Potassium-doped Carbon Research Articles

Development of active hydrogel absorbent pads based on sodium alginate/potassium-doped carbon dots for chilled pork preservation

In this study, potassium-doped carbon dots (K-CDs) were added to sodium alginate (NaAlg) hydrogel to yield high-strength, antibacterial, antioxidant NaAlg hydrogel absorbent pads (NaAlg/K-CDs) to absorb chilled pork exudate during storage. The results revealed that the swelling rates of the NaAlg/K-CDs peaked at 3286.83%, a figure exceeding that of the commercial absorbent pads. Based on the bacterial diversity and richness results, Pseudomonas aeruginosa (P. aeruginosa) was evidently the dominant spoilage organism during chilled pork storage. On storage day 6, the P. aeruginosa population in the NaAlg/K-CDs hydrogel absorbent pad group was 82% of that in the control group. The total volatile basic nitrogen (TVB-N) value of the NaAlg/K-CDs group remained lower than 0.15 mg/g on day 8. The pH, TVB-N, total viable count (TVC), cooking loss, and volatile odour values of the chilled pork in the NaAlg/K-CDs hydrogel absorbent pad group were significantly lower than those in other absorbent pad groups. Moreover, the colour change and shear force values of the chilled pork in the NaAlg/K-CDs hydrogel absorbent pad group were lower than those in the control and wood fiber paper absorbent pad groups. These results indicate that the shelf life of the NaAlg/K-CDs-packaged chilled pork was extended by 2 days compared with that of the control. Therefore, the NaAlg/K-CDs hydrogel absorbent pads potentially inhibited microbial growth and improved the storage quality of chilled pork. This study provides an alternative solution against traditional chilled pork absorbent pads, further promoting the advancement of fresh meat preservation techniques.

Construction of carbonized polymer dots/potassium doped carbon nitride nanosheets Van der Waals heterojunction by ball milling method for facilitating photocatalytic CO2 reduction performance in pure water

When the advancement of conventional heterojunctions is restricted by lattice matching of materials, Van der Waals heterojunctions formed by interlayer Van der Waals force present enormous development prospects with the revolution of graphene and graphene-like materials. Ascribed to similar graphene-like structures, carbonized polymer dots (CPDs) and potassium-doped carbon nitride nanosheets (KCNNS) were stacked by the ball milling method to form a novel Van der Waals heterojunction. Experimental analysis and density functional theory (DFT) calculations demonstrate that the constructed CPDs/KCNNS heterojunctions can effectively suppress sluggish reaction dynamics. CPDs/KCNNS-2 composites demonstrate enhanced CO2 photoreduction performance (78.98 μmol g−1∙h−1) with 100% CO selectivity in pure water, which is 13.71 times higher than that of KCNNS. In-situ FT-IR spectra were employed to identify the intermediates formed in the CO evolution process of CPDs/KCNNS composites. The manuscript provides a scientific reference for the stacking of Van der Waals heterojunction based on C3N4 in the artificial photosynthesis field.

Potassium-doped carbon nitride: Highly efficient photoredox catalyst for selective oxygen reduction and arylboronic acid hydroxylation

Photocatalytic two-electron oxygen reduction reaction for hydrogen peroxide production, a promising liquid energy carrier and an environmentally friendly oxidant, is regard as a promising process owing to its low-cost and environment-friendly advantages compared to the state-of-art anthraquinone oxidation for H2O2 production. Herein, a potassium-doped carbon nitride photocatalyst has been successfully synthesized by the copolymerization of self-assembly supramolecular cyanuric acid and melamine aggregates with introduction of potassium chloride (KCMCN), wherein its band structure was carefully tuned and a new channel for charge transfer was created. Notably, DFT calculations pointed out that a lower absorption energy of oxygen (Eads = 0.27 eV) over KCMCN was estimated than that of MCN (Eads = 1.02 eV) with the introduction of K into carbon nitride framework, which is beneficial for superior H2O2 evolution. The H2O2 yield of KCMCN (317.9 µmol·L−1·h−1) was about 10.7 times higher than bulk carbon nitride at low concentration of sacrificial agent (0.5% isopropanol aqueous solution) and the apparent quantum efficiency (AQE) of KCMCN reached to 7.5% at 420 nm. Furthermore, in-situ photoinduced superoxide radical anion (·O2−) species were generated from dioxygen in KCMCN, which were reacted with arylboronic acids to produce corresponding aryl alcohols through a hydroxylation process under visible light irradiation. This work opens up prospects for providing guidance for other organic synthesis based on the oxidative effect of H2O2 and exploring novel heterogeneous photocatalysts in the field of value-added products formation.

