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Zinc oxide nanoparticles (ZnONPs) exhibit optical, electrical, and magnetic properties depending on their size and morphology. These properties are essential for using ZnONPs in various fields such as cosmetics, electronics and medicine. The properties and applications of ZnONPs depend on how they are synthesized, whether physical, chemical, or biological. This study aimed to produce ZnONPs by utilizing the leaf extract of Moringa oleifera and to study the effect of precursor molarity and leaf extract concentration on physical properties. The precipitated compound was characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), and Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDAX). Here, we prepared ZnONPs under four different molarity (0.2M, 0.3M 0.4M, and 0.5M) and two different leaf extract concentrations (10ml, 15ml). We analyzed the difference obtained in the average particle size in each case. From the XRD the major diffraction peaks are observed at 36.3, 47.53, 36.33, and 36 for 0.2M, 0.3M, 0.4M, and 0.5M, respectively. The average particle size was found to be in the range of 12–30nm. UV study was used to inspect the optical nature of the prepared ZnONPs and SEM confirmed the sample’s morphology. Investigations on the role of precursor molarity and leaf extract concentration in synthesizing ZnONPs indicated that average particle size increases with increasing precursor molarity and leaf extract concentration. The study also suggested that synthesizing metal oxide nanoparticles using botanical extract is an eco-friendly alternative to physical and chemical methods.

White light-absorbing materials are in high demand for catalysis and energy harvesting. Due to the UV (ultraviolet) light absorption capacity of graphene and zinc oxide (ZnO) nanoparticles, the light harvesting of the whole range of visible and near-IR (infra-red) light by utilizing these materials is a significant barrier. In this study, a graphene-ZnO nanoparticle composite was prepared from graphene and ZnO powder through a simple and novel hot solvent process at low temperatures without a catalyst or expensive instrumentation. The fabricated composite was found to absorb light efficiently at an extended range of wavelengths (400–1665nm) with strong absorption intensity. Notably, the in situ graphene-ZnO showed a considerably low intensity of absorption in the visible to the near-IR range; however, when the graphene and ZnO powder were combined as a graphene-ZnO composite by ex situ hot solvent synthesis process, the light absorption intensity significantly increased within the whole range. The observation in this study is the first one that indicates that the ex situ hot solvent process tunes the light absorption properties at the extreme level of the visible- to the near-IR range. The prepared composite also showed excellent electrical conductivity. The graphene powder was also prepared through a straightforward self-developed solvothermal process with the help of the exfoliating agent.

Bio-sensing sensitivity of a spectrally selective nanoparticle based ultraviolet (UV) photodetector is characterized in comparison to a silicon photodiode and a photomultiplier tube (PMT). The nanoparticle based photodetector is comprised of poly-vinyl alcohol (PVA) coated zinc-oxide (ZnO) nanoparticles deposited on an aluminum-gallium-nitride (AlGaN) epitaxially grown substrate. The sensitivity was determined by measuring the fluorescence intensity of the native fluorophore, tryptophan, in Escherichia coli (E-coli, ATCC-25922) cells. Tryptophan intrinsically fluoresces with a peak at 340 nm under 280 nm UV light illumination. It is shown that this detector can sense the concentration of E-coli to 2.5 × 10⁸ cfu/mL while the silicon photodiode cannot detect the intrinsic fluorescence at all. Nevertheless, the PMT outperformed the ZnO nanoparticle-AlGaN substrate based photodetector with the ability to sense E-coli concentrations to 3.91 × 10⁶ cfu/mL. However, because PMT based systems are commonly limited by high dark current, susceptible to environmental changes, sensitive to ambient light, are not spectrally selective and have high power consumption, biological detection systems comprised of these ZnO nanoparticle-AlGaN substrate based photodetectors can be more effective for near real time characterization of potential bacterial contamination.

In this work, a colloid of nanocrystalline ZnO particles was prepared by chemical method, and sprayed on porous silicon (PS) substrate which was prepared by electrochemical etching under a current density of 15 mA/cm² for 10 min. The initial radius of the ZnO particles was found to be (2.2 nm). FTIR spectra exhibit the presence of Zn–O bond which indicates the formation of ZnO particles. Also spectra reveals the formation of SiH_x(x = 1–2) and Si–O bond which indicates the presence of porous layer. High-performance rectification was obtained, with high photoresponsivity of 0.54 A/W at 400 nm. The corresponding quantum efficiency was 166.7%. The results show that ZnO on PS structures act as good candidates for making highly efficient photodiodes.

