Plasma Polymerization of Precipitated Silica for Tire Application.

Pre-treated silica with a plasma-deposited (PD) layer of polymerized precursors was tested concerning its compatibility with Natural Rubber (NR) and its influence on the processing of silica-silane compounds. The modification was performed in a tailor-made plasma reactor. The degree of deposition of the plasma-coated samples was analyzed by ThermoGravimetric Analysis (TGA). In addition, Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM) were performed to identify the morphology of the deposited plasma polymer layer on the silica surface. PD silica samples were incorporated into a NR/silica model compound. NR compounds containing untreated silica and in-situ silane-modified silica were taken as references. The silane coupling agent used for the reference compounds was bis-(3-triethoxysilyl-propyl)disulfide (TESPD), and reference compounds with untreated silica having the full amount and 50% of silane were prepared. In addition, 50% of the silane was added to the PD silica-filled compounds in order to verify the hypothesis that additional silane coupling agents can react with silanol groups stemming from the breakdown of the silica clusters during mixing. The acetylene PD silica with 50% reduced silane-filled compounds presented comparable properties to the in-situ silane-modified reference compound containing 100% TESPD. This facilitates processing as lower amounts of volatile organic compounds, such as ethanol, are generated compared to the conventional silica-silane filler systems.

Techno-economic Assessment of CO2 Electrolysis: How Interdependencies between Model Variables Propagate Across Different Modeling Scales.

The production of base chemicals by electrochemical conversion of captured CO2 has the potential to close the carbon cycle, thereby contributing to a future energy transition. With the feasibility of low-temperature electrochemical CO2 conversion demonstrated at lab scale, research is shifting toward optimizing electrolyser design and operation for industrial applications, with target values based on techno-economic analysis. However, current techno-economic analyses often neglect experimentally reported interdependencies of key performance variables such as the current density, the faradaic efficiency, and the conversion. Aiming to understand the impact of these interdependencies on the economic outlook, we develop a model capturing mass transfer effects over the channel length for an alkaline, membrane electrolyser. Coupling the channel scale with the higher level process scale and embedding this multiscale model in an economic framework allows us to analyze the economic trade-off between the performance variables. Our analysis shows that the derived target values for the performance variables strongly depend on the interdependencies described in the channel scale model. Our analysis also suggests that economically optimal current densities can be as low as half of the previously reported benchmarks. More generally, our work highlights the need to move toward multiscale models, especially in the field of CO2 electrolysis, to effectively elucidate current bottlenecks in the quest toward economically compelling system designs.

A Quantitative Analysis of Electrochemical CO2 Reduction on Copper in Organic Amide and Nitrile-Based Electrolytes.

Aqueous electrolytes used in CO2 electroreduction typically have a CO2 solubility of around 34 mM under ambient conditions, contributing to mass transfer limitations in the system. Non-aqueous electrolytes exhibit higher CO2 solubility (by 5-8-fold) and also provide possibilities to suppress the undesired hydrogen evolution reaction (HER). On the other hand, a proton donor is needed to produce many of the products commonly obtained with aqueous electrolytes. This work investigates the electrochemical CO2 reduction performance of copper in non-aqueous electrolytes based on dimethylformamide (DMF), n-methyl-2-pyrrolidone (NMP), and acetonitrile (ACN). The main objective is to analyze whether non-aqueous electrolytes are a viable alternative to aqueous electrolytes for hydrocarbon production. Additionally, the effects of aqueous/non-aqueous anolytes, membrane, and the selection of a potential window on the electrochemical CO2 reduction performance are addressed in this study. Experiments with pure DMF and NMP mainly produced oxalate with a faradaic efficiency (FE) reaching >80%; however, pure ACN mainly produced hydrogen and formate due to the presence of more residual water in the system. Addition of 5% (v/v) water to the non-aqueous electrolytes resulted in increased HER and formate production with negligible hydrocarbon production. Hence, we conclude that aqueous electrolytes remain a better choice for the production of hydrocarbons and alcohols on a copper electrode, while organic electrolytes based on DMF and NMP can be used to obtain a high selectivity toward oxalate and formate.

