Mn-doped ZnO Research Articles

Mn-doped ZnO nanopowders prepared by sol–gel and microwave-assisted sol–gel methods and their photocatalytic properties

Although the microwave-assisted sol–gel method is quite frequently used for the preparation of oxide nanostructures, the synergism of the reaction pathways is not fully explained. However, state-of-the-art theoretical and practical results of high novelty can be achieved by continuously evaluating the as-synthesized materials. The present paper presents a comparative study of Mn-doped ZnO nanopowders prepared by both sol–gel and microwave-assisted sol–gel methods. The structural, morphological, and optical properties of the as-obtained powders were established and correlated with their newly proved functionality, namely, the ability to photogenerate distinct reactive oxygen species (·OH or O2−) and to act as photoactive materials in aqueous media. The solar light-induced mineralization of oxalic acid by Mn-doped ZnO materials was clearly observed while similar amounts of generated CO2 were measured for both catalysts. These inexpensive semiconductor materials, which proved to be light-responsive, can be further used for developing water depollution technologies based on solar light energy.

Optical properties analysis of gelatin-based prepared Co, Ni, and Mn-doped ZnO nanoparticles in infrared and UV–vis region using Kramers-Kronig methods

This study investigates the structural, optical, and morphological properties of ZnO nanoparticles doped with Ni, Mn, and Co (Zn0.97A0.03O where A = Ni, Mn, and Co, designated as ZN, ZM, and ZC, respectively). X-ray diffraction (XRD) analysis confirms the successful incorporation of dopants into the ZnO lattice without altering its wurtzite structure. Field emission scanning electron microscopy (FESEM) images reveal that doping results in larger and more uniformly distributed particles. Energy-dispersive X-ray spectroscopy (EDX) verifies the presence of Ni, Mn, and Co in the respective samples. Fourier transform infrared (FTIR) spectroscopy indicates an increase in average phonon energies due to doping, as evidenced by the shift in the Zn-O vibration peak. Ultraviolet–visible (UV–vis) spectroscopy shows that doping causes a blue shift in the absorbance peak and increases the optical band gap from 3.17 eV for pure ZnO to 3.22 eV for Co-doped ZnO. Transmission electron microscopy (TEM) and corresponding EDX results further confirm the presence of dopants and illustrate that doped ZnO nanoparticles are larger than pure ZnO particles. These findings provide valuable insights into the impact of doping on ZnO nanoparticles, potentially enhancing their suitability for various technological applications.

Structure, microstructure, and ESR properties of concentration-dependent Zn1-xMnxO nanoparticles

In this study, the estimated stress, strain, and crystallite sizes of different Mn-doped ZnO nanoparticles were calculated using the Williamson-Hall method and compared with the values obtained from the Debye-Scherrer formula. Moreover, defects, and magnetic properties of Mn-doped ZnO nanoparticles at different concentrations were investigated. The sol-gel method was used to synthesize nanoparticles. The X-ray diffraction and Rietveld analysis results confirm that the desired structure is formed and that no secondary phase is present up to an Mn concentration of x=0.2. In and out of plane lattice parameters, cell volumes, bond length, atomic locality, and dislocation density (δ) were clarified. The grain size of the concentration-dependent samples was provided by scanning electron microscope. Photoluminescence (PL) spectra exhibited ultraviolet emission along with a broad band encompassing violet, blue, and red regions, attributed to defect-related and excitonic emissions. These emissions were notably influenced by synthesis conditions and doping elements and ratios. Electron spin resonance properties of the concentration-dependent samples were analyzed to figure out the g-factor through line widths of pike-to-pike (ΔHPP) of ESR spectra. Mn-doped ZnO nanoparticles exhibited ferromagnetism at room temperature.