Potassium-doped carbon nitride supported on SBA-15 for enhanced catalytic Knoevenagel condensation under mild conditions

Knoevenagel condensation reaction is an important reaction for the manufacture of α,β-unsaturated carbonyl compounds. Traditional base catalysts suffer from the disadvantage in catalystproduct separation. Herein, potassium-doped carbon nitride materials supported on SBA-15 (CN/SBA15-KCl) have been prepared through a one-pot calcination method. The characterization results of N2 adsorption–desorption, small-angle XRD, TEM, and SEM revealed that the ordered mesostructures of SBA-15 had been preserved after the loading of carbon nitride and KCl, and nitrogen and potassium species were dispersed on the surface of SBA-15 support. As solid bases, the CN/SBA15-KCl materials demonstrated high and steady catalytic performances in Knoevenagel condensation. Under 50 °C of reaction temperature, the optimized conversion of benzaldehyde was up to 74% at 4 h of reaction time, much higher than other carbon-nitride-based materials. The incorporation of potassium has been proved to enhance the basic strength of CN/SBA15, and therefore improved the catalytic activity.

Potassium-Doped Carbon Nitride: Highly Efficient Photoredox Catalyst for Selective Oxygen Reduction and Arylboronic Acid Hydroxylation

Potassium-Doped Carbon Nitride: Highly Efficient Photoredox Catalyst for Selective Oxygen Reduction and Arylboronic Acid Hydroxylation

Efficient degradation of antibiotics in different water matrices through the photocatalysis of inverse opal K-g-C3N4: Insights into mechanism and assessment of antibacterial activity

The efficient degradation of fluoroquinolone antibiotics and the reduction of their antimicrobial activity were achieved in different water matrices through the photocatalysis of inverse opal potassium-doped carbon nitride (IO K-CN). The IO K-CN photocatalyst with optimum doping ratio of potassium performed much better than bulk carbon nitride and pure inverse opal carbon nitride for removing fluoroquinolone antibiotics, such as levofloxacin (LVX) and norfloxacin (NOR). The remarkably narrowed band gap resulting from potassium doping and the unique properties of the inverse opal construction jointly contributed to enhancing the activity of the photocatalyst. A possible mechanism and degradation pathway for LVX was proposed on the basis of a series of characterizations including electron spin resonance (ESR) experiments, and liquid chromatography-mass spectrometry (LC-MS) analysis. Meanwhile, the byproducts during the LVX photocatalytic degradation were shown to have much lower sterilization effect, implying that the toxicity and the potential risk of LVX were excellently reduced. The potential application for the treatment of antibiotic-containing wastewater was indicated by the excellent treatment efficiency and favorable durability of this photocatalyst.

Expanding Interlayer Spacing of Hard Carbon by Natural K+ Doping to Boost Na-Ion Storage.

Heteroatom-doped carbon is an attractive material for anodes in lithium-/sodium-ion batteries as a replacement for traditional graphite anodes. However, the complex fabrication process and high cost limit practical applications of these carbon materials. Here, we report a low-cost, natural potassium-doped carbon material, which is directly carbonized from the coconut endocarp-a kind of high potassium-containing biomass material. The obtained carbon structure features an expanded d(002)-spacing (0.4 nm) originating from the superhigh potassium content (6654 mg kg-1). Because of the improvement on charge transfer kinetics and electrical properties, the potassium-doped carbon anode exhibits promising electrochemical performance in sodium-ion batteries, including high initial reversible capacity (314 mAh g-1) and good cycle stability (289 mAh g-1 after 200 cycles). Additionally, this work opens up a new approach for the design of heteroatom-doped carbon materials from the viewpoint of being naturally environmental friendly.

Structures and properties of the potassium-doped carbon clusters KCn/KCn +/KCn −(n = 1−10)

A systematic density functional theory study of the potassium-doped small carbon clusters KC n /KC + /KC − (n = 1−10) has been carried out using B3LYP method with 6–311+G* basis set. Several properties including equilibrium geometries, electronic states, relative energies, ionization potentials and electron affinities have been investigated for linear and cyclic isomers. The stability of different structures and states has been discussed according to the relative energy for the same size, and the incremental binding energy for different size. For neutral KC n and cationic KC + clusters, their lowest-lying states mainly have linear structure, while for anionic KC − , they all have fan-like lowest-energy structure, except KC−, KC 3 − , and KC 10 − . The KC n /KC + /KC − clusters have been compared with iso-valent systems LiC n /LiC + /LiC − , NaC n /NaC + /NaC − , and CsC − , and the differences are discussed.

