Dopant Loading Research Articles

The effect of thermal annealing on dopant site choice in conjugated polymers

Solution-processed organic electronic devices often consist of layers of polar and non-polar polymers. In addition, either of these layers could be doped with small molecular dopants. It is extremely important for device stability to understand the diffusion behavior of these molecular dopants under the thermal stress and whether the dopants have preference for the polar or the non-polar polymer layers. In this work, a widely used molecular dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) was chosen to investigate dopant site preference upon thermal annealing between the polar thiophene poly(thiophene-3-[2-(2-methoxy-ethoxy)ethoxy]-2,5-diyl) (S–P3MEET) and non-polar thiophene poly(3-hexylthiophene) (P3HT). F4TCNQ is able to p-type dope both P3HT and S–P3MEET. Further doping studies of S–P3MEET using near edge X-ray absorption fine structure spectroscopy, conductivity measurements and atomic force microscopy show that the F4TCNQ additive competes for doping sites with the covalently attached dopants on the S–P3MEET. Calorimetry measurements reveal that the F4TCNQ interacts strongly with the side-chains of the S–P3MEET, increasing the melting temperature of the side-chains by 30 °C with 5 wt% dopant loading. Next, the thermal stability of doping in the polar/non-polar (S–P3MEET/P3HT) bilayer architectures was investigated. Steady-state absorbance and fluorescence results show that F4TCNQ binds much more strongly in S–P3MEET than P3HT and very little F4TCNQ is found in the P3HT layer after annealing. In combination with reflectometry measurements, we show that F4TCNQ remains in the SP3MEET layer with annealing to 210 °C even though the sublimation temperature for neat F4TCNQ is about 80 °C. In contrast, F4TCNQ slowly diffuses out of P3HT at room temperature. We attribute this difference in binding the F4TCNQ anion to the ability of the ethyl-oxy side-chains of the S–P3MEET to orient around the charged dopant molecule and thereby to stabilize its position. This study suggests that polar side-chains could be engineered to increase the thermal stability of molecular dopant position.

Visible light-driven photocatalytic hydrogen production using Cu-doped SrTiO3

ABSTRACTA new Cu-doped SrTiO3 photocatalyst was synthesized and characterized for uses in the visible-light photocatalytic production of hydrogen from water. The photocatalytic activity was assessed based on the characterization of the photocatalysts (band gap energy, surface area, crystallinity, and morphology) and the effects of varying together the calcination temperature, the Cu:Sr mole ratio, and the photocatalyst loading amount. It was determined that the amount of hydrogen evolved was largely dictated by the amount of Cu dopant present in the photocatalysts. The created Box Behnken Design optimization scenarios suggested the conditions: 850°C, 0.01 Cu:Sr, 0.33 g loading as the optimal conditions for maximum hydrogen production holding all studied factors in range, and the conditions: 850°C, 0.01 Cu:Sr, 0.21 g loading as the optimal conditions for the maximum hydrogen production while minimizing Cu dopant and photocatalyst loading.

Enhanced Charge Transfer Doping Efficiency in J-Aggregate Poly(3-hexylthiophene) Nanofibers

Charge transfer doping efficiencies of π-stacked poly(3-hexylthiophene) (P3HT) aggregate nanofibers are studied using spectroscopic and electron microscopy probes. Solution dispersions of self-assembled P3HT nanofibers are doped in the ground electronic state by adding varying amounts (w/w%) of the strong charge transfer dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). Careful control of self-assembly conditions allows us to select either the H- and J-aggregate limiting forms, which differ primarily in the degree of purity (i.e., molecular weight fractionation) and nanomorphology. Electron paramagnetic resonance (EPR), electronic absorption, and Raman spectroscopy of F4-TCNQ–:P3HT+ species are then used to track doping efficiency with dopant loading. J-aggregate nanofibers exhibit over an order of magnitude larger doping efficiencies than polymorphic H-aggregate nanofibers. The higher purity and order of the former promote intrachain polaron delocalization whereas disorder arising from greater molecular weight polydispersity in the latter instead lead to polaron localization resulting in charge transfer complex formation. Interestingly, J-aggregate nanofiber EPR signals decrease significantly after ∼25% F4-TCNQ loading which we attribute to increased antiferromagnetic coupling between delocalized hole polarons on neighboring P3HT chains leading to spinless interchain bipolarons. Raman spectra excited on resonance with NIR F4-TCNQ–:P3HT+ absorption transitions also reveal quinoid distortions of the P3HT backbone in J-aggregates. We propose that self-assembly approaches to control aggregate packing and purity can potentially be harnessed to achieve long-range, anisotropic charge transport with minimal losses.

