Rhenium Nanoparticles Research Articles

Waste-Derived Caffeine for Green Synthesis of Rhenium Nanoparticles with Enhanced Catalytic Activity in the Hydrogenation of 4-Nitrophenol

Yearly, thousands of tons of wasted coffee grounds are produced according to high coffee consumption. Still, after the coffee brewing, wasted coffee grounds contain some amounts of caffeine (CAF). CAF, in turn, contains multiple O and N chelating atoms in its structure. These have a potential to be reductors for complexes of metals. In this context, within the present study, a set of CAF extracts derived from coffee beans and coffee grounds were obtained and then used for the one-step reduction of ReO4− ions with no additional toxic chemicals. Within this approach, CAF was applied as a secondary, green resource for the synthesis of unique rhenium nanoparticles (ReNPs) containing Re species at 0 and +6 oxidation states. The obtained ReNPs were identified and characterized with the use of X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Further, the capping and stabilization of ReNPs by CAF were verified with the aid of Fourier transformation infrared spectroscopy (FT-IR). The so-obtained “green” ReNPs were then used as a homogenous catalyst in the catalytic hydrogenation of 4-nitrophenol (4-NP). This new nanomaterial revealed a superior catalytic activity, leading to the complete reduction of 4-NP to 4-aminophenol within 40–60 min with a first-order rate constant of 0.255 min−1.

Optimizing interactions for efficient hydrogen evolution reaction by incorporating rhenium nanoparticles on defect-rich carbon

The rich anchoring site on carbon renders it a promising support for catalytically active metal nanoparticles (NPs), thereby enhancing their intrinsic catalytic activity towards hydrogen evolution reaction (HER) through interactions between the support and the metal. However, complex synthesis conditions often compromise the synergy between the metal and support. Herein, we report Re NPs embedded on XC-72 carbon support to investigate the robust interactions in affecting the HER activity. Consequently, Re NPs anchored on defect-rich XC-72 exhibit efficient and robust HER activity in acidic conditions, achieving an extremely low overpotential of 25 mV to deliver a current density of 10 mA cm−2 and a Tafel slope of 78 mV dec−1, surpassing that of Pt/C catalyst. Based on experimental investigations and density functional theory calculations, the high catalytic activities of as-obtained Re/C can be attributed to the enhanced electron transport kinetics facilitated by the interactions between Re NPs and carbon support, the exposure of the active site on Re NPs, and lowered reaction energy barrier towards HER. This study provides valuable insights for the rational development of Re-based efficient catalysts for HER.

Multiparameter optimization of non-thermal plasma-driven synthesis of carbohydrate-stabilized rhenium nanoparticles towards enhancement of their catalytical activity for reduction of nitroaromatic compounds

This study aims to optimize the synthesis of carbohydrate-stabilized rhenium nanoparticles (ReNPs) utilizing cold atmospheric pressure plasma (CAPP), specifically direct current atmospheric pressure glow discharge (dc-APGD), hypothesizing that controlling synthesis parameters will enhance catalytic efficiency in the reduction of nitroaromatic compounds (NACs). The dc-APGD system operated in flowing liquid cathode (FLC-dc-APGD) and flowing liquid anode (FLA-dc-APGD) modes. Design of experiments (DOE) and response surface methodology (RSM) were employed for the first time to optimize ReNPs synthesis by adjustment of the concentration of ReO4- in ReNPs precursor solution, its flow rate, as well as the discharge current. ReNPs were characterized using high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), and X-Ray photoelectron spectroscopy (XPS). In turn, optical emission spectroscopy (OES) was employed for the identification of reactive species generated in the plasma phase that contributed to the synthesis of ReNPs. The resultant sizes, surface charges, and phase compositions were linked with synthesis parameters and then with catalytic activities revealed by the variety of ReNPs. HRTEM photomicrographs showed spherical and spherical-like morphologies of the obtained ReNPs synthesized using FLC-dc-APGD and FLA-dc-APGD modes with the actual sizes of 7.28 ± 2.90 nm and 3.24 ± 0.57 nm, respectively. The optimized conditions yielded ReNPs of exceptional catalytic activity, that reduced 94.9 % (FLC-dc-APGD) and 90.5 % (FLA-dc-APGD) of 4-nitrophenol (4-NP) with the apparent rate constants (k1) 0.269 and 0.107 min−1, respectively. Further, the conversions of 90 % were achieved over FLC-dc-APGD-based ReNPs for nitrobenzene (NB), 2,4,6-trinitrophenol (2,4,6-TNP), 2,4-dinitrophenol (2,4-DNP), and 4-nitroaniline (4-NA). In these cases, the k1 values were 0.235, 0.174, 0.070, 0.001 min−1, respectively. The results allowed to find a correlation between ReNP size distribution, oxidation state, and catalytic activity that suggested a potential for tailored Re nanocatalysts in environmental remediation.

