Observation of excellent photocatalytic and antibacterial activity of Ag doped ZnO nanoparticles

Nanotechnology is the platform with the greatest promise for scientific advancements. One of the advancement is improvement in photocatalytic and antibacterial performance. This work was undertaken to synthesize un-doped and silver (Ag) doped zinc oxide (ZnO) nanoparticles (NPs) using an inexpensive wet chemical method and to investigate the structural and optical properties, photocatalytic and antibacterial activity. The structural analysis from X-ray diffraction (XRD) pattern of un-doped and Ag-doped ZnO NPs displayed hexagonal wurtzite crystal structure and shifting in the peak position confirms the incorporation of Ag in ZnO lattice. Morphological study done by scanning electron microscope reveals spherical shaped NPs and an increase in grain size with Ag doping, the HRTEM images showed the nanocrystalline nature of particle. The Raman spectra showed variation in vibrational characteristics of the nanoparticles with Ag doping. The functional groups were analyzed using Fourier transform-infrared spectroscopy (FTIR). The optical properties were investigated by UV-visible and photoluminescence (PL) spectroscopic techniques. The Ag-doped ZnO NPs have a notably lower band gap than that of un-doped ZnO NPs, i.e. from 3.04 eV to 2.81 eV as studied by UV-visible spectra. The PL study showed decrease in intensity at near band edge emission with increase in Ag doping concentration indicating reduction in the free charge carrier recombination. These variations in the properties play major role in the enhancement of photocatalytic and antibacterial activity with increase in Ag doping concentration as compared to un-doped zinc oxide nanoparticles. The photo degradation efficiency of 99.12 ± 1% against Methylene Blue dye was achieved in the shortest period of 45 minutes ever reported when irradiated under the solar light and efficiency of 97.33 ± 1% was achieved in 15 min under Xenon Short Arc lamp. The antibacterial study was conducted using the Agar well diffusion method where the diameter of the zone of inhibition (ZOI) was increased from 14 mm to 20 mm and 13 mm to 18 mm against the bacteria Escherchia coli and Bacillus subtilis respectively, rendering this material suitable for photocatalytic degradation and antibacterial applications.

Cobalt-Doped ZnO Nanocomposits for Efficient Dye Degradation: Charge Transfer

Doping enhances the optical properties of high-band gap zinc oxide nanoparticles (ZnO NPs), essential for their photocatalytic activity. We used the combustion approach to synthesize cobalt-doped ZnO heterostructure (CDZO). By creating a mid-edge level, it was possible to tune the indirect band gap of the ZnO NPs from 3.1 eV to 1.8 eV. The red shift and reduction in the intensity of the photoluminescence (PL) spectra resulted from hindrances in electron-hole recombination and sp-d exchange interactions. These improved optical properties expanded the absorption of solar light and enhanced charge transfer. The field emission scanning electron microscopy (FESEM) image and elemental mapping analysis confirmed the CDZO's porous nature and the dopant's uniform distribution. The porosity, nanoscale size (25-55 nm), and crystallinity of the CDZO were further verified by high-resolution transmission electron microscopy (HRTEM) and selected area electron image analysis. The photocatalytic activity of the CDZO exhibited much greater efficiency (k=0.131 min-1) than that of ZnO NPs (k=0.017 min-1). Therefore, doped heterostructures show great promise for industrial-scale environmental remediation applications.

A critical mini-review on doping and heterojunction formation in ZnO-based catalysts

This mini-review on doping and heterojunctions for catalysis applications provides a comprehensive overview of key aspects. Doping, when carried out adequately with a uniform distribution, creates a new energy level that significantly enhances charge transfer and light absorption. This new level alters the material's morphology and enhances intrinsic defects. For instance, ZnO, despite its exceptional band edge concerning oxygen reduction and water oxidation redox potentials, faces the issue of electron-hole recombination. However, forming a heterojunction can effectively aid charge transfer and prolong electron-hole relaxation without recombination. This is where the role of doping and heterojunctions becomes crucial. Additionally, incorporating noble metals with S- and Z-scheme heterojunctions offers a promising mechanism for charge transfer and visible light harvesting, further amplifying the catalytic properties.

Green Synthesis of Metal-Doped ZnO Nanoparticles Using Bauhinia racemosa Lam. Extract and Evaluation of Their Photocatalysis and Biomedical Applications

