An electrically conductive, flow-through, fixed bed adsorption membrane (FCME) made of carbon nanotubes (CNT) installed in an electrochemical flow cell, was applied for the highly efficient adsorption and detection of organic pollutants. Three analytes with different chemical nature, i.e., parathion ethyl, tartrazine and diquat, were chosen as model systems to demonstrate the capabilities of the system. Adsorptive stripping voltammetry (AdSV) performed by the FCME provided directly the amount of analyte adsorbed; in contrast to an adsorption column, that monitors the effluent concentration. The adsorption capacity and kinetic constants were obtained by AdSV and were comparable with those predicted by the Thomas model. The FCME enabled the detection of nanomolar levels of tartrazine and parathion, and submicromolar levels of diquat with a linear range of three orders of magnitude. In addition to being a very sensitive analytical tool, FCME is an adsorption membrane that enables its simple electrochemical regeneration.
We studied the direct electron transfer (DET) between glucose and electrogenerated AuCl4- catalysed by glucose oxidase (GOx) and gold nanoparticles (AuNPs) by scanning electrochemical microscopy (SECM). Well-defined AuNPs were prepared and attached onto an insulating surface. Studying the current transients of a gold microelectrode held within a few microns from the surface revealed that the AuNPs interacted with the GOx and were crucial for the DET from the glucose. We investigated very carefully the effect of pH and the size of the AuNPs on electron transfer. AuNPs of 16, 40 and 80 nm diameter were applied. The kinetics of electron transfer was analysed by the Michael-Menten kinetic mechanism. Interestingly, we found that the fastest DET was exhibited by the 40 nm AuNPs at pH 3 and 5. At higher pH, electron transfer was better catalysed by the 80 nm AuNPs. This was rationalized by the effect of the pH on the enzymatic structure and the charge of the AuNPs.
The selective recognition of nanoparticles (NPs) can be achieved by nanoparticle-imprinted matrices (NAIMs), where NPs are imprinted in a matrix followed by their removal to form voids that can reuptake the original NPs. The recognition depends on supramolecular interactions between the matrix and the shell of the NPs, as well as on the geometrical suitability of the imprinted voids to accommodate the NPs. Here, gold NPs stabilized with citrate (AuNPs-cit) were preadsorbed onto a conductive surface followed by electrografting of p-aryldiazonium salts (ADS) with different functional groups. The thickness of the matrix was carefully controlled by altering the scan number. The AuNPs-cit were removed by electrochemical dissolution. The recognition of the NAIMs was determined by the reuptake of the original AuNPs-cit by the imprinted voids. We found that the recognition efficiency is a function of the thickness of the NAIM layer and is sensitive to the chemical structure of the matrix. Specifically, a subtle change of the functional group of the p-aryldiazonium building block, which was varied from an ether to an ester, significantly affected the recognition of the NPs.
Renewable energy technology and effective energy management are the most crucial factors to consider in the progress toward worldwide energy sustainability. Smart window technology has a huge potential in energy management as it assists in reducing energy consumption of indoor lighting and air-conditioning in buildings. Electrochromic (EC) materials, which can electrically modulate the transmittance of solar radiation, are one of the most studied smart window materials. In this work, highly transparent SnO2 inverse opal (IO) is used as the framework to electrochemically deposit amorphous WO3 layer to fabricate hybrid SnO2-WO3 core-shell IO structure. The hybrid structure is capable of effective near infrared (NIR) modulation while maintaining high visible light transparency in the colored and bleached states. By varying the initial diameter of the polystyrene (PS) opal template and the WO3 electrodeposition time, optimal results can be obtained with the smallest PS diameter of 392 nm and 180 s WO3 electrodeposition. In its colored state, the 392-SnO2-WO3-180 core-shell IO structure shows approximate to 70% visible light transparency, 62% NIR blockage at 1200 nm, and approximate to 15% drop in NIR blocking stability after 300 cycles. The SnO2-WO3 core-shell IO structure in this study is a promising EC material for advanced smart window technology.