Peganum Harmala seeds extract: A green synthesis route for Mn-doped ZnO nanoparticles as an adsorbent for crystal violet dye removal

Peganum Harmala seeds extract: A green synthesis route for Mn-doped ZnO nanoparticles as an adsorbent for crystal violet dye removal

Manganese-doped Zinc Oxide recycled from spent alkaline batteries for photocatalysis and supercapacitor applications

In a sustainable future, recycling e-waste will offer an adequate solution to control the raw materials and energy crisis. Our study aims to obtain ZnO-based materials by recycling the alkaline batteries using mild and cost-effective methods. Manganese-doped ZnO materials were obtained through anodic paste annealing at different temperatures. In terms of morphology and structure, particles with rod shape, high crystallinity, and hexagonal symmetry were obtained. The annealing provides an atomic rearrangement ensuring the presence of isolated Mn2+ ions in the ZnO lattice, as evidenced by EPR spectroscopy. The sample defect evolution with the annealing temperature was highlighted by photoluminescence spectroscopy. The photocatalytic and energy storage applications of the obtained sample were investigated. The photocatalytic activity was tested on Rhodamine B and Oxytetracycline under visible light irradiation. The highest photocatalytic efficiency was obtained for Mn-doped ZnO annealed at 700 °C, and the proposed mechanism was based on reactive oxygen species generation correlated with scavengers’ tests, defect’s structure, and pores diameter. Additionally, the samples were used to design symmetric supercapacitors and tested using different electrochemical techniques to prove their energy storage features. As a result, the Mn-doped ZnO particles annealed at 800 °C showed increased specific capacitance of 182 F/g, energy density of 25.2 Wh/kg, and power density of 38.7 kW/Kg without the use of booster materials.

Highly Sensitive and Selective Gas Sensors for Ethanol Based on Mn Doped ZnO Nanoflakes

Highly Sensitive and Selective Gas Sensors for Ethanol Based on Mn Doped ZnO Nanoflakes

Synergistic Integration of Mn-Doped ZnO Nanoparticles with Hibiscus Nano-Host Matrix: Synthesis, Characterization, and Potential Applications

Synergistic Integration of Mn-Doped ZnO Nanoparticles with Hibiscus Nano-Host Matrix: Synthesis, Characterization, and Potential Applications

Facile synthesis of Mn doped ZnO for the sensing of ammonia

The variation of possessions of Mn doped in ZnO thin films grown by SILAR technique for various Mn concentrations presented. Thin films of Mn doped ZnP were deposited and uniformly annealed at 300 °C for a 30 min. The annealed films are then characterized by various methods like XRD, SEM, EDAX, VSM respectively. The x-ray diffraction studies confirm the emergence of ZnO. From the SEM, various morphologies were identified based on concentration of the solution bath employed. Due to this reason, spherical shoot, rice and flower morphologies were observed on the surface of the films. These morphologies may influence the application of ammonia gas sensor. From compositional analysis (EDAX), the presence of dopant and the variation in composition of doped materials were estimated. Magnetic studies shows, these films show ferromagnetic behaviour at room temperature. The ammonia gas response of the Mn doped ZnO thin films varied with Mn concentration of 0, 5 and 10. The outcomes of the gas sensing experiments showed that the Mn doped ZnO thin film was more sensitive to ammonia, but that sensitivity decreased as gas pressure increased. Ammonia gas showed an increase in the acidic surface properties of Mn-doped ZnO thin film. At room temperature, Mn-doped ZnO (0 %, 5 % and 10 %) showed responses of 19.20, 27.61 and 32.26 to 100 ppm NH3 gas, which were significantly higher than those of ZnO. The Mn-doped ZnO sensor shows excellent selectivity compared to ZnO and has good stability.

Sol-Gel technique, characterization and photocatalytic degradation activity of Manganese doped ZnO nanoparticles