Molecular Layer Deposition of Polyurea on Silica Nanoparticles and Its Application in Dielectric Nanocomposites.

Polymer nanocomposites (NCs) offer outstanding potential for dielectric applications including insulation materials. The large interfacial area introduced by the nanoscale fillers plays a major role in improving the dielectric properties of NCs. Therefore, an effort to tailor the properties of these interfaces can lead to substantial improvement of the material's macroscopic dielectric response. Grafting electrically active functional groups to the surface of nanoparticles (NPs) in a controlled manner can yield reproducible alterations in charge trapping and transport as well as space charge phenomena in nanodielectrics. In the present study, fumed silica NPs are surface modified with polyurea from phenyl diisocyanate (PDIC) and ethylenediamine (ED) via molecular layer deposition (MLD) in a fluidized bed. The modified NPs are then incorporated into a polymer blend based on polypropylene (PP)/ethylene-octene-copolymer (EOC), and their morphological and dielectric properties are investigated. We demonstrate the alterations in the electronic structure of silica upon depositing urea units using density functional theory (DFT) calculations. Subsequently, the effect of urea functionalization on the dielectric properties of NCs is studied using thermally stimulated depolarization current (TSDC) and broadband dielectric spectroscopy (BDS) methods. The DFT calculations reveal the contribution of both shallow and deep traps upon deposition of urea units onto the NPs. It could be concluded that the deposition of polyurea on NPs results in a bi-modal distribution of trap depths that are related to each monomer in the urea units and can lead to a reduction of space charge formation at filler-polymer interfaces. MLD offers a promising tool for tailoring the interfacial interactions in dielectric NCs.

Zooplankton community turnover in response to a novel TiO2-coated nano-formulation of carbendazim and its constituents.

Novel nanomaterial-based pesticide formulations are increasingly perceived as promising aids in the transition to more efficient agricultural production systems. The current understanding of potential unintended (eco)toxicological impacts of nano-formulated pesticides is scarce, in particular with regard to (non-target) aquatic organisms and ecosystems. The present study reports the results of a long-term freshwater mesocosm experiment which assessed responses of individual zooplankton taxa and communities to a novel TiO2-coated nano-formulation of the fungicide carbendazim. Population- and community trends were assessed and compared in response to the nano-formulation and its constituents applied individually (i.e. nano-sized TiO2, carbendazim) and in combination (i.e. nano-sized TiO2 & carbendazim). Minimal differences were observed between effects induced by the nano-formulation and its active ingredient (i.e. carbendazim) when applied at equivalent nominal test concentrations (4 µg L-1). Nano-sized TiO2 was found to affect zooplankton community trends when applied separately at environmentally realistic concentrations (20 µg L-1 nominal test concentration). However, when nano-sized TiO2 was applied in combination with carbendazim, nano-sized TiO2 was found not to alter effects on community trends induced by carbendazim. The findings of the current study provide an extensive and timely addition to the current body of work available on non-target impacts of nano-formulated pesticides.

Electrochemical Reduction of CO2 in Tubular Flow Cells under Gas-Liquid Taylor Flow.

Electrochemical reduction of CO2 using renewable energy is a promising avenue for sustainable production of bulk chemicals. However, CO2 electrolysis in aqueous systems is severely limited by mass transfer, leading to low reactor performance insufficient for industrial application. This paper shows that structured reactors operated under gas-liquid Taylor flow can overcome these limitations and significantly improve the reactor performance. This is achieved by reducing the boundary layer for mass transfer to the thin liquid film between the CO2 bubbles and the electrode. This work aims to understand the relationship between process conditions, mass transfer, and reactor performance by developing an easy-to-use analytical model. We find that the film thickness and the volume ratio of CO2/electrolyte fed to the reactor significantly affect the current density and the faradaic efficiency. Additionally, we find industrially relevant performance when operating the reactor at an elevated pressure beyond 5 bar. We compare our predictions with numerical simulations based on the unit cell approach, showing good agreement for a large window of operating parameters, illustrating when the easy-to-use predictive expressions for the current density and faradaic efficiency can be applied.

