Nanoporous platinum–cobalt alloy for electrochemical sensing for ethanol,hydrogen peroxide,and glucose

Nanoporous platinum–cobalt (NP–PtCo) alloy with hierarchical nanostructure is straightforwardly fabricated by dealloying PtCoAl alloy in a mild alkaline solution. Selectively etching Al resulted in a hierarchical three-dimensional network nanostructure with a narrow size distribution at 3 nm. The as-prepared NP–PtCo alloy shows superior performance toward ethanol and hydrogen peroxide (H₂O₂) with highly sensitive response due to its unique electrocatalytic activity. In addition, NP–PtCo also exhibits excellent amperometric durability and long-term stability for H₂O₂ as well as a good anti-interference toward ascorbic acid, uric acid, and dopamine. The hierarchical nanoporous architecture in PtCo alloy is also highly active for glucose sensing electrooxidation and sensing in a wide linear range. The NP–PtCo alloy holds great application potential for electrochemical sensing with simple preparation, unique catalytic activity, and high structure stability.     

Surface and interface engineering in transition metal–based catalysts for electrochemical water oxidation

A tremendous effort has been provided in last two decades to develop efficient transition metal–based heterogeneous catalysts for the electrochemical water oxidation. Several approaches such as composition modulation, heteroatom doping, morphological development, particle size tuning, surface area enhancement, and control over electronic structure have been explored for the designing of the materials with improved water oxidation activity. As the electrochemical process is a surface phenomenon, surface structure plays a crucial role in controlling the water oxidation activity. Rational engineering of the catalyst surface by composition modulation, crystal facet tuning, and generating functional overlayer has been reported to enhance the water oxidation activity. Heteroatom doping, cationic and anionic deficiencies, and ultrathin 2D morphology are also found to promote electrochemical performance. In addition, engineering in the interface provides intrinsic improvement of the catalytic activity and stability for the electrochemical water oxidation. Although, surface and interface engineering of the catalyst has come out as the major factors in the electrochemical water oxidation, no dedicated review is available in this field. In this review, we have described the strategies of improving water oxidation activity of the catalysts by surface and interface engineering. The progress in this field discussed in detail; the challenges have been identified and addressed to attain a clear understanding in this field.     

Cerium oxide nanofiber–based electrochemical immunosensor for detection of sepsis in biological fluid

Sepsis causes life-threatening complications with the highest burden of death and medical expenses in hospitals worldwide. Despite the progression of targeted therapies for sepsis, the challenge of early diagnosis of sepsis-related biomarkers remains. The analysis of the TNF-α and sTREM-1 in biological fluids provides essential information for effective treatments. In this work, we report developing an electrochemical immunosensor for the rapid detection of TNF-α and sTREM-1 proteins in human plasma samples. First, using the electrospinning process, cerium oxide nanofibers were synthesized. Subsequently, the antibodies corresponding to the targeted proteins are immobilized onto the surface-functionalized working electrodes using NHS/EDC chemistry. The proposed immunosensor’s performance in a biological fluid was assessed using an analytical electrochemistry approach. The limit of detection for the electrochemical immunosensors was 0.51 and 0.41 pg/mL for TNF-α and sTREM-1, respectively, with high selectivity and sensitivity for the use as a point of care device.

     

Ferrocene containing N-tosyl hydrazones as optical and electrochemical sensors for Hg2+, Cu2+ and F− ions

Ferrocene containing N-tosyl hydrazones as selective and sensitive optical and electrochemical chemosensors were synthesized and characterized by ¹H NMR, ¹³C NMR, ESI-MS and X-ray analysis. The cation and anion binding studies were carried out using various techniques including electrochemistry, UV–vis and ¹H NMR spectroscopy. Chemosensors 2a and 2b have shown excellent selective recognition toward Hg²⁺, Cu²⁺ and F^? through optical and electrochemical signals. The color of 2a and 2b in solution changed visibly from pale yellow to red upon addition of Hg²⁺ion, while the color of solution changed from pale yellow to yellow green upon addition of Cu²⁺, which can be easily detected by the naked eye.     

