Potassium Dopant Research Articles

Correction: The Copper Oxide with Alkali Potassium Dopant for Heterojunction Solar Cells Application

Correction: The Copper Oxide with Alkali Potassium Dopant for Heterojunction Solar Cells Application

Traces of Potassium Induce Restructuring of the Anatase TiO2(001)-(1×4) Surface from a Reactive to an Inert Structure.

Reconstruction of solid surfaces is generally accompanied by changes in surface activities. Here, via a combined experimental and theoretical study, we successfully identified that a trace amount of potassium dopant restructures the mineral anatase TiO2(001) single-crystal surface from an added molecule (ADM) termination to an added oxygen (AOM) one without changing the (1×4) periodicity. The anatase TiO2(001)-(1×4)-ADM surface terminated with 4-fold coordinated Ti4c and 2-fold coordinated O2c sites is (photo)catalytically active, whereas the anatase TiO2(001)-(1×4)-AOM surface terminated with O2c and inaccessible 5-fold coordinated Ti5c sites is inert. These results unveiled a mechanism of dopant-induced transformation from a reactive to an inert TiO2(001)-(1×4) surface, which unifies the existing arguments about the surface structures and (photo)catalytic activity of anatase TiO2(001)-(1×4).

Accelerating the hydration reaction of potassium carbonate using organic dopants

Potassium carbonate has recently been identified as a promising candidate for thermochemical energy storage. However, as for many salt hydrates, the reaction kinetics is limited, and moreover, the hydration transition is kinetically hindered due to a metastable zone, involving limited mobility. This work aims to improve mobility by using organic potassium dopants, it shows that doping with potassium-formate and -acetate, can accelerate the hydration reaction. It has been shown that these dopants can enhance the hydration rate by two mechanisms i.e. introducing mobility due to adsorption of more water or introducing more surface area, where water adsorption can occur. This work opens up new possibilities for organic dopants to enhance the performance of salt hydrates.

Engineering of graphitic carbon nitride with simultaneous potassium doping sites and nitrogen defects for notably enhanced photocatalytic oxidation performance

Graphitic carbon nitride (g-C3N4) offers exciting opportunities for sustainable photocatalytic oxidation of organic pollutants but suffers from drawbacks of insufficient oxidation driving force and low quantum efficiency. To over the drawbacks, here a simple and effective strategy was developed to engineer g-C3N4 with simultaneous interstitially embedded potassium dopant and nitrogen defects, and the process included supramolecular preorganization followed by KOH-assisted thermal polycondensation. In the prepared DN-K-CN catalysts, potassium doping level and the amount of nitrogen defects were both controllable. With the increment of potassium doping level, the bandgap of the DN-K-CN became narrow, along with continuously downshifted valence band position. The DN-K-CN showed greatly enhanced visible-light photocatalytic oxidation performance with respect to g-C3N4 in the degradation of emerging phenolic pollutants, acetaminophen and methylparaben; meanwhile, the oxidation performance of DN-K-CN depended on potassium doping level and the amount of nitrogen defects. Combination of experimental findings and theory calculations it is confirmed that the enhanced photocatalytic oxidation performance of DN-K-CN was attributed to the synergistic effect of potassium dopant and nitrogen defects, which resulted in the generation of plentiful active oxygen species and the improvement of oxidation driving force of valence holes. The influence of potassium dopant and nitrogen defects on the electronic and band structures of g-C3N4 was revealed; simultaneously, mechanism of the enhanced photocatalytic oxidation performance of g-C3N4 after the introduction of potassium dopant and nitrogen defects was studied. The present work provided new insights into the electronic and band structure tuning for the improvement of the photocatalytic oxidation performance of g-C3N4.

