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On the Toxicity Behaviour of Composite Polyaniline-Zinc Oxide Photocatalytic Nanoparticles and their Surrogate Chemicals
... [40,84] The prevalence of these terms (414, 470, 641, 673, and 855) signifies a substantial body of research investigating the concentration and time-dependent intricacies of employing ZnO NPs in drug delivery. [85][86][87][88] The average publication years for this cluster range from 2016.6 to 2018.1, indicating recent inquiries in this domain. Cluster 2, characterized by "min," "detection," "performance," "degradation," and "nanocomposite," gravitates toward scrutinizing their potential for disease diagnosis through molecule detection, [89][90][91] evaluating performance benchmarks, and analyzing the degradation of active components within zinc oxide nanocomposites. ...
The present investigation offers a thorough bibliometric exploration spotlighting the pivotal utilization of zinc oxide nanostructures, encompassing both zero‐dimensional (0D) nanoparticles and one‐dimensional (1D) nanostructures, within the realm of nanotechnology‐driven drug delivery systems. This analysis particularly illuminates the distinctive potential of these nanostructures in the cancer therapy context, not merely as carriers and deliverers of pharmaceutical agents, but as entities capable of selectively inducing apoptosis in cancer cells through the orchestrated generation of reactive oxygen species (ROS). Recent research endeavors notably underscore the application prospects of ZnO nanostructures in domains like DNA cleavage, bioimaging, and agricultural defense mechanisms. Moreover, the study elucidates the pronounced enhancement in solubility and biocompatibility that these nanostructures bring about when harmoniously integrated into polymeric nanocomposites. Concomitantly, the involvement of polymers in this symbiotic system is unveiled, wherein they play a multifaceted role in dictating release selectivity, thereby facilitating targeted and efficacious interactions with tissues. Functionally engineered polymeric nanocomposites emerge as promising candidates for targeted delivery modalities in cancer treatment, demonstrating an affinity for specific cell receptors and exhibiting enhanced cellular uptake within the size range of 100–200 nm. The study unearths robust associations among pivotal research terminologies through an exhaustive analysis of Link Strength Between Items (LSBI), culminating in the presentation of a cogent map delineating the evolving trends and forthcoming trajectories in this dynamic domain. In summation, this all‐encompassing bibliometric inquiry serves as a poignant testament to the prodigious potential of zinc oxide nanostructures in the realm of forthcoming nanotechnology‐driven drug delivery paradigms.
... non-biodegradable compounds into sludge which may require further treatment [1]. Photodegradation has been found to be an effective way to eliminate organic pollutants because it is relatively low cost, robust, and the catalyst is reusable [2]. ...
Photocatalysis is widely used for wastewater treatment as it is environmentally friendly through elimination of harmful organic compounds by mineralizing it to carbon dioxide and water under light illumination. Morphology control of polyaniline (PANI) is thought to affect the specific surface area and conductivity of the composites which subsequently contribute toward the photodegradation performance. In this research study, a binary system of PANI–TiO2 photocatalyst with different morphologies including nanotubes, nanofibers, nanospheres, star micro-/nanostructure and leaf micro-/nanostructure was fabricated for photodegradation of reactive black 5 (RB5) dye under visible light irradiation. Based on the characterization, PANI–TiO2 composites managed to reduce band gap to 2.68–2.72 eV which is proven to be easily activated under visible light region. Meanwhile, the photoluminescence analysis showed that the electron hole (e⁻h⁺) recombination was also retarded to provide opportunity for more radical generation. The PANI nanotubes (NT-PANI–TiO2) demonstrate highest photodegradation efficiency of 54.4% after 2 h. Interestingly, PANI leaf micro-/nanostructure (L-PANI–TiO2) shows highest increment of 35.3% of L-PANI to 48.8% of L-PANI–TiO2. This demonstrates the effectiveness of PANI nanotubes and leaf structures along with TiO2 as potential photocatalyst composite.
... Due to Particle size, shape, and distribution of particles, they can be adjusted to the desired application which they have many applications in electrical nanodevices. [5][6][7][8][9][10][11][12][13] Among Metal oxide ZnO Nanoparticles shows excellent physical and chemical properties and also extensive application in diverse areas such as coating, solar cell, and photocatalysts. 14 ...
