Deposition Of Palladium Nanoparticles Research Articles

Determining the orderliness of carbon materials with nanoparticle imaging and explainable machine learning.

Carbon materials have paramount importance in various fields of materials science, from electronic devices to industrial catalysts. The properties of these materials are strongly related to the distribution of defects-irregularities in electron density on their surfaces. Different materials have various distributions and quantities of these defects, which can be imaged using a procedure that involves depositing palladium nanoparticles. The resulting scanning electron microscopy (SEM) images can be characterized by a key descriptor-the ordering of nanoparticle positions. This work presents a highly interpretable machine learning approach for distinguishing between materials with ordered and disordered arrangements of defects marked by nanoparticle attachment. The influence of the degree of ordering was experimentally evaluated on the example of catalysis via chemical reactions involving carbon-carbon bond formation. This represents an important step toward automated analysis of SEM images in materials science.

Biogenic Palladium Improved Perchlorate Reduction during Nitrate Co-Reduction by Diverting Electron Flow in a Hydrogenotrophic Biofilm.

Microbial reduction of perchlorate (ClO4-) is emerging as a cost-effective strategy for groundwater remediation. However, the effectiveness of perchlorate reduction can be suppressed by the common co-contamination of nitrate (NO3-). We propose a means to overcome the limitation of ClO4- reduction: depositing palladium nanoparticles (Pd0NPs) within the matrix of a hydrogenotrophic biofilm. Two H2-based membrane biofilm reactors (MBfRs) were operated in parallel in long-term continuous and batch modes: one system had only a biofilm (bio-MBfR), while the other incorporated biogenic Pd0NPs in the biofilm matrix (bioPd-MBfR). For long-term co-reduction, bioPd-MBfR had a distinct advantage of oxyanion reduction fluxes, and it particularly alleviated the competitive advantage of NO3- reduction over ClO4- reduction. Batch tests also demonstrated that bioPd-MBfR gave more rapid reduction rates for ClO4- and ClO3- compared to those of bio-MBfR. Both biofilm communities were dominated by bacteria known to be perchlorate and nitrate reducers. Functional-gene abundances reflecting the intracellular electron flow from H2 to NADH to the reductases were supplanted by extracellular electron flow with the addition of Pd0NPs.

Pd@MgAl LDH/2-ThCA: A sustainable, active and recyclable nanocatalyst system for the rapid and efficient catalytic reduction of organic pollutants

Catalytic reduction of toxic pollutants such as nitroaromatics and organic dyes found in water/wastewater by heterogeneous nano-structured metallic catalysts is a promising method for wastewater treatment. The need for effective and reusable catalyst systems is recently increasing due to the soaring water pollution. For this purpose, in this study, a newly Pd@MgAl LDH/2-ThCA catalyst system was successfully developed by depositing palladium nanoparticles onto a modified MgAl LDH support, characterized and then used to eliminate these contaminants in the presence of NaBH4. Catalytic applications indicated that Pd@MgAl LDH/2-ThCA catalyst efficiently reduced 2-nitroaniline (2-NA), 4-nitrophenole (4-NP), 4-nitroaniline (4-NA), and 4-nitro-o-phenylenediamine (4-NPDA) with rate constants of 0.011 s−1, 0.0075 s−1, 0.017 s−1, and 0.02 s−1, respectively. Additionally, Pd@MgAl LDH/2-ThCA successfully degraded methyl orange (MO) and rhodamine B (RhB) with rate constants of 0.019 s−1 and 0.015 s−1, respectively. Furthermore, it was found that methylene blue (MB) was immediately degraded by Pd@MgAl LDH/2-ThCA. Reusability tests revealed that Pd@MgAl LDH/2-ThCA maintained its activity/stability after the 5 successive cycles, verifying its practical application potential. This paper reveals that Pd@MgAl LDH/2-ThCA is an effective, sustainable, and alternative catalyst system for the treatment of toxic environmental pollutants.

