Shape control of platinum and palladium nanoparticles for catalysis

Metal Nanoparticles as Green Catalysts

Nanoparticles play a significant role in various fields ranging from electronics to composite materials development. Among them, metal nanoparticles have attracted much attention in recent decades due to their high surface area, selectivity, tunable morphologies, and remarkable catalytic activity. In this review, we discuss various possibilities for the synthesis of different metal nanoparticles; specifically, we address some of the green synthesis approaches. In the second part of the paper, we review the catalytic performance of the most commonly used metal nanoparticles and we explore a few roadblocks to the commercialization of the developed metal nanoparticles as efficient catalysts.

Continuous Microfluidic Synthesis of Pd Nanocubes and PdPt Core-Shell Nanoparticles and Their Catalysis of NO2 Reduction

Faceted colloidal nanoparticles are currently of immense interest due to their unique electronic, optical, and catalytic properties. However, continuous flow synthesis that enables rapid formation of faceted nanoparticles of single or multi-elemental composition is not trivial. We present a continuous flow synthesis route for the synthesis of uniformly sized Pd nanocubes and PdPt core-shell nanoparticles in a single-phase microfluidic reactor, which enables rapid formation of shaped nanoparticles with a reaction time of 3 min. The PdPt core-shell nanoparticles feature a dendritic, high surface area with the Pt shell covering the Pd core, as verified using high-resolution scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. The Pd nanocubes and PdPt core-shell particles are catalytically tested during NO₂ reduction in the presence of H₂ in a flow pocket reactor. The Pd nanocubes exhibited low-temperature activity (i.e., <136 °C) and poor selectivity performance toward production of N₂O or N₂, whereas PdPt core-shell nanoparticles showed higher activity and were found to achieve better selectivity during NO₂ reduction retaining its basic structure at relatively elevated temperatures, making the PdPt core-shell particles a unique, desirable synergic catalyst material for potential use in NO_x abatement processes.

Designing active particles for colloidal microstructure manipulation via strain field alchemy

Defects in a crystal can exert forces on each other via strain field interactions. Here we explore the strain-field-mediated interaction between an anisotropic interstitial probe particle and dislocation microstructures in a colloidal crystal composed of particles interacting via steep repulsive isotropic potentials. We optimize the interaction between probe particle and dislocation with the anisotropic shape of the probe as a free parameter. Such alchemical optimization is typically carried out upon the explicitly defined interaction potential parameters; instead, we optimize the strain field of the probe and then map back to particle shape. We distinguish this tactic from other alchemical methods as 'strain alchemy'. We report several findings: (1) a robust mapping exists between strain field calculation methods (the method of eigenstrains) and strains produced by an anisotropic interstitial, (2) optimization of strain field interactions in the strain domain permits rapid evaluation of candidate shapes for interstitials, (3) interstitial mobility barriers can be estimated from the strain field, and (4) strongly interacting and highly mobile interstitial particles can be found that are capable of driving dislocation glide with applied force. Active particle-induced dislocation glide is examined for the cases of edge dislocation arrays and extrinsic dislocation loops. For edge dislocations, particle geometries of alternating large and small diameter segments were found to interact most strongly. For dislocation loops, interstitials with a single small radius segment surrounded by large radius segments are best.

Moving Frontiers in Transition Metal Catalysis: Synthesis, Characterization and Modeling

Nanosized transition metal particles are important materials in catalysis with a key role not only in academic research but also in many processes with industrial and societal relevance. Although small improvements in catalytic properties can lead to significant economic and environmental impacts, it is only now that knowledge-based design of such materials is emerging, partly because the understanding of catalytic mechanisms on nanoparticle surfaces is increasingly improving. A knowledge-based design requires bottom-up synthesis of well-defined model catalysts, an understanding of the catalytic nanomaterials "at work" (operando), and both a detailed understanding and a prediction by theoretical methods. This article reports on progress in colloidal synthesis of transition metal nanoparticles for preparation of model catalysts to close the materials gap between the discoveries of fundamental surface science and industrial application. The transition metal particles, however, often undergo extensive transformations when applied to the catalytic process and much progress has recently been achieved operando characterization techniques under relevant reaction conditions. They allow better understanding of size/structure-activity correlations in these systems. Moreover, the growth of computing power and the improvement of theoretical methods uncover mechanisms on nanoparticles and have recently predicted highly active particles for CO/CO₂ hydrogenation or direct H₂ O₂ synthesis.

