Comparative electrochemical study of self-assembled monolayers of 2-mercaptobenzoxazole, 2-mercaptobenzothiazole, and 2-mercaptobenzimidazole formed on polycrystalline gold electrode

Comparative electrochemical behavior of self-assembled monolayers (SAMs) of three heteroaromatic thiols, 2-mercaptobenzoxazole (MBO), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzimidazole (MBI) are investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the electrode/solution interface are considerably and differently affected by thiols constructing the SAMs. The consumed charges for reductive desorption of SAMs, which is criterion for the amount of chemically adsorbed thiol, are significantly different for these three SAMs, specially for MBT, implying that SAM of MBT is formed through both sulfur atoms; the thiol sulfur and skeleton sulfur of the thiazole ring. Desorption potentials of the SAMs have shown the following order for strength of gold-sulfur bond: MBT > MBO > MBI. Activity of the three SAMs as pH-sensitive interfaces was also investigated and their surface-pK_a values derived from the EIS measurements showed this order for acidic strength of SAMs: MBO > MBT > MBI. This is the same order expected due to the difference in electronegativity of the O, S, and N heteroatoms, and confirms that the most electron-rich ring imidazole is attached to the benzene ring of MBI. A comparison of the interfacial charge transfer resistance variation as a function of gold immersion time in thiols solution reveals that kinetics of Au-MBT assembly is different from those of two others and confirms formation of Au-MBT SAM via both sulfur atoms of MBT.     

Electron-transfer characteristics of ferrocene attached to single-walled carbon nanotubes (SWCNT) arrays directly anchored to silicon(1 0 0)

High-density, surface-mounted ferrocene has been prepared using covalent immobilisation of an alcohol substituted ferrocene derivative to a pre-assembled single-walled carbon nanotubes directly anchored to silicon(1 0 0) surface (SWCNTs-Si). The formation of these ferrocene-modified electrodes (Fc-SWCNTs-Si) has been followed using X-ray photoelectron spectroscopy and atomic force microscopy. Electrochemical results show the surface concentration of ferrocenemethanol molecules is 9.26 × 10⁻⁸ mol cm⁻², which is about 500-1000 times greater than the experimentally measured coverage of ferrocene directly attached to flat Si(1 0 0) surfaces. The reversible one-electron wave of the ferrocene/ferrocenium couple was observed at 490 mV versus Ag⁺/Ag and the apparent rate constant of electron transfer, k_app, was 21 s⁻¹. These results suggest these ferrocene-modified electrodes are excellent candidates for molecular memory devices.     

Kinetics and selectivity of asphaltene hydrocracking

Thermal hydrocracking and catalytic hydrocracking over NiMo/γ-Al₂O₃ of a pentane-insoluble asphaltene were conducted in a microbatch reactor at 430 °C. The experimental data of asphaltene conversion fit second-order kinetics adequately, to give the apparent rate constants of 2.435 × 10⁻² and 9.360 × 10⁻² wt frac⁻¹ min⁻¹ for the two processes respectively. A three-lump kinetic model is proposed to evaluate rate constants of parallel reactions from asphaltenes to liquid oil (k₁) and to gas + coke (k₃), and consecutive reaction from liquid to gas + coke (k₂). The evaluated k₁ is 2.430 × 10⁻² and 9.355 × 10⁻² wt frac⁻¹ min⁻¹, k₂ is 2.426 × 10⁻² and 6.347 × 10⁻³ min⁻¹, and k₃ is 5.416 × 10⁻⁵ and 4.803 × 10⁻⁵ wt frac⁻¹ min⁻¹ for asphaltenes hydrocracking in the presence or absence of the catalyst, respectively. Analysis of selectivity shows that the catalytic hydrocracking process promotes liquid production and inhibits coke formation effectively.     

