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Nitrogen plasma treatment of ZnO and TiO2 nanowire arrays for polymer photovoltaic applications
摘要： This work reports on a simple, yet unique approach to improving the opto-electronic properties of vertically-aligned arrays of rutile TiO2 and Wurzite ZnO nanowires by means of controlled nitrogen doping during exposure to highly kinetic radio-frequency generated N2 plasma radicals. Morphologically, the plasma treatment causes a distortion of the vertical alignment of the nanowires due to a dissociation of the weak Van der Waals force clustering the nanowires. Optical spectroscopy show that plasma treatment increases the light transmission of TiO2 arrays from 48% to 90%, with the ZnO arrays exhibiting an increase from 70% to 90% in the visible to UV range. The as-synthesized TiO2 array has an indirect band gap of 3.13 eV, which reduces to 3.03 eV after N2 treatment, with the ZnO equivalent decreasing from 3.20 to 3.17 eV post plasma exposure. A study of the 3d transition metal near edge fine structure of both Ti and Zn show that the N2 plasma treatment of the nanowires results in nitrogen doping of both TiO2 and ZnO lattices; this is confirmed by scanning transmission electron microscopy coupled with energy dispersive spectroscopy x-ray maps collected of single nanowires, which show a clear distribution of nitrogen throughout the metal-oxide. Application of these structures in P3HT:PCBM polymer blends shows progressive improvement in the photoluminescence quenching of the photoactive layer when incorporating both undoped and nitrogen-doped nanowires.
关键词： Electron energy loss spectroscopy,RF plasma nitrogen doping,One-dimensional nanowire arrays,Hydrothermal synthesis
更新于2025-09-16 10:30:52
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On the origin of the enhancement of defect related visible emission in annealed ZnO micropods
摘要： We report an in-depth analysis of ZnO micropods emission. A strong correlation between defect and interband emissions is observed. ZnO micropods were grown using low-temperature chemical bath deposition (CBD). ZnO micropods exhibited perfectly-crystalline hexagonally-shaped facets with various numbers of branches. Raman studies showed that ZnO micropods contained trapped zinc hydroxide (OH) and imidogen (NH) defects that originate from the precursor solution used in the CBD technique. These defects were evacuated by thermal annealing, leading to the recrystallization in the volume of the micropods and the formation of structural defects at their surface, as attested by scanning electron microscopy and X-ray diffraction. More importantly, the thermal annealing was accompanied by a breakdown of the NH defects, which resulted in a nitrogen doping of the ZnO micropods. The structural changes as well as the nitrogen doping resulted in a drastic change in the photoluminescence (PL) spectrum of the ZnO micropods that exhibited a stronger free exciton UV emission as well as a stronger visible (white) emission. An in-depth low-temperature PL study of both UV and visible emission reveals a strong interplay between the structural-defect bound excitonic UV emission (Y-band) and the deep donor (visible) emission, which suggests a rather complex emission mechanism involving an efficient nonradiative energy transfer between the Y-band states and defect states leading to the enhanced visible emission of ZnO micropods after high temperature annealing.
关键词： nitrogen doping,chemical bath deposition,photoluminescence,ZnO micropods,thermal annealing,defect emission
更新于2025-09-16 10:30:52
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Tailoring of graphene quantum dots for toxic heavy metals detection
摘要： The sensitivity of graphene quantum dots towards toxic heavy metals (THMs; Cd, Hg, Pb) can be improved through doping with nitrogen at the vacant site defects. Using density functional theory, we investigate the adsorption of THMs on the graphene quantum dots (GQDs) and nitrogen-coordinated defective GQDs (GQD@1N, GQD@2N, GQD@3N and GQD@4N) surfaces. Thermochemistry calculations reveal that the adsorption of Pb atom on the surfaces is more favorable than Cd and Hg adsorption. The decoration of the vacant defects with nitrogen on the GQD surface substantially increases the charge transfer and adsorption energy values of THMs on the GQD surface (GQD@4N > GQD@3N > GQD@1N > GQD@2N > GQD). The charge transfer and adsorption energy of lead on each of these surfaces are greater than those of cadmium and mercury (Pb > Cd > Hg). Quantum theory of atoms in molecules analysis and non-covalent interaction plots further validate this result while also confirming that Pb atom has a partially covalent and electrostatic nature of interaction at the nitrogen-coordinated vacant site defects. The electron density values—a criterion of bond strength—for the THM...N interactions are greater than for the THM…C interactions, confirming the observed adsorption energy trends of the THMs on the surfaces. The lowering of the HOMO–LUMO energy gap of the surfaces follows the order Pb > Cd > Hg and also results in increased electrical conductivity, which are consistent with the calculated adsorption energy trends. Significant changes in the energy gap and electric conductivity of the surfaces upon THMs adsorption make them promising sensors for metal detection. Finally, time-dependent density functional theory calculations showed that changes such as peak shifts, peak quenching and appearance of new peaks are seen in the UV–visible absorption spectra of the surfaces upon adsorption of THMs, wherein the shifts in peaks correspond to the magnitude of adsorption energy of THMs on the surfaces. These results should motivate the experimentalists towards using rational and systematic modulation of surfaces as sensors for heavy metal detection.