Atmospheric pressure atomic layer deposition to increase organic solvent resistance of PDMS.

We explore three variants of atomic layer deposition (ALD) to deposit titanium oxide on the soft polymer polydimethylsiloxane (PDMS). We show that the organic solvent resistance of PDMS is increased by two orders of magnitude compared to uncoated PDMS for ALD performed at atmospheric pressure, which results in a unique surface-subsurface coating of PDMS.

Dual promotional effect of Cu x O clusters grown with atomic layer deposition on TiO2 for photocatalytic hydrogen production.

The promotional effects on photocatalytic hydrogen production of Cu x O clusters deposited using atomic layer deposition (ALD) on P25 TiO2 are presented. The structural and surface chemistry study of Cu x O/TiO2 samples, along with first principles density functional theory simulations, reveal the strong interaction of ALD deposited Cu x O with TiO2, leading to the stabilization of Cu x O clusters on the surface; it also demonstrated substantial reduction of Ti4+ to Ti3+ on the surface of Cu x O/TiO2 samples after Cu x O ALD. The Cu x O/TiO2 photocatalysts showed remarkable improvement in hydrogen productivity, with 11 times greater hydrogen production for the optimum sample compared to unmodified P25. With the combination of the hydrogen production data and characterization of Cu x O/TiO2 photocatalysts, we inferred that ALD deposited Cu x O clusters have a dual promotional effect: increased charge carrier separation and improved light absorption, consistent with known copper promoted TiO2 photocatalysts and generation of a substantial amount of surface Ti3+ which results in self-doping of TiO2 and improves its photo-activity for hydrogen production. The obtained data were also employed to modify the previously proposed expanding photocatalytic area and overlap model to describe the effect of cocatalyst size and weight loading on photocatalyst activity. Comparing the trend of surface Ti3+ content increase and the photocatalytically promoted area, calculated with our model, suggests that the depletion zone formed around the heterojunction of Cu x O-TiO2 is the main active area for hydrogen production, and the hydrogen productivity of the photocatalyst depends on the surface coverage by this active area. However, the overlap of these areas suppresses the activity of the photocatalyst.

Impacts of a novel controlled-release TiO2-coated (nano-) formulation of carbendazim and its constituents on freshwater macroinvertebrate communities.

Recently, the delivery of pesticides through novel controlled-release (nano-)formulations has been proposed intending to reduce (incidental) pesticide translocation to non-target sites. Concerns have however been raised with regards to the potentially enhanced toxicity of controlled-release (nano-)formulations to non-target organisms and ecosystems. We evaluated long-term (i.e. 1 and 3 month-) impacts of a novel controlled-release pesticide formulation (nano-TiO2-coated carbendazim) and its individual and combined constituents (i.e. nano-sized TiO2 and carbendazim) on naturally established freshwater macroinvertebrate communities. In doing so, we simultaneously assessed impacts of nano-sized TiO2 (nTiO2), currently one of the most used and emitted engineered nanomaterials world-wide. We determined ecological impacts on diversity (i.e. ß-diversity), structure (i.e. rank abundance parameters), and functional composition (i.e. feeding guilds & trophic groups) of communities and underlying effects at lower organizational levels (i.e. population dynamics of individual taxa). Freshwater macroinvertebrate communities were negligibly impacted by nTiO2 at environmentally realistic concentrations. The controlled-release (nano-)formulation significantly delayed release of carbendazim to the water column. Nevertheless, conventional- (i.e. un-coated-) and nTiO2-coated carbendazim induced a similar set of adverse impacts at all investigated levels of ecological organization and time points. Our findings show fundamental restructuring of the taxonomic- and functional composition of macroinvertebrate communities as a result of low-level pesticide exposure, and thereby highlight the need for mitigating measures to reduce pesticide-induced stress on freshwater ecosystems.

