Neutral Phosphate Buffer Research Articles

Ligand assisted electrocatalytic water oxidation by a copper(ii) complex in neutral phosphate buffer.

The electrocatalytic water oxidation activity of a copper(ii) complex, 1, [Cu(L1H)(L1)(OH2)](ClO4), with a redox active aryl oxime ligand, L1H [L1H = 1-(pyridin-2-yl) ethanone oxime] has been investigated. Complex 1 shows a remarkably high turnover frequency of ∼100 s-1 in neutral phosphate buffer at about 675 mV overpotential with ∼94% faradaic efficiency. Electrochemical analysis suggests the involvement of a ligand moiety in a proton-coupled-electron-transfer (PCET) step during the catalytic cycle of complex 1, which in turn provides a route for accumulation of high oxidizing equivalents at the reaction center.

Modified graphite electrodes as potential cathodic electrocatalysts for microbial electrolysis cells

Microbial electrolysis cell (MEC) is an ecologically clean and innovative technology for hydrogen production. The development of cost-effective cathodes with high catalytic activity for hydrogen evolution reaction (HER) in nearneutral electrolytes is the most critical challenge for the practical application of MEC technology. In this study, graphite electrodes, functionalized with non-noble metal oxides, were produced and after electrochemical pre-treatment investigated as potential cathodes for MEC. The morphology of the developed materials was analyzed by scanning electron microscopy (SEM). Their electrochemical performance in neutral phosphate buffer solution (PBS) was explored by means of linear sweep voltammetry (LSV) and chronoamperometry (CA). The results from both methods show that all modified electrodes exhibit higher electrocatalytic activity towards HER than that of bare graphite, which is a prerequisite for further evaluation of these materials as cathodes in real MEC.

Novel cobalt-fumarate framework as a robust and efficient electrocatalyst for water oxidation at neutral pH

The development of efficient and cost-effective electrocatalysts for oxygen evolution reaction is a priority research area. Metal-organic frameworks (MOFs) have recently captured attention as heterogeneous water oxidation catalysts. In spite of their robustness and stability under specific pH conditions, the relatively low current density achieved is their main drawback. Herein, we explored a cobalt based framework [Co(bpy)(fa)]n(DMF)0.25(bpy)0.25 (1) {bpy = 4,4ʹ-bipyridine, fa = fumarate, DMF = dimethylformamide} as an efficient electrocatalyst for the water oxidation reaction. Compound 1 exhibits excellent activity in a neutral phosphate buffer solution. Chronoamperometric studies show that 1 offers a current density of 10 mA cm−2 at only η = 382 mV. Onset over-potential of 248 mV is observed which holds a Tafel slope value of 84 mV dec−1. The catalyst showed a turnover frequency (TOF) of 2 × 10−3 s−1 for oxygen evolution reaction (OER) at 289 mV. Detailed electrochemical studies, including long-term electrolysis, indicates the potential of compound 1 to be utilized as heterogeneous catalyst toward the oxygen evolution reaction.

Electrochemical detection of glucose at physiological pH using gold nanoparticles deposited on carbon nanotubes

There is currently considerable interest in the development of non–enzymatic glucose sensors and gold is one of the noble metals that enables the oxidation of glucose. Gold nanoparticles with a mean diameter of 7.5 nm were deposited onto the walls of functionalised carbon nanotubes to give a gold loading of 2.0% by weight. This composite was dispersed and cast onto glassy carbon and carbon screen printed electrodes. These electrodes were then used to detect glucose in a neutral phosphate buffer solution, corresponding to physiological pH. Using constant potential amperometry, a linear calibration curve was obtained with a sensitivity of 2.77 ± 0.14 μA/mM, a limit of detection, LOD, of 4.1 μM and a linear region extending to 25 mM. This sensor showed very good selectivity in the presence of ascorbic acid, galactose and fructose, but interference was observed in the presence of uric acid. This interference was eliminated by applying a Nafion® film to the composite electrodes. Due to a lower diffusion of glucose across the Nafion® barrier, the sensitivity of the Nafion® coated composite was reduced to 0.55 ± 0.03 μA/mM and the LOD was increased to 10.0 μM. However, a linear response between 0.1 mM and 25 mM was obtained, which covers the normal and elevated levels of glucose in blood. These sensors showed very good stability when stored in air and it was also possible to re–use the sensors.

