Atomic Layer Deposition of Pt Nanoparticles within the Cages of MIL-101: A Mild and Recyclable Hydrogenation Catalyst

Defined metal atom aggregates precisely incorporated into metal-organic frameworks

Nanosized metal aggregates (MAs), including metal nanoparticles (NPs) and nanoclusters (NCs), are often the active species in numerous applications. In order to maintain the active form of MAs in "use", they need to be anchored and stabilised, preventing agglomeration. In this context, metal-organic frameworks (MOFs), which exhibit a unique combination of properties, are of particular interest as a tunable and porous matrix to host MAs. A high degree of control in the synthesis towards atom-efficient and application-oriented MA@MOF composites is required to derive specific structure-property relationships and in turn to enable design of functions on the molecular level. Due to the versatility of MA@MOF (derived) materials, their applications are not limited to the obvious field of catalysis, but increasingly include 'out of the box' applications, for example medical diagnostics and theranostics, as well as specialised (bio-)sensoring techniques. This review focuses on recent advances in the controlled synthesis of MA@MOF materials en route to atom-precise MAs. The main synthetic strategies, namely 'ship-in-bottle', 'bottle-around-ship', and approaches to achieve novel hierarchical MA@MOF structures are highlighted and discussed while identifying their potential as well as their limitations. Hereby, an overview of standard characterisation methods that enable a systematic analysis procedure and state-of-art techniques that localise MA within MOF cavities are provided. While the perspectives of MA@MOF materials in general have been reviewed various times in the recent past, few atom-precise MAs inside MOFs have been reported so far, opening opportunities for future investigation.

Composition and Structure Progress of the Catalytic Interface Layer for Bipolar Membrane

Bipolar membranes, a new type of composite ion exchange membrane, contain an anion exchange layer, a cation exchange layer and an interface layer. The interface layer or junction is the connection between the anion and cation exchange layers. Water is dissociated into protons and hydroxide ions at the junction, which provides solutions to many challenges in the chemical, environmental and energy fields. By combining bipolar membranes with electrodialysis technology, acids and bases could be produced with low cost and high efficiency. The interface layer or junction of bipolar membranes (BPMs) is the connection between the anion and cation exchange layers, which the membrane and interface layer modification are vital for improving the performance of BPMs. This paper reviews the effect of modification of a bipolar membrane interface layer on water dissociation efficiency and voltage across the membrane, which divides into three aspects: organic materials, inorganic materials and newly designed materials with multiple components. The structure of the interface layer is also introduced on the performance of bipolar membranes. In addition, the remainder of this review discusses the challenges and opportunities for the development of more efficient, sustainable and practical bipolar membranes.

Recent Progress of Atomic Layer Technology in Spintronics: Mechanism, Materials and Prospects

The atomic layer technique is generating a lot of excitement and study due to its profound physics and enormous potential in device fabrication. This article reviews current developments in atomic layer technology for spintronics, including atomic layer deposition (ALD) and atomic layer etching (ALE). To begin, we introduce the main atomic layer deposition techniques. Then, in a brief review, we discuss ALE technology for insulators, semiconductors, metals, and newly created two-dimensional van der Waals materials. Additionally, we compare the critical factors learned from ALD to constructing ALE technology. Finally, we discuss the future prospects and challenges of atomic layer technology in the field of spinronics.

The Applications of Ultra-Thin Nanofilm for Aerospace Advanced Manufacturing Technology

With the development of industrial civilization, advanced manufacturing technology has attracted widespread concern, including in the aerospace industry. In this paper, we report the applications of ultra-thin atomic layer deposition nanofilm in the advanced aerospace manufacturing industry, including aluminum anti-oxidation and secondary electron suppression, which are critical in high-power and miniaturization development. The compact and uniform aluminum oxide film, which is formed by thermal atomic layer deposition (ALD), can prevent the deep surface oxidation of aluminum during storage, avoiding the waste of material and energy in repetitive production. The total secondary electron yield of the C/TiN component nanofilm, deposited through plasma-enhanced atomic layer deposition, decreases 25% compared with an uncoated surface. The suppression of secondary electron emission is of great importance in solving the multipactor for high-power microwave components in space. Moreover, the controllable, ultra-thin uniform composite nanofilm can be deposited directly on the complex surface of devices without any transfer process, which is critical for many different applications. The ALD nanofilm shows potential for promoting system performance and resource consumption in the advanced aerospace manufacturing industry.