Binder-free electrodes with core-shell structures have shown great potential in a variety of important energy storage systems. In order to endow the core-shell hierarchical structure with enhanced electrochemical properties, rationally designed and fabricated hierarchical structures with controllable morphology and great electrical conductivity are highly desired. In this work, a uniform dendritic SCo3O4@NiCo2S4 hierarchical structure grown on Ni foam was successfully designed and synthesized via sulfur-doping of Co3O4 (S-Co3O4) as the inner core with enhanced conductivity. The hierarchical electrode exhibited high areal capacity (10.9 mA h cm(-2) at a current density of 8 mA cm(-2)), a good rate performance (72.5% retention after increasing the current densities from 8 to 30 mA cm(-2)), and excellent cycling stability (97.3% retention after 5000 cycles). Moreover, a hybrid energy storage batterysupercapacitor device, constructed from a S-Co3O4@NiCo2S4 positive electrode and an active carbon (AC) negative electrode, showed high energy density and power density. Contributing to short ion diffusion, large electroactive sites and low contact resistance, our work not only demonstrates a promising electrode for energy storage battery-supercapacitor hybrid (BSH) devices, but also provides an attractive strategy for the design of electrode materials.
Long-term cycling stability is an important criterion and big challenge for pseudocapacitive materials. Ultra-stable manganese doped Co3O4 mesoporous nanoneedles were synthesized via one-step hydrothermal reaction followed by annealing grown on nickel foam (noted as MnxCoyO/NF, x + y = 2.25) for supercapacitors. The Mn doping in Co3O4 was confirmed by several techniques. Among various MnxCoyO/NF electrodes, the Mn1.5Co0.75O/NF demonstrated the superior electrochemical performance, with an excellent cycling stability of 104% capacitance retention after 10 000 charge-discharge cycles at 6 A g(-1), as well as a good capability (668.4 F g(-1) at 1 A g(-1 )compared to that of undoped Co3O4 which is 201.3 F g(-1)). Moreover, the assembled asymmetric supercapacitor based on Mn1.5Co0.75O/NF//graphene performs a high energy density of 25.88 Wh kg(-1) (at 359.5 W kg(-1)) and a high power density of 14.7 kW kg(-1) (at 10.63 Wh kg(-1)). The improved electrochemical properties are mainly owing to the enhanced intrinsic conductivity and electrochemical activity of Co3O4 after doped with appropriate Mn concentration. The three-dimensional nanostructure of mesoporous nanoneedle array grown on NF also provides short ion diffusion path and large active surface areas, contributing to the high rate performance and high energy density. This study may offer a new approach to fabricate the unique 3D nanostructured electrode materials based on doped metal oxides for supercapacitors with long-term cycling stability and high energy density.
Some articles have revealed that the electrodeposition of calcium phosphate (CaP) coatings entails a precursor phase, similarly to biomineralization in vivo. The chemical composition of the initial layer and its thickness are, however, still arguable, to the best of our knowledge. Moreover, while CaP and electrodeposition of metal coatings have been studied utilizing atom-probe tomography (APT), the electrodeposition of CaP ceramics has not been heretofore studied. Herein, we present an investigation of the CaP deposition on a gold substrate. Using APT and transmission electron microscopy (TEM) it is found that a mixture of phases, which could serve as transient precursor phases to hydroxyapatite (HAp), can be detected. The thickness of these phases is tens of nanometers, and they consist of amorphous CaP (ACP), dibasic calcium phosphate dihydrate (DCPD), and octacalcium phosphate (OCP). This demonstrates the value of using atomic-resolved characterization techniques for identifying the precursor phases. It also indicates that the kinetics of their transformation into the more stable HAp is not too fast to enable their observation. The coating gradually displays higher Ca/P atomic ratios, a porous nature, and concomitantly a change in its density.