Synthesis study of size-controlled rhenium nanoparticle systems using reverse micelle-based methodologies

In this study, rhenium nanoparticles were successfully synthesized with precise size control using a water-in-oil microemulsion method under an ambient atmosphere. Spectroscopic characterization using UV-Vis and ESI-MS techniques was used to study the stability of the rhenium(IV) precursor and verify its reduction into rhenium-based nanoparticles. The morphology and size of the rhenium nanoparticles were examined using HR-TEM. The results indicate formation of amorphous rhenium nanoparticles with an average size of 2.2 nm at a water-to-surfactant concentration ratio (W factor) of 10. These rhenium nanoparticles also have good size-stability compared to rhenium colloids generated in water alone. After one week, the particle diameter increased by only 0.6 nm with no evidence of aggregation. An investigation into the effect of various factors on the size and size distribution of the rhenium nanoparticles indicate that the W factor is the most influential parameter (among the considered factors) for size tuning, given that increases in W led to bigger and more polydisperse particles. Additionally, the microemulsion surfactant (AOT) protects the rhenium nanoparticles from their natural tendency to oxidize to perrhenate ion under an air atmosphere. However, a significant consideration in the use of AOT is the previously unreported presence of a chemical impurity which is able to reduce the rhenium(IV) precursor salt and generate rhenium nanoparticles within these microemulsion systems. Our investigation found that this impurity is the sulfite ion which is most likely introduced during manufacturing.

Catalytically enhanced direct degradation of nitro-based antibacterial agents using dielectric barrier discharge cold atmospheric pressure plasma and rhenium nanoparticles

The common utilization of antimicrobial agents in medicine and veterinary creates serious problems with multidrug resistance spreading among pathogens. Bearing this in mind, wastewaters have to be completely purified from antimicrobial agents. In this context, a dielectric barrier discharge cold atmospheric pressure plasma (DBD-CAPP) system was used in the present study as a multifunctional tool for the deactivation of nitro-based pharmacuticals such as furazolidone (FRz) and chloramphenicol (ChRP) in solutions. A direct approach was applied to this by treating solutions of the studied drugs by DBD-CAPP in the presence of the ReO4− ions. It was found that Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS), generated in the DBD-CAPP-treated liquid, played a dual role in the process. On the one hand, ROS and RNS led to the direct degradation of FRz and ChRP, and on the other hand, they enabled the production of Re nanoparticles (ReNPs). The produced in this manner ReNPs consisted of catalytically active Re+4, Re+6, and Re+7 species which allowed the reduction of –NO2 groups contained in the FRz and ChRP. Unlike the DBD-CAPP, the catalytically enhanced DBD-CAPP led to almost FRz and ChRP removals from studied solutions. The catalytic boost was particularly highlighted when catalyst/DBD-CAPP was operated in the synthetic waste matrix. Re-active sites in this scenario led to the facilitated deactivation of antibiotics, achieving significantly higher FRz and ChRP removals than DBD-CAPP on its own.

Thermal shock synthesis of carbon nanotubes supporting small-sized rhenium nanoparticles for efficient electrocatalytic hydrogen evolution

Thermal shock synthesis of carbon nanotubes supporting small-sized rhenium nanoparticles for efficient electrocatalytic hydrogen evolution

Rhenium anchored Ti3C2T x (MXene) nanosheets for electrocatalytic hydrogen production.

Atomically thin Ti3C2T x (MXene) nanosheets with rich termination groups, acting as active sites for effective functionalization, are used as an efficient solid support to host rhenium (Re) nanoparticles for the electrocatalytic hydrogen evolution reaction (HER). The newly designed electrocatalyst - Re nanoparticles anchored on Ti3C2T x MXene nanosheets (Re@Ti3C2T x ) - exhibited promising catalytic activity with a low overpotential of 298 mV to achieve a current density of 10 mV cm-2, while displaying excellent stability. In comparison, the pristine Ti3C2T x MXene requires higher overpotential of 584 mV to obtain the same current density. After being stored under ambient conditions for 30 days, Re@Ti3C2T x retained 100% of its initial catalytic activity for the HER, while the pristine Ti3C2T x retained only 74.8% of its initial value. According to our theoretical calculations using density functional theory, dual Re anchored MXene (Re@Ti3C2T x ) exhibits a near-zero value of Gibbs free energy (ΔG H* = -0.06 eV) for the HER, demonstrating that the presence of Re significantly enhances the electrocatalytic activity of MXene nanosheets. This work introduces a facile strategy to develop an effective electrocatalyst for electrocatalytic hydrogen production.

