Phenyl-capped Aniline Tetramer Research Articles

Single-walled Carbon Nanotube Chemiresistive Sensors for the Identification and Quantification of Disinfectants

Disinfectants are essential to keep water safe as they kill pathogens by oxidizing the cell membrane. Free chlorine, potassium permanganate, monochloramine, hydrogen peroxide, chlorine dioxide, ozone, and hypobromous acid are the most commonly used disinfectants for the disinfection of water.1 Monitoring the concentration of the disinfectant is crucial as the effectiveness mainly depends on the amount of disinfectants present in water.2 Insufficient levels of disinfectant in drinking water could impose health risks as pathogens could regrow in the distribution system. Standard methods for measuring the disinfectant levels are colorimetric and titrimetric.3 For free chlorine, DPD colorimetric method is well established.1 , 4 For potassium permanganate (KMnO4), colorimetric methods (persulfate and periodate) and spectroscopic methods are available.1 , 5 Currently, the monitoring of disinfectants is done on samples collected at the treatment plant and in different locations throughout the distribution system. This reagent-based measurement of discrete samples requires reagents and spectroscopic readout devices and can suffer from interference. Therefore, these methods are not suitable for the continuous monitoring of the disinfectant.6 Furthermore, there is no known method that can differentiate between multiple disinfectants in real samples without any previous knowledge.Two of the most important water quality parameters are pH and oxidation-reduction potential (ORP). Disinfectants undergo different reactions at different pH, resulting in different active species for different pH. ORP measurement can be used to monitor whether the disinfection was successful as oxidants’ reactivity in water depends on redox conditions.7 ORP of a solution is associated with the pH and the concentration of the disinfectant. At a fixed pH, the ORP of a disinfectant will depend on the concentration. Therefore, just by knowing the ORP, we cannot distinguish disinfectant unless the pH or concentration of the oxidant is known.8 , 9 To sort out these parameters, we propose to introduce a chemiresistive sensing array capable of distinguishing and quantifying disinfectants. Due to simpler fabrication techniques, lower cost and the ability to sense various analytes through appropriate ligand, chemiresistors have great promise in water quality sensing.6 , 10 Previously reported chemiresistive sensor for continuous measurement of free chlorine used carbon nanotube (CNT) substrate functionalized with a redox-active aniline oligomer named phenyl capped aniline tetramer (PCAT).11 Oxidation of PCAT attached to the surface of CNT by free chlorine leads to a change in the oxidation state of the oligoaniline; this change in oxidation state in the molecule changes the doping characteristics of CNT leading to a change in resistance of the CNT film. This resistance change was used to quantify the concentration of free chlorine.11 In this work, we have constructed an array of single-walled carbon nanotubes (SWCNT) sensors functionalized with five redox-active molecules. Structurally different from each other, these molecules will create different active sites. Upon interaction with analytes, each molecule will give different magnitudes of responses. Sensor responses are collected for free chlorine and KMnO4 over a range of concentrations for pH 6.5 and 7.5. In general, sensors give increasing responses to the increasing concentration and decreasing pH of the solution. Though the responses from the sensors have a similar trend to the change of the parameters their varied magnitudes make them suitable for an array. Sensor responses are then analyzed with principal component analysis (PCA). PCA analysis shows clear separation between the analytes and as well as to different pH and concentrations of the solutions (figure). We have therefore demonstrated an array of chemiresistive sensors that can distinguish and quantify disinfectants.