β-Cyclodextrin-Functionalized Fe3O4-Supported Pd-Nanocatalyst for the Reduction of Nitroarenes in Water at Mild Conditions.

In this study, a novel heterogeneous catalyst (Fe3O4@β-CD@Pd) has been developed by the deposition of palladium nanoparticles on the β-cyclodextrin-functionalized surface of magnetic Fe3O4. The catalyst was prepared by a simple chemical co-precipitation method and characterized extensively by using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-optical emission spectrometry (ICP-OES) analyses. Herein, the applicability of the prepared material was evaluated for the catalytic reduction of environmentally toxic nitroarenes to the corresponding anilines. The catalyst Fe3O4@β-CD@Pd showed excellent efficiency for the reduction of nitroarenes in water under mild conditions. A low catalyst loading of 0.3 mol % Pd is found to be efficient for reducing nitroarenes in excellent to good (99-95%) yields along with high TON values (up to 330). Nevertheless, the catalyst was recycled and reused up to the 5th cycle of reduction of nitroarene without any loss of significant catalytic activity.

Improved spectral responsivity of porous silicon after the deposition of palladium nanoparticles via laser ablation at different laser energies

In this work, palladium (Pd) nanoparticles (NPs) were synthesized using laser ablation in liquids (LAL) at laser energies of 360, 660, and 800[Formula: see text]mJ and a laser wavelength of 1064[Formula: see text]nm with 200 pulses per shot. The Pd nanoparticle suspension deposited on porous silicon (PS) was investigated. X-ray diffraction (XRD) was used to determine the crystal structure. Field emission-scanning electron microscopy (FE-SEM) revealed the sponge-like structure of the PS and spherical clusters of Pd NPs within it. The optical properties of the prepared solution samples were investigated by testing the absorbance between 250–850[Formula: see text]nm, and energy gap values of ∼2.35, 2.56, and 2.75[Formula: see text]eV were calculated for the laser energies 360, 660, and 800[Formula: see text]mJ, respectively. The electrical properties, including [Formula: see text] and [Formula: see text] of the Al/PS/Si/Al and Al/Pd NPs/PS/Si/Al heterojunctions were calculated from [Formula: see text] measurements. The observed enhancement of the fabricated Pd NPs/PS is shown by the broad spectral response in the visible to near-infrared (vis-NIR) range. The increased spectral responsivity due to coating the PS surface with Pd NPs promotes using these nanostructures in photodetectors.

Supported Pd nanoparticles on micro structured chitosan-MgAl layered double hydroxide hydrogel beads as a sustainable, effective, and recyclable nanocatalyst for Heck cross-coupling reactions

In this study, a heterogeneous nano-system with sustainable, green, highly effective, and easily recoverable properties was developed through deposition of palladium nanoparticles on chitosan-MgAl layered double hydroxide hydrogel beads (CS-MgAl LDH). Full characterization of the system denoted as Pd-CS-MgAl LDH nanocatalyst was performed by various analytical techniques including FT-IR, FE-SEM, EDS, TEM, and XRD analyses. The catalytic activity of Pd-CS-MgAl LDH was then explored in Heck cross coupling reaction, and the tests confirmed that Pd-CS-MgAl LDH is an effective and useful nanocatalyst which can couple different aryl halides with yields in the range of 90–98%. Additionally, it was found that Pd-CS-MgAl LDH nanocatalyst displays higher catalytic performance compared to other reported catalysts. Moreover, Pd-CS-MgAl LDH nanocatalyst was facilely isolated and recycled for 5 successive runs without a discernible change in its performance, showing that Pd-CS-MgAl LDH has good recoverability and practical application potential.

A fine single Pd microwire H2 sensor fabricated by using a femtosecond laser for a wide detection range at room temperature.

