Raman Submicron Spatial Mapping of Individual Mn-doped ZnO Nanorods

Modulation of dielectric and antibacterial properties of Zn0.5Mn0.5O nanoparticles by post growth annealing method

In this manuscript, we have investigated the dielectric and antibacterial potential of hydrothermally synthesized ZnMnO nanoparticles. The synthesized nanoparticles were annealed at various temperatures ranging from 450 to 650 °C with a step of 50 °C to modulate the structural, vibrational, dielectric, and antibacterial properties. XRD data confirmed the hexagonal structure of the synthesized samples and crystalline size was decreased to 4.8 nm at annealing temperature 600 °C. The lattice structure was further verified by Raman spectroscopy measurements, which strongly verified the XRD data due the presence of ZnMnO vibrational modes. The dielectric measurements revealed that the dielectric constant and los tangent were found to be increased with the increase annealing temperature and decreased with frequency, while a.c conductivity has an increasing trend with both parameters (temperature and frequency). The plot of real and complex parts of impedance against frequency demonstrated that both parameters decrease with the increased in frequency. But when we analyzed the behavior of the real part of impedance against the annealing temperature, a degradation in real part behavior is observed. The antibacterial activity of ZnMnO nanoparticles was determined by using the disc diffusion method against E. coli bacteria, which was grown on a Petri dish at room temperature for 24 h. This observation revealed that the samples annealed at 450 °C and 550 °C show remarkable antibacterial sensitivity as compared to other samples. It is concluded that crystalline size of 20 nm is found to be optimal value for good anti-baterial behavior.

Optimization of physical and dielectric properties of Co-doped ZnO nanoparticles for low-frequency devices

In this study, zinc-oxide (ZnO) nanoparticles (NPs) doped with cobalt (Co) were synthesized using a simple coprecipitation technique. The concentration of Co was varied to investigate its effect on the structural, morphological, optical, and dielectric properties of the NPs. X-ray diffraction (XRD) analysis confirmed the hexagonal wurtzite structure of both undoped and Co-doped ZnO-NPs. Scanning electron microscopy (SEM) was used to examine the morphology of the synthesized NPs, while energy-dispersive X-ray spectroscopy (EDX) was used to verify their purity. The band gap of the NPs was evaluated using UV-visible spectroscopy, which revealed a decrease in the energy gap as the concentration of Co2+ increased in the ZnO matrix. The dielectric constants and AC conductivity of the NPs were measured using an LCR meter. The dielectric constant of the Co-doped ZnO-NPs continuously increased from 4.0 × 10-9 to 2.25 × 10-8, while the dielectric loss decreased from 4.0 × 10-8 to 1.7 × 10-7 as the Co content increased from 0.01 to 0.07%. The a.c. conductivity also increased with increasing applied frequency. The findings suggest that the synthesized Co-doped ZnO-NPs possess enhanced dielectric properties and reduced energy gap, making them promising candidates for low-frequency devices such as UV photodetectors, optoelectronics, and spintronics applications. The use of a cost-effective and scalable synthesis method, coupled with detailed material characterization, makes this work significant in the field of nanomaterials and device engineering.

Improvement of the photocatalytic activity of ZnO thin films doped with manganese

In the herein report, we synthesized ZnO thin films doped with manganese (Mn). We studied the impact of Mn doping loads (1 %, 3 %, 5 % wt.) on physicochemical properties of the compounds. Furthermore, we presented the photocatalytic efficiency in removal of methylene blue dye. The structural assay indicated ZnO conserve the wurtzite crystalline structure after dopant insertion. Furthermore, the crystalline size of catalysts was reduced after dopant incorporation. The SEM analysis showed a change in surface morphology after modification of ZnO thin films. Furthermore, Raman spectroscopy verified the Mn insertion inside the ZnO lattice. After the doping process, band gap was reduced by 16 %, in comparison to bare ZnO. After the photocatalytic test, the doped catalysts showed better performance than bare ZnO in removing MB. The best test showed a kinetics constant value of 2.9 × 10-3 min-1 after 120 min of visible irradiation. Finally, the Mn(5 %):ZnO thin film was suitable after five degradation cycles, and the degradation process efficiency was reduced by 32%.