Morphology evolution of fcc Ru nanoparticles under hydrogen atmosphere

Tuning the morphology and structural evolution of metal nanoparticles to expose specific crystal facets in a certain reaction atmosphere is conducive to designing catalysts with a high catalytic activity. Herein, coverage dependent hydrogen adsorption on seven fcc Ru surfaces was investigated using density functional theory (DFT) calculations. The morphology evolution of the fcc Ru nanoparticles under the reactive environment was further illustrated using the multiscale structure reconstruction (MSR) model, which combines the DFT results with the Fowler-Guggenheim (F-G) adsorption isotherm and the Wulff construction. At constant pressure, the shape of a fcc Ru nanoparticle changes from a rhombic dodecahedron to a truncated octahedron with an increase of the temperature. More importantly, the desired Ru morphology, with abundant open facets, was predicted to occur at a high temperature and low pressure. Our results provide an insightful understanding of the reshaping of Ru nanoparticles during real reactions, which is crucial for its rational design for use as a nanocatalyst.

Gas-induced selective re-orientation of Au-Cu nanoparticles on TiO2 (110)

Au-Cu bimetallic nanoparticles (NPs) grown on TiO2(110) have been followed in situ using grazing incidence X-ray diffraction and X-ray photoemission spectroscopy from their synthesis to their exposure to a CO/O2 mixture at low pressure (P < 10-5 mbar) and at different temperatures (300 K-470 K). As-prepared samples are composed of two types of alloyed NPs: randomly oriented and epitaxial NPs. Whereas the introduction of CO has no effect on the structure of the NPs, an O2 introduction triggers a Cu surface segregation phenomenon resulting in the formation of a Cu2O shell reducible by annealing the sample over 430 K. A selective re-orientation of the nanoparticles, induced by the exposure to a CO/O2 mixture, is observed where the randomly oriented NPs take advantage of the mobility induced by the Cu segregation to re-orient their Au-rich core relatively to the TiO2(110) substrate following specifically the orientation ((111)NPs//(110)TiO2) when others epitaxial relationships were observed on the as-prepared sample.

Size and shape control of metal nanoparticles in millifluidic reactors

Engineered metal nanoparticles (metal NPs) possess unique size -dependent optical and electronic properties that could enable new applications in biomedicine, energy generation, microelectronics, micro-optics, and catalysis. For metal NPs to make a mark in these fields, however, new synthetic strategies must be developed that permit NP synthesis on the kilogram scale, while maintaining precise control over NP physiochemical properties (size, shape, composition, and surface chemistry). Currently, NP batch syntheses produce product on the milligram scale and rely on synthetic strategies that are not readily amenable to scale-up. Flow reactor systems (including lab-on-a-chip devices) provide a synthesis platform that can circumvent many of the traditional limitations of batch-scale NP syntheses. These reactors provide more uniform reagent mixing, more uniform heat transfer, opportunities to interface in situ monitoring technology, and allow product yield to be scaled up simply by running multiple reactors in parallel. While many NP syntheses have been successfully transferred to microfluidic reactor systems, microfluidic reactor fabrication is time intensive and typically requires sophisticated lithography facilities. Consequently, millifluidic flow reactors (reactors with channel dimensions of 0.5–10.0 mm) are gaining popularity in NP synthesis. These millifluidic reactors provide many of the same synthetic advantages as microfluidic devices, but are simpler to construct, easier to reconfigure, and more straightforward to interface with in situ monitoring techniques. In this chapter, we will discuss the progress that has been made in developing millifluidic reactors for functionalized metal NP synthesis. First, we will review the basic wet-chemical strategies used to control metal NP size and shape in batch reactors. We will then survey some of the basic principles of millifluidic device design, construction, and operation. We will also discuss the potential for incorporating in situ monitoring for quality control during synthesis. We will conclude by highlighting some particularly relevant examples of millifluidic metal NP synthesis that have set new standards for metal NP size, shape, and surface chemistry control.