The activity of chiral self-assembled monolayers (SAMs) in electrochemistry is reviewed. Chiral SAMs have been used as a means of introducing stereoselectivity in electron transfer at the electrode/electrolyte interface. In most cases, a cysteine-based SAM was used on gold electrodes. Different attempts have involved the application of chiral thiolated molecules, e.g., cyclodextrin, imprinting of chiral objects and competitive complexation. More recently, spintronics in which magnetic fields applied next to chiral SAM induced chiral effects, were also reported. Yet, there is much room for additional and innovative ideas in this field of electrochemistry.
The formation and local deposition of well-shaped Au nanostructures on a nonconducting surface are described. Specifically, the local electroless deposition of Au in aqueous solutions in the presence of various n-alkylpyridinium surfactants is driven by electrochemically generating a flux of AuCl4- at a gold tip close to a 3-mercaptopropyltrimethoxysilane modified Si oxidized wafer. Two reducing agents, NaBH4 and ascorbic acid, were used for the reduction of the gold ions. We studied the effect of the solution temperature, the potential applied to the gold tip and its distance from the surface, the reductant, and the nature of the alkylpyridinium on the structure of the gold deposit. The chloride salts of methylpyridinium, butylpyridinium, cetylpyridinium, 4-carbamoyl-1-cetylpyridinium, and 4-methyl-l-cetylpyridinium were added separately and showed remarkable effect on the shape of the structures that were formed. We find that short chain n-alkylpyridinium salts do not adsorb preferentially on the gold facets, whereas the longer chain n-alkylpyridinium ions cause the formation of well-faceted Au structures, such as cubes, hexagons, and even multipods. Moreover, comparison between local and bulk deposition revealed a significant difference in Au structures that were formed, presumably due to the different concentration profile of the AuCl4-.
Chronoamperometry was used to study the dynamics of Pt nanoparticle (NP) collision with an inert ultramicroelectrode via electrocatalytic amplification (ECA) in the hydrogen evolution reaction. ECA and dynamic light scattering (DLS) results reveal that the NP colloid remains stable only at low proton concentrations (1.0mm) under a helium (He) atmosphere, ensuring that the collision events occur at genuinely single NP level. Amperometry of single NP collisions under a He atmosphere shows that each discrete current profile of the collision event evolves from spike to staircase at more negative potentials, while a staircase response is observed at all of the applied potentials under hydrogen-containing atmospheres. The particle size distribution estimated from the diffusion-controlled current in He agrees well with electron microscopy and DLS observations. These results shed light on the interfacial dynamics of the single nanoparticle collision electrochemistry.
The incorporation of spacers between graphene sheets has been investigated as an effective method to improve the electrochemical performance of graphene papers (GPs) for supercapacitors. Here, we report the design of free-standing GP@NiO and GP@Ni hybrid GPs in which NiO nanoclusters and Ni nanoparticles are encapsulated into graphene sheets through electrostatic assembly and subsequent vacuum filtration. The encapsulated NiO nanoclusters and Ni nanoparticles can mitigate the restacking of graphene sheets, providing sufficient spaces for high-speed ion diffusion and electron transport. In addition, the spacers strongly bind to graphene sheets, which can efficiently improve the electrochemical stability. Therefore, at a current density of 0.5 Ag-1, the GP@NiO and GP@Ni electrodes exhibit higher specific capacitances of 306.9 and 246.1 Fg(-1) than the GP electrode (185.7 Fg(-1)). The GP@NiO and GP@Ni electrodes exhibit capacitance retention of 98.7% and 95.6% after 10000 cycles, demonstrating an outstanding cycling stability. Additionally, the GP@NiO vertical bar GP@Ni delivers excellent cycling stability (93.7% after 10000 cycles) and high energy density. These free-standing encapsulated hybrid GPs have great potential as electrode for high-performance supercapacitors.
