Presence of intrinsic defects and transition from diamagnetic to ferromagnetic state in Co<Superscript>2+</Superscript> ions doped ZnO nanoparticles

In this paper, we report the structural, morphological and magnetic properties of pure and Co²⁺ doped ZnO nanoparticles synthesized using sol–gel auto combustion method. The prepared nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area diffraction pattern (SAED), Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy. The analysis of XRD pattern shows the single phase nature with a hexagonal wurtzite structure for the prepared nanoparticles. The average crystallite sizes of the prepared nanoparticles were found in the range 18–19 nm. SEM images showed that pure and Co²⁺ doped nanoparticles have different morphology. The shape of the prepared nanoparticles is approximately hexagonal shown by TEM image. SAED pattern also confirms the wurtzite structure with single crystalline nature. FTIR spectra showed the characteristic vibrations frequency band of Zn–O. Photo luminescence spectrum showed that two emission peaks, which are ascribed to near band edge transitions and broadened intensive green emission associated with oxygen-vacancy defects. The magnetic properties were measured by vibrating sample magnetometer (VSM) and superconducting quantum interference device with field dependant magnetization at 300 K and temperature dependant magnetization from 0 to 300 K. From VSM analysis, pure ZnO nanoparticles show diamagnetic behavior while Co²⁺ doped ZnO nanoparticles revealed ferromagnetic behaviour at room temperature. The significant changes in M–H loop from diamagnetic behavior to ferromagnetic behavior are due to the intrinsic defects such as oxygen vacancies (Vo) and zinc vacancies (Vz_n). The RTFM has been presented in terms of vacancies in the frame of bound magnetic polaron model.     

Magnetic and antibacterial properties of Zr-doped SnO<Subscript>2</Subscript> nanopowders

Zirconium doped tin oxide (SnO₂:Zr) nanopowders were synthesized by a simple soft chemical route adding various concentrations of zirconyl chloride (0, 5, 10 and 15 wt%). The samples were characterized by techniques like XRD, SEM, TEM, EDX, FTIR spectroscopy, UV–Vis-NIR spectroscopy and photoluminescence spectroscopy. XRD studies confirm that all the samples exhibit rutile tetragonal crystal structure with a strong (1 0 1) preferential growth texture. Hexagonal shaped grains were evinced from the SEM images. Nanosized grains are evinced from the TEM images and EDX spectra confirm the presence of Zr in the doped samples. The bands at 523 and 583 cm^?1 observed in the FTIR spectra which are attributed as the characteristics of γ (Sn–OH) terminal bond of the SnO₂ crystalline phase confirm the presence of Sn–O in the synthesized samples. The doped samples exhibit ferromagnetic behavior. Enhanced antibacterial activity was observed for the doped samples. The obtained results show that zirconium strongly influenced the structural, morphological, optical, magnetic and antibacterial properties of pure SnO₂ nanopowders.     

Influence of magnetic ion doping on structural,optical, magnetic and hyperfine properties of nanocrystalline SnO<Subscript>2</Subscript> based dilute magnetic semiconductors

This article reports the structural, optical and magnetic properties of transition metal (Ni, Co, Mn and Fe) doped SnO₂ nanoparticles prepared by modified Pechini sol–gel method. From the X-ray diffraction studies, it is obvious that all the synthesized samples show a phase purity of rutile tetragonal crystal structure of SnO₂. The morphology was studied and the particle sizes were estimated from the field emission scanning electron microscopy. From photoluminescence spectra, we observed emission due to the presence of singly ionized oxygen vacancies. Raman spectroscopy shows dominant peaks at 644 and 782 cm^?1 which were ascribed to A_1g and B_2g modes of the rutile structure. Isomer shifting due to dopant addition and large quadrupole splitting due to surface defects were observed in Mössbauer spectra. All the samples show ferromagnetic ordering up to 1 T. The relatively stronger ferromagnetic nature in Fe and Co doped SnO₂ is due to the strong p–d exchange interaction. In case of Ni and Mn doped SnO₂ samples, the lack of carrier-mediated interaction due to its inherent semiconducting nature reduces the total magnetic moment observed in these samples. The exchange coupling depends on the dopant type and its concentration.     