Metal doped graphene oxide derived from Quercus ilex fruits for selective and visual detection of iron(III) in water: Experiment and theory

Iron is one of the most abundant metals and an important micronutrient that needs to be consumed in balanced amounts. Excess consumption or deficiency of this micronutrient can have adverse effects on biological functioning of human organs. Hence, the selective detection of this micronutrient is very important. The present work reports a simple and selective sensing of iron (III) in aqueous solutions using potassium doped graphene oxide (K-doped GO), which is synthesized from Quercus ilex fruits via a greener route of solvo-hydrothermal method. The synthesis of K-doped GO is confirmed with the help of various characterisation techniques viz. X-Ray Diffraction (XRD), Raman Spectroscopy, Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray Analysis (EDX), and Fourier Transform Infrared Spectroscopy (FT-IR).The Density Functional Theory (DFT) based first principle simulations are carried out to understand the interactions between K-doped GO and iron ions. The simulations reveal desorption of K-ions from the GO sheet due to the extremely high binding energy of iron ions on GO surface, which destabilizes the oxide groups as well as the potassium dopant. The desorbed K-ions from GO surface may react with water to form potassium hydroxide and subsequent quenching of fluorescence. Thus, the synthesized K-doped GO demonstrates its utility as a heavy metal ion sensor with detection limit of 0.345*10−7 M iron ions via spectrofluorometer. Moreover, this material is capable of detecting the presence of iron ions in water up to a limit of 7 ppm with naked eye.

Pseudohalide substitution and potassium doping in FA0.98K0.02Pb(SCN)2I for high-stability hole-conductor-free perovskite solar cells

Hybrid organic-inorganic halide perovskite solar cells (PSCs) have achieved intriguingly high photoelectric conversion efficiencies (PCEs), but their operational stability is still not satisfactory owing to their vulnerability to moisture and heat. Herein, we report the introduction of pseudohalide thiocyanate ions and potassium dopants into formamidinium lead triiodide (FAPbI3) to obtain a new class of pseudohalide-substituted lead halide perovskites FAPb(SCN)2I that can be prepared in ambient air and exhibit broad-range light absorption. Through the introduction of K+-cation doping, hole-conductor-free PSCs based on a FA0.98K0.02Pb(SCN)2I perovskite light absorber and a low-cost, screen-printable carbon-based counter electrode exhibited a PCE of 13.39%. Importantly, the FA0.98K0.02Pb(SCN)2I-based hole-conductor-free PSCs exhibited an 88% PCE retention even after continuous heating at 100 °C for 1020 h, indicating excellent thermal stability. This study suggests that the compositional engineering of non-iodine X-site pseudohalide anion substitution and A-site cation doping hold great promise for improving the stability of PSCs.

Potassium Doping to Enhance Green Photoemission of Light‐Emitting Diodes Based on CsPbBr3 Perovskite Nanocrystals

AbstractMetal halide perovskite nanocrystals (PeNCs) are emerging as one of the most promising materials for optoelectrical devices such as light‐emitting diode (LED) owing to their tunable band gaps, high color purity, and tolerance to defects. Nevertheless, the materials have not yet demonstrated their full potential in practical applications due to the poor stability of PeNCs and their unsatisfactory performance in devices. In this research, LED devices based on CsPbBr3 NCs are successfully demonstrated as an active light‐emitting layer with enhanced efficiency via potassium doping. The study of the effect of potassium dopant on physicochemical properties of inorganic CsPbBr3 PeNCs shows that potassium cations (K+) remain in the crystal structure of perovskite compound as interstitial defects, which results in better coverage of surface ligands on the PeNCs and improved energy band alignment with adjacent electron injection layer (2,2′,2′‐(1,3,5‐benzinetriyl)‐tris(1‐phenyl‐1‐H‐benzimidazole)) and hole injection layer (poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate) in an LED. As a consequence, the green LED with the K‐doped CsPbBr3 PeNCs shows luminance up to 5759 cd m‐2 and external quantum efficiency (EQE) of 5.6%, which is superior to the pristine device without K‐doping (luminance: 4579 cd m‐2, EQE: 4.8%).

