Constructing high-activity electrocatalysts towards hydrogen evolution reaction (HER) is an essential way to achieve efficient, green and sustainable energy from water electrolysis. In this work, rhodium (Rh) nanoparticles anchored on cobalt (Co)/nitrogen (N)-doped carbon nanofibers (NCNFs) catalyst is prepared by the electrospinning-pyrolysis-reduction method. The synergy effect between Co-NCNFs and Rh nanoparticles contributes to the superior HER activity and favorable durability. The optimized 0.15Co-NCNFs-5Rh sample exhibits ultralow overpotentials of 13 and 18 mV to reach 10 mA cm-2 in an alkaline and acidic electrolyte, surpassing many Rh-based or Co-based electrocatalysts reported in the literature. Additionally, the Co-NCNFs-Rh sample shows a better HER activity than benchmark Pt/C catalyst in an alkaline medium at all current densities and in an acidic condition at higher current densities, offering its promising practical applications. Thus, this work provides an efficient methodology to construct high-performance HER electrocatalysts.

The purpose of this paper is to provide an in-depth review of plasmonic metal nanoparticles made from rhodium, platinum, gold, or silver. We describe fundamental concepts, synthesis methods, and optical sensing applications of these nanoparticles. Plasmonic metal nanoparticles have received a lot of interest due to various applications, such as optical sensors, single-molecule detection, single-cell detection, pathogen detection, environmental contaminant monitoring, cancer diagnostics, biomedicine, and food and health safety monitoring. They provide a promising platform for highly sensitive detection of various analytes. Due to strongly localized optical fields in the hot-spot region near metal nanoparticles, they have the potential for plasmon-enhanced optical sensing applications, including metal-enhanced fluorescence (MEF), surface-enhanced Raman scattering (SERS), and biomedical imaging. We explain the plasmonic enhancement through electromagnetic theory and confirm it with finite-difference time-domain numerical simulations. Moreover, we examine how the localized surface plasmon resonance effects of gold and silver nanoparticles have been utilized for the detection and biosensing of various analytes. Specifically, we discuss the syntheses and applications of rhodium and platinum nanoparticles for the UV plasmonics such as UV-MEF and UV-SERS. Finally, we provide an overview of chemical, physical, and green methods for synthesizing these nanoparticles. We hope that this paper will promote further interest in the optical sensing applications of plasmonic metal nanoparticles in the UV and visible ranges.

Skin and soft tissue infections (SSTIs) are among the most common bacterial infections reported in outpatients. Drug-resistant bacteria are the major cause of treatment failure and increased mortality rate in patients with SSTIs, posing significant challenges to human health. In this study, new-generation rhodium nanoplates (RhNPs) and glycol chitosan- and polydopamine-functionalized RhNPs (Rh@GCS) are developed for the treatment of drug-resistant SSTIs. RhNPs exhibited favorable antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and Ag-resistant MRSA. The modified Rh@GCS exhibited enhanced antibacterial activity and can directly kill various drug-resistant bacteria by increasing the permeability of cell membranes, including gram-positive MRSA and gram-negative multidrug-resistant Escherichia coli (E.coli) and Pseudomonas aeruginosa (PA). Moreover, Rh@GCS effectively inhibited bacterial growth and promoted the healing of skin lesions in MRSA-induced SSTI mouse models. These results suggest that Rh@GCS is a promising nonantibiotic antimicrobial agent for the treatment of drug-resistant SSTIs.

Lateral flow immunoassay (LFIA) is one of the most widely used tools for analysis and field measurement and has the advantages of high efficiency, simple operation, portability, and low cost. Therefore, in this study, we designed a proof-of-concept of LFIA based on rhodium nanoparticles and investigated its improvement by further introducing the tetramethyl benzidine and H2O2 mixture as the substrate to trigger the color reaction. The proposed methods were qualitative research by the naked eye and quantitative measurement by a smartphone and software. Under the optimal condition, the detection of ferritin was successfully established with the limit of detection of 0.3 ng/mL. The lowest visually detectable amount was 0.05 ng/mL. To verify the performance of the RhNPs-LFIA, three spiked serum samples were tested, and the recovery rate increased from 88.9 to 129.9%, revealing that the proposed methods were applicable and practically reliable for testing serum samples. The developed RhNP-based LFIA is highly sensitive and convenient, which provides a promising technology for accurate, rapid, high sensitivity, and high screening detection of ferritin in clinical diagnosis.

Rhodium nanoparticles have recently been described as promising photosensitizers due to their low toxicity in the absence of near-infrared irradiation, but their high cytotoxicity when irradiated. Irradiation is usually carried out with a laser source, which allows the treatment to be localized in a specific area, thus avoiding undesirable side effects on healthy tissues. In this study, a multi-omics approach based on the combination of microarray-based transcriptomics and mass spectrometry-based untargeted and targeted metabolomics has provided a global picture of the molecular mechanisms underlying the anti-tumoral effect of rhodium nanoparticle-based photodynamic therapy. The results have shown the ability of these nanoparticles to promote apoptosis by suppressing or promoting anti- and pro-apoptotic factors, respectively, and by affecting the energy machinery of tumor cells, mainly blocking the β-oxidation, which is reflected in the accumulation of free fatty acids and in the decrease in ATP, ADP and NAD+ levels.

