Nanoporous gold as non-enzymatic sensor for hydrogen peroxide

Nanoporous gold (NPG) fabricated by dealloying Au–Ag film was investigated for the non-enzymatic detection of H₂O₂. The apparent activation energy of H₂O₂ electrochemical reduction on NPG was found to be as low as ∼30 kJ mol⁻¹. The reduction currents at −0.4 V vs. SCE demonstrated a strict linear dependence in a wide H₂O₂ concentration region from 10 μM to 8 mM with a detection limit 3.26 μM. Furthermore, the biosensor based on NPG exhibited high selectivity, good reproducibility, and long-term stability. These results indicate that NPG could be a promising electrochemical material for H₂O₂ detection.     

A novel hydrogen peroxide biosensor based on Au-graphene-HRP-chitosan biocomposites

Graphene was prepared successfully by introducing -SO₃⁻ to separate the individual sheets. TEM, EDS and Raman spectroscopy were utilized to characterize the morphology and composition of graphene oxide and graphene. To construct the H₂O₂ biosensor, graphene and horseradish peroxidase (HRP) were co-immobilized into biocompatible polymer chitosan (CS), then a glassy carbon electrode (GCE) was modified by the biocomposite, followed by electrodeposition of Au nanoparticles on the surface to fabricate Au/graphene/HRP/CS/GCE. Cyclic voltammetry demonstrated that the direct electron transfer of HRP was realized, and the biosensor had an excellent performance in terms of electrocatalytic reduction towards H₂O₂. The biosensor showed high sensitivity and fast response upon the addition of H₂O₂, under the conditions of pH 6.5, potential −0.3 V. The time to reach the stable-state current was less than 3 s, and the linear range to H₂O₂ was from 5 × 10⁻⁶ M to 5.13 × 10⁻³ M with a detection limit of 1.7 × 10⁻⁶ M (S/N = 3). Moreover, the biosensor exhibited good reproducibility and long-term stability.     

Direct synthesis of hydrogen peroxide from hydrogen and oxygen: An overview of recent developments in the process

Hydrogen peroxide (H₂O₂) is an important commodity chemical and its demand is growing significantly in the chemical synthesis due to its “green” character. Currently, H₂O₂ is produced almost exclusively by the anthraquinone auto-oxidation (AO) process. The AO process involves indirect oxidation of hydrogen and thus avoids potentially explosive H₂/O₂ mixture. However, this large-scale process presents significant safety issues associated with the transport of bulk H₂O₂. Moreover, the AO process can hardly be considered an environmentally friendly method. In view of this, more economical and environmentally cleaner routes have been explored for the production of H₂O₂. The liquid-phase catalytic direct synthesis of H₂O₂ from H₂ and O₂ offers an attractive green technology for small-scale/on-site production of H₂O₂. However, the direct synthesis process suffers from two major drawbacks: (i) potential hazards associated with H₂/O₂ mixtures and (ii) poor selectivity for H₂O₂ because the catalysts used for H₂O₂ synthesis are also active for its decomposition and hydrogenation to water as well as for H₂ combustion. These serious issues and the recent developments in the direct H₂O₂ synthesis are discussed in this review. The roles of protons (H⁺) and halide ions in promoting the H₂O₂ selectivity are also examined in detail.     

Plasma depolymerization of chitosan in the presence of hydrogen peroxide

The depolymerization of chitosan by plasma in the presence of hydrogen peroxide (H(2)O(2)) was investigated. The efficiency of the depolymerization was demonstrated by means of determination of viscosity-average molecular weight and gel permeation chromatography (GPC). The structure of the depolymerized chitosan was characterized by Fourier-transform infrared spectra (FT-IR), ultraviolet spectra (UV) and X-ray diffraction (XRD). The results showed that chitosan can be effectively degradated by plasma in the presence of H(2)O(2). The chemical structure of the depolymerized chitosan was not obviously modified. The combined plasma/H(2)O(2) method is significantly efficient for scale-up manufacturing of low molecular weight chitosan.     

