Undoped ZnO Nanoparticles Research Articles

Highly porous, honeycomb like Ag–ZnO nanomaterials for enhanced photocatalytic and photoluminescence studies: green synthesis using Azadirachta indica gum

The preparation of zinc oxide and silver doped zinc oxide nanoparticles using zinc nitrates and silver nitrates as oxidizers and Azadirachta indica gum as a fuel via solution combustion method at 500 °C. The synthesized nanoparticles were characterized by XRD, FTIR, UV-DRS, SEM and TEM studies; these materials were tested for photoluminescence and photocatalytic activity studies. The PXRD data indicated that the synthesized nanoparticles confirmed as hexagonal phase with average crystallite size of 13.33 and 13.34 nm for ZnO and Ag–ZnO respectively. The SEM data revealed that, the material obtained is highly porous and honeycomb like structure. In the photocatalytic degradation of methylene blue, Ag–ZnO nanoparticles have shown the good photocatalytic activity than undoped ZnO nanoparticles. This is due to the presence of Ag on the surface of ZnO catalyst makes the catalyst more sensitive to light and reduce the electron hole recombination. Furthermore, we have also examined the photoluminescence studies for the synthesized materials and it has given the green emission by excitation at 380 nm. In this study, the green synthesis method will produces large quantity of nanomaterials with less time and low cost.

Enhancement of ethanol gas sensing mechanism at high humidity levels and optical features using Sr-doped ZnO NPs

In the present study, undoped and Sr-doped ZnO nanoparticles (NPs) were synthesized with the sol–gel method for enhancing selectivity and sensitivity of ethanol sensing at high humidity levels. The samples were identified through their microstructure, morphology, and surface chemistry. As can be seen from X-ray diffraction (XRD) analysis, the Sr doping significantly affected the crystalline quality of the NPs. The results of gas sensing were examined in terms of operating temperature, doping concentration, gas concentrations, gas type, and relative humidity (RH). The sensitivity was gradually increased by raising the variant humidity of 25–70%. Moreover, sensor response from 15 at 32% RH was increased to 57 at 70% RH for undoped and 6% Sr-doped ZnO NPs, respectively. When the RH rose to 70–90%, the sensitivity decreased gradually. The sensor showed a higher selectivity to ethanol compared to the other gases. Based on the obtained results, the sensors have high sensibility levels for 6% Sr-doped ZnO NPs that is ~ 52 at 240 °C and ~ 27 at room temperature, respectively. The achieved improvement in gas sensing behavior can be attributed to the increase in active site values for O adsorption after adding Sr concentrations.

Photo-degradation of a mixture of dyes using Barium doped ZnO nanoparticles

The potential use of Barium (Ba) doped ZnO nanoparticles for the photo-degradation of a mixture of dyes that mimics natural effluents has been attempted. Undoped and Ba-doped ZnO nanoparticles were efficiently synthesized via co-precipitation method. The effect of Ba concentration on the structural, morphological, optical properties and photocatalytic activity of ZnO nanoparticles was probed. X-ray diffraction analysis disclosed the formation of hexagonal polycrystalline nanoparticles with ZnO wurtzite crystal structure having an average crystallite sizes ranging from 20 nm for pure ZnO up to 28 nm in diameter after adding different ratios of barium. The FE-SEM images revealed rod-like nanoflakes morphology for all of the samples with a clear influence of the presence of Ba impurities on the width of the rods. Mapping analysis showed even Ba distribution in the ZnO lattice. FTIR spectra manifested the presence of the characteristic absorption peak at 400–600 cm−1 of Zn–O stretching modes confirming the target nanoparticles synthesis. While the BET and BJH data analysis indicated increased specific surface area and reduced pore volume as a result of Ba intercalation. The incorporation of Ba into the ZnO matrix has shifted the 371 nm absorption band to 475 nm as observed in photoluminescence spectra for all samples. This red shift in the absorption was reflected in lowering the band energy enabling it to decolorize a dyes mixture under visible light illumination. Based on the aforesaid results, the Ba doping is responsible for the visible light driven photocatalytic activity of the composites.

