NiO NiO Nanoparticles Research Articles

Enhancement of supercapacitor efficiency by Fe3+ doping in hydrothermally synthesized NiO nanoparticles

This study examines the physicochemical and electrochemical characteristics of hydrothermally produced, 800°C-annealed pure and Fe3+ doped (0.02, 0.04, and 0.06 M) NiO nanoparticles(NPs).The face-centred cubic structure of NiO NPs was verified by XRD analysis, and doping resulted in a decrease in crystallite size from 43.92 nm to 19.67 nm.FE-SEM revealed dense and irregularly arranged granular morphologies, while EDAX confirmed successful Fe3+ incorporation into NiO matrix. UV–Vis DRS showed an increase in bandgap energy from 3.15 eV to 3.71 eV. XPS confirmed the presence of Ni2+ and Fe3+ with their elemental compositions. According to BET analysis, Fe3+ doping increases pore size and specific surface area, which raises specific capacitance.VSM analysis of pure and Fe3+ doped NiO NPs demonstrated a transition from a weak ferromagnetic to a distinctive ferromagnetic behaviour, which is beneficial for energy storage as well as data storage applications.The electrochemical studies showed that 0.06 M Fe3+ doped NiO had the maximum specific capacitance of 360.96 F g−1 at the scan rate of 10 mV s−1and EIS Nyquist plots showed enhanced electrical conductivity. These results highlight the possibility of Fe3+ doped NiO NPs as excellent electrode materials for high-efficiency supercapacitors.

Biosynthesis of NiO nanoparticles using Senna occidentalis leaves extract: Effects of annealing temperature and antibacterial activity

In this work a cost effective and ecofriendly green method for the preparation of NiO nanostructures employing Senna occidentalis (S. occidentalis) leaves extract has been reported. XRD studies show that the 400 °C and 500 °C annealed nanostructures were authenticated as pure face centered cubic phase with an average crystallite size are about 27 nm and 15 nm, respectively. The SEM results show that both the annealed samples were nearly spherical with grain sizes ranging between 40 and 700 nm. The band gap of 400 °C and 500 °C annealed NiO nanoparticles (NPs) was estimated to be 5.28 eV and 5.40 eV, respectively from UV-visible studies while the occurrence of Ni-O stretching in the FTIR spectra validates the formation of NiO. Further this work witnesses that the NiO NPs synthesized from the green route offer better antibacterial activity. The observed maximum zone of inhibition of 500 °C annealed NiO NPs was found to be 20 mm and 19 mm for Serratia marcescens and Bacillus cereus strains and indicates that this material can serve as a prospective drug for biomedical application.

Investigation of Nonlinear Optical Properties of NiO Nanoparticles using the Z-Scan Technique

In this research, linear and nonlinear optical properties of NiO nanoparticles (NPs) dissolved in ethanol were investigated. Linear optical characteristics of NiO NPs were studied using a UV-Vis spectrophotometer. The linear absorption coefficient (α0) was 0.88 and 0.57 cm-1 at 405 and 532 nm wavelengths, respectively. The band gap energy rose from 3.56 eV for a sample with a 10-7 g/ml concentration to 3.92 eV for the 10-3 g/ml concentration sample. Using the Z-scan technique, the nonlinear optical characteristics of the NPs were investigated. Two continuous wave laser diodes with 405 and 532 nm wavelengths and different powers were used. The Z-scan system with a closed aperture revealed that NiO NPs have a negative n2 (self-defocusing effect) at various laser powers. n2 increases as the power of the laser increases. The value of n2 was found to be 0.51×10-4 cm2/mW at a wavelength of 405 nm and a power of 0.33 mW. It improved as the laser power increased, reaching a maximum of 0.64×10-4 cm2/mW at a laser power of 1.51 mW. For the laser with a wavelength of 532 nm, the n2 value was 0.27×10-4 cm2/mW for a laser power of 1.01 mW. This value increased to 0.76×10-4 cm2/mW when the laser power increased to 6.2 mW. As measured by the Z-scan system with an open aperture, NiO NPs have a nonlinear absorption coefficient and display a two-photon absorption behavior.

