Rhodium Nanoparticles Research Articles

Novel Enzymatic Rhodium Modified Poly(styrene‐g‐oleic amide) Film Electrode for Hydrogen Peroxide Detection

AbstractNewly synthesized poly(styrene‐g‐oleic amide) was coated onto a rhodium nanoparticle modified glassy carbon (GC) surface for the fabrication of horseradish peroxidase based biosensor used for hydrogen peroxide detection. The rhodium modifed electrode presented ten times higher signal than unmodified electrode even at low elecrtroactive enzyme quantity by enhancing the electron transfer rate at the applied potential of −0.65 V. The biosensor designed by under the optimized rhodium electrodeposition time exhibited a fast response less than 5 s, an excellent operational stability with a relative standard deviation of 0.6 % (n=6), an accuracy of 96 % and a large linear range between 50 μM and 120 mM for hydrogen peroxide. Detection limit and the sensitivity parameters were calculated to be 44 μM and 57 μA mM−1 cm−2, respectively by preserving its entire initial response up to the 15 days, while only 20 % of its initial response was lost at the end of one month.

Nanotitania‐Supported Rhodium(0) Nanoparticles: Superb Catalyst in Dehydrogenation of Dimethylamine Borane

AbstractRhodium(0) nanoparticles, in situ formed from the reduction of rhodium(II) octanoate in toluene solution, are active catalyst in dehydrogenation of dimethylamine borane, however not very stable. When the same nanoparticle formation reaction is performed in the presence of nanotitania it yields the supported rhodium(0) nanoparticles (Rh(0)/nanoTiO2) with an average size of 3.17 ± 0.52 nm, which can be isolated and characterized by a combination of analytical techniques including inductively coupled plasma optical emission spectrometry (ICP‐OES), X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X‐ray (EDX), Brunauer‐Emmett‐Teller (BET) surface area measurement. Rh(0)/nanoTiO2 is highly active and long lived catalyst providing 9700 turnovers in releasing 1 equivalent H2 from dimethylamine borane over 27 h before deactivation and a record initial turnover frequency (TOF) value of 2900 h−1 in H2 generation at 60.0 ± 0.5 °C, which is the highest TOF value ever reported for dehydrogenation of dimethylamine borane using homogeneous or heterogeneous catalyst. Rh(0)/nanoTiO2 is also quite reusable catalyst preserving 57 % of the initial catalytic activity even after the fourth run of dehydrogenation reaction. This report also includes the results of kinetic study on the catalytic dehydrogenation of dimethylamine borane depending on the temperature and catalyst concentration.

Nanoalumina-supported rhodium(0) nanoparticles as catalyst in hydrogen generation from the methanolysis of ammonia borane

Rhodium(0) nanoparticles were in situ formed from the reduction of rhodium(II) octanoate and supported on the surface of nanoalumina yielding Rh(0)/nanoAl2O3 which is highly active catalyst in hydrogen generation from the methanolysis of ammonia borane at room temperature. The kinetics of nanoparticle formation can be followed just by monitoring the volume of hydrogen gas evolved from the methanolysis of ammonia borane. The evaluation of the kinetic data gives valuable insights to the slow, continuous nucleation and autocatalytic surface growth steps of the formation of rhodium(0) nanoparticles. Rh(0)/nanoAl2O3 could be isolated and characterized by a combination of advanced analytical techniques including ATR-IR, PXRD, TEM, XPS, SEM, SEM-EDX and ICP-OES. The results reveal that rhodium(0) nanoparticles are highly dispersed on the surface of nanoalumina. The particle size of Rh(0)/nanoAl2O3 increases with the initial rhodium loading of nanoalumina. Rh(0)/nanoAl2O3 is highly active catalyst in hydrogen generation from the methanolysis of AB providing an exceptional initial turnover frequency of TOF=218min−1 at 25.0±0.5°C, which is the highest value ever reported for rhodium catalysts in hydrogen generation from the methanolysis of ammonia borane.

