A continuing goal in catalysis research is to engineer the composition and structure of noble metal nanomaterials in order to precisely tune their catalytic activity. Herein, we present proof-of-concept results on the synthesis of supported bimetallic core/shell nanoparticles entirely by atomic layer deposition (ALD). ALD is a novel and scalable method, which can be used to prepare noble-metal catalysts on high surface area support materials. Two properties of ALD of noble metals, namely the Volmer−Weber growth and surfaceselectivity, are exploited to decouple primary island growth from subsequent selective shell growth. This concept is applied to synthesize highly dispersed Pd/Pt and Pt/Pd nanoparticles. Indepth characterization of the nanoparticles provides evidence for the core/shell morphology and for the narrow size distribution. The self-limiting nature of the ALD process allows for independent control of the core and shell dimensions, opening up unique possibilities for precise engineering of metallic nanoparticle properties.

The deposition of Pd and Pt nanoparticles by atomic layer deposition (ALD) has been studied extensively in recent years for the synthesis of nanoparticles for catalysis. For these applications, it is essential to synthesize nanoparticles with well-defined sizes and a high density on large-surface-area supports. Although the potential of ALD for synthesizing active nanocatalysts for various chemical reactions has been demonstrated, insight into how to control the nanoparticle properties (i.e. size, composition) by choosing suitable processing conditions is lacking. Furthermore, there is little understanding of the reaction mechanisms during the nucleation stage of metal ALD. In this work, nanoparticles synthesized with four different ALD processes (two for Pd and two for Pt) were extensively studied by transmission electron spectroscopy. Using these datasets as a starting point, the growth characteristics and reaction mechanisms of Pd and Pt ALD relevant for the synthesis of nanoparticles are discussed. The results reveal that ALD allows for the preparation of particles with control of the particle size, although it is also shown that the particle size distribution is strongly dependent on the processing conditions. Moreover, this paper discusses the opportunities and limitations of the use of ALD in the synthesis of nanocatalysts.

Herein, we report the fabrication of hydrogen gas sensors with enhanced sensitivity and excellent selectivity. The sensor device is based on the strategic combination of ZnO nanowires (NWs) decorated with palladium nanoparticles (Pd NPs) and a molecular sieve metal-organic framework (MOF) nanomembrane (ZIF-8). The Pd NPs permit the sensors to reach maximal signal responses, whereas the ZIF-8 overcoat enables for an excellent selectivity. Three steps were employed for the fabrication: (i) coating of a miniaturized sensor with vapor-grown ZnO NWs, (ii) decoration of these NWs with Pd NPs by atomic layer deposition, and (iii) partial solvothermal conversion of the tuned NWs surface to ZIF-8 nanomembrane. The microstructure and composition investigations of the ZIF-8/Pd/ZnO nanostructured materials confirmed the presence of both metallic Pd NPs and uniform ZIF-8 thin membrane layer. The integration of these nanomaterials within a miniaturized sensor device enabled the assessment of their performance for H detection at concentrations as low as 10 ppm in the presence of various gases such as CH, CH, CHOH, and CHCOCH. Remarkably high-response signals of 3.2, 4.7, and 6.7 ( R/ R) have been measured for H detection at only 10, 30, and 50 ppm, whereas no noticeable response toward other tested gases was detected, thus confirming the excellent H selectivity obtained with such a sensor design. The results obtained showed that the performance of gas sensors toward H gas can be greatly increased by both the addition of Pd NPs and the use of ZIF-8 coating, acting as a molecular sieve membrane. Furthermore, the presented strategy could be extended toward the sensing of other species by a judicious choice of both the metallic NPs and MOF materials with tuned properties for specific molecule detection, thus opening a new avenue for the preparation of highly selective sensing devices.

Atomic layer deposition (ALD) is a technology offering the possibility to prepare thin films of high quality materials on high aspect ratio substrates with precise thickness control, high uniformity and excellent conformality, a unique capability. Therefore, this route is particularly suited for the structural modification and pore tailoring of synthetic membranes. ALD coatings have been prepared on a wide variety of membrane substrates, from inorganic templated supports to porous polymers. This minireview aims to provide an extensive summary of the advances of ALD applied to membranes. A selected list of studies will be used to illustrate how the ALD route can be implemented to improve the operational performance of different inorganic, organic, hybrid or composite membranes. Furthermore, the challenges and opportunities of the route for this specific membrane application are also discussed. This work comprehensively shows the benefits of ALD and its application in various facets of membranes and membrane associated engineering processes, and will help exploiting the numerous prospects of this emerging and growing field.