Oxidative desulfurization of Gas oil by polyoxometalates catalysts

Several polyoxometalates: Na₂HPM₁₂O₄₀, H₃PM₁₂O₄₀, Na₂HPM₁₂O₄₀, (VO)H[PM₁₂O₄₀] and (n-Bu₄N)₃[PM₁₂O₄₀] (M = Mo and W) as well as (n-Bu₄N)_3 + x[PW_12−xV_xO₄₀] (x = 0–3) were synthesized and characterized. Benzothiophene, dibenzothiophene and 4,6-dimethyl-dibenzothiophene were used as model sulfur compounds in gas oil. The oxidation reaction was performed using different polyoxometalates as catalyst and H₂O₂/acetic acid. The experimental results show that the W-based polyoxometalate catalysts are more active than the Mo catalysts. The oxidation reactivity of the catalysts depends on the type of countercation: Na⁺ > H⁺ > (VO)⁺ > (n-Bu₄N)⁺. In a series of (n-Bu₄N)_3 + x [PW_12−xV_xO₄₀] (x = 0–3) the order of catalytic activity is V₃ > V₂ > V₁ > V₀. The reactivity order of the sulfur compounds is: dibenzothiophene > 4,6-dimethyldibenzo-thiophene > benzothiophene. The catalytic system in this work was used for the oxidation of gas oil combined with solvent extraction to remove sulfur content in gas oil. Under mild reaction condition, high sulfur removal up to 98% can be achieved with high oil recovery (90%).     

Electrochemical behaviour of (111) B-Doped Polycrystalline Diamond: Morphology/surface conductivity/activity assessed by EIS and CS-AFM

Electrochemical activity, morphology and surface electrical conductivity of Boron-Doped Polycrystalline Diamond films prepared by MPCVD have been investigated. Heterogeneous apparent rate constants of three different redox systems, [Fe(CN)₆]^3−/4−, [IrCl₆]^2−/3− and [Ru(NH₃)₆]^3+/2+ have been measured by both Cyclic Voltammetry and Electrochemical Impedance Spectroscopy on < 100 > textured films with a predominance of (111) faces: first measurements have been done with [Fe(CN)₆]^3−/4− only on as grown samples, and secondly after a mild electrochemical pretreatment the three redox systems have been investigated. “As-grown” samples showed a moderate average activity which was related to the presence of a minority of electronically conducting areas among insulating zones. Electrochemical treatment in neutral conditions substantially increased the activity and heterogeneous apparent rate constants k_app for the three couples were measured in the range of 10^− 2 cm s^− 1 with a good stability in time. Current-sensing AFM images performed ex situ showed that the electrochemically pre-treated material presented a high superficial conductivity whereas the grown sample showed major area of low conductivity.     

A-type zeolite containing Ag/Zn as inorganic antifungal for waterborne coating formulations

The biocide cations Ag⁺ and Zn²⁺ were hosted in the cavities of an ordered aluminosiliceous framework. Starting from sodium A-type zeolite (NaA), LTA containing Ag⁺ (AgA), Zn²⁺ (ZnA) and Ag⁺/Zn (AgZnA) at different cation exchanged levels was obtained and its antifungal properties were evaluated. To determine the minimum inhibitory concentration (MIC) of the exchanged zeolites against Aspergillus niger, [Ag⁺] and [Zn²⁺] values ranging from 50 < [Ag⁺] < 1000 mg L⁻¹ to 650 < [Zn²⁺] < 2000 mg L⁻¹, respectively, were used for NaA, and for AgZnA: 30 < Ag⁺ < 250 mg L⁻¹. The zeolite sample having [Ag⁺] = 100 mg L⁻¹, [Zn²⁺] = 90 mg L⁻¹ produces a growth inhibition comparable to that achieved with 230 mg L⁻¹ of Ag⁺¹ (MIC value obtained for the single cation). The antifungal activity of these products after incorporation in waterborne coating formulations was also determined. Results indicate that Ag⁺ and Zn²⁺ supported on A-type zeolite could be a beneficial tool for the development of waterborne coatings with a longer protection against microbiological attack when compared to traditional organic biocides.     

