Cobalt-Catalyzed Formation of Grignard Reagents via C-O or C-S Bond Activation.

C(aryl)-OMe bond functionalization catalyzed by cobalt(II) chloride in combination with a nacnac-type ligand and magnesium as a reductant is reported. Borylation and benzoylation of aryl methoxides are demonstrated, and C(aryl)-SMe bond borylation can be achieved under similar conditions. This is the first example of achieving these transformations using cobalt catalysis. Mechanistic studies suggest that a Grignard reagent is generated as an intermediate in a rare example of a magnesiation via a C-O bond activation reaction. Indeed, an organomagnesium species could be directly observed by electrospray ionization mass spectroscopic analysis. Kinetic experiments indicate that a heterogeneous cobalt catalyst performs the C-O bond activation.

Highly efficient Ag doped δ-MnO2 decorated graphene: Comparison and application in electrochemical detection of H2O2.

Cytotoxic H2O2 is an inevitable part of our life, even during this contemporary pandemic COVID-19. Personal protective equipment of the front line fighter against coronavirus could be sterilized easily by H2O2 for reuse. In this study, Ag doped δ-MnO2 nanorods supported graphene nanocomposite (denoted as Ag@δ-MnO2/G) was synthesized as a nonenzymatic electrochemical sensor for the sensitive detection of H2O2. The ternary nanocomposite has overcome the poor electrical conductivity of δ-MnO2 and also the severe aggregation of Ag NPs. Furthermore, δ-MnO2/G provided a rougher surface and large numbers of functional groups for doping more numbers of Ag atoms, which effectively modulate the electronic properties of the nanocomposite. As a result, electroactive surface area and electrical conductivity of Ag@δ-MnO2/G increased remarkably as well as excellent catalytic activity observed towards H2O2 reduction. The modified glassy carbon electrode exhibited fast amperometric response time (<2 s) in H2O2 determination. The limit of detection was calculated as 68 nM in the broad linear range (0.005-90.64 mM) with high sensitivity of 104.43 µA mM-1 cm-2. No significant interference, long-term stability, excellent reproducibility, satisfactory repeatability, practical applicability towards food samples and wastewater proved the efficiency of the proposed sensor.

Synthesis of Electrochemically Reduced Graphene Oxide Bonded to Thiodiazole-Pd and Applications to Biosensor.

A novel biosensor for the determination of hydrogen peroxide and glucose was developed based on EGN-TDZ-Pd, as an electrocatalyst. The preparation of graphene oxide (GO) nanosheets was functionalized by combining it with 5-amino-1,3,4-thiadiazole-2-thiol (TDZ) and by covalently bonding it to palladium (Pd) nanoparticles (GO-TDZ-Pd). In the electrochemical investigation, EGN-TDZ-Pd was characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry (CV) and chronoamperometry (CA) were used to characterize the performance of EGN-TDZ-Pd. The proposed H2O2 biosensor exhibited a wide linear range from 10 µM to 6.5 mM. Also, a glucose biosensor was prepared using glucose oxidase and EGN-TDZ-Pd placed onto a glassy carbon electrode (GCE). The GOx/EGN-TDZ-Pd/GCE was easily prepared using a rapid and simple procedure, and it was utilized for highly sensitive glucose determination.

Electrocatalytic Oxidation of Formic Acid in an Alkaline Solution with Graphene-Oxide- Supported Ag and Pd Alloy Nanoparticles.

The electrocatalytic activities of metal-decorated graphene oxide (GO) catalysts were investigated. Electrochemically reduced GO-S-(CH2)4-S-Pd [ERGO-S-(CH2)4-S-Pd] and GO-S-(CH2)4-S-PdAg alloy [ERGO-S-(CH2)4-S-PdAg] were obtained through the electrochemical reduction of GO-S-(CH2)4-S-Pd and GO-S-(CH2)4-S-PdAg in a pH 5 PBS solution. It was demonstrated that the application of ERGO-S-(CH2)4-S-Pd and ERGO-S-(CH2)4-S-PdAg used in a modified GCE improves the electrocatalytic oxidation of formic acid. The addition of an Ag nanoparticle with a carbon chain-Pd in the electrode provides an electrode with very interesting properties for the electrocatalytic oxidation of formic acid. The ERGO-S-(CH2)4-S-Pd and ERGO-S-(CH2)4-S-PdAg were characterized via X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). ERGO-S-(CH2)4-S-Pd and ERGO-S-(CH2)4-S-PdAg can be employed for the electrocatalytic oxidation of formic acid. The electrochemical behaviors of this electrode were investigated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS).