Effect of molecular electrical doping on polyfuran based photovoltaic cells

The electronic, optical, and morphological properties of molecularly p-doped polyfuran (PF) films were investigated over a wide range of doping ratio in order to explore the impact of doping in photovoltaic applications. We find evidence for integer-charge transfer between PF and the prototypical molecular p-dopant tetrafluoro-tetracyanoquinodimethane (F4TCNQ) and employed the doped polymer in bilayer organic solar cells using fullerene as acceptor. The conductivity increase in the PF films at dopant loadings ≤2% significantly enhances the short-circuit current of photovoltaic devices. For higher doping ratios, however, F4TCNQ is found to precipitate at the heterojunction between the doped donor polymer and the fullerene acceptor. Ultraviolet photoelectron spectroscopy reveals that its presence acts beneficial to the energy-level alignment by doubling the open-circuit voltage of solar cells from 0.2 V to ca. 0.4 V, as compared to pristine PF.

Influence of Dopant Loading on the Photo‐ and Electrochemical Properties of (N, O)‐Co‐doped Graphene.

A series of (N, O)-co-doped graphenes with different N and O loadings are prepared by the pyrolysis of natural chitosan. When the percentage of dopant increases, the conduction-band potential and charge-separation quantum yield increase, whereas the charge-separation lifetime decreases.

Tantalum Segregation in Ta-Doped TiO2 and the Related Impact on Charge Separation during Illumination

This investigation was aimed at identifying the influence of applied processing conditions, temperature and oxygen activity, on the segregation of Ta in Ta-doped TiO2. Over the temperature range of 1173–1523 K, it has been observed that the tendency for Ta to segregate is greater under the application of oxidizing conditions (p(O2) = 101 kPa) than that under reducing conditions (p(O2) = ∼10–10 Pa). This respectively manifests as an accumulation and depletion of Ta at the surface of Ta–TiO2 under the respective applied oxygen activities. This behavior has been interpreted in terms of the relative activities of Ta at the surface and bulk during processing. The results indicate that it is possible to substantially alter the concentration of a donor dopant at the surface of TiO2 despite maintaining the bulk dopant loading. In so doing, a TiO2-based homojunction is formed that can be engineered to favor charge separation, as demonstrated by preliminary surface photovoltage measurements. The optimization of thi...

Chiral Periodic Mesoporous Organosilicas: Probing Chiral Induction in the Solid State

The production of a variety of PMO materials made with 1,1′-biphenylene monomers, and the inclusion of 1,1′-binaphthalene dopants is described. The effect of the point of attachment with regard to the biaryl axis was studied, and it was found that the highest level of chirality transfer is obtained when the biaryl axis is not restricted by the polymerization point. In addition, the actual loading of dopant was found to vary considerably depending on the synthesis procedure, and the effect of dopant, even at low level, was magnified under basic conditions when more ordered materials are produced.

Oxidative desulfurization of commercial diesel catalyzed by tert-butyl hydroperoxide polymolybdate on alumina: optimization by Box-Behnken design

In this paper, the performance of oxidative desulfurization of commercial diesel by alumina-supported polymolybdate-based catalyst system was studied. The oxidizing reagent used was tert-butyl hydroperoxide. The catalyst was prepared using wet impregnation method and characterized by FESEM-EDX and X-ray photoelectron spectroscopy. The effects of dopants, catalyst loading, dopant loading, and calcination temperature of the catalyst were investigated. Further investigations on doped molybdenum revealed that Fe–MoO3/Al2O3 catalyst calcined at 500 °C with 10 % of Fe loading and 9 g/L, the catalyst was able to reduce the sulfur in commercial diesel from 440 to 88 ppmw. Response surface methodology involving Box-Behnken was employed to evaluate and optimize Fe–MoO3/Al2O3 preparation parameters (calcinations temperature, catalyst loading, and Fe loading) and their optimum values were found to be 550 °C, 10 g/L and 10 % of calcination temperature, catalyst loading, and Fe loading.

