A sensitive amperometric bromate sensor based on multi-walled carbon nanotubes/phosphomolybdic acid composite film

Polyoxometalate Functionalized Sensors: A Review

Polyoxometalates (POMs) are a class of metal oxide complexes with a large structural diversity. Effective control of the final chemical and physical properties of POMs could be provided by fine-tuning chemical modifications, such as the inclusion of other metals or non-metal ions. In addition, the nature and type of the counterion can also impact POM properties, like solubility. Besides, POMs may combine with carbon materials as graphene oxide, reduced graphene oxide or carbon nanotubes to enhance electronic conductivity, with noble metal nanoparticles to increase catalytic and functional sites, be introduced into metal-organic frameworks to increase surface area and expose more active sites, and embedded into conducting polymers. The possibility to design POMs to match properties adequate for specific sensing applications turns them into highly desirable chemicals for sensor sensitive layers. This review intends to provide an overview of POM structures used in sensors (electrochemical, optical, and piezoelectric), highlighting their main functional features. Furthermore, this review aims to summarize the reported applications of POMs in sensors for detecting and determining analytes in different matrices, many of them with biochemical and clinical relevance, along with analytical figures of merit and main virtues and problems of such devices. Special emphasis is given to the stability of POMs sensitive layers, detection limits, selectivity, the pH working range and throughput.

Electrochemical Sensors for Determination of Bromate in Water and Food Samples-Review

The application of potassium bromate in the baking industry is used in most parts of the world to avert the human health compromise that characterizes bromates carcinogenic effect. Herein, various methods of its analysis, especially the electrochemical methods of bromate detection, were extensively discussed. Amperometry (AP), cyclic voltammetry (CV), square wave voltammetry (SWV), electrochemiluminescence (ECL), differential pulse voltammetry and electrochemical impedance spectroscopy (EIS) are the techniques that have been deployed for bromate detection in the last two decades, with 50%, 23%, 7.7%, 7.7%, 7.7% and 3.9% application, respectively. Despite the unique electrocatalytic activity of metal phthalocyanine (MP) and carbon quantum dots (CQDs), only few sensors based on MP and CQDs are available compared to the conducting polymers, carbon nanotubes (CNTs), metal (oxide) and graphene-based sensors. This review emboldens the underutilization of CQDs and metal phthalocyanines as sensing materials and briefly discusses the future perspective on MP and CQDs application in bromate detection via EIS.

Polyoxometalates in Analytical Sciences

Polyoxometalates (POMs) have been used for spectrophotometric determinations of silicon and phosphorus under acidic conditions, referred to as the molybdenum yellow method and molybdenum blue method, respectively. Many POMs are redox active and exhibit fascinating but complicated voltammetric responses. These compounds can reversibly accommodate and release many electrons without exhibiting structural changes, implying that POMs can function as excellent mediators and can be applied to sensitive determination methods based on catalytic electrochemical reactions. In addition, some rare-earth-metal-incorporated POMs exhibit fluorescence, which enables sensitive determination by the enhancement and quenching of fluorescence intensities. In this review, various analytical applications of POMs are introduced, mainly focusing on papers published after 2000, except for the molybdenum yellow method and molybdenum blue method.

Evolutionary Metal Oxide Clusters for Novel Applications: Toward High-Density Data Storage in Nonvolatile Memories

Because of current fabrication limitations, miniaturizing nonvolatile memory devices for managing the explosive increase in big data is challenging. Molecular memories constitute a promising candidate for next-generation memories because their properties can be readily modulated through chemical synthesis. Moreover, these memories can be fabricated through mild solution processing, which can be easily scaled up. Among the various materials, polyoxometalate (POM) molecules have attracted considerable attention for use as novel data-storage nodes for nonvolatile memories. Here, an overview of recent advances in the development of POMs for nonvolatile memories is presented. The general background knowledge of the structure and property diversity of POMs is also summarized. Finally, the challenges and perspectives in the application of POMs in memories are discussed.

Construction of (3,6)-connected polyoxometalate-based metal–organic frameworks (POMOFs) from triangular carboxylate and dimerized Zn4-ε-Keggin

The methodology of extension of reduced transition metal-grafted ε-Keggin polyoxoanions with two types of terphenyl-based tricarboxylates was used to isolate two (3,6)-connected 3D POMOFs.