Polyaniline/Nanocomposites were synthesized by the In-Situ Polymerization method. Characterization techniques are used to study the Crystalline nature, Particle size with X-Ray Diffraction, and Chemical composition and bonding by FTIR. Electrical properties were studied by using Keithley 6514 meter to know the conductivity of Polyaniline and Polyaniline / ZnO nanocomposites with respective the frequency Increase in Electrical conductivity found due to the addition of ZnO Particle, Magnetic properties were studied to know the behavior of samples like para magnetic, Ferromagnetic or diamagnetic nature obtained results are discussed. Mechanical properties were investigated to study the stress V/S strain and the results are discussed below
Metal-conducting polyaniline (PANI)-based nanocomposite materials have attracted attention in various applications due to their synergism of electrical, mechanical, and optical properties of the initial components. Herein, metal-PANI nanocomposites, including silver nanoparticle-polyaniline (AgNP-PANI), zinc oxide nanoparticle-polyaniline (ZnONP-PANI), and silver-zinc oxide nanoparticle-polyaniline (Ag–ZnONP-PANI), were prepared using the two processes. Nanocomposite-based electrode platforms were prepared by depositing AgNPs, ZnONPs, or Ag–ZnONPs on a PANI modified glass carbon electrode (GCE) in the presence of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS, 1:2) as coupling agents. The incorporation of AgNPs, ZnONPs, and Ag–ZnONPs onto PANI was confirmed by UV-Vis spectrophotometry, which showed five absorbance bands at 216 nm, 412 nm, 464 nm, 550 nm, and 831 nm (i.e., transition of π-π*, π-polaron band transition, polaron-π* electronic transition, and AgNPs). The FTIR characteristic signatures of the nanocomposite materials exhibited stretching arising from C–H aromatic, C–O, and C–N stretching mode for benzenoid rings, and =C–H plane bending vibration formed during protonation. The CV voltammograms of the nanocomposite materials showed a quasi-reversible behavior with increased redox current response. Notably, AgNP–PANI–GCE electrode showed the highest conductivity, which was attributed the high conductivity of silver. The increase in peak currents exhibited by the composites shows that AgNPs and ZnONPs improve the electrical properties of PANI, and they could be potential candidates for electrochemical applications.
Commonly used as biological chemosensors in toxicity assays, Vibrio fischeri bacteria were systematically characterized using complementary physicochemical and biological techniques to elucidate the evolution of their properties under varying environmental conditions. Changing the pH above or below the optimal pH 7 was used to model the long-term stress that would be experienced by V. fischeri in environmental toxicology assays. The spectral shape of bioluminescence and cell-surface charge during the exponential growth phase were largely unaffected by pH changes. The pH-induced modulation of V. fischeri growth, monitored via the optical density (OD), was moderate. In contrast, the concomitant changes in the time-profiles of their bioluminescence, which is used as the readout in assays, were more significant. Imaging at discrete timepoints by scanning electron microscopy (SEM) and helium-ion microscopy (HIM) revealed that mature V. fischeri cells maintained a rod-shaped morphology with the average length of 2.2 ± 1 µm and diameter of 0.6 ± 0.1 µm. Detailed morphological analysis revealed subpopulations of rods having aspect ratios significantly larger than those of average individuals, suggesting the use of such elongated rods as an indicator of the multigenerational environmental stress. The observed modulation of bioluminescence and morphology supports the suitability of V. fischeri as biological chemosensors for both rapid and long-term assays, including under environmental conditions that can modify the physicochemical properties of novel anthropogenic pollutants, such as nanomaterials and especially stimulus-responsive nanomaterials.
Polyaniline modified zinc oxide (PANI-ZnO) photocatalyst composites were synthesized by focusing on dissolution disadvantage of ZnO. In-situ chemical oxidation polymerization method was performed under neutral conditions (PANI-ES) whereas in hybridization method physical blending was applied using emeraldine base of polyaniline (PANI-EB). PANI-ZnO composites were prepared in various ratios of aniline (ANI) to ZnO as 1%, 3%, 6% and 9%. The alterations on the structural and morphological properties of PANI-ZnO composites were compared by Fourier Transform Infrared (FT-IR), Raman Spectroscopy, X-Ray Diffraction (XRD) and Scanning Electron Microscopy-Energy Dispersive X-ray Analysis Unit (SEM-EDAX) techniques. FT-IR and Raman spectroscopy confirmed the presence of PANI in all composites. SEM images revealed the morphological differences of PANI-ZnO composites based on PANI presence and preparation methods. Photocatalytic performances of PANI-ZnO specimens were investigated by following the degradation of methylene blue (MB) in aqueous medium under UVA irradiation. The effects of catalyst dose and initial dye concentration were also studied. MB degradation was followed by both decolorization extents and removal of aromatic fractions. PANI-ZnO composites expressed enhanced photocatalytic performance (~95% for both methods) as compared to sole ZnO (~87%). The hybridization method was found to be more efficient than the in-situ chemical oxidation polymerization method emphasizing the significance of the neutral medium.
In the last years, nanoparticles such as TiO2, ZnO, NiO, CuO and Fe2O3 were mainly used in wastewater applications. In addition to the positive aspects concerning using nanoparticles in the advanced oxidation process of wastewater containing pollutants, the impact of these nanoparticles on the environment must also be investigated. The toxicity of nanoparticles is generally investigated by the nanomaterials’ effect on green algae, especially on Chlorella vulgaris. In this review, several aspects are reviewed: the Chlorella vulgaris culture monitoring and growth parameters, the effect of different nanoparticles on Chlorella vulgaris, the toxicity of photocatalyst nanoparticles, and the mechanism of photocatalyst during oxidative stress on the photosynthetic mechanism of Chlorella vulgaris. The Bold basal medium (BBM) is generally recognized as an excellent standard cultivation medium for Chlorella vulgaris in the known environmental conditions such as temperature in the range 20–30 °C and light intensity of around 150 μE·m2·s−1 under a 16/8 h light/dark cycle. The nanoparticles synthesis methods influence the particle size, morphology, density, surface area to generate growth inhibition and further algal deaths at the nanoparticle-dependent concentration. Moreover, the results revealed that nanoparticles caused a more potent inhibitory effect on microalgal growth and severely disrupted algal cells’ membranes.