Reactive extraction for preparation of hydrogen peroxide under pressure

The preparation of hydrogen peroxide from anthrahydroquinone by reactive extraction was investigated. The integration process of oxidation of anthrahydroquinone by air and extraction of hydrogen peroxide from the organic phase with water was carried out in a sieve plate column under pressure. The conversion of anthrahydroquinone increased with increasing pressure resulting in an increase of hydrogen peroxide concentration in the aqueous phase. However, no change in extraction efficiency of hydrogen peroxide was observed. A mathematical model for gas-liquid-liquid reactive extraction was established. In themodel, the effects of pressure and gas superficial velocity on reaction were considered.With increasing gas superficial velocity, the conversion of anthrahydroquinone increased, and the fraction of hydrogen peroxide extracted reached a plateau with a maximum of 72.94%. However, both the conversion of anthrahydroquinone and the fraction of hydrogen peroxide extracted decreased with increasing organic phase superficial velocity. __________ Translated from Petrochemical Technology, 2007, 36(1): 49–54 [译自: 石油化工]     

A hydrogen peroxide sensor based on a horseradish peroxidase/polyaniline/carboxy-functionalized multiwalled carbon nanotube modified gold electrode

We have developed a polyaniline/carboxy-functionalized multiwalled carbon nanotube (PAn/MWCNTCOOH) nanocomposite by blending the emeraldine base form of polyaniline (PAn) and carboxy-functionalized multiwalled carbon nanotubes (MWCNT) in dried dimethyl sulfoxide (DMSO) at room temperature. The conductivity of the resulting PAn/MWCNTCOOH was 3.6 × 10⁻³ S cm⁻¹, mainly as a result of the protonation of the PAn with the carboxyl group and the radical cations of the MWCNT fragments. Horseradish peroxidase (HRP) was immobilized within the PAn/MWCNTCOOH nanocomposite modified Au (PAn/MWCNTCOOH/Au) electrode to form HRP/PAn/MWCNTCOOH/Au for use as a hydrogen peroxide (H₂O₂) sensor. The adsorption between the negatively charged PAn/MWCNTCOOH nanocomposite and the positively charged HRP resulted in a very good sensitivity to H₂O₂ and an increased electrochemically catalytical current during cyclic voltammetry. The HRP/PAn/MWCNTCOOH/Au electrode exhibited a broad linear response range for H₂O₂ concentrations (86 μM–10 mM). This sensor exhibited good sensitivity (194.9 μA mM⁻¹ cm⁻²), a fast response time (2.9 s), and good reproducibility and stability at an applied potential of −0.35 V. The construction of the enzymatic sensor demonstrated the potential application of PAn/MWCNTCOOH nanocomposites for the detection of H₂O₂ with high performance and excellent stability.     

A novel non-enzymatic hydrogen peroxide sensor based on single walled carbon nanotubes–manganese complex modified glassy carbon electrode

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single wall carbon nanotubes (SWCNTs) and phenazine derivative of Mn-complex. With immersing the GC/CNTs modified electrode into Mn-complex solution for a short period of time 20–100 s, a stable thin layer of the complex was immobilized onto electrode surface. Modified electrode showed a well defined redox couples at wide pH range (1–12). The surface coverages and heterogeneous electron transfer rate constants (k_s) of immobilized Mn-complex were approximately 1.58 × 10⁻¹⁰ mole cm⁻² and 48.84 s⁻¹. The modified electrode showed excellent electrocatalytic activity toward H₂O₂ reduction. Detection limit, sensitivity, linear concentration range and k_cat for H₂O₂ were, 0.2 μM and 692 nA μM⁻¹ cm⁻², 1 μM to 1.5 mM and 7.96(±0.2) × 10³ M⁻¹ s⁻¹, respectively. Compared to other modified electrodes, this electrode has many advantageous such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability.     

Constant concentration method of measuring hydrogen permeation from a hydrogen mixture with Pd membrane

The conventional flow method of measuring hydrogen permeation flux was found to be inaccurate and inadequate to obtain a consistent value of hydrogen flux and permeance because of changing hydrogen concentration along the palladium membrane tube in a hydrogen mixture. We designed a new method in which the hydrogen concentration was kept constant in the retentate. This constant concentration method was a more accurate measurement of hydrogen permeation flux in all of the possible hydrogen mixtures: H₂ + Y with Y = Ar, N₂ and CH₄ and various hydrogen concentrations under different pressure. Permselectivity of the hydrogen mixture was measured under this constant concentration method and was compared with both the conventional flow-through method and separate flow measurement of pure component gases. All three methods gave a different value of permselectivity for the same composite mixture.This method enables us to measure hydrogen flux and permeance accurately in the corresponding composition of the mixture. We found that even with the same partial hydrogen pressure differential for Sieverts’ equation, the hydrogen flux and permeance decreased dramatically with the lowering of hydrogen concentration in the feed.     