Modifying Nanocarbon Films with Switchable Dopant Molecules for the Detection of Aqueous Permanganate

Monitoring disinfectants is essential to maintain water free from pathogens. Permanganate (MnO4 -) is one of the commonly used disinfectants and is applied as potassium permanganate (KMnO4) solution in drinking water and wastewater treatment plants. It is used as a pre-oxidant at the beginning of the treatment process for the control of reduced iron (II) and manganese (II) concentration.1,2 Though dilute KMnO4 solutions are sometimes used as topical antiseptics and astringents, higher concentration (over 200 mg/L) can cause gastrointestinal distress.3 A Do Not Consume concentration of 7 mg/L KMnO4 is recommended based on clinical experience.3 Therefore, to ensure the proper level of permanganate during and after the water treatment process, it is necessary to monitor the concentration of permanganate.Current methods for permanganate detection focus on spectrophotometric measurements (direct and indirect). The direct method involves no additional chemical, however, lacks the suitability for the samples with less than 0.75 mg/L of MnO4 -.4 Indirect methods provide better sensitivity but require the need for reagents like NaI and ABTS (unstable).4 A sensitive single-particle-detection (SPD) method has been reported recently which uses dark-field optical microscopy on graphene nanoplatelets silver (GNP@Ag) core-shell nanoparticles, but, this method is quite complex and requires sample preparation before analysis.1 Moreover, these methods are unsuitable for the implementation in a treatment plant for the online monitoring of disinfectant.To tackle this problem, we introduced a chemiresistive sensing platform capable of quantifying permanganate in aqueous media. Chemiresistive sensors are becoming popular in sensing due to their low cost, easy fabrication technique, and the ability to detect different analyte using appropriate ligand.5 Chemiresisive sensors have been reported before for the continuous measurement of free chlorine using carbon nanotube (CNT) substrate doped with redox-active aniline oligomer named phenyl capped aniline tetramer (PCAT).6 The sensor consists of two parallel electrodes connected by a layer of carbon nanotubes. Oligoanilines are immobilized on the substrate through noncovalent interactions. Oligoanilines are known to dope CNTs differently depending on which one of the three oxidation states they are in (fully reduced, half oxidized, and fully oxidized).7 , 8 Oxidation of this oligoaniline (PCAT) attached to the surface of CNT by permanganate molecule leads to a change in the oxidation state of the oligoaniline; this change in oxidation state in the molecule changes the doping characteristics of CNT leading to a change in resistance of the CNT film. This resistance change can be used to quantify the concentration of permanganate.9 This sensor can be reset with fresh water and reused for further analysis.Here we present a chemiresistive sensing array that can detect permanganate in the aqueous environment. We have functionalized the nanocarbon substrate with five different redox-active molecules. Four of them are pH-responsive and one is not responsive to the pH range used for the analysis. The sensors were tested for the range of 0.17 mg/L to 1.33 mg/L of MnO4 - at a pH range of 6.5 to 9.5. These redox-active molecules create active sites on the substrate, and when in contact with the analyte, dopant molecules attached on the surface react with analytes and give responses. These responses vary in magnitude depending on pH and the redox-active molecule. The sensor responses at different pHs were then analyzed using principal component analysis (PCA) to identify the pH of the permanganate solution. PCA analysis shows a clear separation of different pH solutions. We have therefore demonstrated a nanocarbon based sensing array that is not only capable of continuously measuring the low concentration of permanganate, but also the pH of the aqueous media.

