Zero-valent Metal Research Articles

Plant-mediated synthesis of thermally stable metal-polystyrene nanocomposites for antioxidant and antibacterial food packaging

Annually, millions of individuals are hospitalized worldwide because of illnesses attributed to foodborne pathogens. With the surge in foodborne diseases, the importance of reliable and optimized food packaging has become more crucial than ever. Okra (Abelmoschus esculentus) seed extract was utilized as a mediator for synthesizing thermally stable nanoparticles (NPs) of Fe0, Zn0, Ag0, Fe2O3, ZnO, and Ag2O. These NPs were subsequently incorporated into polystyrene (PS) sheets to fabricate NPs-PS composites. Nanoparticle synthesis with a uniform morphology and size range of 20–60 nm was confirmed through various characterization techniques, including surface plasmon resonance, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) techniques. The antioxidant potential, as determined by the 2,2-diphenylpicrylhydrazyl (DPPH) free radical scavenging and Phosphomolybdenum assay, followed the order of Silver > Iron > Zinc. Conversely, the antimicrobial potential, evaluated through the agar well diffusion method, was in the order of Silver ≈ Zinc > Iron. Zero-valent metal NPs and NPs-PS Composites exhibited superior results compared to metal oxide NPs and NPs-PS Composites. Lemon and Apple slices wrapped in NPs-PS composite sheets exhibited significantly improved shelf life compared to pure PS, demonstrating the high effectiveness of metal NPs modified composites for food packaging by protecting it from oxidative decay and microorganisms.

Enhanced sulfamethazine degradation via peroxydisulfate activation by biochar-supported nano zero-valent iron-copper: The key role of Fe(IV) and electron transfer induced by doped Cu

The effective treatment of antibiotic wastewater is necessary to the cleaner production of many industries. Herein, a novel catalyst of biochar-supported nano zero-valent iron-copper (nZVI/Cu@BC) was synthesized, which showed more efficient activation of peroxydisulfate (PDS) for sulfamethazine (SMZ) degradation than the catalyst before nZVC doping, from 77.81% to 96.44%. And it was found to be mainly owing to the role of Fe(IV) and electron transfer induced by doped Cu. Specifically speaking, the doped Cu caused over an order of magnitude increase in Fe(IV) formation from 1.84×10−10 M to 4.75 × 10−9 M. And the more significant electron transfer between nZVI/Cu@BC, PDS and SMZ was confirmed by series electrochemical tests. In contrast, the formation of SO4·- and OH was still at a low concentration, playing a small role. The different activation mechanisms were identified to be that doped Cu provided Cu(Ⅰ)/Cu(Ⅱ) cycle to accelerate Fe(Ⅱ)/Fe(Ⅲ) cycle for enhanced PDS activation. Besides, the Fe0/Cu0 co-active sites appeared on the material surface after nZVC doping, exhibiting a stronger interaction with PDS. Therefore, nZVI/Cu@BC performed better under a wider pH range as well as complex water environment, and eliminated the toxicity of SMZ due to the nonradical-dominant process. This work provides a new insight into the rational design of nano zero-valent metals for efficient wastewater treatment to ensure cleaner production.

Microscopic evidences for intercalation of nickel and iron into layered oxysulfide La2O2S2

2D transition metal chalcogenides have been examined as versatile platforms for exotic quantum phenomena, optoelectronic and photocatalytic applications. La2O2S2, a layered oxysulfide built of [La2O2]2+ slabs and 2D arrays of [S2]2- dimers, was recently found to be a promising precursor to fabricate such 2D materials. Redox reactions with external zerovalent metals cleaved its S–S bonds, triggering intercalation of those metal guests. This process serves as a novel approach to construct 2D metal sulfides between rigid [La2O2]2+ slabs, but so far demonstrated only for Cu + cations. We herein report that the same intercalation process takes place also when Ni and Fe were used as reagents. While XRD indicated that the reactions with Ni and Fe converted La2O2S2 into the sulfur-deficient La2O2S1.5-x (0 ≤ x ≤ 0.38) phase, our TEM analyses evidenced diffusion of those metals in between [La2O2]2+ slabs at the local scale. This finding suggested the formation of 2D nickel and iron sulfides intergrown with [La2O2]2+ slabs, either as the unprecedented La–O-M-S (M = Ni, Fe) phase, or a biphasic heterostructure. In addition, our computational structure prediction also supported stability of such intergrowth [La2O2][MxS2-y] structures, encouraging future attempts to isolate those elusive 2D materials.