A fascinating problem in the fields of nanoscience and nanobiotechnology has recently emerged, and to tackle this, the production of metal oxide nanoparticles using plant extracts offers numerous benefits over traditional physicochemical methods. In the present investigation, ZnO nanoparticles were fabricated from Bauhinia racemosa Lam. (BR) leaves extract with various transition metal (TM) dopants (Ni, Mn, and Co). Plant leaves extract containing metal nitrate solutions were utilized as a precursor to synthesize the pristine and TM-doped ZnO nanoparticles. Structural, functional, optical, and surface properties of the fabricated samples were studied by using physicochemical and photoelectrochemical measurements. The organic pollutants tetracycline (TC), ampicillin (AMP), and amoxicillin (AMX) were used in the photocatalytic degradation assessment of the fabricated samples. Through X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigation, the fabricated nanoparticles wurtzite crystal structure was verified. Moreover, Fourier transform infrared (FT-IR) analysis verified the existence of functional groups in the fabricated nanoparticles. The migration of electrons from the deep donor level and zinc interstitial to the Zn-defect and O-defect is related to the emission peaks seen at 468, 480, 534, and 450 nm in photoluminescence (PL) spectra. Co-ZnO nanoparticles demonstrated potent and excellent photocatalytic degradation performance for TC (91.09%), AMP (87.97%), and AMX (92.42%) antibiotics within 210, 180, and 150 min of visible light irradiation. Co-ZnO nanoparticles also demonstrated strong antimicrobial performance against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Aspergillus flavus, Aspergillus niger, and Bacillus subtilis. Further investigation of in vitro cytotoxic potential against the A549 cell line (IC50 = 24 ± 0.5 μg/mL) utilizing MTT assay and the free radical scavenging performance of Co-ZnO nanoparticles estimated by DPPH assay utilizing l-ascorbic acid as a reference was also performed. Anti-inflammatory potential is also reviewed by comparing it with the standard drug Diclofenac, and the maximum activity was obtained for Ni-ZnO nanoparticles (IC50 = 72.4 μg/mL).

UV photodetectors based on W-doped ZnO thin films

W-doped ZnO thin films deposited on Si substrates with (100) orientation by sol-gel spin coating method at temperature 500 °C. W/Zn atomic ratio varies from 0% to 4%. Then, the UV detection performance analysis ofp-nheterojunction UV photodetectors based on W-doped ZnO/Si is analyzed. The current-voltage curves of W-doped ZnO/Si are investigated in dark and exhibit diode-like rectifying behavior. Among doped ZnO/Si, sample with atomic ratio of W/Zn = 2% is the best candidate to study photodetector characteristics in UV range. The resulting device exhibits a rectification ratioRRof 5587 at ±5 V, a higher responsivity of 3.84 A W-1and a photosensitivity value of 34 at 365 nm under 0.5 mW cm-2. The experimental findings reveal that the UV detection performance of the heterojunction-based photodetectors strongly dependent on the properties of metal oxide layer. The main goal of this work is to investigate the effect of W doping on the performance of ZnO/Si based photodetectors. Based on our results, it is observed that 2 at% of W dopant is the optimum amount of doping for high performance photodetector of ZnO:W/Si heterojunction thanks to the suppressed recombination ratio and enhanced carrier separation properties in the depletion zone.

Impact of Co-Doping on the Visible Light-Driven Photocatalytic and Photoelectrochemical Activities of Eu(OH)3

The microwave-assisted synthesis approach was used to synthesize Eu(OH)3 and Co-Eu(OH)3 nanorods. Various techniques were used to investigate the structural, optical, and morphological features of the Eu(OH)3 and Co-Eu(OH)3 NRs. Both Eu(OH)3 and Co-Eu(OH)3 NRs were found to be hexagonal with crystallite sizes ranging from 21 to 35 nm. FT-IR and Raman spectra confirmed the formation of Eu(OH)3 and Co-Eu(OH)3. Rod-shaped Eu(OH)3 and Co-Eu(OH)3 with average lengths and diameters ranging from 27 to 50 nm and 8 to 12 nm, respectively, were confirmed by TEM. The addition of Co was found to increase the particle size. Furthermore, with increased Co doping, the band gap energies of Co-Eu(OH)3 NRs were lowered (3.80-2.49 eV) in comparison to Eu(OH)3, and the PL intensities with Co doping were quenched, suggesting the lessening of electron/hole recombination. The effect of these altered properties of Eu(OH)3 and Co-Eu(OH)3 was observed through the photocatalytic degradation of brilliant green dye (BG) and photoelectrochemical activity. In the photocatalytic degradation of BG, 5% Co-Eu(OH)3 had the highest response. However, photoelectrochemical experiments suggested that 10% Co-Eu(OH)3 NRs showed improved activity when exposed to visible light. As a result, Co-Eu(OH)3 NRs have the potential to be a promising visible-light active material for photocatalysis.

Hexagonally close-packed three-dimensional nano-flower entrapped on a heteroatom doped carbon sheets: A sensitive electro-catalyst to determine sulfonamide in environmental samples

Sulfamethazine (SMZ) is one of the antibiotics frequently found with low concentrations in water bodies including drinking water sources and foodstuffs contamination, which affects the environmental ecosystem and humans. Therefore, the detection of SMZ is necessary to protect the biosphere. This work provides an investigation of the SMZ oxidation process using the electrochemical method by hydrothermally synthesized Barium doped Zinc oxide (BZO) with nitrogen and boron-doped reduced graphene oxide (NBRGO). The BZO/NBRGO composite was characterized using FESEM, EDAX, HR-TEM, Raman-spectroscopy, XRD, and XPS. Further, an electrochemical investigation has also made use of EIS, CV, and DPV. The limit of detection (LOD) of the SMZ has been found 0.003 μM with high sensitivity of 12.804 µA µM-1 cm-2 and a linear range (0.01-711 μM). Additionally, the repeatability, reproducibility, and stability of the BZO/NBRGO electrode have an excellent outcome compared with other electrodes. These prepared BZO/NBRGO electrodes have been used for the determination of SMZ in milk and water sample with acceptable recoveries.

