Biogenic synthesis of palladium nanoparticles using Boswellia sarrata and their applications in cross-coupling reactions

A facile and green route for biogenic synthesis of palladium nanoparticles (PdNPs) using aqueous extract of nontoxic and renewable Boswellia sarrata leaves is reported. The as-synthesized PdNPs were systematically characterized by using ultraviolet (UV)–visible spectroscopy, X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The PdNPs were crystalline and cubic in nature with average particle size of ~6 nm and successfully employed as heterogeneous catalyst in the Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions. The PdNPs could be recycled up to five times with modest change in the catalytic activity.     

Modification of vertically aligned carbon nanotube arrays with palladium nanoparticles for electrocatalytic reduction of oxygen

A novel type of palladium nanoparticles-modified multiwalled carbon nanotubes composite-electrode with electrocatalytic activity for oxygen reduction is presented. The nanocomposite was prepared by magnetron sputtering deposition with Pd in Ar atmosphere on MWNTs, which were synthesized on Ta plates by chemical vapor deposition. Both scanning electron microscopy and transmission electron microscopy were employed to observe the surface morphology. The Pd nanoparticles, with diameters around 5 nm, are dispersed at the tips and on the sidewalls of the MWNTs. Voltammetry, amperometry and electrochemical impedance measurements were used to demonstrate the strong electrocatalytic activity of the nanocomposite in acid solution. Compared to the bare MWNT electrode, the PdNPs/MWNT nanocomposite shows a positive shift of the O₂ reduction current at onset potentials from +400 to +500 mV, a concurrent 1.5-fold increase in the O₂ reduction peak current with high stability. The successful preparation of PdNPs/MWNTs nanocomposite by magnetron sputtering deposition opens a new path for an efficient dispersion of promising nanoparticles for fuel cells and O₂ sensors.     

One-pot synthesis of highly dispersed palladium nanoparticles on acetylenic ionic liquid polymer functionalized carbon nanotubes for electrocatalytic oxidation of glucose

A facile method for one-pot synthesis of highly dispersed palladium nanoparticles on acetylenic ionic liquid polymer functionalized carbon nanotubes (PdNPs-AILP-CNTs) has been developed in this paper. The nanohybrids are prepared by polymerization of acetylenic ionic liquid monomers catalyzed by PdCl₂, which is further reduced to PdNPs by NaBH₄ on CNTs in one pot and characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and transmission electron microscopy. The electrocatalytic oxidation of glucose on the PdNPs-AILP-CNT nanohybrids is also investigated by cyclic voltammetry and chronoamperometry. The results show that the PdNPs with a particle size of around 3.5 nm disperse uniformly on CNTs, and PdNPs-AILP-CNT nanohybrids have good electrocatalytic performance for glucose oxidation.     

Highly sensitive detection of hydrogen peroxide at a carbon nanotube fiber microelectrode coated with palladium nanoparticles

We report on a carbon nanotube (CNT) fiber microelectrode coated with palladium nanoparticles (PdNPs) and enabling electrochemical sensing of hydrogen peroxide (H₂O₂). The synergistic effects of the CNT fibers (good mechanical strength and large surface area) and of the PdNPs (high electrocatalytic activity) result in a microelectrode for H₂O₂ that exhibits a 2-s response time, a detection limit as low as 2 μM, a sensitivity of 2.75 A cm^?2 M^?1, and a linear response range from 2 μM to 1.3 mM (R?=?0.9994). The sensor is also selective and not interfered by potentially competing species in biological fluids, thus representing an inexpensive but highly sensitive and selective microsensor for H₂O₂.

Recyclable Polymer‐Supported Nanometal Catalysts in Water

Two types of polymer‐supported nanometal catalysts with high catalytic activity and recyclability in water have been developed. One catalyst was composed of linear polystyrene‐stabilized metal nanoparticles (PS‐MtNPs). A palladium catalyst (PS‐PdONPs) was prepared in water by the thermal decomposition of Pd(OAc)₂ in the presence of polystyrene. The degree of immobilization of Pd, but not the size of the Pd nanoparticles, was dependent on the molecular weight and cross‐linking of the polystyrene. The PS‐PdONPs exhibited high catalytic activity for Suzuki, Heck, and Sonogashira coupling reactions in water and they could be recycled without loss of activity. Linear polystyrene was also suitable as a stabilizer for in situ generated PdNPs and PtNPs. The second catalyst was a polyion complex that was composed of poly[4‐chloromethylstyrene‐co‐(4‐vinylbenzyl)tributylammonium chloride] and poly(acrylic acid)‐stabilized PdNPs (PIC‐PdNPs). Aggregation and redispersion of PIC‐PdNPs were easily controlled by adjusting the pH value of the solution.     

