Development of Nonenzymatic Hydrogen Peroxide Sensor Based on Successive Pd‐Ag Electrodeposited Nanoparticles on Glassy Carbon Electrode

A novel strategy to fabricate hydrogen peroxide (H₂O₂) sensor was developed by electrodepositing palladium? silver nanoparticles (NPs) on a glassy carbon electrode. The morphology of the modified electrode was characterized by Scanning electron microscopy (SEM). The result of electrochemical experiments showed that such constructed sensor had a favorable catalytic ability, high sensitivity, excellent selectivity towards reduction of hydrogen peroxide (H₂O₂). The response to H₂O₂ is linear in the range between 0.30 μM to 2.50 mM, and the detection limit is 0.1 μM (at an S/N of 3).     

Palladium Nanoparticles Embedded into Graphene Nanosheets: Preparation,Characterization, and Nonenzymatic Electrochemical Detection of H2O2

A novel nonenzymatic H₂O₂ sensor based on a palladium nanoparticles/graphene (Pd‐NPs/GN) hybrid nanostructures composite film modified glassy carbon electrode (GCE) was reported. The composites of graphene (GN) decorated with Pd nanoparticles have been prepared by simultaneously reducing graphite oxide (GO) and K₂PdCl₄ in one pot. The Pd‐NPs were intended to enlarge the interplanar spacing of graphene nanosheets and were well dispersed on the surface or completely embedded into few‐layer GN, which maintain their high surface area and prevent GN from aggregating. XPS analysis indicated that the surface Pd atoms are negatively charged, favoring the reduction process of H₂O₂. Moreover, the Pd‐NPs/GN/GCE could remarkably decrease the overpotential and enhance the electron‐transfer rate due to the good contact between Pd‐NPs and GN sheets, and Pd‐NPs have high catalytical effect for H₂O₂ reduction. Amperometric measurements allow observation of the electrochemical reduction of H₂O₂ at 0.5 V (vs. Ag/AgCl). The H₂O₂ reduction current is linear to its concentration in the range from 1×10^?9 to 2×10^?3 M, and the detection limit was found to be 2×10^?10 M (S/N=3). The as‐prepared nonenzymatic H₂O₂ sensor exhibits excellent repeatability, selectivity and long‐term stability.     

Solid‐State Electrochemical Method for Determining Core and Shell Size in Pd@PdO Nanoparticles

Electrochemical characterization of palladium nanoparticles surrounded by a palladium oxide shell (Pd@PdO) is described from a combination of voltammetry plus electrochemical quartz crystal microbalance experiments at nanoparticle deposits on graphite electrodes in contact with aqueous H₂SO₄ and NaOH solutions. A method for determining the metal core size and oxide shell thickness of the Pd@PdO nanoparticles, based on a combination of conventional voltammetry of nanoparticles in DMSO solution and voltammetry of nanoparticle deposits in contact with 0.10 M aqueous NaOH solution, is described.     

Effect of active impurities on the condensation of nanoparticles from supersaturated carbon vapor in the combined laser photolysis of C<Subscript>3</Subscript>O<Subscript>2</Subscript> and H<Subscript>2</Subscript>S