Manganese Dioxide/Reduced Graphene Oxide with Poly(3,4-ethylenedioxythiophene) for Improved Electrocatalytic Oxygen Reduction Reaction.

Poly(3,4-ethylenedioxythiophene)-(PEDOT)-functionalized reduced graphene oxide (rGO) with MnO2 nanoparticles (MnO2/PEDOT/rGO) was prepared using electrochemical methods. The MnO2/ PEDOT/rGO was obtained through the electrochemical reduction of PEDOT/GO and under electrochemical treatment in KMnO4. The PEDOT/rGO and MnO2/PEDOT/rGO were characterized by several instrumental and electrochemical methods. The electrocatalytic 02 reduction for both electrodes was investigated via cyclic and hydrodynamic voltammetry in 0.1 M KOH aqueous solutions. The kinetic analysis in comparison to PEDOT/rGO a significant enhancement was found for the MnO2/PEDOT/rGO. The proposed main path in the oxygen reduction reaction (ORR) mechanism on the MnO2/PEDOT/rGO was the direct four-electron transfer process with faster transfer kinetic rate. The better ORR kinetics were obtained due to the excellent composite formation and well attachment of MnO2 NPs within oxide form. The PEDOT/rGO was less stable for long term use than MnO2/PEDOT/rGO.

Characteristic electronic perturbation by asymmetric arrangements of p-aminophenyl substituents in free-base porphyrins.

We have investigated the perturbed electronic properties of meso-substituted free-base porphyrins with symmetric and asymmetric arrangements of substituents using time-resolved spectroscopic measurements and theoretical calculations. The extent of electronic perturbation by substituents in meso-substituted porphyrins is mainly affected by the isoenergetic condition of frontier MOs of porphine and substituent units, nonorthogonal geometry, and geometrical arrangement of substituents. By using the asymmetric arrangements of p-aminophenyl and pentafluorophenyl substituents, we can induce the electron-rich condition on the porphine unit and the intramolecular charge transfer character in the excited state. On the basis of this work, we can gain further insight into the energetic and geometric factors of substituents, the interaction between porphine and substituent units, and the perturbed photophysical and electronic properties by substituents, which provides a firm basis for further understanding of the catalytic activities or photophysical properties of porphyrins in porphyrin-based molecular catalysts and electronics.

Electrochemical sensing of H2O2 by the modified electrode with pd nanoparticles on multi-walled carbon nanotubes-g-poly(lactic acid).

A simple method has adapted to prepare MWCNT grafted Poly(lactic acid) (MWCNT-g-PLA) by intercalative polymerization of poly(lactic acid) in the presence of multi-wall carbon nanotubes (MWCNT) functionalized with hydroxyl groups. The functionalized MWCNT has obtained from the treatment of methylene diphenyl diisocyanate (MDI) with MWCNT, and then the reaction with 1,4-butanediol (BD) to create functional hydroxyl groups. MWCNT-g-PLA-Pd and MWCNT-g-PLA-Pt have prepared from the MWCNT-g-PLA and metal precursors. The synthesized materials have characterized by 1H-NMR, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM). The MWCNT-g-PLA-Pd is possibilities for employing to electrochemical detection of hydrogen peroxide. Electrocatalytic activities are verified from cyclic voltammetry (CV) and amperometric response in 0.1 M phosphate buffer solution (PBS). The biosensor provided good stability and selectivity towards interferences such as UA, AA, and glucose.

A green preparation of nitrogen doped graphene using urine for oxygen reduction in alkaline fuel cells.

A simple, eco-friendly and efficient harmless chemical approach has been developed for the simultaneous nitrogen (N) doping and reduction of graphene oxide (GO) by cost free human urine using simple refluxing. Large-scale preparation of graphene has been hindered largely by several issues, such as highly toxic reducing agents that are harmful to human health and environment, complicated reduction process and costly chemicals. Human urine is a natural precursor of urea with no cost. In this process, the NH3 has acted as not only reducing but also doping agent that produced via thermal decomposition of urea, while the N doping level of ~11.1 at% is achieved. For the first time we have used urine as a reductant and doping agent in such a high class chemical technology. The simultaneous reduction and N-doping of GO using urine (denoted as UNG) have confirmed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and UV-vis spectroscopy. The resultant UNG has demonstrated to show remarkable electrocatalytic activity toward oxygen reduction reaction (ORR) with better fuel selectivity, and stability than that of the commercially available 20 wt% Pt/C electrode using cyclic voltammetry (CV) and chronoamperometry.