Local structure of potassium doped nickel oxide: A combined experimental-theoretical study

The electronic structure of Mott and charge-transfer insulators can be tuned through charge doping to achieve a variety of fascinating physical properties, e.g., superconductivity, colossal magnetoresistance, and metal-to-insulator transitions. Strong correlations between $d$ electrons give rise to these properties but they are also the reason why they are inherently difficult to model. This holds true especially for the evolution of properties upon charge doping. Here, we hole-dope nickel oxide with potassium and elucidate the resulting structure by using a range of experimental and theoretical tools; potassium is twice as big as nickel and is expected to lead to distortions in its vicinity. Our measurements of the x-ray absorption fine structure (XAFS) show a significant distortion around the dopant and that the dopant is fully incorporated in the nickel oxide matrix. In parallel, the theoretical investigations include developing a Gaussian process for quantum Monte Carlo calculations to determine the lowest energy local structure around the potassium dopant. While the optimal structures determined from density functional theory and quantum Monte Carlo calculations agree very well, we find a large discrepancy between the experimentally determined structures and the theoretical doped structures. Further modeling indicates that the discrepancy is likely due to vacancy defects. Our work shows that potassium doping is a possible avenue to doping NiO, in spite of the size of the potassium dopant. In addition, the Gaussian process opens up a new route towards obtaining structure predictions outside of density functional theory.

Preparation of potassium intercalated carbons by in-situ activation and speciation for CO2 capture from flue gas

Nitrogen and/or sulfur doped carbons were extensively investigated as CO2 adsorbents, however their performance in CO2 capture from combustion flue gas, which is the largest stationary emission source, was less promising. Herein, potassium was used as a dopant for carbon, and a new series of materials, namely potassium intercalated carbons (PICs), were prepared sequentially by oxidation of mesoporous carbon, potassium ion exchange, and calcination. Based on results from FT-IR, XPS, TG-MS, etc., it was found the pre-loaded potassium interacted with the carbon matrix during calcination, enabled great flexibility in: (1) porosity adjustment by “in-situ activation”, and (2) surface chemistry manipulation by potassium intercalation. Taking together, the optimized sample (PIC-700) showed fast and stable CO2 uptake of 5.23 wt.% in flue gas conditions (40 °C, 1 bar, 15%CO2), which is among the highest for carbon-based adsorbents. Such promising performance is directly related to the enhanced CO2 affinity due to the presence of potassium dopants. Dynamic separation of CO2 from 15%CO2/85%N2 showed similar adsorption capacity, and no performance decay could be observed during temperature swing cycles, demonstrating the great potential for the PICs for practical CO2 capture applications.

Development of K-doped ZnO nanoparticles encapsulated crosslinked chitosan based new membranes to stimulate angiogenesis in tissue engineered skin grafts

Nanoparticles are well recognized for their biological applications including tissue-regeneration due to large surface area and chemical properties. In this study, K-doped zinc oxide (ZnO) nanoparticles containing porous hydrogels were synthesized via freeze gelation. The morphology and pore dimensions were studied by scanning electron microscopy (SEM). The chemical structural analysis of the synthesized hydrogels was investigated by Fourier Transform Infrared (FTIR) spectroscopy. In swelling studies, material containing ZnO nanoparticles with 2% potassium dopant concentration CLH-K2.0) showed greater degree of swelling as compared to all other materials. The degradation studied was tested in three different degradation media, i.e. phosphate buffer saline (PBS), lysozyme and hydrogen peroxide and relatively higher degradation was seen in hydrogen peroxide. The synthesized hydrogels were implanted on the chick chorioallantoic membrane (CAM) to investigate their angiogenic potential. The CLH-K2.0 hydrogel stimulated angiogenesis greater than all other materials; blood vessels were attached and grown inside this scaffold, showing its strong angiogenic potential.

The multiple effects of potassium doping on LiVPO4F/C composite cathode material for lithium ion batteries

The intermediate product VPO4/C is synthesized via sol-gel method, then it is mixed with other raw materials and calcined to prepare Li1-xKxVPO4F/C (x = 0, 0.005, 0.01, 0.02). Potassium with large ionic radius partially substitutes the lithium site and slightly increases the unit cell volume. The potassium dopant suppresses the formation of Li3V2(PO4)3 and reduces the particle agglomeration. The doped samples possess lower polarization and higher discharge plateau than the pristine LiVPO4F/C, and Li0.99K0.01VPO4F/C exhibits the best electrochemical performance. With 2.9 wt% amorphous carbon uniformly wrapping the surface, Li0.99K0.01VPO4F/C delivers a reversible capacity of 140.9 mA h g-1 at 0.12 C and maintains 98.3 mA h g-1 at the charge/discharge rate of 10 C. Its specific discharge capacity with a retention of 96.13% decreases from 131.9 to 126.8 mA h g-1 after 125 cycles at the charge/discharge rate of 1 C. The improvement of rate and cycling performance is ascribed to the decrease of charge transfer resistance (88.47 Ω) and the increase of Li+ diffusion coefficient (6.75 × 10−13 cm2 s−1), indicating that potassium doping facilitates the migration and diffusion of Li+ due to the expansion of Li+ pathway.