Tuning the structural, morphological, optical, wetting properties and anti-fungal activity of ZnO nanoparticles by C doping

Sol–gel (SG) and direct precipitation (DP) routes were used to synthesize zinc oxide (ZnO) nanoparticles. C-doping (1At.% and 2At.%) in ZnO nanoparticles was performed by precipitation method (PM) and C doping (10% and 20%) was performed by thermal deposition (TD) method. The structural, morphological, optical, wetting properties and antifungal activity of the undoped and doped nanoparticles were studied. X-ray diffraction (XRD) revealed the hexagonal wurtzite crystalline phase for SG and DP derived nanoparticles. The C-doping of ZnO revealed that there is no transition in crystallinity and phase of ZnO nanostructure. The crystallinity and phase remain the same even after doping of carbon atoms. The XRD results show that the peaks of pure and C-doped ZnO nanoparticles are present in the same phase. Field-emission scanning electron microscopy (FESEM) revealed the morphology of undoped and doped ZnO nanoparticles. Almost spherical nanoparticles were revealed for SG and DP derived pure ZnO nanoparticles. The C-doped ZnO nanoparticles revealed spherical and hexagonal-rod shaped nanoparticles for PM and TD derived nanoparticles, respectively. The doped ZnO showed the increased band gap compared to the band gap of the pure ZnO nanoparticles. Photoluminescence (PL) spectroscopy was performed to find out the optical properties. The hydrophilic nature of DP and SG derived ZnO nanoparticles changed to the hydrophobic nature owing to C doping which is attributed to the variation in the roughness of the doped nanostructures. The doped ZnO nanostructures revealed better resistance to the growth of the ‘Rhizopus Stolonifer’ fungus compared to the undoped ZnO nanoparticles.

The defect state of Yb-doped ZnO nanoparticles using thermoluminescence study

Shallow trapping centers in Yb-doped ZnO nanoparticles were determined using thermoluminescence (TL) measurements applied in the 10–300 K temperature region. Undoped and Yb-doped ZnO nanoparticles were synthesized by sol-gel method. TL glow curve of undoped nanoparticles presented three peaks around 56, 108 and 150 K whereas one additional peak around 83 K was observed in the TL curve of Yb-doped ZnO nanoparticles. The increase of Yb concentration in the nanoparticles increased the TL intensity of this additional peak. Activation energies of interstitial defect centers were found as 20, 82 and 105 meV while energy of trapping center existing due to Yb-doping was obtained as 72 meV using curve fitting and initial rise methods.

Gigahertz acoustic vibrations of Ga-doped ZnO nanoparticle array

In this work, we present an experimental study on the acoustic vibrations of ZnO nanoparticles array with different concentration of Ga dopings by using femtosecond pump-probe technique. The Ga-doped ZnO (GZO) nano-triangle particles with the sizes of 190, 232 and 348 nm are fabricated by nanosphere lithography and pulsed laser deposition method. The result indicates that the frequency of acoustic vibrations of GZO nanoparticles decrease as the Ga-concentration is increased. Importantly, the vibration period of the GZO nanoparticles at the same Ga doping concentration show a nonlinear increase as the nanoparticle size is increased, which is different from the common linear dependency in undoped ZnO nanoparticles. It may be attributed to the crystal structure distortion and elastic characteristics variation due to Ga doping, and the elastic modulus at 7.3% Ga doping is decreased by 30%–60% for GZO nanoparticles with different sizes. The study can be very helpful for evaluating the crystal structure distortion and elastic characteristics of doped nano-materials with optical methods. Besides, it can offer a complementary method of thermal management in ZnO based optoelectronic devices.