Kinetics of asphaltene thermal cracking and catalytic hydrocracking

A pentane-insoluble asphaltene was processed by thermal cracking and catalytic hydrocracking over NiMo/γ-Al₂O₃ in a microbatch reactor at 430 °C. Kinetic analysis shows that the first-order kinetics fits the data of conversion in reaction times ≤ 30 min approximately, but deviates from the data of times over 30 min significantly; whereas the second-order kinetics fits the data of the reaction times up to 60 min adequately, to give the apparent rate constants of 1.704 × 10⁻² and 9.360 × 10⁻² wt frac⁻¹min⁻¹ for the two cracking processes. Furthermore, a three-lump kinetic model is proposed to include parallel reactions of asphaltenes to produce liquid oil (k₁) and gas + coke (k₃), and consecutive reaction from liquid to gas + coke (k₂). The evaluated value of k₁ is 1.697 × 10⁻² and 9.355 × 10⁻² wt frac⁻¹min⁻¹, k₂ is 3.605 × 10⁻² and 6.347 × 10⁻³ min⁻¹ , and k₃ is 6.934 × 10⁻⁵ and 4.803 × 10⁻⁵ wt frac⁻¹min⁻¹ for asphaltenes thermal cracking and catalytic hydrocracking, respectively. Selectivity analysis shows that the catalytic hydrocracking process promotes liquid production and inhibits coke formation effectively.     

Electrochemical and surface analytical studies of the self-assembled monolayer of 5-methoxy-2-(octadecylthio)benzimidazole in corrosion protection of copper

5-Methoxy-2-(octadecylthio)benzimidazole (MOTBI) monolayer was self-assembled on fresh copper surface obtained after etching with nitric acid at ambient temperature. The optimum conditions for formation of self-assembled monolayer (SAM) were established using impedance studies. The optimum conditions are methanol as solvent, 10 mM concentration of the organic molecule and an immersion period of 24 h. The MOTBI SAM on copper surface was characterized by contact angle measurements, X-ray photoelectron spectroscopy and reflection absorption FTIR spectroscopy and it is inferred that chemisorption of MOTBI on copper surface is through nitrogen. Corrosion protection ability of MOTBI SAM was evaluated in aqueous NaCl solution using impedance, electrochemical quartz crystal nanobalance, potentiodynamic polarization and weight-loss studies. While bare copper showed a charge-transfer resistance (R_ct) value of 1.89 kΩ cm² in 0.20 M NaCl aqueous environment, the R_ct value for SAM covered copper surface is 123.4 kΩ cm². The MOTBI SAM on copper afforded corrosion inhibition efficiency of 98-99% in NaCl solution in the concentration range and in the temperature range studied. The SAM functions as a cathodic inhibitor. Quantum chemical calculations showed that MOTBI has relatively small ΔE between HOMO and LUMO and large negative charge in its benzimidazole ring, which facilitate formation of a polymeric [Cu⁺-MOTBI] complex on copper surface.     

Photocatalytic activities for partial oxidation of α-methylstyrene over zeolite-supported titanium dioxide and the influence of water addition to reaction solvent

The photocatalytic reaction in the partial oxidation of α-methylstyrene (α-MS) to acetophenone (AP) was investigated for TiO₂ supported on H-ZSM-5 (H-MFI), H-mordenite (H-MOR), and H-Y-type (H-FAU) zeolites. XRD results demonstrated that the anatase was the stable phase of TiO₂ supported on zeolites. Photocatalytic activities of supported catalysts decreased in the following order: TiO₂/H-MFI >> TiO₂/H-MOR > (TiO₂) > TiO₂/H-FAU >> (blank). TiO₂/H-MFI catalyst exhibited the best performance for photocatalytic oxidation of α-MS to AP. The maximal activity was obtained by 25 wt% TiO₂/H-ZSM-5. The addition of water to the reaction solvent resulted in significantly lowering the photocatalytic activity for TiO₂/H-ZSM-5 catalyst, although its activity for TiO₂ and TiO₂ + H-ZSM-5 mechanical mixture was little influenced by the amount of water added to reaction solvent.     