Safe-and-Sustainable-by-Design Framework Based on a Prospective Life Cycle Assessment: Lessons Learned from a Nano-Titanium Dioxide Case Study.

Safe-and-sustainable-by-design (SSbD) is a concept that takes a systems approach by integrating safety, sustainability, and functionality throughout a product's the life cycle. This paper proposes a framework based on a prospective life cycle assessment for early safety and sustainability assessment. The framework's purpose is to identify environmental sustainability and toxicity hotspots early in the innovation process for future SSbD applicability. If this is impossible, key performance indicators are assessed. Environmental sustainability aspects, such as global warming potential (GWP) and cumulative energy demand (CED), and toxicity aspects, such as human toxicity potential and freshwater ecotoxicity potential, were assessed upon applying the framework on a case study. The case study regarded using nano-titanium dioxide (P25-TiO2) or a modified nano-coated version (Cu2O-coated/P25-TiO2) as photocatalysts to produce hydrogen from water using sunlight. Although there was a decrease in environmental impact (GWP and CED), the modified nano-coated version had a relatively higher level of human toxicity and freshwater eco-toxicity. For the presented case study, SSbD alternatives need to be considered that improve the photocatalytic activity but are not toxic to the environment. This case study illustrates the importance of performing an early safety and environmental sustainability assessment to avoid the development of toxic alternatives.

Controlled growth of ultrasmall Cu2O clusters on TiO2nanoparticles by atmospheric-pressure atomic layer deposition for enhanced photocatalytic activity.

This work presents a gas-phase approach for the synthesis of Cu2O/TiO2powder-based photocatalysts using atomic layer deposition (ALD). The process is carried out in a fluidized bed reactor working at atmospheric pressure using (trimethylvinylsilyl)-hexafluoroacetulacetonate copper(I) as the Cu-precursor and H2O vapor as the oxidizer. The saturating regime of the chemical reactions and the linear growth of ALD are achieved. In combination with the unsaturated regime, the ALD approach enables the deposition of ultrasmall Cu2O clusters with average diameters in the range of 1.3-2.0 nm, narrow particle size distributions and tunable Cu2O loadings on P25 TiO2nanoparticles. The photocatalytic performance of Cu2O/TiO2photocatalysts is investigated by the degradation of organic dyes, including Rhodamine B (RhB), methyl orange, and methylene blue; the results demonstrate that the surface modification of TiO2nanoparticles by Cu2O nanoclusters significantly enhances the photocatalytic activity of TiO2. This is attributed to the efficient charge transfer between Cu2O and TiO2that reduces the charge recombination. The photocatalytic reaction mechanism is further investigated for the degradation of RhB, revealing the dominating role of holes, which contribute to both direct hole oxidation and indirect oxidation (i.e. via the formation of hydroxyl radicals). Our approach provides a fast, scalable and efficient process to deposit ultrasmall Cu2O clusters in a controllable fashion for surface engineering and modification.

Gas Phase Modification of Silica Nanoparticles in a Fluidized Bed: Tailored Deposition of Aminopropylsiloxane.