Structure and electrochemical performance of nanostructured Sn–Co alloy/carbon nanotube composites as anodes for lithium ion batteries

Nanoparticles of Sn–Co alloy were deposited on the surface of multi-walled carbon nanotubes (CNTs) by reductive precipitation of solution of chelating metal salts within a CNTs suspension. The Sn–Co/CNTs nano-composite revealed a high reversible capacity of 424 mA h g^?1 and stable cyclic retention at 30th cycle. The improvement of reversible capacity and cyclic performance of the Sn–Co/CNTs composite is attributed to the nanoscale dimension of the Sn–Co alloy particles and the network of CNTs. Inactive Co as glue matrix of Sn prevents the possible pulverization of nanosized alloy particles. The CNTs could be pinning the Sn–Co alloy particles on their surfaces so as to hinder the agglomeration of Sn–Co alloy particles, while maintaining electronic conduction as well as accommodating drastic volume change during Li insertion and extraction reactions.     

Pt–M (M=Fe,Co, Ni and Cu) electrocatalysts synthesized by an aqueous route for proton exchange membrane fuel cells

Nanostructured Pt–M (M=Fe, Co, Ni, and Cu) alloy catalysts synthesized by a low temperature (70 °C) reduction procedure with sodium formate in aqueous medium have been investigated for oxygen reduction in sulfuric acid and as cathodes in single proton exchange membrane fuel cells (PEMFC). The Pt–M alloy catalysts show improved catalytic activity towards oxygen reduction compared to pure platinum. Among the various alloy catalysts investigated, the Pt–Co catalyst shows the best performance with the maximum catalytic activity and minimum polarization occurring at a Pt:Co atomic ratio of around 1:7. While mild heat treatments at moderate temperatures (200 °C) improve the catalytic activity due to a cleaning of the surface oxides, annealing at elevated temperatures (900 °C) degrade the activity due to an increase in particle size.     

Fe–Co/sulfonated polystyrene as an efficient and selective catalyst in heterogeneous Baeyer–Villiger oxidation reaction of cyclic ketones

A highly efficient catalyst Fe–Co/sulfonated polystyrene (Fe–Co/SPS) was introduced and synthesized, which catalyzed BV oxidation of ketones with aqueous hydrogen peroxide to give the corresponding lactones in high yield and selectivity. Solid acid catalyst of Fe–Co/SPS has been prepared by using the 98-wt% sulfuric acid as the sulfonating agent and CoCl₂ combined FeCl₃ as sources of metal ions. Various physical–chemical characterizations including FT-IR, XRD, SEM and TGA, revealed that bimetallic ions Fe³⁺–Co²⁺ species in the sulfonated polystyrene framework were responsible for the catalytic activities. The BV reaction catalyzed by Fe–Co/SPS highlighted the special effects between metal ions and protonic acids as well as solvent-free heterogeneous catalytic oxidation with excellent conversion.     

Preparation of an ultrafiltration membrane from the copolymer of acrylonitrile–glycidylmethacrylate utilized for immobilization of glucose oxidase

Ultrafiltration membrane has been prepared from the copolymer of acrylonitrile–glycidylmethacrylate and the porosity of the membrane was studied. The asymmetric structure was proved by scanning electron microscopy. The basic characteristics of the membrane were measured – water permeability, water content, membrane selectivity, etc. The membrane obtained was used as a carrier for immobilization of glucose oxidase. The immobilization was carried out covalently by two methods: direct bonding of the enzyme and indirectly by a spacer (hexamethylenediamine) and cross-linking agent (glutar aldehyde). The amount of bound protein and relative activity of the immobilized glucose oxidase were determined. Temperature optimum, pH optimum and storage stability of the immobilized glucose oxidase were determined. It was proved that glucose oxidase immobilized by the direct method shows better characteristics compared with the indirect method.     

Fe–N/C nanofiber electrocatalysts with improved activity and stability for oxygen reduction in alkaline and acid solutions

Fe–N/C nanofiber (Fe–N/CNF) electrocatalysts were prepared by impregnating electrospun polyacrylonitrile nanofibers with iron nitrate (Fe(NO₃)₃) solution and subsequent heat treatment, exhibiting improved activity and stability during oxygen reduction reaction (ORR) both in 0.1 M KOH (pH?=?13) and 0.5 M H₂SO₄ (pH?=?0) electrolyte solutions. Higher treatment temperature and NH₃ atmosphere were preferred by the Fe–N/CNF catalysts, and especially the concentration of Fe(NO₃)₃ solution exerted great effects on the surface morphology, structure, and thus electrocatalytic performance of the catalysts. The Fe–N/CNFs prepared using 0.5 wt% Fe(NO₃)₃ solution showed relatively higher ORR activity in alkaline and acid solutions and better stability especially in 0.5 M H₂SO₄ solution than the catalyst without Fe, probably because Fe could promote the graphitization of the polymer-converted carbon species, enhancing the resistance to electrochemical oxidation and thus the stability of the Fe–N/CNF catalysts.     

