Improvements in the efficiency of combustion within a vehicle can lead to reductions in the emission of harmful pollutants and increased fuel efficiency. Gas sensors have a role to play in this process, since they can provide real time feedback to vehicular fuel and emissions management systems as well as reducing the discrepancy between emissions observed in factory tests and ‘real world’ scenarios. In this review we survey the current state-of-the-art in using porous materials for sensing the gases relevant to automotive emissions. Two broad classes of porous material – zeolites and metal–organic frameworks (MOFs) – are introduced, and their potential for gas sensing is discussed. The adsorptive, spectroscopic and electronic techniques for sensing gases using porous materials are summarised. Examples of the use of zeolites and MOFs in the sensing of water vapour, oxygen, NOx, carbon monoxide and carbon dioxide, hydrocarbons and volatile organic compounds, ammonia, hydrogen sulfide, sulfur dioxide and hydrogen are then detailed. Both types of porous material (zeolites and MOFs) reveal great promise for the fabrication of sensors for exhaust gases and vapours due to high selectivity and sensitivity. The size and shape selectivity of the zeolite and MOF materials are controlled by variation of pore dimensions, chemical composition (hydrophilicity/hydrophobicity), crystal size and orientation, thus enabling detection and differentiation between different gases and vapours.

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Gas sensing using porous materials for automotive applications

Capillary condensation of adsorbates in porous materials.

The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourthly, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.

https://hal-amu.archives-ouvertes.fr/hal-02167914/document

Tackling the Challenges of Enzymatic (Bio)Fuel Cells

This review highlights recent developments in the synthesis of nanosized zeolites. The strategies available for their preparation (organic-template assisted, organic-template free, and alternative procedures) are discussed. Major breakthroughs achieved by the so-called zeolite crystal engineering and encompass items such as mastering and using the physicochemical properties of the precursor synthesis gel/suspension, optimizing the use of silicon and aluminium precursor sources, the rational use of organic templates and structure-directing inorganic cations, and careful adjustment of synthesis conditions (temperature, pressure, time, heating processes from conventional to microwave and sonication) are addressed. An on-going broad and deep fundamental understanding of the crystallization process, explaining the influence of all variables of this complex set of reactions, underpins an even more rational design of nanosized zeolites with exceptional properties. Finally, the advantages and limitations of these methods are addressed with particular attention to their industrial prospects and utilization in existing and advanced applications.

Advances in nanosized zeolites

This review highlights recent developments in the synthesis and unconventional applications of nanosized microporous crystals including framework (zeolites) and layered (clays) type materials. Owing to their microporous nature nanosized zeolites and clays exhibit novel properties, different from those of bulk materials. The factors controlling the formation of nanosized microporous crystals are first revised. The most promising approaches from the viewpoint of large-scale production of nanosized zeolites and clays are discussed in depth. The preparation and advanced applications of nanosized zeolites and clays in free (suspension and powder forms) and fixed (films) forms are summarized. Further the review emphasises the non-conventional applications of new porous materials. A comprehensive analysis of the emerging applications of microporous nanosized crystals in the field of semiconductor industry, optical materials, chemical sensors, medicine, cosmetics, and food industry is presented. Finally, the future needs and perspectives of nanosized microporous materials (zeolites and clays) are addressed.

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Nanosized microporous crystals: emerging applications.

Adsorption properties of zeolites for artificial kidney applications

Adsorption of the uremic toxin p-cresol onto hemodialysis membranes and microporous adsorbent zeolite silicalite

The mass transfer kinetics of toluene and polystyrenes (of which the Mw varies from 162 to 1.85 × 106 g mol−1) through columns filled with silica porous spheres were studied by inverse size exclusion chromatography. The mass transfer parameters were measured by modeling the band broadening of the chromatograms. The experimental height equivalent to a theoretical plate (HETP) data were analyzed using the general rate model in order to determine the effective diffusion coefficient in porous particles as a function of molecular size. The bulk molecular diffusion coefficients were experimentally determined by dynamic light scattering (DLS) and Taylor dispersion analysis (TDA). The topological tortuosity of the porous particles was determined by electrical measurements. The effective molecular diffusion coefficient through porous particles was modeled taking into account exclusion, friction, and at last tortuosity effects. A phenomenological law is proposed to model the evolution of the tortuosity experienced ...

Influence of Molecule Size on Its Transport Properties through a Porous Medium

To examine the mechanism of the thermal hysteresis between freezing and melting for water confined in a network of the ink-bottle pores of ordered silica, we measured the freezing and melting behavior of pore water in seven kinds of KIT-5 samples with various neck and cavity sizes by means of differential scanning calorimetry and X-ray diffractometry. The melting temperature of pore ice depended on the cavity size, whereas the freezing behavior of pore water depended on the neck size. When the neck size is smaller than ∼4 nm in diameter, the pore water in the spherical cavities freezes via homogeneous nucleation on cooling. On the other hand, the freezing behavior of the pore water changed drastically when the diameter of the necks was increased beyond this critical size:  the freezing temperature was increased remarkably and the freezing became very broad. Such a freezing behavior may be accounted for by a gradual percolation of the ice front that grows by traveling through the connected pore network.

Pore-Blocking-Controlled Freezing of Water in Cagelike Pores of KIT-5

The discovery of oxygen and carbon monoxide tolerant [NiFe] hydrogenases was the first necessary step toward the definition of a novel generation of hydrogen fed biofuel cells. The next important milestone is now to identify and overcome bottlenecks limiting the current densities, hence the power densities. In the present work we report for the first time a comprehensive study of herringbone carbon nanofiber mesoporous films as platforms for enhanced biooxidation of hydrogen. The 3D network allows mediatorless hydrogen oxidation by the membrane-bound hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus. We investigate the key physico-chemical parameters that enhance the catalytic efficiency, including surface chemistry and hierarchical porosity of the biohybrid film. We also emphasize that the catalytic current is limited by mass transport inside the mesoporous carbon nanofiber film. Provided hydrogen is supplied inside the carbon film, the combination of the hierarchical porosity of the carbon nanofiber film with the hydrophobicity of the treated carbon material results in very high efficiency of the bioelectrode. By optimization of the whole procedure, current densities as high as 4.5 mA cm−2 are reached with a turnover frequency of 48 s−1. This current density is almost 100 times higher than when hydrogenase is simply adsorbed at a bare graphite electrode, and more than 5 times higher than the average of the previous reported current densities at carbon nanotube modified electrodes, suggesting that carbon nanofibers can be efficiently used in future sustainable H2/O2 biofuel cells.

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Véronique Wernert

Papers

Adsorption properties of zeolites for artificial kidney applications

Adsorption of the uremic toxin p-cresol onto hemodialysis membranes and microporous adsorbent zeolite silicalite

Influence of Molecule Size on Its Transport Properties through a Porous Medium

Pore-Blocking-Controlled Freezing of Water in Cagelike Pores of KIT-5

Carbon nanofiber mesoporous films: efficient platforms for bio-hydrogen oxidation in biofuel cells