Electrochemical behavior of p-tert-butyl calix[8]arene in CH2Cl2

The electrochemical behavior of p-tert-butyl calix[8]arene has been investigated by cyclic voltammetry. The result shows that there is an irreversible electrochemical oxidative wave when the potential ranges from −0.3 to 1.6 V versus Ag/0.1 M AgNO₃ in acetonitrile (Ag/Ag⁺). At 25 °C, the peak potential is ca. 1.43 V (versus Ag/Ag⁺) at scan rate of 0.05 V s⁻¹. The number of the electrons transferred in the electrochemical reaction is four. The diffusion coefficient of p-tert-butyl calix[8]arene is 2.8 × 10⁻⁵ cm² s⁻¹. The diffusion activation energy is 12.3 kJ mol⁻¹.     

Polyaniline Langmuir-Blodgett film modified glassy carbon electrode as a voltammetric sensor for determination of Ag ions

A highly sensitive electrochemical sensor made of a glassy carbon electrode (GCE) coated with a Langmuir-Blodgett film (LB) containing polyaniline (PAn) doped with p-toluenesulfonic acid (PTSA) (LB/PAn-PTSA/GCE) has been used for the detection of trace concentrations of Ag⁺. UV-vis absorption spectra indicated that the PAn was doped by PTSA. The surface morphology of the PAn LB film was characterized by atomic force microscopy (AFM). The electrochemical properties of this LB/PAn-PTSA/GCE were studied using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The LB/PAn-PTSA/GCE was used as a voltammetric sensor for determination of trace Ag⁺ at pH 5.0 using linear scanning stripping voltammetry. Under the optimal experimental conditions, the stripping current was proportional to the Ag⁺ concentration over the range from 6.0 × 10⁻¹⁰ mol L⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, with a detection limit of 4.0 × 10⁻¹⁰ mol L⁻¹. The high sensitivity, selectivity, and stability of this LB/PAn-PTSA/GCE also demonstrated its practical utility for simple, rapid and economical determination of Ag⁺ in water samples.     

An active iron catalyst containing sulfur for Fischer-Tropsch synthesis

A precipitated iron catalyst containing sulfur for Fischer-Tropsch (F-T) synthesis was prepared by means of a novel method using a ferrous sulfate as precursor. Both fixed bed reactor (FBR) and continues stirred tank slurry reactor (STSR) were used to test long-term F-T reaction behaviors over the catalyst. A stability test (1600 h) in FBR showed that the catalyst was active even after 1500 h of time-on-stream with CO conversion of 78% and with C₅⁺ hydrocarbon selectivity of 72 wt% at 250 °C, 2.0 MPa, 2.0 NL/g-cat/h, and H₂/CO=2.0. The test (550 h) in STSR indicated that the catalyst exhibited relatively high activity with CO conversion of 70-76% and C₅⁺ selectivity of 83-86 wt% in hydrocarbon products under the conditions of 260 °C, 2.0 MPa, 2.0 NL/g-cat/h, and H₂/CO=0.67. The deactivation rate of the catalyst was low, accompanied by surprisingly low methane selectivity of 2.0-2.9 wt%. It is shown that a small amount of sulfur (existing as SO₄²⁻) may promote the catalyst by increasing activity and improving the heavier hydrocarbon selectivity. It is also comparable with other typical iron catalysts for F-T synthesis.     