We reported a fine H2 sensor based on single Pd microwires (SPMs) by femtosecond-laser-induced deposition of palladium nanoparticles (PdNPs), which exhibits excellent H2 sensing performance. The PdNPs with good dispersion were prepared by ultrasonic assisted one-step solution synthesis. The sensor has a wide detection range of 0.001–4.0% H2 sensing at room temperature. With the increase of the H2 concentration, the SPM sensor presents two sensing mechanisms, the formation of PdHx and hydrogen induced lattice expansion regulating the conductivity of SPMs. This fine hydrogen sensor is promising to be applied to human health monitoring, environmental air detection and other integrated intelligent devices.

Excellent stability of Pd/mpg-C3N4 in catalytic hydrodebenzylation of 2,4,6,8,10,12-Hexabenzyl-2,4,6,8,10,12- hexaazaisowurtzitane (HBIW)

The low stability and poisoning of the palladium-based catalysts in the debenzylation of HBIW elevated the cost of the hydrogenolysis, and thus restricted the application of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW). To address this problem, Pd/mpg-C3N4 was prepared by depositing palladium nanoparticles on mesoporous graphite carbon nitride (mpg-C3N4), and used for the catalytic hydrogenolysis in the conversion of HBIW to TADBIW under the atmospheric pressure. After optimizing the reaction condition and the usage amount, the highest yield of 81.7 % was obtained at 45℃ after reaction for 8 h when the ratio of palladium to HBIW was 1%. A yield of 74 % was obtained when the ratio of palladium to HBIW was 0.4 %. More importantly, Pd/mpg-C3N4 can be recycled unprecedently for three times in the conversion of HBIW to TADBIW while preserving the reasonable activity. Such results should benefit for promoting the application of HNIW and also the design of the heterogeneous catalysts for hydrodebenzylation.

Towards Size‐Controlled Deposition of Palladium Nanoparticles from Polyoxometalate Precursors: An Electrochemical Scanning Tunneling Microscopy Study

AbstractWe present a novel in situ electrochemical approach to deposit small size‐controlled palladium(0) clusters from 12‐PdII‐oxo‐metalate precursors. These clusters are formed through the reductive surface polarization of a Au(111) support. Electrochemical scanning tunneling microscopy (EC‐STM) reveals that the electrochemical reduction occurs at much lower potentials than that for simple Pd salt solutions. The resulting particles are one atomic layer high and show a narrow size distribution. Precursor mass transport limitations and preconditioning of the solid‐liquid interface at low potentials influence the obtained morphology. In particular, a concomitant reduction mechanism via formation of molecular hydrogen is discussed. The deposited clusters show the typical behavior of small metallic Pd islands in EC‐STM: The apparent cluster height increases reversibly when lowering the potential close to the onset of hydrogen evolution, which is attributed to hydrogen adsorption.

Biomass waste rice husk derived silica supported palladium nanoparticles: an efficient catalyst for Suzuki–Miyaura and Heck–Mizoroki cross-coupling reactions

Here, we report an inexpensive, versatile, and environmentally benign biomass waste rice husk derived amorphous silica-supported palladium (PdNPs/RH-SiO2) nano-catalyst for Suzuki–Miyaura and Heck–Mizoroki cross-coupling reactions. The proposed catalyst was prepared in two steps. In the first step, amorphous SiO2 obtained by calcination of rice husk and the following deposition of palladium nanoparticles by using the chemical reduction method in the second step. The physico-chemical properties of the catalysts were investigated by N2 adsorption–desorption, XRD, XPS, 29Si CP-MAS NMR, and TEM analysis. The palladium content in the catalysts has been determined by ICP-OES analysis. The 1% PdNPs/RH-SiO2 exhibited excellent catalytic performance for Suzuki–Miyaura and Heck–Mizoroki C–C cross-coupling reactions to produce biaryl and stilbene compounds with >99% selectivity and excellent TON values (529 and 524). Furthermore, the catalyst is repeatedly used for four consecutive cycles without a significant drop in the yield.

