Doped ZnO Powders Research Articles

Decisive role of preparation technique on the structural, electrical and magnetic properties of vanadium doped ZnO nanoparticles

1% vanadium doped ZnO powders have been successfully synthesized via two different preparation techniques viz., glycine assisted combustion method and mechanical attrition method to understand their impact on the structure-property relation. X-ray Diffraction study validates the Wurtzite phase formation of ZnO with hexagonal structure. X-ray diffraction peak discloses the marked role of size and strain component. Evidently, the shift of lattice strain with the preparation techniques from compressive to tensile nature show the importance of structure property relations in the ZnO compounds. SEM micrographs depict the formation of densely populated nanograins with networking like structures which is characteristics of combustion synthesized product whereas as top down approach exhibits the presence of coarse grains amidst the broken sea of fine particles. Selected area electron diffraction (SAED) images display ring and bright circular spot pattern with changes in method of preparation, which further clarifies the distinct nature of investigated ZnO:V particles. Vibrational spectral study gives clear evidence on the structural disorder as deduced from the changes associated with longitudinal optical mode phonon scattering. Interestingly, the UV spectral study divulges the increment in optical band gap as well as a strong visible light absorption (about 30 %) for milled ZnO:V over their chemically prepared counterparts. Photoluminescence spectra of milled V doped ZnO upheld the structural disorder taken place with the suppression of Near Band Edge (NBE) transition and the shifting of broad asymmetric defect emission band towards the lower wavelength regime. Impedance study enlightens the crucial role of synthesis method with 5 times enhanced grain boundary resistance along with suppression of grain contribution in the milled samples. Magnetic study highlights the remarkable distinction of preparation route which alters the ferromagnetic ordering in the combustion synthesized samples to conventional diamagnetic signature of the host ZnO in the milled samples.

Efficient process of VOC degradation from the high airflow in conical fluidized photocatalytic reactor by mesoporous C-N doped -ZnO powder under visible light

Mesoporous carbon–nitrogen, doped ZnO powders were synthesized from the zeolite imidazolate framework (ZIF-8) by a facile thermal decomposition in the atmosphere of nitrogen and air, respectively. The prepared material was used as the photocatalyst in a conical fluidized photocatalytic reactor under visible light irradiation for degradation of acetaldehyde (as a model molecule of indoor volatile organic compounds). The synthesized samples were characterized by DRS, BET, EDAX, FTIR, XRD, TGA, and FESEM analysis. DRS analysis revealed that the absorption edge of the prepared samples from ZIF-8 was significantly shifted to the visible range. The band gap and absorption edge of the bare ZIF-8 was changed from 5.1(eV) and 243(nm), respectively, to almost 3(eV) and 400 (nm) in the prepared C-N doped ZnO. FTIR analysis confirmed the existence of carbon and nitrogen in the surface of the prepared material. The N2 adsorption–desorption analysis revealed the IV-type isotherm confirming mesoporous structure with improved specific pore volume. The photocatalytic activity of the samples was evaluated from the airflow polluted with a trace amount of acetaldehyde, under an alkali metal halide lamp in the conical fluidized reactor, and the outlet flow was analyzed by the online GC versus the time. According to the results, all samples exhibited significant photocatalytic activity compared with the bare ZIF-8, and commercial ZnO powder. Almost 90% acetaldehyde removal occurred by the sample prepared by N2 thermal decomposition of ZIF-8 at 600 °C for 120 min, followed by air annealing at 450 °C for 90 min. Subsequently, the reaction rate was investigated and modeled on the base of Langmuir-Hinshelwood type equation as a function of acetaldehyde concentration and light intensity.

Microstructure and thermoelectric properties of Al-doped ZnO ceramic prepared by spark plasma sintering

The high thermal and low electrical conductivities of ZnO ceramics have hindered their thermoelectric applications. The doping of ZnO with group 3 elements can enhance the thermoelectric properties. In this work, Al (2 at%) doped ZnO powder was sintered using spark plasma sintering at varying parameters (such as temperature (550–700 ℃), pressure (250–500 MPa) and the temperature of pressure application (Room Temperature (RT) and Holding Time (HT))). Maximum relative density of 98.9% was achieved at a temperature and pressure of 650 °C and 250 MPa, respectively. The Al-doped ZnO ceramics improved in electrical conductivity which caused a decrease in the Seebeck coefficient because of increased carrier concentration. The reduction in the grain size due to inhibiting growth effects of aluminum lead to a decrease in the thermal conductivity through phonon scattering at the grain boundaries. Hence, ZT of 0016 at 500 °C was obtained. This study indicated that Al-doped ZnO ceramics can be sintered at very low temperature of 650 °C. These conditions allow to retain the nanostructure, which is beneficial in improving the thermoelectric properties.