Electrochemical study of 2-mercaptoimidazole as a novel corrosion inhibitor for steels

From electrochemical methods, polarization resistance and electrochemical impedance spectroscopy, the corrosion susceptibility of pipeline steel samples immersed in 1 M H₂SO₄ was determined using nil and different concentrations of the molecule 2-mercaptoimidazole (2MI). It was found that a corrosion inhibiting efficiency, IE, value of 98.5% was reached when the 2MI concentration in the system increased to 25 ppm. Moreover, at this concentration, the 2MI IE was measured as a function of time finding that the IE kinetics follows the relationship: %IE = 98.5 − 0.03t after 800 h of evaluation. During the first 200 h 2MI IE was higher that 90% then, it decreased to 70% and it remained constant up to 1200 h. It is shown that this compound can affect both the anodic and cathodic processes, thus it can be classified as a mixed-type inhibitor however, from variation of both corrosion potential and polarization resistance with [2MI] it was possible to state that the anodic reaction rate, of the corrosion process, decreases at a greater proportion than the cathodic one. 2MI follows an adsorption mechanism, which can be adequately described by the Langmuir isotherm with an adsorption standard free energy difference (ΔG°_ads) of −26.8 kJ mol⁻¹. In order to analyze the influence of substituting groups, both electron-donating and electron-attracting and the number of π-electrons on the corrosion inhibiting properties of organic molecules, an electrochemical study was carried out on four different molecules having similar chemical framework structure: 2-mercaptoimidazole (2MI), 2-mercaptobenzoimidazole (2MBI) 2-mercapto-5-methylbenzimidazole (2M5MBI) and 2-mercapto-5-nitrobenzimidazole (2M5NBI). It was found that the IE order followed by the molecules tested was 2MI > 2MBI > 2M5MBI > 2M5NBI. Thus 2MI turned out to be the best inhibitor, even superior to the 2MBI. This fact strongly suggests that, contrary to a hitherto generally suggested notion, an efficient corrosion inhibiting molecule does not require to be a large one, also bearing an extensive number of π-electrons.     

Kinetic modeling of a triarylmethane dye decolorization by photoelectro-Fenton process in a recirculating system: Nonlinear regression analysis

The treatment of C.I. Acid Blue 5 solution by electrochemical process was studied under recirculation mode with a cathode containing multi walled carbon nanotubes in the presence of sodium sulfate electrolyte. Comparison of electro-Fenton and photoelectro-Fenton processes at pH 3.0 revealed that 23.04 and 98.25% of the dye was decolorized at 60 min, respectively. The kinetic of dye removal by photoelectro-Fenton process was studied with nonlinear regression analysis. A kinetic model was developed for estimation of pseudo-first order rate constant (k_app) as a function of operational parameters including initial concentration of the dye (10–50 mg/L), flow rate (5–20 L/h), pH (3–9), initial concentration of Fe³⁺ (0.05–0.2 mM) and applied current (0.05–0.45 A). The calculated results, which were obtained from kinetic model, were in consistent with the experimental data (R² = 0.9934). The calculated and experimental data were applied for prediction of the electricity consumption in decolorization processes.     

Microwave enhanced synthesis of chitosan-graft-polyacrylamide

Chitosan-graft-polyacrylamide (Ch-g-PAM) was synthesized without any radical initiator or catalyst using microwave (MW) irradiation. Under optimal grafting conditions, 169% grafting was observed at 80% MW power in 1.16 min. Conventionally under similar conditions a maximum grafting of 82% could be achieved in 1 h using K₂S₂O₈/ascorbic acid as redox initiator coupled with Ag⁺ ions as catalyst and atmospheric oxygen as co-catalyst on a thermostatic water bath at 35±0.2 °C. The representative microwave synthesized graft copolymer was characterized by Fourier transform-infrared spectroscopy, thermo gravimetric analysis and X-ray diffraction measurement, taking chitosan as a reference. The effects of reaction variables as monomer/chitosan concentration, MW power and exposure time on the graft co-polymerization were studied. A probable free radical mechanism for grafting under microwaves has been proposed. The solubility pH for the grafted samples with different extent of grafting was monitored. The adsorption capacity of chitosan was much enhanced after grafting. The microwave synthesized Ch-g-PAM in comparison to that prepared conventionally was found to have much more adsorption ability for Ca²⁺ and Zn²⁺ ions in aqueous solution.     

