Comparison of carbon nanotube modified electrodes for photovoltaic devices

Substrates with four different nanotube modifications have been prepared and their electron transport properties measured. Two modification techniques were compared; covalent chemical attachment of both single and multi-walled carbon nanotubes to transparent conductive (fluorine doped tin oxide) glass surfaces and chemical vapour deposition (CVD) growth of both single and multi-walled carbon nanotubes on highly doped conductive silicon wafers. These carbon nanotube modified substrates were investigated using scanning electron microscopy and substrates with nanotubes grown via CVD have a much higher density of nanotubes than substrates prepared using chemical attachment. Raman spectroscopy was used to verify that nanotube growth or attachment was successful. The covalent chemical attachment of nanotubes was found to increase substrate electron transfer substantially compared to that observed for the bare substrate. Nanotube growth also enhanced substrate conductivity but the effect is smaller than that observed for covalent attachment, despite a lower nanotube density in the attachment case. In both modification techniques, attachment and growth, single-walled carbon nanotubes were found to have superior electron transfer properties. Finally, solar cells were constructed from the nanotube modified substrates and the photoresponse from the different substrates was compared showing that chemically attached single-walled nanotubes led to the highest power generation.     

Recent advances in conjugated polymers for light emitting devices

A recent advance in the field of light emitting polymers has been the discovery of electroluminescent conjugated polymers, that is, kind of fluorescent polymers that emit light when excited by the flow of an electric current. These new generation fluorescent materials may now challenge the domination by inorganic semiconductor materials of the commercial market in light-emitting devices such as light-emitting diodes (LED) and polymer laser devices. This review provides information on unique properties of conjugated polymers and how they have been optimized to generate these properties. The review is organized in three sections focusing on the major advances in light emitting materials, recent literature survey and understanding the desirable properties as well as modern solid state lighting and displays. Recently, developed conjugated polymers are also functioning as roll-up displays for computers and mobile phones, flexible solar panels for power portable equipment as well as organic light emitting diodes in displays, in which television screens, luminous traffic, information signs, and light-emitting wallpaper in homes are also expected to broaden the use of conjugated polymers as light emitting polymers. The purpose of this review paper is to examine conjugated polymers in light emitting diodes (LEDs) in addition to organic solid state laser. Furthermore, since conjugated polymers have been approved as light-emitting organic materials similar to inorganic semiconductors, it is clear to motivate these organic light-emitting devices (OLEDs) and organic lasers for modern lighting in terms of energy saving ability. In addition, future aspects of conjugated polymers in LEDs were also highlighted in this review.     

水溶性带电聚合物黏结剂修饰炭电极用于增强电容去离子性能

电容去离子技术（capacitive deionization,CDI）是一种基于电吸附原理的新型脱盐技术,具有成本低、无污染、能耗小等优点。采用亲水性的羧甲基纤维素钠（CMC）和聚乙烯醇（PVA）黏结剂及其化学修饰得到的具有更多带电基团的磺化羧甲基纤维素（SCMC）和季铵化聚乙烯醇（QPVA）黏结剂制备活性炭电极,能进一步增强活性炭（AC）电极的亲水性和离子选择性。亲水性带电聚合物黏结剂依靠自身的电荷可以有效抑制阳极氧化的副反应,并增强离子吸附驱动力。在500 mg/L NaCl盐溶液,1.2/0 V电压下,AC-CMC//AC-PVA和AC-SCMC//AC-QPVA可分别获得14.58和17.39 mg/g的脱盐量,且在0.8/0 V电压下循环100圈之后,脱盐量的保持率分别为65.48%和80.53%。     

Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties

Novel nanocomposite films, based on graphene oxide (GO) and TiO(2) nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO(2) nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO(2) nanotube composite electrode compared with pristine TiO(2) nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO(2) nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO(2) nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO(2) nanotube arrays.     