The ZnO nanoparticles were synthesized using marine brown algae (Cystoseira) extract and calcination. For comparison, combustion, and sol–gel methods were employed to synthesize nanoparticles to use as material in dye-sensitized solar cells (DSSCs) photoanode. The produced nanoparticles were characterized using structural and morphological studies by FTIR, SEM, and XRD experiments, respectively. The results revealed that the net hexagonal crystal structure was achieved with a crystal size of less than 100 nm, good purity, spherical shape, and a suitable dimension for fabricating DSSCs. They exhibit enhanced properties due to the variation in their characteristics such as average size, size distribution, and morphology. The ZnO nanoparticles were used to fabricate the DSSCs by the doctor blade method, and the efficacy of each cell was evaluated using voltage–current measurement. The results were in good agreement with the characteristic curve of the commercialized DSSC. The best performance for the fabricated DSSCs was achieved using green synthesized ZnO nanoparticles, because of the influence of their morphology such as smaller crystal size, more grain boundaries, and bigger surface area. The cell’s solar-to-electricity conversion efficiency, short-circuit current, open-circuit voltage, and fill factor were measured as ∼1.13%, 3.8mA/cm², 620mV, and 54.3%, respectively. The enhanced photovoltaic properties were ascribed to the flower-like morphological structures of the ZnO nanoparticles prepared using the green synthesis method.

Well-dispersed undoped and copper-doped zinc oxide nanoparticles (Zn${}_{1-x}$Cu${}_x$O, $x$ = 0, 1, 5 and 10 wt.%) have been synthesized by precipitation method at room temperature. X-ray diffraction data revealed that the undoped and copper-doped zinc oxide nanoparticles are in phase pure wurtzite structure and the crystallite size increases from 24 nm to 36 nm with increase in dopant concentration. The optical band gap was found to decrease with increasing dopant concentration, which clearly indicates the blue shift. High-resolution scanning electron microscope image shows that the synthesized samples consist of an assembly of nanopetals. Transmission electron microscope image also confirmed the average particle size of 20–50 nm. Energy-dispersive X-ray spectrum shows that the prepared samples are free from impurities. Photoluminescence spectra exposed that copper ions are doped into the lattice positions of ZnO. A simultaneous differential scanning calorimeter/thermogravimetric analysis combination was used to study the phase variations.

In this study, ZnO nanoparticles and MnO-doped SnO₂-based thick film varistors (TFVs) were fabricated using screen printing technique. The sintering temperature had significant impact on the SZM-based TFVs, especially in terms of grain growth, even at a low sintering temperature of 1100${}^{\circ }$C. The strong solid-state reaction during sintering may be attributed to the large surface area of the 20 nm ZnO nanoparticles that promoted strong surface reaction even at low sintering temperatures. Moreover, the X-ray diffraction lattice constant and full wave at half maximum data indicated that the sintering process also improved the grain crystallinity with the decrease in intrinsic compressive stress. The sintering temperatures also significantly influenced the electrical properties of the SZM-based TFVs with a significant decrease in the breakdown field from 360 V/mm (sample at 1100${}^{\circ }$C) to 158 V/mm (sample at 1250${}^{\circ }$C). The grain boundary resistance ($R_{\mathrm{\text{GB}}})$ also experienced a dramatic drop from 266.4 k$\mathrm{\Omega }$ (sample at 1100${}^{\circ }$C) to 89.46 k$\mathrm{\Omega }$ (sample at 1250${}^{\circ }$C). The sample sintered at 1200${}^{\circ }$C exhibited superior electrical behaviors with a nonlinear exponent of 61 and leakage current of 115 $\mu$A. Furthermore, it achieved high permittivity and low dissipation factor at the low frequency range. The conduction behaviors of ${\mathrm{\text{O}}}^{\prime }$ ions with activation energy of approximately 0.6 eV was dominated by decreasing ${\mathrm{\text{Zn}}}_{\mathrm{\text{Sn}}}^{\prime \prime }$ and ${\mathrm{\text{Mn}}}_{\mathrm{\text{Sn}}}^{\prime \prime }$ defects (around 0.4 eV) with increasing sintering temperature. Therefore, the sintering process can be applied to control the conduction behaviors of SZM-based TFVs doped with ZnO nanoparticle powder and achieve improved structural and electrical properties with good nonlinear behaviors.