Bioreduction of aqueous palladium ions by Shewanella algae under atmospheric conditions

Biohydrometallurgy utilizing microorganisms capable of reducing precious metal ions to zero-valent precious metals is attracting attention as an environmentally benign process, but challenges in terms of recovery costs have hindered its practical application. In this study, we focused on addressing one of the challenges in biohydrometallurgy through the exploration of anaerobic conditions for bioreduction under the atmosphere. Interestingly, we revealed that Shewanella algae cells possess the capability to catalyze formate oxidation and reduce dissolved oxygen by pre-mixing the cell suspension with low concentrations of cytotoxic formate under atmospheric conditions. These findings indicate that bioreduction conditions can be attained without the need for anaerobic manipulation. Furthermore, we demonstrated that a 50% aqua regia leachate containing Pd(II) can be bioreduced under atmospheric condition when neutralized to pH 7 or higher. Finally, the Pd concentration following a 1-h bioreduction was determined to be 7.2 wt% for wet cells and 33 wt% for dry cells, meaning the remarkable ability of bioreduction to achieve significant Pd concentration.

Innovative Strategy for Truly Reversible Capture of Polluting Gases-Application to Carbon Dioxide.

This paper consists of a deep analysis and data comparison of the main strategies undertaken for achieving truly reversible capture of carbon dioxide involving optimized gas uptakes while affording weakest retention strength. So far, most strategies failed because the estimated amount of CO2 produced by equivalent energy was higher than that captured. A more viable and sustainable approach in the present context of a persistent fossil fuel-dependent economy should be based on a judicious compromise between effective CO2 capture with lowest energy for adsorbent regeneration. The most relevant example is that of so-called promising technologies based on amino adsorbents which unavoidably require thermal regeneration. In contrast, OH-functionalized adsorbents barely reach satisfactory CO2 uptakes but act as breathing surfaces affording easy gas release even under ambient conditions or in CO2-free atmospheres. Between these two opposite approaches, there should exist smart approaches to tailor CO2 retention strength even at the expense of the gas uptake. Among these, incorporation of zero-valent metal and/or OH-enriched amines or amine-enriched polyol species are probably the most promising. The main findings provided by the literature are herein deeply and systematically analysed for highlighting the main criteria that allow for designing ideal CO2 adsorbent properties.

Rapid mechanochemical dechlorination of hexachlorobenzene with zero-valent silicon as a novel additive: The attempt of zero-valent nonmetallic

The used of different zero-valent metals as reducing agents for dechlorination of polychlorinated biphenyl (PCB) based on mechanochemical method have been studied intensively, while few studies have been conducted on zero-valent nonmetallic reducing agents. Therefore, in this study, zero-valent silicon (ZVS), easily obtainable from photovoltaic panel waste in near future, has been used to serve the purposes as additive to dechlorinate persistent organic pollutants i.e., hexachlorobenzene (HCB). High-energy ball milling rapidly removes the passivated layer from the ZVS surface, exposing its fresh surface to release free electrons for the dechlorination of HCB at shortened time with eventually condensed amorphous carbon and hydrated silica as final products, safe to the soil. The degradation efficiency could achieve at 96.12% and dechlorination rate at 83.91% within only 60 min milling and 10% additive amount even if the concentration of HCB in simulated contaminated samples was as high as 5%. Various characterizations have been performed to fully analyze the intermediate phases and to understand the decomposition mechanism. Cyclic voltammograms (CV) curve and Tafel polarization scanning test as electrochemical evaluation method were performed to explore the involvement of electron release in the HCB remediation, for explaining the superior performance of ZVS compared to other additives based on radical dechlorination pathway. Overall, this work is expected to introduce a brand-new alternative toward practical application of mechanochemical remediation for the polluted soils, not only from environmental remediation perspective, but also the waste disposal.

Surface-Initiated Zerovalent Metal-Mediated Controlled Radical Polymerization (SI-Mt0CRP) for Brush Engineering.