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.

Complexes of Ag and ZnO nanoparticles with BBR for enhancement of gastrointestinal antibacterial activity through the impacts of size and composition

This study introduces the bioformulations of Ag/BBR and ZnO/BBR complexes against pathogenic bacteria in the gastrointestinal tract. Without the use of toxic reduction agents, Ag and ZnO NPs were prepared using an electrochemical method and then facially mixed with BBR solution to form Ag/BBR and ZnO/BBR complexes. BBR molecules are strongly conjugated with Ag and ZnO NPs through coordinated bonding and electrostatic interaction. As a result, the presence of BBR significantly influenced the nanoparticle growth, resulting in the formation of core/shell structured Ag/BBR and ZnO/BBR NPs with small particle sizes. The antibacterial test showed that BBR, Ag, or ZnO components all contributed to the increase of antibacterial ability of Ag/BBR and ZnO/BBR NPs against both methicillin-resistant Staphylococcus aureus (MRSA) and Salmonella enteritidis (S. enteritidis). The bactericidal ability of Ag/BBR and ZnO/BBR complexes against MRSA was exhibited even at a concentration of four-fold dilution (corresponding to 1.25 g L-1 of BBR and 46.25 mg L-1 of Ag) and two-fold dilution (corresponding to 2.5 g L-1 of BBR and 10 mg L-1 of ZnO), respectively, while that of the Ag/BBR complex against S. enteritidis showed at a concentration of two-fold dilution corresponding to 2.5 g L-1 of BBR and 92.5 mg L-1 of Ag. The results obtained in this study support that Ag/BBR and ZnO/BBR complexes can be potential therapeutic agents against gastrointestinal infections.

ZnO and Ag NP-decorated ZnO nanoflowers: green synthesis using Ganoderma lucidum aqueous extract and characterization

Fungi produce and excrete various proteins, enzymes, polysaccharides, and secondary metabolites, which may be used as media for the "green" synthesis of metal and semiconductor nanoparticles (NPs). ZnO NPs with a flower-like morphology were synthesized by an affordable colloidal route, using an aqueous extract of Ganoderma lucidum as a reducing agent and stabilizer. Each individual "flower" has a large effective surface, which is preserved when the particles are close packed into a dense film, which is advantageous for numerous applications. The phonon Raman spectrum and X-ray diffraction (XRD) pattern prove the high crystallinity of the NPs, with the distinct pattern of a hexagonal (wurtzite) lattice, negligible residual stress, and a crystallite size of 12-14 nm determined from the XRD. The photoluminescence (PL) spectrum of the as-synthesized ZnO NPs contains a structured defect-related feature in the violet-blue range, while the green PL, common for nanostructures synthesized by "green" routes, is very weak. By applying dimethylsulfoxide as an additional passivating agent, the excitonic (UV) PL band was activated without enhancement of the defect-related features. Ag NP-decorated ZnO flowers were synthesized by subsequent silver reduction by pepper extract. The ZnO/Ag NPs exhibited efficient surface-enhanced Raman scattering (SERS) of a standard dye analyte, rhodamine 6G, ensuring the feasibility of other applications that require close contact of ZnO/Ag to other nanostructures or molecules to realize the energy of the charge transfer.

Enhanced photocatalytic degradation of malachite green using manganese oxide doped graphene oxide/zinc oxide (GO-ZnO/Mn2O3) ternary composite under sunlight irradiation

In this work, photocatalytic degradation of malachite green (MG) dye using manganese oxide doped graphene oxide/zinc oxide (GO-ZnO/Mn₂O₃) ternary composite under sunlight irradiation is studied. GO-ZnO/Mn₂O₃ is a novel composite, which is non-toxic and of low cost prepared by the conventional solvothermal route. The synthesized composite was characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), RAMAN spectra, photoluminescence (PL) spectroscopy, Diffuse reflectance spectroscopy (UV-Vis. DRS), and Barrett-Joyner-Halenda (BJH) pore size distribution. The GO-ZnO/Mn₂O₃ composite has a moderately large surface area of 75.35 m²/g and bandgap energy of 1.6 eV. Due to more pollutants adsorbed onto the photocatalyst surface and the reduction in bandgap energy, resulted less recombination rate and shifted the light absorption into the visible region to effectively utilize the sunlight and enhanced degradation of 98.75% is achieved within 30 min of sunlight irradiation for GO-ZnO/Mn₂O₃ composite. Using various scavengers, the main oxidizing radicals for the degradation of MG dye are identified as hydroxyl (^•OH) and superoxide radical (^•O₂^-). The synthesized composite is stable and reproducible as after five successful cycles, there was a small reduction in its degradation efficiency of 11.65%. Keywords: Graphene oxide; Photocatalyst; Malachite green; Bandgap; Scavengers.