The structural and optical characteristics of polystyrene (PS) and ZnO nanoparticles embedded in polystyrene as polymeric nanocomposite foils (PS/ZnO) were examined. The sol–gel process was utilized to make ZnO nanoparticles with a diameter of less than 50 nm. The solution casting process was used to prepare pure PS and PS/ZnO nanocomposite foils. The PS/ZnO nanocomposite foils were very transparent in the visible region as-synthesized, but due to substantial absorption in the UV area, absorbent peaks were formed at 264 nm and 364 nm, and these foils serve as UV absorbers. X-ray diffractometer (XRD) of ZnO embedded polystyrene nanocomposite foils studied the crystal structure of the flexible foils. Optical properties and optical constants including band gap were studied by transmittance, absorbance, and reflectance spectra that are obtained by UV–Vis spectrophotometer. The Wemple DiDomenico single oscillator model was used to estimate the dispersion energy parameters ($E_0$, $E_d$, ${𝜀}_0,{\lambda }_0,S_0)$, optical moments ($M_{-1}$, $M_{-3})$, the density of states ($N$/$m^{\ast }$), dispersion of refractive index ($n_0)$, and plasma frequency (${\omega }_p)$ of the investigated foils. Semi-empirical relations were used to estimate the nonlinear index of refraction ($n_2)$ and third-order optical nonlinear susceptibility (${\chi }^{(3)})$. PS/ZnO nanocomposite foils operate as UV absorbents and are a promising preference for photonic applications due to their optical characteristics.

A ZnO nanoparticles (NPs)/reduced graphene oxide (rGO) composite was fabricated via a simple one-step solvothermal method with graphene oxide (GO) and Zn(NO₃)₂ ⋅ 6H₂O as the precursors. The morphology, crystal structure and optical properties of the synthesized materials were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy and photoluminescence (PL) spectroscopy. The synthesized composite exhibited rGO layers assorted with tiny ZnO NPs. rGO supposedly acted as a template in the solvothermal process, that may promote the preferential attachment of ZnO NPs and prevented the agglomeration of ZnO NPs in the synthesized composite. It was also found that the electrical properties of the composite improved markedly with bare ZnO NPs, without significantly changing the morphology and crystal structure of the ZnO NPs. The main aim of this research is to develop an efficient sensor and to understand the effect of graphene in sensing characteristics. The synthesized composite was exposed to H₂, CO and C₂H₂ gases to confirm its feasibility for gas sensing, and the results showed preferential detection of reducing gases at low temperature.

In this work, n-ZnO/p-Si heterojunction photodetectors were prepared by drop casting of ZnO nanoparticles (NPs) on single crystal p-type silicon substrates, followed by (15–60) min; step-annealing at 600^∘C. Structural, electrical, and optical properties of the ZnO NPs films deposited on quartz substrates were studied as a function of annealing time. X-ray diffraction studies showed a polycrystalline, hexagonal wurtizte nanostructured ZnO with preferential orientation along the (100) plane. Atomic force microscopy measurements showed an average ZnO grain size within the range of 75.9 nm–99.9 nm with a corresponding root mean square (RMS) surface roughness between 0.51 nm–2.16 nm. Dark and under illumination current–voltage (I–V) characteristics of the n-ZnO/p-Si heterojunction photodetectors showed an improving rectification ratio and a decreasing saturation current at longer annealing time with an ideality factor of 3 obtained at 60 min annealing time. Capacitance–voltage (C–V) characteristics of heterojunctions were investigated in order to estimate the built-in-voltage and junction type. The photodetectors, fabricated at optimum annealing time, exhibited good linearity characteristics. Maximum sensitivity was obtained when ZnO/Si heterojunctions were annealed at 60 min. Two peaks of response, located at 650 nm and 850 nm, were observed with sensitivities of 0.12–0.19 A/W and 0.18–0.39 A/W, respectively. Detectivity of the photodetectors as function of annealing time was estimated.