Chemiresistive Detection of Silver Ions in Aqueous Media

Silver is a precious metal that is commonly used in water filters to reduce growth of biofilm within the filter itself. Ionic silver is used as an effective disinfectant for potable water, giving a log10 reduction for L. pneumophilia, P. aeruginosa, and E. coli of 2.4, 4, and 7, respectively.1 In terms of human exposure, silver is not an essential metal therefore any exposure to silver is unwanted. When silver is ingested orally, the most common adverse effect is argyria, which is an extreme blue pigmentation of the skin and abdominal viscera.2 Occupational exposure to silver nitrate has been correlated to respiratory tract irritation.3 Currently there are no guidelines for silver ions in drinking water, and the World Health Organization (WHO) has set a health advisory (not a guideline value) of 100 ppb. The only country with a Maximum Allowable Content (MAC) is Germany, whose drinking water regulations (Trinkwasserverordnung) have a MAC of 80 ppb.4 Here we demonstrate a chemiresistive sensor for the in situ detection of silver (I) in aqueous media. Chemiresistive sensors function through the changes that occur in the electronic structure of the sensor itself. A graphite film attached to two copper contacts at either end is exposed to the silver ions such that only the graphite and not the contacts interact with the ions. To functionalize the graphite, silver (I)-specific ligands, such as bathocuproine, can be deposited onto the film to adsorb onto it, protecting it from interfering ions.5 Chemiresistive sensors have been demonstrated before for the detection of free chlorine in aqueous media. Rather than using graphite, carbon nanotubes (CNT) were utilized as the conductive film, with phenyl-capped aniline tetramer (PCAT) as the chlorine-specific ligand. As the PCAT doped CNT was exposed to chlorine, the PCAT oxidized, and the electronic changes were probed using a bias voltage. The linear range for this sensor was from 60 ppb to 60 ppm, providing sufficient sensitivity for household use.6 When testing other common ions, there were no significant interference's that compete with the response of silver (I) in solution, making this sensor quite selective to silver (I). pH tests show that there is no change in current induced by pH between the range of 6-10 pH. Below 6, the sensor functions as a "proton sensor" due to the protonation of the adsorbed bathocuproine. Above pH 10, AgOH may be formed, which will precipitate out of solution. All tests were performed at an analyte conductance of 31 μS/cm, which is typical for freshwater samples.7 When the fabricated sensor was exposed to silver (I) in aqueous solution, detection of the ions was observed through a step up in the current going through the sensor. Each step up in current was proportional to the concentration of silver (I) in solution. Based on this, a calibration curve was made using the Langmuir Isotherm model and a first-order exponential decay model. For the range of 3 ppb to 1 ppm, both the Langmuir Isotherm and the first-order exponential decay model gave R2 values of 0.9982 and 0.9939, respectively. The sensor could also be reliably reset to the same 0 ppm baseline after use by exposing it to a pH 3 solution. When exposed to silver (I) post-reset, current changes were also quite reproducible, with the values having a relative standard deviation no greater than 1.24%, highlighting the re-usability of this sensor. The limit of detection, calculated using a signal:noise ratio of 3, for this sensor would be 3 ppb.We have therefore demonstrated that chemiresistors based on functionalized nanocarbon films can be used as selective ion sensors in addition to their previously demonstrated application as redox sensors. The toolbox of organometallic chemistry can now be applied to extend this sensing platform to other cations for water quality sensing.

Retraction of "Robust Chemiresistive Sensor for Continuous Monitoring of Free Chlorine using Graphene-Like Carbon".

Free chlorine is widely used in industry as a bleaching and oxidizing agent. Its concentration is tightly monitored to avoid environmental contamination and deleterious human health effects. Here, we demonstrate a solid state chemiresistive sensor using graphene like carbon (GLC) to detect free chlorine in water. A 15-20 nm thick GLC layer on a PET substrate was modified with a redox-active aniline oligomer (phenyl-capped aniline tetramer, PCAT) to increase sensitivity, improve selectivity and impart fouling resistance. Both the bare GLC sensor and the PCAT-modified GLC sensor can detect free chlorine continuously and unlike previous chemiresistive sensors, do not require a reset. The PCAT-modified sensor showed a linear response with a slope of 13.89 (mg/L)-1 to free chlorine concentrations between 0.2 to 0.8 mg/L which is relevant for free chlorine monitoring for drinking water and waste water applications. The PCAT-modified GLC sensors were found to be selective and showed less than 0.5% change in curr...

Robust Chemiresistive Sensor for Continuous Monitoring of Free Chlorine Using Graphene-like Carbon.