Biocatalytic Desymmetrization of Prochiral 3‐Aryl and 3‐Arylmethyl Glutaramides: Different Remote Substituent Effect on Catalytic Efficiency and Enantioselectivity

AbstractCatalyzed by an amidase‐containing Rhodococcus erythropolis AJ270 microbial whole cell catalyst in neutral phosphate buffer at 30 °C, desymmetric hydrolysis of a series of prochiral 3‐aryl and 3‐arylmethylglutaramides efficiently afforded 3‐substituted glutaric acid monoamides in up to 95% yield and >99.5% ee. Even far away from the reaction site, the substituents on the aryl still have a significant effect on the catalytic activity and enantioselectivity and different remote substituent effect was observed for the two types of substrates. The synthetic application of biocatalytic desymmetrization was demonstrated by the facile transformation of the obtained enantiopure (R)‐3‐substituted 4‐carbamoylbutanoic acid products to chiral dihydroquinolinone and δ‐lactone compounds.magnified image

Low-cost nanowired α-MnO2/C as an ORR catalyst in air-cathode microbial fuel cell

In this work, low cost α-MnO2 nanowires and α-MnO2 nanowires supported on carbon Vulcan (α-MnO2/C) have been synthesized via a simple and facile hydrothermal method for application in microbial fuel cells. The prepared samples have been characterized by X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FE-SEM). Electrocatalytic activities of the samples have been evaluated by means of cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in a neutral phosphate buffer solution. EIS was performed at different potentials to gain further insight into the kinetic properties of α-MnO2/C. Both catalysts were used in air cathode microbial fuel cells to achieve power densities of 180 and 111 mWm−2 for α-MnO2/C and pristine α-MnO2 nanowires, respectively. α-MnO2/C functions as a good and economical alternative for Pt free catalysts in practical MFC applications, as shown by the findings of stability test and voltage generation cycles in long-term operation of MFC.

Chemical sensing platform for the Zn+2 ions based on poly(o-anisidine-co-methyl anthranilate) copolymer composites and their environmental remediation in real samples.

A novel nanostructure of poly(o-anisidine-co-methyl anthranilate) (poly(Ani-Co-MA) copolymer has been synthesized by chemical oxidative in situ polymerization technique with equal molar proportion of monomers in the presence of sodium dodecylbenzene sulfonic acid (SDBS) surfactant. The synthesized copolymers were characterized by scanning electron microscope (SEM) and X-ray crystallography (XRD), Fourier transform infrared (FTIR), UV-Vis, thermo-gravimetric analysis (TGA), and simultaneous X-ray photoelectron spectroscopy (XPS) study. The ultraviolet visible spectrum shows the π to π∗ transition and n to π∗ transition. XRD diffraction pattern confirms the amorphous nature of poly(Ani-Co-MA)-SDBS composites. The scanning electron microscope image shows the morphology of the copolymer matrix. For the selective detection of Zn+2 cation in neutral phosphate buffer, it was fabricated Zn+2 cation sensor based on glassy carbon electrode (GCE) coated with poly(Ani-co-MA)-SDBS composites as a thin layer with conducting coating binders. The proposed cation sensor has been found to exhibit the inertness in air and chemical environment, long-term stability with good sensitivity, a broad linear dynamic range practically, a reliable reproducibility, short response time, and high electrochemical activity. The sensitivity (0.3560μAμM-1cm-2) of Zn+2 cation sensor has been calculated from the slope of the calibration curve. The linearity of the calibration curve is found over the linear dynamic range (LDR) 0.1nM~0.01M, and detection limit (DL) is 27.0±1.35pM at the signal to noise ratio of 3. This novel effort may be considered quite reliable and effective to detect Zn+2 cation in environmental and biomedical sectors on a broad scale. Simultaneously, SDBS doped poly(o-anisidine-co-methyl anthranilate) copolymer composites were measured against medically important organisms Escherichia coli. E. ludwigi, and Bacillus subtilis. Graphical abstract ᅟ.