The effect of active H₂S, HS^·, and atomic hydrogen impurities on the condensation of highly supersaturated carbon vapor obtained in the combined laser photolysis of a mixture of C₃O₂ and H₂S diluted with argon was studied. The concentrations of carbon vapor, HS^·, and atomic hydrogen obtained in the laser photolysis of the mixture were determined using the absorption cross sections of C₃O₂ and H₂S molecules measured in this work and the measured amount of absorbed laser radiation. The time profiles of the sizes of growing nanoparticles synthesized in C₃O₂ + Ar and C₃O₂ + H₂S + Ar mixtures were measured using the laser-induced incandescence (LII) method. An improved LII model was developed, which simultaneously took into account the heating and cooling of nanoparticles and the temperature dependence of the thermophysical properties of nanoparticles, as well as the cooling of nanoparticles by evaporation and thermal emission. The size distributions of carbon nanoparticles formed in the presence and absence of active impurities were determined with the use of a transmission electron microscope. The final average size of carbon nanoparticles was found to decrease from 12 to 9 nm upon the addition of H₂S to the system, whereas the rate of nanoparticle growth decreased by a factor of 3, and the properties of nanoparticles changed. In particular, the translational energy accommodation coefficient for Ar molecules at the surface of carbon nanoparticles was found to decrease from 0.44 to 0.30. A comparison of the calculated total carbon balance at the early stage of nanoparticle formation with experimental data demonstrated that the reaction C + H₂S → HCS^· + H, which removes a portion of carbon vapor from the condensation process, has a determining effect on the carbon balance in the system. It was found that HS^· and atomic hydrogen affect the carbon balance in the system only slightly. Thus, the experimentally observed decrease in the rate of nanoparticle growth and in the sizes of nanoparticles can be explained by a decrease in the concentration of free carbon upon the addition of H₂S molecules to the system.     

Oxygen dissociation on palladium and gold core/shell nanoparticles

Oxygen dissociation reaction on gold, palladium, and gold‐palladium core/shell nanoparticles was investigated with plane wave basis set, density functional theory. Bader population analysis of charge and electron distribution was employed to understand the change of catalytic activity as a function of the nanopaticle composition. The nanoparticles’ electronic properties were investigated and the degree of core/shell charge polarization was estimated for each composition. It was found that surface polarization plays an important role in the catalysis of the initial step of electrophile reactions such as oxygen dissociation. We have investigated the O₂ adsorption energy on each nanoparticle and the activation barrier for the oxygen dissociation reaction as a function of the nanoparticle structure. Furthermore, we have investigated the influence of surface geometry, that is., surface bond lengths on the catalytic activity. We have compared the electronic and the geometry effects on the oxygen activation and dissociation. Our design rules for core/shell nanoparticles offer an effective method for control of the surface catalytic activity. Palladium and gold are often used as catalysts in synthetic chemistry. First‐principles calculations elucidate the mechanisms that control the surface reactivity of gold, palladium, and gold‐palladium core shell nanoparticles in oxygen dissociation reactions. Oxygen dissociation is promoted on the gold surface of gold/palladium core‐shell nanoparticles by favorable electron transfer from the core to the shell. Such core‐shell electronic effects can be used for fine‐tuning the nanoparticles catalytic activity.     

A quantitative colorimetric assay of H2O2 and glucose using silver nanoparticles induced by H2O2 and UV

A simple spectrophotometric assay of H2O2 and glucose using Ag nanoparticles has been carried out. Relying on the synergistic effect of H2O2 reduction and ultraviolet （UV） irradiation, Ag nanoparticles with enhanced absorption signals were synthesized. H2O2 served as a reducing agent in the Ag nanoparticles formation in which Ag＋ was reduced to Ago by O2- generated via the decomposition of H2O2 in alkaline media. On the other hand, photoreduction of Ag＋ to Ago under UV irradiations also contributed to the nanoparticles formation. The synthesized nanoparticles were characterized by TEM, XPS, and XRD. The proposed method could determine H2O2 with concentrations ranging from 5.0× 10^-7 to 6.0× 10^-5 tool/ L The detection limit was estimated to be 2.0 × 10^-7 mol/L. Since the conversion of glucose to gluconic acid catalyzed by glucose oxidase was companied with the formation of H2O2, the sensing protocol has been successfully utilized for the determination of glucose in human blood samples. The results were in good agreement with those determined by a local hospital. This colorimetric sensor thus holds great promises in clinical applications.     