Vanadium doped SnO<Subscript>2</Subscript> nanoparticles for photocatalytic degradation of methylene blue

Nanometric V-doped particles with vanadium concentration varying from 0 to 10% were prepared using the polyol method. The influence of the doping on the textural, structural and optical properties was studied by various methods of characterization. X-ray diffraction (XRD) patterns disclose that nanocrystallites of cassiterite, i.e. rutile-like tetragonal structure SnO₂ and the absence of a new vanadium phase in the XRD pattern in the different concentration of doping were formed after annealing, the ordinary crystallite size decreased from 20.6 to 12.3 when the doping concentration increased from 0 to 10%, respectively. Moreover, the N₂ sorption porosimetry and transmission electron microscopic show that all samples synthesized were constituted of an aggregated network of almost spherical nanoparticles, which sizes changed with the altitude in the doping concentration to 10%. In accordance with UV–visible absorption measurements, this diminution of nanoparticles sizes was followed by a decrease in the band gap value from 3.25 eV, for undoped SnO₂, to 2.75 eV, for SnO₂ doped at 10%. On the other part, the photocatalytic activity of undoped and V-doped SnO₂ nanoparticles was studied using methylene blue (MB) as model organic pollutants. The SnO₂ nanoparticles doped at 10% of vanadium disclosed that the discoloration of MB reached 97.4% after irradiation of 120 min, with an apparent constant rate of the degradation reaching 0.035 min^?1 for MB degradation that was about 2.5 times more than that of pure SnO₂ (0.014 min^?1).     

A Novel Approach: Hydrothermal Method of Fine Stabilized Superparamagnetics of Cobalt Ferrite (CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>) Nanoparticles

Spinel CoFe₂O₄ nanoparticles were synthesized by a simple, economical, and eco-friendly hydrothermal method (HM) using metal nitrates and polyvinyl pyrrolidone. The structural, morphological, and magnetic properties of the products were determined and characterized in detail by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL) spectroscopy, vibrating sample magnetometry (VSM), and Brunauer–Emmett–Teller (BET) surface area analysis. Key parameters influencing the structural performance, such as particle size and shape, annealing temperature, functionalization, and magnetic properties, have been comprehensively discussed. The effect of the catalyst and solvent on the catalytic oxidation of benzyl alcohol using the CoFe₂O₄ nanoparticle catalyst prepared by hydrothermal method was also investigated.     

Investigation of ethanol gas sensing properties of Dy-doped SnO<Subscript>2</Subscript> nanostructures

In this paper we report doping induced enhanced sensor response of SnO₂ based sensor towards ethanol at a working temperature of 200 °C. Undoped and dysprosium-doped (Dy-doped) SnO₂ nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD and Raman results verified tetragonal rutile structure of the prepared samples. It has been observed that crystallite size reduced with increase in dopant concentration. In addition, the particle size has been calculated from Raman spectroscopy using phonon confinement model and the values match very well with results obtained from TEM and X-ray diffraction investigations. Dy-doped SnO₂ sensors exhibited significantly enhanced response towards ethanol as compared to undoped sensor. The optimum operating temperature of doped sensor reduced to 200 °C as compared to 320 °C for that of undoped sensor. Moreover, sensor fabricated from Dy-doped SnO₂ nanostructures was highly selective toward ethanol which signifies its potential use for commercial applications. The gas sensing mechanism of SnO₂ and possible origin of enhanced sensor response has been discussed.     