Gas sensors are essential for industry and for a wide range of applications. They are for examples applied in public safety, pollution monitoring, and various industrial processes. Among the different gas sensing technologies, semiconducting metal oxide-based gas sensors are the most popular because of their low price, high sensitivity, short response time, high stability and simple operation. In these gas sensors, because gas adsorption has a direct relationship with the surface area of the sensing material, a higher surface area will result in a higher sensing response. Therefore, along with simple synthesis methods, nanowires (NWs) have recently gained special attention for the realization of gas sensors. In this tutorial review, the synthesis of metal oxide NWs, the fabrication of gas sensors and their sensing mechanisms are discussed. Different gas sensors such as single NW, noble metal functionalized NWs, heterojunctions NWs, self-heating NWs, UV-activated NWs and core-shell NWs are presented. This tutorial review aims to provide a broad vision for the researchers and students working in this upcoming field. 2 I. Toxic gases and vaporsGases are intimately linked to life, as most of the living species continuously need to breathe air, which is basically a mixture of oxygen, nitrogen, argon, and other gases. In addition, many gases are used in our industrial era. For example, liquefied petroleum gas (LPG) is widely used in industry, as well as for cooking and heating purposes. 1 Even though LPG is not toxic, it is highly explosive. 2 Also, hydrogen gas is seen as the next "green fuel" and is currently used in fuel cells, although it is highly explosive. 3,4 In addition to explosive gases, the sources of toxic and pollutant gases have been significantly increased in the recent years, and there are many toxic gases in our atmosphere. 5 Toxic gases can cause harm in low levels over long periods of time (chronic exposure) or in higher concentrations over short periods of time (acute exposure). The threshold limit value (TLV) has been defined as the maximum concentration of a gas, which is allowed for repeated exposure without resulting in adverse health effects. 6 For example, the TLV values for CO, NO2 and H2S gases are 50, 3 and 10 ppm, respectively. 6 Based on the WHO (World Health Organization), air pollution is mainly due to toxic gases and caused around seven million premature deaths in 2012. 7 There are many toxic gases in our surrounding atmosphere. For example, carbon monoxide (CO) poisoning results in over 5000 deaths in the USA. 8 In Denmark, from 1995 to 2015, several hundred people passed away due to CO poisoning. 9 Also, in Iran, as a typical developing country, 836 deaths occurred in 2016due to CO poisoning. 10 CO has not any color, odor and taste, 11 and it has 240 times greater affinity for hemoglobin in comparison with oxygen. It forms carboxyhemoglobin, which leads to a reduced oxygen delivery to tissues and can cause tissue hypoxia. 8,12 Also, CO easily binds to cytochrome oxidase and leads to...

In this work, we report the design and the fine-tuning of boron nitride single nanopore and nanoporous membranes by atomic layer deposition (ALD). First, we developed an ALD process based on the use of BBr and NH as precursors in order to synthesize BN thin films. The deposited films were characterized in terms of thickness, composition, and microstructure. Next, we used the newly developed process to grow BN films on anodic aluminum oxide nanoporous templates, demonstrating the conformality benefit of BN prepared by ALD, and its scalability for the manufacturing of membranes. For the first time, the ALD process was then used to tune the diameter of fabricated single transmembrane nanopores by adjusting the BN thickness and to enable studies of the fundamental aspects of ionic transport on a single nanopore. At pH = 7, we estimated a surface charge density of 0.16 C·m without slip and 0.07 C·m considering a reasonable slip length of 3 nm. Molecular dynamics simulations performed with experimental conditions confirmed the conductivities and the sign of surface charges measured. The high ion transport results obtained and the ability to fine-tune nanoporous membranes by such a scalable method pave the way toward applications such as ionic separation, energy harvesting, and ultrafiltration devices.

High selectivity and sensitivity were measured using a novel type of sensor device, based on ZnO nanowires (NWs) coated with a thin layer of boron nitride (BN) decorated with palladium nanoparticles (NPs).

Atomic layer deposition (ALD) is a thin film deposition technique currently used in various nanofabrication processes for microelectronic applications. The ability to coat high aspect ratio structures with a wide range of materials, the excellent conformality, and the exquisite thickness control have made ALD an essential tool for the fabrication of many devices, including biosensors. This mini-review aims to provide a summary of the different ways ALD has been used to prepare biosensor devices. The materials that have been deposited by ALD, the use of the ALD layers prepared and the different types of biosensors fabricated are presented. A selected list of studies will be used to illustrate how the ALD route can be implemented to improve the operational performance of biosensors. This work comprehensively shows the benefits of ALD and its application in various facets of biosensing and will help in exploiting the numerous prospects of this emerging and growing field.