Enhanced acetone gas sensor via TiO2 nanofiber-NiO nanoparticle heterojunction

We present a high surface area sensor comprising NiO nanoparticles (NPs) incorporated within porous TiO2 nanofibers (NFs), showing a remarkable response to acetone. Initially, we synthesized Polyvinylpyrrolidone (PVP) NFs containing titanium (Ti) and nickel (Ni) salts using a simple electrospinning method. Subsequent calcination of the PVP NFs led to the formation of NiO NPs embedded within the porous TiO2 NFs. The resulting heterostructure material exhibited a significant response to acetone detection, with a ratio of electrical resistance in air (Ra) to that in the presence of gas (Rg) reaching 83 at its optimal operating temperature of 300 °C. Furthermore, it demonstrated stable performance under high relative humidity conditions.

Synthesis of Cu doped NiO for their antioxidant and photocatalytic properties: Green synthesis using Lycopodium Linn

Metal oxide nanoparticles produced by plant extracts are more stable and biocompatible in comparison with those produced by physical and chemical methods. This research focuses on the synthesis of pure and Cu doped NiO nanoparticles (NPs) using Phytolacca dodecandra L'Herit (P.d) leaf extract and evaluation of their antioxidant and photocatalytic activities. The obtained Cu-doped NiONPs have been characterized through X-ray diffraction (XRD), Transmission electron microscope (TEM), Fourier transform infrared (FT-IR), Ultraviolet-visible (UV–Vis), N2 adsorption-desorption and X-ray photoelectron spectra (XPS) analyses in different concentrations (1, 3, and 5 %) of copper at an optimum temperature of 400 °C. The photocatalytic activity of prepared samples was studied by degradation of Rose Bengal (RB) and Methylene Blue (MB) dye aqueous solutions. Under UV radiation for 60 min. 5-Cu-NiO nanophotocatalyst showed degradation efficiency of 98.7 % (0.5 mol/L), high apparent constant (0.9871 min−1) and long term stability towards MB dye. In the antioxidant test, NiO NPs and Cu−NiO NPs prevented the oxidation of 50 % of the H2O2 molecules at a concentration of 363.96 and 350.29 μg/mL, respectively. Moreover, the enhancement of the antioxidant activity of the biosynthesized NiO NPs might be an effect of copper ions present in the particles. Facile and green synthesis process with the excellent degradation performance demonstrates that the Cu doped NiO NPs have a great potential for wastewater treatment applications.

S-scheme NiO/C3N5 heterojunctions with enhanced interfacial electric field for boosting photothermal-assisted photocatalytic H2 and H2O2 production

Heterostructured visible-light-responsive photocatalysts represent a prospective approach to achieve efficient solar-to-chemical energy conversion. Herein, we propose a facile self-assembly technique to synthesize NiO nanoparticles/C3N5 nanosheets (NOCN) heterojunctions for hydrogen (H2) evolution catalysis and hydrogen peroxide (H2O2) production under visible light. In this regard, the black NiO nanoparticles (NPs) were tightly anchored on the surface of C3N5 nanosheets (CNNS) to construct S-scheme NOCN heterojunction, enabling efficient charge separation and high redox capability. Obtained results elucidated that the incorporated NiO NPs significantly promote light-harvesting efficiency and photo-to-thermal capacity over the NOCN composites. The enhanced photothermal effect facilitates the charge carrier transfer rate across the heterojunction and boosts the surface reaction kinetics. Accordingly, the photocatalytic performances of CNNS for H2 release and H2O2 production can be manipulated by introducing NiO NPs. The modified photocatalytic properties of NOCN composites are ascribed to the synergistic effects of all integrated components and the S-scheme heterojunction formation. Impressively, the high H2 evolution photocatalysis efficiency of NOCN nano-catalysts in seawater certifies their potential environmental applicability. Among all, the 12-NOCN nano-catalyst exhibits a higher photocatalytic efficiency for H2 release (112.2 μmol∙g−1∙h−1) and H2O2 production (91.2 μmol∙L−1∙h−1). Besides, the 12-NOCN nano-catalyst reveals excellent recyclability and structural stability. Additionally, the possible mechanism for photothermal-assisted photocatalysis is proposed. This work affords a feasible pathway to design photothermal-assisted S-scheme heterojunctions for diverse photocatalytic applications.