Electrochemical investigation of the dimeric oxo-bridged ruthenium complex in aqueous solution and its incorporation within a cation-exchange polymeric film on the electrode surface for electrocatalytic activity of hydrogen peroxide oxidation

Electrochemical behavior of oxo-bridged dinuclear ruthenium(III) complex ([(bpy)2(H₂O)Ru^III-O-Ru^III(H₂O)(bpy)2]⁴⁺) has been studied in aqueous solution (KCl 0.5 mol L⁻¹) by both cyclic and rotating disk electrode (RDE) voltammetry in order to identify and elucidate the reaction mechanism. Modified electrode containing the oxo-bridged ruthenium complex incorporated into a cation-exchange polymeric film deposited onto platinum electrode surface was studied. Cyclic voltammetry at the modified electrode in KCl solution showed a single-electron reduction/oxidation of the couple Ru^III-O-Ru^III/Ru^III-O-Ru^IV. The modified electrode exhibited electrocatalytic property toward hydrogen peroxide oxidation in KCl solution with a decrease of the overpotential of 340 mV compared with the platinum electrode. The Tafel plot analyses have been used to elucidate the kinetics and mechanism of the hydrogen peroxide oxidation. The first at low overpotential region there is no significant change in the Tafel slope (∼0.130 V dec⁻¹) with varying peroxide concentration. The second region at higher overpotential the slope values (0.91–0.47 V dec⁻¹) were depended on the peroxide concentration. The apparent reaction order for H₂O₂ varies from 0.16 to 0.50 in function of the applied potential. The apparent reaction order (at constant potential) with respect to H⁺ concentration of 10⁻⁵ to 10⁻¹ mol L⁻¹ was 0.25. A plot of the anodic current vs. the H₂O₂ concentration for chronoamperometry (potential fixed = +0.61 V) at the modified electrode was linear in the 1.0 × 10⁻⁵ to 2.5 × 10⁻⁴ mol L⁻¹ concentration range.     

The temperature-programmed desorption of hydrogen from copper surfaces

The desorption kinetics of H₂ from a Cu/ZnO/Al₂O₃ catalyst for methanol synthesis were studied under atmospheric pressure in a microreactor set-up by performing temperature-programmed desorption (TPD) experiments after various pretreatments of the catalyst. Complete saturation with adsorbed atomic hydrogen was obtained by dosing highly purified H₂ for 1 h at 240 K and at a pressure of 15 bar. The TPD spectra showed symmetric H₂ peaks centered at around 300 K caused by associative desorption of H₂ from Cu metal surface sites. H₂ TPD experiments performed with different initial coverages resulted in peak maxima shifting to higher temperatures with lower initial coverages indicating that the desorption of H₂ from Cu is of second order. The microkinetic analysis of the TPD traces obtained with different heating rates yielded an activation energy of desorption of 78 kJ mol^–1 and a corresponding frequency factor of desorption of 3×10¹¹ s^–1> in good agreement with the kinetic parameters obtained with Cu(111) under UHV conditions.     

Kinetics of the formation of symmetrical wax esters from the corresponding alcohols with the use of hydrobromic acid and hydrogen peroxide

The primary aliphatic alcohols n-octanol, n-decanol, and n-dodecanol have been converted to their corresponding symmetrical esters by using HBr and H₂O₂ in the absence of a solvent. The reaction was carried out at 30, 40, and 50°C and at mole ratios of alcohol to HBr of 1∶0.1, 1∶0.2, 1∶0.3, and 1∶0.5. The rate of the reaction was found to increase with increase in the reaction temperature and concentration of HBr. The maximal conversion of n-octanol was 72% at 40°C and a mole ratio of n-octanol to HBr of 1∶0.5. The kinetics of the reaction have been established, and the reaction was found to be first-order with respect to alcohol and bromine concentration in the organic phase, and second-order with respect to both. The second-order rate constants for n-octanol, n-decanol, and n-dodecanol are 27.08, 32.58, and 37.42 mL mol⁻¹ min⁻¹, respectively, at 40°C. The activation energy for the esterification reaction of n-octanol was found to be 16.32 kcal mol⁻¹.     

