N-doped ZnO Nanoparticles Research Articles

Room Temperature NO2-Sensing Properties of N-Doped ZnO Nanoparticles Activated by UV-Vis Light.

Zinc oxide nanoparticles (ZnO NPs) with varying levels of nitrogen (N) doping were synthesized using a straightforward sol-gel approach. The morphology and microstructure of the N-doped ZnO NPs were examined through techniques such as SEM, XRD, photoluminescence, and Raman spectroscopy. The characterization revealed visible changes in the morphology and microstructure resulting from the incorporation of nitrogen into the ZnO lattice. These N-doped ZnO NPs were used in the fabrication of conductometric gas sensors designed to operate at room temperature (RT) for detecting low concentrations of NO2 in the air, under LED UV-Vis irradiation (λ = 400 nm). The influence of nitrogen doping on sensor performance was systematically studied. The findings indicate that N-doping effectively enhances ZnO-based sensors' ability to detect NO2 at RT, achieving a notable response (S = R/R0) of approximately 18 when exposed to 5 ppm of NO2. These improvements in gas-sensing capabilities are attributed to the reduction in particle size and the narrowing of the optical band gap.

Morphological evaluation and boosted photocatalytic activity of N-doped ZnO nanoparticles prepared via Co-precipitation method

Pristine and nitrogen (N) doped zinc oxide (ZnNxO1-x, x = 0, 0.005, 0.01, and 0.02) nanoparticles (NPs) were successfully synthesized using chemical co-precipitation approach. The formation of pure crystalline wurtzite ZnO phase without any second phase during N-doping was confirmed by X-ray diffraction (XRD) analysis of N-doped ZnO samples. X-ray photoelectron spectroscopic (XPS) analysis ensured the effective inclusion of nitrogen into ZnO matrix. The morphological analysis revealed the formation of nanorods as a result of N-doping. The optical band gap calculated from UV–vis spectroscopy was observed to decrease up to 1 mol.% N doping followed by a subtle increase. Photoluminescence (PL) spectra revealed that electron-hole recombination was the least for 1 mol.% N doped ZnO NPs. ZnN0.01O0.99 NPs showed superior photocatalytic activity among all samples due to rod-shaped NPs and reduced electron-hole recombination, which was accessed by the photodegradation of Rhodamine B (RhB).

Electrochemical Sensors based on Fe@Fe2O3 nanowires, N-Doped ZnO and Au nanoparticles for quercetin determination

Electrochemical Sensors based on Fe@Fe2O3 nanowires, N-Doped ZnO and Au nanoparticles for quercetin determination

Synthesis of N-doped ZnO nanoparticles with cabbage morphology as a catalyst for the efficient photocatalytic degradation of methylene blue under UV and visible light.

In this study, the synthesis of nitrogen-doped zinc oxide nanoparticles with a cabbage like morphology (N-ZnONCBs) by a hydrothermal method using zinc acetate dihydrate as a precursor and hydrazine monohydrate as a nitrogen source is reported. N-ZnONCB were characterized using UV-visible Spectroscopy (UV-Vis), Fluorescence Spectroscopy, Fourier Transmittance Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Raman Spectroscopy, Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Dispersive Spectroscopy (EDS) and EDX elemental mapping. N-ZnONCBs were tested for their photocatalytic capabilities in the degradation of methylene blue (MB) under UV-light and visible light irradiation for about 0 to 80 minutes and 0 to 50 min respectively. The N-ZnONCB catalyst demonstrated improved photodegradation efficiency (98.6% and 96.2%) and kinetic degradation rates of MB (k = −0.0579 min−1 and k = −0.0585 min−1) under UV light and visible light irradiation at different time intervals. The photodegradation study was also evaluated with different dosages of N-ZnONCB catalyst, different initial concentrations of MB and variation in the pH (3, 5, 9 and 11) of the solution of MB under UV light and visible light irradiation. The photocatalytic degradation intermediate products were obtained by liquid chromatography mass spectra (LC-MS) and also complete mineralization was determined by using Total Organic Carbon (TOC) studies. This photocatalyst was also tested with 2,4-dichlorophenol (2,4-DCP) under visible light irradiation at different time intervals. Fluorescence and quenching studies were performed for the binding interaction between the N-ZnONCB catalyst and MB dye. A Zetasizer was used to find the charge and average size of the N-ZnONCB catalyst and also the charge of the N-ZnONCB catalyst before and after MB dye solution adsorption. The N-ZnONCB catalyst was also tested for its photostability and reusability with a percentage degradation rate of MB (93.2%) after 4 cycle experiments. These results have clearly demonstrated that the N-ZnONCB catalyst can be applied for the photocatalytic degradation of MB from wastewater samples.