Coexistence of ferromagnetic-antiferromagnetic ground state, exchange bias effect and bandgap narrowing in Cr-doped ZnO nanocrystals derived by simple chemical method

A detailed investigation of the structural, optical and magnetic properties of Cr-doped ZnO nanostructures obtained via a simple chemical method has been carried out. The structural study using X-ray powder diffraction indicates the hexagonal wurtzite structure for undoped ZnO and ZnO doped with 1% Cr, whereas the appearance of a secondary cubic phase (ZnCr2O4) is witnessed with the incorporation of Cr content ≥3% in the ZnO compounds. Furthermore, the secondary phase is observed to increase systematically with the increase of the Cr concentration. Field emission scanning electron microscopy and high-resolution transmission electron microscopy studies indicate cuboid, hexagonal and rod-type structural morphology in all the nanocrystals. The presence of the cubic structure along with the hexagonal structure is further confirmed from the selected area electron diffraction pattern. Raman spectroscopy has been used to study the crystalline quality, defects and disorder present in the host lattice. UV-visible spectra were obtained to study the effect of Cr doping on the optical absorption and hence to determine the bandgap, and show a decrease in bandgap with increasing Cr concentration. PL spectra show near-band-edge emission along with visible emission, which decreases with a higher concentration of Cr-doped nanocrystals. X-ray photoelectron spectroscopy analysis indicates the incorporation of Cr3+ and Cr2+ ions in the ZnO lattice. Detailed magnetic studies reveal the co-existing ferromagnetic (FM) and antiferromagnetic (AFM) ground states, which result in the observation of an exchange bias (EB) effect in all the doped compounds. The observation of an EB effect arises from the coupling between the FM and AFM components in the Cr-containing ZnO nanocrystals, and provides a way to design new principles and materials platform that are useful for futuristic spintronic devices.

Suppression of Visible Emission in Low-Temperature Synthesized Cobalt-Doped ZnO Nanoparticles and Their Photosensing Applications

Cobalt (Co)-doped ZnO nanoparticles have been synthesized at 100 °C using a simple chemical technique, without post-deposition annealing. These nanoparticles are of excellent crystallinity and show a significant reduction in defect density upon Co-doping. By varying the Co solution concentration, it is observed that oxygen-vacancy-related defects are suppressed at lower Co-doping, while the defect density shows an increasing trend at higher doping densities. This suggests that mild doping can significantly suppress the defects in ZnO for electronic and optoelectronic applications. The effect of Co-doping is studied using X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), electrical conductivity, and Mott-Schottky plots. Photodetectors fabricated using pure and Co-doped ZnO nanoparticles show a noticeable reduction in the response time upon Co-doping, which again affirms the reduction in the defect density after Co-doping.

Structural, magnetic and optical properties of disordered double perovskite Gd2CoCrO6 nanoparticles

We have synthesized disordered double perovskite Gd2CoCrO6 (GCCO) nanoparticles with an average particle size of 71 ± 3 nm by adopting a citrate sol-gel method to investigate their structural, magnetic, and optical properties. Rietveld refinement of the X-ray diffraction pattern showed that GCCO is crystallized in a monoclinic structure with space group P21/n, which is further confirmed by Raman spectroscopic analysis. The absence of perfect long-range ordering between Co and Cr ions is confirmed by the mixed valence states of Co and Cr. A Néel transition was observed at a higher temperature of TN = 105 K compared to that of an analogous double perovskite Gd2FeCrO6 due to a greater degree of magnetocrystalline anisotropy of Co than Fe. Magnetization reversal (MR) behavior with a compensation temperature of Tcomp = 30 K was also observed. The hysteresis loop obtained at 5 K exhibited the presence of both ferromagnetic (FM) and antiferromagnetic (AFM) domains. Super-exchange and Dzyaloshinskii-Moriya (DM) interactions between various cations via oxygen ligands are responsible for the observed FM or AFM ordering in the system. Furthermore, UV-visible and photoluminescence spectroscopy demonstrated the semiconducting nature of GCCO with a direct optical bandgap of 2.25 eV. The Mulliken electronegativity approach revealed the potential applicability of GCCO nanoparticles in photocatalytic H2 and O2 evolution from water. Due to a favorable bandgap and potentiality as a photocatalyst, GCCO can be a promising new member of double perovskite materials for photocatalytic and related solar energy applications.

Bos taurus (A-2) urine assisted bioactive cobalt oxide anchored ZnO: a novel nanoscale approach

In this study, a novel synthetic method for cobalt oxide (Co3O4) nanoparticles using Bos taurus (A-2) urine as a reducing agent was developed. In addition to this ZnO nanorods were produced hydrothermally and a nanocomposite is formed through a solid-state reaction. The synthesized materials were characterized through modern characterization techniques such as XRD, FE-SEM with EDS, DLS, zeta potential, FT-IR, Raman spectroscopic analysis, and TGA with DSC. The free radical destructive activity was determined using two different methods viz. ABTS and DPPH. The potential for BSA denaturation in vitro, which is measured in comparison to heat-induced denaturation of egg albumin and results in anti-inflammatory effects of nanomaterial was studied. All synthesized nanomaterials have excellent antibacterial properties, particularly against Salmonella typhi and Staphylococcus aureus. The composite exhibits excellent antioxidant and anti-inflammatory activities in comparison to pure nanomaterials. This reveals that these nanomaterials are advantageous in medicine and drug administration.