Enhanced H2S gas sensing properties of Mn doped ZnO nanoparticles—an impedance spectroscopic investigation

H2S is a toxic gas and causes wide range of health issues by breathing it. Thus, detection of H2S in ppm level with suitable device is very important. Undoped and Mn doped ZnO NPs were synthesised using sol-gel technique and spin coated on alumina substrate to form as a thin film for gas sensing applications. The sensor response was evaluated by the change in an impedance of the film in the absence and presence of H2S gas. The impedance results revealed that the 4% Mn doped ZnO nanoparticles are found to be enhanced sensitivity and selectivity towards H2S than Undoped ZnO nanoparticles and other Mn doped nanoparticles. Response and recovery towards 5 ppm H2S at 150 °C operating temperature is observed for the 4 wt% Mn doped ZnO nanoparticles are ∼22 s and 19 s respectively. Meanwhile 4% Mn doped ZnO showed good selectivity towards H2S against common interfering gases.

Effect of B or N doping on the dielectric and electrical properties of ZnO at room temperature

Boron (B) or nitrogen (N) doped ZnO nanoparticles were fabricated using mechanochemical technique. To research the effect of doping rate on the dielectric and electrical properties, Bn-ZnO and Nn-ZnO (n = 2 and 4 wt%) were obtained. The chemical compositions of the produced metal oxides were determined by Fourier transform infrared spectroscopy (FTIR). Several vibration modes caused by specific substituents were observed for all samples in FTIR spectra. The dielectric spectra were also analysed in the light of earlier results for an elaborative examination. Dielectric behaviours of the undoped and B or N doped ZnO nanostructures were studied by means of dielectric spectroscopy (DS) in the large frequency range 10−2–107 Hz at room temperature. As a result of the dielectric study of ZnO with B or N dopants, remarkable changes in dynamics such as dielectric constant, dielectric loss tangent, capacitance and electrical conductivity were obtained in tune with Koop’s theory. The electrical conductivity response for the entire samples obeyed the Jonscher power law equation, and the hopping mechanism between ionized oxygen vacancies was found to dominate the conduction mechanisms in the undoped and doped ZnO nanoparticles. The maximum dielectric constant in this study (60 at 1 Hz) has been achieved with the N doped ZnO samples. It was also determined that N doping increased the undoped ZnO capacitance value from 5.14 × 10−11 F to 2.64 × 10−10 F, whereas B doping decreased it up to 1.56 × 10−11 F.

Facile Microemulsion Synthesis of Vanadium-Doped ZnO Nanoparticles to Analyze the Compositional, Optical, and Electronic Properties.

In this work, microemulsion method has been followed to synthesize vanadium-doped Zn1−xVxO (with x = 0.0, 0.02, 0.04, 0.06, 0.08, and 0.10) nanoparticles. The prepared samples are characterized by several techniques to investigate the structural, morphology, electronic, functional bonding, and optical properties. X-ray diffractometer (XRD) analysis confirms the wurtzite phase of the undoped and V-doped ZnO nanoparticles. Variation in the lattice parameters ensures the incorporation of vanadium in the lattice of ZnO. Scanning electron microscopy (SEM) shows that by increasing contents of V ions, the average particle size increases gradually. X-ray Absorption Near Edge Spectroscopy (XANES) at the V L3,2 edge, oxygen K-edge, and Zn L3,2 edge reveals the presence and effect of vanadium contents in the Zn host lattice. Furthermore, the existence of chemical bonding and functional groups are also asserted by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). UV–Visible analysis shows that by increasing V+ contents, a reduction up to 2.92 eV in the energy band gap is observed, which is probably due to an increase in the free electron concentration and change in the lattice parameters.