Amperometric urea biosensor based on covalently immobilized urease on an electrochemically polymerized film of polyaniline containing MWCNTs

In this work, polyaniline-multiwalled carbon nanotubes (PANI/MWCNTs) composite were fabricated by electropolymerization method, as a matrix for entrapment of enzyme. Urease has been immobilized by using physical adsorption and electrochemical entrapment technique. A conventional three-electrode system was used. Pencil graphite disk electrode (PGDE), Ag/AgCl (3M KCl) and platinum wire were used as working electrode, reference electrode and counter electrode respectively. The influence of several experimental parameters such as applied potential, type and concentrate of dopant and enzyme loading was explored to optimize the electroanalytical performance of the biosensor. The responses of the enzyme electrodes were measured via monitoring amperometric current at +0.3V (vs. Ag/AgCl). Kinetic parameters operational and storage stabilities were determined. The value of the apparent Michaelis–Menten constant, Imax and sensitivity (Imax/Km) experimentally determined to be 2.02mM, 2.5×10−5Acm−2 and 12×10−5AmM−1cm−2, respectively. The optimized urea biosensor shows a good sensitivity from 10−2M to 10−5M urea concentration range and a response time of about 50s. The detection limit was 0.04mM. The proposed biosensor retained 50% of its original response after 15 days.

Heterostructured Er3+ doped BiVO4 with exceptional photocatalytic performance by cooperative electronic and luminescence sensitization mechanism

Er-BiVO4 has been synthesized by means of mw-assisted hydrothermal method having good photoactivity under sun-like excitation. It is stated that the precursor addition sequence plays a critical role which determine the further structural feature of BiVO4. From the structural and morphological characterization, it can be demonstrated that the presence of Er3+ would induce the stabilization of the tetragonal phase probably due to the formation of tetragonal-ErVO4 seeds previous to BiVO4 formation. The best photocatalytic performance is attained for the sample with 0.75at% Er3+ content. At this dopant loading a mixture of tetragonal and monoclinic phase (70% tetragonal) is obtained. The dramatic increase in the photocatalytic activity for 0.75at% Er-BiVO4 is related to the occurrence of such heterostructure. For this system, the MB degradation rate constant appears drastically higher as bare m-BiVO4. Furthermore, activities of photocatalysts for visible-light-driven O2 evolution have been evaluated, demonstrating that the photocatalytic activity of this Er-doped system (O2 evolution rate, 1014μmolg−1h−1) is 20 times as that of undoped m-BiVO4 (O2 evolution rate, 54μmolg−1h−1). From the obtained results, the cooperative conjunction of electronic and luminescence mechanism involved in the reaction is proposed to be the origin of the enhanced photocatalytic efficiencies of such systems.

A theoretical study of the structures and optical spectra of helical copper–silver clusters

The structures and optical response of helical clusters ("Bernal spirals") with compositions Ag12Cu1(+) and Ag1Cu12(+) are calculated within Kohn-Sham density functional theory and the configuration interaction singles variant of time dependent density functional theory. The effects of dopant position within the cluster on the vertical excitation spectrum are investigated according to the underlying electronic structure of the major transitions. The roles of symmetry and geometry are investigated by calculating the optical response of helical, icosahedral and nanorod-like clusters of Ag13(+), finding local structure to be significant in driving the resultant optical response at the subnanometre scale. Further, it is noted that helical clusters have optical properties which are quite distinct from those of nanorods of similar dimensions. The effect of multiple doping is studied by introducing copper atoms into the centre of the silver helix, over the composition range Ag13(+) to Ag6Cu7(+). There is a complex variation of the major plasmon-like peak over this range, attributed to subtle variations in the influence of the copper 3d band on the excitations and charge transfer for different sites within the cluster. This work suggests that coinage metal nanohelices have unusual, tunable electronic properties, which in addition to their inherent chirality makes them interesting systems to study for chiral catalysis and optoelectronics.