Saussurea costus for sustainable and eco-friendly synthesis of palladium nanoparticles and their biological activities

Palladium nanoparticles have been evaluated as a viable candidate in the realm of biological applications due to their unique features. Saussurea costus extract was used as a stabilizing and reducing agent for the synthesis of palladium nanoparticles with average grain size of 17.6 ± 1.2 nm. The synthesized PdNPs were evaluated for their antioxidant activity, anti Alzheimer's activity, antibacterial and anticancer activities. The nanocharacterization was carried out using different spectroscopic techniques, including UV–visible spectroscopy, Transmission Electron Microscopy, Fourier Transformed Infrared spectroscopy, X-ray Diffraction analysis, X-ray Photoelectron spectroscopy, Energy Dispersive X-ray Spectroscopy, Size distribution, and Zeta potential. The characterization data explained the PdNPs mediated by S.costus extract have spherical form and are disseminated without agglomeration. FTIR and XPS supported the hypotheisis that the biomolecules of S.costus are activing as a reducing and stabilizing agents. The antioxidant activity of PdNPs was assessed using a free radical scavenging assay (DPPH) which exhibited similar results to the ABTS assay i.e. 90 μg/mL IC₅₀ value. Moreover Alzheimer's disease can easily be inhibited by S.costus@PdNPs at 400 mg/mL, with 79.23 ± 1.11 % of inhibition rate against AChE and 76.13 ± 0.43 % towards BChE. S.costus@PdNPs showed comparatively greater antibacterial activity against all four Staphylococcus aureus, Bacillus subtilis Escherichia coli and Pseudomonas aeruginosa microorganisms. Supplementary research carried out on the anti-tumor effects of the generated PdNPs using the colon cancer (HCT-116), hepatocellular carcinoma (HepG2), and breast adenocarcinoma (MCF-7) cell lines. PdNPs showed potent anticancerous activity against all the cell lines. Thus we recommend S.costus@PdNPs as a thearapeutic agent after successful clinical trails in future.     

Hydrogenation of crotonaldehyde and cinnamaldehyde catalyzed by water-soluble palladium complex

The selective hydrogenations of crotonaldehyde and cinnamaldehyde in the aqueous-benzene biphasic system were investigated using water-soluble palladium complex PdCl₂(TPPTS)₂ as catalyst. The hydrogenation rate of crotonaldehyde was higher than that of cinnamaldehyde under similar reaction conditions. The palladium complex selectively catalyzed the hydrogenation of CC bond in crotonaldehyde to form butanal (100%). On the contrary, hydrogenation of both CC and CO bonds in cinnamaldehyde occurred simultaneously, with the amount of phenylpropanal only slightly higher than that of phenylpropanol. However, the reduction of CO bond of cinnamaldehyde could be inhibited by the addition of Na₂CO₃ solution. Therefore, high selectivity to form phenylpropanal (91%) could be obtained by using Na₂CO₃ solution at pH 12.2. Other factors affecting the hydrogenation conversion and selectivity of crotonaldehyde and cinnamaldehyde were also discussed.     

A hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin in palladium nanoparticles/graphene-chitosan nanocomposite film

Thermally two-dimensional lattice graphene (GR) and biocompatibility chitosan (CS) act as a suitable support for the deposition of palladium nanoparticles (PdNPs). A novel hydrogen peroxide (H₂O₂) biosensor based on immobilization of hemoglobin (Hb) in thin film of CS containing GR and PdNPs was developed. The surface morphologies of a set of representative membranes were characterized by means of scanning electron microscopy and showed that the PdNPs are of a sphere shape and an average diameter of 50 nm. Under the optimal conditions, the immobilized Hb showed fast and excellent electrocatalytic activity to H₂O₂ with a small Michaelis–Menten constant of 16 μmol L⁻¹, a linear range from 2.0 × 10⁻⁶ to 1.1 × 10⁻³ mol L⁻¹, and a detection limit of 6.6 × 10⁻⁷ mol L⁻¹. The biosensor also exhibited other advantages, good reproducibility, and long-term stability, and PdNPs/GR–CS nanocomposites film would be a promising material in the preparation of third generation biosensor.     