Functionalized nanoparticles have various applications, for which grafting of a chemical moiety onto the surface to induce/improve certain properties is needed. When incorporated in polymeric matrices, for instance, the modified nanoparticles can alter the interfacial characteristics leading to improvements ofthe macroscopic properties of the nanocomposites. The extent of these improvements is highly dependent on the thickness, morphology and conformity of the grafted layer. However, the common liquid-phase modification methods provide limited control over these factors. A novel gas-phase modification process was utilized, with 3-aminopropyltriethoxysilane (APTES) as precursor, to chemically deposit amino-terminated organic layers on fumed silica nanoparticles in a fluidized bed. A self-limiting surface saturation was achieved when the reaction was done at 200 °C. With this self-limiting feature, we were able to graft multiple layers of aminopropylsiloxane (APS) onto the silica nanoparticles using water as the coreactant. The feasibility of this process was analyzed using thermogravimetric analysis (TGA), diffuse reflectance IR Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and elemental analysis (EA). By altering the number of APTES/water cycles, it was possible to control the thickness and conformity of the deposited aminopropylsiloxane layer. This novel approach allows to engineer the surface of nanoparticles, by introducing versatile functionalized layers in a controlled manner.

Controlled Pulmonary Delivery of Carrier-Free Budesonide Dry Powder by Atomic Layer Deposition.

Ideal controlled pulmonary drug delivery systems provide sustained release by retarding lung clearance mechanisms and efficient lung deposition to maintain therapeutic concentrations over prolonged time. Here, we use atomic layer deposition (ALD) to simultaneously tailor the release and aerosolization properties of inhaled drug particles without the need for lactose carrier. In particular, we deposit uniform nanoscale oxide ceramic films, such as Al2O3, TiO2, and SiO2, on micronized budesonide particles, a common active pharmaceutical ingredient for the treatment of respiratory diseases. In vitro dissolution and ex vivo isolated perfused rat lung tests demonstrate dramatically slowed release with increasing nanofilm thickness, regardless of the nature of the material. Ex situ transmission electron microscopy at various stages during dissolution unravels mostly intact nanofilms, suggesting that the release mechanism mainly involves the transport of dissolution media through the ALD films. Furthermore, in vitro aerosolization testing by fast screening impactor shows a ∼2-fold increase in fine particle fraction (FPF) for each ALD-coated budesonide formulation after 10 ALD process cycles, also applying very low patient inspiratory pressures. The higher FPFs after the ALD process are attributed to the reduction in the interparticle force arising from the ceramic surfaces, as evidenced by atomic force microscopy measurements. Finally, cell viability, cytokine release, and tissue morphology analyses verify a safe and efficacious use of ALD-coated budesonide particles at the cellular level. Therefore, surface nanoengineering by ALD is highly promising in providing the next generation of inhaled formulations with tailored characteristics of drug release and lung deposition, thereby enhancing controlled pulmonary delivery opportunities.

Synthesis of a Rationally Designed Multi-Component Photocatalyst Pt:SiO2:TiO2(P25) with Improved Activity for Dye Degradation by Atomic Layer Deposition.

Photocatalysts for water purification typically lack efficiency for practical applications. Here we present a multi-component (Pt:SiO2:TiO2(P25)) material that was designed using knowledge of reaction mechanisms of mono-modified catalysts (SiO2:TiO2, and Pt:TiO2) combined with the potential of atomic layer deposition (ALD). The deposition of ultrathin SiO2 layers on TiO2 nanoparticles, applying ALD in a fluidized bed reactor, demonstrated in earlier studies their beneficial effects for the photocatalytic degradation of organic pollutants due to more acidic surface Si-OH groups which benefit the generation of hydroxyl radicals. Furthermore, our investigation on the role of Pt on TiO2(P25), as an improved photocatalyst, demonstrated that suppression of charge recombination by oxygen adsorbed on the Pt particles, reacting with the separated electrons to superoxide radicals, acts as an important factor for the catalytic improvement. Combining both materials into the resulting Pt:SiO2:TiO2(P25) nanopowder exceeded the dye degradation performance of both the individual SiO2:TiO2(P25) (1.5 fold) and Pt:TiO2(P25) (4-fold) catalysts by 6-fold as compared to TiO2(P25). This approach thus shows that by understanding the individual materials' behavior and using ALD as an appropriate deposition technique enabling control on the nano-scale, new materials can be designed and developed, further improving the photocatalytic activity. Our research demonstrates that ALD is an attractive technology to synthesize multicomponent catalysts in a precise and scalable way.