Pulsed electrodeposition of Pt nanoclusters on carbon nanotubes modified carbon materials using diffusion restricting viscous electrolytes

A simple method for achieving high dispersion and small platinum nanoparticles down to only 2 or 3 nm on structured carbon supports (carbon nanotubes-modified PAN-based carbon fiber and carbon nanotubes-modified graphite foil) is presented. Pulsed electrodeposition of Pt nanoparticles was performed at increased viscosity of the H₂PtCl₆ containing electrolyte by addition of glycerol. The catalyst nanoparticle size can be controlled by varying the amount of glycerol added into the aqueous H₂PtCl₆ solution, and adjusting the number of the potential pulses. The shape and size of the Pt nanoparticles was characterized by scanning electron microscopy and transmission electron microscopy. The electrocatalytic properties of Pt nanoparticles with respect to O₂ and H₂O reduction were investigated by means of cyclic voltammetry, and the improved catalytic activity of the Pt nanoparticles/carbon nanotubes surfaces could be proved.     

A novel nonenzymatic hydrogen peroxide sensor based on multi-wall carbon nanotube/silver nanoparticle nanohybrids modified gold electrode

A novel strategy to fabricate hydrogen peroxide (H₂O₂) sensor was developed based on multi-wall carbon nanotube/silver nanoparticle nanohybrids (MWCNT/Ag nanohybrids) modified gold electrode. The process to synthesize MWCNT/Ag nanohybrids was facile and efficient. In the presence of carboxyl groups functionalized multi-wall carbon nanotubes (MWCNTs), silver nanoparticles (Ag NPs) were in situ generated from AgNO₃ aqueous solution and readily attached to the MWCNTs convex surfaces at room temperature, without any additional reducing reagent or irradiation treatment. The formation of MWCNT/Ag nanohybrids product was observed by transmission electron microscope (TEM), and the electrochemical properties of MWCNT/Ag nanohybrids modified gold electrode were characterized by electrochemical measurements. The results showed that this sensor had a favorable catalytic ability for the reduction of H₂O₂. The resulted sensor could detect H₂O₂ in a linear range of 0.05-17 mM with a detection limit of 5 × 10⁻⁷ M at a signal-to-noise ratio of 3. The sensitivity was calculated as 1.42 μA/mM at a potential of −0.2 V. Additionally, it exhibited good reproducibility, long-term stability and negligible interference of ascorbic acid (AA), uric acid (UA), and acetaminophen (AP).     

Flow Injection Amperometric Analysis of H2O2 at Platinum Nanoparticles Modified Pencil Graphite Electrode

A Pt nanoparticle modified Pencil Graphite Electrode (PGE) was proposed for the electrocatalytic oxidation and non‐enzymatic determination of H₂O₂ in Flow Injection Analysis (FIA) system. Platinum nanoparticles (PtNPs) electrochemically deposited on pretreated PGE (p.PGE) surface by recording cyclic voltammograms of 1.0 mM of H₂PtCl₆ solution in 0.10 M KCl at scan rate of 50 mV s⁻¹ for 30 cycles. Cyclic voltammograms show that the oxidation peak potential of H₂O₂ shifts from about +700 mV at bare PGE to +50 mV at PtNPs/p.PGE vs. Ag/AgCl /KCl (sat.). It can be concluded that PtNPs/p.PGE exhibits a good electrocatalytic activity towards oxidation of H₂O₂. Then, FI amperometric analysis of H₂O₂ was performed under optimized conditions using a new homemade electrochemical flow cell which was constructed for PGE. Linear range was found as 2.5 μM to 750.0 μM H₂O₂ with a detection limit of 0.73 μM (based on S_b/m of 3). As a result, this study shows the first study on the FI amperometric determination of H₂O₂ at PtNPs/p.PGE which exhibits a simple, low cost, commercially available, disposable sensor for H₂O₂ detection. The proposed electrode was successfully applied to determination of H₂O₂ in real sample.     