Free chlorine is widely used in industry as a bleaching and oxidizing agent. Its concentration is tightly monitored to avoid environmental contamination and deleterious human health effects. Here, we demonstrate a solid state chemiresistive sensor using graphene like carbon (GLC) to detect free chlorine in water. A 15-20 nm thick GLC layer on a PET substrate was modified with a redox-active aniline oligomer (phenyl-capped aniline tetramer, PCAT) to increase sensitivity, improve selectivity, and impart fouling resistance. Both the bare GLC sensor and the PCAT-modified GLC sensor can detect free chlorine continuously and, unlike previous chemiresistive sensors, do not require a reset. The PCAT-modified sensor showed a linear response with a slope of 13.89 (mg/L)-1 to free chlorine concentrations between 0.2 and 0.8 mg/L which is relevant for free chlorine monitoring for drinking water and wastewater applications. The PCAT-modified GLC sensors were found to be selective and showed less than 0.5% change in current in response to species such as nitrates, phosphates and sulfates in water. They also were resistant to fouling from organic material and showed only a 2% loss in signal. Tap water samples from residential area were tested using this sensor which showed good agreement with standard colorimetric measurement methods. The GLC and PCAT-GLC sensors show high sensitivity and excellent selectivity to free chlorine and can be used for continuous automated monitoring of free chlorine.

Surface Mobility and Nucleation of a Molecular Switch: Tetraaniline on Hematite

Understanding the dynamics of organic thin film formation is crucial to quality control in organic electronics and smart coatings. We have studied the nucleation and growth of the reduced and the oxidized states of phenyl-capped aniline tetramer (PCAT) deposited on hematite(1000) surfaces by physical vapor deposition. The fully reduced PCAT molecules form 2D islands on the surface, whereas the fully oxidized molecules form 3D islands. Through scaled island size distribution, it was found that the critical island sizes, i, for the reduced and oxidized molecules are i = 4 and 5, respectively. From the dependence of the island density on substrate temperature, the activation energies for the diffusion of the molecules away from the critical cluster were calculated to be 1.30 and 0.55 eV, respectively. At low temperatures, the reduced and the oxidized PCAT molecules form compact islands on the surface. At higher temperatures, the reduced islands become dendritic, whereas the oxidized islands become slightly dendritic. The attempt frequencies for surface diffusion of the reduced and the oxidized islands were estimated to be about 5 × 1025 and 8 × 1011 s–1, respectively. The former value is in line with the high degree of surface wetting by the reduced PCAT, whereas the latter value shows the higher degree of intermolecular interaction in the fully oxidized PCAT and the low degree of its interaction with the iron oxide surface. Interconversion between oxidized and reduced islands through exposure to a reducing environment, and its impact on island morphology was examined. We also found that the presence of Fe2+ defects on the hematite surface did not impact the nucleation and growth of the molecular islands, likely due to a discrepancy in time scale. This study elucidates the interactions between an oligoaniline-based molecular switch (PCAT) and hematite surfaces as a function of molecular oxidation state, with applications in molecular electronics, chemical sensors, and smart coatings.

Pencil-Drawn Chemiresistive Sensor for Free Chlorine in Water

Free chlorine concentration in drinking water is an important control parameter throughout the distribution network, since both too-low and too-high concentrations can lead to health hazards, with 0.52 ppm being a typically acceptable range. Although colorimetric and electrochemical methods exist for measuring free chlorine, they require either the addition of chemicals during manual sampling or maintenance intensive instrumentation, such as reference electrodes. We have previously demonstrated a simple, reliable, reagent-fee solid-state chemiresistive sensor for continuous monitoring of aqueous free chlorine concentrations based on a functionalized carbon nanotube film. Here, we show that the same sensing principle can be translated to lower cost materialsas simple as a line drawn between two contacts using a free IKEA pencil. While IKEA (HB grade, about 70 graphite) pencils work well enough for quantitative free chlorine sensors, the use of 9B grade pencils (90 graphite) results in higher sensitivity. Bare pencil line sensors show a nonselective response to a wide range of aqueous species; pencil lines functionalized with a redox-active aniline oligomer (phenyl-capped aniline tetramer), however, are highly selective to oxidant species, namely free chlorine, in a demonstrated range of 0.0660 ppm. The resulting sensors are cost-effective, durable, resettable, reusable, and resistant to fouling. In contrast to electrochemical sensors, they do not require the use of a reference electrode. They can be operated continuously online for drinking water quality monitoring.