Manganese ions substituted ZnO nanoparticles: Synthesis, microstructural and optical properties

Nanocrystalline Mn ions doped ZnO powder samples with a generic formula Zn1-xMnxO (x = 0.00, 0.02, 0.04, and 0.06) were prepared using conventional co-precipitation method. Confirmation of pure single-phase formation of all the ZnO samples was obtained by x-ray diffraction profiles. An average crystallite size in between 25 nm and 30 nm was calculated using Scherrer's formula. Williamson-Hall plots verified the existence of microstrain within the nanocrystals. Presence of bivalent, trivalent and tetravalent Mn ions in ZnO matrix was confirmed by x-ray photoelectron spectra analysis. Room temperature UV–Vis spectra studies confirmed that all the samples showed strong absorption near violet-blue region of EM spectrum. Photoluminescence spectra analysis confirmed the presence of both zinc and oxygen vacancies in doped samples.

Defects and dopant alliance towards bound magnetic polarons formation and mixed magnetic characteristics in Fe doped ZnO nanoparticles

Fe doped ZnO powders, Zn1-xFexO (x=0–0.03) confirmed to be single phased using X-ray diffraction (XRD) measurement (step size of 0.01°) revealed a change in oxidation state of Fe with increased fraction of Zinc interstitials, Zni and Oxygen vacancy, Vo defects through Photoelectron spectroscopy and Photoluminescence (PL) studies. The Raman and PL spectra have registered the inclusion of Vo-Zni complex defects also. An ideal position of E2(Low) Raman mode justifies the effectual cationic substitution of Fe species. Inclusion of paramagnetic (PM) component is successfully substantiated through Bound Magnetic Polaron (BMP) model fitting. For x=0.01, a residual PM component is ensured through temperature dependent magnetization, M(T) characteristics as well. A close fit of the Field cooled (FC) branch by the 3-D spin wave model (T=99−300K) points towards the intrinsic nature of ferromagnetism mediated by the effectual substitution of Fe2+ ions and the inclusion of BMPs. At lower temperature (T<99K), a good fit to the Curie-Weiss model (C–W) quantifies an estimated cluster size of the order of 10−3, subtle enough to restrict the introduction of spin glass state, thereby justifying the suitability of these nanoparticles for spintronics applications. Excellent PM properties are achieved for x=0.03 at T=300K.

Study of Low Temperature Preparation of Al Doped ZnO Powder and its Photocatalytic Properties

Aluminum doped ZnO crystal powders have been successfully prepared by sol-gel method with low temperature (150°C) crystallization process. The AlNO3 as material dopant were varied by 0.5 wt% and 1.0 wt% relate to 5 mmol of zinc acetate dihydrate as precursor. Degradation of the methylene blue (MB) was used to evaluate the photocatalytic property. The results showed that all ZnO samples have spherical morphology with hexagonal wurtzite crystal structures. The ZnO powder with 0.5 wt % of aluminum has a better photocatalytic property that related to the optical characteristics. The optimum of Al content (0.5wt%) reduces the crystallite size and give some advantages in optical characteristics that directly relate to the increments in photocatalytic behavior. The photodegradation rate of Al doped ZnO 0.5 wt% is increase almost 100% compared with ZnO undoped. The stability and reusability of 0.5 wt% Al doped ZnO as photocatalyst, is also observed by monitoring the photocatalytic behavior under 14 hours irradiation (in three recycle used)