The nuclear disasters of Chernobyl and Fukushima presented an urgent need for finding solutions to treatment of radioactive wastes. Among the by-products of nuclear fission is radioactive Cs-137, which evokes an environmental hazard due to its long half-life (> 30 years) and high solubility in water. In this work, a water-soluble organic ligand, readily obtained from alloxan and 1,3,5-benzenetriol, has been found to selectively bind and precipitate Cs+ ions from aqueous solutions. The special rigid structure of the ligand, which consists of a ``tripodal'' carbonyl base above and below an aromatic plane, contributes to the size-driven selectivity towards the large Cs+ ions and the formation of a giant, insoluble supramolecular complex. In addition to the low costs of the ligand, high yields and effectiveness in precipitating Cs+ ions, the Cs- complex revealed a high endurance to continuous doses of gamma-radiation, increasing its potential to act as a precipitating agent for Cs-137.
Controlling the permeability and porosity of an inorganic layer using biomolecule building blocks has raised interest for nanotechnological applications. The challenge lies mostly in the fabrication, usually a long, expensive and tedious process, involving many steps. Using biomaterials for this purpose is highly appealing; due to both ease of fabrication and the final output, that contains a bioelement. The biomolecule, specifically, stable protein 1 (SP1), serving as the scaffold for our pattern, is of great stability and durability, and presents size, charge and structural selectivity towards electroactive species. Here, we demonstrate the ability of SP1 to form a rigid template within a sol-gel matrix, allowing selective electron transfer to the gold electrode. Specifically, a thiolated SP1 was first adsorbed on a gold surface followed by filling the non-occupied areas by sol-gel. The latter was electrochemically deposited. The various steps were carefully characterized. Finally, we studied the electrochemistry of numerous redox couple at the Au/SP1/sol-gel interface and found that the nanochannel array shows charge and structural selectivity, which is based on the interactions between the redox species and the functionalities of SP1. The resulted surface shows promise towards electrochemical sensing applications.
The development of printed electronics has gained much attention as an alternative for conventional metal-based electronics, mainly due to the ability to print electronic circuits on plastics and by much cheaper means as compared with conventional microelectronics. Here we report on a single stage formation of a highly corrosion resistance coating with hydrophobic properties on printed-Cu nanoparticles. Our method is based on the synergistic effect of benzotriazole (BTA) as corrosion inhibitor and trimethylsiloxysilicate (TMS) as hydrophobic component. Printed-Cu coated with such TMS/BTA layer exhibited excellent corrosion resistance in 3.5% NaCl solution, reducing the dissolution of Cu into soluble species by one order of magnitude.
More than 50% of solar energy comes from the infrared region (as radiant heat) of the solar spectrum. Electrochromic (EC) materials, which can dynamically modulate the transmittance of infrared (IR) radiation, can be effectively applied in smart windows for thermal management in buildings. In this work, a core-shell TiO2-WO3 inverse opal (IO) structure was fabricated through the electrodeposition of WO3 onto TiO2 IO templates. The TiO2 IO templates were synthesized by introducing TiO2 into the voids of a polystyrene (PS) colloidal crystal template, followed by calcination to remove the PS microspheres. It was found that the TiO2-WO3 IO core-shell structure can modulate NIR transmittance at wavelengths from 700 to 1600 nm in the NIR range when potential is applied in LiClO4/PC electrolyte. When -0.3 V is applied, up to 60% of NIR radiation in this range can be blocked. The NIR transmittance can be modulated by tuning the applied potential. This study focuses on comparing the novel TiO2-WO3 IO structure with electrodeposited WO3 thin film to fully elucidate the effect of the inverse opal morphology and the TiO2-WO3 hybrid system on the optical properties. Results show that the NIR blockage can be sustained up to 90% after 1200 reversible cycles for TiO2-WO3 IO structure. The greater surface area of the IO structure increases the number of active sites available for the redox reactions by providing a larger contact area with the electrolyte. The more electroactive area with improved charge transfer enhances the overall NIR transmittance contrast as compared to bulk WO3 thin film. Furthermore, the addition of WO3 to TiO2 to form a composite has been shown to enhance cycling performance and device lifespan.