Reagent-Free Quantification of Aqueous Free Chlorine via Electrical Readout of Colorimetrically Functionalized Pencil Lines.

Colorimetric methods are commonly used to quantify free chlorine in drinking water. However, these methods are not suitable for reagent-free, continuous, and autonomous applications. Here, we demonstrate how functionalization of a pencil-drawn film with phenyl-capped aniline tetramer (PCAT) can be used for quantitative electric readout of free chlorine concentrations. The functionalized film can be implemented in a simple fluidic device for continuous sensing of aqueous free chlorine concentrations. The sensor is selective to free chlorine and can undergo a reagent-free reset for further measurements. Our sensor is superior to electrochemical methods in that it does not require a reference electrode. It is capable of quantification of free chlorine in the range of 0.1-12 ppm with higher precision than colorimetric (absorptivity) methods. The interactions of PCAT with the pencil-drawn film upon exposure to hypochlorite were characterized spectroscopically. A previously reported detection mechanism relied on the measurement of a baseline shift to quantify free chlorine concentrations. The new method demonstrated here measures initial spike size upon exposure to free chlorine. It relies on a fast charge built up on the sensor film due to intermittent PCAT salt formation. It has the advantage of being significantly faster than the measurement of baseline shift, but it cannot be used to detect gradual changes in free chlorine concentration without the use of frequent reset pulses. The stability of PCAT was examined in the presence of free chlorine as a function of pH. While most ions commonly present in drinking water do not interfere with the free chlorine detection, other oxidants may contribute to the signal. Our sensor is easy to fabricate and robust, operates reagent-free, and has very low power requirements and is thus suitable for remote deployment.

Interactions of Different Redox States of Phenyl-Capped Aniline Tetramers with Iron Oxide Surfaces and Consequences for Corrosion Inhibition

The phenyl capped aniline tetramer (PCAT) is known for its redox properties and is being studied for its ability to inhibit corrosion of iron and steel in addition to being of interest for sensors and molecular electronics. Here we investigate the interactions, orientation and corrosion inhibition ability of all three oxidation states of the free base form of PCAT with iron oxide surfaces. Raman spectroscopy demonstrates interconversion of these molecules to one another due to charge transfer to the surface. Polarized mid-IR spectroscopy and atomic force microscopy were used to elucidate the molecular orientations on the surface. Electrochemical impedance spectroscopy shows the corrosion resistance of fully reduced PCAT coatings on low carbon steel to be higher than that for half-oxidized and fully oxidized PCAT coatings. A weight loss test, laser line measurements and Raman spectroscopy reveal that even though half-oxidized PCAT initially shows a lower corrosion resistance due to transformation into the fully oxidized form, with time it transforms back into the half-oxidized form and protects the surface. Fully oxidized PCAT molecules show opposite behavior, causing the degradation of the surface over time. We thus attained a deeper insight into the interplay of the different oxidation states for corrosion control.

Interfacial Charge Transfer between Phenyl-Capped Aniline Tetramer Films and Iron Oxide Surfaces

Redox-active organic compounds have been studied as corrosion inhibitors for steel. Even though it is clear that chemical interactions at the organic–metal oxide interface are behind this inhibitive process, the detailed mechanism is not yet fully understood. Using phenyl-capped aniline tetramer (PCAT), we have elucidated the interactions at the interface with iron oxide. We demonstrate the partial reduction of fully oxidized PCAT and the partial oxidation of fully reduced PCAT upon interaction with iron oxide. X-ray photoelectron spectroscopy reveals the appearance of charged nitrogen structures in PCAT deposited on hematite. Iron oxide films in contact with reduced PCAT show a higher conductance due to the introduction of defects, resulting in n-doping. In contrast, the iron oxide film in contact with oxidized PCAT shows a lower conductance, indicating that defects in the film are removed via oxidation, thus reducing the doping level. This is consistent with accepted models for corrosion inhibition, in ...