Green synthesis of NiO NPs for metagenome-derived laccase stabilization: Detoxifying pollutants and wastes

Laccases play a crucial role in neutralizing environmental pollutants, including antibiotics and phenolic compounds, by converting them into less harmful substances via a unique oxidation process. This study introduces an environmentally sustainable remediation technique, utilizing NiO nanoparticles (NPs) synthesized through green chemistry to immobilize a metagenome-derived laccase, PersiLac1, enhancing its application in pollutant detoxification. Salvadora persica leaf extract was used for the synthesis of NiO nanoparticles, utilizing its phytochemical constituents as reducing and capping agents, followed by characterization through different analyses. Characterization of NiO nanoparticles revealed distinctive FTIR absorption peaks indicating the nanoparticulate structure, while FESEM showed structured NiO with robust interconnections and dimensionality of about 50nm, confirmed by EDX analysis to have a consistent distribution of Ni and O. The immobilized PersiLac1 demonstrated enhanced thermal stability, with 85.55 % activity at 80 °C and reduced enzyme leaching, retaining 67.93 % activity across 15 biocatalytic cycles. It efficiently reduced rice straw (RS) phenol by 67.97 % within 210 min and degraded 70–78 % of tetracycline (TC) across a wide pH range (4.0–8.0), showing superior performance over the free enzyme. Immobilized laccase achieved up to 71 % TC removal at 40–80 °C, significantly outperforming the free enzyme. Notably, 54 % efficiency was achieved at 500 mg/L TC by immobilized laccase at 120 min. This research showed the potential of green-synthesized NiO nanoparticles to effectively immobilize laccase, presenting an eco-friendly approach to purify pollutants such as phenols and antibiotics. The durability and reusability of the immobilized enzyme, coupled with its ability to reduce pollutants, indicates a viable method for cleaning the environment. Nonetheless, the production costs and scalability of NiO nanoparticles for widespread industrial applications pose significant challenges. Future studies should focus on implementation at an industrial level and examine a wider range of pollutants to fully leverage the environmental clean-up capabilities of this innovative technology.

3D self-assembled polar vs. non-polar NiO nanoparticles nanoengineered from turbostratic Ni3(OH)4(NO3)2 and ordered β-Ni(OH)2 intermediates.

A surfactant-free ammonia and carbamide precursor-modulated engineering of self-assembled flower-like 3D NiO nanostructures based on ordered β-Ni(OH)2 and turbostratic Ni3(OH)4(NO3)2 nanoplate-structured intermediates is reported. By employing complementary structural and spectroscopic techniques, fundamental insights into structural and chemical transformations from intermediates to NiO nanoparticles (NPs) are provided. FTIR, Raman and DSC analyses show that the transformation of intermediates to NiO NPs involves subsequent loss of NO3- and OH- species through a double-step phase transformation at 306 and 326 °C corresponding to the loss of free interlayer ions and H2O species, respectively, followed by the loss of chemically bonded OH- and NO3- ions. Transformation to NiO NPs via the ammonia route proceeds as single-phase transition, accompanied with a loss of OH- species at 298 °C. The full transformation to NiO NPs of both intermediates is achieved at 350 °C through annealing in the air atmosphere. Ammonia-derived NPs maintain nanoflower morphology by self-assembling into nanoplates, which is enabled by H2O-mediated adhesion on the NiO NPs' {100} neutral surfaces. Structural transformations of turbostratic Ni3(OH)4(NO3)2 nanoplates result in the formation of NiO NPs dominantly shaped by inert polar OH-terminated (111) atomic planes, leading to the loss of the initial self-assembled 3D structure. DFT calculations support these observations, confirming that H2O adsorbs dissociatively on polar {111} surfaces, while only physisorption is energetically feasible on {100} surfaces. NiO NPs obtained via two different routes have overall different properties: carbamide-derived NPs are 3 times larger (15.5 vs. 5.4 nm), possess a larger band gap (3.6 vs. 3.2 eV) and are more Ni deficient. The intensity ratio of surface optical (SO) modes to transversal and longitudinal optical modes is ∼40 times higher in the NiO NPs obtained from β-Ni(OH)2 compared to Ni3(OH)4(NO3)2-derived NPs. The SO phonon lifetime is an order of magnitude shorter in NiO obtained from β-Ni(OH)2, reflecting a much smaller NP size. The choice of a precursor defines the size, morphology, crystallographic surface orientations and band gap of the NiO NPs, with Ni deficiency providing pathways for utilizing them as p-type materials, allowing for the precise nanoengineering of polar and neutral surface-dominated NiO NPs, which is of exceptional importance for use in catalysis.