We present a novel gas phase detection prototype based on assembling core-shell nanospheres made of a silver core and coated with a molecularly imprinted polymer (MIP) adsorbed onto an interdigitated array (IDA) electrode chemiresistor (CR). The core-shell nanospheres, AgNP@MIPs, were imprinted with linalool, a volatile terpene alcohol, as a model system. The thickness of the MIP layer was tuned to a few nanometers to enable the facile ingress and egress of the linalool, as well as to enhance the electrical transduction through the Ag core. The AgNP@MIPs were spread onto the IDA-CR modified with various positively charged polymers, by drop casting and dip-coating. The AgNP@MIPs were characterized by various techniques such as extra high-resolution scanning and tunnelling electron microscopy and X-ray diffraction. The MIP recognition event was transduced into a measurable increase in the resistance. The response to linalool exposure and removal was fast and the device was fully recovered and could be reused. Finally, the difference in the resistance change between imprinted and non-imprinted nanospheres was substantial.
The sensing performance of a Langmuir-Blodgett monolayer was significantly improved by controlling the film organization at the air-water interface. Cellulose acetate (CA) and 4-tert-butylcalix  arene (calix) were co-spread and formed a Langmuir film, which was efficiently transferred onto a preoxidized gold electrode, Au-ox. The modified gold electrode was applied as a fast, highly sensitive electrochemical sensing platform for the quantitative determination of a model molecule, dopamine (DA). The modified gold electrode, CA-calix/Au-ox, demonstrated better recognition and sensing ability towards dopamine as compared with electrodes modified by a single component. Under the optimized conditions, the reduction peak currents at the CA-calix/Au-ox increased linearly within the concentration range of dopamine from 5 to 100 and 100-7500 nM, and exhibited a very low limit of detection (LOD) of 2.54 nM (S/N = 3). These results suggest a simple, superior and efficient approach for the controllable rearrangement of Langmuir-Blodgett monolayers on a molecular level. The electroanalytical performance was optimized from the perspective of the electrode-electrolyte interface. (C 2018 Elsevier B.V. All rights reserved.
Nanoparticles imprinted matrices (NAIMs) is a new approach, in which nanoparticles (NPs) are imprinted in a matrix followed by their removal to form highly selective voids that can recognize the original NPs. In this study, the effect of a sol-gel matrix on the imprinting and reuptake of gold nanoparticles (AuNPs) is examined. Specifically, indium tin oxide (ITO) films were modified with a positively charged polymer, on which the negatively charged AuNPs stabilized with citrate (AuNPs-cit) were adsorbed. This was followed by the electrochemical deposition of sol-gel matrices with different thicknesses and functional groups onto the ITO/AuNPs-cit. Electrochemical oxidation dissolved the AuNPs-cit and formed cavities in the sol-gel films, which fit both the size and shape of the AuNPs-cit. Reuptake of these NPs from an aqueous solution was successful using the imprinted films, whereas the non-imprinted films did not re-uptake the AuNPs-cit. Furthermore, the thickness of the sol-gel layers as well as the type of the silanes that were deposited play an important role on the recognition ability of the NAIM. Finally, we found that the NAIMs are selective, and larger AuNPs-cit were not recognized by the imprinted matrix.
Understanding the nature of interactions between inorganic surfaces and biomolecules, such as amino acids and peptides, can enhance the development of new materials. Here, we present single molecule force spectroscopy (SMFS) measurements of the interactions between an atomic force microscopy (AFM) probe, modified with various amino acids, and a titanium dioxide surface. Specifically, we study the affinity of amino acids toward a titanium dioxide surface bearing hydrophobic (Leu), aromatic (Phe) and hydrophilic (Orn) residues. We find that aromatic interactions dominate over aliphatic in their affinity to the titanium dioxide surface. In addition, we show that by combining aromatic and hydrophilic moieties in a single amino acid (NH2-Phe), the adhesion of the latter to the surface increases. Furthermore, the affinity of positively charged amino acids to the titanium dioxide surface is higher than that of uncharged, and can be increased more, with elevating the pH of the buffer above the pK(a) of the basic residues. The kinetic and thermodynamic parameters imply that the dynamics of the surface-amino acid interface are mostly governed by hydrophobic interactions.