C-Heterogenized Re Nanoparticles as Effective Catalysts for the Reduction of 4-Nitrophenol and Oxidation of 1-Phenylethanol

Rhenium nanoparticles (Re NPs) supported on Norit (activated carbon—C) and graphene (G) were prepared by a solvothermal method under microwave irradiation (MW). The synthesised heterogeneous catalysts were characterised and tested as reduction and oxidation catalysts, highlighting their dual catalytic behaviour. In the first case, they were used, for the first time, to reduce 4-nitrophenol, in aqueous medium, under MW irradiation. Re catalysts were easily recovered by centrifugation and recycled up to six times without significant activity loss. However, the same Re catalysts in MW-assisted oxidation of 1-phenylethanol with no added solvent experienced a significant loss of activity when recycled. The higher activity of the rhenium nanoparticles supported on graphene (Re/G) catalyst in both reactions was assigned to the higher dispersion and smaller particle size of Re NPs when graphene is the support.

Rhenium nanoparticles for the delivery of HSP 90 inhibitors: A new drug delivery platform designed by molecular dynamics simulation

Owing to its degradability in vivo, the renal clearance rate of ReNPs is much higher than that of AuNPs. It is of great significant to explore the possibility of ReNPs to construct drug delivery platform. In this work, ReNPs drug delivery platform for the HSP 90 inhibitors (17-AAG and RGD) was evaluated by means of molecular dynamics simulation, and the molecular mechanism of drug release was further studied. The results indicated that ReNPs platform not only possessed good biocompatibility and stability, but also was more suitable for the delivery of HSP 90 inhibitors than AuNPs platform. This study proposed a complete solution of molecular simulation for the design and evaluation of novel nanoparticle drug platforms, which could be a convenient technical support to investigate the application of nanomaterials in biomedicine.

Employing DNA scaffold with rhenium electrocatalyst for enhanced HER activities

The replacement of Pt based catalysts for HER is still being a bottleneck and efforts have been made for finding new catalysts and here Rhenium nanoparticles (NPs) with the backing of bio-molecule deoxyribonucleic acid (DNA) was prepared as stable solutions. Depending upon the variation in the concentrations of DNA, two stable solutions namely, Re@DNA (0.055 M) and (0.083 M) were prepared. The formed Re NPs were in ultra-lesser size of 5 nm and with chain-like entities. The Re@DNA was stable as solution and directly drop-casted for electrochemical HER studies in 0.5 M H2SO4. The exploitation of DNA here as a scaffold avoids external binders and itself acted as a binder in HER studies. The HER studies revealed that for reaching 10 mA cm−2 current density, Re@DNA (0.055 M) showed lesser overpotential of 228 mV with a Tafel slope value of 137 mV/dec. Cycling study showed the activation of catalysts that is evidenced from the calculated ECSA from the post HER Cdl studies. Moreover, the overpotential required at 10 mA cm−2 was reduced to 152 mV which indicates high active nature of the Re@DNA. The post HER study revealed the stable nature of chain like structures of Re@DNA along with exposed sites after continuous cathodization.

Investigation of the activity and selectivity of supported rhenium catalysts for the hydrodeoxygenation of 2-methoxyphenol

Despite the recognized efficacy of rhenium (oxide) for promoting hydrogenolysis of the CO bond of biomass-derived oxygenates when combined with a hydrogenation metal such as Pd or Ru, the hydrogenation function of rhenium itself is relatively unexplored. Herein, we investigated the activity and selectivity of rhenium nanoparticles supported on various metal oxides for the hydrodeoxygenation of guaiacol, i.e., 2-methoxyphenol. Catalytic experiments performed at 280 °C and 20 bar H2 in a batch reactor revealed that rhenium itself adequately catalyzes the demethoxylation and dehydroxylation of guaiacol, producing completely deoxygenated products of cyclohexane/benzene. The reduced and unreduced rhenium catalysts (Re vs. ReOx) exhibited similar catalytic activity, and both bulk rhenium oxide (ReO3 and Re2O7) and supported rhenium oxide, i.e., ReOx/SiO2, were completely reduced to metallic rhenium after the reaction, suggesting that metallic rhenium is mainly responsible for the hydrogenolysis of guaiacol. Among the catalysts tested, Re/SiO2 exhibited the highest guaiacol conversion (98%) and the highest selectivity for fully deoxygenated cyclohexane (58%), followed by TiO2, Al2O3, ZrO2, and CeO2. The catalytic activity was generally correlated with the rhenium dispersion as measured by transmission electron microscopy and CO-chemisorption. Despite its high activity, sintering and leaching of rhenium occurred for SiO2 support, whereas the second most active TiO2-supported rhenium catalyst was leaching-resistant. Using Re/TiO2 as a benchmark catalyst, the effects of the rhenium loading, the mesoporosity of TiO2, and reaction conditions on the conversion of guaiacol were further explored.

