Tetrafullerene conjugates for all-organic photovoltaics

The synthesis of two new tetrafullerene nanoconjugates in which four C60 units are covalently connected through different pi-conjugated oligomers (oligo(p-phenylene ethynylene) and oligo(p-phenylene vinylene)) is described. The photovoltaic (PV) response of these C60-based conjugates was evaluated by using them as the only active material in organic solar cells, showing a low PV performance. Photophysical studies in solution demonstrated a very fast ( approximately 10 ps) deactivation of the singlet excited state of the central core unit to produce both charge-separated species (i.e., C60*--oligomer+*-(C60)3 and C60 centered singlet excited states). The charge-separated state recombines partly to the C60 centered singlet state that undergoes subsequent intersystem crossing. Photophysical studies carried out in films support these data, exhibiting long-lived triplet excited states. For both tetrafullerene arrays, the low yield of long-lived charge carriers in thin films accounts for the limited PV response. On the contrary, utilizing the oligo(p-phenylene vinylene) centered precursor aldehyde as an electron donor and antennae unit and mixing with the well-known C60 derivative PCBM, the photophysical studies in films show the formation of long-lived charges. The PV devices constructed from these mixtures showed a relatively high photocurrent of 2 mA cm(-2). The sharp contrast between the nanoconjugates and the physical blends tentatively was attributed to improved charge dissociation and the collection of more favorable energy levels in the blends as a result of partial aggregation of both of the components.     

Mass-sensitive micro- and nanosensors for detecting the vapors of explosives and associated substances

The main analytical characteristics of mass-sensitive micro- and nanosensors for detecting the vapors of explosives and associated substances are compared. The limits of detection, sensitivity, sensor setting time (response speed) and recovery time after the action of an analyte, and the selectivity of cantilever sensors, quartz crystal microbalances, surface acoustic wave sensors, and flexural plate wave sensors are considered. The effectiveness of the use of the nanosized structures of mass-sensitive sensors, and bio- and nanostructured specific coatings is analyzed.     

A miniature chemiresistor sensor for carbon dioxide

A carpet-like nanostructure of polyaniline (PANI) nanothin film functionalized with poly(ethyleneimine), PEI, was used as a miniature chemiresistor sensor for detection of CO₂ at room temperature. Good sensing performance was observed upon exposing the PEI–PANI device to 50–5000 ppm CO₂ in presence of humidity with negligible interference from ammonia, carbon monoxide, methane and nitrogen dioxide. The sensing mechanism relied on acid–base reaction, CO₂ dissolution and amine-catalyzed hydration that yielded carbamates and carbonic acid for a subsequent pH detection. The sensing device showed reliable results in detecting an unknown concentration of CO₂ in air.     

Multilayered Cu–Ti deposition on silicon substrates for chemiresistor applications

Abstract

On the perspective to develop CuO–TiO₂ MOS, multilayered Cu and Ti thin layers were alternatively deposited on silicon wafers using 25?keV Ar?+?ion beam sputtering and, subsequently, oxidized by thermal annealing in air at 400?°C for 24?h. The deposited films have variable ratios of the Cu and Ti % at. One of the main goal is to obtain such multilayers avoiding the presence of Cu–Ti–O compounds. The samples were characterized in terms of composition (by RBS and SIMS analyses) and morphology (by AFM and SEM investigations). In particular, SIMS maps allows to observe the spatial distribution and thickness of each phase of the Cu/Ti multilayers, and further to observe Cu diffusion and mixing with Ti, as well as phase separation of CuO and TiO₂ in the samples. The reasons of this effect represent an open issue that has to investigated, in order to improve the MOS fabrication.     

Use of high resolution continuum source atomic absorption spectrometry as a detector for chemically generated noble and transition metal vapors

Vapor generation and atomization conditions in a heated quartz tube to detect Ag, Cd, Co, Cu, Ni and Zn using High Resolution Continuum Source AAS (HRCSAAS), were optimized. Vapors were generated after mixing acidified solutions containing 8-hydroxiquinoline (oxine) with sodium tetrahydroborate. Afterwards, they were swept to the heated quartz cell by an argon flow.Reaction loop size and temperature of the quartz cell were optimized for each element. A temperature of 960 °C was selected as a compromise value to detect most of the metals. Afterwards, a Plackett–Burmann design was proposed to select which parameters were most important. Type of acid and its concentration were the most statistical significant variables. Optimum conditions for sequential detection of Cd, Cu, Ni and Zn were: 1 mg L^− 1 Co as catalyst, 250 mg L^− 1 oxine, 0.6 M nitric acid, 1.75% (w/w) sodium tetrahydroborate (prepared in 0.4 (w/v)% NaOH), a reaction loop of 250 µL, and a 25 L h^− 1 carrier Ar flow. Ag and Co were each detected in their own optimized conditions. Analytical performance of the system was evaluated in connection with a selected pixel number, and spectral correction was used to eliminate NO absorption bands interference in Zn detection. Detection limits were in the range of 1.5–18 μg L^− 1 for Ag, Cu, Cd and Zn, whereas sensitivity was worst for Co (169 μg L^− 1) and Ni (586 μg L^− 1). Atomization in a quartz cell of Co and Ni volatile species, generated by an addition of sodium tetrahydroborate to an acidified solution of the analytes, was reported for the first time in this paper. Precision expressed as RSD(%) had values lower than 10% except for Ni.     