Development of All Solid State Sensors for Environmental Water Monitoring: Dissolved Oxygen and Free Chlorine

Water contaminations in both natural water resource before collection and in treated drinking water during transportation jeopardise the supply of clean drinking water [1], [2]. Effective wastewater treatments, pollution controls in surface water and contamination free drinking water are three major goals to combat the water pollution sources on public and environmental health. Long term and continuous on-line sensing systems that can provide highly accurate data in real time can be the key component to benefit all these three aspects. However, the development of a comprehensive sensing system that can detect all parameters is labor and cost intensive. Thus, appropriate selection of targeted indicator is important in order to design a sufficient and practical sensing system. Since oxygen is an essential compound during the degradation of water containments, the dissolved oxygen (DO) level is always an important factor for water monitoring. Therefore, DO concentration is one of the primary factors for monitoring pollution in nature water. Additionally, DO is one of the major parameters that has to be precisely controlled during the wastewater treatment [3], [4]. Exceeding required DO concentration can cause waste of energy during aeration, whereas low DO concentration can cause failure treatment processes. Furthermore, free chlorine is one of the most common used disinfectants to ensure the drinking water quality during transportation and in wastewater treatment process for degradation of organic contaminants. The free chlorine concentration has to be strictly controlled to meet the requirement of different applications. For example, the residual chlorine in wastewater discharge is regulated as 0 ppm to prevent the damage in natural eco-system. Nevertheless, the residual chlorine in drinking water has to be maintained between 2 - 0.5 ppm to ensure drinking water safety. The DO and free chlorine is hence selected as the targeted indicators for the on-line sensing systems of water contamination prevention. Generally, the colorimetric methods are always the standard most widely used water monitoring techniques. For example, Winkler Method for DO sensing [5], and N,N-diethyl-p-phenylenediamine (DPD) method for free chlorine sensing [6]. These techniques are accurate and low interference; however, these techniques are expensive, tedious and labor intense which restricted their real-world application in on-line sensor developments. Among all the other sensing strategies, electrochemical methods are usually simple and low cost which are adequate for environmental sensing applications. However, there are still some challenges of the developments of on line DO and free chlorine sensors which needed to be overcome. Conventional DO sensors are expensive as they use platinum in their construction. Additionally, these sensors bio-foul when used in natural or waste water, which leads to reduced sensitivity and unstable performance. These problems are solved by i) replacing Pt with hemin as the low cost alternative for electrocatalysing the oxygen reduction reaction, and ii) using silicone rubber (PDMS) functionalized with polyethyleneglycol (PEG) as the anti-biofouling gas permeable membrane to provide selectivity with an increased device lifetime (a). This DO sensor has a sensitivity of 4.8 (µA/cm2)/(ppm) of dissolved oxygen in a concentration range of 0-20 ppm (b). [7] Additionally, a solid state palladium reference electrode composed by high surface area Pd nanostructure is also integrated with this DO sensor. The Pd/H electrode composed is able to maintain stable electrical potential for more than 5 hours after charging hydrogen. The all solid-state feature allows this sensing device to be applied in long-term on-line DO sensing. On the other hand, although several free chlorine sensors do exist, none of them is capable of long term and continuous on line sensing. We developed a resettable switching of doping states in carbon nanotube (CNT) films due to the chemical oxidation and reduction of phenyl-capped aniline tetramer (PCAT) adsorbed on it (c). The PCAT-CNT sensor obtains sufficient sensitivity (50 nA/ppm) and detection range (0.06-60 ppm) to ensure the safety of free chlorine level contained in drinking water (d). In addition, a cathodic polarization process after the sensing is found to electrochemically reset this sensor back to the original state so that the sensor can be used for subsequent sensing. In short, this sensor is reagent-free and resettable, suitable for long term and continuous monitoring the free chlorine level in drinking water [8]. Reference 1. Environ. Sci. Technol., v. 43, p. 240 2009. 2. Proc. Natl. Acad. Sci. , vol. 103 , pp. 7210 2006. 3. Environ. Int., vol. 30, p. 249 4. Chem. Eng. J., vol. 162, p. 1 5. Mar. Chem., vol. 122, p. 83 6. Guidelines for Canadian Drinking Water Quality - Chlorine, Ottawa 7. Sensors Journal, IEEE, vol. 14 p.3400 8. Appl. Phys. Lett., vol. 106, p. 063102 Figure 1

