Effect Of Ni Doping Research Articles

Effect of Ni doping on structural, optical and gas sensing properties of ZnO films for the development of acetone sensor devices

The development of sensor materials for environmental air surveillance is very challenging. In order to meet the demand, the present study corelates the effect of nickel doping on structural, optical, morphological and gas sensing ability of zinc oxide thin films. The films were deposited on the glass substrates using spray pyrolysis technique. The crystalline character and morphological analysis of the films were characterized by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM). The hexagonal wurtzite structure of polycrystalline nature is observed from the XRD patterns. The preferred orientation is (101), however doping has significantly triggered (002) orientation. Systematic decrement in the lattice parameters and bond length have been observed which led to structural distortions as result of mismatch in ionic radii of dopant and host materials. FESEM analysis reveals that thin film samples exhibit nanoflake morphology. A well-defined morphology is observed with Ni doping. The compositional analysis (Energy dispersive X-ray spectroscopy) shows that the Ni content was increased with doping which confirm the successful Ni doping. Optical analysis of the samples was performed using UV–Vis spectroscopical analysis. Transmission spectra indicated the highest transmission value in the case of undoped ZnO samples (More than 80%). Gradually decreasing band gap values of ZnO films were observed with Ni doping. The sensor response was investigated for undoped and Ni doped ZnO samples at room temperature in the absence and presence of acetone with 50 ppm concentration. Optimum response (∼78%) is obtained for Ni doped ZnO (2% Ni) samples with response time of 33s. Spray synthesized 2% Ni doped ZnO thin film samples show promising approach to achieve high response at ambient temperature.

Study the effect of Ni doping on structural, optical and electrical properties of Zn1-xNixO thin films deposited by spray pyrolysis technique

The effect of Ni doping on structural, optical and electrical properties of deposited Zn1-xNixO thin films on glass substrate by spray pyrolysis technique has been studied. The main objective of this research is to study the change of the physical and optical properties of Zn1-xNixO thin films that are fabricant to semiconductor with different doping levels x. These levels are 0 at.%, 2 at.%, 4 at.%, 8 at.% and 12 at.%. The transmission spectra show that the Zn1-xNixO thin films have a good optical transparency in the visible region from 88 to 95%. The optical gap energy of the Zn1-xNixO thin films varied between 3.25 and 3.35 eV. The urbach energy varied between 65 and 230 meV. However, the Zn0.88Ni0.12O thin films have many defects with maximum value of urbach energy. The Zn0.88Ni0.12O thin films have minimum value of optical gap energy. The Zn0.88Ni0.12O thin films have maximum value of the electrical conductivity which is 9.40 (Ω.cm)-1 . The average electrical conductivity of our films is about (7.52 (Ω.cm)-1 ). XRD patterns of the Zn1- xNixO thin films indicate that films are polycrystalline with hexagonal wurtzite structure.

CO2 dissociation and hydrogenation on pure and Ni-doped Fe(1 1 1). A DFT theoretical approach

Using the density functional theory, we have investigated the effect of Ni doping on the Fe(111) surface in two reactions involving CO2: its dissociation to CO and O, and the formation of HCOO. These competitive reactions are of great interest because they are the first ones occurring during CO2 hydrogenation reactions to obtain hydrocarbons. Three bimetallic surfaces were considered: Ni as a substituent in the first layer (Ni1L), in the second layer (Ni2L), and as an adatom (Niad). In all the cases, the presence of Ni inhibits CO2 adsorption in comparison with Fe(111). For Fe(111) and Ni1L-Fe(111), we have obtained an adsorption state where the CO2 molecule is particularly activated, being this configuration different from the most stable adsorption mode. On these surfaces, a two-step reaction was proposed; first, the migration from the most stable state to the activated geometry, and then its dissociation. On Fe(111), the two-step dissociation was found to be kinetically more favored than the direct mechanism. Among the bimetallic surfaces, only Niad-Fe(111) is more favorable kinetically for CO2 dissociation in comparison with Fe(111). Concerning the hydrogenation process to form HCOO, it was found that the reaction is inhibited on mixed Ni-Fe sites.