ConspectusThe surface-tethered polymer brush has become a powerful approach to tailoring the chemical and physical properties of surfaces and interfaces and revealed broad application prospects in widespread fields such as self-cleaning, surface lubrication, and antibiofouling. Access to these diverse functional polymer brushes is highly dependent on versatile and powerful surface-initiated controlled radical polymerization (SI-CRP) strategies. However, conventional SI-CRP typically requires oxygen exclusion, large amounts of catalysts and monomer solution, and a long reaction time, making it time-consuming and sophisticated. When using a two-plate system consisting of an initiator-bearing substrate and a metal plate, we and our collaborators introduced surface-initiated zerovalent metal-mediated controlled radical polymerization (SI-Mt0CRP). In the SI-Mt0CRP setup, a metal(0) plate (Cu, Fe, Zn, or Sn) is placed proximately to an initiator-functionalized substrate and forms a confined polymerization system which considerably simplifies the synthesis of a wide range of polymer brushes with high grafting densities over large areas (up to the meter scale).In comparison to classical SI-ATRP (catalyzed by metal salts), SI-Mt0CRP demonstrates oxygen tolerance, high controllability, good retention of chain-end functionality, and facile recyclability of the metal catalysts (i.e., metal foil/plate). Taking advantage of the confined geometry of the SI-Mt0CRP setup, polymer brushes with various conformations and architectures are easily accessible while consuming only microliter volumes of monomer solution and without complicated operations under ambient conditions. Owing to these attractive characteristics, SI-Mt0CRP has become a versatile technique for functionalizing materials for targeted applications, ranging from the areas of surface science to materials science and nanotechnology.In this Account, we summarize the recent advances of SI-Mt0CRP catalyzed by zerovalent metals (e.g., Cu, Fe, Zn, and Sn) and highlight the intrinsic advantages of the featured experimental setup, compared with the "classical" SI-CRP in which metal salt, powder, or wire is applied. We further discuss the synthetic features and proposed mechanism of SI-Mt0CRP while emphasizing the various external technologies' (including "on water" reaction, galvanic replacement, lithography, and capillary microfluidic) integrated polymerization systems. We also describe structural polymer brushes, including block copolymers, patterned and gradient structures, and arrayed and binary polymer brushes. Finally, we introduce the diverse polymer brushes that have been prepared using these techniques, with a focus on targeted and emerging applications. We anticipate that the discussion presented in this Account will promote a better understanding of the SI-Mt0CRP technique and advance the future development of practical surface brushing.

Hexabranched dendrimers encapsulated metallic copper nanoparticles and their catalytic evaluation for the conversion of para-nitrophenol to para-aminophenol

Two new hexanuclear copper (II) complexes, [Cu6(G2hexpyD)(DMF)24](TFA)12 and [Cu6(G2hexbzaD)(DMF)18](TFA)12, where G2hexpyD and G2hexbzaD are second-generation dendrimers (G = 2) and TFA is trifluoroacetate, have been synthesized. The prepared copper (II) complexes have been fully characterized. Furthermore, to prepare dendrimer encapsulated copper nanoparticles (G2dendrimer-CuNPs), metal ions were chemically reduced by NaBH4 in 2-methoxyethanol, which yielded zero-valent metal particles with a narrow size distribution. The catalytic reduction of para-nitrophenol to para-aminophenol by G2dendrimer-CuNPs was evaluated in the presence of NaBH4. The reduction reaction was completed in 3 min. The reaction progress was monitored by electronic absorption spectroscopy. The rate constant was calculated to be 0.0073 and 0.0079 s−1 for G2hexbzaD-CuNPs and G2hexpyD-CuNPs, respectively. The results revealed that G2dendrimer-CuNPs exhibit high catalytic performance in the conversion of para-nitrophenol to para-aminophenol. Easy separation, low price, high recyclability and great efficiency are the main advantages of G2dendrimer-CuNPs that make them as the suitable catalysts for the catalytic reduction of para-nitrophenol.