Theoretical Evaluation of Electron Transport in Aniline Tetramer-based Dye-sensitized Solar Cells

The essential electron transporting function of EPAT in phenyl-capped aniline tetramer (EPAT)/tert-butylpyridine (TBP)-based dye-sensitized solar cells (DSC) is evaluated by density functional theory (DFT). DFT-based molecular modeling coupled with molecular mechanics optimization reveal that EPAT molecules in-situ self-organizes to dimeric molecular complexes through van der Waals and Coulombic interactions. TBP molecules assist to form TBP-hydrogen-bonded EPAT complexes, (EPAT-H-TBP)2 and (EPAT-H-2TBP)2. The molecular complexes have stacked structures as well, and the electron-accepted states of radical anions, (EPAT-H-TBP)2.− and (EPAT-H-2TBP)2.− give narrow band gaps (0.26∼0.28eV), and the singly occupied molecular orbitals (SOMO) are comparable in configurations with the lowest unoccupied molecular orbital (LUMO). We understand that electron in photo-irradiated EPAT/TBP phase should transport effectively by hopping on SOMO of (EPAT-H-TBP)2.− and (EPAT-H-2TBP)2.−.

A carbon nanotube based resettable sensor for measuring free chlorine in drinking water

Free chlorine from dissolved chlorine gas is widely used as a disinfectant for drinking water. The residual chlorine concentration has to be continuously monitored and accurately controlled in a certain range around 0.5–2 mg/l to ensure drinking water safety and quality. However, simple, reliable, and reagent free monitoring devices are currently not available. Here, we present a free chlorine sensor that uses oxidation of a phenyl-capped aniline tetramer (PCAT) to dope single wall carbon nanotubes (SWCNTs) and to change their resistance. The oxidation of PCAT by chlorine switches the PCAT-SWCNT system into a low resistance (p-doped) state which can be detected by probing it with a small voltage. The change in resistance is found to be proportional to the log-scale concentration of the free chlorine in the sample. The p-doping of the PCAT-SWCNT film then can be electrochemically reversed by polarizing it cathodically. This sensor not only shows good sensing response in the whole concentration range of free chlorine in drinking water but is also able to be electrochemically reset back many times without the use of any reagents. This simple sensor is ideally suited for measuring free chlorine in drinking water continuously.

A phenyl-capped aniline tetramer for Z907/tert-butylpyridine-based dye-sensitized solar cells and molecular modelling of the device

Z907-sensitized solar cells incorporating a phenyl-capped aniline tetramer (EPAT) as a substitute of the iodine/iodide redox couple in the electrolytes produce an enhanced open-circuit voltage and short circuit photocurrent density when tert-butylpyridine (TBP) is added to the electrolyte.

Electroactive polymer with oligoanilines in the main chain and azo chromophores in the side chain: synthesis, characterization and dielectric properties

By an oxidative coupling polymerization approach, we have synthesized a novel electroactive polymer with good solubility containing alternating phenyl-capped aniline tetramer in the main chain and azo chromophores in the side chain. Dielectric properties of the as-synthesized polymer were investigated in detail and gratifying results have been observed. Firstly, a large enhancement in the dielectric constant was achieved utilizing the method of doping the conjugated oligoaniline segments with hydrochloric acid. Secondly, the adjustment of dielectric constant was implemented primarily by means of exposing the samples to UV and visible irradiation, mainly owing to the photoisomerization derived from azo chromophores in the side chain. The detailed characteristics of the as-synthesized polymer were systematically studied by Fourier-transform infrared (FTIR) spectra, nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). UV-vis spectra were used to monitor the photoisomerization and doping process of the polymer. The thermal characteristics of the polyamide were evaluated by thermogravimetric analysis (TGA). Moreover, the electrochemical activity of the polymer was explored by cyclic voltammogram (CV) measurement, showing that the intrinsic electroactivity of the oligoaniline was maintained in the polymer.