Dechlorination of 2,4-dichlorophenol in a hydrogen-based membrane palladium-film reactor: Performance, mechanisms, and model development

We created a hydrogen-based membrane palladium-film reactor (MPfR) by depositing palladium nanoparticles (PdNPs) on hollow-fiber membranes via autocatalytic hydrogenation to form a Pd-film. The MPfR was used for hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP). HDC performances and mechanisms were systematically evaluated, and a continuous-flow dechlorination model was established. Approximately 87% of the input 2,4-DCP was reduced to the end-product phenol (P), while 2-chlorophenol (2-CP) was an intermediate, but only at 2%. Selective adsorption of the 2,4-DCP onto the Pd-film and fast desorption of P facilitated efficient dechlorination. Modeling results represented well the concentrations of 2,4-DCP and its intermediates. It demonstrated three dechlorination pathways: The majority of 2,4-DCP was completely dechlorinated to P in an adsorbed state without release of monochlorphenol, some 2,4-DCP was degraded to 2-CP that was released and subsequently adsorbed and reduced to P, and a small amount was reduced to 4-CP that was released and subsequently adsorbed and reduced to P. Analysis based on Density Functional Theory suggests that the pathway of full dechlorination was dominant due to its thermodynamically favorable adsorption configuration, with both Cl atoms bonded to Pd. This study documents full dechlorination of 2,4-DCP in the MPfR and the interacting roles of adsorption and HDC.

Synthesis and Thermal Stability of Palladium Nanoparticles Supported on γ-Αl2O3

Background: Deposition of palladium nanoparticles from colloidal solution on various supports produces palladium catalysts with a predetermined size and concentration of the palladium nanoparticles, which allows to study the nanoparticle size effects and support influence on palladium catalytic properties. Objective: The goal of the present work was the development of a preparation method of systems supported on γ-Al2O3 palladium nanoparticles with a controlled size and determination of their thermal stability in oxidizing and reducing atmospheres. Methods: We demonstrated the preparation of Pd/γ-Al2O3 composite by precipitation of the size-controlled palladium nanoparticles with a narrow size distribution from colloidal solution. The composites were characterized by X-ray diffraction (XRD), and transmission electron microscope (TEM) methods. Result: The size and size distribution of the nanoparticles supported on γ-Al2O3 were found to be increasing upon precipitation due to strong Pd/γ-Al2O3 interaction. A significant enlargement of the supported nanoparticles occured at 300°C. The aggregation of the nanoparticles was observed at temperatures above 500°C resulting in an increase in their size. Conclusion: Our findings are not only applicable for the preparation of a model Pd supported on the γ-Al2O3 catalyst but could be applicable to the designing of the Pd-containing catalyst for important industrial high-temperature processes.

Methyl Salicylate Functionalized Magnetic Chitosan Immobilized Palladium Nanoparticles: An Efficient Catalyst for the Suzuki and Heck Coupling Reactions in Water

AbstractA heterogeneous catalyst was fabricated by immobilization of chitosan (CS) on magnetic Fe3O4 following the deposition of palladium nanoparticles on its modified surface. The prepared catalyst was characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDX). The catalyst was investigated for the Suzuki‐Miyaura and Heck‐Mizoroki cross‐coupling reactions and afforded arylated products with high turnover number TON (980) and turnover frequency TOF (980 h−1). The optimized catalytic system was found practical and green as catalyst loading was low (0.10 mol%), water used as solvent and the catalyst was separated with external magnet. A wide variety of aryl halides including electro withdrawing and releasing groups were investigated and found excellent to good yield of Suzuki and Heck cross‐coupled products. Furthermore, the catalyst was recovered and reused up to seven times for Suzuki coupling reactions with 97% efficiency.

Palladium nanoparticles anchored on amphiphilic Janus-type cellulose nanocrystals for Pickering interfacial catalysis.