The synergy of Ni doping and oxygen vacancies over CeO2 in visible light-assisted thermal catalytic methanation reaction

The photo-assisted thermal catalytic system has provided a new alternative way to drive highly efficient CO2 methanation reaction. In this work, we investigated the role of visible light for thermal catalytic methane synthesis, emphasizing the synergy effect of Ni doping and oxygen vacancies for the hydrogenation of CO2 over Ni-CeO2 catalysts. It was found that the optimal 7.5 wt% Ni-CeO2 catalysts exhibited the best visible light-promoted CO2 methanation performance. At 250 °C, the light-promoted performance increased from 0.67 to 0.93 mmol−1·g−1·h which increased by 39 %. Extensive characterization demonstrates that heteroatom Ni doping increases the content of oxygen vacancies which narrows the band gap and improves the electron density of the catalyst, resulting in accelerating the transformation of carbonate and CO intermediate species which is beneficial to yield CH4. Furthermore, the visible-light-induced regeneration of oxygen vacancies also provides more active site to facilitate the adsorption and activation of CO2 which co-promoted the photo-assisted thermal catalytic CO2 methanation reaction. The synergy effect of Ni doping and oxygen vacancies provide a new strategy to design a high-efficiency photo-assisted thermal catalyst.

Structural features of 18R-type long-period stacking ordered phase in Mg85Zn6Y9 alloy and the Ni doping effect on its hydrogen storage properties

Magnesium-based alloys with 18R-type long-period stacking ordered (LPSO) structures have attracted wide attention for structural and functional applications. To understand hydrogen storage properties of 18R phase, the Mg85Zn6Y9 alloy with 94 wt.% of 18R-type LPSO phase is prepared in this work. The 18R phase has a layered structure where Y-Zn-Mg and Mg layers alternately stack along the c-axis. In the Y-Zn-Mg layers, Y, Zn and partial Mg sites are co-occupied by Y and Mg, Zn and Mg, and Mg and Zn/Y atoms, respectively. Thus the 18R phase is easily decomposed into α-MgH2, γ-MgH2, YH2, YH3, C14-type Laves phase MgZn2 and minor CsCl-type Y(Mg,Zn) during ball milling under hydrogen atmosphere. After further hydrogen absorption-desorption cycling, Y(Mg,Zn) disappears gradually and C14 phase transforms into C15-type Laves phase. By contrast, the Mg85Zn6Y9 alloy has better hydrogen storage kinetics and cycle durability than pure Mg because of the catalytic effect of YH2/YH3 on hydrogen absorption-desorption and inhibition role of Laves phase in Mg crystallite growth. Moreover, the introduction of Ni into Mg85Zn6Y9 sample leads to a further decrease in activation energy of hydrogen desorption from 106.39 to 96.78 kJ mol−1 due to the formation of Mg2Ni. This work not only provides new insights into structural features and hydrogen storage characteristics of 18R phase but offers an effective method for improving hydrogen storage properties.

Transition to n-type Thermoelectric Conduction in Ni-doped FeSe2 Alloys

We investigated the effect of Ni doping on the electrical, thermal, and thermoelectric transport properties of FeSe2 polycrystalline alloys. FeSe2 alloys exhibit both n-type and p-type conduction at different temperatures and thus their practicality as a thermoelectric material is somewhat limited. In this study, Fe1-xNixSe2 polycrystalline samples withx = 0, 0.01, 0.05, 0.075, 0.1, and 0.125 were synthesized, and it was shown that Ni doping in FeSe2 alloys induces n-type conduction in the entire temperature range. The electrical conductivity is gradually increased with an increase in carrier concentration as Ni doping increases, from 8.52 (x = 0) to 329 S/cm (x = 0.125) at 300 K. The maximum power factor of 0.61 mW/mK2 was observed in the Fe1-xNixSe2 sample atx = 0.01 at 600 K. Other Ni-doped samples exhibited power factors between 0.31 and 0.34 mW/mK2 at 600 K. The thermal conductivity gradually decreased from 6.9 (x = 0) to 4.2 W/mK (x = 0.125) with Ni doping because of the additional point-defect phonon scattering of the Ni substitutes. As a result, a zT of 0.11 was observed inx = 0.01 at 600 K, while the zT of the other Ni-doped samples exhibited 0.056-0.069 at 600 K.