Six new lanthanide metal–organic frameworks as luminescent sensors for the detection of 1-N,TDGA, UA,and HA in urine

Abstract

The hydrothermal reaction of Ln(NO₃)₃·6H₂O with H₂tyia (H₂tyia = 5-(triazol-1-yl) isophthalic acid) afforded the lanthanide organic frameworks (Ln-MOFs), [Eu₂(tyia)₃(H₂O)₃]_n (1) and {[Ln₂(tyia)₃·(H₂O)₃]· 3H₂O}_n (Ln?=?Tb 2, Dy 3, Sm 4, Gd 5, and Nd 6). Compounds were characterized by routine methods: PXRD, elemental analysis, solid-state luminescence properties analysis, TGA, FT-IR, and single-crystal X-ray crystallography. In this work, the luminescent properties of 2, 4, 5, and 6 and the responsiveness of various chemical components contained in urine were investigated. These MOFs detect 1-naphthol (1-N), urinary thiodiglycolic acid (TDGA), uric acid (UA), and hippuric acid (HA), which are the final metabolites of carbaryl, vinyl chloride monomers, purine, and toluene, respectively. These new Ln-MOFs offer the potential for biomarkers or metabolic sensors and show excellent selective and sensitive luminescence detection of 1-N, TDGA, UA, and HA.     

Recent developments in Pt–Co catalysts for proton-exchange membrane fuel cells

Development of Pt-based oxygen reduction reaction catalysts with high efficiency and high durability is central to the application of proton-exchange membrane fuel cell systems. Pt–Co bimetallic catalysts have drawn extensive attention owing to their capability of delivering high performance and long lifetime for fuel cell applications including light-duty and heavy-duty vehicles. However, further improvements in durability and performance are needed to meet market requirements. To fully exploit the potential of Pt–Co catalysts, new insights into the relationship between catalyst properties and fuel cell performance and durability are needed, and more effective methods to tailor the features of Pt–Co catalysts need to be developed. This review provides a summary and perspective on recent efforts, including work on customizing the Pt shell and Pt:Co ratio, tailoring the crystal structure, and improving carbon support properties, with a particular emphasis on mechanisms leading to enhancement of mass activity, power density, and durability in membrane electrode assembly testing.     

Pd–Co alloy as an efficient recyclable catalyst for the reduction of hazardous 4-nitrophenol

Research on Chemical Intermediates - Palladium–Cobalt (Pd–Co) alloys with different atomic ratios were synthesized successfully by borohydride-assisted chemical reduction method....     

Preparation and electrochemical performance of graphene–Pt black nanocomposite for electrochemical methanol oxidation

This work reports the preparation, characterization, and electrocatalytic characteristics of a new metallic nanocatalyst. The catalyst, Pt black–graphene oxide (Pt-GO), was prepared by deposition of Pt black on the surface of graphene oxide nanosheet and characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and voltammetry. The Pt-graphene (Pt-GR) composite modified glassy carbon electrode (Pt-GR/GCE) was prepared with cyclic voltammetric scanning of Pt-GO/GCE in the potential range from ?1.5 to 0.2 in 0.1 M phosphate buffer solution at 50 mV·s^?1 for 5 cycles. The electrocatalytic properties of the Pt-GR/GCE for methanol (CH₃OH) oxidation have been investigated by cyclic voltammetry (CV); high electrocatalytic activity of the Pt-GR/GCE can be observed. This may be attributed to the high dispersion of Pt catalyst and the particular properties of GR support. The long-term stability of Pt-GR composite was investigated in 0.05 M CH₃OH in 0.1 M H₂SO₄ solution. It can be observed that the peak current decreases gradually with the successive scans. The loss may result from the consumption of methanol during the CV scan. It also may be due to the poisoning organic compounds. The results imply that the Pt-GR composite has good potential applications in fuel cells.     