Pd nanoparticles supported on reduced graphene oxide as an effective and reusable heterogeneous catalyst for the Mizoroki–Heck coupling reaction

A general method for the synthesis of palladium nanoparticles loaded on reduced graphene oxide functionalized with diethylenetriamine (PdNPs/rGO-NH₂) using a sonochemical procedure is described. The heterogeneous nanocomposite was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, thermogravimetric analysis, high-angle annular dark field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, UV–visible absorption, and inductively coupled plasma optical emission spectrometry. The PdNPs/rGO-NH₂ was very effective for the Mizoroki–Heck coupling reaction of several aryl iodide compounds with different alkenes in the presence of triethylamine. The reaction provides the coupling products in good to excellent yields (59–100%). Additionally, the PdNPs/rGO-NH₂ catalyst can be reutilized for six successive runs without any apparent diminution of its catalytic reactivity.     

Unsupported palladium nanoparticles for ethanol cyclic voltammetric sensing in alkaline media

Carbon-supported palladium nanostructures have had a recent rise in their use for ethanol oxidation applications. In this work, we present the use of unsupported palladium nanoparticles (PdNPs), synthesized by sodium borohydride chemical reduction method, for ethanol electrochemical sensing. The unsupported PdNPs were studied for ethanol oxidation in alkaline media by cyclic voltammetry, and additionally were characterized using transmission electron microscopy, and x-ray photoelectron spectroscopy. The performance of unsupported PdNP-modified glassy carbon electrodes for the electrochemical ethanol oxidation in 1.0 M potassium hydroxide (KOH) solution was studied by cyclic voltammetry. These electrochemical results demonstrated that the unsupported PdNPs have very promising catalytic activity towards the oxidation of ethanol in alkaline media with good detection performance in the concentration range of 2304 to 288 ppm (i.e., 50.00 to 6.25 mM). The detection limit and linear correlation coefficient were 49.3 ppm (1.10 mM) and 0.9998, respectively. The unsupported PdNP-modified glassy carbon electrodes presented good cyclic voltammetric stability for ethanol sensing application in alkaline media.     

An electrochemical ascorbic acid sensor based on palladium nanoparticles supported on graphene oxide

In this study, an electrochemical ascorbic acid (AA) sensor was constructed based on a glassy carbon electrode modified with palladium nanoparticles supported on graphene oxide (PdNPs-GO). PdNPs with a mean diameter of 2.6 nm were homogeneously deposited on GO sheets by the redox reaction between PdCl₄²⁻ and GO. Cyclic voltammetry and amperometric methods were used to evaluate the electrocatalytic activity towards the oxidation of AA in neutral media. Compared to a bare GC or a Pd electrode, the anodic peak potential of AA (0.006 V) at PdNPs-GO modified electrode was shifted negatively, and the large anodic peak potential separation (0.172 V) of AA and dopamine (DA), which could contribute to the synergistic effect of GO and PdNPs, was investigated. A further amperometric experiment proved that the proposed sensor was capable of sensitive and selective sensing of AA even in the presence of DA and uric acid. The modified electrode exhibited a rapid response to AA within 5 s and the amperometric signal showed a good linear correlation to AA concentration in a broad range from 20 μM to 2.28 mM with a correlation coefficient of R = 0.9991. Moreover, the proposed sensor was applied to the determination of AA in vitamin C tablet samples. The satisfactory results obtained indicated that the proposed sensor was promising for the development of novel electrochemical sensing for AA determination.     

Evaluation of antioxidative capacity via measurement of the damage of DNA using an electrochemical biosensor and an ionic liquid solvent

We report on the electrodeposition of palladium nanomaterials in choline chloride–based ionic liquid ethaline. A glassy carbon electrode (GCE) was modified with cobalt nanoparticles (acting as sacrificial templates) and a GCE modified with palladium nanoparticles (PdNPs) were fabricated and used to study the electrocatalytic oxidation of hydrazine (N₂H₄). Scanning electron microscopy revealed that the PdNP modified GCE has a uniform morphology. Zero current potentiometry was used for in-situ probing the changes in interfacial potential of the oxidation of hydrazine. An amperometric study showed that the PdNP modified GCE possesses excellent electrocatalytic activity towards N₂H₄. The modified electrode displays a fast response (<2 s), high sensitivity (74.9 μA m(mol L^?1)^?1?cm^?2) and broad linearity in the range from 0.1 to 800 μmol L^?1 with a detection limit of 0.03 μmol L^?1 (S/N?=?3).