Graphical Abstract:

Tuning Ion Complexing To Rapidly Prepare Hollow Ag-Pt Nanowires with High Activity toward the Methanol Oxidization Reaction

Hollow Pt-based nanowires (NWs) have important applications in catalysis. Their preparation often involves a two-step process in which M (M=Ag, Pd, Co, Ni) NWs are prepared and subsequently subjected to galvanic reaction in solution containing a Pt precursor. It is challenging to achieve a simple one-step preparation, because the redox potential of Pt^IV /Pt or Pt^II /Pt to Pt is high, and therefore, Pt atoms always form first. This work demonstrates that an appropriate pH can decrease the redox potential of Pt^IV /Pt and allows the one-step preparation of high-quality hollow Pt-Ag NWs rapidly (10 min). Moreover, it is easy to realize large-scale preparation with this method. The NW composition can be adjusted readily to optimize their performance in the electrocatalytic methanol oxidization reaction (MOR). Compared with commercial Pt/C, NWs with appropriate Ag/Pt ratios exhibit high stability, activity, and CO tolerance ability.

1D alloy ultrafine Pt-Fe nanowires as efficient electrocatalysts for alcohol electrooxidation in alkaline media

Fuel cells have been gaining much interest due to their advantages of high energy conversion efficiency, easy handling, etc., whereas some drawbacks of anode catalysts regarding limited performances have seriously restricted their practical applications. Therefore, the development of anode nanocatalysts with higher activity and stability has become an urgent need. In view of this, we have developed a facile wet-chemical approach to synthesize 1D alloy ultrafine Pt-Fe NWs, and we have also revealed the formation mechanism of the ultrafine Pt-Fe NWs using time-dependent studies. More importantly, 1D ultrafine nanowires with anisotropy, superior flexibility, high surface area and excellent conductivity are promising candidates for the improvement of nanocatalytic activity and stability enhancement. Therefore, the electrocatalytic activities of ultrafine Pt3Fe NWs in the oxidation of ethylene glycol and glycerol are 3.9 and 2.5 times greater than that of commercial Pt/C, respectively. Moreover, they provide excellent long-term stability. Our efforts may potentially promote the commercialization of fuel cells to some extent.

Switching of Current Rectification Ratios within a Single Nanocrystal by Facet-Resolved Electrical Wiring

Here we show that within a single polyhedral metal oxide nanoparticle a nanometer-scale lateral or vertical sliding of a small metal top contact ( e. g., <50 nm) leads to a 10-fold change in current rectification ratios. Electron tunneling imaging and constant-force current-potential analysis in atomic force microscopy demonstrate that within an individual p-n rectifier (a Cu₂O nanocrystal on silicon) the degree of current asymmetry can be modulated predictably by a set of geometric considerations. We demonstrate the concept of a single nanoscale entity displaying an in-built range of discrete electrical signatures and address fundamental questions in the direction of "landing" contacts in single-particle diodes. This concept is scalable to large 2D arrays, up to millimeters in size, with implications in the design and understanding of nanoparticle circuitry.

Synthesis of hafnium nanoparticles and hafnium nanoparticle films by gas condensation and energetic deposition

In this work we study the fabrication and characterization of hafnium nanoparticles and hafnium nanoparticle thin films. Hafnium nanoparticles were grown in vacuum by magnetron-sputtering inert-gas condensation. The as deposited nanoparticles have a hexagonal close-packed crystal structure, they possess truncated hexagonal biprism shape and are prone to surface oxidation when exposed to ambient air forming core-shell Hf/HfO₂ structures. Hafnium nanoparticle thin films were formed through energetic nanoparticle deposition. This technique allows for the control of the energy of charged nanoparticles during vacuum deposition. The structural and nanomechanical properties of the nanoparticle thin films were investigated as a function of the kinetic energy of the nanoparticles. The results reveal that by proper adjustment of the nanoparticle energy, hexagonal close-packed porous nanoparticle thin films with good mechanical properties can be formed, without any additional treatment. It is shown that these films can be patterned on the substrate in sub-micrometer dimensions using conventional lithography while their porosity can be well controlled. The fabrication and experimental characterization of hafnium nanoparticles is reported for the first time in the literature.

