Particle Size Of Zinc Oxide Research Articles

Hybrid photoanode of TiO2-ZnO synthesized by co-precipitation route for dye-sensitized solar cell using phyllanthus reticulatas pigment sensitizer

We report synthesis and characterization of hybrid photoanode made up of Titanium Dioxide (TiO2) and Zinc Oxide (ZnO) nanoparticles prepared by a co-precipitation process. Though TiO2 is the most preferred anode for Dye Sensitized Solar Cell (DSSC), the charge recombination between electrode and electrolyte poses a major challenge. ZnO photoelectrode is a potential alternative due to higher carrier mobility but has a slower electron injection than TiO2. To maximize the benefits of both, a co-precipitation synthesis of TiO2/ZnO is proposed in this work as a promising alternative. The co-precipitation process produces metal oxides TiO2 and ZnO and eventually yields the Anatase TiO2 and Wurtzite ZnO. The experimental investigations of the new co-precipitation process show improved control of particle size, shape, and uniform distribution of ZnO and yet preserve the economy and simplicity of synthesis. The study shows an average crystallite size of 10 nm to 22 nm for TiO2 and 17 nm to 35 nm for ZnO. Wurtzite phase varies from 4.5% to 10.8% in a co-precipitated photoanode. The deconvolution of the typical Photoluminescence (PL) curve shows two distinct bands for ZnO and TiO2 cantered around 390 nm and 460 nm. The study shows that the co-precipitated TiO2/ZnO has a bandgap of less than 3.2 eV, this paves the way for reduced recombination and improved device performance. Further, we fabricated a prototype of a DSSC using photoanode of TiO2/ZnO and a sensitizer of natural plant pigment extracted from Phyllanthus reticulatas and successfully tested the prototype DSSC.

Biogenic zinc oxide, copper oxide and selenium nanoparticles: preparation, characterization and their anti-bacterial activity against Vibrio parahaemolyticus

The present study investigates biogenic preparation of zinc oxide (ZnO), copper oxide (CuO) and selenium (Se) nanoparticles using the marine brown alga Sargassum swartzii. The prepared nanomaterials were characterized using X-ray diffraction pattern (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and UV–Vis diffuse reflectance spectroscopy (DRS-UV) analysis. The particle size of biogenic ZnO, CuO and Se nanoparticles was ca. 32, 32 and 21 nm, respectively. The isolation of bacterial pathogenic strain Vibrio parahaemolyticus (V. parahaemolyticus) from the diseased shrimp and virulent genes (toxR and tlh) confirmed by PCR technique. Further, the molecular characterized using 16S ribosomal RNA gene sequences and identified new strain V. parahaemolyticus strain (GRCORNICRA001). Anti-bacterial activity of biogenic nanomaterials (ZnO, CuO and Se) was investigated against isolated V. parahaemolyticus using well diffusion method and growth inhibitory assay. The minimum inhibitory concentration (MIC) was 25, 25 and 10 µg mL−1 of ZnO, CuO and Se nanoparticles, respectively. The results show that there is a strong bacterial inhibition in a dose-dependent manner. Further, SEM analysis revealed that the interaction of nanomaterials with V. parahaemolyticus, resulted in a surface tension change that leads to membrane depolarization, formation of abnormal textures such as membrane rupture, membrane blebs, membrane clumping, and also caused cell death. Results of this effort highlighted the way for the future that these nanomaterials incorporated with shrimp feed for the management of aquatic diseases.

Health effects after inhalation of micro- and nano-sized zinc oxide particles in human volunteers