Multifunctional ZnO-Co3O4 @ polymer hybrid nanocoatings with controlled adsorption, photocatalytic and anti-microbial functions for polluted water systems

Triple action pollutant responsive multi-layer hybrid nanocoatings of architecture PEI(PAA/ZnO-Co3O4)n were constructed through ZnO-Co3O4 binary oxide co-precipitation followed by its inclusion in multi-layer polymeric thin films using Layer-by-Layer (LbL) deposition. Characterization of the designed architecture was carried out via FTIR, XRD, UV-Vis, and Raman spectroscopic studies to evaluate the chemical nature, bonding, and crystallographic behavior of ZnO-Co3O4. Peaks of ZnO-Co3O4 were recorded at 586.38, 486.08, and 443.64 cm-1 while pronounced shifting of ZnO characteristic E2 (high) peak ~ 450 cm-1 and appearance of modes around 495, 530, 630, and 719 cm-1 indexed via Raman studies validated Co3O4 impregnation into ZnO structure. XRD patterns of ZnO-Co3O4 compared to their previously reported pristine structures also justified the formation of binary oxide as unit composite. SEM micrographs confirmed homogenous multi-layered depositions while EDX analysis confirmed their uniform elemental distribution in the unit structure. Sequential multi-layer buildup up to 48 layer pairs was monitored using ellipsometry with maximum film thickness ~ 89 nm and by UV-Vis at 376 nm. The prepared thin films exhibited significant photodegradation of methylene blue ~ 91% and Cu (II) adsorption capacity ~ 89% within first 90 min of contact, along with prominent bactericidal efficiency against E. coli within 24 h of reaction time. FAAS, ICP-OES, and UV-Vis spectroscopy analyses make these multifunctional hybrid nanocoatings promising for industrial wastewater as well as drinking water purification setups. Furthermore, protuberant recycling and regenerative capacity make these hybrid nanocoatings an eco-friendly system for hydro-remediation.

Vertically Oriented Zinc Oxide Nanorod-Based Electrolyte-Gated Field-Effect Transistor for High-Performance Glucose Sensing

Nanomaterial-based biosensors are a promising fit for portable and field-deployable diagnosis sensor devices due to their mass production, miniaturization, and integration capabilities. However, the fabrication of highly stable and reproducible biosensor devices is challenging. In this work, we grow a vertically oriented architecture of zinc oxide nanorods onto the active working area (i.e., the channel between the source and drain) of a field-effect transistor (FET) using a low-temperature hydrothermal method. The glucose oxidase enzyme was immobilized on the zinc oxide nanorod surface by a physical adsorption method to fabricate the electrolyte-gated FET-based glucose biosensor. The electrical properties of the electrolyte-gated FET biosensor were measured with different glucose concentrations. We found a linear increase in current up to 80 mM glucose concentration with high sensitivity (74.78 μA/mMcm²) and a low detection limit (∼0.05 mM). We illustrate a highly reproducible fabrication process of zinc oxide nanorod-based FETs, where vertically grown nanorods with a higher surface-to-volume ratio enhance the enzyme immobilization, provide a microenvironment for longer enzyme activity, and translate to better glucose sensing parameters. Additionally, our electrolyte-gated FET biosensor showed promising application in freshly drawn mouse blood samples. These findings suggest a great opportunity to translate into practical high-performance biosensors for a broad range of analytes.

Green Synthesis of Metal Oxides Semiconductors for Gas Sensing Applications

During recent decades, metal oxide semiconductors (MOS) have sparked more attention in various applications and industries due to their excellent sensing characteristics, thermal stability, abundance, and ease of synthesis. They are reliable and accurate for measuring and monitoring environmentally important toxic gases, such as NO₂, NO, N₂O, H₂S, CO, NH₃, CH₄, SO₂, and CO₂. Compared to other sensing technologies, MOS sensors are lightweight, relatively inexpensive, robust, and have high material sensitivity with fast response times. Green nanotechnology is a developing branch of nanotechnology and aims to decrease the negative effects of the production and application of nanomaterials. For this purpose, organic solvents and chemical reagents are not used to prepare metal nanoparticles. On the contrary, the synthesis of metal or metal oxide nanoparticles is done by microorganisms, either from plant extracts or fungi, yeast, algae, and bacteria. Thus, this review aims at illustrating the possible green synthesis of different metal oxides such as ZnO, TiO₂, CeO₂, SnO₂, In₂O₃, CuO, NiO, WO_3, and Fe₃O₄, as well as metallic nanoparticles doping.