Carbon nanotube sheet electrodes for anisotropic actuation of dielectric elastomers

The performance of dielectric electroactive polymer (D-EAP) based actuators depends critically on the electrode characteristics. Among the most challenging issues in the application of D-EAPs is the device-level complexity in producing sufficient directional actuation at acceptably low electric fields. In this work, a simple carbon nanotube (CNT) based electrode for D-EAP actuators is demonstrated that vastly improves directional strain response originating from the mechanical anisotropy of the electrode material. In this novel approach, highly aligned carbon nanotube (CNT) sheet electrodes are applied on acrylate adhesive films show high directed linear actuation strain of greater than 40% at a relatively low electric field (100 V μm⁻¹). The fiber-oriented CNT sheet applied around the D-EAP film, exhibits strong interaction between CNT fibers in the electrode and the D-EAP film to produce a robust conductive-nanolayer at the interface, on actuation cycling. The design paradigm provides a great potential for the fabrication of soft linear actuators.     

Molecular electronic devices based on single-walled carbon nanotube electrodes

As the top-down fabrication techniques for silicon-based electronic materials have reached the scale of molecular lengths, researchers have been investigating nanostructured materials to build electronics from individual molecules. Researchers have directed extensive experimental and theoretical efforts toward building functional optoelectronic devices using individual organic molecules and fabricating metal-molecule junctions. Although this method has many advantages, its limitations lead to large disagreement between experimental and theoretical results. This Account describes a new method to create molecular electronic devices, covalently bridging a gap in a single-walled carbon nanotube (SWNT) with an electrically functional molecule. First, we introduce a molecular-scale gap into a nanotube by precise oxidative cutting through a lithographic mask. Now functionalized with carboxylic acids, the ends of the cleaved carbon nanotubes are reconnected with conjugated diamines to give robust diamides. The molecular electronic devices prepared in this fashion can withstand and respond to large environmental changes based on the functional groups in the molecules. For example, with oligoanilines as the molecular bridge, the conductance of the device is sensitive to pH. Similarly, using diarylethylenes as the bridge provides devices that can reversibly switch between conjugated and nonconjugated states. The molecular bridge can perform the dual task of carrying electrical current and sensing/recognition through biological events such as protein/substrate binding and DNA hybridization. The devices based on DNA can measure the difference in electrical properties of complementary and mismatched strands. A well-matched duplex DNA 15-mer in the gap exhibits a 300-fold lower resistance than a duplex with a GT or CA mismatch. This system provides an ultrasensitive way to detect single-nucleotide polymorphisms at the individual molecule level. Restriction enzymes can cleave certain cDNA strands assembled between the SWNT electrodes; therefore, these strands maintain their native conformation when bridging the ends of the SWNTs. This methodology for creating novel molecular circuits forges both literal and figurative connections between chemistry, physics, materials science, and biology and promises a new generation of integrated multifunctional sensors and devices.     

Carbon nanotube/graphene composite for enhanced capacitive deionization performance

In this study, single-walled carbon nanotubes were combined with graphene oxide nanosheets in aqueous dispersion and then chemically reduced to form the carbon nanotube/graphene (CNT/G) composite as electrodes for capacitive deionization (CDI). The structure of the CNT/G composite was highly porous, with single-walled carbon nanotubes (SWCNTs) sandwiched between graphene sheets that functioned as spacers and provided diffusion paths for smooth and rapid ion conduction. The associated increase in the electrical double-layer capacitance enhanced capacitive deionization performance. The CNT/G composite achieved a specific capacitance of 220 F/g and an electrosorption capacity of 26.42 mg/g with 100% regeneration, showing great potential as a high performance electrode material in CDI applications.     

碳纳米管上电沉积钯对乙醇的电催化氧化研究

采用电化学循环伏安法沉积Pd纳米颗粒,在碳纳米管(CNT)电极表面获得了粒径约为20 nm而且分散性良好的Pd纳米颗粒,而玻碳(GC)电极表面上Pd纳米颗粒趋向于堆积形成紧密的Pd金属薄膜。研究发现,在碱液中Pd/CNT电极对乙醇的催化活性要高于Pd/GC电极,而交流阻抗实验发现,Pd/GC电极的阻抗半圆明显大于碳纳米管,表明了Pd/CNT电极对乙醇的催化速率明显优于Pd/GC电极。不同Pd载量以及环境温度影响实验发现,Pd/CNT电极上峰电流的增长速率要明显大于Pd/GC电极,而不同乙醇浓度实验进一步表明,Pd/CNT电极对于乙醇浓度的响应要比Pd/GC的灵敏。     