Amperometric detection of hydrogen peroxide at nano-nickel oxide/thionine and celestine blue nanocomposite-modified glassy carbon electrodes

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5–120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2–12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k_s) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 × 10⁻¹⁰ mol cm⁻², 6.12 s⁻¹, 5.9 × 10⁻¹⁰ mol cm⁻² and 6.58 s⁻¹, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) × 10³ M⁻¹ s⁻¹ and 5.5 (±0.2) × 10³ M⁻¹ s⁻¹, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM⁻¹ nA μM⁻¹ and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM⁻¹, and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction.     

Kinetics of the reactive absorption of hydrogen sulfide into aqueous ferric sulfate solutions

The reactive absorption of H₂S into aqueous Fe₂(SO₄)₃ solutions, was studied in a stirred cell reactor operated batchwise with and without a flat interface. The temperature was varied from 25°C to 65°C and the concentrations of aqueous Fe₂(SO₄)₃ solutions ranged from 0.025 to . The corresponding initial pH values ranged from 2 to 0.8, respectively. Additional measurements were conducted at other pH values by addition of NaOH. The H₂S partial pressure was varied between 0 and . The rate of H₂S absorption was measured by recording the pressure drop as a function of time during batch absorption experiments. In this system the absorbed H₂S reacts with ferric iron and is oxidized to elemental sulfur. The kinetic results are in agreement with enhanced absorption due to a fast chemical reaction according to the film theory. The reaction of ferric sulfate and H₂S appears to proceed irreversibly and is first order in both the total concentrations of ferric iron and H₂S. The activation energy for the reaction was calculated to be .     

Formation of a robust and stable film comprising ionic liquid and polyoxometalate on glassy carbon electrode modified with multiwalled carbon nanotubes: Toward sensitive and fast detection of hydrogen peroxide and iodate

A robust and stable film comprising n-octylpyridinum hexafluorophosphate ([C₈Py][PF₆]) and 1:12 phosphomolybdic acid (PMo₁₂) was prepared on glassy carbon electrodes modified with multiwall carbon nanotubes (GCE/MWCNTs) by dip-coating. The cyclic voltammograms of the GCE/MWCNTs/[C₈Py][PF₆]-PMo₁₂ showed three well-defined pairs of redox peaks due to the PMo₁₂ system. The surface coverage for the immobilized PMo₁₂ and the average values of the electron transfer rate constant for three pairs of redox peaks were evaluated. The GCE/MWCNTs/[C₈Py][PF₆]-PMo₁₂ showed great electrocatalytic activity towards the reduction of H₂O₂ and iodate. The kinetic parameters of the catalytic reduction of hydrogen peroxide and iodate at the electrode surface and analytical features of the sensor for amperometric determination of hydrogen peroxide and iodate were evaluated.     

Electrochemical oxidation of hydrogen peroxide at a bromine adatom-modified gold electrode in alkaline media

Bromine (Br)-adatom (Br_(ads)) was in situ fabricated onto polycrystalline gold (Au (poly)) electrode in Br⁻-containing alkaline media. The surface coverage of Br_(ads) (Γ_Br) varied only in the submonolayer coverage within the investigated potential window under potentiodynamic condition because of the coadsorption of hydroxyl ion (OH⁻) in alkaline media. The in situ fabricated Br_(ads)-submonolayer-coated Au (poly) electrode was successfully used for the electrochemical oxidation of hydrogen peroxide (H₂O₂). About five times higher oxidation current was achieved at the modified electrode as compared with the bare electrode. The enhancement of the electrode activity towards the electrochemical oxidation of H₂O₂ was explained based on the enhanced electrostatic attraction between the anionic HO₂⁻ molecules and Br_(ads)-adlayer-induced positively polarized Au (poly) electrode surface.     

Hydrogen peroxide sensor based on modified vitreous carbon with multiwall carbon nanotubes and composites of Pt nanoparticles-dopamine

Sensors using nanostructured materials have been under development in the last decade due to their selectivity for the detection and quantification of different compounds. The physical and chemical characteristics of carbon nanotubes provide significant advantages when used as electrodes for electronic devices, fuel cells and electrochemical sensors. This paper presents preliminary results on the modification of vitreous carbon electrodes with Multiwall Carbon Nanotubes (MWCNTs) and composites of Pt nanoparticles-dopamine (DA) as electro-catalytic materials for the hydrogen peroxide (H₂O₂) reaction. Chemical pre-treatment and consequent functionalization of MWCNTs with carboxylic groups was necessary to increase the distribution of the composites. In addition, the presence of DA was important to protect the active sites and eliminate the pasivation of the surface after the electro-oxidation of H₂O₂ takes place. The proposed H₂O₂ sensor exhibited a linear response in the 0-5 mM range, with detection and quantification limits of 0.3441 mM and 1.1472 mM, respectively.     