Electrocatalytic reduction of bromate based on Pd nanoparticles uniformly anchored on polyaniline/SBA-15

A nano-composite electrocatalyst of Pd nanoparticles (Pd-NPs) anchored on polyaniline (PANI) supported by mesoporous SBA-15 (Pd-NPs/PANI/SBA-15), was synthesized using an in situ chemical method. Transmission electron microscopy showed that the Pd-NPs were homogeneously dispersed. Fourier-transform infrared and X-ray photoelectron spectroscopies confirmed that the Pd-NPs in the metallic state (Pd(0)) were predominantly immobilized on nitrogen sites in the PANI chains. The electrochemical performance of Pd-NPs/PANI/SBA-15 for electrocatalytic reduction of bromate (BrO3(-)) in an acidic medium was investigated by cyclic voltammetry (CV) and amperometric measurement. The reduction peak in the CV curves in the region 0.12 to -0.22V (vs. SCE) corresponded to response of BrO3(-) electroreduction, and the reduction peak current was well fitted linearly to the BrO3(-) concentration. It is proposed that the bromate ions diffuse to the Pd-NPs active sites and then the electrocatalytic reduction occurred with the H(+) doped in PANI. Furthermore, by amperometric measurement, Pd-NPs/PANI/SBA-15 showed relatively high sensitivity with respect to BrO3(-) concentration in the range of 8μmolL(-1) to 40mmolL(-1). Continuous CV for 200 cycles proved that Pd-NPs/PANI/SBA-15 had excellent electrocatalytic stability. These results show that Pd-NPs/PANI/SBA-15 is effective for electrocatalytic reduction of BrO3(-) and has great potential for the fabrication of BrO3(-) electrochemical sensor.

An electrochemiluminescence sensor for bromate assay based on a new cationic polythiophene derivative

A sensitive electrochemiluminescence (ECL) sensor was fabricated for bromate assay based on a cationic polythiophene derivative, poly[3-(1,1'-dimethyl-4-piperidinemethylene)thiophene-2,5-diyl chloride] (PTh-D)/nafion modified Au electrode. Bromate was used as the coreactant as well as detecting analyte in the ECL sensor for the first time. The prepared PTh-D exhibited excellent solubility, strong and stable cathodic ECL activity. PTh-D can be immobilized on the surface of Au electrode via AuS bonding and nafion and chitosan were also used to immobilize PTh-D. The fabricated sensor exhibited a good linear relationship between the ECL intensities and the concentrations of BrO3(-) ranging from 1 μM to 0.1 M with a detection limit of 1 μM. This proposed method not only expands the application of PTh-D, but also opens new doors toward the detection of BrO3(-).

Syntheses, structures and electrochemical properties of a class of 1-D double chain polyoxotungstate hybrids [H(2)dap][Cu(dap)(2)](0.5)[Cu(dap)(2)(H2O)][Ln(H(2)O)3(α-GeW(11)O(39))]·3H(2)O

A series of novel organic-inorganic hybrid 1-D double chain germanotungstates [H2dap][Cu(dap)2]0.5[Cu(dap)2(H2O)][Ln(H2O)3(α-GeW11O39)]·3H2O [Ln = La(III) (1), Pr(III) (2), Nd(III) (3), Sm(III) (4), Eu(III) (5), Tb(III) (6), Er(III) (7)] (dap = 1,2-diaminopropane) have been hydrothermally prepared and structurally characterized by elemental analyses, powder X-ray diffraction (PXRD), IR spectra, thermogravimetric (TG) analyses, X-ray photoelectron spectroscopy (XPS) and single-crystal X-ray diffraction. The most prominent structural feature of 1-7 is that the [Ln(H2O)3(α-GeW11O39)](5-) moieties are firstly connected with each other via the W-O-Ln-O-W bridges creating a 1-D {[Cu(dap)2(H2O)][Ln(H2O)3(α-GeW11O39)]}n(3n-) polymeric chain and then two adjacent antiparallel 1-D polymeric chains are linked together through [Cu(dap)2](2+) linkages giving rise to the rare organic-inorganic hybrid 1-D Cu(II)-Ln(III) heterometallic double-chain architectures. To the best of our knowledge, 1-7 represent the first 1-D double-chain Cu(II)-Ln(III) heterometallic germanotungstates. The variable-temperature magnetic susceptibilities of 2, 4 and 7 have been investigated. Furthermore, the solid-state electrochemical and electro-catalytic properties of 3 and 4 have been measured in 0.5 mol L(-1) Na2SO4 + H2SO4 aqueous solution by entrapping them in a carbon paste electrode. 3 and 4 display apparent electro-catalytic activities for nitrite, bromate and hydrogen peroxide reduction.

