Ni-doped TiO2 Research Articles

Synthesis and characterization of Ni-doped TiO2 activated carbon nanocomposite for the photocatalytic degradation of anthracene

Nickel-doped titanium dioxide nanoparticles (NDT) deposited on pine cone activated carbon (PAC) have been successfully synthesized by a hydrothermal method. The as synthesized nanocomposite was characterized by X-ray diffraction pattern (XRD), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron (XPS), Fourier transform infrared (FT-IR), UV–visible diffuse reflectance spectra (UV–vis DRS), Photoluminescence (PL), BET surface area, and pHzpc. The characterization results of the prepared nanocomposite revealed that Ni-TiO2 was loaded on the surface of PAC, and had a higher surface area and narrower bandgap than TiO2 nanoparticles. The visible-light photocatalytic activity of the Ni-TiO2@C nanocomposite towards anthracene degradation was found to be 99.9% in 50 mins leading to end products of (1E, 3Z)-hexa-1,3,5-trien-1-ol (1a; m/z = 96), and (1E, 3E)-penta-1,3-dien-1-ol. The synthesized Ni-TiO2@C nanocomposite exhibited a better photocatalytic activity towards the photocatalytic degradation of anthracene as compared to the TiO2 nanomaterial (22.5%) and TiO2/activated carbon nanocomposite (31%) under similar conditions. The photodegradation of anthracene followed the pseudo first-order rate kinetics. The Ni-TiO2@C nanocomposite had excellent regeneration properties till the fifth cycle of use during which it degraded around 73% anthracene.

Ni-doped TiO2 nanocubes wrapped by CNTs for synergic photocatalytic CH4 conversion

Direct conversion of CH4 to high valued chemicals under mild conditions is attractive but full of challenges. Here, we present a ternary composite that consists of Ni-doped TiO2 nanocubes (NCs) and CNTs as a new kind of catalyst (denoted as CNTs-Ni@TiO2 NCs) for CH4 photocatalytic conversion to C1 oxygenated products at 30 °C. Using H2O2 as an oxidant, a high C1 oxygenated products yield and selectivity of 1.43 mol/(molNi·h) and 95.6% can be reached in 2 h at 30 °C. The superior photocatalytic performance resulted from the synergistic effects of TiO2 NCs, Ni species, and CNTs such as enhanced visible light absorption, improved electron/hole separation and charge transfer property, and lowered C-H bond cleavage energy required for CH4 activation, were carefully studied. Good reusability of the catalyst was studied by recycle experiments. Possible reaction mechanism based on the radical routes were carefully discussed by combining in-situ Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, radical scavenger experiments and density functional theory calculation.

Improved photodegradation of antibiotics pollutants in wastewaters by advanced oxidation process based on Ni-doped TiO2.

The number of antibiotic compounds in wastewaters has been growing globally due to the covid-19 problem. Using antibiotics to treat the patients would produce larger amounts of these compounds into the environment with negative impacts. Hence, finding out the method for the elimination of toxic organic pollutants as well as antibiotics in water is urgent (In this study, the treatment of antibiotic pollutants including cefalexin (CF) and tetracycline (TC) was investigated by applying the advanced oxidation process based on Ni-doped TiO2 (Ni-TiO2). The characterizations technologies such as XRD, XPS, UV-vis, PL, and PC indicated that Ni doping would improve the photocatalytic performance of TiO2. In the photodegradation experiments, the Ni-TiO2 possessed high photocatalytic degradation efficiencies with 93.6% for CF and 82.5% for TC. Besides, the removal rates of antibiotics after five cycles are higher than 75%, implying excellent stability of Ni-TiO2 photocatalyst. The result from the treatment of wastewater samples revealed that the Ni-TiO2 photocatalytic had good performance for removal of CF and TC at a high level of 88.6 and 80.2%, respectively.