Effect of Mn doping on structural,optical and magnetic properties of SnO<Subscript>2</Subscript> nanoparticles by solvothermal processing

This paper highlights on the consequence of replacing tetravalent Sn⁴⁺ ions of the SnO₂ by divalent Mn²⁺ ions on their structural, optical and magnetic properties. Samples of Sn_1?xMn_xO₂ with x?=?0.01, 0.02, 0.03 and 0.04 were synthesized using microwave irradiated solvothermal process. The X-ray powder diffraction patterns reveal the rutile tetragonal phase of all doped SnO₂ samples with no secondary phases. The transmission electron microscopy results show the formation of spherical nanoparticles of size 10–16 nm. Morphological changes were observed by scanning electron microscopy. The functional groups were investigated using Fourier Transform Infrared Spectroscopy studies. Optical studies were carried by UV–Vis Spectroscopy and Fluorescence Spectroscopy. Electron Paramagnetic resonance was used to calculate the Lande splitting factor ‘g’. The magnetic properties were using Vibrating Sample Magnetometer. SnO₂ with lower Mn doping shows ferromagnetism.     

VLS and VS effect on ferromagnetic behaviour of SnO2 nanobelts

Fabrication of SnO₂ nanobelts has been carried out by employing vapour liquid solid (VLS) and vapour solid (VS) mechanism. Nanobelts obtained by VLS mechanism were fabricated at relatively low temperature using Fe powders as a catalyst by means of chemical vapour deposition (CVD) technique. Direct thermal evaporation of SnO₂ nanobelts was carried out at 1350°C in the atmosphere of Argon gas via VS mechanism. In both cases, ramp rate was adjusted to 10°C/min. The structural, compositional and morphological characterisations of synthesised SnO₂ nanobelts were conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X?ray spectroscopy (EDS). Magnetic behaviour of the nanobelts was studied by vibrating sample magnetometer (VSM). Cathodoluminescence (CL) spectra were studied using Renishaw Raman spectroscopy system. The growth of nanobelts is found to be homogeneous and dense. The nanobelts formed by VLS mechanism show ferromagnetic behaviour along with some other exciting results whereas the nanobelts formed by VS mechanism show a diamagnetic behaviour. The observed room temperature ferromagnetism in SnO₂ nanobelts is superior to other oxides.     

A facile one step synthesis of SnO<Subscript>2</Subscript>/CuO and CuO/SnO<Subscript>2</Subscript> nanocomposites: photocatalytic application

Here novel photocatalysts, SnO₂/CuO and CuO/SnO₂ nanocomposites were successfully synthesized by chemical method at room temperature. X-ray Diffraction (XRD), transmission electron microscopy (TEM), Fourier transform Infrared (FT-IR), UV–Visible (UV–Vis) and photoluminescence (PL) spectroscopy were utilized for characterization of the nanocomposites. The photocatalytic activity of the nanocomposites was investigated. The hybrid nanocomposites exhibited high photocatalytic activity as evident from the degradation of methylene blue (MB) dye. The result revealed substantial degradation of the MB dye (92 and 69.5% degradation of SnO₂/CuO and CuO/SnO₂, respectively) under visible light illumination with short period of 30 min. Their large conduction band potential difference and the inner electrostatic field formed in the p–n heterojunction provide a strong driving force for the photogenerated electrons to move from Cu₂O to SnO₂ under visible light illumination. The excellent photodegradation of methylene blue suggested that the heterostructured SnO₂/CuO nanocomposite possessed higher charge separation and photodegradation abilities than CuO/SnO₂ nanocomposite under visible light irradiation.     