A NiO-nanostructure-based electrochemical sensor functionalized with supramolecular structures for the ultra-sensitive detection of the endocrine disruptor bisphenol S in an aquatic environment.

Herein, NiO nanoparticles (NPs) functionalized with a para-hexanitrocalix[6]arene derivative (p-HNC6/NiO) were synthesized by using a facile method and applied as a selective electrochemical sensor for the determination of bisphenol S (BPS) in real samples. Moreover, the functional interactions, phase purities, surface morphologies and elemental compositions of the synthesized p-HNC6/NiO NPs were investigated via advanced analytical tools, such as Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Additionally, the synthesized p-HNC6/NiO NPs were cast on the surface of a bare glassy carbon electrode (GCE) via a drop casting method, which resulted in uniform deposition of p-HNC6/NiO/GCE over the surface of the GCE. Additionally, the developed p-HNC6/NiO/GCE sensor demonstrated an outstanding electrochemical response to BPS under optimized conditions, including a supporting electrolyte, a Briton-Robinson buffer electrolyte at pH 4, a scan rate of 110 mV s-1 and a potential window of between -0.2 and 1.0 V. The wide linear dynamic range was optimized to 0.8-70 μM to obtain a brilliant linear calibration curve for BPS. The limit of detection (LOD) and limit of quantification (LOQ) of the developed sensor were estimated to be 0.0059 and 0.019 μM, respectively, which are lower than those of reported sensors for BPS. The feasibility of the developed method was successfully assessed by analyzing the content of BPS in waste water samples, and good recoveries were achieved.

Complex magnetic behaviour and photocatalytic response in narrowed band gap NiO nanoparticles synthesized by novel Lepidagathis ananthapuramensis leaf extract

The present work focussed on the detailed investigation on structural, morphological, optical, photocatalytic, and magnetic properties of NiO nanoparticles (NPs) derived by a novel Lepidagathis ananthapuramensis leaf extract. The structural information using X-ray powder diffraction and Raman spectroscopy method indicates a single phase NiO hexagonal crystal structure for the sample calcined at ≥ 600 °C. Field emission scanning electron microscopy and high-resolution transmission electron microscopy studies noticed the various morphologies. UV–Visible, photoluminescence, and X-ray photoelectron spectroscopy confirmed the presence of both Ni2+ and Ni3+ ions with the narrowed band gap. Thorough magnetic studies indicate the existence of antiferromagnetic, ferromagnetic and superparamagnetic nature of NiO NPs. The photocatalytic activity of NiO NPs for the photocatalytic degradation of methylene blue dye in the presence of sunlight showed considerable results. This study can help us to deliver the wide range of properties which can be utilised in the field of magnetism and photocatalysis.

Facile auto-flash-combustion synthesis and characterization of visible-light-driven photocatalytic active Mn (II, III) loaded NiO nanoparticles

The opto-photocatalytic applications of Mn-doped NiO nanoparticles (NPs) are discussed. A facile synthesis of NiO doped with different Mn contents is performed and studied using experimental techniques. The structural properties and microstructural parameters of Mn:NiO NPs were examined by X-ray diffraction patterns. The average crystallite sizes of the pure NiO and 1.0-, 2.5-, 5.0-, 10-wt.% Mn-doped NiO NPs were found to be 25–19 nm by Williamson–Hall plots and 23–18 nm by the Debye–Scherer method. The crystallite size decreases with increasing doping concentration in the NiO host lattice. The optical bandgaps are found to be 3.53, 3.46, 3.39, 3.24, and 3.12 eV for pure NiO and 1.0-, 2.5-, 5.0-, and 10-wt.% Mn:NiO NPs, respectively, using the Kubelka–Munk function. X-ray photoelectron spectroscopy spectra of 2.5-wt.% Mn:NiO NPs were recorded for Mn, Ni, and O to determine the oxidation states. The photocatalytic performances of pure NiO and Mn:NiO NPs are examined. The 2.5-wt.% Mn:NPs exhibit the best photocatalytic performance owing to the greatest activation sites. The mechanism of the photocatalytic decolorization reaction is also investigated. The results demonstrate the high ability of Mn:NiO NPs as photocatalysts for methylene blue dye degradation, with 92% removal.