In this study, different additives such as cetyltrimethylammonium bromide (CTAB), aluminum nitrate and tri-n-octylphosphine oxide (TOPO) are selected, respectively, to bind zinc acetate in order to investigate its role in the formation of ZnO nanoparticles. Accordingly, the morphology and size of produced ZnO nanoparticles are affected by existence of the additives through XRD analyses and TEM observations. The particle size was found to be 32, 14, 15, and 28 nm for pure zinc acetate, zinc acetate/TOPO, zinc acetate/CTAB, and zinc acetate/aluminum nitrate, respectively. It is observed that the TOPO and CTAB decrease the size of ZnO nanoparticles, while the doping of aluminum to the precursor has no effect on its particle size. The obtained ZnO nanoparticles exhibited the direct optical bandgap of about 3.40–3.45 eV and their photoluminescence spectrum has a UV emission peak at about 363 nm which is slightly blue-shifted due to the smaller particle size of the ZnO nanoparticles in the presence of TOPO and CTAB additives.

The optical and electrical studies on ZnO thin film are reported. Thin film of ZnO is deposited on glass substrate by physical vapor deposition method. In this method, Zn powder is evaporated at a temperature of 400°C in the presence of oxygen and argon gases, and the resulting ZnO is deposited on the glass substrate which is kept at liquid nitrogen temperature. The crystallinity of this ZnO film is studied using XRD technique. The XRD pattern suggests that the nature of this film is polycrystalline. The prominent peaks observed at 31.78, 34.34, 36.18, and 56.32 correspond to the (100), (002), (101), and (110) planes, confirming the formation of hexagonal zinc oxide phase (JCPD 36-1451 for wurtzite zinc oxide). The XRD spectrum very clearly demonstrates that the film deposited in oxygen atmosphere has a dominant (101) orientation. The d_hkl values are estimated for this as-deposited ZnO thin-film. It is observed that these calculated values in close agreement with the reported d_hkl values for ZnO. Debye–Scherrer equation is used to estimate the size of these nanoparticles. It is found that size estimated by Debye–Scherrer equation agrees well with the size observed by TEM images. It is clear from the transmission electron microscope (TEM) images that the film contains nanoparticles of ZnO and the diameter of these nanoparticles varies from 5–20 nm. In optical properties, the UV visible spectrum of these nanoparticles is recorded in the wavelength range (300–900 nm). The absorption coefficient increases exponentially with the increase in photon energy. The direct optical band gap is calculated which comes out to be 3.54 eV. The value of Urbach energy (E_U) is also calculated using the slope of the plot ln α versus photon energy and it comes out to be 805.8 meV. For electrical properties, the DC conductivity of ZnO film deposited on glass substrate is measured in the temperature range of 450–300 K. On the basis of temperature dependence of DC conductivity of ZnO film, it is suggested that the conduction takes place via thermally activated process.

In the present work, Zinc Oxide nanoparticles (ZnO Nps) have been prepared by a simple and low temperature solution combustion method using Zinc nitrate as a precursor and solid water melon juice as a novel fuel for the first time. The structure and morphology of the synthesized ZnO NPs have been analyzed using various analytical techniques such as Powder X-ray diffraction, FTIR spectroscopy, Raman spectroscopy, UV-Visible spectroscopy, photoluminescence spectroscopy, scanning electron microscope and transmission electron microscope. ZnO NPs show good photo catalytic activity for the degradation of methylene blue (MB) dye. It also shows significant antibacterial activities against three bacterial strains.