Multiple approaches for enhancing all-organic electronics photoluminescent sensors: Simultaneous oxygen and pH monitoring

Key issues in using organic light emitting diodes (OLEDs) as excitation sources in structurally integrated photoluminescence (PL)-based sensors are the low forward light outcoupling, the OLEDs’ broad electroluminescence (EL) bands, and the long-lived remnant EL that follows an EL pulse. The outcoupling issue limits the detection sensitivity (S) as only ~20% of the light generated within standard OLEDs can be forward outcoupled and used for sensor probe excitation. The EL broad band interferes with the analyte-sensitive PL, leading to a background that reduces S and dynamic range. In particular, these issues hinder designing compact sensors, potentially miniaturizable, that are devoid of optical filters and couplers. We address these shortcomings by introducing easy-to-employ multiple approaches for outcoupling improvement, PL enhancement, and background EL reduction leading to novel, compact all-organic device architectures demonstrated for simultaneous monitoring of oxygen and pH. The sensor comprises simply-fabricated, directionally-emitting, narrower-band, multicolor microcavity OLED excitation and small molecule- and polymer-based organic photodetectors (OPDs) with a more selective spectral response. Additionally, S and PL intensity for oxygen are enhanced by using polystyrene (PS):polyethylene glycol (PEG) blends as the sensing film matrix. By utilizing higher molecular weight PS, the ratio τ₀/τ₁₀₀ (PL decay time τ at 0% O₂/τ at 100% O₂) that is often used to express S increases ×1.9 to 20.7 relative to the lower molecular weight PS, where this ratio is 11.0. This increase reduces to ×1.7 when the PEG is added (τ₀/τ₁₀₀ = 18.2), but the latter results in an increase ×2.7 in the PL intensity. The sensor's response time is <10 s in all cases. The microporous structure of these blended films, with PEG decorating PS pores, serves a dual purpose. It results in light scattering that reduces the EL that is waveguided in the substrate of the OLEDs and consequently enhances light outcoupling from the OLEDs by ~60%, and it increases the PL directed toward the OPD. The multiple functional structures of multicolor microcavity OLED pixels/microporous scattering films/OPDs enable generation of enhanced individually addressable sensor arrays, devoid of interfering issues, for O₂ and pH as well as for other analytes and biochemical parameters.     

Use of a gas-sensor array for detecting volatile organic compounds (VOC) in chemically induced cells

An application of gas sensors for rapid bioanalysis is presented. An array of temperature-modulated semiconductor sensors was used to characterize the headspace above a cell culture. Recombinant Saccharomyces cerevisiae yeast cells, able to respond to 17-estradiol by producing a reporter protein, were used as a model system. Yeast cells had the DNA sequence of the human estrogen receptor stably integrated into the genome, and contained expression plasmids carrying estrogen-responsive sequences and the reporter gene lac-Z, encoding the enzyme -galactosidase. The sensor-response profiles showed small but noticeable discrimination between cell samples induced with 17-estradiol and non-induced cell samples. The sensor array was capable of detecting changes in the volatile organic compound composition of the headspace above the cultured cells, which can be associated with metabolic changes induced by a chemical compound. This finding suggests the possibility of using cross-selective gas-sensor arrays for analysis of drugs or bioactive molecules through their interaction with cell systems, with the advantage of providing information on their bioavailability.     

Humidity effect on the monolayer-protected gold nanoparticles coated chemiresistor sensor for VOCs analysis

Two gold-thiolate monolayer-protected nanoparticles were synthesized and used as interfacial layers on chemiresistor sensors for the analysis of violate organic compounds (VOCs). Toluene, ethanol, acetone and ethyl acetate were chosen as the target vapors. Both the resistance and capacitance were measured as the function of analyte concentrations. The effect of humidity on the sensor sensitivity to VOCs was investigated. The sensitivity decreases with humidity increasing, depending on the hydrophobicity of the target compounds. Less effect was observed on the higher hydrophobic compounds. While the relative humidity (RH) increased from 0 to 60%, the sensitivity to acetone decreased by 39 and 37%, respectively on the Au-octanethiol (C₈Au) and Au-2-phenylethanethiol (BC₂Au) coated sensors, while the sensitivity to toluene decreased by 12 and 14%, respectively. These results show that the sensors coated with hydrophobic compounds protected-metal nanoparticles can be employed in high humidity for hydrophobic compounds analysis. The resistance responses to VOCs are rapid, reversible, and linear, while the capacitance response is not sensitive and consequently not applicable for VOCs analysis. The response mechanism was also discussed based on the sensor response to water vapor. The capacitance response is not sensitive to the film swelling in dry environment.     