Effect of Ni-Doping on the Hydrogen Storage Properties of Nanoscale MgH2

Effect of Ni-Doping on the Hydrogen Storage Properties of Nanoscale MgH2

Effect of Ni doping on the adsorption and visible light photocatalytic activity of ZnO hexagonal nanorods

Pristine and 1, 1.5, 2, 2.5 and 3 wt% Ni doped ZnO nanorods are prepared by hydrothermal technique as an effective photocatalyst for the removal of Malachite Green (MG) dye from aqueous media. Kinetic modelling of photocatalytic degradation and adsorption properties of the catalysts are done by pseudo first order (PFO), pseudo second order (PSO), fractal like psuedo first order (FPFO), fractal like psuedo second order (FPSO), elovich, exponential and intra particle diffusion (IPD) models. In contrary to the general trend, adsorption efficiency of ZnO is decreased while photocatalytic property got enhanced with doping. As-prepared catalysts are well characterised using XRD, FESEM, XPS, EDS, BET, UV and PL. This study points out the effect of Ni doping on the adsorption and visible light photocatalytic properties of ZnO nanostrutures via detailed kinetic modelling and explanation through various characterisation techniques and show cases their practical application in the field of waste water management. Water quality analysis was done post to degradation studies and the purified water samples have pH in the permissible range of drinking water which shows the efficient removal of dye molecules from the solution.

Magnetocaloric properties and critical behavior of magnetic phase transition in La(Fe0.94−xNixCo0.06)11.4Si1.6B0.25 alloys

For the widespread application of solid magnetic refrigeration technology, this is one of the key technologies to realize the wide temperature range of magnetic entropy change near room temperature. In this paper, the effect of Ni-doping on the magnetocaloric properties and the temperature range of magnetic entropy change was studied for La(Fe0.94−xNixCo0.06)11.4Si1.6B0.25 alloy subjected to the industrial high-frequency suspension furnace. The results show that the Curie temperature of the alloy system can be adjusted to room temperature by changing the Ni content, and the temperature range of magnetic entropy change can be expanded effectively. In addition, the critical behavior of the industrial grade purity alloy system was evaluated by modified Arrott-plot and critical isotherm analysis methods, and the optimal values of critical parameters were obtained, providing a novel thermodynamic method to determine the critical behavior of magnetic phase transition in La(FeSi)13 alloy system.

A highly efficient room-temperature formaldehyde gas sensor based on a Ni-doped ZnO hierarchical porous structure decorated with NiS illuminated by UV light

Developing room-temperature formaldehyde gas sensors with superior response-ability is crucial for many applications including the detection of indoor air pollutants. Herein, we synthesized a series of Ni-doped ZnO (Ni-ZnO) hierarchical porous structures decorated with NiS (NiS/Ni-ZnO) composite materials by the simple hydrothermal method, and the room-temperature (25 ± 1 ℃) UV light-activated photoelectronic formaldehyde sensors based on the ZnO, Ni-ZnO and NiS/Ni-ZnO composites were presented and compared. The response value of 0.2% NiS/0.4% Ni-ZnO material reached 330% toward 10 ppm formaldehyde gas, which was nearly 2.5 times higher than that of pure ZnO, and the faster response/recovery time (39.4 s/40.7 s) was obtained using UV light at room temperature. XPS, SPV, TPV spectrum analysis, and density functional theory (DFT) calculation showed that 0.2% NiS/0.4% Ni-ZnO sensor's excellent sensing performance was due to the synergistic effect of Ni doping and NiS modification which improved the separation efficiency and accelerated the migration of charge carriers. Here, the relationship between the response time of photoelectric gas sensors and the behavior of photogenerated carriers is firstly discussed in detail, which provides new insight into the development of room-temperature photoelectric gas sensors with superior response-ability. • NiS/Ni-ZnO hierarchical porous structure has been fabricated using hydrothermal method. • NiS/Ni-ZnO sensor exhibits fast response and high responsivity to formaldehyde at room temperature. • Excellent gas sensing performance of NiS/Ni-ZnO sensor is explained from the dynamic behavior of photogenerated carriers. • The relationship between the response time of gas sensor and the behavior of carriers is firstly discussed in detail.

Effect of Ni Doping on the Optical Properties of ZnO Thin Films Prepared by Sol-Gel Spin Coating and Investigation of ZnO Powder Nanostructures

Thin films of Nickel-doped ZnO have been prepared by sol-gel spin coating process. The doping concentration of Ni by weight has been adjusted as 0%, 2% and 5% .In order to examine the effect of doping on the optical properties , ZnO thin films has been characterized by UV-Vis spectroscopy, this shows Nickel doping affects the transmission in regards to the thin films and the band gap. The observed value of gap energy for 2% of Ni by weight is 3.25eV; also, the urbach energy value of “EU” is contrast with the values of energy gap.For ZnO powder nanostructures, we studied the microstructural and morphological properties, it have been characterized by optical microscope and first-principals computing. The ZnO replicas were clearly observed, the band structure and density of states of phase of crystal ZnO computed using Ab Initio methods, confirmed that pure ZnO is a direct band gap semiconductor for B3 phase, whose phase B3 is of ZnS type Blende.