Effect of B, N, Ge, Sn, K doping on electronic-transport properties of (5, 0) zigzag carbon nanotube

In this paper the effect of impurity on the electronic properties and quantum conductance of zigzag (5, 0) carbon nanotube have been studied by using the Density Functional Theory (DFT) combined with Non-Equilibrium Green’s Function (NEGF) formalism with TranSIESTA software. The effect of Boron (B), Nitrogen (N), Germanium (Ge), Tin (Sn) and Potassium (K) impurities on the CNT conduction behavior and physical characteristics, like density of states (DOS), band structure, transmission coefficients and quantum conductance was considered and discussed simultaneously. The current−voltage (I−V) curves of all the proposed models were studied for comparative study under low-bias conditions. The distinct changes in conductance reported as the positions, number and type of dopants was varied in central region of the CNT between two electrodes at different bias voltages. This suggested conductance enhancement mechanism for the charge transport in the doped CNT at different positions is important for the design of CNT based nanoelectronic devices. The results show that Germanium, Tin and Potassium dopant atoms has increased the conductance of the model manifold than other doping atoms furthermore 10 Boron and 10 Nitrogen dopant atoms showed the amazing property of Negative Differential Resistance (NDR).

Effects of potassium interstitial doping on thermoelectric properties of Sr0.7Ba0.3Nb2O6−δ ceramics

The thermoelectric properties of potassium interstitial doped Sr0.7Ba0.3KxNb2O6−δ ceramics were investigated in the temperature range from 323 to 1073 K. The thermoelectric power factor is improved enormously due to the potassium interstitial doping combined with a reductive calcination method. The potassium dopants not only act as carrier donors but also modulate the electronic structures. Thus, the electrical conductivity increases remarkably, and the Seebeck coefficient, meanwhile, maintains considerable values at high temperatures. Only the moderate doping content x = 0.10 contributes to reducing the lattice thermal conductivity. Thus, the sample Sr0.7Ba0.3K0.1Nb2O6−δ shows the highest ZT value of 0.23 at 1073 K.

Electronic properties of doped and defective NiO: A quantum Monte Carlo study

NiO is a canonical Mott (or charge-transfer) insulator and, as such, is notoriously difficult to describe using density functional theory (DFT)--based electronic structure methods. Doped Mott insulators such as NiO are of interest for various applications but rigorous theoretical descriptions are lacking. Here, we use quantum Monte Carlo methods, which very accurately include electron-electron interactions, to examine energetics, charge structures, and spin structures of NiO with various point defects, such as vacancies and substitutional doping with potassium. The formation energy of a potassium dopant is significantly lower than that of a Ni vacancy, making potassium an attractive monovalent dopant for NiO. We compare our results with DFT results that include an on-site Hubbard $U$ ($\mathrm{DFT}\phantom{\rule{0.28em}{0ex}}+\phantom{\rule{0.28em}{0ex}}U$) to account for correlations and find relatively large discrepancies for defect formation energies as well as for charge and spin redistributions in the presence of point defects. Beyond fitting to a single property, it is unlikely that single-parameter tuning of the $\mathrm{DFT}\phantom{\rule{0.28em}{0ex}}+\phantom{\rule{0.28em}{0ex}}U$ will be able to obtain accurate accounts of complex properties in these materials. Responses that depend in subtle and complex ways on ground-state properties, such as charge and spin densities, are likely to contain quantitative and qualitative errors.

Tuning the Emission Energy of Chemically Doped Graphene Quantum Dots.