Multi‐Enzyme Immobilized Anodes Utilizing Maltose Fuel for Biofuel Cell Applications

AbstractMulti‐enzyme immobilized carbon‐felt electrodes are fabricated for application as a bioanode in biofuel cells to utilize both maltose and glucose as the fuel. The unique combination of three enzymes (maltase, mutarotase, and glucose oxidase) enables us to utilize maltose as the fuel for the bioanode. The new electrode based on carbon felt (CF) demonstrates a high oxidation current density of 6.5 mA cm−2 at 0.34 V vs. Ag/AgCl in a neutral phosphate buffer solution containing 0.025 mol dm−3 (≡M) maltose in a half‐cell configuration. Furthermore, we improve the bioanode performance by changing the surfactant from cetyltrimethylammonium bromide (CTAB) to Triton X‐100® (TX), which is used as a carbon nanotube (CNT) dispersant in the bioanode preparation process. A superior current density of 17 mA cm−2 at 0.34 V vs. Ag/AgCl is demonstrated with the multi‐enzyme bioanode by using TX as the CNT dispersant, owing to the good dispersion of CNTs attached to CF and the reduced deactivation and leakage of the enzymes. A maltose/O2 biofuel cell, composed of the multi‐enzyme immobilized bioanode and a biocathode based on bilirubin oxidase and mediator, delivers a maximum power density of 2.3 mW cm−2 and an open‐circuit voltage of 0.69 V in 0.2 M phosphate buffer solution containing 50 mM maltose.

Enhanced hemoglobin electroactivity on carbon in electrolytes or binders containing water-miscible primary alcohols

Herein we demonstrate for the first time, the commonly overlooked impact of water-miscible primary alcohols on hemoglobin (Hb) electroactivity. When Hb is cast into biosensor films, the binder solvent is often an alcohol; however, the impact of alcohols on Hb electroactivity is unknown. It is well-established that Hb electroactivity is inhibited by the protein structure and that alcohols disturb this structure; thus, probing the alcohol-Hb relationship is vital to evaluate electrochemical results using binder-immobilized Hb. Using differential pulse voltammetry on glassy carbon in neutral pH phosphate buffer, we show a twofold higher Hb response when the Nafion binder contains alcohol, indicating the alcohol significantly changes Hb electroactivity. Significant changes are seen for alcohol concentrations as low as 10%. When binders are necessary for a Hb-containing film, a low methanol content is preferred; ethanol and propanol should be avoided.Conversely, Hb quantification is 53× higher in alcohol-containing electrolytes, due to changes to both the Hb and carbon. Methanol-containing electrolyte exhibits an ultra-low 0.78 nM Hb detection limit. This detection limit is twofold lower than any previously reported for solution-based Hb detection and on par with surface-immobilized Hb, while having the advantages of simplicity, ease of application and low cost.

Palladium nanoparticles immobilized on polymer-functionalized magnetic nanoparticles for the determination of hydrogen peroxide

In this paper, the application of palladium nanoparticles supported on hyperbranched poly (ethylene glycol)-block-poly(citric acid)-functionalized Fe3O4 magnetic nanoparticles (Pd@PCA-b-PEG-Fe3O4) were evaluated as a new electrocatalyst in electrochemical sensing. The Pd@PCA-b-PEG-Fe3O4 was immobilized on the surface of a glassy carbon electrode (GCE) for the electrochemical reduction of hydrogen peroxide (H2O2). This electrode material was characterized by scanning electron microscopy (SEM), the transmission electron microscopy (TEM), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The Pd@PCA-b-PEG-Fe3O4 showed good electrocatalytic activity toward the reduction of H2O2 in the neutral phosphate buffer solution (pH 7.0). Moreover, the potential utility of the sensor was demonstrated by applying it to the analytical determination of H2O2 concentration. The results showed that the electrocatalytic current increased linearly with the H2O2 concentration in the range of 0.1–50.0 µM and the detection limit was 0.03 µM. Finally, the sensor has been successfully applied to determine H2O2 in water and urine samples with good accuracy and precision.