Thermal atomic layer deposition of gold nanoparticles: controlled growth and size selection for photocatalysis.

Gold nanoparticles have been extensively studied for their applications in catalysis. For Au nanoparticles to be catalytically active, controlling the particle size is crucial. Here we present a low temperature (105 °C) thermal atomic layer deposition approach for depositing gold nanoparticles on TiO2 with controlled size and loading using trimethylphosphino-trimethylgold(iii) and two co-reactants (ozone and water) in a fluidized bed reactor. We show that the exposure time of the precursors is a variable that can be used to decouple the Au particle size from the loading. Longer exposures of ozone narrow the particle size distribution, while longer exposures of water broaden it. By studying the photocatalytic activity of Au/TiO2 nanocomposites, we show how the ability to control particle size and loading independently can be used not only to enhance performance but also to investigate structure-property relationships. This study provides insights into the mechanism underlying the formation and evolution of Au nanoparticles prepared for the first time via vapor phase atomic layer deposition. Employing a vapor deposition technique for the synthesis of Au/TiO2 nanocomposites eliminates the shortcomings of conventional liquid-based processes opening up the possibility of highly controlled synthesis of materials at large scale.

Nanoengineering of Crystal and Amorphous Surfaces of Pharmaceutical Particles for Biomedical Applications.

The morphology, size, and surface properties of pharmaceutical particles form an essential role in the therapeutic performance of active pharmaceutical ingredients (APIs) and excipients as constituents in various drug delivery systems and clinical applications. Recent advances in methods for surface modification, however, rely heavily on liquid-phase-based modification processes and afford limited control over the thickness and conformality of the coating. Atomic layer deposition (ALD), on the other hand, enables the formation of conformal nanoscale films on complex structures with thickness control on the molecular level, while maintaining the substrate particle size and morphology. Moreover, this enables nanoengineering of surfaces of pharmaceutical particles also in the dry state. Successful nanoengineeering of crystal and amorphous surfaces of pharmaceutical particles is demonstrated in this study whereby functional properties, such as dissolution and dispersibility, were tailored for drug delivery applications. This expands on our initial work on ALD of alumina on pharmaceutical particles within the lower micro- to higher nanosize ranges to here probe both crystalline and amorphous lactose substrate surfaces (d50 = 3.5 and 21 µm). In addition, both water and ozone coreactants were evaluated, the latter having not been evaluated previously for pharmaceutical particles. The deposition process is carried out at ambient conditions in a fluidized bed reactor for a low number of cycles (i.e., from 4 to 14). Improved dissolution and extended release were achieved by the ALD nanoengineering of both crystalline and amorphous surfaces. This novel concept opens up exciting opportunities to produce more complex materials and structures using temperature- and moisture-sensitive drugs, e.g., targeting and drug delivery opportunities, as well as delivering new functionalities for novel applications in the pharmaceutical, medical, biological, and advanced materials fields. The prospects for advancing inhaled drug delivery are exemplified by the ALD surface nanoengineering concept.

Suppressing the Photocatalytic Activity of TiO2 Nanoparticles by Extremely Thin Al2O3 Films Grown by Gas-Phase Deposition at Ambient Conditions.

This work investigated the suppression of photocatalytic activity of titanium dioxide (TiO2) pigment powders by extremely thin aluminum oxide (Al2O3) films deposited via an atomic-layer-deposition-type process using trimethylaluminum (TMA) and H2O as precursors. The deposition was performed on multiple grams of TiO2 powder at room temperature and atmospheric pressure in a fluidized bed reactor, resulting in the growth of uniform and conformal Al2O3 films with thickness control at sub-nanometer level. The as-deposited Al2O3 films exhibited excellent photocatalytic suppression ability. Accordingly, an Al2O3 layer with a thickness of 1 nm could efficiently suppress the photocatalytic activities of rutile, anatase, and P25 TiO2 nanoparticles without affecting their bulk optical properties. In addition, the influence of high-temperature annealing on the properties of the Al2O3 layers was investigated, revealing the possibility of achieving porous Al2O3 layers. Our approach demonstrated a fast, efficient, and simple route to coating Al2O3 films on TiO2 pigment powders at the multigram scale, and showed great potential for large-scale production development.