Modification of Flexible Electrodes for P-Type (Nickel Oxide) Dye-Sensitized Solar Cell Performance Based on the Cellulose Nanofiber Film.

The preparation of flexible electrode, including working electrode (WE) and counter electrode (CE), for dye-sensitized solar cells (DSSCs) utilizing metal oxides using environmentally friendly sustainable TEMPO-oxidized cellulose nanofibers (TOCNFs) is reported in this work. A new type of flexible electrode for the DSSCs, which were made of cellulose nanofiber composites with nickel hydroxide [CNF/Ni(OH)2] substrate films and cellulose nanofiber composites with polypyrrole (CNF/PPY). Nickel hydroxide, Ni(OH)2, has been prepared hydrothermally in the presence of TOCNFs, [TOCNF@Ni(OH)2]. Similarly, the conductive polymer substrate has also been prepared from a composite consisting of TOCNF and PPY, TOCNF@ PPY film, by means of polymerization for the CE. Overall, the prepared electrodes both WE from CNF/Ni(OH)2 substrates and CE from the TOCNF@PPY substrate film were revealed as the novelty of this work and which no one has introduced previously. Although NiO nanoparticles (NPs) coated on the Ni(OH)2/TOCNF electrode also produced a good power conversion efficiency, PCE (0.75%); nevertheless, the NiO NP treatment with carbon dots boosted the efficiency up to 1.3%.

Fabrication and modeling of laser ablated NiO nanoparticles decorated SnO2 based formaldehyde sensor

In this study, we have reported the fabrication of p-NiO/n-SnO2 heterojunction based formaldehyde (HCHO) sensor by decorating the surface of pre-deposited SnO2 thin film with laser ablated NiO nanoparticles (NPs). In atmospheric air, NiO NPs were produced by a moving laser beam on the surface of pure (99.99%) Ni pellet to decorate sputtered deposited SnO2 thin film directly to form NiO/SnO2 p-n heterojunction. After fabrication, gas sensing properties of NiO/SnO2 sensor were investigated systemically towards HCHO and it exhibited higher response (Ra/Rg) of about 31.04 towards 50 ppm HCHO at 210 °C with good selectivity compared with pristine SnO2 sensor. Moreover, adsorption (Ka) and desorption rate constant (Kd), response time (τres), recovery time (τrec) and surface coverage (θ) of NiO/SnO2 sensor were extracted from experimental data using Langmuir gas adsorption-desorption model via curve fitting method and the models demonstrated the irreversible type of gas sensing behaviour towards HCHO. The experimental results revealed that the laser ablation method has a great potential to use as alternative chemical free surface decoration route to fabricate metal oxide heterojunction based sensors for the detection of formaldehyde or other toxic gases.

Engineered synthetic nanobody-based biosensors for electrochemical detection of epidermal growth factor receptor

Two engineered synthetic nanobody-based nanobiocomposite platforms were developed for label-free electrochemical detection of the epithelial growth factor receptor (EGFR) biomarker. Screen-printed carbon electrodes (SPCE) were decorated either with NiO nanoparticles (NPs) or poly(thiophene acetic acid) (PTAA) to link the anti-EGFR nanobody (Nb) and form nanobiocomposites for detecting the EGFR biomarker by electrochemical impedance spectroscopy (EIS). The nanoarchitectures were prepared by in situ electrosynthesis of NiO NPs or PTAA layers at SPCEs. A modified version of the 9G8 Nb (Nb9G8m), specific for the EGFR (anti-EGFR), was designed and produced as the nanobiosensor bioreceptor. This Nb was engineered to provide a hexahistidine tag (6xHis-tag) and a lysine (Lys) dual functionality to form a (6xHis-tag)/Ni2+ or Lys/PTAA interface. The biosensing interfaces were characterized by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and EIS. The nanobody/nanobiocomposite-based biosensors detected EGFR proteins in a linear range from 0.25 to 50 μg mL−1 and 0.5 to 50 μg mL−1, with limits of detection of 0.46 μg mL−1 and 1.14 μg mL−1, for NiO- and PTAA-based platforms, respectively. The biosensing platforms offer high simplicity, specificity, and selectivity to detect EGFR, but Nbs can be readily engineered to detect other (glycol)proteins. Finally, as a proof of concept, the EGFR was detected in several tumor cell lines, differentiating biomarker expression among them.

