Atomic Layer Deposition Route To Tailor Nanoalloys of Noble and Non-noble Metals

Bimetallic nanozyme-bioenzyme hybrid material-mediated ultrasensitive and automatic immunoassay for the detection of aflatoxin B1 in food

Aflatoxin B1 (AFB1) is one of the most prevalent and dangerous biotoxin in crops and feedstuff, which poses a great threat to human health and also cause significant financial losses. Therefore, there is an urgent need to develop an effective method for AFB1 detection. In this work, we developed an automatic reaction equipment and nanozyme-enhanced immunosorbent assay (Auto-NEISA) for sensitive and accurate detection of AFB1 by combining the highly effective signal probes with a self-designed automated immunoreactive equipment. Wherein, polystyrene (PS) nanoparticles were used as signal carriers for loading a massive in situ-synthesized platinum and palladium bimetallic nanozyme, which could enrich horseradish peroxidase-labeled goat anti-mouse antibody (HRP-Ab2) on the nanozyme surface to form a bimetallic nanozyme-bioenzyme hybrid material for multiple signal amplification. The entire reaction could be automatically completed by the self-developed immunoreactive equipment. The Auto-NEISA method realized the sensitive detection of AFB1 with a wide linear detection range of 10-104 pg/mL, at a low limit of detection (LOD) of 5.52 pg/mL. The LOD was 65-fold lower than that of the enzyme-linked immunosorbent assay (ELISA). Additionally, Auto-NEISA was successfully applied to detect AFB1 in real food samples, demonstrating that it has considerable potential for detecting food contaminants with high accuracy and efficiency.

Emerging single atom catalysts in gas sensors

Single atom catalysts (SACs) offer unprecedented opportunities for high-efficiency reactions taking place in many important fields of catalytic processes, electrochemistry, and photoreactions. Due to their maximized atomic utilization and unique electronic and chemical properties, SACs can provide high activity and excellent selectivity for gas adsorption and electron transport, leveraging SACs that enhance the detection sensitivity and selectivity to target gases. In the past few years, SACs including both noble (Pt, Pd, Au, etc.) and non-noble (Mn, Ni, Zn etc.) metals have been demonstrated to be very useful in optimizing sensing performances. However, a comprehensive review on this topic is still missing. Herein, we summarize the synthesis technologies of SACs that are applicable to gas sensors. The electronic and chemical interactions between SACs and host sensing materials, which are crucial to sensor functions, are discussed. Then, we highlight the application progress of various SACs in gas sensors. Prospects in the creation of new sensing materials with emerging SACs and versatile supports are also present. Finally, the challenges and prospects of SACs in the future development of sensors are analyzed.

Aligning time-resolved kinetics (TAP) and surface spectroscopy (AP-XPS) for a more comprehensive understanding of ALD-derived 2D and 3D model catalysts

Spectro-kinetic characterization of complex catalytic materials, i.e. relating the observed reaction kinetics to spectroscopic descriptors of the catalyst state, presents a fundamental challenge with a potentially significant impact on various...

Controlled synthesis of Fe-Pt nanoalloys using atomic layer deposition

We report the phase and size-controlled synthesis of Fe-Pt nanoalloys, prepared via a two-step synthesis procedure. The first step is the deposition of bilayers consisting of iron oxide and Pt films of desired thicknesses using atomic layer deposition, followed by a temperature-programmed reduction treatment of the film under H₂/N₂ atmosphere. This method enables the phase pure synthesis of all three Fe-Pt alloy phases, namely Fe₃Pt, FePt, and FePt₃, as revealed by in situ x-ray diffraction and x-ray fluorescence measurements. It is also demonstrated that by changing the total thickness of the bilayers while keeping the Pt/(Pt + Fe) atomic ratio constant, the size of the resulting bimetallic nanoparticles can be tuned, as confirmed by scanning electron microscopic measurements.

Recent progress in heterogeneous metal and metal oxide catalysts for direct dehydrogenation of ethane and propane

Metal and metal oxide catalysts for non-oxidative ethane/propane dehydrogenation are outlined with respect to catalyst synthesis, structure–property relationship and catalytic mechanism.