Ru Catalyst Encapsulated into the Pores of MIL-101 MOF: Direct Visualization by TEM

Ru catalyst nanoparticles were encapsulated into the pores of a Cr-based metal-organic framework (MOF)-MIL-101. The obtained material, as well as the non-loaded MIL-101, were investigated down to the atomic scale by annular dark-field scanning transmission electron microscopy using low dose conditions and fast image acquisition. The results directly show that the used wet chemistry loading approach is well-fitted for the accurate embedding of the individual catalyst nanoparticles into the cages of the MIL-101. The MIL-101 host material remains crystalline after the loading procedure, and the encapsulated Ru nanoparticles have a metallic nature. Annular dark field scanning transmission electron microscopy, combined with EDX mapping, is a perfect tool to directly characterize both the embedded nanoparticles and the loaded nanoscale MOFs. The resulting nanostructure of the material is promising because the Ru nanoparticles hosted in the MIL-101 pores are prevented from agglomeration-the stability and lifetime of the catalyst could be improved.

Surface modification and functionalization of powder materials by atomic layer deposition: a review

Powder materials are a class of industrial materials with many important applications. In some circumstances, surface modification and functionalization of these materials are essential for achieving or enhancing their expected performances. However, effective and precise surface modification of powder materials remains a challenge due to a series of problems such as high surface area, diffusion limitation, and particle agglomeration. Atomic layer deposition (ALD) is a cutting-edge thin film coating technology traditionally used in the semiconductor industry. ALD enables layer by layer thin film growth by alternating saturated surface reactions between the gaseous precursors and the substrate. The self-limiting nature of ALD surface reaction offers angstrom level thickness control as well as exceptional film conformality on complex structures. With these advantages, ALD has become a powerful tool to effectively fabricate powder materials for applications in many areas other than microelectronics. This review focuses on the unique capability of ALD in surface engineering of powder materials, including recent advances in the design of ALD reactors for powder fabrication, and applications of ALD in areas such as stabilization of particles, catalysts, energetic materials, batteries, wave absorbing materials and medicine. We intend to show the versatility and efficacy of ALD in fabricating various kinds of powder materials, and help the readers gain insights into the principles, methods, and unique effects of powder fabrication by ALD.

Bulk and local structures of metal-organic frameworks unravelled by high-resolution electron microscopy

The periodic bulk structures of metal-organic frameworks (MOFs) can be solved by diffraction-based techniques; however, their non-periodic local structures-such as crystal surfaces, grain boundaries, defects, and guest molecules-have long been elusive due to a lack of suitable characterization tools. Recent advances in (scanning) transmission electron microscopy ((S)TEM) has made it possible to probe the local structures of MOFs at atomic resolution. In this article, we discuss why high-resolution (S)TEM of MOFs is challenging and how the new low-dose techniques overcome this challenge, and we review various MOF structural features observed by (S)TEM and important insights gained from these observations. Our discussions focus on real-space imaging, excluding other TEM-related characterization techniques (e.g. electron diffraction and spectroscopy).

Combining nanoparticles grown by ALD and MOFs for gas separation and catalysis applications

Supported metallic nanoparticles (NPs) are essential for many important chemical processes. In order to implement precisely tuned NPs in miniaturized devices by compatible processes, novel nanoengineering routes must be explored. Atomic layer deposition (ALD), a scalable vapor phase technology typically used for the deposition of thin films, represents a promising new route for the synthesis of supported metallic NPs. Metal–organic frameworks (MOFs) are a new exciting class of crystalline porous materials that have attracted much attention in the recent years. Since the size of their pores can be precisely adjusted, these nanomaterials permit highly selective separation and catalytic processes. The combination of NPs and MOF is an emerging area opening numbers of applications, which still faces considerable challenges, and new routes need to be explored for the synthesis of these NPs/MOF nanocomposites. The aim of this paper is double: first, it aims to briefly present the ALD route and its use for the synthesis of metallic NPs. Second, the combination of ALD-grown NPs and MOFs has been explored for the synthesis of Pd NPs/MOF ZIF-8, and several selected examples were ALD-grown NPs and MOFs have been combined and applied gas separation and catalysis will be presented.

Creation of gallium acid and platinum metal sites in bifunctional zeolite hydroisomerization and hydrocracking catalysts by atomic layer deposition

Active sites in bifunctional zeolite catalysts were engineered using atomic layer deposition (ALD). Gallium acid and platinum metal sites were introduced to zeolites via ALD and investigated for a hydroconversion reaction.

Plasma-assisted atomic layer deposition of conformal Pt films in high aspect ratio trenches

To date, conventional thermal atomic layer deposition (ALD) has been the method of choice to deposit high-quality Pt thin films grown typically from (MeCp)PtMe₃ vapor and O₂ gas at 300 °C. Plasma-assisted ALD of Pt using O₂ plasma can offer several advantages over thermal ALD, such as faster nucleation and deposition at lower temperatures. In this work, it is demonstrated that plasma-assisted ALD at 300 °C also allows for the deposition of highly conformal Pt films in trenches with high aspect ratio ranging from 3 to 34. Scanning electron microscopy inspection revealed that the conformality of the deposited Pt films was 100% in trenches with aspect ratio (AR) up to 34. These results were corroborated by high-precision layer thickness measurements by transmission electron microscopy for trenches with an aspect ratio of 22. The role of the surface recombination of O-radicals and the contribution of thermal ALD reactions is discussed.