Photoelectrochemical hydrogen generation with nanostructured CdS/Ti–Ni–O composite photoanode

Composite photocatalysts have aroused great interest due to combination of favorable electronic and optical properties. Herein, novel CdS/Ti–Ni–O composite photoanodes were constructed through anodic fabrication of nanostructured Ni-doped TiO2 (Ti–Ni–O) oxide films and CdS deposition by successive ionic layer adsorption and reaction (SILAR). The morphology and composition evolution, optical properties and photoelectrochemical (PEC) performance of the photoanodes were investigated. The composite nanofilms mainly consisted of micropores and nanotubes. The CdS/Ti–Ni–O composite photoanode demonstrated remarkable PEC hydrogen generation properties with a high photocurrent density (6.72 mA·cm−2 at 0 V vs Ag/AgCl) which was 18.2 times to that of the bare Ti–Ni–O photoanode. The synergy of Ni-doping and CdS-coupling on the enhancement of PEC performance offers useful ideas to the exploitation of effective photocatalysts and contributes to the development of solar-driven PEC hydrogen generation.

Removal of chlorhexidine digluconate from aqueous solution by heterogenous photocatalysis using sunlight-driven Ni-doped TiO2 material

Photoactive Ni-TiO2 was synthesized through green hydrothermal method with preferential photocatalytic performance in visible and solar light for synthetic and formulated wastewater treatment. Incorporation of this transition metal into TiO2 was examined by XRD, FTIR, UV–visible DRS, XPS, SEM-EDS and HRTEM analysis. According to the Langmuir–Hinshelwood model, the photodegradation of the chlorhexidine digluconate under solar (R2=0.986) and simulated visible light (R2=0.982), follows a pseudo-first-order kinetics. The interaction of operational fractions, such as S/C ratio, irradiation time, and pH of the reaction mixture, were evaluated using the RSM. Although complete mineralization of CHD was not achieved using Ni-TiO2 under visible light, but the parent compound was mineralized to some extent, as demonstrated by TOC reduction (85.71%-synthetic wastewater and 61.17%-formulated wastewater), UV254 (89.91% synthetic wastewater and 55.39%-formulated wastewater) and UV280 (68.23%-synthetic wastewater and 68.23%-formulated wastewater) absorbance variations. Based on the identified transformed products, the possible degradation pathway was proposed and bacterial susceptibility test on Bacillus cereus DPAML065 was performed to evaluate the toxicity of oxidation intermediates. Comparative studies about energy consumption and removal efficiency during simulated visible light/Ni-TiO2 and sunlight/ Ni-TiO2 mediated treatment system for formulated wastewater revealed that sunlight/ Ni-TiO2 mediated treatment system was high energy efficient (1.67 kWhKg-1) system.

Preparation and characterization of a novel Ni-doped TiO2 nanotube-modified inactive electrocatalytic electrode for the electrocatalytic degradation of phenol wastewater

A Ni-TiO2-NTs substrate and SnO2-Sb catalytic layer are formed on a Ni-Ti surface by the anodic oxidation method and sol-gel method, respectively, and a Ni-Ti/Ni-TiO2-NTs/SnO2-Sb electrode is successfully prepared for use as an electrocatalytic oxidation anode for wastewater treatment. Scanning electron microscopy (SEM) analysis shows that the Ni-TiO2-NTs base layer has a highly ordered and vertically formed nanotube array morphology, and the SnO2-Sb catalyst layer has a uniform and dense nanoparticle morphology. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses show that the base layer is made of Ni-TiO2 and the catalyst layer consists of SnO2-Sb. Electrochemical analysis shows that the oxygen evolution potential (OEP) of the electrode is increased to 2.3 V, and the working life is extended to 653 h. Using phenol as the treatment target, the phenol degradation rate reaches 87% in 3 h, and the COD removal rate reaches 54.2%. Compared with the traditional Ti/SnO2-Sb electrode, the current efficiency increases by 1.57 times, and the energy consumption decreased by 59.92%. Therefore, the Ni-Ti/Ni-TiO2-NTs/SnO2-Sb electrode is a promising electrochemical anode material for the treatment of phenol wastewater.

Surface morphology and optical properties of sol-gel synthesized TiO2 nanoparticles: Effect of Co, Pd and Ni-doping

Pristine and Co, Pd, Ni-doped TiO2 nanoparticles were synthesized by using the facile Sol-Gel method. Surface morphology was studied using SEM micrographs indicating the presence of agglomerated grains doped TiO2 nanoparticles. The optical band gap of pure and doped TiO2 nanoparticles has been studied using UV DRS spectroscopy. The band gap of the doped samples decreases except for Co–TiO2. The decrement in the band gap is due to the charge transfer from the dopant energy level of Pd3+ and Ni3+ to the conduction band of TiO2 as well as the defects caused by the Pd3+ and Ni3+ doping in TiO2 lattice.