A highly sensitive chemical gas detecting device based on N-doped ZnO as a modified nanostructure media: A DFT+NBO analysis

We presented a density functional theory study of the adsorption of O3 and NO2 molecules on ZnO nanoparticles. Various adsorption geometries of O3 and NO2 over the nanoparticles were considered. For both O3 and NO2 adsorption systems, it was found that the adsorption on the N-doped nanoparticle is more favorable in energy than that on the pristine one. Therefore, the N-doped ZnO has a better efficiency to be utilized as O3 and NO2 detection device. For all cases, the binding sites were located on the zinc atoms of the nanoparticle. The charge analysis based on natural bond orbital (NBO) analysis indicates that charge was transferred from the surface to the adsorbed molecule. The projected density of states of the interacting atoms represent the formation of chemical bonds at the interface region. Molecular orbitals of the adsorption systems indicate that the HOMOs were mainly localized on the adsorbed O3 and NO2 molecules, whereas the electronic densities in the LUMOs were dominant at the ZnO nanocrystal surface. By examining the distribution of spin densities, we found that the magnetization was mainly located over the adsorbed molecules. For NO2 adsorbate, we found that the symmetric and asymmetric stretches were shifted to a lower frequency. The bending stretch mode was shifted to the higher frequency. Our DFT results thus provide a theoretical basis for why the adsorption of O3 and NO2 molecules on the N-doped ZnO nanoparticles may increase, giving rise to design and development of innovative and highly efficient sensor devices for O3 and NO2 recognition.

Photoactivity of N-doped ZnO nanoparticles in oxidative and reductive reactions

Abstract N-doped ZnO is a prospective material for photocatalytic reactions. However, only oxidative paths are well investigated in the literature. This paper describes a comparative study about ZnO and ZnO:N potential for oxidative and reductive reactions, probed by rhodamine B dye photodegradation and CO2 photoreduction. The materials were prepared by the polymeric precursor method, using urea as a nitrogen source, and different heat treatments were used to observe their effects on surface decontamination, crystallinity, particle sizes and shapes, and photocatalytic performance. ZnO and ZnO:N presented a wurtzite crystalline structure and nanometric-scale particles. Samples submitted to higher temperatures showed lower specific surface areas, but higher crystallinity and lower contents of species adsorbed on their surfaces. On the other hand, the photocatalysts annealed in shorter times presented smaller crystallite sizes and lower crystallinity. These factors influenced the photoactivity in both conditions, i.e., oxidation and reduction reactions, under the ultraviolet and visible light, indicating that structural factors influenced the adequate charge separation and consequent photocatalytic activity since the as-synthesized samples were versatile photocatalysts in both redox reactions.

An innovative gas sensor system designed from a sensitive nanostructured ZnO for the selective detection of SOx molecules: a density functional theory study

The adsorption behaviors of SOx molecules on pristine and N-doped ZnO nanoparticles were investigated using density functional theory calculations (DFT).

Preparation of N-doped ZnO-loaded halloysite nanotubes catalysts with high solar-light photocatalytic activity.

N-doped ZnO nanoparticles were successfully assembled into hollow halloysite nanotubes (HNTs) by using the impregnation method. The catalysts based on N-doped ZnO-loaded HNTs nanocomposites (N-doped ZnO/HNTs) were characterized by X-ray diffraction (XRD), transmission electron microscopy-energy dispersive X-ray (TEM-EDX), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), UV-vis and Fourier transform infrared spectroscopy (FT-IR) techniques. The XRD pattern showed ZnO nanoparticles with hexagonal structure loaded on HNTs. The TEM-EDX analysis indicated ZnO particles with the crystal size of ca.10 nm scattered in hollow structure of HNTs, and furthermore the concentration of N atom in nanocomposites was up to 2.31%. The SEM-EDX verified most of N-ZnO nanoparticles existing in hollow nanotubes of HNTs. Besides containing an obvious ultraviolet absorbance band, the UV-vis spectra of the N-doped ZnO/HNTs catalysts showed an available visible absorbance band by comparing to HNTs and non-doped ZnO/HNTs. The photocatalytic activity of the N-doped ZnO/HNTs catalysts was evaluated by the degradation of methyl orange (MO) solution with the concentration of 20 mg/L under the simulated solar-light irradiation. The result showed that the N-doped ZnO/HNTs catalyst exhibited a desirable solar-light photocatalytic activity.