Novel heterogeneous Rh-incorporated graphitic-carbon nitride for liquid-phase carbonylation of methanol to acetic acid

A novel heterogeneous rhodium-incorporated graphitic carbon nitride (Rh-g-C3N4) was investigated for a liquid-phase carbonylation of methanol to acetic acid (AA) to overcome disadvantages of the commercialized Rh-based homogeneous catalysts. The heterogeneous Rh-g-C3N4 catalyst showed a superior catalytic activity in a liquid-phase carbonylation with AA yield above 82% under the reaction conditions of 413K and CO pressure of 4.0MPa, where the initially formed MA intermediate can be easily hydrolyzed to form AA. A higher dispersion of the incorporated rhodium nanoparticles in the g-C3N4 matrix with a small crystallite size was responsible for a higher catalytic activity with a less leaching degree of active rhodium metals. The novel Rh-g-C3N4 with rhodium content of 1–3wt% can be a candidate to substitute the commercial homogeneous Rh complex catalyst for AA production by methanol carbonylation.

Mesoporous metallic rhodium nanoparticles

Mesoporous noble metals are an emerging class of cutting-edge nanostructured catalysts due to their abundant exposed active sites and highly accessible surfaces. Although various noble metal (e.g. Pt, Pd and Au) structures have been synthesized by hard- and soft-templating methods, mesoporous rhodium (Rh) nanoparticles have never been generated via chemical reduction, in part due to the relatively high surface energy of rhodium (Rh) metal. Here we describe a simple, scalable route to generate mesoporous Rh by chemical reduction on polymeric micelle templates [poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA)]. The mesoporous Rh nanoparticles exhibited a ∼2.6 times enhancement for the electrocatalytic oxidation of methanol compared to commercially available Rh catalyst. Surprisingly, the high surface area mesoporous structure of the Rh catalyst was thermally stable up to 400 °C. The combination of high surface area and thermal stability also enables superior catalytic activity for the remediation of nitric oxide (NO) in lean-burn exhaust containing high concentrations of O2.

2D Mapping of NMR Signal Enhancement and Relaxation for Heterogeneously Hyperpolarized Propane Gas

Hyperpolarized (HP) propane is a promising contrast agent for magnetic resonance imaging (MRI) of lungs and for studying porous media. The parahydrogen-induced polarization (PHIP) technique is a convenient approach to produce pure propane gas with enhanced proton polarization, when hydrogenation of propylene with parahydrogen is performed over heterogeneous catalysts. Here, we present a new approach of multidimensional mapping of the efficiency of pairwise parahydrogen addition using PHIP-echo pulse sequence. We use this approach to study the performance of three model heterogeneous Rh/TiO2 catalysts in the production of HP propane gas. The three catalysts with 1.0, 13.7, and 23.2 wt % of supported rhodium nanoparticles have been characterized by X-ray photoelectron spectroscopy (XPS) and high resolution transition electron microscopy (HRTEM). By varying the fractions of parahydrogen and propylene in the reactant mixture as well as the gas mixture pressure, 2D maps of PHIP-echo NMR signal and 2D maps of H...

TiO2 nanoparticles doped with Celestine Blue as a label in a sandwich immunoassay for the hepatitis C virus core antigen using a screen printed electrode