The influences of Ni, Ag-doped TiO2 and SnO2, Ag-doped SnO2/TiO2 nanocomposites on recombination reduction in dye synthesized solar cells

In this work, the effects of doped nanoparticles (NPs) and nanocomposites (NCs) such as SnO2/TiO2 NCs, Ni-doped TiO2 NPs, Ag-doped TiO2 NPs and Ag-doped SnO2/TiO2 NCs as photoanode on the performance of Dye synthesized Solar Cells (DSSCs) were studied. The compounds were successfully synthesized using hydrothermal and sol-gel methods. XRD was used to examine the crystalline structures and the effects of dopants and nanocomposites on the crystal form of TiO2. Moreover, FE-SEM and TEM analysis showed that the produced NPs and NCs were porous and their shape, size and dispersion degree were different. Furthermore, by using FTIR spectra, the chemical species of the grown crystals were identified. Besides, variations band-gap were observed through the analysis of optical absorption spectra. In addition, EIS was used to analyze the effect of dopants and nanocomposites TiO2 on charge transfer resistance in the DSSCs. These studies indicated that the DSSCs photovoltaic properties largely depend on the compounds and structure of photoanodes. To this end, the current-voltage characteristics and Incident Photon-to-electron Conversion Efficiency (IPCE) measurements were used to evaluate the performance of DSSCs. As seen, while the conversion efficiency of the DSSC samples varies from 1.2 to ~6.93%, the DSSC-based on Ag-doped SnO2/TiO2 exhibit the highest conversion efficiency, i.e., 6.93%. It is owing to its lower charge transfer resistance, recombination and higher short-circuit photocurrent.

Plasmonic Ag supported on Ni-doped TiO2 nanospheres for rapid microbial inactivation under visible light

Ni-doped TiO2 nanospheres decorated with silver plasmonic nanoparticles (Ni-TiO2/Ag) have been successfully synthesized via sol-gel method and photo-deposition approach. In contrast with pure TiO2 and Ni-TiO2, the Ni-TiO2/Ag composite photocatalysts exhibit markedly enhanced visible-light photocatalytic sterilization efficiencies towards Escherichia coli (E. coli). And more importantly, antifungal experiment reveals that the composite can also disinfect ca. 2.0 log10 cfu·mL−1Fusarium graminearum (F. graminearum) macroconidia within 3 h. The highly efficient antimicrobial activities are ascribed to the introduction of Ni doping and Ag nanoparticles, which increases the visible light utilization and promotes the separation of electron-hole pairs. The photocatalytic disinfection mechanism is studied with scavengers trapping experiments and electron spin-resonance spectroscopy (ESR), which verifies the key role of •O2- and •OH during the microbial inactivation. Our study indicates that the Ni-TiO2/Ag nanocomposite has great potential for use in pathogenic microorganism remediation.

Sol-gel TiO2 nanostructures single doped with copper and nickel as nanocatalysts for enhanced performance for the Liebeskind–Srogl reaction

Design of nanostructured catalytic materials plays a strategic role in the synthesis of organic compounds with outstanding physicochemical properties. In this regard, titanium dioxide nanostructures doped with a single metal, namely, nickel and copper, were successfully prepared by a sol-gel method, and their phase structures, elemental compositions and morphologies were extensively characterised. In particular, X-ray diffraction (XRD) diffractograms and Raman spectra mainly revealed a rutile-phase structure for Cu-doped TiO2 and a biphasic anatase–rutile structure for Ni-doped TiO2. In addition, catalytic activities of Cu- and Ni-doped titanium dioxide nanostructures were evaluated for the synthesis of pyridopyrimidine derivatives from sulphur intermediates by the Liebeskind–Srogl reaction under UV illumination. Under the optimized reaction conditions, the target compounds were obtained in a yield of up to 87% by using the Cu-doped TiO2 catalyst and with a slightly lower yield of up to 79% for Ni-doped TiO2 in 12 h. Overall, the catalytic activity of Cu-doped TiO2 was greater than that of Ni-doped TiO2.