Synthesis and characterization of a novel electroactive polymer with oligoaniline and nitrile groups

By oxidative coupling polymerization approach, we have synthesized a novel electroactive polymer with alternating phenyl-capped aniline tetramer in the main chain and nitrile group in the side chain. The detailed characteristics of the as-synthesized polymer were systematically studied by Fourier-transform infrared (FTIR) spectra, nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). UV–vis spectra were used to monitor the oxidation process of the polymer. Moreover, the electrochemical behavior of the polymer was explored by cyclic voltammogram (CV), showing that the intrinsic electroactivity of the oligoaniline was maintained in the polymer and two distinct reversible oxidative states were observed. The thermogravimetric analysis (TGA) indicated that the polymer possessed good thermal resistance due to the introduction of the rigid and polar nitrile groups in side chains. The reactivity of nitrile group provides the probability of modifying and functionalizing the polymer further, and creating a series of novel functional polymers.

Investigation of Corrosion-Inhibiting Aniline Oligomer Thin Films on Iron Using Photoelectron Spectroscopy

Polyaniline (PANI) is capable of inhibiting corrosion on iron by inducing the formation of a passive oxide film. The underlying mechanism however, is unknown. We have used photoelectron emission spectromicroscopy of thin films of a model PANI oligomer to investigate its interaction with the iron oxide film covering the iron surface. The oligomer chosen was a phenyl-capped aniline tetramer (PCAT). Thin undoped films of PCAT in its leucoemeraldine form were prepared by physical vapor deposition to obtain films from ∼1 A to over 10 nm thick. Films were investigated with a photoelectron emission microscope (PEEM) using synchrotron radiation to obtain spatially resolved valence band photoemission spectra. Analysis of PEEM results suggest that PCAT is capable of migrating several micrometers along the substrate surface and causes a decrease in substrate work function wherever present. High-resolution core level and valence band photoelectron spectroscopy using a laboratory-based photon source was used to charac...

Synthesis and characterization of electroactive copolymer with phenyl-capped aniline tetramer in the main chain by oxidative coupling polymerization

A novel electroactive alternating copolymer, with fixed conjugated length of oligoaniline (phenyl-capped aniline tetramer) in the main chain, was successfully synthesized via oxidative coupling polymerization. The structure of the copolymer was systematically studied by Fourier-transform infrared (FTIR) spectra, NMR, elemental analysis (EA), UV–vis spectra and X-ray powder diffraction (XRD). And its electrochemical behavior was studied by cyclic voltammetry (CV) measurement. It was found that the obtained copolymer bearing phenyl-capped aniline tetramer segments had a reversible electrochemical property in the cyclic voltammetry, and the copolymer was oxidized to its emeraldine oxidation state and then to the pernigraniline oxidation state, which was same as that of polyaniline. Moreover, the thermal properties of the copolymer were evaluated by thermogravimetric analysis (TGA). The electrical conductivity of the obtained copolymer was about 1.43 × 10 −7 S cm −1 at room temperature.

Synthesis of a new electroactive poly(aryl ether ketone)

In this communication, we report for the first time the synthesis of a new electroactive poly(aryl ether ketone) derived from the phenyl-capped aniline tetramer. The general properties are studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The polymer has high serving temperature and good thermal stability. And its chemical oxidation process was studied by UV–Vis spectra. It was found the polymer was oxidized to its EB form and then to the pernigraniline oxidation state, which is same as the PANI.