Recovery of platinum group metal resources from high-level radioactive liquid wastes by non-contact photoreduction

Recovery of platinum group metals (PGMs) including palladium (Pd), rhodium (Rh), and ruthenium (Ru) from high-level radioactive liquid waste (HLLW) possesses enormous environmental and economic benefits. A non-contact photoreduction method was herein developed to selectively recover each PGM from HLLW. Soluble Pd(II), Rh(III), and Ru(III) ions were reduced to insoluble zero-valent metals and separated from simulated HLLW containing neodymium (Nd) as a representative for lanthanides, another main component in HLLW. Detailed investigation on the photoreduction of different PGMs revealed that Pd(II) could be reduced under 254- or 300-nm UV exposure using either ethanol or isopropanol as reductants. Only 300-nm UV light enabled the reduction of Rh(III) in the presence of ethanol or isopropanol. Ru(III) was the most difficult to reduce, which was only realized by 300-nm UV illumination in isopropanol solution. The effects of pH was also studied, suggesting that lower pH favored the separation of Rh(III) but hindered the reduction of Pd(II) and Ru(III). A delicate three-step process was accordingly designed to achieve the selective recovery of each PGM from simulated HLLW. Pd(II) was reduced by 254-nm UV light with the help of ethanol in the first step. Then Rh(III) was reduced by 300-UV light in the second step after the pH was adjusted to 0.5 to suppress the Ru(III) reduction. In the third step, Ru(III) was reduced by 300-nm UV light after isopropanol was added and the pH was adjusted to 3.2. The separation ratios of Pd, Rh, and Ru exceeded 99.8%, 99.9%, and 90.0%, respectively. Meanwhile, all Nd(III) still remained in the simulated HLLW. The separation coefficients between Pd/Rh and Rh/Ru exceeded 56,000 and 75,000, respectively. This work may provide an alternative method to recover PGMs from HLLW, which minimize the secondary radioactive wastes compared with other approaches.

Zero-valent metal incorporated cellulose acetate oxygen scavenging system for packaging of liquid food

Preserving packaged food from oxidative degradation is essential to improve the food quality and shelf life. This work focuses on synthesizing inexpensive zero-valent metal-incorporated polymeric films with a high oxygen scavenging rate, thus decreasing dissolved oxygen and bacterial growth. The optimal solvent for film synthesis was determined, with CADMSO films demonstrating the highest scavenging rate of 0.028 day−1. Next, zero-valent Fe, Cu, and Al nanoparticles were synthesized and incorporated into cellulose acetate films for use in active packaging. The resulting ZFe films showed the highest scavenging rate of 0.994 day−1 followed by ZCu and ZAl films with rates of 0.604 day−1, and 0.3516 day−1, respectively. Both ZFe and ZCu films exhibited potent antibacterial effects against gram-positive and gram-negative bacteria after 24 h, with reductions exceeding 99%. ZAl films showed a 99% reduction in bacterial colonies for gram-positive and a 97.5% reduction for gram-negative after 24 h. When tested with fruit juice, ZFe films exhibited the greatest scavenging capacity, achieving a 100% reduction in dissolved oxygen within 5 days. The films exhibited stability, as observed from FTIR and TGA analysis. The films' potent oxygen scavenging and bactericidal properties suggest that they may have applications as packaging agents.

Ir0/graphdiyne atomic interface for selective epoxidation.

The development of catalysts that can selectively and efficiently promote the alkene epoxidation at ambient temperatures and pressures is an important promising path to renewable synthesis of various chemical products. Here we report a new type of zerovalent atom catalysts comprised of zerovalent Ir atoms highly dispersed and anchored on graphdiyne (Ir0/GDY) wherein the Ir0 is stabilized by the incomplete charge transfer effect and the confined effect of GDY natural cavity. The Ir0/GDY can selectively and efficiently produce styrene oxides (SO) by electro-oxidizing styrene (ST) in aqueous solutions at ambient temperatures and pressures with high conversion efficiency of ∼100%, high SO selectivity of 85.5%, and high Faradaic efficiency (FE) of 55%. Experimental and density functional theory (DFT) calculation results show that the intrinsic activity and stability due to the incomplete charge transfer between Ir0 and GDY effectively promoted the electron exchange between the catalyst and reactant molecule, and realized the selective epoxidation of ST to SO. Studies of the reaction mechanism demonstrate that Ir0/GDY proceeds a distinctive pathway for highly selective and active alkene-to-epoxide conversion from the traditional processes. This work presents a new example of constructing zerovalent metal atoms within the GDY matrix toward selective electrocatalytic epoxidation.