Ultrathin Uniform Platinum Nanowires via a Facile Route Using an Inverse Hexagonal Surfactant Phase Template

We present an attractive method for the fabrication of long, straight, highly crystalline, ultrathin platinum nanowires. The fabrication is simply achieved using an inverse hexagonal (H_II) lyotropic liquid crystal phase of the commercial surfactant phytantriol as a template. A platinum precursor dissolved within the cylindrical aqueous channels of the liquid crystal phase is chemically reduced by galvanic displacement using stainless steel. We demonstrate the production of nanowires using the H_II phase in the phytantriol/water system which we obtain either by heating to 55 °C or at room temperature by the addition of a hydrophobic liquid, 9- cis-tricosene, to relieve packing frustration. The two sets of conditions produced high aspect nanowires with diameters of 2.5 and 1.7 nm, respectively, at least hundreds of nanometers in length, matching the size of the aqueous channels in which they grow. This versatile approach can be extended to produce highly uniform nanowires from a range of metals.

Biosynthesis of palladium nanoparticles using Diospyros kaki leaf extract and determination of antibacterial efficacy

Palladium, the building block of white gold, has been found to exhibit extraordinary properties in nanotechnological products produced in recent years. The most prominent feature of palladium is adsorbing and storing high levels of hydrogen. Therefore, the demand for palladium in the world increased excessively in the 2000s. In the present study, palladium nanoparticles (PdNPs) were biosynthesized by the extract of Diospyros kaki leaves as bio-stimulator. D. kaki, also called persimmon, was collected in a local area in Istanbul Turkey. PdNP formation was screened by analyzing UV-Vis spectrophotometer at 250-550 nm. The nanoparticles were characterized by scanning electron microscope which revealed that the biosynthesized PdNPs were in sizes ranging from 50 to 120 nm. Fourier transform infrared spectroscopy applied on both D. kaki leaf extract and PdNPs was used to decide on the reactive groups managing the reduction of the biosynthesized nanoparticles. Also, the PdNPs showed reasonably proficient antibacterial efficacy for both Escherichia coli and Staphylococcus aureus and the zones of inhibition were found as 18 and 10.5 mm, respectively.

Platinum nanoparticles in nanobiomedicine

Oxidative stress-dependent inflammatory diseases represent a major concern for the population's health worldwide. Biocompatible nanomaterials with enzymatic properties could play a crucial role in the treatment of such pathologies. In this respect, platinum nanoparticles (PtNPs) are promising candidates, showing remarkable catalytic activity, able to reduce the intracellular reactive oxygen species (ROS) levels and impair the downstream pathways leading to inflammation. This review reports a critical overview of the growing evidence revealing the anti-inflammatory ability of PtNPs and their potential applications in nanomedicine. It provides a detailed description of the wide variety of synthetic methods recently developed, with particular attention to the aspects influencing biocompatibility. Special attention has been paid to the studies describing the toxicological profile of PtNPs with an attempt to draw critical conclusions. The emerging picture suggests that the material per se is not causing cytotoxicity, while other physicochemical features related to the synthesis and surface functionalization may play a crucial role in determining the observed impairment of cellular functions. The enzymatic activity of PtNPs is also summarized, analyzing their action against ROS produced by pathological conditions within the cells. In particular, we extensively discuss the potential of these properties in nanomedicine to down-regulate inflammatory pathways or to be employed as diagnostic tools with colorimetric readout. A brief overview of other biomedical applications of nanoplatinum is also presented.

Palladium Nanoparticles: Toxicological Effects and Potential Implications for Occupational Risk Assessment

The increasing technological applications of palladium nanoparticles (Pd-NPs) and their consequent enhancing release into the community and occupational environments, have raised public health concerns regarding possible adverse effects for exposed subjects, and particularly for workers chronically and highly exposed to these materials, whose toxico-kinetic and dynamic behavior remains to be fully understood. Therefore, this review aimed to critically analyze literature data to achieve a more comprehensive knowledge on the toxicological profile of Pd-NPs. Results from available studies demonstrated the potential for these chemicals to affect the ecosystem function, to exert cytotoxic and pro-inflammatory effects in vitro as well as to induce early alterations in different target organs in in vivo models. However, our revision pointed out the need for future studies aimed to clarify the role of the NP physico-chemical properties in determining their toxicological behavior, as well as the importance to carry out investigations focused on environmental and biological monitoring to verify and validate experimental biomarkers of exposure and early effect in real exposure contexts. Overall, this may be helpful to support the definition of suitable strategies for the assessment, communication and management of Pd-NP occupational risks to protect the health and safety of workers.