Effects of Ni Doping and Silica Gel Bead Support on Characteristics of TiO2 Catalyst

Effects of Ni Doping and Silica Gel Bead Support on Characteristics of TiO2 Catalyst

Effect of Ni doping on the electro-optic property in K(Ta0.6Nb0.4)O3 films

The rising of thin-film-based plasmonic electro-optic (EO) devices triggers considerable exploitation of ferroelectric oxide thin films with large EO response. In this study, epitaxial (001)-orientated Ni-doped K(Ta0.6Nb0.4)O3 (KTN) films were fabricated on SrRuO3/SrTiO3 substrates via pulsed laser deposition. In comparison with a pure KTN film, a larger withstand electric field was achieved by Ni doping. The EO measurements revealed that the doping of Ni ions induced a decrease in the effective EO coefficient. Instead, the variation of refractive index by the applicable maximum electric field was increased due to the increment of withstand electric field, particularly for the case of 2% Ni dopant.

Tunning of rheological and magnetic properties of Ni doped magnetite based magnetic nanofluid

The effect of nickel doping on the structural and magneto-rheological properties of Fe3O4 based nanomagnetic fluids (NMFs) having the composition NixFe3-xO4 (0 ≤ x ≤ 0.8) has been studied. The structural and compositional analysis confirmed the nanoscale regime (∼10 nm) of samples prepared by chemical co-precipitation method and structural analysis was performed by XRD pattern to ascertain the effect of Ni doping. From the UV–Visible spectroscopy studies, the energy band gap was found to be in the range 2.2–3.0 eV with increase in Ni concentration. The magnetic measurements reveal the lower values of coercivity and remanence. The magneto-rheological measurements confirm that in all samples shows a non-Newtonian shear thinning behavior and the increase of viscosity and dipolar interactions while increasing the magnetic field. Whereas in absence of field, higher grain boundaries enhance the interlayer friction and higher viscosity with Ni doping.

Structure and Electrochemical Properties of LaMn1‐XNixO3

AbstractLaMn1‐xNixO3 nanoparticles were synthesized through hydrothermal synthesis and calcinations. The structural and electrochemical properties were studied to evaluate the effect of Ni doping on the materials as supercapacitor electrodes. The LaMn0.5Ni0.5O3 sample presented a capacitance of 183 F ⋅ g−1(current density of 1 A ⋅ g−1) and a capacity retention of 83.5 % after 2000 charge‐discharge cycles. Theoretical calculations were performed to provide more insight into the electrochemical performance.

First-principle study of the effects of Ni doping and point vacancy on the magnetic and absorption spectrum and itinerant electron properties of ZnO

At present, determining which system contains the characteristics of itinerant electrons is unclear by considering the coexistence of Ni doping and O vacancies or Zn vacancies in the ZnO system. The effects of Ni doping and point vacancy on the magnetic and absorption spectra and itinerant electronic properties of ZnO were studied by using first principles. Results show that the binding energy of Zn30NiO32 and Zn31NiO31 systems are large, and the systems are stable. The Zn30NiO32 system containing the O1−-2p state has the characteristics of itinerant electrons. The Zn31NiO31 system has no characteristics of itinerant electrons. The Zn31NiO31 system has room temperature ferromagnetism. The more the oxygen vacancy and the increase in Ni atom doping ratio, the higher the increase in the total magnetic moment of the doped system. This condition is consistent with bound magnetopolaron theory.

Ni doping effect on the electronic, structural and optical properties of ZnO nanoparticles prepared by Co-precipitation route

Nanoparticles (NPs) synthesized by the co-precipitation technique show many attractive properties such as small particle size, high crystallinity, high average pore diameter and high specific surface area. However, numerous reports show that some characteristics of the Ni-doped ZnO (NZO) NPs remain controversial such as optical bandgap (Eg), surface morphology and defect level. In this study, pure ZnO and NZO NPs at different Ni contents (x) were successfully prepared using the co-precipitation method. Phase analysis confirms the hexagonal wurtzite crystallinity of the samples. XRD peak shows that the Ni may substituted ZnO structure as the peaks shift toward higher angles with increasing x. Meanwhile, the formation of NiO secondary phases was significant at 12.50% Ni content. Densely packed spherical shaped structures with nanoparticle agglomeration are observed at low x, while some nanorod shaped structures appear at higher x. The stretching vibrations of the Zn–O bond are observed in the NZO NPs. The absorption edge shifts to higher wavelengths with the increase in x. This study provides consistent results in the phase analysis, morphology and structural parameters. The decrease in Eg agrees with the photoluminescence measurements. The emission spectra confirm the presence of interstitial zinc and singly ionized oxygen vacancies.