The performances of higher alcohol synthesis over nickel modified K2CO3/MoS2 catalyst

Ni modified K₂CO₃/MoS₂ catalyst was prepared and the performance of higher alcohol synthesis catalyst was investigated under the conditions: T = 280–340 °C, H₂/CO (molar radio) = 2.0, GHSV = 3000 h^− 1, and P = 10.0 MPa. Compared with conventional K₂CO₃/MoS₂ catalyst, Ni/K₂CO₃/MoS₂ catalyst showed higher activity and higher selectivity to C₂⁺OH. The optimum temperature range was 320–340 °C and the maximum space-time yield (STY) of alcohol 0.30 g/ml h was obtained at 320 °C. The selectivity to hydrocarbons over Ni/K₂CO₃/MoS₂ was higher, however, it was close to that of K₂CO₃/MoS₂ catalyst as the temperature increased. The results indicated that nickel was an efficient promoter to improve the activity and selectivity of K₂CO₃/MoS₂ catalyst.     

An electrochemical DNA biosensor developed on novel multinuclear nickel(II) salicylaldimine metallodendrimer platform

An electrochemical DNA biosensor (EDB) was prepared using an oligonucleotide of 21 bases with sequence NH₂-5′-GAGGAGTTGGGGGAGCACATT-3′ (probe DNA) immobilized on a novel multinuclear nickel(II) salicylaldimine metallodendrimer on glassy carbon electrode (GCE). The metallodendrimer was synthesized from amino functionalized polypropylene imine dendrimer, DAB-(NH₂)₈. The EDB was prepared by depositing probe DNA on a dendrimer-modified GCE surface and left to immobilize for 1 h. Voltammetric and electrochemical impedance spectroscopic (EIS) studies were carried out to characterize the novel metallodendrimer, the EDB and its hybridization response in PBS using [Fe(CN)₆]^3−/4− as a redox probe at pH 7.2. The metallodendrimer was electroactive in PBS with two reversible redox couples at E°′ = +200 mV and E°′ = +434 mV; catalytic by reducing the E_pa of [Fe(CN)₆]^3−/4− by 22 mV; conducting and has diffusion coefficient of 8.597 × 10⁻⁸ cm² s⁻¹. From the EIS circuit fitting results, the EDB responded to 5 nM target DNA by exhibiting a decrease in charge transfer resistance (R_ct) in PBS and increase in R_ct in [Fe(CN)₆]^3−/4− redox probe; while in voltammetry, increase in peak anodic current was observed in PBS after hybridization, thus giving the EDB a dual probe advantage.     

Microstructure and piezoelectric properties of CuO-doped 0.95(K0.5Na0.5)NbO3-0.05Li(Nb0.5Sb0.5)O3 lead-free ceramics

The effects of sintering temperature and the addition of CuO on the microstructure and piezoelectric properties of 0.95(K_0.5Na_0.5)NbO₃-0.05Li(Nb_0.5Sb_0.5)O₃ were investigated. The KNN-5LNS ceramics doped with CuO were well sintered even at 940 °C. A small amount of Cu²⁺ was incorporated into the KNN-5LNS matrix ceramics and XRD patterns suggested that the Cu²⁺ ion could enter the A or B site of the perovskite unit cell and replace the Nb⁵⁺ or Li⁺ simultaneously. The study also showed that the introduction of CuO effectively reduced the sintering temperature and improved the electrical properties of KNN-5LNS. The high piezoelectric properties of d₃₃ = 263 pC/N, k_p = 0.42, Q_m = 143 and tan δ = 0.024 were obtained from the 0.4 mol% CuO doped KNN-5LNS ceramics sintered at 980 °C for 2 h.     