Enhanced Surfactant Supramicellar Assembly by Hydrophobic Dopants

The light scattering peak (LS peak) near the surfactant critical micelle concentration (cmc) demonstrates that low hydrophobic dopant levels can cause supramolecular assembly of surfactants into metastable structures much more massive than dopant-free micelles. These supramicellar assemblies (SA) exist over the entire LS peak region, which extends from above the cmc down to well below the cmc. Dodecanol (D) was the dopant, and sodium dodecyl sulfate (SDS) and dodecyl trimethyl ammonium bromide (DTABr) were the surfactants in this work. Well above the cmc dopant is solubilized by micelles. The SA appear above the cmc, dependent on dopant level and solution ionic strength, as seen by an abrupt increase in LS. Hence, the micelles do not simply release their hydrophobic payload at the cmc; rather, the dopant causes a morphological change from normal micelles above the LS peak concentration regime into SA as the LS regime is entered from above the cmc. Below the cmc the LS peak has a cutoff concentration corresponding to the solubility limit of dodecanol in water, which can be termed a "critical supramicellar assembly concentration" (csac). A three-component model is proposed that self-consistently yields maximum micellar dopant loading, SA mass, and dopant solubility in solution. The constancy of SA molar mass under widely different ionic strength and dopant levels conditions is surprising and not currently understood.

Diesel soot combustion ceria catalysts

Different aspects of the ceria-catalyzed Diesel soot combustion reactions have been critically discussed, such as the high catalytic activity of ceria for Diesel soot combustion in comparison to some other potential catalysts, the potential ceria-catalyzed Diesel soot combustion mechanisms (the so-called NO2-assisted mechanism and the active oxygen mechanism) and the effect of ceria doping with suitable cations like those of Pr, La or Zr. Ceria must be doped in order to enhance thermal stability, but ceria doping also changes different physicochemical and catalytic properties of ceria. Zr-doping, for instance, has a double role on ceria as soot combustion catalyst: enhances ceria oxidation capacity of the adsorbed NOx species (positive effect) but stabilizes NO2 on surface (negative effect). The surface properties of a ceria catalyst are usually more important than those of bulk: high surface area/small crystal size usually has a positive effect on the catalyst performance and, in mixed oxides, the surface composition also plays a role. The optimal dopant loading depends on the foreign cation being, for instance, around 5–10%, 20–30% and 50 mol% for La3+, Zr4+, and Pr3+/4+, respectively.

The effect of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane charge transfer dopants on the conformation and aggregation of poly(3-hexylthiophene)

The effect of the strong electron acceptor, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), on poly(3-hexylthiophene) (P3HT) aggregates is studied. F4-TCNQ is commonly used as a dopant for P3HT, however, relatively little is currently known about its effect on polymer conformation and packing in the presence of fullerenes. Resonance Raman and optical spectra of pristine P3HT or blends with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) doped with F4-TCNQ up to ∼10% w/w show a loss of pristine-type P3HT aggregates with increasing dopant concentration. Complexed P3HT chains possess greater backbone planarity due to hole injection which is corroborated from density functional theory (DFT) calculations of oligothiophene surrogates and F4-TCNQ. Morphologies of doped P3HT/PCBM systems are characterized using scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS) detection and images reveal mixed clusters of P3HT/F4-TCNQ fibril-like domains that increase in size with dopant loading. The apparent preference of F4-TCNQ for P3HT aggregates is attributed to efficient charge separation stemming owing to the more polarizable nature of chains comprising the aggregate π-stack.

Hydrothermal synthesis and characterization of Nd-doped ZnSe nanoparticles with enhanced visible light photocatalytic activity

In the present study, Nd3+-doped ZnSe nanoparticles with variable Nd contents were successfully synthesized via a hydrothermal process using Neodymium (III) chloride hexahydrate as the doping source. X-ray diffraction, UV–Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy and transmission electron microscopy were used for characterization of the synthesized nanoparticles. It was confirmed by the DRS analysis that both of the undoped and Nd-doped ZnSe samples had significant optical absorption in the visible light range. The photocatalytic performance of as-synthesized nanoparticles was investigated towards the decolorization of C. I. Acid Orange 7 solution under visible light irradiation. Results indicated that the loading of Nd dopant into ZnSe nanoparticles significantly enhanced the photocatalytic activity of pure ZnSe with increasing Nd loading up to 6 mol% (color removal efficiency of 24.31 % for ZnSe and 84.20 % for Nd0.06Zn0.94Se after 120 min of treatment) and then the photocatalytic activity began to decrease.