SnO<Subscript>2</Subscript>-based thin films with excellent photocatalytic performance

SnO₂ semiconductor is a new-typed promising photocatalyst, but wide application of SnO₂-based photocatalytic technology has been restricted by low visible light utilization efficiency and rapid recombination of photogenerated electrons–holes. To overcome these drawbacks, we prepared B/Fe codoped SnO₂–ZnO thin films on glass substrates through a simple sol–gel method. The photocatalytic activities of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) and formaldehyde. UV–Vis absorption spectroscopy and photoluminescence (PL) spectra results revealed that the B/Fe codoped SnO₂–ZnO film not only enhanced optical absorption properties but also improved lifetime of the charge carriers. X-ray diffraction (XRD) results indicated that the nanocrystalline SnO₂ was a single crystal type of rutile. Field emission scanning electron microscopy (FE-SEM) results showed that the B/Fe codoped SnO2–ZnO film without cracks was composed of smaller nanoparticles or aggregates compared to pure SnO2 film. Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the B/Fe codoped SnO₂–ZnO was 85.2 m² g^?1, while that of the pure SnO₂ was 20.7 m² g^?1. Experimental results exhibited that the B/Fe codoped SnO₂–ZnO film had the best photocatalytic activity compared to a pure SnO₂ or singly-modified SnO₂ film.     

Synthesis and enhanced ethanol sensing performance of nanostructured Sr doped SnO<Subscript>2</Subscript> thick film sensor

In the present paper we have synthesized pristine and Sr doped SnO₂ in order to prepare a selective ethanol sensor with rapid response–recovery time and good repeatability. Pristine as well as Sr (2, 4 and 6 mol%) doped SnO₂ nanostructured powder was synthesized by using a facile co-precipitation method. The samples were characterized by TG–DTA, XRD, HR-TEM, SAED, FEG-SEM, SEM–EDAX, XPS, UV–Vis and FTIR spectroscopy techniques. The gas response performance of sensor towards ethanol, acetone, liquid petroleum gas and ammonia has been carried out. The results demonstrate that Sr doping in SnO₂ systematically decreases crystallite size, increases the porosity and hence enhances the gas response properties of pristine SnO₂ viz. lower operating temperature, higher ethanol response and better selectivity towards ethanol. The response and recovery time for 4 mol% Sr doped SnO₂ thick film sensor at the operating temperature of 300 °C were 2 and 7 s, respectively.     

Synthesis of undoped and Fe nanoparticles doped SnO<Subscript>2</Subscript> nanostructure: study of structural,optical and electrocatalytic properties

In this study, undoped and nano Fe doped SnO₂ nanostructures were synthesized by hydrothermal method. Characterization of the synthesized nanostructures was performed by X-ray diffraction and scanning electron microscopy. For investigation of optical properties, photo luminescence and UV–Vis spectrum were taken. The electrochemical response of the carbon paste electrode modified with synthesized nanostructures toward levodopa (L-Dopa) was studied. Cyclic voltammetry studies using prepared modified electrodes showed outstanding electrocatalytic properties towards electro-oxidation of L-Dopa and a significant reduction was observed in anodic over voltage compared to the bare electrode. Obtained results indicated the effective role of the employed dopant. Best response in terms of the current enhancement, overvoltage reduction, and reversibility improvement of the L-Dopa oxidation reaction under experimental conditions was obtained by modified electrode with Fe doped SnO₂ nanoparticles.     

Band gap narrowing and photocatalytic studies of Nd<Superscript>3+</Superscript> ion-doped SnO<Subscript>2</Subscript> nanoparticles using solar energy

Pure and Nd³⁺-doped tin oxide (SnO₂) nanoparticles have been prepared by the sol–gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive spectroscopy and UV–visible spectroscopy. The XRD patterns of all the samples are identified as tetragonal rutile-type SnO₂ phase which is further confirmed by TEM analysis. Neodymium doping introduces band gap narrowing in the prepared samples and enhances their absorption towards the visible-light region. The photocatalytic activity of all the samples was evaluated by monitoring the degradation of methylene blue solution under day light illumination and it was found that the photocatalytic activity significantly increases for the samples calcined at 600 than 400°C, which is due to the effective charge separation of photogenerated electron–hole pairs. The efficiency of photocatalysts was found to be related to neodymium doping percentage and calcination temperature.     

Magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> nanospheres: preparation and photocatalytic activity

A facile and efficient approach for the fabrication of Fe₃O₄@TiO₂ nanospheres with a good core–shell structure has been demonstrated. Products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that Fe₃O₄@TiO₂ nanocomposites exhibited high degree of crystallinity, excellent magnetic properties at room temperature. Furthermore, the as-prepared Fe₃O₄@TiO₂ nanocomposites exhibited good photocatalytic activity toward the degradation of Rhodamine B (RhB) solution. Additionally, the recycling experiment of Fe₃O₄@TiO₂ nanocomposites had been done, demonstrating that Fe₃O₄@TiO₂ nanocomposites have high efficiency and stability.     

Magnetic properties of (Co,Al) co-doped SnO<Subscript>2</Subscript> nanoparticles

The desired size of pure SnO₂ and Co (1, 3, 5 mol%) with constant 5 mol% of Al co-doped into SnO₂ nanoparticles are synthesized by chemical co-precipitation method. The raw materials used in synthesis are SnCl₂.2H₂O, AlCl₃, Co (C₂H₃O₂).4H₂O, aqueous NH₄OH and Polyethyleneglycol (PEG) from AR grade. The XRD pattern of pure and co-doped samples confirm the formation of tetragonal rutile phase of SnO₂ nanoparticles with average particle size 25 and 20 nm respectively. Micrographs of scanning electron microscope (SEM) for pure and (Co, Al) co-doped into SnO₂ show that the prepared nanoparticles are agglomerate and spherical in shape. The EDAX spectra of prepared nanoparticles indicate the presence of Co²⁺, Al³⁺, Sn⁴⁺ and O²⁺ and also confirm stoichiometric proportions of raw material in the formation of SnO₂. Transmission electron microscope (TEM) reveals that the surface morphology of pure and co-doped samples are spherical, and average size of particles is ~20 nm. Magnetization measurements from M-H curves of VSM show that the ferromagnetism at low concentration of Co and at higher concentration of Co shows weak ferromagnetism due to super exchange coupling among neighboring ions. The bound magnetic polarons model supports the observed ferromagnetic behavior.     

Comparative Studies of Microwave and Sol–Gel-Assisted Combustion Methods of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanostructures: Synthesis,Structural, Morphological,Opto-magnetic,and Antimicrobial Activity

Nickel ferrite NiFe₂O₄ nanoparticles (NPs) were successfully synthesized by using nickel nitrate, ferric nitrate, citric acid, and ethyl cellulose as a surfactant by a simple sol–gel-assisted combustion method (SACM) and microwave-assisted combustion method (MACM). Structural, morphological, optical, and magnetic properties of the obtained powder were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL) spectroscopy, and vibrating sample magnetometry (VSM). XRD results show that the resultant powder was pure crystalline with cubic structure. The average crystalline size was found to be 18.8 and 10.2 nm synthesized by SACM and MACM, respectively. FT-IR spectra indicate the type of bonds between Ni–O and Fe–O (metal and oxygen). SEM images show that the morphology of the powder consists of well-defined structure. VSM results showed a ferromagnetic behavior of the sample. Antimicrobial activity of NiFe₂O₄ nanoparticles was performed. Both sample 1 (SACM) and sample 2 (MACM) show good inhibition in the zone 100 μg/ml. While comparing, sample 2 shows high inhibition than sample 1.     

Effects of Nd concentration on structural and magnetic properties of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Zinc ferrite nanomaterials have been received significant attention in recent years on account of their potential applications in the fields of electronics, optoelectronics and magnetics. To enhance the magnetic properties of zinc ferrites, Nd-doped zinc ferrites (ZnFe_2?xNd_xO₄, x?=?0, 0.01, 0.02, 0.03) nanoparticles (NPs) have been prepared by the sol–gel method. The effects of Nd doping concentration on the structural and magnetic properties of zinc ferrites were studied. The results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy indicated that the Nd ions were incorporated into the crystal lattice of ZnFe₂O₄ and substituted for the Fe³⁺ sites. Unlike pure zinc ferrites with paramagnetism, Nd doped ZnFe₂O₄ NPs were superparamagnetic at room temperature. Vibrating sample magnetometry results showed, with the increase of Nd content, the saturation magnetization of Nd doped ZnFe₂O₄ NPs increased.     