Photocatalysis using semiconductor metal oxide stands out as a highly effective and efficient method for eliminating organic pollutants from wastewater. This study aims to assess the photocatalytic capabilities of Mn doped ZnO nanocomposites in degrading methylene blue (MB) dye under ultra-violet light exposure. This study details the synthesis of ZnO photocatalysts through a straightforward one-step sol-gel method, incorporating varying levels of Mn-doping (0%, 2% & 4%). The structural and optical attributes were examined using techniques such as powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and UV-Vis diffuse reflectance spectra. X-ray diffraction analyses verified the presence of a hexagonal wurtzite crystal structure in all synthesized samples, exhibiting a high degree of crystallinity. In addition, an investigation into the impact of Mn impurities on the photocatalytic performance of ZnO catalysts was conducted in the context of methylene blue (MB) degradation. The experimental findings revealed that the Mn doped ZnO nanoparticles produced exhibited significantly superior photocatalytic performance compared to pure ZnO when used in breaking down methylene blue under UV-light exposure. This study proposes that these Mn doped ZnO could serve as a highly effective photocatalyst for treating water contaminated with certain chemically persistent synthetic organic dyes. The improved photocatalytic capabilities of ZnO nanostructures doped with Mn were ascribed to the synergistic impact of increased surface area in ZnO nanosphere and enhanced efficiency in charge separation resulting from optimized Mn doping. A potential explanation for the heightened photocatalytic performance of Mn-doped ZnO nanostructures is proposed tentatively.

A comparative study on green synthesis and characterization of Mn doped ZnO nanocomposite for antibacterial and photocatalytic applications

Biological and green synthesis of nanomaterial is a superior choice over chemical and physical methods due to nanoscale attributes implanted in a green chemistry matrix, have sparked a lot of interest for their potential uses in a variety of sectors. This research investigates the growing relevance of nanocomposites manufactured using ecologically friendly, green technologies. The transition to green synthesis correlates with the worldwide drive for environmentally sound procedures, limiting the use of traditional harsh synthetic techniques. Herein, manganese was decorated on ZnO NPs via reducing agent of Withania-extract and confirmed by UV-spectrophotometry with highest peak at 1:2 ratio precursors, and having lower bandgap energy (3.3 eV). XRD showed the sharp peaks and confirms the formation of nanoparticles, having particle size in range of 11–14 nm. SEM confirmed amorphous tetragonal structure while EDX spectroscopy showed the presence of Zn and Mn in all composition. Green synthesized Mn-decorated ZnO-NPs screened against bacterial strains and exhibited excellent antimicrobial activities against gram-negative and gram-positive bacteria. To check further, applicability of synthesized Mn-decorated Zn nanocomposites, their photocatalytic activity against toxic water pollutants (methylene blue (MB) dye) were also investigated and results showed that 53.8% degradation of MB was done successfully. Furthermore, the installation of green chemistry in synthesizing nanocomposites by using plant extract matrix optimizes antibacterial characteristics, antioxidant and biodegradability, helping to build sustainable green Mn decorated ZnO nanomaterial. This work, explains how biologically friendly Mn-doped ZnO nanocomposites can help reduce the environmental impact of traditional packaging materials. Based on these findings, it was determined that nanocomposites derived from biological resources should be produced on a wide scale to eradicate environmental and water contaminants through degradation.

Influence of compacting pressure on the electrical properties of ZnO and ZnO:Mn ceramics

Undoped and Mn-doped ZnO ceramics were prepared from the powders compacted at different pressures and sintered in air at high temperature. Their structural, optical, light emitting and electrical characteristics as well as the distribution of chemical elements were studied. It was found that an increase in compacting pressure stimulates an increase in direct current conductivity in both undoped and doped samples. In the case of doped samples, this effect was accompanied by a decrease in the height of potential barriers at the grain boundaries. It is found that electron concentration in ceramic grains, estimated from the modelling of infrared reflection spectra, remained relatively constant. The analysis of luminescence spectra and spatial zinc distribution revealed that the increase in compacting pressure results in the accumulation of interstitial zinc at the grain boundaries forming channels with enhanced conductivity. These findings provide an explanation for the evolution of electrical properties of ceramic samples with compacting pressure.