Antimicrobial Activity of Photoactive Cerium Doped Zinc Oxide

Biofouling and biofilms exist as ubiquitous, undesirable accumulation of flora and fauna upon a given substrate when being immersed into an aquatic medium. Therefore, a novel antifouling based materials with the incorporation of nanotechnology has been developed for the prevention of biofouling in its initial stage through photocatalytic treatment. This study investigated the antimicrobial properties of photoactive Cerium (Ce) doped ZnO powder and explores its potential properties for future antifouling application. ZnO nanoparticles was doped with 0.4 mol% Ce was synthesized through the combination of modified citrate gelation technique and solid state sintering. The successful preparation of Ce doped ZnO was confirmed by XRD and SEM. The antimicrobial activity of Ce doped ZnO against E. coli and S. aureus was determined through antibacterial susceptibility test by agar well diffusion method whilst its photocatalytic inactivation efficiency against selected bacteria was analysed through photodegradation testing under UV light irradiation. The findings demonstrated that the synthesized Ce doped ZnO powder exhibited antibacterial effect against Gram-positive bacteria (S. aureus) and excellent photocatalytic efficiency to inactivate both Gram-negative (E. coli) and Gram-positive (S. aureus). 2 g/L of Ce doped ZnO catalyzed the 100% disinfection of both bacteria in 180 min of UV light exposure. Thus, this proved that Ce doped ZnO powder has the potential as efficient antifouling agent.

Influence of Bi doping on the luminescence of ZnO phosphors

Bismuth doped ZnO powder has been synthesized through solid-state chemical reaction and their optical properties investigated. A red emission band at 650 nm from bismuth has been observed and corresponding to the transition from 3P1 state to ground state (1S0). Two peaks at 384 and 432 nm in the excitation spectrum have been assigned to the field component of 3P1 state of bismuth. A weak energy transfer from the host bismuth was observed at room temperature. However, the relative intensity of the broad band from the host to the exciton lines was found to be 30 times weaker than that in ZnO. The reduction of the intensity of the broad band is ascribed to the decreasing of oxygen vacancies in bismuth doped ZnO. Doping with bismuth will greatly reduce the concentration of oxygen vacancies.

Li doped ZnO based DSSC: Characterization and preparation of nanopowders and electrical performance of its DSSC

Abstract In this study, microwave-assisted hydrothermal method (MW-HT) has been used to synthesize the nanopowders of Li doped ZnO, which are used in fabrication of dye-sensitized solar cell (DSSC). XRD examinations have shown that Li doped ZnO nanopowders synthesized in different concentration have highly crystallized hexagonal structure. To investigate the morphology of nanopowders, scanning electron microscopy (SEM) has been used and the results have revealed the nanoflower morphology of Li doped ZnO powders. Kubelka-Munk function has been utilized to determine the band gap of bare and dye loaded Li doped ZnO samples and an increase from 3.21 eV to 3.24 eV has been observed in the band gap as increasing Li content. The results of solar cell performance of the fabricated Li doped ZnO based DSSC samples have been exhibited that the efficiency of cells increases as the Li doping ratio is boosted and it has been observed the highest efficiency value of 1.23% for LZ10-DSSC.

Methylene Blue Photodegradation under Visible Irradiation on Ag-Doped ZnO Thin Films

This study synthesized and characterized Ag-doped ZnO thin films. Doped ZnO powders were synthesized using the sol-gel method, and thin films were fabricated using the doctor blade technique. The Ag content was determined by optical emission spectrometers with inductively coupled plasma (ICP plasma). Additionally, X-ray diffraction, Raman spectroscopy, Atomic Force Microscopy (AFM), diffuse reflectance, and X-ray photoelectron spectroscopy (XPS) measurements were used for physicochemical characterization. Finally, the photocatalytic degradation of methylene blue (MB) was studied under visible irradiation in aqueous solution. The Langmuir-Hinshelwood model was used to determine the reaction rate constant of the photocatalytic degradation. The physicochemical characterization showed that the samples were polycrystalline, and the diffraction signals corresponded to the ZnO wurtzite crystalline phase. Raman spectroscopy verified the ZnO doping process. The AFM analysis showed that roughness and grain size were reduced after the doping process. Furthermore, the optical results indicated that the presence of Ag improved the ZnO optical properties in the visible range, and the Ag-doped ZnO thin films had the lowest band gap value (2.95 eV). Finally, the photocatalytic degradation results indicated that the doping process enhanced the photocatalytic activity under visible irradiation, and the Ag-doped ZnO thin films had the highest MB photodegradation value (45.1%), as compared to that of the ZnO thin films (2.7%).