纳米硫化镉修饰玻碳电极对血红蛋白的直接电化学和生物电催化

0IntroductionStudies of direct electrochemistry of proteins orenzymes at electrodes can serve as a basis for build-ing electrochemical biosensors,enzymatic bioreactors,and biomedical devices[1].This approach simplifiessuch devices without using mediators and is of partic-ular significance for fabricating the third generationbiosensors[2].For example,if a protein or enzyme im-mobilized on electrode surface is capable of directelectron transfer without loss of bioactivities,it can beused in the …     

Direct Electrochemistry of Hemoglobin Immobilized on Carbon‐Coated Iron Nanoparticles for Amperometric Detection of Hydrogen Peroxide

A novel method for preparation of hydrogen peroxide biosensor was presented based on immobilization of hemoglobin (Hb) on carbon‐coated iron nanoparticles (CIN). CIN was firstly dispersed in a chitosan solution and cast onto a glassy carbon electrode to form a CIN/chitosan composite film modified electrode. Hb was then immobilized onto the composite film with the cross‐linking of glutaraldehyde. The immobilized Hb displayed a pair of stable and quasireversible redox peaks and excellent electrocatalytic reduction of hydrogen peroxide (H₂O₂), which leading to an unmediated biosensor for H₂O₂. The electrocatalytic response exhibited a linear dependence on H₂O₂ concentration in a wide range from 3.1 μM to 4.0 mM with a detection limit of 1.2 μM (S/N=3). The designed biosensor exhibited acceptable stability, long‐term life and good reproducibility.     

Facile Synthesis of Amino Shell-Magnetic Core Nanoparticles and Application for Direct Electrochemistry

This paper reports a core-shell nanoparticle system coated on the carbon paste electrode (CPE) for determination of hydrogen peroxide. The amino-functionalized shell-magnetic core nanoparticles have been proven to be an effective material for Hb immobilization. The core-shell nanoparticle system was constructed by immobilizing hemoglobin (Hb) on amino-functionalized shell@magnetic core composite nanoparticles (NH₂-SiO₂-CoFe₂O₄) with the bridge of gold nanoparticles (AuNPs). Electrochemical impedance spectroscopy, cyclic voltammetry, and chronoamperometry were used to characterize the obtained biosensor. The Hb/AuNPs/NH₂-SiO₂-CoFe₂O₄/CPE showed a linear range from 1.9 × 10^?6 to 4.6 × 10^?3 M, with a detection limit of 6.3 × 10^?7 M (S/N = 3) under the optimized experimental conditions. A good affinity was shown due to the small apparent Michaelis–Menten constant of 2.68 mM.     

Pd based on 2-Aminopyrimidine and 1H-benzo[d]imidazol-2-amine functionalizedFe3O4 nanoparticles as novel recyclable magnetic nanocatalysts for Ullmann coupling reaction

In this study, Pd based on 2-Aminopyrimidine and 1H-benzo[d]imidazol-2-amine functionalized Fe₃O₄ magnetic nanoparticles [(Pd-APM-PSi-Fe₃O₄) and (Pd-BIA-PSi-Fe₃O₄)] was designed and used for the synthesis of di aryl ether by Ulmann cross-coupling reactions. Ulmann reaction performed with mixing of the arylhalides and phenol derivatives in DMF solvent. The prepared catalysts were characterized with various analytical techniques such as FT-IR, XRD, TGA, SEM, TEM, EDX, ICP and VSM. Pd-APM-PSi-Fe₃O₄ and Pd-BIA-PSi-Fe₃O₄ catalysts demonstrated good to excellent yields catalytic efficiency for Ulmann reactions in comparison with to commercial palladium catalysts. The catalyst is easily recycled and reused without loss of the catalytic activity. The combined merits of reusable catalyst conditions make the condensation with safe operation, no leaching of pd into environment, low pollution, rapid access to products and simple workup. Also, these novel magnetic nanocatalysts are superior to the industry standard Pd in every relevant aspect. They feature a way higher initial activity, a much more convenient separation, better recycling, and less contamination of the products. Last but not least, they can be very easily prepared from commercially available Fe₃O₄ nanoparticles using standard laboratory equipment.     