N-Doped ZnO Nanoparticle-Carbon Nanofiber Composites for Use as Low-Cost Counter Electrode in Dye-Sensitized Solar Cells

【Nitrogen-doped ZnO nanoparticle-carbon nanofiber composites were prepared using electrospinning. As the relative amounts of N-doped ZnO nanoparticles in the composites were controlled to levels of 3.4, 9.6, and 13.8 wt%, the morphological, structural, and chemical properties of the composites were characterized by means of field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In particular, the carbon nanofiber composites containing 13.8 wt% N-doped ZnO nanoparticles exhibited superior catalytic properties, making them suitable for use as counter electrodes in dye-sensitized solar cells (DSSCs). This result can be attributed to the enhanced surface roughness of the composites, which offers sites for $I_3{^-}$ ion reductions and the formation of Zn3N2 phases that facilitate electron transfer. Therefore, DSSCs fabricated with 13.8 wt% N-doped ZnO nanoparticle-carbon nanofiber composites showed high current density ( $16.3mA/cm^2$ ), high fill factor (57.8%), and excellent power-conversion efficiency (6.69%); at the same time, these DSSCs displayed power-conversion efficiency almost identical to that of DSSCs fabricated with a pure Pt counter electrode (6.57%).】

Influence of N-doping on photocatalytic activity of ZnO nanoparticles under visible light irradiation

N-doped ZnO nano-particles are synthesized by preparing pristine ZnO using sol–gel method and later nitrogenating it by passing nitrogen gas. XRD analysis of sample showed the formation of pure wurtzite phase of ZnO. Optical studies showed a red-shift in the absorbance spectrum after N doping. Raman analysis also supports the formation of defect states in ZnO. The photocatalytic activity of ZnO and N-doped ZnO is evaluated by evaluating rate of degradation of methylene blue and phenol at room temperature under visible light. The N-doped ZnO shows higher photocatalytic activity compared to pristine ZnO and Degussa P-25. The enhancement in the activity is attributed to nitrogen doping induced elevated absorption, high oxygen vacancies and small particle size of the ZnO nanoparticles.

Synthesis, characterization and photocatalytic activities of Ag-N-codoped ZnO nanoparticles for degradation of methyl red

Ag-N-codoped zinc oxide nanoparticles were synthesized by a one-step impregnation of Ag in N-doped ZnO nanoparticles. The morphologies and structures of the as-synthesized nanomaterials were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-Vis spectrophotometric techniques. Photocatalytic degradation of methyl red dye using synthesized photocatalysts was studied under solar as well as UV irradiations. Modified zinc oxide photocatalysts showed higher photocatalytic activity compared to pure zinc oxide both under solar as well as UV irradiations. Calcined zinc oxide shows better photocatalytic activity than commercial zinc oxide under both solar and UV irradiations. Highest catalytic activity of Ag-N co-doped zinc oxide (ANZ) among the undoped, Ag-doped and N-doped photocatalysts was attributed to the lower rate of recombination of the photogenerated electrons and holes as well as its lower band gap energy. Photocatalytic degradation of methyl red dye follows pseudo first order kinetics for all the nanoparticles so-obtained. KEY WORDS: Nanoparticles, Photocatalysis, Zinc oxide, Impregnation, Methyl red Bull. Chem. Soc. Ethiop. 2013, 27(2), 221-232DOI: http://dx.doi.org/10.4314/bcse.v27i2.7

A facile method for synthesis of N-doped ZnO mesoporous nanospheres and enhanced photocatalytic activity

A facile synthesis route is reported for preparation of N-doped mesoporous ZnO nanospheres by a solvothermal treatment of Zn(NO3)2·6H2O which provides a source of both zinc and nitrogen. A variety of different spectroscopic and analytical techniques, such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis and X-ray photoelectron (XPS) spectroscopies were used to characterize the physicochemical properties of catalysts. The photocatalytic activities of the composites were evaluated by the degree of degradation of rhodamine B in aqueous solutions at room temperature with near-UV light irradiation. These nanocomposites exhibit higher photocatalytic activity compared with pure ZnO nanoparticles. The enhancement of photocatalytic activity of N-doped ZnO nanoparticles is mainly attributed to their absorption of more photons and reduced electron-hole pair recombination. Our one-step, environmentally friendly synthetic method may provide a new means of designing and synthesizing series of N-doped metal oxide semiconductors for use in photo-assisted catalytic reactions.