Ferromagnetic Behavior and Magneto-Optical Properties of Semiconducting Co-Doped ZnO

ZnO is a well-known semiconducting material showing a wide bandgap and an n-type intrinsic behavior of high interest in applications such as transparent electronics, piezoelectricity, optoelectronics, and photovoltaics. This semiconductor becomes even more attractive when doped with a few atomic percent of a transition metal. Indeed, e.g., the introduction of substitutional Co atoms in ZnO (ZCO) induces the appearance of room temperature ferromagnetism (RT-FM) and magneto-optical effects, making this material one of the most important representatives of so-called dilute magnetic semiconductors (DMSs). In the present review, we discuss the magnetic and magneto-optical properties of Co-doped ZnO thin films by considering also the significant improvements in the properties induced by post-growth irradiation with atomic hydrogen. We also show how all of these properties can be accounted for by a theoretical model based on the formation of Co-V_O (oxygen vacancy) complexes and the concurrent presence of shallow donor defects, thus giving a sound support to this model to explain the RT-FM in ZCO DMSs.

Biogenic synthesis of silver anchored ZnO nanorods as nano catalyst for organic transformation reactions and dye degradation

In this study, we are reporting biogenic synthesis of silver nanoparticles and hydrothermal synthesis of zinc oxide nanoparticles. Using convenient mechanical milling methods, nanocomposites with superior photocatalytic and catalytic properties are synthesized. Herein, we have adopted a green, eco-friendly, and economical route for the synthesis of Ag nanoparticles using Zingiber officinalae rhizome extract in an aqueous solution. The synthesized materials were characterized using UV–Vis spectroscopy, XRD, SEM & FE-SEM, FT-IR, Raman, and a particle size analyzer with zeta potential analysis. The photocatalytic activities of Ag, ZnO and their composites were studied by observing the degradation of methylene blue and crystal violet dyes under natural sunlight. Then the catalytic efficacies of synthesized nanoparticles for various organic transformation reactions were studied. Ag–ZnO nanocomposites were predicted to have improved photocatalytic activity and organic transformation reactions, allowing them to be used in environmental remediation applications.

The effect of Mn and Co dual-doping on the structural, optical, dielectric and magnetic properties of ZnO nanostructures

This paper addresses the effect of Mn (2%, fixed) and Co (2, 4, and 6%, varied) substitution on the structural, optical, dielectric and magnetic responses of ZnO nanoparticles synthesized by the co-precipitation chemical route. The X-ray diffraction analysis confirms the hexagonal wurtzite structure of ZnO. The incorporation of co-doping in the ZnO host, indicated by peak shifting in the XRD patterns, enhanced the crystallite size of the Mn/Co dual-doped ZnO nanoparticles. The FTIR spectra show a characteristic peak around 875 cm-1 assigned to Zn-O stretching, this validates the formation of the wurtzite structure of ZnO. Raman spectroscopy reveals the characteristic band of the wurtzite structure of ZnO nanoparticles along with coupled vibration modes of Mn/Co with the donor defect states in the doped samples. Enhanced optical absorption in the visible region and a significant red-shift in the absorption band edge were found due to doping. The optical band gap is found to decrease from 3.45 eV to 3.15 eV when Co doping increases up to 6%. The dielectric properties, strongly frequency-dependent, decrease with increasing Co doping while the electrical conductivity increases. Ferromagnetism is observed in all the doped samples, and its origin is attributed to an increase in oxygen vacancies which form bound magnetic polarons. It can be inferred that the doping of Mn and Co can be an effective tool to tune the physical properties of ZnO nanoparticles for potential spintronics and high-frequency applications.

The role of size-controlled CeO2 nanoparticles in enhancing the stability and photocatalytic performance of ZnO in natural sunlight exposure

In order to enhance the photocatalytic performance and stability, the various proportions of the size controlled cerium oxide (CeO₂) nanoparticles were dispersed at the pre-synthesized ZnO. Although, the expected dual absorption onsets, probably due to the diminutive difference between the bandgaps of CeO₂ (∼2.9 eV) and ZnO (∼3.1 eV), were not observed however, a blue shift in the bandgap energy of ZnO was witnessed with the increasing surface density of CeO₂ particles. The delayed excitons recombination process with the increasing concentration of CeO₂ nanoparticles was verified by the PL spectra. The structural investigation by Raman and XRD analysis revealed the surface attachment of CeO₂ particles without altering the rock-salt lattice of ZnO. The morphological and fine microstructural analysis established the uniform distribution of evenly sized CeO₂ particles at the surface of ZnO with the discrete fringe patterns of both the entities whereas the XPS analysis confirmed the majority of Ce⁴⁺ in dispersed CeO₂. In comparison to pure ZnO, cyclic voltammetric (CV) analysis, under illumination, exposed the supportive role of surface residing CeO₂ particles in eradicating the photo-corrosion of ZnO whereas the chronopotentiometry (CP) predicted the prolonged life-span of the excitons. Compared to pure ZnO, an appreciably high activity was revealed for 10% CeO₂ loading as compared to pure ZnO for the removal of mono and di-nitrophenol derivatives and their mixtures under natural sunlight exposure. The variations in the removal rates in the mixture as compared to individual nitrophenol exposed the structure-based priority of ROS for the respective phenol. The significantly enhanced photocatalytic activity of the composite catalysts revealed the incremental role of surface-mounted CeO₂ entities in boosting the generation of ROS under sunlight irradiation. The experimental observations were correlated and compiled to establish the mechanism of the removal process.