Effects of Eu3+ co-doping on the structural and optical properties of Ce3+ doped ZnO powder synthesized by chemical bath deposition method

In this study undoped, Ce3+-, Eu3+- doped and Ce3+: Eu3+ and co-doped ZnO nanopowders were synthesized by the chemical bath deposition (CBD) method. The samples were annealed at 700 °C for 2 h using an open furnace. The aim in this study was to investigate the energy transfer processes between Ce3+ and Eu3+ ions into ZnO powders. The X-Ray diffraction results indicated an increase in the crystallite sizes while scanning electron microscopy shown aggregation for the Ce3+: Eu3+ co-doped ZnO nanopowders. Ultraviolet–visible spectra exhibited red and blue shift in the Ce3+-, Eu3+ doped and Ce3+: Eu3+ co-doped ZnO nanopowders, respectively. The emission peaks at 582, 617, 659 and 705 nm are attributed to Eu3+ intra-4f transitions of 5D0→7F1,5D0→7F2,5D0→7F3 and 5D0→7F4 when excited by 465, 534 and 582 nm after co-doping. The chromaticity diagram show colour co-ordination in the orange vertex.

Optimization of Gallium concentration to improve the performance of ZnO nanopowders for nanophotonic applications

This study reports the effects of gallium concentration on the properties of doped zinc oxide nanopowders. Both pure and gallium doped zinc oxide (GZO) nanoparticles were prepared via a simple and effective sol-gel method. The structural, morphological and optical properties of synthesized GZO nanopowders were investigated using different characterization methods such as X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer, UV–Vis diffuse reflectance spectroscopy, Transmission electron microscopy, Photoluminescence spectroscopy, X-ray and ion-beam-induced luminescence (IBIL) measurements. Firstly, in the presence of Ga ions in the host the purity of synthesized sample was evaluated by X-ray diffraction analysis. X-ray photoelectron spectroscopy confirmed the presence of bonding states of Zn, O, and Ga on the surface of powders. Raman spectroscopy analysis showed that the increase of Ga content upper than 1 at.% leads to an increase in the number of defects in the ZnO lattice. Field emission scanning electron microscopy (FESEM) confirmed that the uniform integration of spherical and hexagonal rod shape particles can be found in the doped samples. According to FESEM images, the particle size of prepared nanopowders increased from 101 to 200 nm by increasing in the Ga doping concentration. The photoluminescence, X-ray and ion beam induced luminescence results of the pure and doped ZnO powders revealed novel blue-green emission band from 400 up to 550 nm at room temperature. Optical and structural studies confirmed the optimized Ga concentration is 1 at.%.

Structural Characterization of ZnO and Al Doped ZnO Powders Synthesis in Aqueous Solutions

Undoped and Al-doped ZnO (AZO) powders have been synthesized by hydrolytic and hydrothermal synthesis from Zn(NO3)2 , AlCl3 using KOH 1M concentraction like hydrolisis agent. The structural properties of prepared powders were studied using XRD and FTIR spectroscopy. Presence of aluminium in the hydrothermal powders is correlated with the presence of Zn-Al hydrotalcite like structure.

Room temperature ferromagnetic behavior in the nanocrystals of Fe doped ZnO synthesized by soft chemical route

Abstract In the present study, nanocrystalline undoped and Fe (5 wt.%) doped ZnO powder has been synthesized by soft chemical route. The structural, nano/microstructural, vibrational and magnetic properties of these samples have been studied as a function of calcination temperature (400 °C to 1100 °C). X-ray diffraction analysis of Fe doped ZnO powder has shown the major nanocrystalline wurtzite (ZnO) phase and the minor cubic spinel-like secondary nanocrystalline phase at 700 °C. At calcination temperature of 700 °C, the magnetization and coercivity have been enhanced in Fe doped ZnO. As the calcination temperature increased to 1100 °C, the major phase of ZnO and minor cubic spinel-like secondary phase turned into bulk in doped ZnO. Interestingly, the reduced magnetization and zero coercivity have been observed in this case. These changes are attributed to the conversion of secondary nanocrystalline ferromagnetic spinel phase to its bulk paramagnetic phase. The degree of inversion i.e. the occupancy of both sites with different symmetry by ferric ions is proposed to be solely responsible for the unusual behavior.

