieved. The deposition process allowed for the control of the wettability of the surfaces to water and organic solvents, leading to the generation of hydrophobic but alcohol-philic surfaces. The liquid entry pressure of the films to water was found to be 8 bar from plasma polymerization as oppose to 3 bar for the bare nano-porous support only. In addition, the ideal separation selectivity for ethanol to water, up to 6.5, highlight the impact of both the surface energy and level of cross-linking of the hexamethyldisiloxane nanostructures on the diffusion mechanisms. This new atmospheric plasma deposition strategy opens-up cost-effective and environmentally friendly routes for the design of the smart Janus membrane with customizable properties and performance.

Smart electrically responsive hybrid ion-selective membranes for selective gated transport of ionic species

Ion-exchange membrane materials have been developed to allow for selective transport based on the absolute charge and valence of the species. The transport of ions across the dense, charge neutral membranes is dominated by a hopping mechanism between ionic sites. The ionic transport rate is therefore limited by both process conditions, including primarily the concentration of ionic species in solution and the current passing across the system, and also material properties including the overall resistance and ionic site density of the membrane. A route to tackle this challenge is to develop gated ionic transport materials from electrically responsive hybrid ion-exchange membranes able to alter their ionic conductance under external stimuli. Here, hybrid ion-exchange membranes were synthesized by incorporating selective anion or cation exchange resins across porous electrically conductive reinforcement materials for application in electro-dialysis. The electrically conductive nature of the reinforcement allowed for the super-imposition of a secondary electrical field acting as a gate keeper for the direct polarisation of the hybrid membranes upon electro-dialysis operation. The secondary electrical field generated across pairs of hybrid ion-exchange membranes was shown to provide an additional driving force either blocking the transport or promoting the migration of ionic species by up to 6 fold. Ionic transport mechanisms across the selective gated ion-exchange membranes are also discussed considering the response of the system under specific current/voltage stimuli. This novel approach offers unprecedented control over the ionic transport mechanisms with potential applications in microfluidics, resource recovery, desalination and chemical synthesis, offering a cost-effective solution to selective ionic transport.