Potassium-doped carbon nanotubes toward the direct electrochemistry of cholesterol oxidase and its application in highly sensitive cholesterol biosensor

We demonstrate herein a newly developed serum total cholesterol biosensor by using the direct electron transfer of cholesterol oxidase (ChOx), which is based on the immobilization of cholesterol oxidase and cholesterol esterase (ChEt) on potassium-doped multi-walled carbon nanotubes (KMWNTs) modified electrodes. The KMWNTs accelerate the electron transfer from electrode surface to the immobilized ChOx, achieving the direct electrochemistry of ChOx and maintaining its bioactivity. As a new platform in cholesterol analysis, the resulting electrode (ChOx/KMWNTs/GCE) exhibits a sensitive response to free cholesterol, with a linear range of 0.050–16.0 μmol L −1 and a detection limit of 5.0 nmol L −1 (S/N = 3). Coimmobilization of ChEt and ChOx (ChEt/ChOx/KMWNTs/GCE) allows the determination of both free cholesterol and esterified cholesterol. The resulting biosensor shows the same linear range of 0.050–16.0 μmol L −1 for free cholesterol and cholesteryl oleate, with the detection limit of 10.0 and 12.0 nmol L −1 (S/N = 3), respectively. The concentrations of total (free and esterified) cholesterol in human serum samples, determined by using the techniques developed in the present study, are in good agreement with those determined by the well-established techniques using the spectrophotometry.

In vitro detection of superoxide anions released from cancer cells based on potassium-doped carbon nanotubes–ionic liquid composite gels

A newly developed electrochemical biosensor for the determination of superoxide anions (O(2)˙(-)) released from cancer cells using potassium-doped multi-walled carbon nanotubes (KMWNTs)-1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF(6)) ionic liquid composite gels is demonstrated. The KMWNTs-[BMIM]PF(6) can electrocatalyze oxygen reduction to generate a strong current signal in neutral solution. Compared with KMWNTs without [BMIM]PF(6) or MWNTs-[BMIM]PF(6) composites, the KMWNTs-[BMIM]PF(6) can enhance the oxygen reduction peak current by 6.2-fold and 2.8-fold, which greatly increases the detection sensitivity of oxygen. Then, O(2)˙(-) biosensors are fabricated by mixing superoxide dismutase (SOD) in the KMWNTs-[BMIM]PF(6) gels via monitoring oxygen produced by an enzymic reaction between SOD/O(2)˙(-) without the help of electron mediators. The resulting biosensors show a linear range from 0.04 to 38 μM with a high sensitivity of 98.2 μA mM(-1), and a lower detection limit of 0.024 μM. The common interferents such as hydrogen peroxide (H(2)O(2)), ascorbic acid (AA), uric acid (UA), and metabolites of neurotransmitters, do not interfere with the detection of O(2)˙(-). The proposed biosensor is tested to determine O(2)˙(-) in vitro and from liver cancer and leukemia cells and shows good application potential in biological electrochemistry.

Electron Emission Originated from Free-Electron-like States of Alkali-Doped Boron−Nitride Nanotubes

We investigate the electronic structures and electron emission properties of alkali-doped boron-nitride nanotubes (BNNTs) using density-functional theory calculations. We find that the nearly free-electron (NFE) state of the BNNT couples with the alkali atom states, giving rise to metallic states near the Fermi level. Unlike the cases of potassium-doped carbon nanotubes, not only the s but the d orbital state substantially takes part in the hybridization, and the resulting metallic states preserve the free-electron-like energy dispersion. Through first-principles electron dynamic simulations under applied fields, it is shown that the alkali-doped BNNT can generate an emission current 2 orders of magnitude larger than the carbon nanotube. The nodeless wave function at the Fermi level, together with the lowered work function, constitutes the major advantage of the alkali-doped BNNT in electron emission. We propose that the alkali-doped BNNT should be an excellent electron emitter in terms of the large emission current as well as its chemical and mechanical stability.

Hydrogen in potassium-doped carbon nanotubes studied by positron annihilation

The positron lifetime for potassium-doped carbon nanotubes (K-NTs) ascribed to positrons in trapping centers is shortened upon exposure of the K-NTs to hydrogen. Thermal desorption of hydrogen from hydrogenated K-NTs shows a peak around 510 K, where a hydrogenated potassium-graphite intercalation compound (K-GIC) shows a peak. The absorbed hydrogen is bonded with K-NTs in the same manner as found in hydrogenated K-GIC, and their positron-trapping centers are located in a more negatively charged region, such as a two-dimensional structure of hydride ions.