Controlling of surface morphology of ZnO nanopowders via precursor material and Al doping

In this paper, the optimization studies on the structural, morphological and electrical properties of undoped and Al doped ZnO nanopowders by microwave assisted hydrothermal method were performed. The ZnO nanopowders were prepared in different zinc acetate and NaOH molarities and after the determination of the best powder conditions, Al doped ZnO powders were obtained under these conditions. The surface morphology of ZnO nanoparticles is influenced by the starting solution type and molarity. Different morphologies of ZnO microstructures were obtained by adjusting the concentration of Zn2+ and OH−. The structural, morphological, electrical and optical properties of these nanopowders were investigated using X-ray diffractometer, scanning electron microscopy, DC electrical measurements and reflectance measurements. The incorporation of Al in ZnO nanopowder was also changed the morphology of these powders. The presence of Al+3 ions in ZnO nanopowder was determined by XPS measurements. Conductivity and resistivity values of ZnO nanopowders varied with Al incorporation. As the amount of Al in ZnO increases, their resistivities have decreased and their conductivities have increased. The optical band values of Al doped ZnO nanopowders were found via reflectance measurements using kubelka-munk function. As a result of Burstein-moss effect, the optical band values increased with the increase of the Al dopant.

Structural, optical and charge density analysis of Al doped ZnO Materials

The hexagonal structured Zn1−xAlxO (x = 0.00, 0.04, 0.06, 0.08 and 0.10) materials was synthesized by co-precipitation method. Structural, morphological and photoluminescence properties of Al doped ZnO powders were investigated by powder X-ray diffraction, scanning electron microscopy and photoluminescence characterizations, respectively. Structural analysis was done by Rietveld refinement technique. The spherical shaped morphology was observed in ZnO:Al powders. The bonding features were analyzed by using electron density distribution studies and the photoluminescence properties of Zn1−xAlxO (x = 0.00, 0.04, 0.06, 0.08 and 0.10) was also revealed.

Relationship between ferromagnetism and formation of complex carbon bonds in carbon doped ZnO powders.

We have investigated the possible relationship between defects, carbon bonds and the associated magnetic properties of carbon doped ZnO powders with intentional nominal carbon concentrations of 0, 1, 3, 5, 8 and 10 mol%. The samples were prepared by mechanical milling assisted by solid state reaction and carefully characterized using different techniques. X-ray diffraction and micro-Raman analysis revealed structural changes below and above the nominal carbon doping concentration of 3 mol% along with formation of intrinsic defect complexes. It was found that the oxygen and zinc content and the band gap of ZnO gradually decrease with increasing carbon content. XPS studies revealed the formation of Zn-O-C and O-C-O bonds and partial substitution of oxygen by carbon, in the form of Zn-C in all samples. When the nominal doping concentration increased above 3 mol%, formation of C-Zn-C bonds was drastically increased. The undoped ZnO sample was diamagnetic and free pure graphitic carbon was paramagnetic, while the 3 mol% carbon doped ZnO sample displayed the maximum saturation magnetization. The room temperature ferromagnetism (RTFM) has been ascribed to the presence of Zn-O-C, O-C-O and O-Zn-C bonds, where oxygen atoms may play a crucial role for mediating the long range magnetic interaction. C-Zn-C bonds decrease the saturation magnetization by encouraging antiferromagnetic behavior and the formation of intrinsic defects related with the carbon doping seem to have no influence on the RTFM observed.