Inhalation of ZnO particles can cause inflammation of the airways and metal fume fever. It is unclear if different sizes of the particles alter these effects. However, various studies report higher biological activity of other nano-sized particles compared to microparticles. No effects at all were observed after inhalation of micro- and nano-sized zinc oxide (ZnO) particle concentrations of 0.5 mg/m3. Studies with different particle sizes of ZnO at higher exposures are not available. Accordingly, we hypothesized that inhalation of nano-sized ZnO particles induces stronger health effects than the inhalation of the same airborne mass concentration of micro-sized ZnO particles. 16 healthy volunteers (eight men, eight women) were exposed to filtered air and ZnO particles (2.0 mg/m3) for 2 h (one session with nano- and one with micro-sized ZnO) including 1 h of cycling at moderate workload. Effect parameters were symptoms, body temperature, inflammatory markers in blood and in induced sputum. Induced sputum was obtained at baseline examination, 22 h after exposure and at the end of the final test. The effects were assessed before, immediately after, about 22 h after, as well as two and three days after each exposure. Neutrophils, monocytes and acute-phase proteins in blood increased 22 h after micro- and nano-sized ZnO exposure. Effects were generally stronger with micro-sized ZnO particles. Parameters in induced sputum showed partial increases on the next day, but the effect strengths were not clearly attributable to particle sizes. The hypothesis that nano-sized ZnO particles induce stronger health effects than micro-sized ZnO particles was not supported by our data. The stronger systemic inflammatory responses after inhalation of micro-sized ZnO particles can be explained by the higher deposition efficiency of micro-sized ZnO particles in the respiratory tract and a substance-specific mode of action, most likely caused by the formation of zinc ions.

Synthesis of nano-zinc oxide with different morphologies and its application on fabrics for UV protection and microbe-resistant defense clothing

A liquid precipitation method was used to prepare zinc oxide nanoparticles in three diverse media: water, methanol, and ethylene glycol. The studied materials were examined by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and ultraviolet-visible spectroscopy. X-ray diffraction patterns showed a hexagonal Wurtzite structure of zinc oxide with a nanocrystalline size. Acquired powders showed different morphologies (rod, star, and spherical structures), which were affected by the nature of the solvent in the reaction. The different zinc oxide powders have varied optical band gaps. Scanning electron microscopy examinations confirmed the arrangement of nano-zinc oxide on the surfaces of the materials. The zinc oxide-covering procedure was carried out on cotton, polyester, and 50/50 wt% polyester/cotton blended fabrics using a simple dip and curing system. The cotton fabric treated with nanorod zinc oxide exhibited the highest ultraviolet protection factor with a value of 247.2. The antimicrobial properties of untreated and treated fabrics with nano-zinc oxide were measured against Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Staphylococcus aureus), and diploid fungus (Candida albicans). The results showed the antimicrobial action relies on the morphological structure and the particle size of zinc oxide and that it increases with a reduced particle size. The cotton fabric treated with 26 nm nonspherical zinc oxide particles showed the highest antimicrobial efficiency with values of 91.4%, 86.8%, and 84.7% for Staphylococcus aureus, Escherichia coli, and Candida albicans, respectively. The mechanical properties of treated fabrics were studied. The results confirm that nano-zinc oxide is highly useful for improving the performance of defense textile products because of its biocompatibility, environmental friendliness, and nontoxicity.

The role of NaOH content, grinding time, and drying temperature in controlling the shape and size of nano ZnO synthesized by a green chemistry approach

Zinc oxide (ZnO) has been widely exploited in different technological applications in virtue of its unique physical and chemical qualities. This study was designed to prepare ZnO nanorods for diagnostic applications using a simple, low cost, and solvent-deficient method with clarifying the effect of different experimental parameters on the shape and the size of the ZnO product. Under different experimental conditions, the synthesis was performed via a solid-state reaction of zinc sulfate and sodium hydroxide using the grinding method. The purity of nano ZnO products was investigated by X-ray diffractometer (XRD) while the size and the shape were demonstrated by high- resolution transmission electron microscopy (HRTEM). The XRD results confirmed the production of pure ZnO nanocrystals. The HRTEM micrographs illustrated the preparation of a mixture of nanospheroids and nanorods particles, nanorods with minor nanospheroids particles, and long nanorods particles when the applied mole ratio of (ZnSO4.7H2O: NaOH) was (1:2), (1:4), and (1:8) respectively. Our findings confirmed the vital role of NaOH in controlling the shape and the particle size of nano ZnO. Since ZnO nanorods can be easily prepared under mild environmentally friendly conditions, it is proposed that the described experimental conditions can be adapted for large scale production.