KH570 firmly anchors Ag+/Ag0 on TiO2 nanotubes to enhance organics removal during photocatalytic activation of peroxymonosulfate

To enhance the photocatalytic activation of peroxymonosulfate (PMS), the precious metal was used to modify the catalyst. However, the catalyst suffered from metal leaching due to the oxidation of zero-valent metal into the ionic state by PMS. Herein, the silane coupling agent, KH570, was selected to fix metal Ag on the surface of TiO2 nanotubes arrays (TiO2NTAs) firmly and dispersedly. The prepared Ag/KH570/TiO2NTAs were efficient visible-light (VL) photocatalytic PMS activators for the degradation of bisphenol A (BPA). The Ag/KH570/TiO2NTAs/PMS/VL system exhibited a higher degradation rate (kobs = 0.1 min−1) and exceptional stability even after 30 cycles (0.098 min−1) compared to Ag/TiO2NTAs/PMS/VL system (0.074 and 0.015 min−1 for first and fourth use, respectively). KH570 well-dispersed Ag0 on the surface of TiO2NTAs showed significantly enhanced VL absorption, photo-generated current, and electro-transfer ability, which boosted PMS activation. The Ag0 also activated PMS and converted to Ag+, which was quickly reduced to Ag0 again by photo-generated electrons. KH570 well-immobilized Ag0/Ag+ promoted above catalytic cycles with minimal Ag leaching. Activation of PMS by the photo-generated electrons and Ag0 resulted in the generation of •OH and SO4•−, which seized the principal position for BPA removal. The wide pH adaptability and production of more oxidant in water matrixes (Cl−, HCO3−, and humic acid) enabled Ag/KH570/TiO2NTAs/PMS/VL system to exhibit excellent performance in the actual waterbodies (groundwater and tap water). This work would provide useful information in the construction of stable zero-valent metal modified catalysts for the (photo)catalytic activation of PMS/persulfate.

Electrochemical-Shock Synthesis of Nanoparticles from Sub-femtoliter Nanodroplets

ConspectusNanoparticles have witnessed immense development in the past several decades due to their intriguing physicochemical properties. The modern chemist is interested not only in methods of synthesizing nanoparticles with tunable properties but also in the chemistry that nanoparticles can drive. While several methods exist to synthesize nanoparticles, it is often advantageous to put nanoparticles on a variety of conductive substrates for multiple applications (such as energy storage and conversion). Despite enjoying over 200 years of development, electrodeposition of nanoparticles suffers from a lack of control over nanoparticle size and morphology. There have been heroic efforts to address these issues over time. With an understanding that structure-function studies are imperative to understand the chemistry of nanoparticles, new methods are necessary to electrodeposit a variety of nanoparticles with control over macromorphology and also microstructure.This Account details our group's efforts in overcoming challenges of classical nanoparticle electrodeposition by electrodepositing nanoparticles from water nanodroplets. When a nanodroplet full of metal salt precursor is incident on the electrode biased sufficiently negative to drive electroplating, nanoparticles form at a fast rate (on the order of microseconds to milliseconds). We start with the general nuts-and-bolts of the experiment (nanodroplet formation and methods for electrodeposition). The deposition of new nanomaterials often requires one to develop new methods of measurement, and we detail new measurement tools for quantifying nanoparticle porosity and nanopore tortuosity within single nanoparticles. We achieve nanopore characterization by using Focused Ion Beam milling and Scanning Electron Microscopy. Owing to the small size of the nanodroplets and fast mass transfer (the contents of a femtoliter droplet can be electrolyzed in only a few milliseconds), the use of nanodroplets also allows the electrodeposition of high entropy alloy nanoparticles at room temperature.We detail how a deep understanding of ion transfer mechanisms can be used to expand the library of possible metals that can be deposited. Furthermore, simple ion changes in the dispersed droplet phase can decrease the cost per experiment by orders of magnitude. Finally, electrodeposition in aqueous nanodroplets can also be combined with stochastic electrochemistry for a variety of interesting studies. We detail the quantification of the growth kinetics of single nanoparticles in single aqueous nanodroplets. Nanodroplets can also be used as tiny reactors to trap only a few molecules of a metal salt precursor. Upon reduction to the zerovalent metal, electrocatalysis at very small metal clusters can be probed and evaluated with time using steady-state electrochemical measurements. Overall, this burgeoning synthetic tool is providing unexpected avenues of tunability of metal nanoparticles on conductive substrates.