Effect of Ni and Al doping on structural, optical, and CO2 gas sensing properties of 1D ZnO nanorods produced by hydrothermal method

In the present study, the one-dimensional ZnO nanorod structures are produced within the different nickel and aluminum molecular weight ratios of 0-7% using the hydrothermal method. It is found that the aluminum (Al) and nickel (Ni) impurities with different ionic radius, chemical valence, and electron configurations of outer shell cause to vary the fundamental characteristic features including the crystallinity quality, crystallite size, surface morphology, nanorod diameter, optical absorbance, energy band gap, resistance, gas response, and gas sensing properties. The structural analyses performed by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the samples are found to crystallize in the hexagonal wurtzite structure. The presence of optimum nickel and aluminum in the crystal system improves considerably the crystallinity quality and surface morphology. Additionally, the combination of electron dispersive X-ray (EDX) and XRD results declare that the Ni and Al impurities incorporate successfully into the ZnO crystal structure. Moreover, the diameters of nanorod structures in 1D orientation are determined to be 80 nm or below. The hexagonal wurtzite-type ZnO nanorod structure prepared by 5% Ni has more space between the nanorods and thus presents higher response to the CO₂ detection. Further, the optical absorbance spectra display that the band gap value is observed to decrease regularly with the increment in the doping level as a result of band shrinkage effect depending on the enhancement of mobile hole carrier concentrations in the crystal structure. In other words, the doping mechanism leads to vary the homogeneities in the interfacial charges, nanorod diameters, ZnO oxide layer composition and thickness. The last test conducted in this study is responsible for the determination of CO₂ gas sensing levels. The obtained gas sensing results are further compared with each other and literature findings. It is observed that 5% Ni-doped sample provides more successful results than other samples in the sensing CO₂ gas at the different concentrations. All in all, the paper establishing a strong methodology between doping mechanism and change in the fundamental characteristic features of hexagonal wurtzite-type ZnO with the aid of advanced microscopy techniques will become pioneering research to answer key questions in materials sciences and electronic research.

Enhanced Optical and Antibacterial Activity of Hydrothermally Synthesized Cobalt-Doped Zinc Oxide Cylindrical Microcrystals

Cobalt (Co) doped zinc oxide (ZnO) microcrystals (MCs) are prepared by using the hydrothermal method from the precursor's mixture of zinc chloride (ZnCl2), cobalt-II chloride hexahydrate (CoCl2·6H2O), and potassium hydroxide (KOH). The smooth round cylindrical morphologies of the synthesized microcrystals of Co-doped ZnO show an increase in absorption with the cobalt doping. The antibacterial activity of the as-obtained Co-doped ZnO-MCs was tested against the bacterial strains of gram-negative (Escherichia coli, Klebsiella pneumonia) and gram-positive bacteria (Staphylococcus aureus, Streptococcus pyogenes) via the agar well diffusion method. The zones of inhibition (ZOI) for Co-doped ZnO-MCs against E. coli and K. pneumoniae were found to be 17 and 19 mm, and 15 and 16 mm against S. Aureus and S. pyogenes, respectively. The prepared Co-doped ZnO-MCs were thus established as a probable antibacterial agent against gram-negative bacterial strains.

Influence of Cu doping on the local electronic and magnetic properties of ZnO nanostructures

In this paper, we report the existence of defect induced intrinsic room-temperature ferromagnetism (RTFM) in Cu doped ZnO synthesized via a facile sol-gel route. The wurtzite crystal structure of ZnO remained intact up to certain Cu doping concentrations under the present synthesis environment as confirmed by the Rietveld refined X-ray diffraction pattern with the average crystallite size between 35 and 50 nm. Field emission scanning electron microscopy reveals the formation of bullet-like morphologies for pure and Cu doped ZnO. Diffuse reflectance UV-vis shows a decrease in the energy band gap of ZnO on Cu doping. Further, these ZnO samples exhibit strong visible photoluminescence in the region of 500-700 nm associated with defects/vacancies. Near-edge X-ray absorption fine-structure measurements at Zn, Cu L3,2- and O K-edges ruled out the existence of metallic Cu clusters in the synthesized samples (up to 2% doping concentration) supporting the XRD results and providing the evidence of oxygen vacancy mediated ferromagnetism in Cu : ZnO systems. The observed RTFM in Cu doped ZnO nanostructures can be explained by polaronic percolation of bound magnetic polarons formed by oxygen vacancies. Further, extended X-ray absorption fine-structure data at Zn and Cu K-edges provide the local electronic structure information around the absorbing (Zn) atom. The above findings for ZnO nanostructures unwind the cause of magnetism and constitute a significant lift towards realizing spin-related devices and optoelectronic applications.