Efficient photocatalytic degradation of furosemide by a novel sonoprecipited ZnO over ion exchanged clinoptilolite nanorods

This work presents, a detailed investigation for photocatalytic degradation of the drug furosemide (FRS) using zinc oxide (ZnO) supported on ion-exchanged natural zeolite clinoptilolite (ICLT). The ZnO/ICLT nanophotocatalysts were effectively synthesized by sonoprecipitation method which enhanced the photocatalytic performance by increasing the surface area and decreasing the particle size, compared to conventional precipitated samples. Microstructure and optical properties of prepared catalysts were characterized using XRD, XRF, FESEM, surface particle size distribution, TEM, EDX, BET, BJH, DRS and UV-visible spectroscopy techniques. XRD data confirmed the formation of ZnO. FESEM images revealed small particle size of active metals and low numbers of agglomerations which is in accordance with EDX dot mapping results. The average particle size of ZnO in ZnO(15%)/ICLT whit sonication was 20.5 nm whereas it was 34.8 nm without sonication. Moreover, the literature review indicated that ultrasound irradiation during the precipitation of samples has not been studied yet which highlight the importance of evaluating this nanophotocatalyst for wastewater treatment applications. The maximum degradation rate was observed for 15 wt% ZnO among various contents of ZnO used in synthesized nanocomposites. The influence of key operational parameters such as catalyst dosage, initial FRS concentration and pH on the photocatalytic degradation was assessed. Total organic carbon mineralization rate of FRS solution and energy consumption were also assessed to compare the ability of different processes in FRS degradation. Results showed also excellent reusability of fabricated nanophotocatalyst. Finally a plausible degradation mechanism for photocatalytic degradation of FRS was proposed.

Energy dispersive X-ray spectroscopy study of compound semiconductor zinc orthotitanate prepared by solid state reaction method

In this work, the compound semiconductor nanoparticles of Zinc Orthotitanate (Zn2TiO4) was prepared by solid state reaction method. Titanium dioxide (TiO2) and Zinc oxide (ZnO) are two of the most versatile semiconductor materials used as the starting material for this purpose. The particle size from the FESEM image was found in the range of 40–180 nm after solid state reaction which is in consistent with the particle size of ZnO and TiO2 grinded individually. The different structural, morphological and optical characterizations of this compound semiconductor Zn2TiO4 is already been reported. Energy dispersive X-ray spectroscopy (EDX) is one of the important techniques to characterize the aforementioned material in terms of its purity and stoichiometriness. But however, there is hardly any work reported in this direction. So in this work detail EDX study was used in order to determine the element composition that present in the sample. The result of EDX study revealed that the synthesized Zn2TiO4 nanoparticles were of high purity, which contains high Zn, Ti and O element composition. The mass percentages Zn, Ti and O closely match with the ideal value of Zn2TiO4 nanocomposite.

Zinc oxide from aloe vera extract: two-level factorial screening of biosynthesis parameters

Zinc oxide (ZnO) was biosynthesised from aloe vera plant extract. The aloe vera plant extract was used as a reducing agent in biosynthesis process. Green synthesis method was proposed because it is cost effective and environmentally friendly. ZnO was characterised using SEM, EDX, FTIR, and XRD analyses. The antibacterial property was tested against Escherichia coli. The effects of aloe vera volume (2–50) mL, precursor concentration (0.001–0.300) M, reaction time (20 min–48 h), and temperature of the reaction (26–200) °C on ZnO characteristics were investigated and screened using a two-level factorial method. Based on the observation and ANOVA analysis result, precursor concentration was the only significant parameter that affected the production of the ZnO nanoparticles (NPs). The EDX analysis proved the presence of ZnO while the SEM analysis confirmed the average size of ZnO particle size was in the range of (18–618) μm with a rod-shape appearance. The XRD analysis showed that the average crystallite size was 0.452 μm and it was in the hexagonal phase. It was also proven to have antibacterial property against E. coli.

Analysis of the physicochemical properties of antimicrobial compositions with zinc oxide nanoparticles

ABSTRACT In this study, an antimicrobial composition based on polyvinyl alcohol (PVA) and zinc oxide (ZnO) was developed. The aim of the work was to obtain a film-forming product for antimicrobial treatment of surfaces. To improve the physical, mechanical, and film-forming properties of the compositions, three natural stabilizing agents were added to the formulation: gelatine, guar gum and hydroxyethyl cellulose. Formulations with different concentrations of each stabilizer were tested, and the physicochemical properties of the obtained products were measured. The size of zinc oxide particles in obtained compositions varied from 232 to 692 nm. The compositions had a slight acidic nature. Their pH ranged from 6.84 to 6.99. The average density of products was equal to 1.37 × 103 (kg/m3). It was confirmed that zinc oxide nanoparticles do not penetrate through a model dermal membrane which is a desired effect concerning their toxicity. The antimicrobial activity of the obtained compositions was assessed against Aspergillus niger strain. After 24 h of studying, the growth inhibition was in 71% greater than in reference material. After statistical analysis of the results, it was concluded in order to achieve the most desirable physicochemical and utilitarian properties, the concentrations of gelatine, guar gum and hydroxyethylcellulose should be equal to 0.5%, 0.03% and 0.055%, respectively.