Enhancing triethylamine sensing of ZIF-derived ZnO microspheres arising from cobalt doping and defect engineering

Reasonable doping is beneficial to the generation of defects, which is a feasibility strategy to improve the ZnO sensing performance. Herein, we presented an in situ self-sacrificing template strategy for fabricating Co doped h-ZnO core-shell structures (h-ZnO/ZnCo_x) with different defect contents, pyrolyzing hierarchical porous ZnO (h-ZnO) sub-microspheres coated by zeolite imidazolate frameworks (h-ZnO/ZIF-ZnCo_x). The investigations of X-ray photoelectron (XPS), photoluminescence (PL) and Raman spectra indicate that donor defects include zinc interstitial (Zn_i) and oxygen vacancy (V_O) in h-ZnO/ZnCo_x can be tuned by Co dopant (x = 0-30%). Resultantly, the h-ZnO/ZnCo_x exhibits a significantly enhanced response and selectivity towards triethylamine (TEA), beyond the undoped h-ZnO, and 15% Co-doped h-ZnO (h-ZnO/ZnCo_15%) conducts the maximum responses of 1020 to 50 ppm TEA at 573 K, in the top set for the similar type of sensors. Further, the sensing mechanism of h-ZnO/ZnCo_x is elaborated, possibly resulting from abundant active oxygen species conversed from more oxygen adsorbed which corresponds to cobalt doping generating rich donor-related defects and additional electrons in h-ZnO/ZnCo_15%.

Structural, Magnetic, and Optical Properties of Mn2+ Doping in ZnO Thin Films

MnxZn1−xO thin films (x = 0%, 1%, 3%, and 5%) were grown on corning glass substrates using sol–gel technique. Single-phase hexagonal wurtzite structure was confirmed using X-ray diffraction. Raman analysis revealed the presence of Mn content with an additional vibrational mode at 570 cm−1. The surface morphology of the samples was observed by scanning electron microscopy which suggested that the grain size increases with an increase in Mn concentration. The optical bandgap increases with increasing Mn concentration due to a significant blueshift in UV–visible absorption spectra. The alteration of the bandgap was verified by the I–V measurements on ZnO and Mn-ZnO films. The various functional groups in the thin films were recorded using FTIR analysis. Magnetic measurements showed that MnxZn1−xO films are ferromagnetic, as Mn induces a fully polarised state. The effect of Mn2+ ions doping on MnxZn1−xO thin films was investigated by extracting various parameters such as lattice parameters, energy bandgap, resistivity, and magnetisation. The observed coercivity is about one-fifth of the earlier published work data which indicates the structure is soft in nature, having less dielectric/magnetic loss, and hence can be used as ultra-fast switching in spintronic devices.

A Durable Ni-Zn Microbattery with Ultrahigh-Rate Capability Enabled by In Situ Reconstructed Nanoporous Nickel with Epitaxial Phase

Powering device for miniaturized electronics is highly desired with well-maintained capacity and high-rate performance. Though Ni-Zn microbattery can meet the demand to some extent with intrinsic fast kinetic, it still suffers irreversible structure degradation due to the repeated lattice strain. Herein, a stable Ni-Zn microbattery with ultrahigh-rate performance is rationally constructed through in situ electrochemical approaches, including the reconstruction of nanoporous nickel and the introduction of epitaxial Zn(OH)₂ nanophase. With the enhanced ionic adsorption effect, the superior reactivity of the superficial nickel-based nanostructure is well stabilized. Based on facile miniaturization and electrochemical techniques, the fabricated nickel microelectrode exhibits 63.8% capacity retention when the current density is 500 times folded, and the modified hydroxides contribute to the great stability of the porous structure (92% capacity retention after 10 000 cycles). Furthermore, when the constructed Ni-Zn microbattery is measured in a practical metric, excellent power density (320.17 mW cm^-2 ) and stable fast-charging performance (over 90% capacity retention in 3500 cycles) are obtained. This surface reconstruction strategy for nanostructure provides a new direction for the optimization of electrode structure and enriches high-performance output units for integrated microelectronics.