Synthesis of N-doped ZnO nanoparticles with improved photocatalytical activity

Abstract ZnO nanoparticles with diameters of 20–50 nm were initially prepared by solvothermal route using ZnCl 2 and ethylene glycol as raw materials. With the as-prepared ZnO nanoparticles as precursor and melamine as N source, N-doped ZnO nanoparticles were then successfully obtained by a simple, efficient, and environmentally-friendly vacuum atmosphere method. Both the undoped and N-doped ZnO nanoparticles have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectrometry. The N-doped ZnO nanoparticles were found to exhibit obviously improved photocatalytic performance for the degradation of methyl orange under simulated daylight irradiation in comparison with the undoped ZnO nanoparticles. The extending light absorption towards the visible-light region and increased crystallinity of the N-doped ZnO nanoparticles contribute equally to the improved photocatalytic performance. The present vacuum atmosphere method opens up a new strategy for preparing other N-doped oxide semiconductors such as TiO 2 .

Effect of Mn doping on the structural and optical properties of sol-gel derived ZnO nanoparticles

Abstract Un-doped and Mn-doped ZnO nanoparticles were successfully synthesized in an ethanolic solution by using a sol-gel method. Material properties of the samples dependence on preparation conditions and Mn concentrations were investigated while other parameters were controlled to ensure reproducibility. It was observed that the structural properties, particle size, band gap, photoluminescence intensity and wavelength of maximum intensity were influenced by the amount of Mn ions present in the precursor. The XRD spectra for ZnO nanoparticles show the entire peaks corresponding to the various planes of wurtzite ZnO, indicating a single phase. The diffraction peaks of doped samples are slightly shifted to lower angles with an increase in the Mn ion concentration, signifying the expansion of the lattice constants and increase in the band gap of ZnO. All the samples show the absorption in the visible region. The absorbance spectra show that the excitonic absorption peak shifts towards the lower wavelength side with the Mn-doped ZnO nanoparticles. The PL spectra of undoped ZnO consist of UV emission at 388 nm and broad visible emission at 560 nm with varying relative peak intensities. The doping of ZnO with Mn quenches significantly the green emission while UV luminescence is slightly affected.

P-Type Nitrogen-Doped ZnO Nanoparticles Stable under Ambient Conditions

Zinc oxide is considered as a very promising material for optoelectronics. However, to date, the difficulty in producing stable p-type ZnO is a bottleneck, which hinders the advent of ZnO-based devices. In that context, nitrogen-doped zinc oxide receives much attention. However, numerous reviews report the controversial character of p-type conductivity in N-doped ZnO, and recent theoretical contributions explain that N-doping alone cannot lead to p-typeness in Zn-rich ZnO. We report here that the ammonolysis at low temperature of ZnO(2) yields pure wurtzite-type N-doped ZnO nanoparticles with an extraordinarily large amount of Zn vacancies (up to 20%). Electrochemical and transient spectroscopy studies demonstrate that these Zn-poor nanoparticles exhibit a p-type conductivity that is stable over more than 2 years under ambient conditions.

All-inorganic Light Emitting Devices Based on Semiconducting Nanoparticles

AbstractWe demonstrate light emitting devices based on ZnO nanoparticles and realized without any additional organic support layers. Pure ZnO devices showed electroluminescence in the visible and the UV spectral range at voltages below 10 V. In order to facilitate hole injection and to stabilize device operation, additional p-type inorganic support layers were introduced. Sputtered NiO layers are shown to improve the stability of the device and its I/V behavior. First bilayer devices consisting of a layer sequence of p-doped Si and naturally n-doped ZnO nanoparticles revealed promising electro-luminescence results with a high contribution in the UV spectral range at reduced current densities.