Electrochemical characterisation of patterned carbon nanotube electrodes on silane modified silicon

Previously we have used atomic force anodisation lithography, with a self-assembled monolayer of hexadecyltrichlorosilane as a resist, to pattern silicon oxide nanostructures onto a p-type silicon (1 0 0) substrate. A condensation reaction was used to immobilise carbon nanotubes with high carboxylic acid functionality directly to the silicon oxide. A further condensation reaction using this surface attached the molecule ferrocenemethanol to the bound nanotubes. These new nanostructures were used as electrodes to observe the oxidation and reduction of ferrocene. However, because the small currents measured are near the detection limits of the electrochemical system used, important electrode kinetics could not to be obtained. A scribing approach made larger regions of oxidised silicon leading to the creation of larger scale patterned arrangements of carbon nanotubes allowing measurement of important electrochemical parameters such as electrode kinetics, electron transfer rates and surface concentration of redox molecules. Knowledge of these characteristics has provided insights into the behaviour of the microelectrodes created using atomic force microscopy.     

Characterization of parylene deposition process for the passivation of organic light emitting diodes

The chemical vapor condensation process of Parylene-N thin films was investigated and applied to the passivation of the organic light emitting diodes (OLEDs). The effects of process variables on the deposition rate were studied, and it was found that the deposition rate of Parylene increases with increasing precursor sublimation temperature but decreases with increasing substrate temperature. The dependence of deposition rate was well explained by the condensation polymerization model of the monomer on the surface. The Parylene film was used as a passivation layer for OLEDs, and as a result, the lifetime of the passivated OLEDs was increased by a factor of about 2.3 compared with that of non-passivated OLEDs. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Using multiwalled carbon nanotube modified electrodes for the adsorptive striping voltammetric determination of hesperidin

Hesperidin, a flavone glycoside found in the skins and juices of citrus fruits, can be detected using multiwalled carbon nanotube (MWCNT)-modified electrodes using the technique of adsorptive stripping voltammetry (AdSV) with accumulation at open circuit potential. This is relevant because hesperidin can be used as an indication of the citrus fruit juice's freshness. The oxidation mechanism to explain the observed voltammetry corresponds to the redox chemistry of the guaiacol sub-unit within the hesperidin molecular structure. Hesperidin could be detected over a linear range up to 30 μM, and with a detection limit of 0.61 μM and 7 nM, with less than 5% variation between different electrodes, using cyclic voltammetric or square wave adsorptive stripping techniques respectively. This methodology was extended to MWCNT-modified screen-printed electrodes (MWCNT-SPEs), allowing the development of a cheap, mass produced, disposable sensor that we show is capable of measuring the concentration of hesperidin in real orange juice samples, and be applied within the citrus fruit industry.     

Carbon nanotube bottles for incorporation,release and enhanced cytotoxic effect of cisplatin

Carbon nanotubes (CNTs) have emerged as promising drug delivery systems particularly for cancer therapy, due to their abilities to overcome some of the challenges faced by cancer treatment, namely non-specificity, poor permeability into tumour tissues, and poor stability of anticancer drugs. Encapsulation of anticancer agents inside CNTs provides protection from external deactivating agents. However, the open ends of the CNTs leave the encapsulated drugs exposed to the environment and eventually their uncontrolled release before reaching the desired target. In this study, we report the successful encapsulation of cisplatin, a FDA-approved chemotherapeutic drug, into multi-walled carbon nanotubes and the capping at the ends with functionalised gold nanoparticles to achieve a “carbon nanotube bottle” structure. In this proof-of-concept study, these caps did not prevent the encapsulation of drug in the inner space of CNTs; on the contrary, we achieved higher drug loading inside the nanotubes in comparison with data reported in literature. In addition, we demonstrated that encapsulated cisplatin could be delivered in living cells under physiological conditions to exert its pharmacological action.     