Synthesis and Tribological Behavior of Metal Sulfide Nanoparticles Produced by Thermosolvolysis of Sulfur-Containing Precursors

Tetraalkylammonium molybdenum and rhenium thiometallates with different alkyl groups have been synthesized. The compounds obtained have been characterized by spectral and thermal methods. By thermosolvolysis of tetraalkylammonium thiometallates at 155–165°С in a DMF medium, particles of MoS3 and Re2S7 sulfides soluble in nonpolar hydrocarbons owing to the treatment of their surface with surfactants (alkenylsuccinimide) have been prepared. The particle size of these sulfides ranges within 8–110 nm depending on the nature of the precursor. A high friction-reducing activity of molybdenum nanoparticles in a mineral lubricating oil medium and antiwear activity of rhenium nanoparticles in mineral and synthetic lubricating oils have been shown.

Deoxydehydration of Biomass-Derived Polyols with a Reusable Unsupported Rhenium Nanoparticles Catalyst

Oxorhenium catalysts effectively transform biomass-derived polyols into corresponding alkenes via deoxydehydration (DODH) with a secondary alcohol as a hydrogen donor. This study describes the preparation of unsupported rhenium oxide nanoparticles (ReOx NPs), their use as DODH heterogeneous catalyst, and changes in the speciation and structure of Re during catalysis leading to a possible mechanism for DODH by a heterogeneous catalyst. The unsupported nanoparticles catalyze various polyols transformation to produce alkenes with high efficiency and recyclability. X-ray spectroscopy analysis shows that the structure of as-prepared ReOx NPs is similar to perrhenate with oxidation state between Re(VI) and Re(VII). Under reaction conditions and postcatalysis, the ReOx NPs are reduced by approximately two oxidation units. Kinetic isotope effect demonstrates that dissociation of a C–H bond during reduction of ReOx NPs by 3-octanol is part of the rate-determining step. Based on all experimental observations, the m...

Reactivity of Re2O7 in aromatic solvents – Cleavage of a β-O-4 lignin model substrate by Lewis-acidic rhenium oxide nanoparticles

The nature of the active species in a dehydration reaction using the “catalyst” Re2O7 is investigated. During studies on the cleavage of the β-O-4 bond of a lignin model substrate, apparent “TOFs” of 240 h−1 and good selectivities of up to 73% for the sensitive product phenylacetaldehyde (compared to other applied (Lewis) acids) are observed. However, divergent kinetic data during the studies led to an in-depth investigation on the activation mechanism of Re2O7 in the applied apolar, aprotic medium. Here, it is shown, that, in fact, Re2O7 itself is completely inactive in the dehydration reaction, but forms even at low temperatures mixed valence rhenium nanoparticles, which promote the desired reaction. The nanoparticles are characterized by XPS, DLS and TEM. In order to discriminate whether either dissolved rhenium compounds or nanoparticles are the active species, 17O NMR studies and kinetic experiments are performed. An activation mechanism of rhenium heptoxide is suggested based on a careful analysis of byproducts under catalytic conditions and application of selected potential catalysts. Furthermore, an outlook is given, as these nanoparticles might participate in numerous other catalytic reactions.

Orientation rhenium nanoparticles delivery target on human gum cancer cells, tissues and tumors under synchrotron radiation

Orientation rhenium nanoparticles delivery target on human gum cancer cells, tissues and tumors under synchrotron radiation

Activated porous carbon supported rhenium composites as electrode materials for electrocatalytic and supercapacitor applications