Structural investigations of ZnO nanostructure

Undoped and Mn-doped ZnO samples with different percentages of Mn content (1, 5 and 10 at%) were synthesized by a dip coating sol–gel method. We have studied the structural, chemical and optical properties of the samples by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy. The XRD spectra show that all the samples are hexagonal wurtzite structures. We note that doping favors c-axis orientation along (002) planes. Up to 5 at% of Mn doping level, the c- axis lattice parameter shifts towards higher values with the increase of manganese content in the films. The expansion of the lattice constant of ZnO–Mn indicates that Mn is really doped into the ZnO. The SEM investigations of all samples revealed that the crystallites are of nanometer size. The sur- face quality of the ZnO–Mn film increases with Mn doping but no significant change of the grain size is observed from SEM images. The transmittance spectra show that the trans parency of all the samples is greater than 85 %. We note, also, that a small doping (1 %) lowered the refractive index while the thickness of the layers and the gap increase. However, on raising the proportion of Mn beyond 5 %, practically the same values of index and gap as pure ZnO are found.

Enhancing photocatalytic efficiency with Mn-doped ZnO composite carbon nanofibers for organic dye degradation

<abstract> <p>In this study, Mn-doped ZnO composite carbon nanofibers (Mn-ZnO/CNFs) were prepared via a simple blending and electrospinning (ES) method, followed by a thermal treatment. These fibers were used to investigate the photocatalytic degradation of an organic dye under UV and visible light irradiation. The results showed that Mn-ZnO/CNFs were successfully prepared under the same conditions used for CNFs preparation conditions, which induced a morphological change from a smooth to a rough surface compared to the CNFs. Energy dispersive X-ray (EDX), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) analyses confirmed the formation of Mn-doped ZnO on the CNFs' surface. Furthermore, the addition of the catalyst significantly increased in the specific surface area, and a N<sub>2</sub> adsorption-desorption isotherm analysis revealed that all samples had mesoporous characteristics with a type IV isotherm index. The photocatalytic activity of the Mn-ZnO/CNFs carbonized at 650 ℃ using methylene blue (MB) dye as a model pollutant was investigated. All prepared samples effectively removed the MB with a degradation rate of 70-90%. The kinetic reaction rate was described using the simplified Langmuir-Hinshelwood equation. Overall, the CNFs and composites nanofibers developed through moderate thermal treatment processes possessed a high specific surface area and oxygen vacancy, enabling their potential use as adsorbents and as a catalyst support for reactions at room-to-elevated temperatures, as well as photocatalysts for the removal of organic contaminants.</p> </abstract>

Mn Doped ZnO Film for Ethanol Vapor Detection

It has become a major challenge to develop highly sensitive and selective ZnO gas sensors to detect the leakage of toxic and explosive gases due to their high operating temperature. This article reports the design, characterization, and application of a Mn-doped ZnO thin film for ethanol gas vapor detection at a relatively lower temperature. To achieve this, undoped (0%) and Mn doped ZnO thin films were prepared using a spin coating technique and their structural, morphological and optical characterizations were carried out using XRD, SEM, EDX and UV-vis spectrophotometer. The XRD analysis showed a polycrystalline ZnO structure with the preferred orientations along (100), (002), (101), (102), (110), (103), and (200) planes. Upon Mn doping, the average crystallite size and band gap of ZnO were found to be decreased, which indicated that Mn ions substitute into the lattice of ZnO. Interestingly, SEM images revealed the grainy like porous ZnO surfaces. The EDX results confirmed the presence of Mn dopant in the ZnO lattice. In the doped films, the changes in particle size and grain boundaries of nanocrystalline ZnO resulted changes in sensitivity and operating temperature of ZnO gas sensor. The sensitivity measurements towards ethanol vapor showed significant decrease of the operating temperature from 220°C to 160°C as Mn concentration was increased from 0 to 5%. As-prepared Mn-doped ZnO sensors will be useful for sensing ethanol vapor at relatively low temperature.

Dual-Functional Manganese-Doped ZnO-MOF Hybrid Material with Enhanced Hydrolytic Stability: A Fluorescent Photoinduced Electron Transfer Sensor for the Ultraselective Detection of Acetic Acid and Chromium (VI).