Metal-doped TiO2 nanocatalysts in an MX2/urea mixture for the synthesis of benzothiazoles bearing substituted pyrrolidin-2-ones: Enhanced catalytic performance and antibacterial activity

Solvents and catalysts are among the key factors in achieving the green chemical synthesis of bioactive compounds. In this regard, metal-doped nanoparticles, as a heterogeneous catalyst, in urea-based deep eutectic mixtures were used to prepare a series of pyrrolidinone-substituted benzothiazoles. In the strategy developed herein, pyrrolidinone derivatives were synthesized by reacting different arylamines with dimethyl itaconate using water as the solvent in a microwave. Then, the as-obtained pyrrolidinone derivatives were reacted with 2-aminothiophenol under microwave irradiation with the assistance of a deep eutectic mixture (CuCl2 or NiCl2/urea) and Cu- or Ni-doped TiO2 nanoparticles to afford the final derivative incorporating both pyrrolidin-2-one and benzothiazole rings. To determine the optimum reaction conditions, the effect of temperature, solvent nature, and reaction time was investigated. Under the optimal operation conditions, high reaction yields were achieved. The developed strategy exhibited advantages of a short reaction time, eco-friendliness, and high productivity. Finally, the obtained derivatives were examined in terms of their antibacterial potential against selected Gram-negative and Gram-positive bacterial strains: Eight of the derivatives exhibited activity against the tested bacteria.

Nickel-enhanced electrochemical activities of shape-tailored TiO2{001} nanocrystals for water treatment: A combined experimental and DFT studies

Understanding the reaction mechanism at the solid/liquid interface is necessary to improve the catalytic activity of electrode materials for water treatment. In this study, the photoelectrocatalytic degradation of rhodamine B (RhB) and phenol in water was studied using undoped and Ni-doped TiO2 with {001} facets (TiO2{001}). Under visible light irradiation, Ni-doped TiO2 electrodes exhibited higher contamination removal efficiency than undoped ones. Photoluminescence detection and density functional theory calculations revealed that the Ni-doped TiO2 provides a better hydroxyl radical yield and adsorption capacity than the undoped TiO2, which could be a major reason for the improvement of the catalytic activity of Ni-doped TiO2. The diffuse reflectance spectroscopy data showed that introducing the Ni2+ ions into TiO2 can shift the absorption edge towards the visible light region, which also contributes to the excellent photoelectrocatalytic performance. This work provides a strategy for improving the electrochemical performance of TiO2 and an in-depth understanding of the doping and catalytic mechanism of Ni2+ ions.

Impact of Ni metal ion concentration in TiO2 nanoparticles for enhanced photovoltaic performance of dye sensitized solar Cell

The undoped and Ni-doped TiO2 (Ni = 0.1, 0.3, 0.5 M) are synthesized and analyzed for application as dye-sensitized solar cell. The structural, optical and surface properties of the prepared samples are investigated using XRD, FTIR, Raman, UV–Vis, BET and XPS. The morphology and elemental composition of the materials are also studied using FESEM and EDX. The fabricated dye-sensitized solar cells are analyzed using electrochemical impedance spectroscopy and I–V characterization. The XRD studies reveal well crystalline nature of the samples. The anatase phase is confirmed for undoped TiO2 and mixed phase is observed for Ni-doped TiO2. The crystallite size calculated using Scherrer formula is found to increases for 0.1 and 0.3 M Ni metal ions doped into TiO2 lattice, beyond 0.3 M concentration it tends to decrease. The Raman peaks show the shift towards lower wave number upto 0.3 M Ni concentration, beyond this it tends to shift to higher wavenumber. Absorption spectra show the redshift for Ni doped TiO2 and the obtained optical bandgap for undoped and Ni doped TiO2 (Ni = 0.1, 0.3, 0.5 M) are 3.08, 2.53, 2.26, and 2.39 eV respectively. From the FESEM analysis the spherical shape morphology is observed and the element composition of Ti, O, Ni are confirmed by the EDX analysis. The specific surface area and pore size are calculated using BET analysis. The XPS is used to analyze the chemical environment and it confirms the successful Ni ions insertion into TiO2 lattice sites. The charge transfer resistance, shunt resistance and electron life time are calculated from electrochemical impedance study, which shows that the charge recombination can be reduced through Ni dopant. The obtained results show an interesting feature for Ni metal ions concentration beyond 0.3 M in TiO2 nanostructure. From XRD, Raman and UV–Vis results, there seems to be a threshold for the concentration 0.3 M of Ni in TiO2. Enhanced photocurrent conversion efficiency is obtained for 0.3 M Ni doped TiO2 photoanode-based DSSC.