Superparamagnetic POT/Fe3O4 nanoparticle composites with supported Au nanoparticles as recyclable high-performance nanocatalysts

A novel method has been developed to successfully synthesize Fe₃O₄ nanoparticles with tunable size and morphology supported on shells of poly(o-Toluidine)(POT) hollow microspheres. The as-prepared POT/Fe₃O₄ nanoparticle composites can be used as novel and magnetic-responsive catalyst supports to produce highly efficient and recyclable noble metal catalysts. The size of Fe₃O₄ nanoparticles supported on shells of POT hollow microspheres can be tuned from 4 to 12 nm by changing the concentration of Fe ions. The roles of the doping acid of POT and Zeta potentials of Fe₃O₄ nanoparticles and POT in the formation of the POT/Fe₃O₄ nanoparticle composites were discussed. Furthermore, gold nanoparticles that were supported on the as-synthesized POT/Fe₃O₄ nanoparticle composites have been achieved by utilizing the reactivity of POT towards Au ions. The size of gold nanoparticles can be tuned by altering the concentration of HAuCl₄. Finally, the catalytic activity of the obtained POT/Fe₃O₄/Au composites for 4-nitrophenol (4NP) reduction is investigated. The results demonstrate that such magnetic-responsive polymer-supported gold nanoparticles can be easily recovered and reused five times still remains high catalytic performance, which indicate their potential applications in the field of catalysis.     

Synthesis of Core-Shell (Pd-Au) Bimetallic Nanoparticles in Microemulsions

Palladium-gold core-shell nanoparticles were synthesized in the aqueous domains of water in oil microemulsions by the sequential reduction of H₂PdCl₄ and HAuCl₄. The nanoparticles were characterized by ultraviolet-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). The UV-vis spectra confirm the presence of palladium nanoparticles after reducing H₂PdCl₄. These particles have been used as seeds for the core-shell particles. UV-vis spectra show that, after reducing HAuCl₄, the surface plasmon absorption of the nanoparticles is dominated by gold, revealing the encapsulation of the palladium seeds. These results agree with crystallographic analysis performed with high-resolution TEM pictures, as well as with selected area electron diffraction. The TEM pictures show the core-shell nanoparticles with an average diameter of 9.1 nm, as compared with 5 nm for the palladium seeds, in good agreement with the used Pd:Au molar ratio.     

Palladium nanoparticle‐decorated magnetic pomegranate peel‐derived porous carbon nanocomposite as an excellent catalyst for Suzuki–Miyaura and Sonogashira cross‐coupling reactions

Porous carbon (PC) material was prepared from the carbonization of pomegranate peel waste. Subsequently, magnetically separable Fe₃O₄@PC was synthesized from Fe₃O₄ nanoparticles decorated on PC by the co‐precipitation method of iron ions. Finally, Fe₃O₄@PC was successfully decorated with palladium nanoparticles in a simple route by reducing H₂PdCl₄ in the presence of sodium dodecylsulfate, which was used as both surfactant and reducing agent. Additionally, the effect of temperature on the carbonization process was studied. The Pd/Fe₃O₄@PC nanocomposite was used as an efficient and heterogeneous catalyst for Suzuki–Miyaura and Sonogashira cross‐coupling reactions in an environmentally friendly medium.     

Low‐cost Nickel Complex Dye‐sensitized Titania Nanoparticle/nanotube Composites for Solar Cells

In this work, high‐performance dye‐sensitized solar cells (DSSCs) based on new low‐cost visible nickel complex dye (VisDye), TiO₂ nanoparticle/nanotube composites electrodes, carbon nanoparticles counter electrodes, and ionic liquids electrolytes have been fabricated. The electronic structure, optical spectroscopy, and electrochemical properties of the VisDye were studied. Experimental results indicate that it is beneficial to improve the electron transport and power conversion efficiency using the nickel complex VisDye and TiO₂ nanoparticle/nanotube composites. Under optimized conditions, the solar energy conversion efficiencies were measured. The short‐circuit current density (J_SC), the open‐circuit voltage (V_OC), the fill factor (FF), and the overall efficiency (η) of the DSSCs are 10.01 mA/cm², 516 mV, 0.68, and 3.52%, respectively. This study demonstrates that the combination of new VisDye with TiO₂ nanoparticle/nanotube composites electrodes and carbon nanoparticles counter electrodes provide a way to fabricate highly efficient dye‐sensitized solar cells in low‐cost production.     