ZnO thin film-nanowire array homo-structures with tunable photoluminescence and optical band gap

The growth and optical behavior of ZnO thin film-nanowire array homo-structures is reported. The ZnO films are deposited on glass substrates by thermal evaporation and subjected to heat treatment at 400 °C for 2 h to achieve crystallinity and stoichiometry. The surface comprises spherical grains or elongated flakes depending on thickness of films. These films are introduced in to a hydrothermal reactor in a medium of zinc acetate and HMTA to realize the nanostructures. The process results in the formation of ZnO nanowires with dimensions that are strongly dependent on the surface microstructure of the ZnO films. The role of temperature (90-180 °C) and duration (10 min to 10 h) of hydrothermal processing is investigated in detail. It is demonstrated that low temperature and short duration are ideal for producing nanowires with diameter < 100 nm, while longer durations and higher temperatures lead to large diameter and long length nanowires. Interestingly, all wires converge to a hexagonal shape with increase in duration or temperature. The lowest diameter of the vertically aligned nanowires is 50 nm and length upto 10 μm is achieved. Optical band gap of the homo-structures is of the order of 3.4-3.5 eV. Raman and photoluminescence spectra indicate the presence of defects in the films. The thin films exhibit a strong defect related photoluminescence peak centred around 550 nm. The nanowires grown on the films display both the UV-near band edge peak as well as the defect related peak. However, the intensity of the defect peak decreases with increase in length of the nanowires indicating that the photoluminescence of the homo-structures can be tuned by changing the surface microstructure of the films and also the aspect ratio of the nanowires.

A novel non-enzymatic H2O2 sensor using ZnMn2O4 microspheres modified glassy carbon electrode

With a facile solvothermal technique, ZnMn₂O₄ microspheres were synthesized in this work, which were used as enzyme mimics for the electrocatalytic reduction of H₂O₂. The morphology, crystal phase and structure of the ZnMn₂O₄ microspheres underwent characterization under X-ray diffraction spectroscopy, Raman spectroscopy, energy-dispersive spectroscopy, and scanning electron microscopy. The synthesized ZnMn₂O₄ microspheres showed an average diameter of 2 μm with great crystallinity, and exhibited excellent catalytical activity towards H₂O₂ electroreduction in alkaline media. The glassy carbon electrode modified by ZnMn₂O₄ microspheres showed a linear amperometric response for H₂O₂ in a wide concentration range of 0.02 ˜ 15 mM with detection limit of 0.13 μM under the optimized conditions. Besides, the sensor proposed here was successfully used to determine H₂O₂ in milk, suggesting that ZnMn₂O₄ microspheres can be used for non-enzymatic electrochemical sensor applications.

Raman scattering enhancement of a single ZnO nanorod decorated with Ag nanoparticles: synergies of defects and plasmons

Surface-enhanced Raman scattering (SERS) of a single ZnO nanorod (NR) is demonstrated by coating with Ag nanoparticles (NPs). An enhancement factor of 1.2×10³ and 4.4×10² has been obtained for E₂ (high) mode (437  cm^-1) and A₁ (TO) mode (378  cm^-1), respectively. Electron paramagnetic resonance measurements reveal an unintentional donor state in ZnO NRs. The enhancement of deep-level emission and micro-absorption mapping of a single ZnO NR further confirms the presence of the donor state. The SERS is believed to result from the charge transfer between ZnO NRs and Ag NPs, which can be enhanced by the empty donor state in ZnO. Finally, single ZnO NRs coated with Ag can be used as good SERS substrates for small molecule detection. This Letter highlights the interaction between point defects and the SERS effect down to a single semiconductor NR.