Doped Zinc Oxide Nanoparticles: Synthesis, Characterization and Potential Use in Nanomedicine

Smart nanoparticles for medical applications have gathered considerable attention due to an improved biocompatibility and multifunctional properties useful in several applications, including advanced drug delivery systems, nanotheranostics and in vivo imaging. Among nanomaterials, zinc oxide nanoparticles (ZnO NPs) were deeply investigated due to their peculiar physical and chemical properties. The large surface to volume ratio, coupled with a reduced size, antimicrobial activity, photocatalytic and semiconducting properties, allowed the use of ZnO NPs as anticancer drugs in new generation physical therapies, nanoantibiotics and osteoinductive agents for bone tissue regeneration. However, ZnO NPs also show a limited stability in biological environments and unpredictable cytotoxic effects thereof. To overcome the abovementioned limitations and further extend the use of ZnO NPs in nanomedicine, doping seems to represent a promising solution. This review covers the main achievements in the use of doped ZnO NPs for nanomedicine applications. Sol-gel, as well as hydrothermal and combustion methods are largely employed to prepare ZnO NPs doped with rare earth and transition metal elements. For both dopant typologies, biomedical applications were demonstrated, such as enhanced antimicrobial activities and contrast imaging properties, along with an improved biocompatibility and stability of the colloidal ZnO NPs in biological media. The obtained results confirm that the doping of ZnO NPs represents a valuable tool to improve the corresponding biomedical properties with respect to the undoped counterpart, and also suggest that a new application of ZnO NPs in nanomedicine can be envisioned.

Bi-doping improves the magnetic properties of zinc oxide nanowires

Room-temperature ferromagnetism in the large and direct bandgap diluted magnetic semiconductor zinc oxide (ZnO) is attributed to the intrinsic defects and p-orbital–p-orbital (p–p) coupling interaction. However, due to oxidation, the ferromagnetism induced by defects is unstable. In the present work, the solution process synthesis route was utilized to grow pristine and bismuth-doped, highly crystalline ZnO nanowire (ZnO NW)-based samples. The FE-SEM images showed that the grown ZnO NWs have a preferred orientation along the c-axis in the (001) direction due to the anisotropic crystal nature of ZnO. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Bi, and at a higher doping content, the bismuth oxide phase appeared. The XRD patterns showed the wurtzite crystal structure, and the large intensity of the (002) peak suggests that most of the reflection was from the top hexagonal face of the NWs, and thus, the wires are predominantly aligned along the c-axis. The TEM analysis further confirmed the crystal growth direction along the (001) direction. The UV-Visible absorption and PL measurements also showed a decrease in the bandgap with an increase in doping concentration, which may be associated with the sp–d exchange interaction between the localized d-electrons and band electrons of the Bi ions. Bi-doping tended to increase the PL intensity in the visible region. The magnetic properties measured by SQUID at 4 and 300 K showed ferromagnetic behaviour for both the pristine and Bi-doped samples. However, the saturation magnetization for the Bi-doped samples was higher compared to that of the pristine ZnO samples until the threshold doping value. The obtained results demonstrated that Bi-doping can be used to tune both the optical and magnetic properties of ZnO NWs, hence paving the way for future spintronics and spin-polarized optoelectronics applications.

Room-temperature ferromagnetism in the large and direct bandgap diluted magnetic semiconductor zinc oxide (ZnO) is attributed to the intrinsic defects and p-orbital–p-orbital (p–p) coupling interaction.

Theoretical model investigating the magnetic properties of cobalt-doped ZnO

We propose a theoretical model to investigate the magnetic properties of cobalt-doped ZnO (ZnO:Co) thin films qualitatively. The model was built on the dilute Co dopants in the host of ZnO forming the magnetic Co⁺² ions and the energy level of the magnetic ions crossing the band edge of ZnO resulting in a magnetic interaction between the Co⁺² spins and the spins of the electrons from the conduction band of ZnO. The mechanism of the ferromagnetism revealed in the studied system is proposed here to be induced not only by the mediated conducting electrons via spin interactions but also by the Coulomb excitations, arising from the electrons localized by the oxygen vacancies. This approach of including Coulomb excitation in the modified carrier-mediated model could explain well the magnetic properties of ZnO:Co and solves the drawback of the carrier-mediated model in interpreting the appearance of ferromagnetism in the insulating ZnO:Co. We propose that the Coulomb excitations induced by the electrons captured by the oxygen vacancies are an essential element in the magnetic ZnO, which reveals the fact that the bound magnetic polaron model without considering the Coulomb excitation is insufficient to describe the magnetic properties of ZnO.

Segregation tendencies of transition-metal dopants in wide band gap semiconductor nanowires

The segregation tendency of an impurity in a semiconductor nanowire can be tuned by adjusting the Fermi level position.

Impact of Mn-dopant concentration in observing narrowing of band-gap, urbach tail and paramagnetism in anatase TiO2 nanocrystals

In addition to the numerous applications of Mn-doped TiO₂, it could be a potential candidate as a dilute magnetic semiconductor.

The structure and photoluminescence of a ZnO phosphor synthesized by the sol gel method under praseodymium doping

This work outlines some interesting results regarding the effects of Pr³⁺ substitution on the structural and optical properties of (x = 0 and 0.02) samples.