Zn source-dependent magnetic properties of undoped ZnO nanoparticles from mechanochemically derived hydrozincite

Out of many functionalities of zinc oxide, its magnetic properties are only sparsely explored. Herein we report on the evolution of ferromagnetism of undoped ZnO nanoparticles, depending on the zinc source used for the synthesis. We started from mechanochemical synthesis of phase pure nanocrystalline hydrozincite, Zn5(CO3)2(OH)6 (ZnHC) by milling a mixture comprising either Zn(NO3)2·6H2O or ZnCl2, and Na2CO3 for 10 min. Zinc oxide nanoparticles with specific surface over 70 m2/g were obtained by subsequent heating of ZnHC up to 300 °C. Ferromagnetism was observed only for ZnO nanoparticles derived from Zn(NO3)2, while those from ZnCl2 were conventionally diamagnetic. X-ray photoelectron, Raman, as well as electron paramagnetic resonance spectrograms consistently showed significantly higher concentration of oxygen vacancies in the Zn(NO3)2-derived ZnO. We also referred to the difference in the charging states of oxygen vacancies by detailed observation of EPR spectra. Since the formation of ZnO from ZnHC is topotactic, the difference in the lattice imperfection was discussed in terms of the hydration energy of the coexisting NO3− or Cl− anion. The present simple mechanochemical – thermal procedure offers a facile method for obtaining well-dispersed active ZnO nanoparticles. More importantly, the new synthesis method offers possibility of controlling their magnetic properties by choosing anionic species of the starting zinc source.

Development of an impedimetric non enzymatic sensor based on ZnO and Cu doped ZnO nanoparticles for the detection of glucose

In this research, pure and copper-doped Zinc oxide nanoparticles (Cu-ZO) have been prepared by sol gel method. Lots of tests have been carried out for the prepared samples such as crystallinity analysis, microstructures observation and electrochemical property investigations. The electrochemical behavior of the electrodes were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). These analyses show that the ZnO and Cu-ZO samples are promising for the development of cost effective non-enzymatic electrochemical glucose biosensors with good features. The prepared Cu-ZO samples sensor represent higher sensitivity and superior electro catalytic activity as compared to that observed for the undoped ZnO nanoparticles. It exhibit a large linear detection range from 10−9 M to 10−5 M and low detection limit of 10−9 M. It is believed that the copper doping revealed a significant effect on the electrochemical properties because it provide more electro catalytic actives sites and more electron transfer for glucose oxidation. Furthermore, measurements in the presence of interfering species haven't affected the response of the analyte of interest which prove the good selectivity of the Cu-ZO. Finally, the electrode was successfully applied to the assess the glucose level in human serum samples.

PHOTOCATALYTIC DEGRADATION OF PHARMACEUTICAL DRUG ZIDOVUDINE BY UNDOPED AND 5 % BARIUM DOPED ZINC OXIDE NANOPARTICLES DURING WATER TREATMENT: SYNTHESIS AND CHARACTERISATION

Objective: To study the photocatalytic degradation of pharmaceutical drug zidovudine (ZDV) by synthesized undoped zinc oxide nanoparticles (ZONPs) and 5% (mole ratio) barium doped zinc oxide nanoparticles (BZONPs) during water treatment.Methods: Kinetics studies were carried out with the help of UV-Visible Spectrophotometer. High-Resolution Mass Spectrophotometry (HR-MS) was used to identify products. A photo-reactor with mercury lamp was used as an external source of light energy. Optical power meter was used for the measurement of light intensity. The particle size of the synthesized photocatalysts was identified with the help of siemens x-ray diffractometer (XRD). The surface topography of photocatalysts was done by scanning electron microscope (SEM). Transmission electron microscopy (TEM) was used for the studies of particle size and morphology.Results: Five degraded products of ZDV are identified by HR-MS. A suitable electron-hole pair mechanism is projected. XRD patterns show that the intensity of peak is slightly stronger in ZONPs. There is an increase in the rate of photocatalytic degradation of ZDV by adding different quantities of photocatalyst from 0.05 g l-1 to 0.1 g l-1. The kinetic data reveals that there is an initial increase in the values of rate constants with the increase in the concentration of ZDV. The kinetic data indicate that the values of rate constants are higher at pH = 9. There is an increase in the rate constant values with an increase in the light intensities of UV lamp.Conclusion: The rates of photocatalytic degradation of ZDV were found to be higher using 5 % (mole ratio) BZONPs as a photocatalyst.