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition

Supported nanoparticles are commonly applied in heterogeneous catalysis. The catalytic performance of these solid catalysts is, for a given support, dependent on the nanoparticle size, shape, and composition, thus necessitating synthesis techniques that allow for preparing these materials with fine control over those properties. Such control can be exploited to deconvolute their effects on the catalyst's performance, which is the basis for knowledge-driven catalyst design. In this regard, bottom-up synthesis procedures based on colloidal chemistry or atomic layer deposition (ALD) have proven successful in achieving the desired level of control for a variety of fundamental studies. This review aims to give an account of recent progress made in the two aforementioned synthesis techniques for the application of controlled catalytic materials in gas-phase catalysis. For each technique, the focus goes to mono- and bimetallic materials, as well as to recent efforts in enhancing their performance by embedding colloidal templates in porous oxide phases or by the deposition of oxide overlayers via ALD. As a recent extension to the latter, the concept of area-selective ALD for advanced atomic-scale catalyst design is discussed.

Intermetallic compounds in catalysis - a versatile class of materials meets interesting challenges

The large and vivid field of intermetallic compounds in catalysis is reviewed to identify necessities, strategies and new developments making use of the advantageous catalytic properties of intermetallic compounds. Since recent reviews summarizing contributions in heterogeneous catalysis as well as electrocatalysis are available, this contribution is not aiming at a comprehensive literature review. To introduce the field, first the interesting nature of intermetallic compounds is elaborated - including possibilities as well as requirements to address catalytic questions. Subsequently, this review focuses on exciting developments and example success stories of intermetallic compounds in catalysis. Since many of these are based on recent advances in synthesis, a short overview of synthesis and characterisation is included. Thus, this contribution aims to be an introduction to the newcomer as well as being helpful to the experienced researcher by summarising the different approaches. Selected examples from literature are chosen to illustrate the versatility of intermetallic compounds in heterogeneous catalysis where the emphasis is on developments since the last comprehensive review in the field.

Nanoscale Au-ZnO Heterostructure Developed by Atomic Layer Deposition Towards Amperometric H2O2 Detection

Nanoscale Au-ZnO heterostructures were fabricated on 4-in. SiO2/Si wafers by the atomic layer deposition (ALD) technique. Developed Au-ZnO heterostructures after post-deposition annealing at 250 °C were tested for amperometric hydrogen peroxide (H2O2) detection. The surface morphology and nanostructure of Au-ZnO heterostructures were examined by field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), etc. Additionally, the electrochemical behavior of Au-ZnO heterostructures towards H2O2 sensing under various conditions is assessed by chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that ALD-fabricated Au-ZnO heterostructures exhibited one of the highest sensitivities of 0.53 μA μM-1 cm-2, the widest linear H2O2 detection range of 1.0 μM-120 mM, a low limit of detection (LOD) of 0.78 μM, excellent selectivity under the normal operation conditions, and great long-term stability. Utilization of the ALD deposition method opens up a unique opportunity for the improvement of the various capabilities of the devices based on Au-ZnO heterostructures for amperometric detection of different chemicals.

Surface mobility and impact of precursor dosing during atomic layer deposition of platinum:in situmonitoring of nucleation and island growth

The nucleation rate and diffusion-driven growth of Pt nanoparticles are revealed within situX-ray fluorescence and scattering measurements during ALD: the particle morphology at a certain Pt loading is similar for high and low precursor exposures.

Co–Pt bimetallic nanoparticles with tunable magnetic and electrocatalytic properties prepared by atomic layer deposition

Magnetism tuning and hydrogen evolution reaction activity optimization can be achieved for Co–Pt BMNPs prepared by ALD.