A density functional theory study of hydrogen recombination and hydrogen-deuterium exchange on Ga/H-ZSM-5

Density functional theory calculations have been carried out to determine the thermodynamic stability of various Ga species in gallium-exchanged ZSM-5, the thermodynamics of H₂ adsorption, and the most favorable pathway for H₂/D₂ exchange. The portion of the zeolite associated with Ga was represented by a cluster containing 7, 21, or 33 atoms. The B3LYP hybrid method was used to account for the effects of electron exchange and correlation. The most likely form of Ga expected in freshly exchanged and calcined ZSM-5 is ZGa(OH)₂. H₂ reduction of this species is projected to produce ZGa(H)(OH) and ZGa(H)₂. While the thermodynamics of H₂ desorption from ZGa(H)₂ are favorable, the process is projected to be slow because of a high activation barrier. The most favorable pathway for H₂/D₂ exchange over ZGa(H)₂ proceeds via Z(D)(Ga(H)₂(D)) as an intermediate. Similar calculations have been carried out for H₂/D₂ exchange over H-ZSM-5. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of Pt addition on vanadium-incorporated TiO2 catalysts for photodecomposition of ammonia

This study investigated the effect of adding Pt components to V-TiO₂ for highly concentrated ammonia photodecomposition. Pt components were introduced to the V-TiO₂ photocatalysts by using two method types: the common sol-gel (Pt-V-TiO₂) and impregnation (Pt/V-TiO₂) methods. The observed X-ray diffraction (XRD) peaks were assigned to V₂O₅ at 19.5, 27.5 and 30.20° in V-TiO₂, and to Pt metals at 39.80° (111) in Pt/V-TiO₂. The Pt component of Pt-V-TiO₂ was identified at Pt²⁺ from the Pt4f_7/2 and Pt4f_5/2 bands at 73.6 and 77.4 eV in XPS bands, respectively, but the band was shifted to a lower binding energy in Pt/V-TiO₂. The H₂ temperature-programmed reduction (TPR) curves showed that the temperature of reduction from Ti³⁺ to Ti⁰ was decreased by Pt addition and that the area was larger in Pt-V-TiO₂ than in Pt/V-TiO₂. The NH₃ decomposition was slightly increased with vanadium addition compared to that of pure TiO₂, and the decomposition was further enhanced with Pt addition. Particularly, the NH₃ (1,000 ppm) decomposition reached 100% over Pt/V-TiO₂ after 120 min, although about 10–30% of the ammonia was converted into undesirable NO₂ and NO.     

The removal of cephalexin antibiotic in aqueous solutions by ultrasonic waves/hydrogen peroxide/nickel oxide nanoparticles (US/H2O2/NiO) hybrid process

ABSTRACT

Antibiotics are non-biodegradable and can remain for a long time at aquatic environments and they have a big potential bio-accumulation in the environment. The antibiotics are broadly metabolized by humans, animals and plants and they or their metabolites, after metabolization, are entered into the aquatic environment. This study aimed to optimize the operational parameters by Taguchi design and to carry out the kinetic studies for removal of cephalexin antibiotic from aqueous solutions by US/H₂O₂/NiO hybrid process. This experimental study was performed on a laboratory scale in a 500 mL pyrex-made reactor. The main operational parameters to influence the US/H₂O₂/NiO process were identified as the initial concentration of CEX (20–80 mg/L), hydrogen peroxide (H₂O₂) (10–40 mL/L), NiO nanoparticle (2.5–10 mg/L) and reaction time (15–90 min) and therefore, the influence of these factors were studied. Under optimum conditions (pH = 3, reaction time = 90 min, CEX = 40 mg/L, NiO = 7.5 mg/L and H₂O₂ = 30 mL/L) and using the US/H₂O₂/NiO process, the removal efficiencies of CEX, COD and TOC were 93.86%, 72.46% and 54.55%, respectively. The percentage contribution of each factor was also determined. Results introduced the solution pH as the most powerful factor, and its percentage contribution value was up to 94% in the studied process. It was also identified that the removal of CEX antibiotic using the hybrid process obeys the pseudo-first-order kinetics.