A Correlative Investigation of Photoconductive Behaviour of Bare and Al-Doped ZnO Thin Films

Zinc Oxide (ZnO) nanoparticles exhibit a wide range of applications owing to their unique properties such as low cost, non-toxicity, abundance in nature and suitability for doping. In the present study, ZnO and Aluminium doped Zinc Oxide (Al-ZnO) nanoparticle thin films were prepared on FTO glass substrate by sol-gel and spin coating methods. The structural and morphological characteristics of the undoped and Al-doped ZnO nanoparticles were examined by X-ray Diffraction (XRD) and High Scanning Electron Microscope (HR-SEM) analysis, respectively. The XRD studies revealed the hexagonal wurtzite structure of the as-synthesized ZnO samples and the crystallite size was estimated using Scherrer’s formula to be 28 and 30 nm respectively, in the case of the undoped and doped ZnO nanoparticles. The average particle sizes in nanoscale were analysed using FESEM and found to be 38 nm and 42 nm for the bare and doped samples. The surface area of the as-synthesised particles were correspondingly estimated as 46 m2/g and 25 m2/g and their relative pore volume and diameter were determined using BET analysis. The field dependent photoconductivity of Al-ZnO shows a significant increase as against the bare ZnO.

Co3O4-ZnO P-N Heterostructure Nanomaterials Film and its Enhanced Photoelectric Response to Visible Lights at Near Room Temperature

In this paper, Co3O4-ZnO nanomaterials with Co3O4 doping mass fractions of 0%, 2.13%, 4.13%, and 6.13% were prepared by sol-gel method. In order to explain and confirm the influence of the incorporation of Co3O4 on the surface morphology and gas sensitivity of ZnO at a relatively low gas concentration, additional studies such as XRD, XPS, SEM, EDS and UV-vis spectroscopy were performed. And its photoelectric response to 100 ppm acetone at near room temperature and visible light irradiation was studied. Due to the formation of P-N heterojunctions, the Co3O4-ZnO heterostructural nanoparticles has a highe response to low concentrations of acetone gas than undoped ZnO nanoparticles even at operating temperatures as low as 30oC. The addition of Co3O4 improves the sensitivity and selectivity of ZnO thick films. The sensitivity of the 4.13wt% Co3O4-ZnO sample to 100 ppm acetone at a working temperature of 30oC was 24.36. The light excitation effect was significantly enhanced. Under visible light irradiation, the sensitivity can reach 37.21. In addition, the Co3O4-ZnO P-N heterojunction model was combined with visible light excitation theory to further explore the mechanism of gas sensing reaction.

5% Barium doped zinc oxide semiconductor nanoparticles for the photocatalytic degradation of Linezolid: synthesis and characterisation

Undoped zinc oxide nano-particles (ZONPs) and 5% (mole ratio) barium doped zinc oxide nano-particles (BZONPs) were synthesized by chemical precipitation method. These semiconducting materials were used for the photocatalytic degradation of antibacterial drug Linezolid (LNZ) for the pH ranging from 4.0 to 8.0. X-ray diffraction (XRD) patterns show that the intensity of peak is slightly stronger in ZONPs than in 5% (mole ratio) BZONPs. The calculated average grain size using Scherrer equation for ZONPs and 5% (mole ratio) BZONPs are found to be 35.08 (± 3) nm and 24.39 (± 2) nm respectively. Scanning Electron Microscopy images show that both semiconductor materials are uniform and homogeneous with closely aggregate oval in shape. Energy dispersive X-ray spectroscopy (EDX) of 5% (mole ratio) BZONPs shows that the mass percentage of zinc is 71.2, oxygen is 23.9 and barium is 4.78. The influences of different parameters on the photocatalytic degradation of LNZ were investigated thoroughly. The rate of photocatalytic degradation of LNZ was increased first from 0.05 to 0.1 g/L dosage of photocatalyst but after that the rate decreases with increase of dosage of photocatalyst. The kinetic data reveals that there was initial increase in the rate of reaction with increase in the [LNZ]. The effect of pH indicates that there is increase in the rate of reaction from pH 4.0 to 8.0.The rate of degree of mineralization of LNZ is found higher at the higher light intensities of UV lamp.