Encapsulation of flexible organic light emitting diodes by UV-cure epoxy siloxane

In this research, a silicon additive was synthesized by reaction of the hydroxyl terminated poly-dimethyl siloxane (PDMS-OH) with 3-glycidoxy propyl tri-methoxy silane (TMS-epoxy). The synthesized silicon additive characterized and evaluated to use as a curing agent for preparing high-performance and impermeable epoxy resin for encapsulation of flexible optoelectronic devices such as thin film photovoltaics and polymer light-emitting diodes to protect them against water penetration and increase their lifespan. The synthesized additive was characterized by FTIR, NMR, and elemental analysis. Thermal properties of the UV curable resin were investigated by using DSC and DMTA. The prepared UV cure epoxy resin exhibited an appropriate melting temperature (56.19 °C). Contact angle test, SEM, and calcium test was used to investigate the properties of UV-cured coating resin. The water contact angle of the cured prepared resin film showed good hydrophobicity. The SEM results confirmed the uniformity of cured film and UV cure resin dispersion. Transparency and flexibility of the cured film to encapsulate the flexible light emitting diodes are acceptable. The permeability of cured film to water vapor was evaluated by calcium test, which shows the cured film suitability to encapsulate the FOLED. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48033.     

Cycle and rate performance of chemically modified super-aligned carbon nanotube electrodes for lithium ion batteries

Super-aligned multi-walled carbon nanotubes (MWCNTs), which had been produced in large-scale, were oxidized by H₂O₂ and HNO₃. The surface defects and oxygen-containing functional groups introduced during the oxidizing process were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The surface modification of MWCNTs improved the electrochemical properties. As a result, H₂O₂-treated and HNO₃-treated MWCNTs displayed reversible capacities of 364 mA h/g and 391 mA h/g, respectively, after 80 galvanostatic cycles, corresponding to 143% and 154% improvements compared with pristine MWCNTs. The rate capability was also increased. At a current density of 3500 mA/g, H₂O₂-treated and HNO₃-treated MWCNTs exhibited reversible capacities of 66 mA h/g and 156 mA h/g, respectively. In contrast, pristine MWCNTs were only able to deliver 27 mA h/g at this current density.     

Fabrication of carbon nanotube and dysprosium nanowire modified electrodes as a sensor for determination of curcumin

Two sensitive sensors for determination of curcumin (CM) were described. CM can be detected using multiwall carbon nanotube (MWCNT)-modified electrodes and dysprosium nanowire carbon paste electrode using the technique of adsorptive stripping voltammetry (AdSV) in stationary solution and the fast Fourier transform voltammetry at the flowing solution. Both electrodes did show less passivation effect that occurs on the unmodified electrodes and displayed better stability and reproducibility. This electrode enabled selective determination of CM in the presence of interfering species. Under optimized conditions, CM could be detected over a linear range with a detection limit of 5.0 × 10⁻⁹ mol L⁻¹ and 5.0 × 10⁻¹⁰ mol L⁻¹ for the traditional square wave and fast Fourier transform square wave voltammetry (FFTSWV) with RSD between 0.2 and 0.5%. Comparison with other reported methods showed these studies are about 100 times more sensitive than previous ones. Good selectivity and high sensitivity obtained by Square wave voltammetry can open new possibilities of direct CM determination.     

The pH-dependence of oxygen reduction on multi-walled carbon nanotube modified glassy carbon electrodes

The pH-dependence of oxygen electroreduction has been investigated on multi-walled carbon nanotube (MWCNT) modified glassy carbon (GC) electrodes. Various surfactants were used in the electrode modification: dihexadecyl hydrogen phosphate, cetyltrimethylammonium bromide, sodium dodecyl sulfate and Triton X-100. Electrochemical experiments were carried out in 0.5 M H₂SO₄ solution, acetate buffer (pH 5), phosphate buffers (pH 6, 7 and 8), borate buffer (pH 10), 0.01 M KOH, 0.1 M KOH and in 1 M KOH solution, using the rotating disk electrode (RDE) method. The oxygen reduction behaviour of MWCNT-modified GC electrodes at different pHs was compared. The RDE results revealed that the half-wave potential (E_1/2) of oxygen reduction was higher in solutions of high pH. At lower pHs (pH < 10) the value of E_1/2 did not essentially depend on the solution pH. A comparison with previous studies on bare GC showed that the pH-dependence of the half-wave potential of oxygen reduction on MWCNT-modified GC electrodes follows a similar trend to that observed for bare GC.     