Origin of synergistic effects in bicomponent cobalt oxide-platinum catalysts for selective hydrogenation reaction

The synergistic nature of bicomponent catalysts remains a challenging issue, due to the difficulty in constructing well-defined catalytic systems. Here we study the origin of synergistic effects in CoO_x-Pt catalysts for selective hydrogenation by designing a series of closely contacted CoO_xPt/TiO₂ and spatially separated CoO_x/TiO₂/Pt catalysts by atomic layer deposition (ALD). For CoO_x/TiO₂/Pt, CoO_x and platinum are separated by the walls of titania nanotubes, and the CoO_x-Pt intimacy can be precisely tuned. Like CoO_xPt/TiO₂, the CoO_x/TiO₂/Pt shows higher selectivity to cinnamyl alcohol than monometallic TiO₂/Pt, indicating that the CoO_x-Pt nanoscale intimacy almost has no influence on the selectivity. The enhanced selectivity is ascribed to the increased oxygen vacancy resulting from the promoted hydrogen spillover. Moreover, platinum-oxygen vacancy interfacial sites are identified as the active sites by selectively covering CoO_x or platinum by ALD. Our study provides a guide for the understanding of synergistic nature in bicomponent and bifunctional catalysts.

Formation and Functioning of Bimetallic Nanocatalysts: The Power of X-ray Probes

Bimetallic nanocatalysts are key enablers of current chemical technologies, including car exhaust converters and fuel cells, and play a crucial role in industry to promote a wide range of chemical reactions. However, owing to significant characterization challenges, insights in the dynamic phenomena that shape and change the working state of the catalyst await further refinement. Herein, we discuss the atomic-scale processes leading to mono- and bimetallic nanoparticle formation and highlight the dynamics and kinetics of lifetime changes in bimetallic catalysts with showcase examples for Pt-based systems. We discuss how in situ and operando X-ray spectroscopy, scattering, and diffraction can be used as a complementary toolbox to interrogate the working principles of today's and tomorrow's bimetallic nanocatalysts.

Wafer-Scale Fabrication of Sub-10 nm TiO2-Ga2O3 n-p Heterojunctions with Efficient Photocatalytic Activity by Atomic Layer Deposition

Wafer-scale, conformal, two-dimensional (2D) TiO₂-Ga₂O₃ n-p heterostructures with a thickness of less than 10 nm were fabricated on the Si/SiO₂ substrates by the atomic layer deposition (ALD) technique for the first time with subsequent post-deposition annealing at a temperature of 250 °C. The best deposition parameters were established. The structure and morphology of 2D TiO₂-Ga₂O₃ n-p heterostructures were characterized by the scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), etc. 2D TiO₂-Ga₂O₃ n-p heterostructures demonstrated efficient photocatalytic activity towards methyl orange (MO) degradation at the UV light (λ = 254 nm) irradiation. The improvement of TiO₂-Ga₂O₃ n-p heterostructure capabilities is due to the development of the defects on Ga₂O₃-TiO₂ interface, which were able to trap electrons faster.

Kinetics, energetics, and size dependence of the transformation from Pt to ordered PtSn intermetallic nanoparticles

The outstanding catalytic activity and chemical selectivity of intermetallic compounds make them excellent candidates for heterogeneous catalysis. However, the kinetics of their formation at the nanoscale is poorly understood or characterized, and precise control of their size, shape and composition during synthesis remains challenging. Here, using well-defined Pt nanoparticles (5 nm and 14 nm) encapsulated in mesoporous silica, we study the transformation kinetics from monometallic Pt to intermetallic PtSn at different temperatures by a series of time-evolution X-ray diffraction studies. Observations indicate an initial transformation stage mediated by Pt surface-controlled intermixing kinetics, followed by a second stage with distinct transformation kinetics corresponding to a Ginstling-Brounstein (G-B) type bulk diffusion mode. Moreover, the activation barrier for both surface intermixing and diffusion stages is obtained through the development of appropriate kinetic models for the analysis of experimental data. Our density-functional-theory (DFT) calculations provide further insights into the atomistic-level processes and associated energetics underlying surface-controlled intermixing.

Kinetics of Lifetime Changes in Bimetallic Nanocatalysts Revealed by Quick X-ray Absorption Spectroscopy

Alloyed metal nanocatalysts are of environmental and economic importance in a plethora of chemical technologies. During the catalyst lifetime, supported alloy nanoparticles undergo dynamic changes which are well-recognized but still poorly understood. High-temperature O₂ -H₂ redox cycling was applied to mimic the lifetime changes in model Pt₁₃ In₉ nanocatalysts, while monitoring the induced changes by in situ quick X-ray absorption spectroscopy with one-second resolution. The different reaction steps involved in repeated Pt₁₃ In₉ segregation-alloying are identified and kinetically characterized at the single-cycle level. Over longer time scales, sintering phenomena are substantiated and the intraparticle structure is revealed throughout the catalyst lifetime. The in situ time-resolved observation of the dynamic habits of alloyed nanoparticles and their kinetic description can impact catalysis and other fields involving (bi)metallic nanoalloys.

