Ordered mesoporous materials have great potential in the field of gas sensing. Today various template-assisted synthesis methods facilitate the preparation of silica (SiO2) as well as numerous metal oxides with well-defined, uniform and regular pore systems. The unique nanostructural properties of such materials are particularly useful for their application as active layers in gas sensors based on various operating principles, such as capacitive, resistive, or optical sensing. This review summarizes the basic aspects of materials synthesis, discusses some structural properties relevant in gas sensing, and gives an overview of the literature on ordered mesoporous gas sensors.

Uniform and pinhole-free electron-selective TiO layers are of utmost importance for efficient perovskite solar cells. Here we used a scalable and low-cost dip-coating method to prepare uniform and ultrathin (5-50 nm) compact TiO films on fluorine-doped tin oxide (FTO) glass substrates. The thickness of the film was tuned by changing the TiCl precursor concentration. The formed TiO follows the texture of the underlying FTO substrates, but at higher TiCl concentrations, the surface roughness is substantially decreased. This change occurs at a film thickness close to 20-30 nm. A similar TiCl concentration is needed to produce crystalline TiO films. Furthermore, below this film thickness, the underlying FTO might be exposed resulting in pinholes in the compact TiO layer. When integrated into mesoscopic perovskite solar cells there appears to be a similar critical compact TiO layer thickness above which the devices perform more optimally. The power conversion efficiency was improved by more than 50% (from 5.5% to ∼8.6%) when inserting a compact TiO layer. Devices without or with very thin compact TiO layers display J-V curves with an "s-shaped" feature in the negative voltage range, which could be attributed to immobilized negative ions at the electron-extracting interface. A strong correlation between the magnitude of the s-shaped feature and the exposed FTO seen in the X-ray photoelectron spectroscopy measurements indicates that the s-shape is related to pinholes in the compact TiO layer when it is too thin.

A nanocomposite material based on copper(II) oxide (CuO) and its utilization as a highly selective and stable gas-responsive electrical switch for hydrogen sulphide (H 2 S) detection is presented. The material can be applied as a sensitive layer for H 2 S monitoring, e.g., in biogas gas plants. CuO nanoparticles are embedded in a rigid, nanoporous silica (SiO 2 ) matrix to form an electrical percolating network of low conducting CuO and, upon exposure to H 2 S, highly conducting copper(II) sulphide (CuS) particles. By steric hindrance due to the silica pore walls, the structure of the network is maintained even though the reversible reaction of CuO to CuS is accompanied by significant volume expansion. The conducting state of the percolating network can be controlled by a variety of parameters, such as temperature, electrode layout, and network topology of the porous silica matrix. The latter means that this new type of sensing material has a structure-encoded detection limit for H 2 S, which offers new application opportunities. The fabrication process of the mesoporous CuO@SiO 2 composite as well as the sensor design and characteristics are described in detail. In addition, theoretical modeling of the percolation effect by Monte-Carlo simulations yields deeper insight into the underlying percolation mechanism and the observed response characteristics.

Crystalline, mesoporous alumina (Al2O3) materials with specific surface areas up to 400 m2 g–1 have been synthesized by means of structure replication (nanocasting) using CMK‐8 carbon as a structure matrix. A crucial step during this synthesis procedure is the conversion of aluminum nitrate into aluminum hydroxide by treatment with ammonia vapor. The impact of this step was investigated in some detail. Prolonged vapor treatment has a positive impact on the crystallinity of the final Al2O3 products but at the same time leads to loss of mesoscopic structural order and porosity.

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