Influence of interfacial polymerization on the crystallinity, molecular weight, conductivity and redox behavior of poly(2,3-dimethyl aniline)

The synthesis of crystalline nanofibers of poly (2,3-dimethyl aniline) using interfacial polymerization is reported with dichloromethane-water and hexane-water interfaces as illustrations. Apart from the differences in the morphology, molecular weight and conductivity, there exist remarkable variations in the optical and electrical properties of the interfacially synthesized polymer in comparison with the conventional single phase method. Furthermore, the morphologies and conductivities of the polymer vary with the choice of interfaces and are attributed to the rate of polymerization as well as the solvent polarity. The origin of the crystallinity is ascribed to the reaction kinetics as well as nature of the oxidant. The electrochemical sensing of hydrogen peroxide using poly (2, 3-dimethyl aniline)-coated glassy carbon electrodes is investigated in neutral phosphate buffer solutions.

ROS-Responsive Chalcogen-Containing Polycarbonates for Photodynamic Therapy.

Reactive oxygen species (ROS)-responsive polymers have attracted attention for their potential in photodynamic therapy. Herein, we report the ROS-responsive aliphatic polycarbonates prepared by the ring-opening polymerization (ROP) of three six-membered cyclic carbonate monomers with ethyl selenide, phenyl selenide or ethyl telluride groups. Under catalysis of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), all three monomers underwent the controlled anionic ROP, showing a feature of equilibrium polymerization due to the bulky effect of 5,5-disubstituents. With PEG macroinitiator, three series amphiphilic block copolymers were prepared. They could form spherical nanoparticles of ∼100 nm, which were stable in neutral phosphate buffer but dissociated rapidly under triggering of H2O2. We studied the H2O2-induced oxidation profiles of selenide- or telluride-containing small molecules by 1H NMR and revealed the factors that affect the oxidation kinetics and products. On this basis, the oxidative degradation mechanism of the copolymer nanoparticles has been clarified. Under the same oxidative condition, the telluride-containing nanoparticle degraded with the fastest rate while the phenyl selenide-based one degraded most slowly. These ROS-responsive nanoparticles could load photosensitizer chlorin e6 (Ce6) and anticancer drug doxorubicin (DOX). Under red light irradiation, Ce6-sensitized production of 1O2 that triggered the degradation of nanoparticles, resulting in an accelerated payload release. In vitro cytotoxicity assays demonstrate that the nanoparticles coloaded with DOX and Ce6 exhibited a synergistic cell-killing effect to MCF-7 cells, representing a novel responsive nanoplatform for PDT and/or chemotherapy.

Photoelectrochemical Properties of Surface-Modified ZnSe:Cu(In,Ga)Se2 Photocathodes for Efficient and Durable Overall Water Splitting