The role of Carica papaya latex bio-catalyst and thermal shock in water on synthesizing rice husk

A bio-catalyst made of natural resources, such as Carica papaya latex, is very challenging for nanoparticle separation. In addition, differences in thermal conditions between nanoparticles affect the movement of substances in the separation process. The study experimentally investigated the role of Carica papaya latex bio-catalyst and thermal shock in water on synthesizing rice husk (RH). The synthesis retained the Mg and C elements attached to SiO₂, which were generally neglected during the process. The study's objective was to evaluate the effectiveness of biocatalysts and thermal effects on the separation of Mg-SiO₂-C from rice husk carbon nanoparticles (CNPs-RH). The research involved various treatment processes, such as RH pyrolysis in obtaining charcoal, High energy milling (HEM) to have carbon particles, and washing to get nano-sized carbon particles. The bonding of elemental compounds to rice husk carbon particles (CPs-RH) was released using NaOH and coagulation using a bio-catalyst. Coagulated CPs-RH was injected into water at a temperature of 60–70 °C to have a thermal shock effect for H₂O clusters in Na⁺ and Mg²⁺ ions attached to the surface of the nanoparticles. Several tests were carried out, such as the SEM-EDX, TEM, XRD, and FTIR tests, to investigate the two nanoparticle clusters formed up to the nanometer scale. The results indicated that CNPs-RH nanoparticles consist of spherical particles with a diameter of 1.2 nm, while Mg-SiO₂-C nanoparticles have a diameter of 0.6 nm. Both are classified as amorphous. Based on the FTIR test, CNPs-RH is hydrophilic, while Mg-SiO₂-C is hydrophobic. Thermal shock in water strengthens the ion's mobility, increasing the interfacial dipole forces between nanoparticles and accelerating the separation process.     

A novel H(2)O(2) amperometric biosensor based on gold nanoparticles/self-doped polyaniline nanofibers

A new kind of gold nanoparticles/self-doped polyaniline nanofibers (Au/SPAN) with grooves has been prepared for the immobilization of horseradish peroxidase (HRP) on the surface of glassy carbon electrode (GCE). The ratio of gold in the composite nanofibers was up to 64%, which could promote the conductivity and biocompatibility of SPAN and increase the immobilized amount of HRP molecules greatly. The electrode exhibits enhanced electrocatalytic activity in the reduction of H₂O₂ in the presence of the mediator hydroquinone (HQ). The effects of concentration of HQ, solution pH and the working potential on the current response of the modified electrode toward H₂O₂ were optimized to obtain the maximal sensitivity. The proposed biosensor exhibited a good linear response in the range from 10 to 2000 μM with a detection limit of 1.6 μM (S/N = 3) under the optimum conditions. The response showed Michaelis–Menten behavior at larger H₂O₂ concentrations, and the apparent Michaelis–Menten constant K_m was estimated to be 2.21 mM. The detection of H₂O₂ concentration in real sample showed acceptable accuracy with the traditional potassium permanganate titration.     

Enhancement of Fe3O4/Au Composite Nanoparticles Catalyst in Oxidative Degradation of Methyl Orange Based on Synergistic Effect

Enhancement of Fe₃O₄ /Au nanoparticles (Fe₃O₄ /Au NPs ) catalyst was observed in the oxidative degradation of methyl orange by employing H₂O₂ as oxidant. To evaluate the catalytic activity of Fe₃O₄ /Au nanoparticles, different degradation conditions were investigated such as the amounts of catalyst, H₂O₂ concentration and pH value. Based on our data, methyl orange was degraded completely in a short time. The enhanced catalytic activity and increased oxidation rate constant may be ascribed to synergistic catalyst‐activated decomposition of H₂O₂ to •OH radical, which was one of the strong oxidizing species. Besides, Fe₃O₄ /Au nanoparticles have exhibited satisfying recycle performance for potential industrial application.