Intermetallic Pd-Y nanoparticles/N-doped carbon nanotubes as multi-active catalysts for oxygen reduction reaction, ethanol oxidation reaction, and zinc-air batteries.

Intermetallic nanomaterials are unique in terms of their band gap, atomic-level arrangement, and well-defined stoichiometry, which allows them to exhibit significantly enhanced catalytic performance in electrochemical applications. However, the preparation of durable intermetallic catalysts with a lower content of platinum group metals is challenging, while the lack of control over the loss of active components limits their long-term application due to weak interaction between the support and the nanostructure. Here, we have designed the intermetallic alloyed nanoparticles (NPs) of PdY on N-doped carbon nanotubes (PdY/NCNTs) as a multifunctional catalyst for the oxygen reduction reaction (ORR), the ethanol oxidation reaction (EOR), and zinc-air batteries (ZABs). The strong adhesion through nitrogen ensures the anchoring of alloyed PdY NPs on the NCNTs, which restrains atomic migration and sintering during their conversion to intermetallic phases. This study confirms that there is negligible active site leaching owing to the strong and multiple dative bonds between the NCNTs and PdY NPs. Therefore, this catalyst exhibits remarkable catalytic activity, resulting in a mass activity of 1317 and 2902 mA mgPd-1 at jk and jf for the ORR and the EOR, respectively, and remains stable for a longer period. In addition, the PdY/NCNT-containing air cathode-fabricated ZAB achieved a higher power density (0.236 W cm-2) compared to the benchmark Pt/C.

The nanostructure of nitrogen atom linked carbon nanotubes with platinum employed to the electrocatalytic oxygen reduction.

Multi-walled carbon nanotube grafted Pt nanoparticles via nitrogen atom (MWCNT-N-Pt) has chemically synthesized and characterized as an efficient oxygen reduction reaction (ORR) catalysts. Structural and morphological properties of the electrocatalyst have characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) techniques. The electrochemical properties have evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and hydrodynamic voltammetry techniques. The electrochemical properties toward ORR of MWCNT-N-Pt have evaluated in 0.1 mol L(-1) HClO4 aqueous solution. The electrocatalytic reduction of O2 at the MWCNT-N-Pt catalyst establishes a pathway of four-electron transfer reduction into H2O. Hydrodynamic voltammetry reveals that the modified electrode has catalyzed effectively at higher potential. The value of transferred electron number and other kinetic parameters have demonstrated that the MWCNT-N-Pt is highly facilitated than that of bulk Pt to electrocatalytic oxygen reduction with comparatively low Pt content (27.04 Wt%) and higher electrochemical surface area (ESA(Pt)) 94.34 m2 gPt(-1).

Simultaneous determination of serotonin and dopamine at the PEDOP/MWCNTs-Pd nanoparticle modified glassy carbon electrode.

Electrochemical determination of dopamine (DA) and serotonin (5-HT) have been studied at a modified glassy carbon electrode (GCE) in 0.1 M phosphate buffer solution (PBS) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at pH 7.4, all over the interfering biomolecule ascorbic acid (AA). The GCE was modified by palladium-functionalized, multi-walled carbon nanotubes (MWCNTs-Pd) with electrochemical deposition of poly 3,4-ethylenedioxy pyrrole (PEDOP), denoted as PEDOP/MWCNTs-Pd/GCE, and investigated by SEM and EIS experiments. The highly electrocatalytic activity of the modified electrode toward 5-HT and DA was demonstrated from the sensitive and well-separated voltammetric experiment. The oxidation peaks found were 0.165 and 0.355 mV for DA and 5-HT, respectively. The composite film shows a significant accumulation effects on two species, as well as the mutual interference among the analytes. This biosensor was best in response compared to other modified electrodes made in the same lab. The lowest detection limits were found to be 5.0 x 10(-9) and 1.0 x 10(-8) for 5-HT and DA, respectively. The respective linear ranges were determined as 1.0 x 10(-7) to 2.0 x 10(-4) and 1.0 x 10(-7) to 2.0 x 10(-4) for 5-HT and DA.

Electrocatalytic reduction of H2O2 on thiolate graphene oxide covalently to bonded palladium nanoparticles.