Synthesis of zinc borate using water soluble additives: Kinetics and product characterization

Abstract Zinc borate was synthesized from the reaction of zinc oxide and boric acid in the absence or presence of seven different water soluble additives. Additive concentration and zinc oxide particle size were varied to investigate their effect on the growth kinetics of zinc borate particles. Zinc borate particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Samples taken from the reaction mixture during the synthesis were analyzed for determining the concentration of zinc oxide, boron oxide, and zinc borate. The results reveal the formation of zinc borate with the molecular formula 2ZnO·3B2O3·3H2O in the form of irregular platelets. The product retains its hydrate up to 300 °C. The reaction rate was found to increase when additives or nanosize zinc oxide were used. However, a lag time is observed in the presence of additives while the reaction completion time remains unaffected. The experimental kinetics data were fit to the logistic model. The variation of the model parameters with experimental conditions was also investigated. The results reveal that the specific reaction rate increases with the increasing concentration of additives and the decreasing size of zinc oxide particles.

Green Synthesis of ZnO Nano Particles Using Chlorella vulgaris Extract as Additives

The application of nano zinc oxide in health-related fields calls for green and environmentally friendly synthetic methods. In this paper, Chlorella vulgaris extract was used to synthesize uniform nano sized zinc oxide particles. The results indicate that Chlorella vulgaris extract can effectively reduce the size of zinc oxide particles. The as synthesized ZnO particles using Chlorella vulgaris extract as additive are about 20-40nm.

Effects of organic solvents on morphologies, photoluminescence, and photocatalytic properties of ZnO nanostructures

Employing organo-metal zinc acetylacetonate (Zn(acac)2) as the zincic source, various zinc oxide (ZnO) products with different morphologies have been synthesised via a typical solvothermal method in different polar organic solvents. Quasi-spherical and rod-like structures with diverse sizes are successfully fabricated in the methanol, ethanol, 1-propanol, isopropanol, and acetone solutions of NaOH, respectively. Moreover, their microstructures and morphologies have been investigated by X-ray powder diffraction and electron microscopy. A possible growth mechanism has been proposed. The various morphologies of ZnO are attributed to the discrepant polarity and viscosity of organic solvents and the supersaturation levels of reactants. Furthermore, the size-depended photoluminescence and photocatalytic properties of various structures of ZnO are also studied. It is believed that the different but regular photoelectric behaviours are resulting from the surface states and specific surface areas which are related to the exposed polarity facets as well as the size of ZnO particles.

Effect of Milling Speed and Time on Ultrafine ZnO Powder by High Energy Ball Milling Technique

The particle size of commercial zinc oxide (ZnO) powder has been found in micron scale. For the improvement of ZnO properties, size reduction in nanoscale is required. In this work, the particle size of ultrafine ZnO powder was reduced by high energy ball milling technique. commercial grade ZnO powder with average size 0.8 μm was used as starting material. Milling speed and time of high energy milling process are considered as crucial parameters affecting size reduction of ZnO particles. Crystalline structure, surface morphological and particle size of the milled samples were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and particle analyzer, respectively. The results suggested that ZnO patterns after milling process with various milling speed and time were identically in hexagonal crystalline phase affirmed by XRD result. SEM images indicate that size of ZnO products distinctly decrease according to the increase of milling time and speed. ZnO particle size after milling process was found in ultrafine power in range of 200-400 nm. These results suggest that particle size of the commercial ZnO powders can be effectively minimized to few hundred nanometer range depending on force attraction and suitable rotation during milling process with specific speed and time. Moreover, the significant milling parameters will be studied to find the optimum condition for the production of ZnO particles in nanoscale.