Effect of synthesis routes on the microstructural properties of nano zero-valent metals of Fe and Cu synthesized from the industrial copper solvent extraction process

Nano zero-valent iron (NZVI) and nano zero-valent copper (NZVC) synthesizing from the present industrial solution could be attractive due to some advantages such as preparing advanced materials through cost-effective methods and solving their disposal problems. Moreover, the present microstructural investigation probed the influence of synthesis routes used on NZVI and NZVC properties. Accordingly, the microstructural properties of nano zero-valent metals (NZVMs) synthesized through the green and chemical methods were calculated by the Rietveld method. The obtained results verified that NZVI was synthesized with titrating NaBH4 and green tea extract by chemical and green techniques from the industrial raffinate solution. NZVC was prepared from the industrial Cu-enriched solution through green and chemical techniques by titrating ascorbic acid and NaBH4, respectively. XRD and Energy Dispersive Spectroscopy (EDS) proved that NZVMs were synthesized and fairly oxidized. Microstructural studies also revealed that the amorphization degree was increased from 62.2% and 2.7% in the green NZVI and NZVC to 89.8% and 86.81% in chemically synthesized NZVI and NZVC, respectively. Considering green NZVMs, the crystallite size and unit cell were reduced in chemically synthesized NZVMs. Also, the microstrain changed from 2.79E-4% and 3.2E-3% in the green NZVI and NZVC to 2.4E-2% and 6.2E-4% in chemically synthesized NZVI and NZVC, respectively. The findings of this study indicated that the chemically synthesized NZVMs had smaller particles, crystallite size, unit cells and a higher amorphization degree, in favor of reactivity promotion and oxidation progress.

Super-Branched PdCu Alloy for Efficiently Converting Carbon Dioxide to Carbon Monoxide.

The alloying of noble metals with Cu is one of the most effective strategies for improving catalytic performance and reducing cost in electrocatalytic carbon dioxide reduction reactions (CO2RR). Previous works usually focused on the influence of morphology and composition on the catalytic activity, but lacked the study of the valence state ratio of metals and the electron transfer behavior on alloys. In this work, PdCu-2 alloy (Pd/Cu molar ratio is 1:2) was obtained by a simple one-step solvothermal method, which can effectively convert CO2 to CO with a maximum Faradaic efficiency (FE) of 85% at -0.9 V (vs. RHE). Then, the effect of the chemical state of Pd and Cu on the catalytic performance was investigated. The X-ray photoelectron spectroscopy (XPS) shows that the binding energy of Pd in PdCu alloy has a negative shift, which has affected the adsorption of key intermediates. When the proportion of oxidized state and zero-valent metal in the alloy is about 1:2, the PdCu alloy shows the best catalytic activity. In addition, the transient photovoltage (TPV) measurements further demonstrate that due to the introduction of Cu, the electron transfer rate of PdCu-2 becomes the slowest, which helps the accumulation of electrons on PdCu-2 and leads to the improvement of catalytic performance for electrocatalytic CO2RR. This work can provide more insights into the alloy catalysts of electrocatalytic CO2RR.

Towards selective synthesis of quinoxalines by using transition metals-doped carbon aerogels

Transition metal (TM)-carbon aerogels, where TM = Mo, Fe, Co or Cu, were found to be active and selective catalysts for the synthesis of quinoxalines 1, from o-phenylenediamine 2 and α-hydroxy ketones 3, becoming an efficient and sustainable alternative to other carbon-based catalysts or even MOF.Doping metal phase consisting of the corresponding metal oxides but also as zero-valent metals depending on the metal and carbonization temperature, and metal loading at the surface of carbon aerogel are key factors conditioning both reactivity and selectivity. Although metal oxides are probably the predominant active catalytic species, zero-valent metals nanoparticles (Cu0 or Co0) could be implied in the last dehydrogenation step of the reaction. Moreover, the additional functionalization with oxygenated surface groups (Co-1000PO catalyst) resulted on an enhanced reactivity probably due to the cooperation between both functions. Remarkably, Mo-500 catalyst was the most efficient sample selectively leading to the quinoxaline 1a in high conversion.Finally, our results strongly suggest different operative pathways when using TM-doped carbon aerogels depending on the metallic phase at the carbon surface. While TM-doped carbon aerogels (where TM = Fe, Co, or Cu) probably act catalyzing a sequential acid-base steps and subsequent aromatization leading to the corresponding quinoxaline 1a, Mo-doped catalyst would work via the initial oxidation of α-hydroxy ketones followed by condensation-dehydration reactions.