The electrocatalytic reduction of hydrogen peroxide on thioalted graphene oxide (t-GO) covalent bonded to palladium nanoparticles was used as the basis of an H2O2 biosensor. Poly (diallydimethylammonium chloride)-coated t-GO-Pd on glassy carbon electrodes was easily and quickly prepared and gave sensitive measurements of H2O2 concentration. The Pd nanoparticles covalently bonded to the thiolated graphene oxide were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy. Comparable results for H2O2 determination were obtained from cyclic voltammetric and amperometric measurements. The proposed H2O2 biosensor exhibited a wide linear range of 10 microM to 10 mM, and a low detection limit of 0.22 microM (S/N = 3), at an applied potential of -0.1 V by the amperometric method.

Electrocatalytic oxidation of formic acid by poly(diallyldimethylammonium chloride) and Pt/Pd-functionalized carbon nanotubes mixtures.

Improving the catalytic activity of the anode catalyst is an important task in the direct formic acid fuel cell (DFAFC). In this study, the catalysts were prepared by dispersing either platinum or palladium metal on the surface of thiolated multi-walled carbon nanotubes (t-MWCNTs), denoted as t-MWCNT-Pt and t-MWCNT-Pd, respectively. These modified t-MWCNT and poly(diallyldimethylammonium chloride) (PDDA) were ultrasonically mixed and loading on a glassy carbon electrode (GCE) for formic acid (FA) oxidation and the catalytic activities were then investigated by using cyclic voltammetry (CV) and chronoamperometry (CA) methods. The as-formed catalysts were characterized by several methods. To optimize the catalytic performance, we investigated the catalysts separately and together (in different ratios) for FA oxidation. The PDDA mixed catalyst demonstrated a slightly better performance. These results indicated that the PDDA/(t-MWCNT-Pt + t-MWCNT-Pd) catalyst exhibited better activity than that of the corresponding other catalysts.

Electrocatalytic oxidation of hydrazine and hydroxylamine by graphene oxide-Pd nanoparticle-modified glassy carbon electrode.

Pd nanoparticle catalysts supported by thiolated graphene oxide (tGO) on a glassy carbon electrode (GCE), and denoted as tGO-Pd/GCE, are used in this study for the electrochemical determination of hydroxylamine and hydrazine. The physicochemical properties of tGO-Pd were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). They showed strong catalytic activity toward the oxidation of hydroxylamine and hydrazine. Cyclic voltammetry (CV) and amperometry were used to characterize the sensors' performances. The detection limits of hydroxylamine and hydrazine by tGO-Pd/GCE were 0.31 and 0.25 microM (s/n = 3), respectively. The sensors' sensitivity, selectivity, and stability were also investigated.

Covalent hybridization of thiolated graphene sheet and platinum nanoparticles for electrocatalytic oxygen reduction reaction.

A covalently bonded thiolated graphene sheet-supported platinum electrocatalyst (GOS-Pt) has synthesized for electrochemical oxygen reduction reaction (ORR) in neutral media. The catalyst's structural features are characterized by transmission electron microscopy (TEM), energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). Its activity towards the ORR has investigated by using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring disk electrode (RRDE) in 0.1 mol l(-1) phosphate buffer solution (PBS) at pH 7, which is also used to assess the catalyst's kinetic parameters. On a glassy carbon electrode (GCE), the catalyst shows a significant catalytic activity, with its electrocatalysis of O2 reduction occurring via four-electron transfer reduction to H2O with minimal generation of H2O2.

Poly-cobalt[tetrakis(o-aminophenyl)porphyrin] nanowire and single-walled carbon nanotube for the analysis of hydrogen peroxide.

Nanowires of poly-cobalt[tetrakis(o-aminophenyl)porphyrin] (PCoTAPPNW) were fabricated by electrochemical polymerization by the cyclic voltammetric method in anodic aluminum oxide membranes. A glassy carbon electrode (GCE) modified by PCoTAPPNW and single-walled carbon nanotubes (SWNT) without any binder was investigated with voltammetric methods in phosphate buffer saline (PBS) at pH 7.4. The PCoTAPPNW + SWNT/GCE exhibited strongly enhanced voltammetric and amperometric sensitivity towards hydrogen peroxide (H2O2), which shortened the response time (< 5 seconds), showed detection limit of 1.0 microM and enhanced the sensitivity for H2O2 detection with 194 microA mM(-1) cm(-2). The PCoTAPPNW + SWNT/GCE can be used to monitor H2O2 at very low concentration in physiological pH as an efficient electrochemical H2O2 sensor.

Determination of serotonin on a glassy carbon electrode modified by electropolymerization of meso-tetrakis(2-aminophenyl)porphyrin and single walled carbon nanotubes.