Electrochemical sensors based on carbon nanotubes

This review focuses on recent contributions in the development of the electrochemical sensors based on carbon nanotubes (CNTs). CNTs have unique mechanical and electronic properties, combined with chemical stability, and behave electrically as a metal or semiconductor, depending on their structure. For sensing applications, CNTs have many advantages such as small size with larger surface area, excellent electron transfer promoting ability when used as electrodes modifier in electrochemical reactions, and easy protein immobilization with retention of its activity for potential biosensors. CNTs play an important role in the performance of electrochemical biosensors, immunosensors, and DNA biosensors. Various methods have been developed for the design of sensors using CNTs in recent years. Herein we summarize the applications of CNTs in the construction of electrochemical sensors and biosensors along with other nanomaterials and conducting polymers.

Carbon-nanotube-assisted high loading and controlled release of polyoxometalates in biodegradable multilayer thin films

Carbon nanotubes loaded with peptides, proteins and drugs can translocate across the cell membrane. This big advantage has attracted increasing attention to design a novel delivery system using nanotubes. Polyoxometalate (POM) is a promising antitumor drug and it shows a very strong interaction with carbon nanotube surfaces. In this paper, a novel complex of POM-modified single-walled carbon nanotubes (SWNTs) and chitosan was fabricated through a layer-by-layer self-assembly process. With the addition of SWNTs, the loading of POM in this thin film was doubled in the high ionic strength. The initial burst release of POMs in the (POM/chitosan)(n) thin film was suppressed in the (POM-SWNT/chitosan)(n) thin film. Also the instability of POMs in a physiologically relevant pH environment was overcome. The strong interaction between POMs and SWNTs was believed to be the determinant factor in the higher loading and prolonged release of POMs in (POM-SWNT/chitosan)(n) thin films.

Immobilization of [Cu(bpy)2]Br2 complex onto a glassy carbon electrode modified with alpha-SiMo12O40(4-) and single walled carbon nanotubes: application to nanomolar detection of hydrogen peroxide and bromate

A simple procedure has been used for preparation of modified glassy carbon electrode with carbon nanotubes and copper complex. Copper complex [Cu(bpy)(2)]Br(2) was immobilized onto glassy carbon (GC) electrode modified with silicomolybdate, alpha-SiMo(12)O(40)(4-) and single walled carbon nanotubes (SWCNTs). Copper complex and silicomolybdate irreversibly and strongly adsorbed onto GC electrode modified with CNTs. Electrostatic interactions between polyoxometalates (POMs) anions and Cu-complex, cations mentioned as an effective method for fabrication of three-dimensional structures. The modified electrode shows three reversible redox couples for polyoxometalate and one redox couple for Cu-complex at wide range of pH values. The electrochemical behavior, stability and electron transfer kinetics of the adsorbed redox couples were investigated using cyclic voltammetry. Due to electrostatic interaction, copper complex immobilized onto GC/CNTs/alpha-SiMo(12)O(40)(4-) electrode shows more stable voltammetric response compared to GC/CNTs/Cu-complex modified electrode. In comparison to GC/CNTs/Cu-complex the GC/CNTs/alpha-SiMo(12)O(40)(4-) modified electrodes shows excellent electrocatalytic activity toward reduction H(2)O(2) and BrO(3)(-) at more reduced overpotential. The catalytic rate constants for catalytic reduction hydrogen peroxide and bromate were 4.5(+/-0.2)x10(3) M(-1) s(-1) and 3.0(+/-0.10)x10(3) M(-1) s(-1), respectively. The hydrodynamic amperommetry technique at 0.08 V was used for detection of nanomolar concentration of hydrogen peroxide and bromate. Detection limit, sensitivity and linear concentration range proposed sensor for bromate and hydrogen peroxide detection were 1.1 nM and 6.7 nA nM(-1), 10 nM-20 microM, 1 nM, 5.5 nA nM(-1) and 10 nM-18 microM, respectively.

Phosphomolybdate-modified multi-walled carbon nanotubes as effective mediating systems for electrocatalytic reduction of bromate

Electrocatalytic properties (towards reduction of bromate in 0.5moldm(-3) H(2)SO(4)) of multi-walled carbon nanotubes (CNTs) modified with phosphododecamolybdate (PMo(12)) monolayers have been diagnosed using cyclic voltammetry and amperometry. The ability of negatively charged PMo(12)-modified CNTs to attract electrostatically ultra-thin, positively charged conducting polymer (PEDOT or polypyrrole) structures is explored to grow in controlled manner hybrid organic-inorganic network electrocatalytic films. Due to the presence of three-dimensionally distributed CNTs, the films' conductivity and porosity are improved. The hybrid systems utilizing polypyrrole, rather than PEDOT, have produced fairly higher bromate electroreduction catalytic currents. Comparison is also made to Nafion-stabilized dispersion of PMo(12)-modified CNTs inks. The latter system is characterized by good stability and relatively the highest sensitivities with respect to bromate concentration.