Unraveling the effect of Gd doping on the structural, optical, and magnetic properties of ZnO based diluted magnetic semiconductor nanorods

The structural, magnetic, and optical properties of the pristine and Gd-doped ZnO nanorods (NRs), prepared by facile thermal decomposition, have been studied using a combination of experimental and density functional theory (DFT) with Hubbard U correction approaches. The XRD patterns demonstrate the single-phase wurtzite structure of the pristine and doped ZnO. The rod-like shape of the nanoparticles has been examined by FESEM and TEM techniques. Elemental compositions of the pure and doped samples were identified by EDX measurement. Due to the Burstein–Moss shift, the optical band gaps of the doped samples have been widened compared to pristine ZnO. The PL spectra show the presence of complex defects. Room temperature magnetic properties have been measured using VSM and revealed the coexistence of paramagnetic and weak ferromagnetic ordering in Gd³⁺ doped ZnO-NRs. The magnetic moment was increased upon addition of more Gd ions into the ZnO host lattice. The DFT+U calculations confirm that the presence of vacancy-complexes has a significant effect on the structural, electronic, and magnetic properties of a pristine ZnO system.

Gd doped ZnO nanorods.

Defect mediated mechanism in undoped, Cu and Zn-doped TiO2 nanocrystals for tailoring the band gap and magnetic properties

Oxide based dilute magnetic semiconductor materials have been of great interest over the years due to their potential use in spintronic devices. However, the variations in the magnetic behavior of the materials have raised concerns regarding the origin of ferromagnetic properties which still needs to be explored. Manipulation of magnetic behavior in oxide based dilute magnetic semiconductors has become a challenge due to the interplay of intrinsic defects present in the material. TiO2 nanocrystals have been studied largely due to their challenging optical and magnetic properties. The present investigation studies in detail the structural, morphological, optical and magnetic behavior of non-magnetic element (Cu and Zn) doped TiO2, synthesized via a simple sol-gel technique. X-ray diffraction patterns and Raman spectra confirm the anatase phase and high resolution transmission electron microscopic results clearly indicate the formation of highly crystalline nanocrystals in all the samples with particle size ranging from 5-15 nm. Energy dispersive X-ray fluorescence spectroscopic studies reveal the compositional homogeneity of all the investigated samples. The presence of functional groups and molecular interactions were identified by Fourier transform infrared spectroscopy. Optical properties were studied through UV-visible and photoluminescence spectroscopy from which a significant reduction in band gap in Cu-doped TiO2 nanocrystals was found. X-ray photoelectron spectra confirm the presence of Ti3+, Cu2+, Cu+ and Zn2+ in Cu and Zn-doped TiO2 samples. The concept of bound magnetic polarons associated with the vacancy defects at both Ti, Cu, Zn and oxygen sites is used to explain the induced weak ferromagnetic behavior in undoped, Cu and Zn-doped TiO2 at room temperature. The overlapping of bound magnetic polarons could be the source of ferromagnetism irrespective of the non-magnetic nature of the dopant ion. The concentration of bound magnetic polarons is estimated using a Langevin fit and a detailed understanding of the variation of defect mediated magnetic properties is established with the help of PL analysis. A significant reduction in bandgap along with enhanced magnetization observed in the Cu-doped TiO2 material makes it suitable as a potential candidate for spintronics and magneto-optics applications. Room temperature magnetic properties of the Zn doped sample show a diamagnetic tail which is explained based on the defect centers and oxidation states of dopant ions present in the sample which is further verified with the help of XPS results.

Bacteria killing in ICU associated infections: antibacterial nanosheets as disinfectant

Here we propose Zn–CuO@GO nanosheets that induce rapid bacterial lysis via physically penetrating and wrapping into the cell wall. Such an irreversible damage make them promising as ICU disinfectants to combat ICU-associated multidrug resistant bacteria.

Fiber optic magnetic field sensor using Co doped ZnO nanorods as cladding

A fiber optic magnetic field sensor is proposed and experimentally demonstrated. Pristine and Co doped ZnO nanorods of different Co concentrations (5, 10, 15 and 20 at%) were synthesized using a hydrothermal method. The synthesized nanorods were subjected to various characterization methods like X-ray diffraction (XRD), optical absorption, scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometry and X-ray photoelectron spectroscopy (XPS). XRD and XPS analysis confirms that the Co ions were successfully incorporated into the Zn site of the wurtzite ZnO lattice without altering the structure. The pristine and Co doped ZnO nanorods showed remarkable changes in the M–H loop where the diamagnetic behavior of ZnO changes to paramagnetic when doped with Co. The sensor structure is composed of cladding modified fiber coated with Co doped ZnO nanorods as a sensing material. The modified cladding is proportionally sensitive to the ambient magnetic field because of the magneto-optic effect. Experimental results revealed that the sensor has an operating magnetic field range from 17 mT to 180 mT and shows a maximum sensitivity of ∼18% for 15 at% Co doped ZnO nanorods. The proposed magnetic field sensor would be attractive due to its low cost fabrication, simplicity of the sensor head preparation, high sensitivity and reproducibility.

A fiber optic magnetic field sensor based on Co doped ZnO nanorods is proposed and demonstrated. The sensor has an operating magnetic field range of 17 mT to 180 mT and shows a maximum sensitivity of ∼18% for 15 at% Co doped ZnO nanorods.