A chemically modified electrode [poly(TAPP)-SWNT/GCE] was prepared by electropolymerization of meso-tetrakis(2-aminophenyl)porphyrin (TAPP)-single walled carbon nanotubes (SWNT) on the surface of a glassy carbon electrode (GCE). This modified electrode was employed as an electrochemical biosensor for the determination of serotonin concentration and exhibited a typical enhance effect on the current response of serotonin and lower oxidation overpotential. The biosensor was very effective to determined 5-HT in a mixture. The linear response was in the range 2.0 x 10(-7) to 1.0 x 10(-5) M, with a correlation coefficient of 0.999 [i(p)(microA) = 3.406 C (microM)+0.132] on the anodic current, with a detection limit of 1 x 10(-9) M. Due to the relatively low currents and different potentials in the electrochemical responses to ascorbic acid and dopamine, the modified electrode is a useful and effective sensing device for the selective and sensitive serotonin determination in the presence of ascorbic acid and dopamine.

Pyrrolinium-Substituted Persistent Zwitterionic Ferrocenate Derivative Enabling the Application of Ferrocene Anolyte.

Here, we report the imidazolium-/pyrrolinium-substituted persistent zwitterionic ferrocenate derivatives, which were characterized by electron paramagnetic resonance (EPR) and 57Fe Mössbauer spectroscopy. Additional theoretical studies on these zwitterionic ferrocenate derivatives clearly explain the origin of their thermal stability and the orbital interactions between iron and imidazolium-/pyrrolinium-substituted zwitterionic cyclopentadienyl ligand. Exploiting the facile Fe(II/I) redox chemistry, we successfully demonstrated that the pyrrolinium-substituted ferrocene derivative can be applied as an example of derivatized ferrocene anolyte for redox-flow batteries. These zwitterionic ferrocenate derivatives will not only deepen our understanding of the intrinsic chemistry of ferrocenate but have the potential to open the way for the rational design of metallocenate derivatives for various applications.

Determination of Dopamine in the Presence of Ascorbic Acid by Nafion and Single-Walled Carbon Nanotube Film Modified on Carbon Fiber Microelectrode.

Carbon fiber microelectrode (CFME) modified by Nafion and single-walled carbon nanotubes (SWNTs) was studied by voltammetric methods in phosphate buffer saline (PBS) solution at pH 7.4. The Nafion-SWNTs/CFME modified microelectrode exhibited strongly enhanced voltammetric sensitivity and selectivity towards dopamine (DA) determination in the presence of ascorbic acid (AA). Nafion-SWNTs film accelerated the electron transfer reaction of DA, but Nafion film as a negatively charged polymer restrained the electrochemical response of AA. Voltammetric techniques separated the anodic peaks of DA and AA, and the interference from AA was effectively excluded from DA determination. Linear calibration plots were obtained in the DA concentration range of 10 nM - 10 µM and the detection limit of the anodic current was determined to be 5 nM at a signal-to-noise ratio of 3. The study results demonstrate that DA can be determined without any interference from AA at the modified microelectrode, thereby increasing the sensitivity, selectivity, and reproducibility and stability.

The insight study of SnO pico size particles in an ethanol-water system followed by its biosensing application.

Pico sized Stannous oxide particles (SnO PPs) were synthesized in an ethanol-water solvent system on the surface of nitrogen doped graphene oxide (GO). The highly conductive support was a combination of dual interactions between 4-aminomethylbenzylamine (AMBA) and GO. The oppositely positioned -NH2 linkers of the AMBA were covalently incorporated into the GO matrix through condensation reaction followed by the strong π - π stacking interactions between aromatic rings of AMBA and GO. The change in the local chemical environment of GO via dual interactions provided a suitable atmosphere for the growth and dispersion of SnO PPs on GO-AMBA surface. The possible mechanism for the formation of SnO in an ethanol-water solvent system was evaluated. Furthermore, a light was shed on the factors responsible for the pico size of SnO particles synthesis along with its phenomenal distribution on the GO-AMBA surface. The catalyst containing SnO PPs was deployed as a biosensor for the detection of ascorbic acid (AA) for the very first time. A very wide linear range of 5.0 × 10-5-7.0 × 10-3 M, limit of detection (LOD) of 1.19 × 10-5 M along with excellent practical feasibility, storage stability, repeatability and selectivity towards AA electrooxidation showed the excellent synergy between nitrogen-rich GO surface and SnO PPs. The sensitivity (885.54 µAmM-1cm-2) of the catalyst was the most attractive feature, as it was obtained in the presence of 5 and 2-fold higher concentration of UA and DA interfering species respectively.