ZrIV metal–organic framework based on terephthalic acid and 1,10-phenanthroline as an adsorbent for solid phase extraction of tetracycline antibiotics

Zr^IV metal–organic framework based on terephthalic acid and 1,10-phenanthroline has been prepared by solvothermal method. The product represents an effective adsorbent for solid phase extraction of tetracycline antibiotics from aqueous media.     

Paper-like free-standing polypyrrole and polypyrrole–LiFePO4 composite films for flexible and bendable rechargeable battery

Highly flexible, paper-like, free-standing polypyrrole and polypyrrole–LiFePO₄ composite films were prepared using the electropolymerization method. The films are soft, lightweight, mechanically robust and highly electrically conductivity. The electrochemical behavior of the free-standing films was examined against lithium counter electrode. The electrochemical performance of the free-standing pure PPy electrode was improved by incorporating the most promising cathode material, LiFePO₄, into the PPy films. The cell with PPy–LiFePO₄ composite film had a higher discharge capacity beyond 50 cycles (80 mA h/g) than that of the cell with pure PPy (60 mA h/g). The free-standing films can be used as electrode materials to satisfy the new market demand for flexible and bendable batteries that are suitable for the various types of design and power needs of soft portable electronic equipment.     

Chiral metal–organic framework used as stationary phases for capillary electrochromatography

Metal–organic frameworks (MOFs) have received great attention as novel media in separation sciences because of their fascinating structures and unusual properties. However, to the best of our knowledge, there has been no attempt to utilize chiral MOFs as stationary phases in capillary electrochromatography (CEC). In this study, a homochiral helical MOF [Zn₂(D-Cam)₂(4,4′-bpy)]_n (D-Cam = D-(+)-camphoric acid, 4,4′-bpy = 4,4′-bipyridine) was explored as the chiral stationary phase in open tubular capillary electrochromatography (OT-CEC) for separation of chiral compounds and isomers. The MOFs coated column has been developed using a simple procedure via MOFs post-coated on the sodium silicate layer. The baseline separations of flavanone and praziquantel were achieved on the MOFs coated column with high resolution of more than 2.10. The influences of pH, organic modifier content and buffer concentration on separation were investigated. Besides, the separations of isomers (nitrophenols and ionones) were evaluated. The relative standard deviations (RSDs) for the retention time of run-to-run, day-to-day and column-to-column were 1.04%, 2.16% and 3.07%, respectively. The results demonstrated that chiral MOFs are promising for enantioseparation in CEC.     

Fe3O4 Nanoparticles as an Efficient and Magnetically Recoverable Catalyst for Friedel–Crafts Acylation Reaction in Solvent-Free Conditions

Application of Fe₃O₄ nanoparticles (NPs) as a robust, very efficient, and magnetically recoverable catalyst was investigated in Friedel–Crafts acylation (FCA) of ferrocene and aromatic compounds. This reaction was performed with acid chlorides in solvent-free conditions at room temperature. The catalyst was easily separated by an external magnetic field from the reaction mixture. The separated catalyst was recycled for several consecutive runs without appreciable loss of its catalytic activity.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

A novel electrochemical sensing strategy for rapid and ultrasensitive detection of Salmonella by rolling circle amplification and DNA–AuNPs probe

A novel electrochemical sensing strategy was developed for ultrasensitive and rapid detection of Salmonella by combining the rolling circle amplification with DNA–AuNPs probe. The target DNA could be specifically captured by probe 1 on the sensing interface. Then the circularization mixture was added to form a typical sandwich structure. In the presence of dNTPs and phi29 DNA polymerase, the RCA was initiated to produce micrometer-long single-strand DNA. Finally, the detection probe (DNA–AuNPs) could recognize RCA product to produce enzymatic electrochemical signal. Under optimal conditions, the calibration curve of synthetic target DNA had good linearity from 10 aM to 10 pM with a detection limit of 6.76 aM (S/N = 3). The developed method had been successfully applied to detect Salmonella as low as 6 CFU mL⁻¹ in real milk sample. This proposed strategy showed great potential for clinical diagnosis, food safety and environmental monitoring.