Manufacturing and characterization of ZnO and ZnO-doped frit crystal by physical and optical methods

This study was carried out to determine the physical and optical properties of zinc oxide (ZnO) and ZnO-doped Frit. Two groups of ZnO were prepared, namely, pure ZnO and ZnO-doped Frit. ZnO was prepared as ZnO disc and ZnO powder, and its high surface area and other characterized physical properties were expected to be the figure of merit in increasing the radiation interaction. Field emission scanning electron microscope and energy-dispersive X-ray (EDX) (FESEM) were utilized for analysis purposes. The particle size of pure ZnO was larger than ZnO-doped Frit in which ZnO-doped Frit particle size ranged in the scope of 260 nm, while pure ZnO was in the scope of 300 nm. The bond of the ZnO-doped Frit was better compared to pure ZnO. Raman spectroscopy characterization studies showed that the tops for both spectra displayed the same Raman shift. More top in ZnO-doped Frit was seen due to its bigger amount of impurities in the crystal. The energy gap for discs by UV of P338 was 3.37 eV, while the energy gap for ZnO-doped Frit was 3.26 eV. This study yielded impressive results in terms of the manufacture of ZnO, whereby the energy gap was proved by Ultraviolet–visible (UVV) device. In contrast, the ZnO-doped Frit generated inadequate result due to the small percentage used.

Effects on structure, surface oxygen defects and humidity performance of Au modified ZnO via hydrothermal method

In this paper, different approaches for the preparation of gold (Au) modified zinc oxide (ZnO) humidity sensors were investigated. Experimental results show that ZnO modified with gold nanoparticles (AuNPs) or chloroauric acid (HAuCl4) enhances the concentration of oxygen vacancy defects on the surface of ZnO, which can improve the sensitivity of such a ZnO humidity sensor. As compared to AuNPs-modified ZnO, the modification of HAuCl4 reduces the size of ZnO and Au particles and exhibits better humidity performance. This is due to that smaller Au particles can further promote dissociation and electrolysis conduction processes so as to enhance the adsorption activity of HAuCl4-modified ZnO nanocomposites. Humidity experiments indicate that HAuCl4-modified ZnO acquires more than 4 orders of magnitude for the impedance changes in RH range from 11% to 95% with high sensitivity, good linearity, small hysteresis (~2.35%) and short response/recovery time (15 s/6 s). The results indicate that smaller Au particle can improve the hysteresis and response of the ZnO humidity sensor. Thus, Au particles with small size are a key parameter for the design of Au modified ZnO humidity sensors with high performance, which has a potential in the fast detection of humidity.

Effect of Zinc Oxide Modification by Indium Oxide on Microstructure, Adsorbed Surface Species, and Sensitivity to CO

Additives in semiconductor metal oxides are commonly used to improve sensing behavior of gas sensors. Due to complicated effects of additives on the materials microstructure, adsorption sites and reactivity to target gases the sensing mechanism with modified metal oxides is a matter of thorough research. Herein, we establish the promoting effect of nanocrystalline zinc oxide modification by 1 – 7 at.% of indium on the sensitivity to CO gas due to improved nanostructure dispersion and concentration of active sites. The sensing materials were synthesized via an aqueous coprecipitation route. Materials composition, particle size and BET area were evaluated using X-ray diffraction, nitrogen adsorption isotherms, high-resolution electron microscopy techniques and EDX-mapping. Surface species of chemisorbed oxygen, OH-groups and acid sites were characterized by probe molecule techniques and infrared spectroscopy. Zinc oxide particle size was found to decrease and the BET area to increase with the amount of indium. The additive was observed in the form of amorphous indium oxide segregated on agglomerated crystalline ZnO nanoparticles. The concentration of surface species was found to be higher on In-modified zinc oxide. With the increase of indium content, the sensor response of ZnO(In) to CO was improved. Using in situ infrared spectroscopy, it was shown that oxidation of CO molecules was enhanced on the modified zinc oxide surface. The effect of modifier was attributed to promotion of surface OH-groups and enhancement of CO oxidation on the segregated indium ions, as suggested by DFT in previous work.