Transition of Emission Colours as a Consequence of Heat-Treatment of Carbon Coated Ce3+-Doped YAG Phosphors.

To modify the luminescence properties of Ce3+-doped Y3Al5O12 (YAG) phosphors, they have been coated with a carbon layer by chemical vapor deposition and subsequently heat-treated at high temperature under N2 atmosphere. Luminescence of the carbon coated YAG:Ce3+ phosphors has been investigated as a function of heat-treatment at 1500 and 1650 °C. The 540 nm emission intensity of C@YAG:Ce3+ is the highest when heated at 1650 °C, while a blue emission at 400-420 nm is observed when heated at 1500 °C but not at 1650 °C. It is verified by X-ray diffraction (XRD) that the intriguing luminescence changes are induced by the formation of new phases in C@YAG:Ce3+-1500 °C, which disappear in C@YAG:Ce3+-1650 °C. In order to understand the mechanisms responsible for the enhancement of YAG:Ce3+ emission and the presence of the blue emission observed for C@YAG:Ce3+-1500 °C, the samples have been investigated by a combination of several electron microscopy techniques, such as HRTEM, SEM-CL, and SEM-EDS. This local and cross-sectional analysis clearly reveals a gradual transformation of phase and morphology in heated C@YAG:Ce3+ phosphors, which is related to a reaction between C and YAG:Ce3+ in N2 atmosphere. Through reaction between the carbon layer and YAG host materials, the emission colour of the phosphors can be modified from yellow, white, and then back to yellow under UV excitation as a function of heat-treatment in N2 atmosphere.

Low-temperature atomic layer deposition delivers more active and stable Pt-based catalysts.

We tailored the size distribution of Pt nanoparticles (NPs) on graphene nanoplatelets at a given metal loading by using low-temperature atomic layer deposition carried out in a fluidized bed reactor operated at atmospheric pressure. The Pt NPs deposited at low temperature (100 °C) after 10 cycles were more active and stable towards the propene oxidation reaction than their high-temperature counterparts. Crucially, the gap in the catalytic performance was retained even after prolonged periods of time (>24 hours) at reaction temperatures as high as 450 °C. After exposure to such harsh conditions the Pt NPs deposited at 100 °C still retained a size distribution that is narrower than the one of the as-synthesized NPs obtained at 250 °C. The difference in performance correlated with the difference in the number of facet sites as estimated after the catalytic test. Our approach provides not only a viable route for the scalable synthesis of stable supported Pt NPs with tailored size distributions but also a tool for studying the structure-function relationship.

Understanding and Controlling the Aggregative Growth of Platinum Nanoparticles in Atomic Layer Deposition: An Avenue to Size Selection.

We present an atomistic understanding of the evolution of the size distribution with temperature and number of cycles in atomic layer deposition (ALD) of Pt nanoparticles (NPs). Atomistic modeling of our experiments teaches us that the NPs grow mostly via NP diffusion and coalescence rather than through single-atom processes such as precursor chemisorption, atom attachment, and Ostwald ripening. In particular, our analysis shows that the NP aggregation takes place during the oxygen half-reaction and that the NP mobility exhibits a size- and temperature-dependent scaling. Finally, we show that contrary to what has been widely reported, in general, one cannot simply control the NP size by the number of cycles alone. Instead, while the amount of Pt deposited can be precisely controlled over a wide range of temperatures, ALD-like precision over the NP size requires low deposition temperatures (e.g., T < 100 °C) when growth is dominated by atom attachment.