Biosynthesis of Highly Dispersed Palladium Nanoparticles Using Astraglmanna Aqueous Extract

Biosynthesis of nanoparticles has received increased attention due to a growing need to develop environmentally benign technologies in material synthesis and employment of secondary metabolites from plant extract that has emerged as a novel technology for this purpose. In this study, a rapid and biogenic process for fabrication of palladium nanoparticles (PdNPs) is reported. Highly dispersed palladium nanoparticles were successfully prepared by using aqueous extract of Astraglmanna, a non‐toxic and eco‐friendly material, without extra surfactant, capping agent, and template. The PdNPs were characterized by using UV—Visible spectroscopy, scanning electron microscope ‐ energy dispersive spectra (SEM‐EDX), Fourier transform infra red spectroscopy (FTIR), dynamic light scattering (DLS) and X‐ray diffraction (XRD) analysis. Transmission electron microscopic (TEM) images of the PdNPs were recorded and mean size of the biosynthesized nanoparticles was found to be approximately 15 nm.     

Behavior of Palladium Nanoparticles in the Absence or Presence of Cobalt Tetraaminophthalocyanine for the Electrooxidation of Hydrazine

We report on the electrodeposition of palladium nanoparticles (PdNPs) on a glassy carbon electrode (GCE) and onto a poly‐CoTAPc‐GCE (CoTAPc=cobalt tetraamino phthalocyanine) surface. The electrodes are denoted as PdNPs‐GCE and PdNPs/poly‐CoTAPc‐GCE, respectively. PdNPs/poly‐CoTAPc‐GCE showed the best activity for the oxidation of hydrazine at the lowest potential of ?0.28 V and with the highest currents. The results were further supported by electrochemical impedance spectroscopy (EIS) which showed that there was less resistance to charge transfer for PdNPs/poly‐CoTAPc‐GCE compared to PdNPs‐GCE. The catalytic rate constant for hydrazine oxidation was 6.12×10⁸ cm³ mol^?1 s^?1 using PdNPs/poly‐CoTAPc‐GCE.     

Development of magnetic,ferrite supported palladium catalysts for 2,4-dinitrotoluene hydrogenation

Cobalt, copper, and nickel ferrite spinel nanoparticles have been synthesized by using a combination of sonochemical treatment and combustion. The magnetic nanoparticles have been used as supports to prepare ~4 wt% palladium catalysts. The ferrites were dispersed in an ethanolic solution of Pd(II) nitrate by ultrasonication. The palladium ions were reduced to metallic Pd nanoparticles, which were then attached to the surface of the different metal oxide supports. Thus, three different catalysts (Pd/CoFe₂O₄, Pd/CuFe₂O₄, Pd/NiFe₂O₄) were made and tested in the hydrogenation of 2,4-dinitrotoluene (DNT). A possible reaction mechanism, including the detected species, has been envisaged based on the results. The highest 2,4-diaminotoluene (TDA) yield (99 n/n%) has been achieved by using the Pd/NiFe₂O₄ catalyst. Furthermore, the TDA yield was also reasonable (84.2 n/n%) when the Pd/CoFe₂O₄ catalyst was used. In this case, complete and easy recovery of the catalyst from the reaction medium is ensured, as the ferrite support is fully magnetic. Thus, the catalyst is very well suited for applicationy in the hydrogenation of DNT or other aromatic nitro compounds.     

Functionalization of Reduced Graphene Oxide with β‐cyclodextrin Modified Palladium Nanoparticles for the Detection of Hydrazine in Environmental Water Samples

A sensitive and selective hydrazine sensor was developed by β‐cyclodextrin modified palladium nanoparticles decorated reduced graphene oxide (PdNPs‐β‐CD/rGO) nanocomposite. The PdNPs‐β‐CD/rGO hybrid material was prepared by simple electrochemical method. The hydrophobic cavity of β‐CD ineracts with palladium nanoparticles by hydrophobic interaction and further it is uniformly assembled on the rGO surface through hydrogen bond formation, which is clearly confirmed by FT‐IR, FESEM and TEM. The high electrocatalytic activity of hydrazine oxidation was observed at −0.05 V (vs. Ag/AgCl) on PdNPs‐β‐CD/rGO modified electrode; due to the excellent stabilization, high catalytic activity and large surface area of the PdNPs‐β‐CD/rGO composite. The PdNPs‐β‐CD/rGO fabricated hydrazine sensor exhibited an excellent analytical performance, including high sensitivity (1.95 μA μM⁻¹ cm⁻²), lower detection limit (28 nM) and a wide linear range (0.05 to 1600 μM). We also demonstrated that the PdNPs‐β‐CD/rGO nanocomposite modified electrode is a highly selective and sensitive sensor towards detection of hydrazine among the various interfering species. Hence, the proposed hydrazine sensor is able to determine hydrazine in different water samples.     