关键词： Adsorption energy,Toxic heavy metals,Charge transfer,UV–visible absorption spectra,Nitrogen doping,Density functional theory,HOMO–LUMO energy gap,Graphene quantum dots
更新于2025-09-16 10:30:52
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Electrochemical sensing of mercury ions in electrolyte solutions by nitrogen-doped graphene quantum dot electrodes at ultralow concentrations
摘要： Electrochemical detection of mercury ions in aqueous solution was investigated at indium tin oxide (ITO) conducting glass electrode modified by nitrogen-doped graphene quantum dots (N-doped GQDs). The N-doped GQDs with an average particle size of 4.5 nm were synthesized through an infrared-assisted pyrolysis of citric acid and urea at 250°C. The GQD sample contains high oxidation and amidation level, i.e., O/C and N/C atomic ratios: 37.6% and 30.7%, respectively. The electrochemical sensing toward Hg2+ ions was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Based on the CV and EIS analyses, both the reductive and oxidative peak currents as well as the equivalent series resistance demonstrate a decreasing trend with increased Hg2+ concentration. The detection limit of N-doped GQD/ITO electrodes toward Hg2+ ions reached 10 ppb with the accumulation time of 32 s. The GQD/ITO electrodes also exhibit superior selectivity toward the target contaminant (i.e. Hg2+ ion). Accordingly, the functionalized GQDs pave the way for engineering the electrochemical sensors capable of detecting toxic Hg2+ ions with superb sensitivity and selectivity.
关键词： Nitrogen doping,Electrolyte solution,Infrared-assisted synthesis,Graphene quantum dots,Mercury ions
更新于2025-09-16 10:30:52
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Rapid and green synthesis of fluorescent carbon dots from starch for white light-emitting diodes
摘要： A simple and green synthesis of fluorescent carbon dots (CDs) was achieved by a microwave-assisted hydrothermal method using potato starch as the carbon source. CDs with a maximum quantum yield of 2.46% were prepared by hydrothermal treatment of a 1 mg/mL starch solution at 220 oC for 30 min. Nitrogen doped CDs (N-CDs) were obtained under the same conditions using starch and ethylenediamine as the carbon and nitrogen sources, respectively, and their quantum yield was twice that of the undoped CDs. Both the CDs and N-CDs exhibit excellent water solubility and good thermal stability, emit blue fluorescence under UV light, but the fluorescent intensity of the latter is obviously higher than that of the former. Two white light-emitting diodes using the CD/starch composite and N-CDs as the phosphors emit yellowish white light and white light, respectively with xy coordinates of (0.38, 0.45) and (0.33, 0.35) in the Chromaticity Diagram of the Commission Internationale de L'Eclairage, suggesting that they have great potential application in optoelectronic devices.
关键词： Fluorescent carbon dots,Nitrogen doping,Light-emitting diodes,Microwave-assisted hydrothermal,Starch
更新于2025-09-16 10:30:52
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Investigation of nitrogen and iron co-doped TiO2 films synthesized in N2/CH4 via pulsed laser deposition technique
摘要： Nitrogen and iron ions co-doped titania films have been synthesized by PLD technique in nitrogen/methane (N2/CH4) (5:1) media at 1 mbar. Most of the samples are XRD amorphous but a certain amount of crystalline rutile is detected by Raman measurements. The presence of rutile phase only and its low crystallinity degree can be caused by nitrogen doping of oxide matrix. The most intensive VIS absorption and the lowest band gap values are observed for 5% Fe2O3 or Fe3O4 titania films that are supported by the highest nitrogen amount on the surface. The strongest photocatalysts in process of dichromate reduction under either UV or VIS irradiation are shown to be the films obtained from 5% iron oxide in titania target and synthesized at 550 °C as a result of optimal content of Ti–N and Ti–O–Fe structural fragments as revealed by XPS. The presence of Fe3+ and Fe2+ surrounded by oxygen as well as Fe–N bonds is confirmed by XPS data.