Influence of embedded NiO-nanoparticles on the nonlinear absorption of tungsten disulfide nanolayers

2D transition metal dichalcogenides possess fascinating properties due to their direct bandgap, strong spin-orbit coupling, and promising electronic/mechanical properties. In this work, we synthesized pure tungsten disulfide (WS2) nanolayers and NiO nanoparticles (NPs) decorated in few-layered WS2 and measured the third-order nonlinear optical properties using femtosecond Z-scan measurements. The open aperture Z-scan data illustrated that the inclusion of NiO nanoparticles into the WS2 layers increases the nonlinear absorption at 800 and 400 nm wavelengths. Furthermore, we observed the switchability of the nonlinear absorption from saturable absorption to two-photon absorption or reverse saturable absorption by changing the pump intensity. Thus, the embedded NiO NPs played a crucial role in the variation of intensity-dependent nonlinear absorption mechanism of WS2 nanolayers and thus can be helpful for various optical applications such as laser pulse compression and optical limiting to prevent over-exposure of protective photosensitive sensors by intense ultrashort laser pulses.

Human biomonitoring and personal air monitoring. An integrated approach to assess exposure of stainless-steel welders to metal-oxide nanoparticles

In welding, there is a potential risk due to metal-oxide nanoparticles (MONPs) exposure of workers. To investigate this possibility, the diameter and number particles concentration of MONPs were evaluated in different biological matrices and in personal air samples collected from 18 stainless-steel welders and 15 unexposed administrative employees engaged in two Italian mechanical engineering Companies. Exhaled breath condensate (EBC) and urine were sampled at pre-shift on 1st day and post-shift on 5th day of the workweek, while plasma and inhalable particulate matter (IPM) at post-shift on 5th day and analysed using the Single Particle Mass Spectrometry (SP-ICP-MS) technique to assess possible exposure to Cr2O3, Mn3O4 and NiO nanoparticles (NPs) in welders. The NPs in IPM at both Companies presented a multi-oxide composition consisting of Cr2O3 (median, 871,574 particles/m3; 70 nm), Mn3O4 (median, 713,481 particles/m3; 92 nm) and NiO (median, 369,324 particles/m3; 55 nm). The EBC of welders at both Companies showed Cr2O3 NPs median concentration significantly higher at post-shift (64,645 particles/mL; 55 nm) than at pre-shift (15,836 particles/mL; 58 nm). Significantly lower Cr2O3 NPs median concentration and size (7762 particles/mL; 44 nm) were observed in plasma compared to EBC of welders. At one Company, NiO NPs median concentration in EBC (22,000 particles/mL; 65 nm) and plasma (8248 particles/mL; 37 nm) were detected only at post-shift. No particles of Cr2O3, Mn3O4 and NiO were detected in urine of welders at both Companies. The combined analyses of biological matrices and air samples were a valid approach to investigate both internal and external exposure of welding workers to MONPs. Overall, results may inform suitable risk assessment and management procedures in welding operations.

Fabrication of TiO2/NiO p-n Nanocomposite for Enhancement Dye Photodegradation under Solar Radiation.

A p-n nanocomposite based on TiO2 nanotubes (NTs) and NiO nanoparticles (NPs) was designed and optimized in this study to improve the photocatalytic performance of methylene blue (MB). The hydrothermal technique has been used to produce TiO2/NiO nanocomposites with different NiO NPs weight ratios; 1TiO2:1NiO, 1TiO2:2NiO, and 1TiO2:3NiO. The crystal phase, chemical composition, optical properties, and morphology of TiO2/NiO were explored by various techniques. TiO2 NTs have a monoclinic structure, while NiO NPs have a cubic structure, according to the structural study. The bandgap of TiO2 NTs was reduced from 3.54 eV to 2.69 eV after controlling the NiO NPs weight ratio. The TiO2/2NiO nanocomposite showed the best photodegradation efficiency. Within 45 min of solar light irradiation, the efficiency of MB dye degradation using TiO2/2NiO hits 99.5% versus 73% using pure TiO2 NTs. Furthermore, the catalytic photodegradation efficiency did not deteriorate significantly even after five reusability cycles, intimating the high stability of the TiO2/2NiO nanocomposite. This suggests that the loading of NiO NPs into TiO2 NTs lowers the recombination of photo-produced electron/hole pairs and enlarged solar spectral response range, which results in improved photocatalytic activity. The mechanism of charge transfer in the TiO2/NiO and kinetic models were discussed for the photodegradation of MB.