Size-dependent catalytic kinetics and dynamics of Pd nanocubes: a single-particle study

Due to the well-known significant effect of the size on the catalytic activity of nanocatalysts, here we use single-molecule fluorescence microscopy to study the size-dependent catalytic kinetics and dynamics of individual Pd nanocubes. A series of size-dependent catalytic properties were revealed in both product formation and product desorption processes. It was found that, due to the different adsorption mechanisms of substrate molecules on Pd nanocubes, H2 adsorption is independent of the size of Pd nanocubes, while the large flat resazurin molecules show stronger adsorption on larger sized Pd nanocubes. Apparently, the Pd nanocubes can be divided into three types: when the size of the Pd nanocube is small, substrate binding can prohibit product desorption and product desorption prefers the direct pathway; when the size is in an appropriate range, the product desorption process could be independent of substrate binding and shows no selectivity between two parallel desorption pathways; if the size is large enough, substrate binding can promote product desorption and product desorption prefers the indirect pathway. We also observed the surface-restructuring-induced dynamic heterogeneity of individual Pd nanocubes in both product formation and desorption processes with timescales of about tens to one hundred seconds. The activity fluctuation of individual Pd nanocubes was found to be mainly due to the spontaneous surface-restructuring rather than the catalysis. Furthermore, we estimated the size-dependent activation energies and time scales of spontaneous dynamic surface restructuring, which are fundamental to heterogeneous catalysis. The work presented here reveals new insight into nanocatalysis and exemplifies the advantages of the single-molecule approach in probing the catalytic properties of nanocatalysts.

Colloidal nanoparticle size control: experimental and kinetic modeling investigation of the ligand-metal binding role in controlling the nucleation and growth kinetics

Despite the major advancements in colloidal metal nanoparticles synthesis, a quantitative mechanistic treatment of the ligand's role in controlling their size remains elusive. We report a methodology that combines in situ small angle X-ray scattering (SAXS) and kinetic modeling to quantitatively capture the role of ligand-metal binding (with the metal precursor and the nanoparticle surface) in controlling the synthesis kinetics. We demonstrate that accurate extraction of the kinetic rate constants requires using both, the size and number of particles obtained from in situ SAXS to decouple the contributions of particle nucleation and growth to the total metal reduction. Using Pd acetate and trioctylphosphine in different solvents, our results reveal that the binding of ligands with both the metal precursor and nanoparticle surface play a key role in controlling the rates of nucleation and growth and consequently the final size. We show that the solvent can affect the metal-ligand binding and consequently ligand coverage on the nanoparticles surface which has a strong effect on the growth rate and final size (1.4 nm in toluene and 4.3 nm in pyridine). The proposed kinetic model quantitatively predicts the effects of varying the metal concentration and ligand/metal ratio on nanoparticle size for our work and literature reports. More importantly, we demonstrate that the final size is exclusively determined by the nucleation and growth kinetics at early times and not how they change with time. Specifically, the nanoparticle size in this work and many literature reports can be predicted using a single, model independent kinetic descriptor, (growth-to-nucleation rate ratio)^1/3, despite the different metals and synthetic conditions. The proposed model and kinetic descriptor could serve as powerful tools for the design of colloidal nanoparticles with specific sizes.

Combination of palladium nanoparticles and tubastatin-A potentiates apoptosis in human breast cancer cells: a novel therapeutic approach for cancer

BACKGROUND

Breast cancer is the most common malignant disease that occurs in women. Histone deacetylase (HDAC) inhibition has recently emerged as an effective and attractive target for the treatment of cancer. The aim of this study was to investigate the efficacy of a combined treatment of tubastatin A (TUB-A) and palladium nanoparticles (PdNPs) against MDA-MB-231 human breast cancer cells using two different cytotoxic agents that work by two different mechanisms, thereby decreasing the probability of chemoresistance in cancer cells and increasing the efficacy of toxicity, to provide efficient therapy for advanced stage of cancer without any undesired side effects.