关键词： Pulsed laser deposition,Magnetite,Photocatalysis,Hematite,Titania,Nitrogen doping
更新于2025-09-16 10:30:52
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Solvothermal synthesis of in situ nitrogen-doped Ti3C2 MXene fluorescent quantum dots for selective Cu2+ detection
摘要： Two-dimensional MXenes have attracted increasing attention from researchers in the optical, electrical and thermal fields due to their high electric conductivity, thermal conductivity and mechanical properties. MXene quantum dots (QDs) have been highly desired to achieve selective ion detection using highly fluorescent media. In this study, a facile route using amine-assisted solvothermal tailoring was developed to prepare in situ nitrogen-doped Ti3C2 MXene QDs. Pristine MXene was exfoliated to yield MXene with a few layers. Diethylenetriamine, few-layer MXene and N,N-dimethylformamide were blended to perform a solvothermal process, yielding in situ nitrogen-doped MXene QDs with an ~1 nm thickness and ~6.2 nm size. The formation of QDs was dynamically monitored. The reduction in the QD size depended on tailoring and in situ nitrogen doping. Fluorescence properties of those QDs were studied. Nitrogen-doped QDs exhibited different fluorescence-quenching responses to various metal cations. Selective Cu2+ detection using the nitrogen-doped QDs mainly depended on a static fluorescence-quenching mechanism. This study might provide opportunities for the large-scale fabrication of in situ element-doped MXene fluorescent QDs.
关键词： MXene,Quantum dot,Nitrogen doping,Fluorescence,Ion detection
更新于2025-09-12 10:27:22
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Simultaneous Photoreduction and Nitrogen Doping of Graphene Oxide for Supercapacitors by Direct Laser Writing
摘要： Graphene-based supercapacitors have attracted tremendous attention owing to their outstanding electrochemical performance. In terms of material, nitrogen(N)-doped graphene(NDG) displays enhanced specific capacitance and rate performance compared with bare graphene used as a supercapacitor electrode. However, it still remains a challenge to develop a facile and simple method of NDG in cost-effective manner. Here, we used a simple direct laser writing technique to accomplish the simultaneous photoreduction and N-doping of graphene oxide(GO) using urea as a N source. The N content of the resultant reduced N-doped graphene oxide(NGO) reached a maximum value of 6.37%. All reduced NGO(NRGO)-based supercapacitors exhibited a higher specific capacitance than those based on pure reduced GO(RGO). Interestingly, the electrochemical performance of NRGO-based supercapacitors varied with different contents of N species. Therefore, we can control the properties of the obtained NRGOs by adjusting the doping ratios, an important step in developing effective graphene-based energy storage devices.
关键词： Simultaneous photoreduction and nitrogen-doping,Direct laser writing,Graphene based supercapacitor
更新于2025-09-11 14:15:04
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Photocatalyst properties depend on the mix
摘要： Photocatalysts use light to power chemical reactions in a whole host of applications from fuel cells to water remediation. There are many ways to improve the performance of titania (TiO2) photocatalysts from using catalyst support materials, which increase photosensitization rates, and help break down organic pollutants, to doping or co-doping with other atoms to expand the absorption range. Since using metal atoms such as dopants is problematic for water treatment if they leach into the environment, non-metallic dopants like nitrogen (N) are considered safer. Researchers from the University of South Africa have used these two strategies in conjunction to produce N-doped TiO2 photocatalysts on a carbon nanotube (CNT) support and systematically compared the effects of using different synthesis routes. Edward N. Nxumalo and his team find that photocatalysts with distinctly different properties and performance are produced depending on whether a hydrothermal or solgel synthetic route is used.
关键词： Carbon nanotubes,Hydrothermal synthesis,Solgel synthesis,Nitrogen doping,Photocatalysts,TiO2
更新于2025-09-11 14:15:04
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Combined adsorption process and photocatalytic degradation of some commercial herbicides over N-doped TiO <sub/>2</sub> particles supported on recyclable magnetic hexagonal mesoporous silica
摘要： Magnetic hexagonal mesoporous silica (magnetic HMS) containing N-doped TiO2 was prepared by hydrothermal method and used for the removal of trifluralin, 2,4-dichlorophenoxyacetic acid, and glyphosate herbicides at the presence and absence of UV/visible lights. The prepared samples were found as efficient for the removal of the herbicides and easily recyclable after treatment by UV irradiation. A red shift effect by nitrogen doping was also observed in the prepared samples resulting photocatalytic activity at the presence of visible light. Kinetic studies indicated that the photodegradation followed as the first order and kUV ≈ 10kvis. The results also showed synergetic effects between the adsorption of herbicides on the surface of magnetic HMS and photoreactions over N-doped TiO2 species.
关键词： nitrogen doping,titanium oxide,herbicide,HMS,Photocatalyst
更新于2025-09-09 09:28:46