Preparation and Characterization of Copper, Iron, and Nickel Doped Titanium Dioxide Photocatalysts for Decolorization of Methylene Blue

The visible-light response is a necessary condition for titanium dioxide (TiO2) photocatalyst to function as a visible light active photocatalyst. This condition can be solved by investigation of the bandgaps and the optimization of doping levels of multivalency metal-doped TiO2. In this study, pure and Cu, Fe, and Ni-doped TiO2 photocatalysts were prepared by the sol‐gel method. The photocatalysts were characterized using XRD, FTIR, FESEM, EDX, N2 physisorption, and UV‐Vis spectrophotometry techniques. The XRD patterns of all pure TiO2 and Cu/TiO2, Fe/TiO2, and Ni/TiO2samples showed the dominant structure of the anatase TiO2 phase. The presence of functional groups at the interface of TiO2 particles was showed by FTIR. The FESEM analysis showed that the particle size of the prepared samples was uniform with spherical morphology. EDX results showed that TiO2 has successfully incorporated Cu, Fe, and Ni metals onto its surface. The BET analysis showed that the specific surface area of the doped samples increased with the amount of doping. The optical properties of all samples were carried out using UV-DRS measurements and their obtained bandgap energies were in the range of 3.22 - 3.42 eV. The pure TiO2 displayed more than 98% and 97% decolorization rates for MB solution at the end of irradiation time of 5 h under UV and visible light, respectively. Among the doped samples, 3 mol% Ni/TiO2 and Cu/TiO2 demonstrated the highest photocatalytic activity (97.65%) under UV light and 6 mol% Ni/TiO2 under visible light for MB (96.86%) decolorization.

Magnetic Ni-Doped TiO2 Photocatalysts for Disinfection of Escherichia coli Bacteria.

Ni-doped TiO2 nanoparticles have been synthesized by a modified sol–gel method. The crystal phase composition, particle size, and magnetic and optical properties of the samples were comprehensively examined using x-ray diffraction analysis, transmission electron microscopy, Brunauer–Emmett–Teller surface area analysis, Raman spectroscopy, magnetization measurements, and ultraviolet–visible (UV–Vis) absorption techniques. The results showed that the prepared Ni-doped TiO2 samples sintered at 400°C crystallized completely in anatase phase with average particle size in the range from 8 nm to 10 nm and presented broad visible absorption. The bactericidal efficiency of TiO2 was effectively enhanced by Ni doping, with an optimum Ni doping concentration of 6% (x = 0.06), at which 95% of Escherichia coli were killed after just 90 min of irradiation. Density functional theory (DFT) calculations revealed good agreement with the experimental data. Moreover, the Ni dopant induced magnetic properties in TiO2, facilitating its retrieval using a magnetic field after use, which is an important feature for photocatalytic applications.

Methanol production from CO2 reduction over Ni/TiO2 catalyst

Photocatalytic reduction of carbon dioxide into methanol fuel over the Ni-doped TiO2 catalyst has been investigated. The experiments were carried out in a 50 ml batch reactor under UV irradiation. Ni/TiO2 photocatalysts were prepared by an impregnation method. The properties of the catalyst were characterized by X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflectance (UV–DR). Moreover, the effect of reaction time and Ni loading on the methanol conversion were investigated. The result indicated that the maximum of methanol production was obtained after the irradiation of 3 h and slightly reduced due to the methanol oxidation process. The Ni loading catalyst showed the higher methanol concentration than that over undoped TiO2 because Ni could trap the electron during irradiation and reduce electron–hole pair recombination by the p–n junction of TiO2. The highest methanol production rate of 272.45μmol/gcat was obtained over 4% wt Ni/TiO2 catalyst, which was 20 times higher methanol production rate than that over the commercial TiO2 catalyst (P25). Moreover, the stability of catalysts could be recycled four times with high activity of CO2 reduction to methanol. Therefore, 4% wt. Ni/TiO2 catalyst, low cost, showed better potential and activity in reducing CO2 emission to the environment.