Exfoliation of MoS2 by zero-valent transition metal intercalation.

Exfoliation of bulk molybdenum disulfide (MoS2) into few-layered nanosheets is achieved with the assistance of zero-valent transition metal (Co0, Ni0, Cu0) intercalation. The as-prepared MoS2 nanosheets are characterized to consist of 1T- and 2H-phases with an enhanced electrocatalytic hydrogen evolution reaction (HER) activity. This work provides a novel strategy to prepare 2D MoS2 nanosheets using mild reductive reagents, which is expected to avoid the undesired structural damage from conventional chemical exfoliation.

Silver nanoparticles in electrochemical immunosensing and the emergence of silver-gold galvanic exchange detection.

Nanoparticle-based electrochemical immunosensors demonstrate high sensitivity toward biomarker detection due to the large surface area of the nanoparticles and their ability to amplify the signal of the target molecule. Additionally, they have a fast response time, relatively lower cost, and can be easily miniaturized for point-of-care applications. Among noble metals, silver nanoparticles (AgNPs) have been extensively used in electrochemical sensors due to their unique properties, such as catalytic activity and excellent electrical conductivity. This Feature Article describes six approaches for incorporating AgNPs in electrochemical platforms, featuring the most recent developments in the silver-gold galvanic exchange-based detection strategy. With a few exceptions, many of these detection methods use AgNP oxidation into Ag+ ions, followed by electrodeposition of Ag+ ions onto the working electrode as zero-valent Ag metal and a final stripping step using a voltammetric technique. Combining these steps provides desirable low detection limits and good sensitivity for various biomarkers. A few other methods involved the reduction of Ag+ ions and depositing them as Ag metal onto the electrode using a reagent mixture so that the striping analysis could be performed. Typically, this reagent mixture includes Ag+ ions, a reducing agent, or an enzyme substrate. Besides, AgNPs have also been directly used to modify the surface of electrodes to facilitate kinetically favored redox-mediated electrochemical reactions. In addition to Ag detection methods, this report will also provide recent examples to illustrate how the size and shape of AgNPs impact the detection limits and sensitivity of an electrochemical assay. Finally, we discuss recent developments in lab-on-a-chip type immunosensors designed explicitly for Ag-based metalloimmunoassay detection, and we envision that this article will provide a comprehensive summary of the operational principles and new insights into such immunoassay systems.

Vapor-phase synthesis of low-valent metal–organic frameworks from metal carbonyl synthons

We demonstrate the facile vapor-phase synthesis of a novel, porous zero-valent metal–organic framework from the reaction between volatile M(CO)6 (M = Mo, W) and 4,4'-bipyridine precursors.

One-Step Carbothermal Reduction Synthesis of Metal-Loaded Biochar Catalyst for In Situ Catalytic Upgrading of Plastic Pyrolysis Products

A novel biochar-supported metal catalyst was prepared in this study using a one-step carbothermal reduction synthesis method for the catalytic pyrolysis of plastics. Several catalysts with different metals (Cu, Fe, Ni, and Ru) loaded on three biochar supports from lignin, soybean straw, and Chlorella vulgaris were evaluated using XRD, FTIR, NH3-TPR, and TEM. Zerovalent metal nanoparticles, including Ni, Cu, and Ru, and various functional groups were observed on the biochar surface. The chemical selectivities of gasoline hydrocarbons (C4–C12 hydrocarbons) reached 76.2% with a remarkable catalytic cracking effect of Ni/lignin biochar on low density polyethylene (LDPE). Catalytic performance was comparable to that of the Ru-based catalyst, which contributed to 85.6% of gasoline hydrocarbons. The Ni/lignin catalytic cracking of plastic waste simulated by LDPE, polypropylene (PP), and polystyrene (PS) showed a maximum selectivity of 87.9% for C4–C12 hydrocarbons and yields of 78.1 mg/g for benzene, toluene, and xylene (BTX). The mechanism related to the cleavage of long chain radicals of polyethylene, polypropylene, and polystyrene as well as the aromatization of aliphatics were proposed.