VISIBLE LIGHT ACTIVECu2+/TiO2NANOCATALYST FOR DEGRADATION OF DICHLORVOS

The advantage of doping of TiO2with copper has been utilized for enhanced degradation of pesticide under visible light irradiation. The sol–gel method has been undertaken for the synthesis of copper-doped TiO2by varying the dopant loadings from 0.25 wt.% to 1.0 wt.% of Cu2+. The doped samples were characterized by UV-Visible Diffuse Reflectance Spectroscopy (DRS), N2adsorption–desorption (BET), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrometry (EDS). The photocatalytic activity of the catalyst was tested by degradation of dichlorvos under visible light illumination. The results found that 0.75 wt.% of Cu2+doped nanocatalysts have better photo catalytic activity than the rest of percentages doped, undoped TiO2and Degussa P25. The reduction of band gap was estimated and the influence of the process parameters on photo catalytic activity of the catalyst has been explained.

Effect of Fe3O4loading on the conductivities of carbon nanotube/chitosan composite films

Nanocomposite films were made by a simple solution casting method in which multi-walled carbon nanotubes (MWCNT) and magnetite nanoparticles (Fe3O4) were used as dopant materials to enhance the electrical conductivity of chitosan nanocomposite films. The films contained fixed CNT concentrations (5, 8, and 10 wt%) and varying Fe 3O4 content. It was determined that a 1:1 ratio of CNT to Fe3O4 provided optimal conductivity according to dopant material loading. X-ray diffraction patterns for the nanocomposite films, were determined to investigate their chemical and phase composition, revealed that nanoparticle agglomeration occurred at high Fe3O4 loadings, which hindered the synergistic effect of the doping materials on the conductivity of the films.

Influences of fly ash and fluorgypsum on the hydration heat and compressive strength of cement

The hydration heat of pure cement, fly ash single-doped cement, as well as fly ash and fluorgypsum co-doped cement were investigated by means of micro-calorimetry with an eight-channel micro-calorimeter. The results showed that the hydration heat and the hydration rate could be reduced significantly by fly ash and fluorgypsum. However, the reduction was not proportional to the loading of dopant. The exothermic peak of the co-doped cement was appeared earlier than that of the single-doped cement. As the temperature decreased, the hydration heat and the hydration rate of both the doped cement were reduced, and the exothermic peak appeared later. The effect of fly ash and fluorgypsum on the compressive strength of cement was also investigated. The results revealed that the early compressive strength of concrete made up of the co-doped cement was largely higher than that of the single-doped cement. Based on the experiment results obtained in this article, we could conclude that fluorgypsum is a suitable additive for the single-doped cement.

Post-Doping of ZnO with Cu and its Effect on their Photocatalytic Production of Active Oxygen Species

Cu doping zinc oxides (ZnOs) were prepared by a post doping process with CuCl2 at high temperature. With the increase of the dopant loading, the lattice constant c decreased firstly and then increased, which indicated that the doped Cu atoms substituted for Zn atoms at lower loading and extra dopant of the Cu atoms existed as interstitial atoms. UV-Vis diffuse reflectance spectra (UV-DRS) illustrated that the energy band gap was effectively narrowed after Cu doping. The photocatalytic production of hydroxyl radical (•OH) and superoxide anion (O2-) were determined by terephthalic acid with fluorescence spectrophotometer and nitroblue tetrazolium with UV-Vis spectrophotometer respectively, and the results showed that both the photocatalytic production of •OH and O2- were deceased with the increase of the dopant concentration, which indicated that the recombination centers were formed in the samples.

Relationship between surface area and crystal size of pure and doped cerium oxides

Pure and Zr, La or Pr-doped cerium oxides were characterised by transmission electron microscopy (TEM), N 2 adsorption-desorption at −196 °C and X-ray diffraction (XRD). For crystal sizes calculation, the Scherrer and Williamson-Hall equations were compared, and the relationship between surface area and crystal size was critically discussed. It was demonstrated that the Williamson-Hall equation must be used instead of the Scherrer equation to calculate crystal sizes, since the latter equation underestimated the crystal size while the former one provided suitable values by taking into account the strain contribution to line broadening. The miscalculation of crystal size by using the Scherrer equation affected both pure and doped cerium oxides, but the size underestimation became more important for high dopant loading. Under the conditions of the BET surface area measurements, N 2 molecules were adsorbed on the surface of the single crystals identified by XRD.