METHODS

PdNPs were synthesized using a novel biomolecule called R-phycoerythrin and characterized using various analytical techniques. The combinatorial effect of TUB-A and PdNPs was assessed by various cellular and biochemical assays and also by gene expression analysis.

RESULTS

The biologically synthesized PdNPs had an average size of 25 nm and were spherical in shape. Treatment of MDA-MB-231 human breast cancer cells with TUB-A or PdNPs showed a dose-dependent effect on cell viability. The combination of 4 μM TUB-A and 4 μM PdNPs had a significant inhibitory effect on cell viability compared with either TUB-A or PdNPs alone. The combinatorial treatment also had a more pronounced effect on the inhibition of HDAC activity and enhanced apoptosis by regulating various cellular and biochemical changes.

CONCLUSION

Our results suggest that there was a strong synergistic interaction between TUB-A and PdNPs in increasing apoptosis in human breast cancer cells. These data provide an important preclinical basis for future clinical trials on this drug combination. This combinatorial treatment increased therapeutic potentials, thereby demonstrating a relevant targeted therapy for breast cancer. Furthermore, we have provided the first evidence for the combinatorial effect and mechanism of toxicity of TUB-A and PdNPs in human breast cancer cells. The novelties of the study were identification of a combination therapy that consists of suitable therapeutic molecules that kill cancer cells and also exploration of two different possible mechanisms involved to reduce chemoresistance in cancer cells.

Production of High-Value Nanoparticles via Biogenic Processes Using Aquacultural and Horticultural Food Waste

The quantities of organic waste produced globally by aquacultural and horticulture are extremely large and offer an attractive renewable source of biomolecules and bioactive compounds. The availability of such large and diverse sources of waste materials creates a unique opportunity to develop new recycling and food waste utilisation strategies. The aim of this review is to report the current status of research in the emerging field of producing high-value nanoparticles from food waste. Eco-friendly biogenic processes are quite rapid, and are usually carried out at normal room temperature and pressure. These alternative clean technologies do not rely on the use of the toxic chemicals and solvents commonly associated with traditional nanoparticle manufacturing processes. The relatively small number of research articles in the field have been surveyed and evaluated. Among the diversity of waste types, promising candidates and their ability to produce various high-value nanoparticles are discussed. Experimental parameters, nanoparticle characteristics and potential applications for nanoparticles in pharmaceuticals and biomedical applications are discussed. In spite of the advantages, there are a number of challenges, including nanoparticle reproducibility and understanding the formation mechanisms between different food waste products. Thus, there is considerable scope and opportunity for further research in this emerging field.

An In situ TEM study of the surface oxidation of palladium nanocrystals assisted by electron irradiation

The surface oxidation of palladium nanocrystals plays an important role in changing the active sites and subsequently influencing the catalytic reactivity. Such a microscopy study on surface oxidation, down to the atomic scale, is essential for understanding the structure-property correlations of palladium nanocrystal based catalysts. Herein, we present an in situ atomic scale study on the surface oxidation behavior of palladium nanocrystals, which is induced by electron beam irradiation under low oxygen partial pressure and at room temperature inside an environmental transmission electron microscope. We found that: (i) surface oxidation initially started at the edge sites with atomic steps or vertex sites, which served as active sites for oxidation; (ii) the oxidation reaction proceeded with a much faster rate on the {111} surface, indicating a certain crystallography preference; (iii) nanometer-sized palladium monoxide islands were formed on the surfaces eventually. The results from our in situ studies provide insightful knowledge, and will be of certain importance for the design of improved functional catalysts in future.

Highly active Pd–Ni nanocatalysts supported on multicharged polymer matrix

In this article, we report the synthesis of mono- and bimetallic Pd–Ni nanocomposites supported on a multicharged polymeric matrix for catalytic applications.