Electrochemical properties of surface-confined films of single-walled carbon nanotubes functionalised with cobalt(II)tetra-aminophthalocyanine: Electrocatalysis of sulfhydryl degradation products of V-type nerve agents

This paper describes detailed comparative electrochemical and electrocatalytic behaviours of basal plane pyrolytic graphite electrodes (BPPGEs) modified with single-wall carbon nanotube (BPPGE-SWCNT) and SWCNTs functionalised with cobalt(II) tetra-aminophthalocyanine by physical (BPPGE-SWCNT-CoTAPc_(mix)), chemical (BPPGE-SWCNT-CoTAPc_(cov)) and electrochemical adsorption (BPPGE-SWCNT-CoTAPc_(ads)) processes. SWCNT improves both solution and surface electrochemistry of CoTAPc. Electrochemical kinetics of the SWCNT-CoTAPc modified BPPGE yielded different k_s values, indicative of different rate-determining steps for the cathodic and anodic reactions. Electrochemical impedance spectroscopy (EIS) analyses in the presence of [Fe(CN)₆]^3−/4− as a redox probe revealed that the SWCNT and SWCNT-CoTAPc_(mix) films have comparable data in terms of solution resistance (R_s), electron transfer resistance (R_et), Warburg impedance (Z_w) and electron-transfer rate constant (k_app). Also, these surface-confined films showed comparable electrocatalytic responses towards the detection of V-type nerve agent sulfhydryl hydrolysis products, dimethylaminoethanethiol (DMAET) and diethylaminoethanethiol (DEAET). Using the BPPGE-SWCNT-CoTAPc_(mix), the estimated catalytic rate constants and diffusion coefficients were higher for DEAET than for the DMAET. Also, the detection limits of approximately 8.0 and 3.0 μM for DMAET and DEAET were obtained with sensitivities of 5.0 and 6.0 × 10⁻² A M⁻¹ for DMAET and DEAET, respectively. BPPGE-SWCNT-CoTAPc showed better potential discrimination for detection of these sulfhydryl analytes than the BPPGE-SWCNT, the latter exhibited enhanced catalytic response for the sulfhydryls than the former.     

Tetracarboxylic acid cobalt phthalocyanine SAM on gold: Potential applications as amperometric sensor for H2O2 and fabrication of glucose biosensor

This report describes the applications of cobalt tetracarboxylic acid phthalocyanine (CoTCAPc) self-assembled monolayer (SAM) immobilized onto a preformed 2-mercaptoethanol (Au-ME) SAM on gold surface (Au-ME-CoTCAPc SAM) as a potential amperometric sensor for the detection of hydrogen peroxide (H₂O₂) at neutral pH conditions. The Au-ME-CoTCAPc SAM sensor showed a very fast amperometric response time of approximately 1 s, good linearity at the studied concentration range of up to 5 μM with a coefficient R² = 0.993 and a detection limit of 0.4 μM oxidatively. Also reductively, the sensor exhibited a very fast amperometric response time (∼1 s), linearity up to 5 μM with a coefficient R² = 0.986 and a detection limit of 0.2 μM. The cobalt tetracarboxylic acid phthalocyanine self-assembled monolayer was then evaluated as a mediator for glucose oxidase (GOx)-based biosensor. The GOx (enzyme) was immobilized covalently onto Au-ME-CoTCAPc SAM using coupling agents: N-ethyl-N(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS), and the results demonstrated a good catalytic behavior. Kinetic parameters associated with the enzymatic and mediator reactions were estimated using electrochemical versions of Lineweaver-Burk and Hanes equation, and the stability of the sensor was tested. The biosensor (Au-ME-CoTCAPc-GOx SAM) electrode showed good sensitivity (7.5 nA/mM) with a good detection limit of 8.4 μM at 3σ, smaller Michaelis-Menten constant (4.8 mM from Hanes plot) and very fast response time of approximately 5 s.