Developing green and sustainable Pickering interfacial catalysts for organic reactions in water is of great importance to both the environment and human health. In this study, Janus-type amphiphilic cellulose nanocrystals (CNCs) were synthesized by the surface modification of hydrophilic CNCs with hydrophobic alkyl chains for efficient Pickering emulsion stabilization. Further deposition of palladium nanoparticles on amphiphilic CNCs provides catalytic activity for organic reactions in water, which occur at the interface of water and the organic reactant phase. Different reactions, hydrogenation and C-C coupling, were performed using the obtained Pickering interfacial catalyst. Excellent results were achieved in both reactions. The catalyst developed in our study is expected to advance the field of environment-friendly catalyst systems for green chemistry.

Laser-assisted preparation of Pd nanoparticles on carbon cloth for the degradation of environmental pollutants in aqueous medium.

Laser ablation in liquid (LAL), one of the attractive methods for fabrication of nanoparticles, was used for the modification of carbon cloth (CC) by deposition of palladium nanoparticles (Pd NPs); a simple stirring method was deployed to deposit Pd NPs on the CC surface. Characterization techniques viz X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) were applied to study the surface of the ensuing samples which confirmed that LAL technique managed to fabricate and deposit the Pd NPs on the surface of CC. In addition, the catalytic prowess of the carbon cloth-Pd NPs (CC/Pd NPs) was investigated in the NaBH4- or HCOOH-assisted reduction of assorted environmental pollutants in aqueous medium namely hexavalent chromium [Cr(VI)], 4-nitrophenol (4-NP), congo red (CR) and methylene blue (MB). The CC/Pd NPs system has advantages such as high stability/sustainability, high catalytic performance and easy reusability.

Pulse Electrodeposition of Palladium Nanoparticles onto Silicon in DMSO

The deposition of palladium nanoparticles (PdNPs) on the surface of n-Si (100) substrate by pulsed electrolysis in dimethyl sulfoxide (DMSO) solutions of Pd(NO3)2 was investigated. It has been shown that nonaqueous medium (DMSO) contributes the Pd (II) recovery at high cathode potential values avoiding side processes to occur. In combination with the pulse mode, this allows the deposition of spherical PdNPs with their uniform distribution on the silicon surface. We established that the main factors influencing the geometry of PdNPs are the value of the cathode potential, the concentration of palladium ions in solution, and the number of pulse-pause cycles. It is shown that with increasing Ecathode value there is a tendency to increase the density of silicon surface filling with nanoparticles. As the concentration of Pd(NO3)2 increases from 1 to 6 mM, the density of silicon surface filling with PdNPs and their average size also increase. We found that with increasing the number of pulse-pause cycles, there is a predominant growth of nanoparticles in diameter, which causes 2D filling of the substrate surface.

Deposition of palladium nanoparticles on the silicon surface via galvanic replacement in DMSO

The palladium deposition on the silicon surface has been investigated by the method of galvanic replacement in a solution of dimethyl sulfoxide. When activating by fluoride ions the spherical metal nanoparticles and their agglomerates with uniform distribution over the substrate surface are formed. The main factors influencing the geometry of nanoparticles are the palladium ions concentration, temperature and deposition time. It has been established that the concentration of reducible metal ions in the range of 1–2 mM l−1 provides the precipitation of palladium nanoparticles with the sizes up to 100 nm. The increase in temperature from 30 to 50 °C essentially increases the galvanic replacement rate, resulting in the increase of the nanoparticles size and the formation of agglomerates. The increase in replacement time leads to the enlargement of nanoparticles size without an increase in their number, indicating that the nucleation occurs predominantly in the initial period of this process.

Chemically deposited palladium nanoparticles on graphene for hydrogen sensor applications

Graphene decorated by palladium (Pd) nanoparticles has been investigated for hydrogen sensor applications. The density of Pd nanoparticles is critical for the sensor performance. We develop a new chemical method to deposit high-density, small-size and uniformly-distributed Pd nanoparticles on graphene. With this method, Pd precursors are connected to the graphene by π-π bonds without introducing additional defects in the hexagonal carbon lattice. Our method is simple, cheap, and compatible with complementary metal-oxide semiconductor (CMOS) technology. This method is used to fabricate hydrogen sensors on 3-inch silicon wafers. The sensors show high performance at room temperature. Particularly, the sensors present a shorter recovery time under light illumination. The sensing mechanism is explained and discussed. The proposed deposition method facilitates mass fabrication of the graphene sensors and allows integration with CMOS circuits for practical applications.