Tuning the emission energy of graphene quantum dots (GQDs) and understanding the reason of tunability is essential for the GOD function in optoelectronic devices. Besides material-based challenges, the way to realize chemical doping and band gap tuning also pose a serious challenge. In this study, we tuned the emission energy of GQDs by substitutional doping using chlorine, nitrogen, boron, sodium, and potassium dopants in solution form. Photoluminescence data obtained from (Cl- and N-doped) GQDs and (B-, Na-, and K-doped) GQDs, respectively exhibited red- and blue-shift with respect to the photoluminescence of the undoped GQDs. X-ray photoemission spectroscopy (XPS) revealed that oxygen functional groups were attached to GQDs. We qualitatively correlate red-shift of the photoluminescence with the oxygen functional groups using literature references which demonstrates that more oxygen containing groups leads to the formation of more defect states and is the reason of observed red-shift of luminescence in GQDs. Further on, time resolved photoluminescence measurements of Cl- and N-GQDs demonstrated that Cl substitution in GQDs has effective role in radiative transition whereas in N-GQDs leads to photoluminescence (PL) quenching with non-radiative transition to ground state. Presumably oxidation or reduction processes cause a change of effective size and the bandgap.

Single-Walled Carbon Nanotube Thermopile For Broadband Light Detection

We designed a thermopile based on a PN doping profile engineered in a suspended film of single-walled carbon nanotubes (SWNTs). Using estimates of the film local Seebeck coefficients, the SWNT thermopile was optimized in situ through depositions of potassium dopants. The overall performances of the thermopile were found to be comparable to state-of-the-art SWNT bolometers. The device is characterized at room temperature by a time response of 36 ms, typical of thermal detectors, and an optimum spectral detectivity of 2 × 10(6) cm Hz(1/2)/W in the visible and near-infrared. This paper presents the first thermopile made of a suspended SWNT film and paves the way to new applications such as broadband light (including THz) detection and thermoelectric power generation.

Thermal, UV and FTIR spectral studies in alkali metal cinnamates

A single crystal of sodium and potassium cinnamates was grown by slow evaporation of methanol solution at room temperature. The effect of metals sodium and potassium on the electronic structure of cinnamic acid was studied. In this research many analytical methods such as FTIR, UV, second harmonic generation (SHG) and TG–DTA were used: The spectroscopic studies lead to conclusions containing the distribution of the electronic charge in molecule, the delocalisation of π electrons and the reactivity of metal complexes. The SHG efficiency is more pronounced in the presence of sodium and potassium dopant in the growth medium. Incorporation of sodium and potassium increase the thermal stability ensuring the suitability of material for possible non-linear optical (NLO) application up to 180 °C.

Zintl phase as dopant source in the flux synthesis of Ba1−xKxFe2As2 type superconductors

Use of the Zintl phase KSn as a source of potassium dopant in tin flux syntheses of Ba(1-x)K(x)Fe(2)As(2) allows for incorporation of large amounts of potassium with much less attack on reaction vessels compared to the use of elemental potassium as a reactant; it also enables further study of tin incorporation into the products.

Effect of La and K on the microstructure and dielectric properties of Bi0.5Na0.5TiO3-PbTiO3

Small amounts of lanthanum and potassium dopants could modify the microstructure and dielectric properties of 0.90Bi0.5Na0.5TiO3-0.10PbTiO3 and 0.88Bi0.5Na0.5TiO3-0.12PbTiO3 solid solutions. La lowered both phase transition temperatures of ferroelectric to antiferroelectric and antiferroelectric to paraelectric. It also decreased the maximum value of relative dielectric permittivity of the composition. In contrast, K shifted the first phase transition to the lower temperature but insignificantly affected the Curie temperature and raised the maximum dielectric permittivity. Furthermore, K influenced the microstructure in the way to enhance the long grains of this solid solution but La inhibited this effect.

Electrical conductivity of BaRuO 3 ceramics

BaRuO 3 and Ba 1−xK xRuO 3 ceramics contain a mixture of 4H and 9R polytypes whose volume fraction depends on quenching temperature and the concentration of potassium dopant. Both polytypes have a room temperature resistivity of ∼10mOmegacm, but with opposite signs for the temperature coefficient. The negative temperature coefficient for the 9R polytype is ascribed to localisation effects arising from the existence of two distinct crystallographic Ru sites.