Electronic structure of potassium-doped carbon nanotubes

The electronic structure of potassium-doped (12,0) carbon nanotube bundle is studied by using density-functional theory. The material contains one potassium atom inside the unit cell, and the stoichiometry is KC 48. It is found that the effect of doping is not simple charge-transfer. The nearly free electron state couples with the potassium 4s state, and the hybridized state is pulled down to the Fermi level. The state is distributed inside the tube rather than near the carbon wall. The doped system is thus a multi-carrier conductor in which carriers transfer inside the tube as well as on the tube wall.

Electronic structure of potassium-doped carbon nanotubes

We present a density functional study of zigzag carbon nanotubes containing potassium atoms inside. We find that the effect of potassium doping is not simple charge transfer. The nearly free electron state of nanotube couples with the $\mathrm{K} 4s$ orbital. The state comes downward as the tube is thicker and crosses the Fermi level when the diameter is as large as $0.8--1\mathrm{nm}$. It is distributed near the center of the tube and extends to the tube direction, which suggests high conductivity via this state.

High H 2 Uptake by Alkali-Doped Carbon Nanotubes Under Ambient Pressure and Moderate Temperatures

Lithium- or potassium-doped carbon nanotubes can absorb approximately 20 or approximately 14 weight percent of hydrogen at moderate (200 degrees to 400 degrees C) or room temperatures, respectively, under ambient pressure. These values are greater than those of metal hydride and cryoadsorption systems. The hydrogen stored in the lithium- or potassium-doped carbon nanotubes can be released at higher temperatures, and the sorption-desorption cycle can be repeated with little decrease in the sorption capacity. The high hydrogen-uptake capacity of these systems may be derived from the special open-edged, layered structure of the carbon nanotubes made from methane, as well as the catalytic effect of alkali metals.

Electronic Properties of Potassium-Doped Carbon Nanotube Lattice

ABSTRACTWe study the electronic structure of potassium-doped crystalline lattice of so-called (10.10) carbon nanotubes in the framework of the density-finctional theory. Tie stoichiometrv of the material studied is K2C80 which was originally proposed in designing the superconducting doped nanotube material based on tile size of dopants and the charge transfer being favorable for superconductivity. Electronic band dispersions obtained are actually found to be very similar to those of the pristine (10,10) nanotube lattice with the upward shift of the Fermi energy by 1 eV above the second conduction-band miinimum. Tie system therefore possesses higher Fermi-level density of states than the pristine material with rather sinmple charge transfer from K to C sites, and is confirned to be a good candidate for a naxiotube superconductor.

Kinetics of nitric oxide reduction with pure and potassium-doped carbon

The kinetics of the reduction of nitric oxide with pure and potassium-doped carbon, NO+C=1/2 N2+CO, were investigated. For the reaction of NO with pure carbon, measurements were made in the temperature range from 1750 K to 2130 K and at initial NO pressures between 5×10−3 Pa and 7×10−2 Pa. The reaction was first order with respect to nitric oxide at NO pressures below 3×10−2 Pa. The activation energy was 54 kJ/mol for temperatures below 2000 K, while at higher temperatures a second (parallel) reaction became noticeable with a definitely higher activation energy. Potassium-doped carbon was prepared by a molecular beam technique. AES studies verified that potassium was intercalated into the graphite surface and that the potassium-to-carbon ratio changed continuously with sample temperature. The reduction of NO with K-doped carbon was investigated in the temperature range from 710 K to 1080 K and at initial NO pressures between 7×10−5 Pa and 6×10−4 Pa while monitoring, in-situ using AES the K/C-ratio of the surface. The NO reduction rate rose linearly with K/C. Compared to pure carbon, the reaction rate for the NO reduction with K-doped carbon increased by a factor in the range of 104. The activation energy for the NO reduction with K-doped carbon was found to be 82 kJ/mol.

Adsorption and reduction of nitrogen monoxide by potassium-doped carbon

Neither the adsorption nor the reduction of nitrogen monoxide occurs at 360 °C on pure carbon, but significant reduction of NO, giving N2 and CO2, proceeds on potassium-doped carbons. The uptake of NO on carbon is increased markedly by doping potassium salts and the adsorbed NO undergoes decomposition and/or desorption giving N2O (25–250 °C), NO (250–400 °C) and CO2(400 °C) in vacuum. Isotope labelling experiments using 15NO and N218O suggest that the N2O is produced by the decomposition of (NO)2(a) and that the NO and CO2 are caused by the reaction of NO2(a) with carbon. O(a) and NO2(a) are the predominant species during the reaction of NO on K-doped carbon, and NO2(a) suppresses the reaction of NO with carbon.