Atomic layer oxidation on graphene sheets for tuning their oxidation levels, electrical conductivities, and band gaps

Graphene sheets that can exhibit electrical conducting and semiconducting properties are highly desirable and have potential applications in fiber communications, photodetectors, solar cells, semiconductors, and broadband modulators. However, there is currently no efficient method that is able to tune the band gap of graphene sheets. This work adopts an efficient atomic layer oxidation (ALO) technique to cyclically increase the oxidation level of graphene sheets, thus, tuning their electrical conductance, band-gap structure, and photoluminescence (PL) response. The O/C atomic ratio as an increasing function of the ALO cycle number reflects two linear regions: 0.23% per cm2 per cycle (0-15 cycles) and 0.054% per cm2 per cycle (15-100 cycles). The excellent correlation coefficients reveal that the ALO process follows a self-limiting route to step-by-step oxidize graphene layers. The interlayer distance of ALO-graphene sheets shows an obvious increase after the ALO treatment, proved by X-ray diffraction. As analyzed by X-ray photon spectroscopy, the hydroxyl or epoxy group acts as a major contributor to the interlayer spacing distance and oxidation extent in the initial ALO stage, as compared to carbonyl and carboxyl groups. The ALO mechanism, based on Langmuir-Hinshelwood and Eley-Rideal models, is proposed to clarify the formation of oxygen functionalities and structural transformation from pristine graphene sheets to oxidized ones during the ALO cycle. With a tunable oxidation level, the electrical resistivity, semiconductor character, and PL response of ALO-graphene samples can be systematically controlled for desired applications. The ALO approach is capable of offering a straightforward route to tune the oxidation level of graphene sheets or other carbons.

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.

Systematic Identification of Promoters for Methane Oxidation Catalysts Using Size- and Composition-Controlled Pd-Based Bimetallic Nanocrystals

Promoters enhance the performance of catalytic active phases by increasing rates, stability, and/or selectivity. The process of identifying promoters is in most cases empirical and relies on testing a broad range of catalysts prepared with the random deposition of active and promoter phases, typically with no fine control over their localization. This issue is particularly relevant in supported bimetallic systems, where two metals are codeposited onto high-surface area materials. We here report the use of colloidal bimetallic nanocrystals to produce catalysts where the active and promoter phases are colocalized to a fine extent. This strategy enables a systematic approach to study the promotional effects of several transition metals on palladium catalysts for methane oxidation. In order to achieve these goals, we demonstrate a single synthetic protocol to obtain uniform palladium-based bimetallic nanocrystals (PdM, M = V, Mn, Fe, Co, Ni, Zn, Sn, and potentially extendable to other metal combinations) with a wide variety of compositions and sizes based on high-temperature thermal decomposition of readily available precursors. Once the nanocrystals are supported onto oxide materials, thermal treatments in air cause segregation of the base metal oxide phase in close proximity to the Pd phase. We demonstrate that some metals (Fe, Co, and Sn) inhibit the sintering of the active Pd metal phase, while others (Ni and Zn) increase its intrinsic activity compared to a monometallic Pd catalyst. This procedure can be generalized to systematically investigate the promotional effects of metal and metal oxide phases for a variety of active metal-promoter combinations and catalytic reactions.

Size- and composition-controlled Pt–Sn bimetallic nanoparticles prepared by atomic layer deposition

An atomic layer deposition (ALD) based recipe is demonstrated for the fully-tailored synthesis of Pt–Sn bimetallic nanoparticles.

Formation and stability of an active PdZn nanoparticle catalyst on a hydrotalcite-based support for ethanol dehydrogenation

A subsequent hydrogen–air treatment prior to reaction is important for a highly active innovative nanoparticle PdZn catalyst for ethanol dehydrogenation.