Structural,morphological, optical and gas sensing properties of pure and Ce doped SnO<Subscript>2</Subscript> thin films prepared by jet nebulizer spray pyrolysis (JNSP) technique

Pure and cerium (Ce) doped tin oxide (SnO₂) thin films are prepared on glass substrates by jet nebulizer spray pyrolysis technique at 450 °C. The synthesized films are characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive analysis X-ray, ultra violet visible spectrometer (UV–Vis) and stylus profilometer. Crystalline structure, crystallite size, lattice parameters, texture coefficient and stacking fault of the SnO₂ thin films have been determined using X-ray diffractometer. The XRD results indicate that the films are grown with (110) plane preferred orientation. The surface morphology, elemental analysis and film thickness of the SnO₂ films are analyzed and discussed. Optical band gap energy are calculated with transmittance data obtained from UV–Visible spectra. Optical characterization reveals that the band gap energy is found decreased from 3.49 to 2.68 eV. Pure and Ce doped SnO₂ thin film gas sensors are fabricated and their gas sensing properties are tested for various gases maintained at different temperature between 150 and 250 °C. The 10 wt% Ce doped SnO₂ sensor shows good selectivity towards ethanol (at operating temperature 250 °C). The influence of Ce concentration and operating temperature on the sensor performance is discussed. The better sensing ability for ethanol is observed compared with methanol, acetone, ammonia, and 2-methoxy ethanol gases.     

Synthesis of silver and sulphur codoped TiO<Subscript>2</Subscript> nanoparticles for photocatalytic degradation of methylene blue

In the present work, silver and sulphur codoped TiO₂ (Ag–S/TiO₂) photocatalysts were effectively prepared by sol–gel technique. The prepared samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray analysis (EDX), Fourier transform infrared (FTIR) spectroscopy, diffuse reflectance UV–Vis spectroscopy (UV-DRS) and photoluminescence (PL). The XRD patterns consisted of anatase crystalline phases and the particle size and shape of the prepared samples were observed by SEM and HR-TEM. The presence of doping ions was confirmed by EDX analysis, the decreased band-gap energy of Ag–S codoped TiO₂ nanoparticles was investigated by UV-DRS. The decreased in the intensity of Ag–S codoped TiO₂ was absorbed due to the lower separation of electron–hole pairs were confirmed by PL spectrum. The Ag–S codoped TiO₂ showed higher photocatalytic activity than pure and single-doped TiO₂ in the photodegradation of methylene blue (MB) aqueous solution under visible light irradiation. The given work was a good model to associate the considering of the synergistic effect of metal and non-metal codoped TiO₂ in the photocatalysis and photo electrochemistry.     

Electrical and optical studies in polyaniline nanofibre–SnO2 nanocomposites

Polyaniline nanofibre–tin oxide (PAni-SnO₂) nanocomposites are synthesized and mixed with polyvinyl alcohol (PVA) as stabilizer to cast free-standing films. Composite films are characterized by X-ray diffraction studies (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence spectroscopy (PL) and UV-visible spectroscopy. XRD confirms the formation of PAni nanofibre–SnO₂ nanocomposite. From TEM images, diameter of the polyaniline nanofibre and SnO₂ nanoparticles in the PAni-SnO₂ nanocomposite are found to be 20–60 nm. SEM results show fibrous morphology of the PAni nanofibre and spherical morphology of polyaniline-SnO₂ composites. The nanocomposites exhibit high relative photoluminescence intensity in violet as well as green–yellow region of visible spectrum. From electrical conductivity measurement, it is confirmed that PAni nanofibre–SnO₂ nanocomposite follows Mott’s one-dimensional variable range hopping (VRH) model.