PH response of zwitterionic polydopamine layer to palladium deposition in the microchannel

In this study, the pH-response of the zwitterionic polydopamine layer to the palladium deposition in a capillary microchannel and the resultant catalytic performance for the nitrobenzene hydrogenation were explored. Experimental results showed that the polydoapmine layer exhibited the switchable surface charge from positive to negative with increasing the pH value. Under low K2PdCl4 concentration, the intrinsic low pH not only allowed most palladium to be deposited at the inlet region of the microchannel, but also provided more accessible sites for the anion PdCl42− deposition. Such property resulted in less palladium deposited at the outlet region because of the limited supply of the precursor and poor mass transfer, while an excellent size distribution of the deposited palladium nanoparticles at both the inlet and outlet of the microreactor was obtained. With the increase of the K2PdCl4 concentration, the increased pH value of the precursor solution aggravated the dispersity of the deposited palladium species and led to large palladium particles at the upstream of the microreactor. The gradually lowered pH value of the precursor solution along the microchannel and the large concentration gradient could directly intensify the anion PdCl42− deposition. Thus, an inverse palladium distribution between the inlet and outlet regions was observed due to the shift of surface potential from negative to positive along the microchannel. Such feature influenced both the catalytic activity and the durability for the nitrobenzene hydrogenation. The obtained results in this work are beneficial for not only the controllable metal catalyst preparation but also the improvement in the economy utilization of catalyst.

2D Materials for the Electro Oxidation of Formic Acid

In recent years Direct Formic Acid Fuel Cells (DFAFCs) have attracted interest as alternative energy sources. Formic acid is abundant as it is a by-product of multiple industrial processes and it can be obtained from the oxidation of biomass. In addition, due to the capacity to use high concentrations of fuel, DFAFCs are effective at room temperature which makes it an ideal candidate for portable energy applications and it has a low permeability, which clearly distinguishes it from other Proton Exchange Membrane Fuel Cells (PEMFCs). This allows it to generate higher power densities ~160 mW/cm2 at room temperature outperforming other liquid fuel cells such as Direct Methanol Fuel Cells (DMFCs) with power densities of ~50 mW/cm2. However, a few obstacles prevents its optimization, first the behaviour and loading of the catalytic material and second the proper selectivity of the proton exchange membrane. For this the synthesis of a new catalytic material has been carried out, by the deposition of palladium Nano-particles in graphene oxide and reduced graphene oxide, obtained by the electrochemical exfoliation of graphite in order to introduce doping agents in the graphene matrix such as nitrogen, sulphur and boron and with it improve its catalytically activity and reduce catalyst loadings in DFAFCs. To address the second obstacle hindering DFAFCs, a comparative analysis of proton exchange membranes of the Nafion family was carried out and the intrinsic conductivity, dimensional stability as well as its operational temperature was observed for its use in formic acid fuel cells. From the results obtained a high performance was observed using a polytetrafluoroethylene reinforce membrane (Nafion XL) at room temperature. The membrane displayed a higher resistance to dimensional change when exposed to a wide range of formic acid concentrations, showing a maximum increase of 10% of its planar dimension while other membranes such as Nafion 117,115 and 211 had a significantly higher increase up to 45%. Results indicated that a reinforced membrane could be more suitable for DFAFCs, not only by possessing a higher dimensional stability but also due to it having a higher hydrophobicity due to the reinforcement and the lower content of sulfonic groups present in the copolymer. These changes would address the dehydration of the membrane, a factor substantially affecting the performance of the cell.