In recent years, the synthesis of metal-organic framework (MOF)─nanocomposites has received wide attention from the scientific fraternity due to the presence of a tunable hierarchical architecture and invasive versatility in applications. The present work focuses on the solvothermal synthesis of a novel hybrid MOF-nanocomposite through the impregnation of Mn-doped ZnO nanoparticles onto the matrix of a pioneer metal-organic framework that is composed of zinc metal connected with terephthalic acid linkers (MOF-5). The hierarchical arrangements of the prepared material were further assessed by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HR-TEM), UV-visible, photoluminescence (PL), and dynamic light scattering (DLS) measurements. The porosity analysis via nitrogen sorption measurements at 77 K showed that the material is porous with hierarchical micro-, wide micro-, and mesopores. The SAED pattern confirms the polycrystallinity of the material, which is in good agreement with the data obtained from PXRD analysis. Effective integration of Mn-doped ZnO onto the MOF structure was confirmed by XPS analysis, and the study further identified the oxidation state of the elements present. The synthesized analyte is an efficient fluorescent chemosensor for the detection of acetic acid, which can find further potential applications in intracellular imaging. Interestingly, the same compound also selectively detects the presence of Cr(VI) ions, thereby acting as a dual sensor, which finds applications in the sensing and removal of environmental contaminants. The material showed a sharp and intense emission at 569 nm at an excitation wavelength of 320 nm, and it exhibits high quenching efficiencies of 99.87 and 71.43% toward the sensing of μM level concentration of acetic acid and Cr2O72-, respectively. The highly efficient fluorescent sensing of pollutants, even at a shorter linear range, discarded the possibility of sensing the pollutants at higher concentration ranges. The Ksv value for the detection of acetic acid and Cr(VI) is found to be 3.7017 × 106 and 11.0324 × 106 M-1, respectively, which further confirms the higher sensing ability of the synthesized fluorophore. The mechanistic studies and density functional theory calculations of Mn-doped ZnO@MOF-5 reveal that photoinduced electron transfer plays a significant role in the turn-off response toward acetic acid and Cr2O72- ions. In the case of acetic acid, in addition to photoinduced electron transfer, hydrogen bonding interactions may also lead to fluorescence quenching. To the best of our knowledge, no precedent work has been reported for the sensing of acetic acid in the solution state. All other fluorescent sensing reports put forward the sensing and adsorption of acetic acid in the gaseous state, which makes this material a pioneer among others for the detection of acetic acid in the solution phase.

Optical properties of Zn0.75Mg0.25O:Mn ceramics

Mn-doped ZnO, MgO and Zn0.75Mg0.25O samples ([Mn] = 0.1 at.%) were produced by conventional solid-state technique and investigated by means of XRD, EPR, absorption, photocurrent, photo- and cathodoluminescence methods. It was shown that Zn0.75Mg0.25O solid solution with hexagonal structure has the bandgap of Eg ∼3.65 eV. The quenching of host defect-related luminescence in ZnO:Mn and in hexagonal Zn0.75Mg0.25O:Mn was observed, while the Mn-related emission being absent. The energy level of MnZn2+ center in hexagonal Zn0.75Mg0.25O:Mn was found to be at 2.16 eV below conduction band (c-band) bottom and all excited states of MnZn2+ ions, including the lowest one, reside in c-band, as it takes place in ZnO:Mn. It is concluded that the necessary condition to obtain Mn-related light emission in Mn-doped alloys is to make deeper the lowest excited level of MnZn2+ ions. One of the solutions is to produce Zn1-xMgxO:Mn solid solution with the bandgap energy larger than 4.0 eV using nonequilibrium fabrication approaches.

RKKY exchange interactions in two-dimensional Mn-doped ZnO dilute magnetic semiconductor

In this paper, we have theoretically studied the RKKY indirect exchange interactions in a two-dimensional model of Zn1-xMnxO dilute magnetic semiconductor. Under the RKKY interaction framework, we have calculated the exchange coupling constants for four different doped samples of host ZnO, which are 5%, 10%, 15%, and 20%. The carrier density for the respective configurations is taken as 0.1, 0.5, 0.75, and 1 hole per dopant, considering long-range interactions controlled by the cutoff scale in the RKKY range function. The variation of magnetic coupling strength with the carrier density is also examined, and the overall magnetic behavior of the proposed 2-D system is estimated.

