Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

Verified syntheses of mesoporous materials

Semiconducting metal oxides are frequently used as gas-sensing materials. Apart from large surface-to-volume ratios, well-defined and uniform pore structures are particularly desired for improved sensing performance. This article addresses the role of some key structural aspects in porous gas sensors, such as grain size and agglomeration, pore size or crack-free film morphology. New synthesis concepts, for example, the utilisation of rigid matrices for structure replication, allow to control these parameters independently, providing the opportunity to create self-diagnostic sensors with enhanced sensitivity and reproducible selectivity.

Porous Metal Oxides as Gas Sensors

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.

Mesoporous materials as gas sensors

A weak acid selective etching strategy was put forward to fabricate oxide-based hollow nanoparticles (HNPs) using core/shell nanostructures of active metal/oxide nanoparticles as sacrificial templates. ZnO-based HNPs, including pure ZnO, Au/ZnO, Pt/ZnO, and Au/Pt/ZnO HNPs with diameter below 50 nm and shell thickness below 6 nm has been first achieved at low temperature. The diameter, thickness, and even sizes of ZnO and noble metal ultrafine crystals of HNPs can be well adjusted by the etching process. Synchronous with the formation of HNPs, the internal metal−semiconductor interfaces can be controllably eliminated (Zn−ZnO) and reconstructed (noble metal−ZnO). Excitingly, such microstructure manipulation has endued them with giant improvements in related performances, including the very strong blue luminescence with enhancement over 3 orders of magnitude for the pure ZnO HNPs and the greatly improved photocatalytic activity for the noble metal/ZnO HNPs. These give them strong potentials in relevant appli...

ZnO-based hollow nanoparticles by selective etching: elimination and reconstruction of metal-semiconductor interface, improvement of blue emission and photocatalysis.

Photoluminescent ZnO/SBA-15 mesoporous materials are prepared by directly grind zinc nitrate into the as-prepared samples occluded with template, and this solvent-free method not only saves time and energy, but also enables a large amount of zinc oxide to be highly dispersed in the channels of mesoporous silica. The resulting composites exhibit photoluminescence (PL) properties with the ZnO quantum confinement, and the dispersed ZnO in SBA-15 illustrates a similar UV emission to crystalline ZnO nanostructures. Besides, this photoluminescence is used to try to detect the nitrosamine content in solution by quenching PL spectra for the first time, suggesting potential applications of ZnO/SBA-15 in sensing carcinogens such as N′-nitrosonornicotine (NNN) in the environment.

Fabrication of photoluminescent ZnO/SBA-15 through directly dispersing zinc nitrate into the as-prepared mesoporous silica occluded with template

Rapid Functionalization of Mesoporous Materials: Directly Dispersing Metal Oxides into As‐Prepared SBA‐15 Occluded with Template

In‐Situ Coating of SBA‐15 with MgO: Direct Synthesis of Mesoporous Solid Bases from Strong Acidic Systems

In situ coating metal oxide on SBA-15 in one-pot synthesis

Solid-state grinding is a simple and effective method to include guest species into the channels of ordered mesoporous materials with a different degree of filling. After calcination, a monolayer or several monolayers of guest species can not only form highly dispersed oxide species and other surface species on the hosts whether the template is occluded in the channels or not, but the guest species can also fill the mesoporous channels in the host and thus lead to nanowires or nanoarrays. Solid-state salt inclusion is faster and more convenient than other inclusion routes. The absence of a solvent not only saves the time otherwise needed for evaporation but also leads to a higher degree of filling through a simple inclusion step as the void space in the pores is not occupied by the solvent. Also, the lack of competitive adsorption of solvent molecules enhances the interaction between the guest species included and the silica wall, which facilitates the high dispersion of oxide species. However, host–guest interactions that are too strong may disturb the self-crystallization of guest species in the mesopores leading to imperfect nanocasting of the mesostructure.

Zheng Ying Wu

Papers

Fabrication of photoluminescent ZnO/SBA-15 through directly dispersing zinc nitrate into the as-prepared mesoporous silica occluded with template

Rapid Functionalization of Mesoporous Materials: Directly Dispersing Metal Oxides into As‐Prepared SBA‐15 Occluded with Template

In‐Situ Coating of SBA‐15 with MgO: Direct Synthesis of Mesoporous Solid Bases from Strong Acidic Systems

In situ coating metal oxide on SBA-15 in one-pot synthesis

Fabrication of Metal Oxides Occluded in Ordered Mesoporous Hosts via a Solid-State Grinding Route: The Influence of Host–Guest Interactions