The Modification of Structural, Optical and Antibacterial Activity Properties of Rare Earth Gadolinium-Doped ZnO Nanoparticles Prepared by Co-Precipitation Method

Gd doped ZnO nanoparticles with differing dopant concentration are synthesized by co-precipitation method and analysed for their structural, morphological and optical properties. XRD profiles confirmed that the synthesized material is nano-crystalline ZnO with well-crystalline and hexagonal wurtzite structure. FESEM images delineated hexagonal formed in ZnO nanoparticles. The assimilation band gap observed 463 cm−1 is credited to the ZnO extending vibrations and EDX affirms the synthesis of undoped and Gd doped ZnO nanoparticles. Optical properties of the nanoparticles were examined by photoluminescence study and it uncovered band edge emission for all synthesized materials with additional emissions in visible region because of the presence of opening and interstitial deformities. The antibacterial effectiveness of Gd doped ZnO nanoparticles were investigated against a Gram positive and Gram negative bacteria.

A Review of Doped and Undoped ZnO Nanoparticles for Fabrication of Gas Sensor

A Review of Doped and Undoped ZnO Nanoparticles for Fabrication of Gas Sensor

Gd-doped ZnO nanoparticles: Synthesis, structural and thermoluminescence properties

Structural and thermoluminescence (TL) properties of Gd-doped ZnO nanoparticles were investigated in the present study. TL glow curves recorded in the 10–300 K range presented three overlapped peaks around 56, 110 and 155 K for undoped ZnO nanoparticles. The Gd-doping to the ZnO nanoparticles resulted in shift of peak maximum temperatures to lower values and decrease of activation energies associated with the observed peaks. Activation energies of trapping centers were also reported. Taking into account the previously reported studies on defect characterization of ZnO compound, revealed centers were associated with interstitial defects. Structural characteristics of the synthesized nanoparticles were investigated by x-ray diffraction and scanning electron microscopy measurements.

Increasing the reactive sites of ZnO nanoparticles by Li doping for ethanol sensing

Gas sensing in metal oxide semiconductors can be enhanced by creating more number of gas adsorption (reactive) sites. With this aim, Li-doped ZnO nanoparticles with chunk-shaped morphology is synthesized, which provide more adsorption sites due to its morphology and due to the presence of oxygen vacancies. XRD analysis of undoped and Li-doped (2 and 5 at.%) ZnO nanoparticles revealed the hexagonal wurtzite structure and SEM and TEM analyses showed the chunk-shaped morphology in all the samples. The presence of pores and voids between the nanoparticles in the chunk-shaped morphology plays a significant role in the gas sensing mechanism. PL analysis showed that compared to ZnO nanoparticles, Li-doped ZnO nanoparticles possess more number of oxygen vacancies, zinc interstitials, and Li interstitials, the important factors that enhance the sensitivity of Li-doped ZnO nanoparticles. As expected, Li-doped ZnO nanoparticles showed more sensitivity compared to undoped ZnO nanoparticles toward ethanol.

Photoluminescence and Nonlinear Optical Properties of Transition Metal (Ag, Ni, Mn) Doped ZnO Nanoparticles.

ZnO nanoparticles doped with transition metal (Ag, Ni, Mn) were prepared by using co-precipitation method. Absorption spectra showed exciton peak for ZnO nanoparticles at 367 nm and for Ag, Ni, Mn doped ZnO nanoparticles at 328, 354 nm and 342 nm respectively. Photoluminescence dynamics showed shallow level-trap and deep-level emission where the intensity of deep-level trap increases with transition metal doping due to the oxygen deficiency. Nonlinear absorption measurements showed the two-photon absorption increasing with transition metal following the trend Ag > Ni > Mn when excited with 532 nm, 30 ps laser pulses. The transition metal doped and un-doped ZnO nanoparticles can be used as optical limiters.