Fe–Co co-doping effects on antiferromagnetic core of NiO nanoparticles

The Fe and Co single and co-doping effects on the structural and magnetic properties of NiO nanoparticles (NPs) have been studied. The Fe and Co doping into NiO system did not induce any other possible secondary phase (other than NiO) and the average crystallite size was found to be in a narrow range of 33–40 nm which is suitable for studying the doping effects. Room temperature ferromagnetic resonance (FMR) measurements demonstrated the existence of a net magnetization in antiferromagnetic (AFM) NiO NPs which was observed to be increased with an increasing Fe doping and decreasing Co doping concentration. The scattered differential FMR signal for 8% Co doped NiO NPs revealed the presence of randomly oriented magnetic moments in the core of the NPs. However, decreasing the Co doping concentration and increasing the Fe doping concentration increased the degree of homogeneity of the spin structure in the system. The M − H loops taken at room temperature with S-like shape confirmed the presence of a weak ferromagnetism in the Fe doped samples in accordance with FMR analysis and attributed to the double exchange mechanism in these NPs. In ZFC/FC curves, a small peak at low temperatures, in the range of 9–18 K for all the samples, indicates the magnetization contribution from the uncompensated surface spins of these NPs. In addition, a relatively broad peak for higher Fe doping concentrations at higher temperatures indicates the onset of magnetization from the core of these NPs, where Fe and Ni ions may couple parallel or anti-parallel to each other. In summary, Co–Fe co-doping induced a core magnetization in AFM NiO NPs system and makes it attractive for various magnetic applications.

Structural, optical analysis, and Poole–Frenkel emission in NiO/CMC–PVP: Bio-nanocomposites for optoelectronic applications

The properties and related applications of biopolymer-based nanocomposites are dependent on the composition of the polymeric blend and the type and morphology of the nanofillers used. In this work, high purity NiO nanoparticles (NP) were prepared by a facile sol-gel route and introduced into carboxymethyl cellulose–polyvinyl pyrrolidone (CMC–PVP) blend. The crystallinity, surface morphology, and chemical composition of the resulting films were studied using FE-SEM, XRD, EDX and FTIR spectroscopy to evaluate the NiO NP's dispersion level inside the blend and their influence on the film structure and complexation with the functional groups in the blend. UV–Vis–NIR spectroscopy showed that the NiO NP reduce the transparency of the resulting films from 90 to 43.1% and interestingly modified their reflectivity. The optical bandgap was determined using two different approaches and found to decrease (from 5.1 to 4.5 eV) upon increasing the NP content. The current–voltage (I–V) characteristics were found to be of a non-ohmic type. The DC conductivity (σdc) was significantly increased and the activation energy (Ea) decreased after loading 1.2 wt% NiO. The possible conduction mechanisms have been discussed. The results indicate that novel NiO/CMC–PVP nanocomposites can be prepared with improved conductivity, reduced band gap, and highly improved refractive index. Therefore, these materials are suitable for coatings and lenses as well as for engineering, electrochemical and optoelectronic applications.

Antiferromagnetic spin correlations above the bulk ordering temperature in NiO nanoparticles: Effect of extrinsic factors

NiO has been considered one of the attractive materials for advanced technological applications such as antiferromagnetic (AF) spintronics in recent years. For a working application, an adequate knowledge of AF ordering temperature TN and spin correlations is vital. This study intends to understand extrinsic factors affecting the TN and AF spin correlations from ∼63 nm NiO nanoparticles (NPs). The micro-Raman scattering combined with neutron powder diffraction shows that NiO NPs retain T°N ∼ 523 K (similar to bulk NiO TN). The additional anomalies observed at TN' ∼ 560 K and TN'' = 669 K indicated the persistence of AF spin correlations above TN, which are suppressed relative to those observed in bulk NiO. The origin of anomalies above TN was interpreted simply as extrinsic factors such as wide distribution in the particle size and weak interparticle interaction.