Overall water splitting using a photoelectrochemical (PEC) cell composed of a photocathode and photoanode connected in a series is an attractive method to produce hydrogen from water under sunlight. Because driving forces of two photoelectrodes are combined for the water splitting reaction, narrow-gap materials can be used to achieve high solar-to-hydrogen conversion efficiency (STH). However, the STHs obtained from a PEC cell without any external bias voltage reported so far have been less than 1%. This is because of insufficient onset potentials and photocurrent values of photoelectrodes. For the sake of overcoming the drawbacks, (ZnSe)0.85(CuIn0.7Ga0.3Se2)0.15 ((ZnSe)0.85(CIGS)0.15) thin film photocathodes have recently been developed and reported to show a high onset potential of 0.89 VRHE and long absorption edge of 850-900 nm.2 These properties are suitable for use in the PEC cell. (ZnSe)0.85(CIGS)0.15 thin films are prepared by co-evaporation onto Mo-coated soda-lime glass substrates. Subsequently, CdS, a binary of Mo/Ti and Pt are deposited onto the photocathode surface as a buffer layer, surface conductor and hydrogen evolution reaction (HER) catalyst, respectively.3 The surface-modified (ZnSe)0.85(CIGS)0.15 photocathodes show a relatively high photocurrent value of 12 mA cm-2 at 0 VRHE and sufficient stability in a span of hours at potentials of more negative than 0.5 VRHE under simulated sunlight in a neutral potassium phosphate buffer solution.4 However, at potentials more positive than 0.5 VRHE, the photocurrent value attributed to HER dramatically decreases by half in just one hour mainly due to self-oxidation of the surface sulfide layer, accompanying detachment of the Mo/Ti and Pt at the surface. The poor stability at the positive potentials has made it difficult to construct durable PEC cell using the photocathodes. In this work, effects of surface modifications onto PEC properties of (ZnSe)0.85(CIGS)0.15 photocathodes are investigated. For the sake of suppressing the surface corrosion, the CdS layer was passivated with In2S3, which was formed by using chemical bath deposition (CBD).5 Figure 1 shows the current-time curves of the surface-modified (ZnSe)0.85(CIGS)0.15 photocathodes at 0.6 VRHE under simulated sunlight. Without the CBD treatment, the photocurrent value decreased by 50% in one hour under light irradiation. On the other hand, the In2S3-modified photocathode showed relatively stable PEC HER and the decline of the photocurrent value in one hour was decreased to 25%. It is highly possible that the improvement of stability originates from low solubility of indium oxide or hydroxide generated by the self-oxidation process, while the cadmium oxide and hydroxide are relatively soluble, which can cause corrosion of the surface. Furthermore, effects of oxide-coating onto the stability of the (ZnSe)0.85(CIGS)0.15 photocathode during PEC hydrogen evolution have also been investigated. Among various kinds of coating processes, direct formation of the oxide layer by photoelectrodeposition without annealing the photocathode is an effective method without exerting a bad influence on the underlying sulfide and selenide materials. In the presentation, the details of preparation conditions and PEC properties will be discussed. References J. W. Ager, M. R. Shaner, K. A. Walczak, I. D. Sharp and S. Ardo, Energy Environ. Sci. 2015, 8, 2811–2824.H. Kaneko, T. Minegishi, M. Nakabayashi, N. Shibata, Y. Kuang, T. Yamada and K. Domen, Adv. Funct. Mater. 2016, 26, 4570–4577.H. Kumagai, T. Minegishi, N. Sato, T. Yamada, J. Kubota and K. Domen, J. Mater. Chem. A 2015, 3, 8300–8307.H. Kaneko, T. Minegishi, M. Nakabayashi, N. Shibata and K. Domen, Angew. Chemie Int. Ed. 2016, 55, 15329–15333.F. Jiang, Gunawan, T. Harada, Y. Kuang, T. Minegishi, K. Domen and S. Ikeda, J. Am. Chem. Soc. 2015, 137, 13691–13697. Figure 1

ROS-Activated Ratiometric Fluorescent Polymeric Nanoparticles for Self-Reporting Drug Delivery.

Reactive oxygen species (ROS)-responsive theranostic nanomedicines have attracted wide interest in recent years because ROS stress is implicated in some pathological disorders such as inflammatory diseases and cancers. In this article, we report a kind of innovative ROS-responsive theranostic polymeric nanoparticles that are able to load hydrophobic drugs and to fluorescently self-report the in vitro or intracellular drug release under ROS triggering. The fluorescent nanoparticles were formed by amphiphilic block copolymers consisting of a poly(ethylene glycol) (PEG) segment and an oxidation-responsive hydrophobic block. The copolymers with different hydrophobic block lengths were synthesized by the atom transfer radical polymerization of a phenylboronic ester-containing acrylic monomer with a small fraction of a ROS-activatable 1,8-naphthalimide-based fluorescent monomer, using PEG-Br as the macroinitiator. The copolymer nanoparticles were stable in neutral phosphate buffer but degraded upon H2O2 triggering, with the degradation rate depending on the hydrophobic block length and the concentration of H2O2. The degradation of nanoparticles was accompanied by a colorimetric change of the fluorophore from blue to green, which affords the nanoparticles the ability to detecting H2O2 by a ratiometric fluorescent approach. Moreover, the nanoparticles could encapsulate doxorubicin (DOX) and the H2O2-triggered DOX release was well associated with the change in ratiometric fluorescence. Confocal laser scanning microscope results reveal that the fluorescent nanoparticles were internalized into A549 cells through the endocytosis pathway. The ROS-stimulated degradation of the nanoparticles and intracellular DOX release and the fate of the degraded polymers could be monitored by ratiometric fluorescent imaging. Finally, the naked nanoparticles and the degradation products are cytocompatible, whereas the DOX-loaded ones exhibit concentration-dependent cytotoxicity. Of importance, the stimulation with exogenous H2O2 or lipopolysaccharide enhanced obviously the cell-killing capability of the DOX-loaded nanoparticles because of the ROS-enhanced intracellular DOX release.