Three-Dimensional-Printed Photocatalytic Sponges Decorated with Mn-Doped ZnO Nanoparticles.

The present work reports on the fabrication of high-density polyethylene sponges, decorated with Mn-doped ZnO nanostructures. The sponges were developed utilizing three-dimensional printing technology, while Mn-doped ZnO nanostructures, with varying doping levels, were grown at mild temperatures. The nanostructures were fully characterized by means of scanning electron microscopy, X-ray diffraction, and Raman spectroscopy, revealing the existence of Mn doping. Moreover, their photocatalytic properties were investigated using the degradation/decolorization of a commercially available liquid laundry detergent, based on synthetic, less foaming ingredients, under UV irradiation. The Mn-doped ZnO nanostructures show better photocatalytic activity at higher doping levels. This study demonstrates that it is possible to achieve the adequate degradation of a typical detergent solution in water by means of low-cost and environmentally friendly approaches, while Mn-doped ZnO/HDPE nanostructures are good candidates for real environmental applications.

Doping Engineering to Modulate Lattice and Electronic Structure for Enhanced Piezocatalytic Therapy and Ferroptosis.

Piezocatalytic therapy, which generates reactive oxygen species (ROS) under mechanical force, has garnered extensive attention for its use in cancer therapy owing to its deep tissue penetration depth and less O2 -dependence. However, the piezocatalytic therapeutic efficiency is limited owing to the poor piezoresponse, low separation of electron-hole pairs, and complicated tumor microenvironment (TME). Herein, a biodegradable, porous Mn-doped ZnO (Mn-ZnO)nanocluster with enhanced piezoelectric effect is constructed via doping engineering. Mn-doping not only induces lattice distortion to increase polarization but also creates rich oxygen vacancies (OV ) for suppressing the recombination of electron-hole pairs, leading to high-efficiency generation of ROS under ultrasound irradiation. Moreover, Mn-doped ZnO shows TME-responsive multienzyme-mimicking activityandglutathione (GSH) depletion ability owing to the mixed valence of Mn (II/III), further aggravating oxidative stress. Density functional theory calculations show that Mn-doping can improve the piezocatalytic performance and enzyme activity of Mn-ZnO due to the presence of OV . Benefiting from the boosting of ROS generation and GSH depletion ability, Mn-ZnO can significantly accelerate the accumulation of lipid peroxide and inactivate glutathione peroxidase 4 (GPX4) to induce ferroptosis. The work may provide new guidance for exploring novel piezoelectric sonosensitizers for tumor therapy.

On the vibrational properties of transition metal doped ZnO: Surface, defect, and bandgap engineering

We present a comprehensive study on the structure and optical properties of Mn-and Co-doped ZnO samples prepared via solid-state reaction method with different dopant concentrations and atmospheres. The samples were structural and chemically characterized via X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray excited photoelectron spectroscopy. The optical characterization was performed via Raman, photoluminescence, and diffuse photoreflectance spectroscopies. Emphasis was done on the studies of their vibrational properties. The structural data confirm the incorporation of Mn and Co ions into the wurtzite ZnO lattice. It is demonstrated that the usual observed additional bands in the Raman spectrum of transitional metal (TM) doped ZnO are related to structural damage, deriving from the doping process, and surface effects. The promoted surface optical phonons (SOP) are of Fröhlich character and, together with the longitudinal optical (LO) polar phonons, are directly dependent on the ZnO electronic structure. The enhancement of SOP and LO modes with TM-doping is explained in terms of nonhomogeneous doping, with the dopants concentrating mainly on the surface of grains, and a resonance effect due to the decrease of the ZnO bandgap promoted by the introduction of the 3d TM levels within the ZnO bandgap. We also discuss the origin of the controversial vibrational mode commonly observed in the Mn-doped ZnO system. It is stated that the observation of the analyzed vibrational properties is a signature of substitutional doping of the ZnO structure with tuning of ZnO optical absorption into the visible range of the electromagnetic spectrum.