In this work, zinc nanoparticles were prepared using the low-temperature plasma method at different times 3min, 5min, 7min, 9min, where the initial reactions of zinc lead to the formation of nanoparticles. The metal interacts with the ionized plasma under different conditions and may turn into an oxide such as exposing the sample to air and raising the temperature of the solution a few degrees as a result of high voltage and within a certain range. The atmospheric pressure plasma system acts as the cathode, while the zinc metal strip acts as the anode. A series of techniques were used, including the use of X-ray diffraction (XRD), ultraviolet-visible spectroscopy and scanning electron microscopy (FESEM). The X-ray diffraction results showed that the samples have polycrystalline structures with hexagonal and cubic structures with a time difference, and the X-ray diffraction results showed the conversion of zinc particles into zinc oxides. FESEM images reveal particle size and shape. The ZnO nanoparticles prepared by the mentioned method seem to form different nanoshapes such as starfish and mushroom nanoparticles. The UV-visible results showed that the samples had an energy gap of about 3.4eV at a time of 3min, and this value decreases with increasing reaction time. The appearance of zinc oxides increases gradually with the passage of time. These results provide credibility for the fabrication of ZnO nanostructures for use in future gas sensing applications, despite the inhomogeneity of particle size among ZnO particles, the sensor was also fabricated to detect nitrogen gas (NH3) with different concentrations (17.25ppm, 46.38ppm, 78.58ppm). at room temperature. The ZnO sample showed the highest sensitivity (88.1%) at 7min. The sensitivity showed different results and increased with reaction time and gas concentration. However, response and recovery time are moderate and decrease as reaction time increases.

Introduction: The potential of zinc oxide (ZnO) and iron oxide (Fe₂O${}_3)$ nanoparticles (NPs) to induce toxic effects, especially genotoxicity, has been demonstrated in previous studies and is in part related to the ability of NPs to produce ROS. The use of antioxidants is an effective method to reduce NP-induced genotoxicity. The aim of this study was to determine the protective role of vitamin C as a potent antioxidant in ZnO-and Fe₂O₃ NP-induced genotoxicity in the HGF-1 cell line.

Methods: Different concentrations of ZnO and Fe₂O₃ NPs (50$\mu$g, 100$\mu$g, and 150$\mu$g/mL) were used to achieve the best concentration for further evaluation. HGF-1 cells were incubated with different concentrations of vitamin C 24h before the NPs. The cells were then exposed to ZnO and Fe₂O₃ NPs at a concentration of 100$\mu$g/mL for 1h. The possible genoprotective effects of vitamin C were determined using a comet assay.

Results: The results of this study showed that all concentrations of vitamin C could reduce the DNA damage induced by ZnO and Fe₂O₃ NPs.

Discussion: In conclusion, vitamin C could be considered a potent genoprotective agent against ZnO- and Fe₂O₃ NP-induced genotoxicity.

Zinc oxide (ZnO) nanoparticles (NPs) are synthesized by one-step femtosecond laser ablation of zinc powders in n-methyl pyrrolidone (NMP) at room temperature. The as-prepared ZnO NPs are fairly stable, water-soluble and have abundant surface functional groups resulting in a strong fluorescence in the visible region. By further annealing the ZnO NPs in the reacting solvent up to 120^∘C, the photoluminescence (PL) intensity of material can be significantly enhanced. Besides, the PL of ZnO NPs can change from blue to green by controlling the annealing temperature. The products exhibit excellent temperature sensing with high temperature sensitivity and a 1.3% change per ^∘C response over a linear temperature sensing range (6–84${}^{\circ }\text{C})$ in aqueous buffer, which matches well with the physiologically relevant temperatures. Hence, the ZnO nanoparticle system can serve as a promising candidate for practical fluorescent temperatures nanosensors which can be used for accurate temperature monitoring within biological systems.