The authors describe an electrochemical immunoassay for the core antigen of hepatitis C virus (HCV). The method is based on the use of a screen-printed carbon electrode (SPCE) that was modified with a Nafion@TiO2 nanocomposite and loaded with secondary antibody (Ab2) to entrap Celestine Blue (CB). The material has architecture of the type CB/Ab2/Nafion@TiO2. A nanocomposite consisting of graphene, ionic liquid and fullerene was deposited on the SPCE first, and rhodium nanoparticles (RhNPs) were then deposited on the surface of modified electrode in order to immobilize primary antibody (Ab1). The antigen and CB/Ab2/Nafion@TiO2 were conjugated one by one to form a sandwich-type immunocomplex. The signal was obtained by differential pulse voltammetry whose intensity is related to the concentration of the antigen. The assay, if operated at a working voltage of typically 0.35 V (vs. Ag/AgCl) has a response that is linear in the 0.1 to 250 pg⋅mL−1 HCV core antigen concentration range, and the limit of detection is as low as 25 fg⋅mL−1. The assay was applied to the determination of the HCV core antigen in spiked human serum samples. In our perception, the method represents a promising platform for the detection of various antigens if appropriate antibodies are available.

Tetraphosphines with tetra(biphenyl)silane and -stannane cores as rigid scaffold linkers for immobilized catalysts

The silane Si(p-C6H4-p-C6H4Br)4 and the stannane Sn(p-C6H4-p-C6H4Br)4 have been synthesized and characterized. For the silane a single crystal X-ray structure has been obtained. Tetralithiation of the silane with nBuLi and quenching with the corresponding chlorophosphines gave the tetraphosphines Si(p-C6H4-p-C6H4PR2)4 with (R = Ph, Cy, iPr, tBu). Tetralithiation of Sn(p-C6H4-p-C6H4Br)4 led to cleavage of the Sn-C bonds. Therefore, Sn(p-C6H4-p-C6H4PPh2)4 was synthesized by Br/Li exchange of p-Br-C6H4-p-C6H4PPh2 with nBuLi and reaction with SnCl4. The silanes have been immobilized on silica by generating three phosphonium groups per molecule that were bound to the surface via strong electrostatic interactions. The remaining phosphine group was subsequently coordinated to Wilkinson's catalyst via ligand exchange. All solids have been characterized by quantitative 31P solid-state NMR spectroscopy. The catalysts, immobilized via the tetraphosphine linker scaffolds with biphenyl spacers, showed high activities and selectivities with respect to the hydrogenation of 1-dodecene. They have been recycled 9 times in a batchwise manner. All immobilized catalysts eventually formed rhodium nanoparticles that retained their catalytic activity even after being exposed to air.

Engineering Functions into Platinum and Platinum-Rhodium Nanoparticles in a One-Step Microwave Irradiation Synthesis.

Platinum (Pt) and platinum–rhodium (PtRh) nanoparticles (NPs) are active catalysts for a range of important industrial reactions, and their response has been shown to be affected by size, morphology, composition, and architectural configuration. We report herein the engineering of these functionalities into NPs by suitably modifying our single‐step fabrication process by using microwave irradiation dielectric heating. NPs with different morphologies are acquired by manipulating the reaction kinetics with the concentration of the capping agent while keeping the reaction time constant. Pt@Rh core@shell octopod‐cube, Pt‐truncated‐cube, and cube and small‐sphere NPs having “near‐monodisperse” distributions and average sizes in the range of 4 to 18 nm are obtained. By increasing the microwave time the composition of Pt@Rh can be tuned, and NPs with a Rh‐rich shell and a tunable Pt100−xRhx (x≤41 at %) core are fabricated. Finally, alloy bimetallic PtRh NPs with controlled composition are designed by simultaneous tuning of the relative molar ratio of the metal precursors and the microwave irradiation time.

Product selectivity in plasmonic photocatalysis for carbon dioxide hydrogenation

Photocatalysis has not found widespread industrial adoption, in spite of decades of active research, because the challenges associated with catalyst illumination and turnover outweigh the touted advantages of replacing heat with light. A demonstration that light can control product selectivity in complex chemical reactions could prove to be transformative. Here, we show how the recently demonstrated plasmonic behaviour of rhodium nanoparticles profoundly improves their already excellent catalytic properties by simultaneously reducing the activation energy and selectively producing a desired but kinetically unfavourable product for the important carbon dioxide hydrogenation reaction. Methane is almost exclusively produced when rhodium nanoparticles are mildly illuminated as hot electrons are injected into the anti-bonding orbital of a critical intermediate, while carbon monoxide and methane are equally produced without illumination. The reduced activation energy and super-linear dependence on light intensity cause the unheated photocatalytic methane production rate to exceed the thermocatalytic rate at 350 °C.