Gasoline Desulphurization by Reactive Adsorption on ZnO /Bentonite

Desulfurization of atmospheric distillation (DA) gasoline was performed by reactive adsorption on ZnO/ bentonite. The adsorbent was characterized by determining the distribution of particle sizes of zinc oxide powdered, adsorption isotherm and textural characteristics of granulated adsorbent. Adsorption experiments of atmospheric distillation gasoline were performed in continuous system at 280-320oC, 5-25 bar and volume hourly space velocities of 1-1.5 h-1. The adsorption on ZnO/ bentonite has been favored by increased pressure and operating temperature.

Hydrothermal synthesis and characterization of Tungsten-doped ZnO nanoparticles as an environmentally friendly substance

Hexagonal-structured zinc oxide (ZnO) is a semiconductor material with various industrial and cosmetic applications. Some of the main limitations of ZnO are aggregation, poor dispersibility, and wide energy gap, which limit its efficiency in some applications. The present study aimed to synthesize tungsten (W)-doped ZnO nanostructures using a hydrothermal method and characterize the particles to discover their application potency in various fields. To do so, 0.5%, 1.0%, and 2.0% of tungsten oxide (WO) were incorporated into the structure of ZnO, and the properties of the particles were determined via SEM, XRD, FTIR, AFM, DLS, and UV-Vis spectroscopy and zeta potential analysis. According to the obtained SEM images and XRD patterns, the prepared particles possessed hexagonal, non-aggregated structures. Furthermore, the UV-Vis spectra and AFM micrograms indicated that the doping of the ZnO nanostructures with tungsten caused a spectral shift in the absorbance of ZnO nanoparticles from the UV region to the visible light spectrum, increasing their relative roughness. According to DLS analysis, doping decreased the particle size of ZnO. In general, our findings demonstrated that the doping of ZnO nanostructures with tungsten could promote their efficiency and applicability in the treatment of environmental pollutants.

Effects of ZnO particle size on properties of asphalt and asphalt mixture

Micro or nano zinc oxide (ZnO), as a modifier, can significantly improve some properties of asphalt and asphalt mixture, but the effect of ZnO particle size is still unclear. In this paper, three different spherical sized ZnO nanoparticles (2 µm, 80 nm and 350 nm in average diameter) were made by homogeneous precipitation method and sol-gel method. Asphalt binders and asphalt mixtures modified by ZnO and ZnO/SBS (styrene-butadiene-styrene) were produced by means of a high shear mixer. The effects of ZnO particle size on physical properties of asphalt were analyzed through penetration test, softening point test, ductility test, dynamic shear rheological test (DSR), bending beam rheometer test (BBR) and aging test; and the effects on asphalt mixtures were characterized using the Marshall test, freeze-thaw splitting test, rutting test and a three-point bending beam test. Results show that the decrease of ZnO size in asphalt binder can weaken its creep stiffness, and increase its softening point, ductility, viscosity, anti-rutting factor, creep rate and anti-aging ability. In addition, with the decrease of ZnO size, the high temperature stability, water stability and low temperature crack resistance of asphalt mixture are improved. Finally, based on the test results, the optimum size of ZnO particle is determined as 80 nm.

ZnO Nanoparticles: Effect of Size on Bacterial Bioluminescence, Seed Germination, Algal Growth, and Gene Mutation

Effect of zinc oxide (ZnO) nanoparticles (NPs) size was evaluated in the context of bacterial bioluminescence, seed germination, gene mutation in bacteria, and algal growth. Different sensitivities and half maximal effective concentration (EC50s) were observed, showing orders of toxicity: bacterial bioluminescence (0.31–0.40 mg/L) > algal growth (1.08–2.90 mg/L) > seed germination (6.56–9.98 mg/L). Furthermore, size of NPs plays a critical role in toxicity. The mutation ratio decreases with increase in the size of NPs, with 2.4 for 5 nm and 1.1 for 80 nm, at 100 mg/L of ZnO NPs. Effect ZnO particle size differed according to tested assays. Under exposure conditions with large sizes, toxicity of ZnO NPs increased on seed germination, but decreased on algal growth and gene mutation. Toxicity results of algal growth and seed germination showed statistically significant differences (p < 0.05) between 5 and 80 nm ZnO NPs. In the case of bacterial bioluminescence, no significant differences were observed among each of the sizes tested. These findings show that a toxicity evaluation of NPs needs to consider the different effects with respect to particle sizes and tested organisms for an accurate assessment of toxicity.