Microorganism mediated biosynthesis of metal chalcogenides; a powerful tool to transform toxic effluents into functional nanomaterials

Cadmium contained in soil and water can be taken up by certain crops and aquatic organisms and accumulate in the food-chain, thus removal of Cd from mining or industrial effluents - i.e. Ni-Cd batteries, electroplating, pigments, fertilizers - becomes mandatory for human health. In parallel, there is an increased interest in the production of luminescent Q-dots for applications in bioimaging, sensors and electronic devices, even the present synthesis methods are economic and environmentally costly. An alternative green pathway for producing Metal chalcogenides (MC: CdS, CdSe, CdTe) nanocrystals is based on the metabolic activity of living organisms. Intracellular and extracellular biosynthesis of can be achieved within a biomimetic approach feeding living organisms with Cd precursors providing new routes for combining bioremediation with green routes for producing MC nanoparticles. In this mini-review we present the state-of-the-art of biosynthesis of MC nanoparticles with a critical discussion of parameters involved and protocols. Few existing examples of scaling-up are also discussed. A modular reactor based on microorganisms entrapped in biocompatible mineral matrices - already proven for bioremediation of dissolved dyes - is proposed for combining both Cd-depletion and MC nanoparticle's production.

Nanoengineering a library of metallic nanostructures using a single microfluidic reactor

Microfluidic synthesis in a microfabricated reactor enables fast and facile synthesis of a wide library of metallic nanostructures: monometallic, bimetallic, anisotropic growth and heterostructures. Specific nanostructures are realized by selection of flow pattern and synthesis parameters. The technique is shown to have advantages over conventional batch technologies. Not only does it allow faster scalable synthesis, but also realization of nanostructures hitherto not reported such as Pt-Ru, Pt-Ni and Pt-Co nanodendrites, Pt-Pd heterostructures, Ag-Pd core-shell NPs, Au-Pd nanodumbbells and Au-Pd nanosheets.

Surfactant-Mediated One-Pot Method To Prepare Pd-CeO2 Colloidal Assembled Spheres and Their Enhanced Catalytic Performance for CO Oxidation

A simple, one-pot method to fabricate ordered, monodispersed Pd-CeO₂ colloidal assembled spheres (CASs) was developed using the surfactant-mediated solvothermal approach, which involves a tunable self-assembled process by carefully controlling different chemical reactions. The evolution process and formation mechanism of the CASs were thoroughly investigated by time-controlled and component-controlled experiments. For CO oxidation, this CAS nanocatalyst exhibited much higher catalytic activity and thermal stability than Pd/CeO₂ prepared by an impregnation method, and its complete CO conversion temperature is ∼120 °C. The enhanced catalytic performance for CO oxidation could be attributed to the synergistic effect of highly dispersed PdO species and Pd²⁺ ions incorporated into the CeO₂ lattice. For this CAS catalyst, each sphere can be viewed as a single reactor, and its catalytic performance can be further improved after being supported on alumina, which is obviously higher than results previously reported. Furthermore, this method was used to successfully prepare M-CeO₂ CASs (M = Pt, Cu, Mn, Co), showing further that this is a new and ideal approach for fabricating active and stable ceria-based materials.

Metal Bromide Controlled Interfacial Aromatization Reaction for Shape-Selective Synthesis of Palladium Nanostructures with Efficient Catalytic Performances

Herein, the effect of diverse metal bromides for the shape evolution of palladium nanostructures (Pd NS) has been demonstrated. Aromaticity-driven reduction of bromopalladate(II) is optimized to reproducibly obtain different Pd NS at the water/organic layer interface. In this soft interfacial strategy, a redox potential driven reaction has been performed, forming the thermodynamically more stable (>10(4) -fold) PdBr4 (2-) precursor from PdCl4 (2-) by adding extra metal bromides. In the process, the reductant, Hantzsch dihydropyridine ester (DHPE), is aromatized. Interestingly, alkali metal bromides devoid of coordination propensity exclusively evolve Pd nanowires (Pd NWs), whereas in the case of transition metal bromides the metal ions engage the 'N' donor of DHPE at the interface, making the redox reaction sluggish. Hence, controlled Pd nanoparticles growth is observed, which evolves Pd broccolis (Pd NBRs) and Pd nanorods (Pd NRs) at the interface in the presence of NiBr2 and CuBr2 , respectively, in the aqueous solution. Thus, the effect of diverse metal bromides in the reaction mixture for tailor-made growth of the various Pd NS is reported. Among the as-synthesized materials, the Pd NWs stand to be superior catalysts and their efficiency is almost 6 and 2.5 times higher than commercial 20 % Pd/C in the electrooxidation of ethanol and Cr(VI) reduction reaction by formic acid, respectively.