Morphologically controllable synthesis of Rh nanoparticles (NPs) was achieved by the use of additives during polyol synthesis. The effect of salts and surfactant additives including PVP, sodium acetate, sodium citrate, CTAB, CTAC, and potassium bromide on Rh NPs morphology was investigated. When PVP was used as the only additive, trigonal NPs were obtained. Additives containing Br- ions (CTAB and KBr) resulted in NPs with a cubic morphology, while those with carboxyl groups (sodium citrate and acetate) formed spheroid NPs. The use of Cl- ions (CTAC) resulted in a mixture of polygon morphologies. Cytotoxicity of these NPs was evaluated on macrophages and ovarian cancer cell lines. Membrane integrity and cellular activity are both influenced to a similar extent, for both the cell lines, with respect to the morphology of Rh NPs. The cells exposed to trigonal Rh NPs showed the highest viability, among the NP series. Particles with a mixed polygon morphology had the highest cytotoxic impact, followed by cubic and spherical NPs. The Rh NPs were further demonstrated as contrast agents for X-ray fluorescence computed tomography (XFCT) in a small-animal imaging setting. This work provides a detailed route for the synthesis, morphology control, and characterization of Rh NPs as viable contrast agents for XFCT bio-imaging.

Magnetically separable catalysts attract considerable attention in catalysis due to their facile separation from the reaction medium. This propensity is crucial for efficient multiple use of precious noble metal nanoparticles in catalysis. In fact, the isolation of catalysts from the reaction medium by filtration and washing results usually in the loss of huge amount of activity in the subsequent run of catalysis. Although many transition metal nanoparticle catalysts have been reported for the H2 generation from the hydrolysis of ammonia borane, there is no study reporting the magnetically separable rhodium based catalysts for the hydrolytic dehydrogenation of ammonia borane. Here, we report the preparation of rhodium(0) nanoparticles supported on the surface of Fe3O4 and CoFe2O4 magnetic nanopowders as the first example of magnetically separable rhodium nanocatalysts. The resulting magnetically separable Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles are highly active, long-lived and reusable catalysts in H2 generation from the hydrolysis of ammonia borane providing a turnover frequency value of 273 and 720  min-1, respectively, at 25.0 ± 0.1 °C. These magnetically separable catalysts show high reusability and long-term stability in the hydrolysis reaction. They retain their complete initial activity even after the 5th use releasing exactly 3.0 equivalent H2 gas per mole of ammonia borane. The long-term stability tests show that Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles provide a total turnover number of 125,000 and 245,000, respectively, in releasing H2 from the hydrolysis of ammonia borane at room temperature. The long term stability and reusability of magnetically separable Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles make them attractive catalysts for hydrogen generation in fuel cell applications.

An in situ and facile nanocasting procedure has been developed to embed Rhodium nanoparticles (RhNPs) in mesoporous carbon (MC) matrix via carbonizing β-Cyclodextrin capped RhNPs (β-CDs@RhNPs) as a source of both carbon and metal, in the presence of SBA-15 as hard template. Firstly, β-CDs was used to coat and stabilize the RhNPs, and then coated RhNPs was applied as carbon source during the carbonization step. In this way, biocompatible materials are used as much as possible. The transmission electron microscopy, field emission scanning electron microscopy, Fourier transform infrared, BET surface area and X-ray diffraction devices were used to characterize the nanomaterials. The nanocomposite (RhNPs-MC) was casted on the glassy carbon electrode (GCE) to fabricate an electrochemical sensor (RhNPs-MC/GCE). This sensor shows high efficiency toward simultaneous determination of Morphine (Mp) and Buprenorphine (Bp), electrochemically, what other modified electrodes cannot do. For Mp, the linear range and limit of detection were obtained 0.1-20 μM and 40 nM, respectively, and these data were obtained about 0.1-14 μM and 45 nM for Bp determination. Less steps of synthesis, biocompatibility and facility are the major advantages of the process, and some benefits of the sensor are its separate signals, fast response time, sensitivity, and simple use without need for pretreatment.

Hyperpolarization techniques are key to extending the capabilities of MRI for the investigation of structural, functional and metabolic processes in vivo. Recent heterogeneous catalyst development has produced high polarization in water using parahydrogen with biologically relevant contrast agents. A heterogeneous ligand-stabilized Rh catalyst is introduced that is capable of achieving 15 N polarization of 12.2±2.7 % by hydrogenation of neurine into a choline derivative. This is the highest 15 N polarization of any parahydrogen method in water to date. Notably, this was performed using a deuterated quaternary amine with an exceptionally long spin-lattice relaxation time (T1 ) of 21.0±0.4 min. These results open the door to the possibility of 15 N in vivo imaging using nontoxic similar model systems because of the biocompatibility of the production media and the stability of the heterogeneous catalyst using parahydrogen-induced polarization (PHIP) as the hyperpolarization method.

In plasmon-enhanced heterogeneous catalysis, illumination accelerates reaction rates by generating hot carriers and hot surfaces in the constituent nanostructured metals. In order to understand how photogenerated carriers enhance the nonthermal reaction rate, the effects of photothermal heating and thermal gradients in the catalyst bed must be confidently and quantitatively characterized. This is a challenging task considering the conflating effects of light absorption, heat transport, and reaction energetics. Here, we introduce a methodology to distinguish the thermal and nonthermal contributions from plasmon-enhanced catalysts, demonstrated by illuminated rhodium nanoparticles on oxide supports to catalyze the CO2 methanation reaction. By simultaneously measuring the total reaction rate and the temperature gradient of the catalyst bed, the effective thermal reaction rate may be extracted. The residual nonthermal rate of the plasmon-enhanced reaction is found to grow with a superlinear dependence on illumination intensity, and its apparent quantum efficiency reaches ∼46% on a Rh/TiO2 catalyst at a surface temperature of 350 °C. Heat and light are shown to work synergistically in these reactions: the higher the temperature, the higher the overall nonthermal efficiency in plasmon-enhanced catalysis.