Solution-Processed Nb-Substituted BaBiO3 Double Perovskite Thin Films for Photoelectrochemical Water Reduction

Photoelectrochemical (PEC) water reduction is a long-term strategical technology for hydrogen production. In this work, we synthesize a series of compact and nano/mesoporous Nb-substituted BaBiO3 [i.e., Ba2Bi(Bi1–xNbx)O6, 0 ≤ x ≤ 0.93, BBNO] thin films using cost-effective chemical solution methods. The synthesized BBNO alloy based thin films demonstrate tunable bandgaps from 1.41 eV (x = 0) to 1.89 eV (x = 0.93) to efficiently absorb the solar spectrum and p-type conductivities suitable for hydrogen production. The photoelectrodes with a configuration fluorine-doped SnO2/BBNO (0 ≤ x ≤ 0.93)/Pt produce cathodic photocurrents of 0.05–1 mA·cm–2 at 0 VRHE (volt versus reversible hydrogen electrode) measured in a neutral (pH = 7.2) phosphate buffer and under simulated AM 1.5G illumination (100 mW·cm–2). The BaBiO3 without Nb alloying based electrode delivers the best photocurrent of 1 mA·cm–2 at 0 VRHE but is subjected to severe corrosions during the PEC related tests. Alloying Nb has an obvious influence on enhancing the material stability against corrosion. With Nb alloying, the screen-printed nanoporous BBNO (x = 0.6, bandgap = 1.62 eV) based photoelectrode generates a better photocurrent of 0.2 mA·cm–2 at 0 VRHE with a highly positive onset at 1.5 VRHE enabling unbiased water reduction.

Photo-electrochemical hydrogen production from neutral phosphate buffer and seawater using micro-structured p-Si photo-electrodes functionalized by solution-based methods

Micro-structured p-Si/TiO2/NiOx allows for efficient photoelectrochemical H2 production from seawater.

Highly selective non-enzymatic electrochemical sensor based on a titanium dioxide nanowire-poly(3-aminophenyl boronic acid)-gold nanoparticle ternary nanocomposite.

A novel three component (titanium dioxide nanowire (TiO2 NW), poly(3-aminophenyl boronic acid) (PAPBA) and gold nanoparticles (Au NPs)) based ternary nanocomposite (TNC) (designated as TiO2 NW/PAPBA–Au TNC) was prepared by a simple two-stage synthetic approach and utilized for the fabrication of a non-enzymatic (enzyme-free) glucose (NEG) sensor. In stage 2, the PAPBA–Au NC was formed by oxidative polymerization of 3-APBA using HAuCl4 as oxidant on the surface of pre-synthesized TiO2 NW via electrospinning (stage 1). The formation of PAPBA–Au NC as the shell on the surface of the TiO2 NW (core) was confirmed by field emission scanning electron microscopy (FE-SEM). Notably, we obtained a good peak to peak separation, and a high peak current for the redox Fe(CN)63−/4− process indicating excellent electron transfer capability at the glassy carbon electrode (GCE)/TiO2 NW/PAPBA–Au TNC interface. Also, the fabricated TiO2 NW/PAPBA–Au TNC provides excellent electrocatalytic activity towards glucose detection in neutral (pH = 7.0) phosphate buffer solution. The detection of glucose was monitored using differential pulse voltammetry. The obtained sensitivity and detection limits are superior to many of the TiO2 based enzymatic and non-enzymatic glucose sensors reported in the literature. Furthermore, the TiO2 NW/PAPBA–Au TNC sensor is preferred because of its high selectivity to glucose in the presence of co-existing interfering substances and practical application for monitoring glucose in human blood serum samples.