Graphene based chemiresistor sensors for the detection of toxic air pollutants: A theoretical overview

The advancements in present world like industrial revolution, transport system, agriculture, food industry, pharmaceutical industry and electricity generation have made our life easy and comfortable in many aspects but they also have deleterious effects on our life. The pollution from industries, household waste, combustion of fossils etc. has introduced many harmful chemicals in air and water which have badly affected the life on our planet. The presence of undesirable gases in air has serious adverse effects on health and quality of life. Therefore, monitoring of these substances becomes important.Graphene based chemiresistor sensor are proved to be promising materials for the detection of toxic air pollutants. This article summarizes the recent progress of Density functional theory (DFT) based studies in the field of graphene based gas sensors. This article discusses the working mechanism of graphene based chemiresistor and also provides the information that how the sensing ability can be enhanced. The information given in the article will help the young researchers in the selection of suitable dopant and nano-clusters for graphene based surfaces to make them more selective and sensitive towards the analytes.     

Molecular structure design of planar zwitterionic polymer electrode materials for all-organic symmetric batteries

All-organic symmetric lithium-ion batteries (LIBs) show promising prospects in sustainable energy storage systems, due to their environmental friendliness, structural diversity and low cost. Nevertheless, it remains a great challenge to explore suitable electrode materials and achieve excellent battery performance for all-organic symmetric LIBs. Herein, a squaraine-anthraquinone polymer (PSQ) electrode material was designed through rational molecular engineering. The well-designed extended π-conjugated system, donor–acceptor structure, abundant redox-active sites and rational manipulation of weak inter-/intramolecular interactions endow the PSQ electrode with outstanding electrochemical performance. The capacity of the PSQ cathode can be optimized to 311.5 mA h g⁻¹ by in situ carbon-template polymerization. Impressively, PSQ-based all-organic symmetric LIBs displayed high reversible capacity (170.8 mA h g⁻¹ at 50 mA g⁻¹), excellent rate performance (64.9% capacity retention at 4000 mA g⁻¹vs. 50 mA g⁻¹), ultralong cycle life up to 30 000 cycles at 2000 mA g⁻¹ and 97% capacity retention after 2500 cycles at 500 mA g⁻¹, which is one of the best comprehensive battery performances among the all-organic LIBs reported thus far.

A squaraine-linked polymer (PSQ) was applied in all-organic symmetric batteries. Attributed to its well-designed molecular strucuture, PSQ shows excellent electrochemical performance, which is one of the best results among the all-organic LIBs.     

Single-walled carbon nanotubes chemiresistor aptasensors for small molecules: picomolar level detection of adenosine triphosphate

Here we report single walled-carbon nanotubes (SWNTs)-based chemiresistor aptasensors for highly sensitive and selective detection of weakly or uncharged molecules using the displacement format. As a proof-of-concept we demonstrate the detection of ATP, a small weakly charged molecule, by displacement of the ssDNA anti-ATP aptamer hybridized to a small capture oligonucleotide covalently attached on SWNTs, with picomolar sensitivity and selectivity over GTP.     

KCl-assisted,chemically reduced graphene oxide for high-performance supercapacitor electrodes

Journal of Solid State Electrochemistry - Graphene with highly flaky state has been successfully prepared through chemical reduction process with the assistance of potassium chloride (KCl) to...     

Discrete models for chemically reacting systems

Nonequilibrium spatially distributed chemically reacting systems are usually described in terms of reaction-diffusion equations. In this article, a hierarchy of discrete models is studied that show similar spatio-temporal structure and can be used to explore the complex phenomena occurring in these systems. We consider cellular automaton models where space, time and chemical concentrations are discrete and the dynamics is embodied in a simple updating rule, coupled map lattices where space and time are discrete variables but chemical concentrations are continuous and the dynamics is given by a nonlinear function and, lastly, lattice gas cellular automaton models that view the system on a microscopic or mesoscopic level where space, time and particle velocities are discrete.     

A new 3D cupric coordination polymer as chemiresistor humidity sensor:narrow hysteresis,high sensitivity,fast response and recovery

A new three-dimensional coordination polymer composed of Cu~(2+) centres and semiquinoid linkers(dhbq~(2-)) was synthesized which was composed by two independent,enantiomeric,interpenetrated[Cu_2(dhbq)_3]~(2-) networks with(10,3)-a topology.The compound has good water stability and typical behaviors of semiconductor,whose conductivity increases along with raising temperature.The chemiresistive humidity sensor made from this material shows good properties including linear sensitivity,high response,fast response and recovery,and particularly narrow hysteresis during humidity adsorption and desorption