In this study, we developed highly dispersed rhenium nanoparticles decorated on activated carbon (Re@CDACs). The activated carbons were derived from the biomass raw materials cardamom pods (Elettaria cardamomum L) via carbonization followed by activation with ZnCl2 at high temperature. The Re NPs synthesis was achieved by decomposition of [Re2(CO)10] complex via a facile microwave thermal reduction technique. The as-prepared Re@CDACs nanocomposites were characterized by a combination of state-of-the-art techniques. The Re@CDACs nanocomposites so prepared were utilized for electrocatalytic oxidation of sunset yellow (SY) and supercapacitor applications. The Re@CDACs-modified electrodes were found to show extraordinary electrochemical performance for sensitive and selective detection of SY with a wide linear range of 0.05–390 μM and a detection limit and sensitivity of 16 nM (S/N = 3) and 91.53 μA μM−1, respectively, surpassing other modified electrodes. Moreover, these Re@CDACs catalysts were also found to exhibit a higher specific capacitance of 181 F g-1 at a current density of 1.6 A g−1 in 1.0 M H2SO4 electrolyte. The specific capacitance retention of 90% was achieved after 2500 cycles at current density 2.0 A g−1. Therefore, we have demonstrated that the Re@CDACs nanocomposite materials could be used as a promising electrode material in electrochemical oxidation of SY and energy storage applications.

Synthesis and Physicochemical Properties of Rhenium Nanoparticles

This work describes the physicochemical properties of stable rhenium nanoparticles (Re NPs) which were synthesized by the chemical and radiation–chemical methods in a reverse-micelle solution (RMS) of nanoparticles. The methods of UV-VIS spectrophotometry, fluorometry, atomic-force and transmission electron microscopies, and small-angle X-ray scattering were used. It was found that the sizes of Re NPs varied within the range from 1 to 18 nm depending on the synthesis conditions and procedures.

Synthesis and characterisation of supported Re nanoparticles for the synthesis of biofuels

Supported rhenium nanoparticles have been synthesised via wet impregnation and sol immobilisation. Deionised water was used as the solvent for both methods and the supports used were zirconia (ZrO2) and sulphated-zirconia (SO4-ZrO2). Characterisation involved BET surface area measurements, X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD showed that samples were crystalline while BET showed that nanoparticles synthesised via sol immobilisation had a higher surface area while those synthesised via impregnation had a higher pore volume and diameter. Adsorption-desorption isotherms revealed that the particles were mesoporous (2-50 nm), which is in agreement with the data obtained from TEM.

Polymer Encapsulated Self-Assemblies of Ultrasmall Rhenium Nanoparticles: Catalysis and SERS Applications

Ultrafast formation of stable and self-assembled rhenium (Re) nanoparticles (NPs) using a poly allylamine hydrochloride (PAH) scaffold within 120 s of wet-chemical reaction at room temperature in aqueous solution has been reported. The average diameters of the two different sets of Re NPs synthesized are ∼0.7 ± 0.25 and ∼1.7 ± 0.3 nm, which can be easily achieved by controlling the polymer to Re7+ molar ratio. The small-size Re NPs are formed in solution, self-assembled together to form the chain-like or necklace-like structure. The synthesized Re NPs were used in two different potential applications, such as in catalysis and in surface-enhanced Raman scattering (SERS) studies. Catalysis study was done for 4-nitroaniline (4-NA) reduction with excess NaBH4 taking two different sets of Re NPs as catalyst. The highest catalytic rate for nitroaromatics reduction ever reported of ∼1.52 × 10–1 min–1 has been observed with large-size Re NPs as catalyst. In SERS, methylene blue (MB) was used as a Raman probe molecule. Strong SERS enhancements were observed with both sets of Re NPs due to their ultrasmall size, narrow interparticle gap, and self-assembled structure in PAH scaffold. These closely tethered and self-assembled Re NPs generated more surface active “hot spots” that resulted in good SERS enhancement. The present synthesis route is easy, cost effective, and fast and can generate stable Re NPs which could further be applied in interdisciplinary fields other than catalysis and SERS in the near future.

Well-dispersed rhenium nanoparticles on three-dimensional carbon nanostructures: Efficient catalysts for the reduction of aromatic nitro compounds

Rhenium nanoparticles (ReNPs) supported on ordered mesoporous carbon (OMC) as a catalyst (Re/OMC) through a solvent-evaporation induced self-assembly (ELSA) method were prepared. The synthesized heterogonous catalyst was fully characterized using X-ray diffraction, field emission transmission electron microscopy, N2 sorption, metal dispersion, thermogravimetric analysis, Raman, Fourier-transform infrared, and X-ray photon spectroscopies. In addition, the catalyst was applied to reduce the aromatic nitro compounds (ANCs) for the first time in aqueous media and the reactions were monitored by following the intensity changes in the UV–vis absorption spectra with respect to time. This method provides the advantages of obtaining a high rate constant (k), green reaction conditions, simple methodology, easy separation and easy workup procedures. Moreover, the catalyst can be easily recovered by centrifugation, recycled several times and reused without any loss of activity. The higher activity of this catalyst was attributed to higher dispersion and smaller particle size of ReNPs as observed from FE-TEM and XRD results.