Structural, magnetic, and optical properties of degenerated Ni and (Ga/Zn) co-doped TiO2 nanocomposites

Titanium oxide (TiO2) codoped with Ni-Ga and Ni-Zn nanoparticles were synthesized by the thermal co-precipitation method. The energy-dispersive x‐ray fluorescence, X‐Ray Diffraction, UV–visible absorption spectroscopy, and magnetization methods were performed to study the elemental content, crystalline structure, optical and magnetic properties, respectively. The roadmap of the present work is to explore the conditions of fabrication of dilute magnetic semiconductors, TiO2. It was established that the hydrogenation of the host-doped samples is required to create ferromagnetic properties. It was reported that the effect of doping with non-magnetic Ga3+ and Zn2+ ions created magnetic properties in the hydrogenated Ni-doped TiO2. Some optical properties of undoped and host TiO2 nanopowders were investigated using the diffuse reflectance spectroscopy (DRS) method. The higher magnetic energy observed with Ni/Ga-co-doped TiO2 was reported and discussed by itinerant electrons.

High-Temperature Hydrogen Sensing Performance of Ni-Doped TiO2 Prepared by Co-Precipitation Method.

This work deals with the substantially high-temperature hydrogen sensors required by combustion and processing technologies. It reports the synthesis of undoped and Ni-doped TiO2 (with 0, 0.5, 1 and 2 mol.% of Ni) nanoparticles by a co-precipitation method and the obtained characteristics applicable for this purpose. The effect of nickel doping on the morphological variation, as well as on the phase transition from anatase to rutile, of TiO2 was investigated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The resistive sensors prepared with these powders were tested toward H2 at 600 °C. The results indicate that 0.5% Ni-doped TiO2 with almost equal amounts of anatase and rutile shows the best H2 sensor response (ΔR/R0 = 72%), response rate and selectivity. The significant improvement of the sensing performance of 0.5% Ni-doped TiO2 is mainly attributed to the formation of the highest number of n-n junctions present between anatase and rutile, which influence the quantity of adsorbed oxygen (i.e., the active reaction site) on the surface and the conductivity of the material.

Synthesis of Ni-doped anatase TiO2 single crystals loaded on wood-based activated carbon for enhanced photodegradation of triphenylmethane dyes.

In this work, the Ni-doped anatase TiO2 single crystals loaded on activated carbon (Ni-T/AC) were synthesized by a sol-gel method. The chemical compositions and physical properties of as-prepared materials were analyzed by XRD, TEM, BET, FTIR, XPS, and PL characterizations. The obtained results implied that all of samples presented anatase phase with a clear mesoporous structure. The photocatalytic properties of nanocomposites were evaluated through photodegradation of crystal violet (CV), basic fuchsine (BF), and malachite green (MG). The results revealed that the catalyst Ni-T/AC-loaded AC exhibited an excellent photocatalytic activity compared with the original TiO2, and the photodegradation efficiency for CV, BF, and MG is 99.00%, 94.85%, and 98.89% after 120min of irradiation, respectively. This enhancement may be ascribed to the small crystallite size, large specific surface area, and pore volume of the photocatalysts. In addition, the possible degradation mechanism and pathway for triphenylmethane dyes (TPMs) were also well investigated. This work provides a new, low-cost, and effective route to improve the performance of TiO2 for effective removing TPMs.

Structure and AC conductivity of zinc and nickel-doped TiO2 nanocomposite synthesized by simple incipient wet impregnation method

The characterization of Zn/TiO2 and Ni/TiO2 composites has been investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The AC conductivity was measured in the frequency range 0.1 kHz to 3 MHz at temperatures from 25 to 100 °C. X-ray diffraction results revealed the presence of the anatase phase of TiO2, while presenting low peaks of rutile phase attributed to the Ni and Zn traces in the TiO2. A peak shift was appearing for Ni-doped TiO2 due to the change in the ionic radius which reduced the average particle size from 19 to 15 nm. The electrical conductivity was constant at low frequencies and increased with increasing frequency and doping with Zn and Ni, confirming the semiconductor nature of the samples and indicating localized/reorientation conduction mechanism. Interestingly, the frequency-dependent activation energy was found to be affected by the type of dopants.