Hydrogen induced changes of optical and magnetic properties of nanocrystalline Zn0.95Gd0.03M0.02O (M=Al,Mg): Experimental and DFT studies

This research work aims to study the effect of co-doping by Al3+ to increase the electronic charge carrier concentration inversely to Mg2+. Zn0.97Gd0.03O, Zn0.95Gd0.03Mg0.02O, and Zn0.95Gd0.03Al0.02O nanopowders were synthesised by simultaneous thermal co-decomposition of a mixture of cadmium and metal complexes, followed by hydrogenation at 350 and 600 °C. This study aimed at establishing the preparation conditions including hydrogenation that were essential for the creation of room temperature ferromagnetic order starting from the paramagnetic Gd-doped ZnO by using structural and electronic consequences of codoping with ions of Al or Mg. X-ray diffraction analysis confirms total doping of (Gd, Mg and Al) impurities into ZnO host lattice as well as the absence of secondary compounds/oxides in the synthesised solid solutions. The reflectance has been found to be significantly affected upon co-doping and hydrogenation, while the energy band gap decreases slightly; i.e. Eg = 3.23–3.00 eV. Magnetic measurements reveal that all the as-synthesised doped ZnO powders gained paramagnetic behaviour defeating the diamagnetic characteristic of ZnO, due to the presence of Gd ions with an effective magnetic moment in the range 8.04–7.12 μB. The hydrogenation in the present work conditions did not change the paramagnetic behaviour except for ZnO:Gd:Al-H, showing a partial a magnetic order overlapping with paramagnetic component, resulting in a coercivity of 170.2 Oe, remanence of 0.550 memu/g, and saturation magnetization of 2.14 memu/g. Therefore, the conditions including hydrogenation that were necessary to create FM ordering were determined.First-principles calculations indicate that the Gd doped ZnO systems own large spin polarized effect due to the interaction between Gd-f and O-p electrons. The Mg and Al dopants can modulate the values of magnetic moments.

Thermal studies of Mn2+-doped ZnO powders formation by sol–gel method

In the present contribution, the study of nanostuctured powders of Mn2+-doped ZnO with different doping concentration (1, 2, 5 at%) was approached. The samples were synthesized by sol–gel method, and the influence of the Mn content on the thermal behavior of the resulted gels was established by thermogravimetric and thermodifferential analysis. Based on the results obtained by thermal analysis, the gels were isothermally treated at 500 °C, 1 h. The XRD powder measurements revealed that all samples had hexagonal wurtzite structure and no other secondary phases were observed suggesting that the Mn2+ ions have substituted Zn sites. Moreover, the incorporation of Mn2+ into ZnO lattice was also confirmed by Infrared and Raman spectroscopy. Energy-dispersive X-ray analysis indicates the existence of Mn2+ in all samples, even in that with 1 at% Mn. The morphology of the samples depends on Mn2+ concentrations. A decrease in the grain size with the increase in Mn2+ concentration was observed. Mn2+-doped ZnO nanopowders with desired structure and properties as promising materials in potential piezoelectric applications, were obtained.

Visible photocatalytic activity of metal ion doped and undoped nano ZnO for the degradation of acidal Navy Blue 3BR

&#x0D; &#x0D; &#x0D; Metal (Mn, Cu, Co) doped and undoped Nano ZnO, prepared by chemical precipitation method and calcined at 300oC was characterized by XRD, FE-SEM, FT-IR, DRS and TEM. These photo catalysts can be effectively degrade organic contaminants using visible light irradiation. Doping reduces the intra granular resistance and recombination of the photo generated electron–hole pairs. The photo activity of undoped and doped ZnO powders was evaluated by monitoring the photo-decolourization of the aqueous solutions of Acidal Navy Blue 3BR (ANB 3BR) dye under visible irradiation. The disappearance of dye molecules followed pseudo-first-order kinetics. The effect of various parameters namely, pH of the medium, catalyst loading, initial dye concentration and kinetics of photo degradation of ANB 3BR was investigated. The rate of degradation was found to be strongly influenced by all above mentioned parameters. The reduction in the chemical oxygen demand (COD) of the decolorized aqueous samples revealed a possibility of complete destruction of the organic molecules along with colour removal. Experimental data were analyzed by model equations such as Langmuir and Freundlich isotherms and it was found that the Langmuir isotherm model best fitted the adsorption data. The results showed that the doped (Mn, Cu, Co) percentage (0.25, 0.5, 0.75, 1, 1.5%) were successfully doped into the ZnO and that manganese and copper-doping reduced the photo catalytic activity of ZnO, Co doped ZnO increase the photo catalytic activity.1%, 0.75%, 0.75% of Mn, Cu, Co doped in ZnO can be used in photo catalytic experiments.&#x0D; &#x0D; &#x0D;