Enhancing the electroluminescence properties of novel blue light emitting polymer and MEH‐PPV based white light emitting polymer devices by processing condition optimization

A series of triarylaminooxadiazole‐containing tetraphenylsilane light emitting polymer (PTOA) and poly(2‐methoxy, 5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene‐vinylene) (MEH‐PPV) based white light emitting polymer devices (PLEDs) were fabricated to study blue and orange–red emitter composition and light emitting layer processing effects on white emission electroluminescence properties. Color purity, current turn‐on voltage, brightness, and current efficiency were strongly determined by MEH‐PPV content and the thin film processing condition. The intensity of PTOA blue emission was equal to that of MEH‐PPV orange–red emission when the device was fabricated by a polymer composite film containing 10 wt % of MEH‐PPV. Color purity [Commission Internationale de L'Eclairage (CIE_x,y) coordinates (0.26,0.33)] was nearly white emission under applied 8 V. The brightness and current efficiency of PTOA‐MEH‐PPV composite film based devices increased as MEH‐PPV content increased. Furthermore, white emission blue shifted with increasing spin‐rate of thin film coating and applied voltage. Low turn‐on voltage, high current density, and high brightness were obtained for the device fabricating with light emitting layer coating with high spin‐rate. Moreover, low current efficiency was obtained for the PLED with a thinner light‐emitting layer. A white emission CIE (0.28,0.34) was obtained for PTOA‐MEH‐PPV based white PLED. White PLED brightness and efficiency can be as high as 700 cd/m² and 0.78 cd/A, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Electrical properties of dye‐doped colour tunable organic light emitting diode

In this work, we report on the electrical properties of dye‐doped colour tunable organic light‐emitting diode (OLED). The device structure is glass substrate/indium tin oxide/N,N′‐di(naphthalen‐1‐yl)‐N,N′‐diphenyl‐benzidine (NPB) 30 nm/Alq₃:DCM 50 nm/Aluminum (Al) 150 nm where NPB is the hole transport layer. Alq₃:DCM is the emitting layer which made of tris(8‐hydroxyquinoline) aluminium (Alq₃) doped with 4‐(Dicyanomethylene)‐2‐methyl‐6‐(4‐dimethyl‐aminostyryl)‐4H‐pyran (DCM) organic dye. The influence of doping concentration has been investigated by current density–voltage measurement, luminance intensity–voltage characteristic, electroluminescence (EL) and impedance spectroscopy, respectively. The EL spectrum exhibits the shifted of peak position from green to red region. The threshold voltage of the device decreased at the low DCM doping concentration (1 wt.%), in contrast, when the increase in the doping concentrations then the threshold voltage will be increased. The highest luminance intensity and lowest turn‐on voltage of OLED can be observed at doping concentration about of 1 wt.% of DCM. The impedance characteristics of the dye‐doped OLED can be modelled by simply adopting the conventional equivalent circuit with the simple combination of resistors and capacitors network. © 2012 Canadian Society for Chemical Engineering     

Electrochemical determination of phloroglucinol using a carbon nanotube modified electrode enhanced by surfactant

A novel technique is utilized to detect trace amounts of phloroglucinol. In pH 5.0, 0.1 mol L⁻¹ HAc–NaAc buffer solution, phloroglucinol exhibited a stable and sensitive oxidation signal at a glassy carbon electrode modified with multi-wall carbon nanotube. By using the surfactant cetyl pyridinium chloride, the electrochemical response was greatly enhanced. The mechanism was systematically explored. In the range 9.0 × 10⁻⁷–3.0 × 10⁻⁴ mol L⁻¹, the oxidation peak currents of phloroglucinol have a linear relationship with concentration: the limit of detection was estimated to be 2.5 × 10⁻⁷ mol L⁻¹ (S/N = 3). The method was adopted to detect the content of phloroglucinol injection, and the recovery was from 97.5% to 103.0%.