Hysteresis‐Suppressed Reversible Oxygen‐Redox Cathodes for Sodium‐Ion Batteries

AbstractOxygen‐redox‐based cathode materials for sodium‐ion batteries (SIBs) have attracted considerable attention in recent years owing to the possibility of delivering additional capacity in the high‐voltage region. However, they still suffer from not only fast capacity fading but also poor rate capability. Herein, P2‐Na0.75[Li0.15Ni0.15Mn0.7]O2 is introduced, an oxygen‐redox‐based layered oxide cathode material for SIBs. The effect of Ni doping on the electrochemical performance is investigated by comparison with Ni‐free P2‐Na0.67[Li0.22Mn0.78]O2. The Na0.75[Li0.15Ni0.15Mn0.7]O2 delivers a specific capacity of ≈160 mAh g−1 in the voltage region of 1.5–4.6 V at 0.1 C in Na cells. Combined experiments (galvanostatic cycling, neutron powder diffraction, X‐ray absorption spectroscopy, X‐ray photoelectron spectroscopy, and nuclear magnetic resonance (7Li NMR)) and theoretical studies (density functional theory calculations) confirm that Ni substitution not only increases the operating voltage and decreases voltage hysteresis but also improves the cycling stability by reducing Li migration from transition metal to Na layers. This research demonstrates the effect of Li and Ni co‐doping in P2‐type layered materials and suggests a new strategy of using Mn‐rich cathode materials via oxygen redox with optimization of doping elements for SIBs.

Effect of Ni Doping and Vacancy Defects on the Sensing Characteristics of Graphene for NO<sub>2</sub> and CO Detection: A DFT Study

The sensing characteristics of pristine, Ni-doped, and C-vacancy graphene towards CO and NO2 gas molecules were studied using density functional theory (DFT). The adsorption energies, electronic properties, charge transfer, and stable geometries were calculated to evaluate the gas-surface interaction mechanisms. Both pristine and vacancy graphene have smaller CO and NO2 adsorption energies and charge transfer than the Ni-doped graphene, whereas the adsorption energy on Ni-doped vacancy graphene is higher than that of Ni-doped graphene. The results indicate that both CO and NO2 gas molecules only attach to pristine graphene through weak physical adsorption. Stronger chemisorption occurs when the gas molecules adsorb on the surface of vacancy, Ni-doped, and Ni-doped vacancy graphene. Additionally, the results demonstrated that Ni-doped vacancy graphene has higher sensitivity and selectivity towards the NO2.

Synergistic effect of Ni doping and oxygen vacancies on the visible light photocatalytic properties of Ag2O nanoparticles

Chemisorbed oxygens on photocatalysts can be photo-excited and favorably generate reactive oxygen species like superoxide radicals. In the present research, we prepare oxygen vacancy (OV) mediated and Ni-doped Ag2O nanoparticles by similar hydrothermal protocols. Doping Ag2O by the higher oxidation state Ni enhanced the chemisorbed oxygen on the surfaces of the prepared nanoparticles but reduced the OV proportion. The inclusion of OVs widened the bandgap of Ag2O nanoparticles, which was also validated by density functional theory (DFT) calculations. DFT formation energy calculations indicated that the dopant Ni atom could be substituting an Ag site in the Ag2O lattice. X-ray diffraction (XRD) analysis showed that doping caused Ag2O lattice contraction possibly due to the smaller Ni substituting the larger Ag atom. X-ray photoelectron spectroscopy (XPS) analysis showed that OV-mediated Ag2O nanoparticles have a negative conduction band position and Ni-doping slightly narrowed the bandgap along with a more positive valence band position. DFT calculations also showed shifting of the density of states (DOS) due to Ni doping in OV Ag2O. Both OV mediated and Ni-doped Ag2O nanoparticles photocatalyzed ciprofloxacin (CIP) degradation under visible light irradiation. Increased chemisorbed oxygen due to Ni-doping enhances the CIP degradation rate.