Adsorption and Activation of Water on Cuboctahedral Rhodium and Platinum Nanoparticles

Rh and Pt are widely used as the components in heterogeneous catalysts for multiple industrial applications. Because the metals are typically in the form of nanoparticles in real catalysts, it is important to carefully select models for the computational prediction of the catalytic properties. Here we report a first-principles study on the water activation, an important step in numerous catalytic reactions, using the finite-size Rh and Pt nanoparticle models and compare them to the extended surface models. We show that regardless of the model, adsorption and activation of water is practically identical for both metals, whereas the dissociation is energetically more favorable on Rh. The experimentally observed difference thus must be attributed to stronger interaction of dissociated water with the metal surfaces or to the presence of the oxide support. Through a selection of descriptors, we demonstrate that the extended surface models cannot fully represent the atomic and electronic structures of the small...

The Influence and Removability of Colloidal Capping Agents on Carbon Monoxide Hydrogenation by Zirconia‐Supported Rhodium Nanoparticles

AbstractBy using wet‐chemical methods, cubic, tetrahedral, and randomly shaped Rh nanoparticles (NPs) with different surface terminations were synthesized and subsequently deposited on ZrO2 supports. To guide the NP shape, three capping agents were used during the synthesis: polyvinylpyrrolidone (PVP), trimethyl(tetradecyl)ammonium bromide (TTAB), and oleylamine (OAm). TTAB and PVP could not be completely removed from the final catalyst, leaving a capping residue as confirmed by X‐ray photoelectron spectroscopy (XPS). In contrast, OAm could be fully removed. The influence of the NP shape and the influence of the capping agents were evaluated under CO hydrogenation conditions. Both the PVP and TTAB residues blocked parts of the Rh surface and dominated catalytic activity beyond the effects from NP shape and surface termination. OAm could be successfully removed. The extent of metal surface blocking by the capping residue, probed by chemisorption, is larger than the observed reduction in CO hydrogenation activity. This suggests that a majority of less‐active sites are being blocked by the capping residue and that successful removal of the residue from the most active sites is possible.

Electrochemical sensor based on rhodium nanoparticles stabilized in zwitterionic surfactant forp-coumaric acid analysis

A new sensor was developed for the analysis of phenolic compounds by coating the surface of a glassy carbon electrode (GCE) with rhodium nanoparticles stabilized in 3-(1-tetradecyl-3-imidazolium) propanesulfonate (ImS3-14), a zwitterionic surfactant. The modifier was found to lower the electron transfer resistance by enhancing the electrical conductivity on the electrode surface. Some phenolic compounds were tested to determine the increase in the electroanalytical response when employing the proposed sensor in comparison to the bare GCE. p-Coumaric acid showed the greatest peak enlargement and, thus, it was selected as the target analyte. Chronocoulometry studies indicated that the increase in the peak is due to the adsorption of the p-coumaric acid on the sensor surface. The optimized analysis conditions were obtained in acetate buffer pH 4.0 employing differential pulse voltammetry, which provided a limit of detection of 472 nmol/L. The recoveries ranged from 98.3% to 104.4%, indicating satisfactory accuracy for the proposed method. The sensor exhibited good repeatability and reproducibility (both intraday and interday) and was applied successfully in the determination of p-coumaric acid in a cellulosic matrix.