Intratumoral Visualization of Oxaliplatin within a Liposomal Formulation Using X-ray Fluorescence Spectrometry

Microsynchrotron radiation X-ray fluorescence spectrometry (μ-SR-XRF) is an X-ray procedure that utilizes synchrotron radiation as an excitation source. μ-SR-XRF is a rapid, nondestructive technique that allows mapping and quantification of metals and biologically important elements in cell or tissue samples. Generally, the intratumor distribution of nanocarrier-based therapeutics is assessed by tracing the distribution of a labeled nanocarrier within tumor tissue, rather than by tracing the encapsulated drug. Instead of targeting the delivery vehicle, we employed μ-SR-XRF to visualize the intratumoral microdistribution of oxaliplatin (l-OHP) encapsulated within PEGylated liposomes. Tumor-bearing mice were intravenously injected with either l-OHP-containing PEGylated liposomes (l-OHP liposomes) or free l-OHP. The intratumor distribution of l-OHP within tumor sections was determined by detecting the fluorescence of platinum atoms, which are the main elemental components of l-OHP. The l-OHP in the liposomal formulation was localized near the tumor vessels and accumulated in tumors at concentrations greater than those seen with the free form, which is consistent with the results of our previous study that focused on fluorescent labeling of PEGylated liposomes. In addition, repeated administration of l-OHP liposomes substantially enhanced the tumor accumulation and/or intratumor distribution of a subsequent dose of l-OHP liposomes, presumably via improvements in tumor vascular permeability, which is also consistent with our previous results. In conclusion, μ-SR-XRF imaging efficiently and directly traced the intratumor distribution of the active pharmaceutical ingredient l-OHP encapsulated in liposomes within tumor tissue. μ-SR-XRF imaging could be a powerful means for estimating tissue distribution and even predicting the pharmacological effect of nanocarrier-based anticancer metal compounds.

Independent tuning of size and coverage of supported Pt nanoparticles using atomic layer deposition

Synthetic methods that allow for the controlled design of well-defined Pt nanoparticles are highly desirable for fundamental catalysis research. In this work, we propose a strategy that allows precise and independent control of the Pt particle size and coverage. Our approach exploits the versatility of the atomic layer deposition (ALD) technique by combining two ALD processes for Pt using different reactants. The particle areal density is controlled by tailoring the number of ALD cycles using trimethyl(methylcyclopentadienyl)platinum and oxygen, while subsequent growth using the same Pt precursor in combination with nitrogen plasma allows for tuning of the particle size at the atomic level. The excellent control over the particle morphology is clearly demonstrated by means of in situ and ex situ X-ray fluorescence and grazing incidence small angle X-ray scattering experiments, providing information about the Pt loading, average particle dimensions, and mean center-to-center particle distance.

The performance of supported nanoparticle catalysts is closely related to their size, shape and interparticle distance. Here, the authors introduce an atomic layer deposition-based strategy to independently tune the size and coverage of platinum nanoparticles with atomic-level precision.

Design and Electrochemical Study of Platinum-Based Nanomaterials for Sensitive Detection of Nitric Oxide in Biomedical Applications

The extensive physiological and regulatory roles of nitric oxide (NO) have spurred the development of NO sensors, which are of critical importance in neuroscience and various medical applications. The development of electrochemical NO sensors is of significant importance, and has garnered a tremendous amount of attention due to their high sensitivity and selectivity, rapid response, low cost, miniaturization, and the possibility of real-time monitoring. Nanostructured platinum (Pt)-based materials have attracted considerable interest regarding their use in the design of electrochemical sensors for the detection of NO, due to their unique properties and the potential for new and innovative applications. This review focuses primarily on advances and insights into the utilization of nanostructured Pt-based electrode materials, such as nanoporous Pt, Pt and PtAu nanoparticles, PtAu nanoparticle/reduced graphene oxide (rGO), and PtW nanoparticle/rGO-ionic liquid (IL) nanocomposites, for the detection of NO. The design, fabrication, characterization, and integration of electrochemical NO sensing performance, selectivity, and durability are addressed. The attractive electrochemical properties of Pt-based nanomaterials have great potential for increasing the competitiveness of these new sensors and open up new opportunities in the creation of novel NO-sensing technologies for biological and medical applications.

Nanoparticles for Catalysis

Nanoscience emerged in the last decades of the 20th century with the general aim to determine those properties that appear when small particles of nanometric dimensions are prepared and stabilized.[...].