Di-branched triphenylamine dye sensitized TiO2 nanocomposites with good photo-stability for sensitive photoelectrochemical detection of organophosphate pesticides

Herein, a di-branched di-anchoring dye, T(TA)2, with triphenylamine as electron donor, thiophene as electron transfer π-bridge, and acrylic acid as both acceptor and anchoring groups, was synthesized and coupled with TiO2 nanoparticles for the highly sensitive photoelectrochemical (PEC) assay of organophosphate pesticides (OPs). The T(TA)2 exhibited good anchoring stability to TiO2 nanoparticles in neutral buffer solutions. Under 2 h continual irradiation, the T(TA)2-TiO2 nanocomposites respectively kept 99.7% and 85.9% of their initial photocurrents in neutral Tris-HCl and phosphate buffer solutions. Neither degradation nor desorption of T(TA)2 from TiO2 nanoparticles was observed during the continual irradiation in the Tris-HCl solutions. The stability was not only superior to its analogues either possessing one branch, with cyanoacrylic acid as anchoring groups, or without thiophene in the π-bridge, but also better than the Ru(II) complex N719 and the porphyrin dye sensitized TiO2 nanocomposites. The nanocomposites also showed highly photocatalytic ability towards the oxidation of ascorbic acid and thiocholine (TCh). Since the latter is the enzymatic hydrolysis product of acetylcholinesterase (AChE) and the activity of AChE can be inhibited by OPs, the T(TA)2-TiO2/FTO was further used for PEC assay of OPs. Using parathion as a model analyte, the PEC method showed a wide linear range from 2 × 10−12-4 × 10−6 g mL−1 and an extremely low limit of detection of 5.6 × 10−13 g mL−1. Regarding these good analytical performances, this study may provide some guidance and pave the way for the applications of dye-TiO2 nanocomposites in a lot of PEC devices required to be performed in aqueous solutions.

An approach for electrochemical functionalization of carbon nanotubes/1-amino-9,10-anthraquinone electrode with catechol derivatives for the development of NADH sensors

A new type of modified electrode, consisting of electro generated quinone redox mediator and carbon nanotubes (CNT) for electrocatalytic oxidation of reduced form of β-nicotinamide adenine dinucleotide (NADH) has been developed. The CNT functionalized with 1-amino-9,10-anthraquinone electrodes (GC/CNT/AAQ) were subjected to cyclic voltammetry in the presence of selected 1,2-dihydroxybenzene derivatives (catechol, 3-methoxycatechol and 4-methylcatechol). As a result, the electroactive quinone adducts were synthesized directly on the electrode surface via Michael addition mechanism. The structures of novel compounds were established using complementary computational studies and then were confirmed by HPLC-ESI-MS method. Electrochemical characterization of the electrodes after modification was carried out by cyclic voltammetry in broad range of pH. The heterogeneous electron transfer rate constants (ks) for the studied quinone modified electrodes were estimated and the obtained values (between 9.8 and 16.7 s−1) suggest moderate electron transfer kinetics. The electrodes displayed remarkable catalytic activity toward NADH oxidation in neutral phosphate buffer (pH = 7.4). The incorporation of quinone moieties onto electrode surface resulted in significantly decreased oxidation potential and enhanced current as compared to unmodified electrodes. NADH has been successfully determined at 0.1 V vs. Ag/AgCl, on all developed electrodes. The established method is characterized by linearity, low limits of detection (from 0.63 to 1.15 μM) and quantitation (from 1.9 to 3.47 μM), high sensitivity, suitable accuracy, repeatability and precision.

Activation of commercial Pt/C catalyst toward glucose electro-oxidation by irreversible Bi adsorption

The effect of irreversibly adsorbed Bi on commercial Pt/C catalyst toward glucose electro-oxidation reaction (GOR) in different electrolytes (acidic, neutral, alkaline) is studied. Bi is successfully deposited on Pt/C from Bi3+ containing acidic solution from 0 to 90% coverage degree. The stability of the Bi layer in acid and alkaline corresponded to previous studies and started to dissolve at 0.7 V and 0.8 V versus reversible hydrogen electrode (RHE), respectively. However, in neutral phosphate buffer the layer showed remarkable stability to at least 1.2 V versus RHE. Bi modification at low (20%) and high (80%) coverage showed the highest increase in the activity of Pt/C toward GOR by a factor up to 7 due to the increased poisoning resistance of the modified catalyst. The effect of poisoning was especially reduced at high Bi coverage (80%), which shows that adsorbate blocked by Bi through the third-body effect is effective. Finally, with or without Bi modification GOR on Pt/C was most active in alkaline conditions.