Facile synthesis rhodium nanoparticles decorated single layer graphene as an enhancement hydrogen peroxide sensor

A simple approach to develop a single layer graphene decorated with rhodium nanoparticles (RhNPs) on a flexible polyethylene terephthalate (PET) substrate is presented. The ability to control the distribution and size of the RhNPs on the CVD graphene support upon changing the electrodeposition conditions is demonstrated. The distribution of the RhNPs systematically increased with increasing of the electrodeposition time. The electrodeposition mechanism of rhodium on graphene substrates was also investigated by compared with theoretical curves for 3D progressive and instantaneous nucleation. The successful formation of the Rh decorated graphene was confirmed by scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The greatly enhanced electrocatalytic activity of the RhNPs-CVD graphene surfaces has been illustrated in connection to voltammetric and chronoamperometric measurements of hydrogen peroxide. Such CVD graphene decorated with RhNPs allows for high mass transport access and catalytic activity which provide high sensitivity and low detection limit. Based on its electrochemical enhancement, the RhNPs-CVD graphene assembly offers a promising sensing platform for next-generation flexible sensors for hydrogen peroxide or biosensors applications.

Visualization of stable ferritin complexes with palladium, rhodium and iridium nanoparticles detected by their catalytic activity in native polyacrylamide gels.

The reductive discoloration of azo dye, Congo red, catalyzed by noble metal nanoparticles was used to visualize protein-metal complexes in native polyacrylamide gels after counterstaining with Coomassie blue. This technique was used to characterize the synthesis of palladium, rhodium and iridium nanoparticles encapsulated in Pyrococcus furiosus ferritin.

N2O-emission-free exhaust remediation by Rh-NbOx nanocomposites developed from Rh3Nb alloy precursor

Metal-oxide nanocomposites comprising rhodium (Rh) nanoparticles (<50 nm) and oxygen-deficient niobium oxides (NbOx: x < 5/2) were developed from Rh3Nb alloy precursors.

Thermoregulated phase-separable rhodium nanoparticle catalyst for selective hydrogenation of α,β-unsaturated aldehydes and ketones

Highly efficient and recyclable thermoregulated phase-separable Rhnano catalysts applied for the selective hydrogenation of α,β-unsaturated aldehydes and ketones are presented.

Water as a catalytic switch in the oxidation of aryl alcohols by polymer incarcerated rhodium nanoparticles

Rh nanoparticles that were inactive in toluene, were converted into a powerful catalyst for aryl alcohol oxidation by the presence of water in the reaction media.

Green Biosynthesis of Rhodium Nanoparticles Via Aspalathus Linearis Natural Extract

Green Biosynthesis of Rhodium Nanoparticles Via Aspalathus Linearis Natural Extract This contribution report on the bio-synthesis of Rhodium metallic nanoparticles (Rh NPs) synthesized for the 1st time by a completely green process using Aspalathus linearis natural plant extract as an effective bio-oxidizing/bio-reducing agent as well as a capping compound. Their morphological, structural and optical properties were investigated using various complementary surface/interface characterization techniques such as HR-TEM, HR-SEM, EDS, XRD, XPS, UV and ATR-FTIR spectroscopy. The results confirm the formation of quais - monodisperse spherical Rh NPs in the range of 0.8-1.6 nm.

Synthesis of novel promising materials via impregnation of crosslinked polymeric networks with metal complexes in supercritical carbon dioxide

Three types of polymers, phenol-formaldehyde copolymer and polypropyleneimine and polyamidoamine dendrimers, are synthesized using the polycondensation method. Mesoporous polymeric networks are formed by treating the above dendrimers with crosslinking agents. Impregnation of polymeric networks with rhodium acetylacetonate in supercritical carbon dioxide has been carried out for the first time and its optimal conditions have been determined. Using Raman spectroscopy, it has been shown that the metal content in polymer networks falls in the range 0.3–2.0 mass % depending on the type of the polymer and the crosslinking agent and on the crosslinking degree. Polymer samples including rhodium nanoparticles have been prepared by reducing immobilized rhodium acetylacetonate with molecular hydrogen. According to the preliminary data, the resulting samples possess extremely high activity as catalysts for hydrogenation of unsaturated compounds.