Ultrasonic (US) and UV-C disinfection technologies have been successfully used in wastewater treatment plants (WWTPs) for disinfection purposes. The US technology is typically used as a pre-treatment step to break down larger particles and make them more susceptible to disinfection. The UV-C technology is commonly used as a final disinfection step in many WWTPs. The study aimed to assess the potential of using Zinc Oxide (ZnO) Nanoparticles (NPs) to improve the effectiveness of UV-C and US disinfection methods in treating wastewater effluent, offering a more comprehensive solution to wastewater treatment. In this experimental study, a Laboratory US Bath (40kHz) and a UV-C lamp (16W) were used. In order to investigate the effectiveness of ZnO NPs in the reduction of microbial load, 5mg/L of ZnO NPs was added to the effluent samples. Then, samples were examined for Total Coliform (TC) and Fecal Coliform (FC) reduction by the standard MPN/100mL test. The Chick‘s law was used to calculate the efficiency of microbial load. The relationship between variables was determined by regression analysis using Excel and SPSS-ver 21 software. In this study, the samples were examined in three groups: Samples that were only exposed to sonication or received UV-C radiation with Turbidity of 18 NTU (Group A) and Turbidity of 5 NTU (Group B), and Samples that received 5 mg/L of ZnO NPs (Group C). By increasing the time from 0.5 min to 10 min in the presence of UV-C, the amount of microbial population decreased, and 2 min was considered the optimal time. The maximum removal efficiencies by US for TC were 74.07,77.7, 85.1% (40∘C) and 92.5,100, and 100% (60∘C) in group A (in 30 min sonication), 85.7, 85.7, 100% (40∘C), respectively, and were 100% in other groups (B and C), respectively. The maximum removal efficiencies by US for FC were 76.4%, 88.2%, and 100% (40∘C) and 88.2%, 100%, and 100% (60∘C) in group A (in 30 min sonication), respectively, and were 100% in other groups (B and C). In this study, an important increase in the disinfection ability of ZnO NPs has been observed in the presence of US and UV-C. So, the ZnO NPs/UV-C and ZnO NPs/US processes are valuable alternatives to conventional disinfection processes by over 90% improvement of disinfection efficiency.

The defect structure of ZnO nanoparticles is characterized by means of high-field electron paramagnetic resonance (EPR) spectroscopy. Different point and complex defects could be identified, located at the "bulk" or the surface region of the nanoparticles. In particular, by exploiting the enhanced g-value resolution at a Larmor frequency of 406.4 GHz, it could be shown that the resonance commonly observed at g = 1.96 is comprised of several overlapping resonances from different defects. Based on the high-field EPR analysis, the development of a space-charge layer could be monitored that consists of (shallow) donor-type defects at the "bulk" and acceptor-type and complex defects at the surface. Application of a core-shell model allows to determine the thickness of the depletion layer to 1.0 nm for the here studied compounds [J.J. Schneider et al., Chem. Mater.22, 2203 (2010)].

Azadirachta indica (Neem) gum was effectively used in the combustion process as the sustainable fuel for the synthesis of ZnO nanoparticles using zinc nitrate as the metal precursor. Thermal degradation of gum intermediate, which contains uniformly distributed Zn ions in gum matrix, by means of exothermic combustion reaction results in the formation of ZnO nanoparticles at a relatively lower temperature of 220^∘C. Further, the phase stabilization of ZnO nanoparticles was performed at 700^∘C for 3 h in ambient condition, which also led to the complete removal of organic residues. FTIR, XRD, SEM-EDX and TEM characterization of the ZnO nanoparticles reveals its phase purity and organic-free nature with a size ranging between 40 and 60 nm. Its optical activities were studied by UV–Visible and photoluminescence studies and the UV–Visible analysis reveals its band gap energy as 3.17 eV. Further, the synthesized ZnO nanoparticles showed splendid germicidal activity against Staphylococcus aureus (gram-positive bacteria), Escherichia coli (gram-negative bacteria) and Candida albicans (fungal pathogen). In addition, the bio-synthesized ZnO nanoparticles showed excellent antioxidant behavior with the 81% of free radical quenching while employing 100$\mu$g/mL nanoparticle concentration.

Undoped and Al-doped ZnO (AZO) nanoparticles (NPs) have been successfully synthesized by the simple sol-gel method. The NPs have been characterized by a number of techniques as x-ray diffraction (XRD), UV-visible spectroscopy and scanning electron microscopy (SEM) at room temperature for 0%, 0.5%, 1% and 2% of Al concentration. The structural characteristics were examined using XRD and SEM with EDS. XRD analysis reveals that all samples crystallizes in polycrystalline nature with wurtzite lattice and exhibit no other impurity phase. The average crystallite size decreases with increase in Al concentration. The absorption spectra indicate increase in optical energy gap (E_g) with increase in Al ion doped into the ZnO lattice site.