Growth of palladium nanoparticles on nanostructured highly ordered pyrolytic graphite

We report on the growth of palladium nanoparticles on the basal plane of as‐cleaved highly oriented pyrolytic graphite (HOPG) samples, and on CO₂ ion sputtered nanostructured HOPG surfaces. The morphology of Pd nanostructures grown at room temperature is investigated by scanning tunneling microscopy (STM). The STM observations indicate that the morphology of the Pd films is strongly dependent on the HOPG surface. Stabilized Pd particles only form on the sputtered surface, while ramified Pd particles decorate the clean HOPG terraces. The prestructuring of HOPG surface leads to a selective location of particles at the rim of the nanopits generated by the CO₂ ion sputtering and annealing of the surface. The correlation between size, form, density, spatial distribution of the Pd nanoparticles and the quantity of metal added on surface is discussed. We also describe trench channeling of graphite or graphene basal planes by means of Pd nanoparticles in an ambient environment. Copyright © 2014 John Wiley & Sons, Ltd.     

A facile synthesis of palladium nanoparticles supported on functional carbon nanotubes and its novel catalysis for ethanol electrooxidation

In this study, a novel material, palladium nanoparticles-carboxylic functional carbon nanotubes (PdNPs-CFCNTs), based on PdNPs supported on CFCNTs was synthesized by a facile spontaneous redox method. The material reveals high electrochemical activity and excellent catalytic characteristic for alcohol electrooxidation on a glassy carbon electrode (GCE) in an alkaline medium. The preparation mechanism was studied by the galvanic cell effect between PdCl₄²⁻ and functional defect sites on CFCNTs. Results from UV-visible absorption spectroscopy and electrochemical impedance spectroscopy revealed that the reduction of PdCl₄²⁻ to metallic Pd was successfully achieved. Morphologies of PdNPs supporting on CFCNTs (PdNPs-CFCNTs) were also characterized by transmission electron micrograph. PdNPs-CFCNTs with the best electrocatalytic characteristics were obtained under the condition as: the weight ratio of Pd to CFCNTs was kept at 2:1, the temperature was kept at 70 °C in the synthesis, and the scan rate of the applied potential was selected at 60 mV s⁻¹. The results indicate that PdNPs-CFCNTs could be a great potential material in direct ethanol fuel cells and ethanol sensors.     

A sensitive electrochemical aptasensor based on palladium nanoparticles decorated graphene–molybdenum disulfide flower-like nanocomposites and enzymatic signal amplification

In the present study, with the aggregated advantages of graphene and molybdenum disulfide (MoS₂), we prepared poly(diallyldimethylammonium chloride)–graphene/molybdenum disulfide (PDDA–G–MoS₂) nanocomposites with flower-like structure, large surface area and excellent conductivity. Furthermore, an advanced sandwich-type electrochemical assay for sensitive detection of thrombin (TB) was fabricated using palladium nanoparticles decorated PDDA–G–MoS₂ (PdNPs/PDDA–G–MoS₂) as nanocarriers, which were functionalized by hemin/G-quadruplex, glucose oxidase (GOD), and toluidine blue (Tb) as redox probes. The signal amplification strategy was achieved as follows: Firstly, the immobilized GOD could effectively catalyze the oxidation of glucose to gluconolactone, coupling with the reduction of the dissolved oxygen to H₂O₂. Then, both PdNPs and hemin/G-quadruplex acting as hydrogen peroxide (HRP)-mimicking enzyme could further catalyze the reduction of H₂O₂, resulting in significant electrochemical signal amplification. So the proposed aptasensor showed high sensitivity with a wide dynamic linear range of 0.0001 to 40 nM and a relatively low detection limit of 0.062 pM for TB determination. The strategy showed huge potential of application in protein detection and disease diagnosis.     

In situ generation of palladium nanoparticles: ligand-free palladium catalyzed ultrafast Suzuki-Miyaura cross-coupling reaction in aqueous phase at room temperature

An ultrafast and highly efficient ligand-free Suzuki-Miyaura cross-coupling reaction between aryl bromides/iodides and arylboronic acids using palladium chloride as catalyst in PEG400/H₂O in air at room temperature has been developed. TEM showed that palladium nanoparticles were generated in situ from PdCl₂/PEG400/H₂O without use of other reductants. The catalyst system can be recycled to reuse three times with good yields.