Polyaniline (PANI)-wrapped TiO2 nanorods (PANI/TiO2), obtained through the oxidative polymerization of aniline at the surface of hydrothermally presynthesized TiO2 nanorods, were evaluated as photocatalysts for the degradation of Bisphenol A (BPA). Fourier-transform infrared spectroscopy analysis revealed the successful incorporation of PANI into TiO2 by the appearance of peaks at 1577 and 1502 cm–1 that are due to the C═C and C–N stretch of the benzenoid or quinoid ring in PANI. Brunauer–Emmett–Teller analysis revealed that PANI/TiO2 had almost double the surface area of TiO2 (44.8999 m²/g vs 28.2179 m²/g). Transmission electron microscopy (TEM) analysis showed that TiO2 nanorods with different diameters were synthesized. The TEM analysis showed that a thin layer of PANI wrapped the TiO2 nanorods. X-ray photon spectroscopy survey scan of the PANI/TiO2 nanocomposite revealed the presence of C, O, Ti, and N. Photocatalytic activity evaluation under UV radiation through the effect of key parameters, including pH, contact time, dosage, and initial concentration of BPA, was carried out in batch studies. Within 80 min, 99.7% of 5 ppm BPA was attained using the 0.2 g/L PANI/TiO2 photocatalyst at pH 10. The quantum yield (QY) of these photocatalysts was evaluated to be 9.86 × 10–5 molecules/photon and 2.82 × 10–5 molecules/photon for PANI/TiO2 and TiO2, respectively. PANI/TiO2 showed better performance than as-synthesized TiO2 with a rate constant of 4.46 × 10–2 min–1 compared to 2.18 × 10–2 min–1. The rate of degradation of PANI/TiO2 was also superior to that of TiO2 (150 mmol/g/h vs 74.89 mmol/g/h). Nitrate ions increased the rate of degradation of BPA, while humic acid consistently inhibited the degradation of BPA. LC–MS analysis identified degradation products with m/z 213.1, 135.1, and 93.1. The PANI/TiO2 nanocomposite was reused up to five cycles with a removal of at least 80% in the fifth cycle. LC–MS results revealed three possible BPA degradation intermediates. LC–MS analysis identified degradation products which included protonated BPA, [C14H13O2⁺], and [C9H11O⁺]. The PANI/TiO2 nanocomposite demonstrated superior photocatalytic activity with respect to improved QY and figure of merit and lower energy consumption.
Polyaniline (PANI)-materials have recently been proposed for environmental remediation applications thanks to PANI stability and sorption properties. As an alternative to conventional PANI oxidative syntheses, which involve toxic carcinogenic compounds, an eco-friendly procedure was here adopted starting from benign reactants (aniline-dimer and H2O2) and initiated by ultraviolet (UV)-irradiated TiO2. To unlock the full potential of this procedure, we investigated the roles of TiO2 and H2O2 in the nanocomposites synthesis, with the aim of tailoring the properties of the final material to the desired application. The nanocomposites prepared by varying the TiO2:H2O2:aniline-dimer molar ratios were characterized for their thermal, optical, morphological, structural and surface properties. The reaction mechanism was investigated via mass analyses and X-ray photoelectron spectroscopy. The nanocomposites were tested on both methyl orange and hexavalent chromium removal. A fast dye-sorption was achieved also in the presence of interferents and the recovery of the dye was obtained upon eco-friendly conditions. An efficient Cr(VI) abatement was obtained also after consecutive tests and without any regeneration treatment. The fine understanding of the reaction mechanism allowed us to interpret the pollutant-removal performances of the different materials, leading to tailored nanocomposites in terms of maximum sorption and reduction capability upon consecutive tests even in simulated drinking water.
Polyaniline/zinc oxide (PANI/ZnO) composite photocatalysts were prepared from neutral media by in situ chemical oxidation of aniline (ANI) in the presence of different amounts of diethylene glycol (DEG). The PANI/ZnO composite photocatalysts were synthesized to efficiently remove organic dye (acid blue, AB25) from model wastewater. The PANI/ZnO composite photocatalysts were studied with the intention of efficient removal of organic dye (acid blue, AB25) from wastewater to obtain low-cost heterogeneous catalysts that offer high catalytic activity and stability. The conductive PANI polymer, which absorbs Vis irradiation, was used in this work as ZnO absorbs only ultraviolet (UV) irradiation; thus, the composite photocatalysts’ activity was broadened into the Vis region. Characterization of the composite photocatalysts was done by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, electric conductivity, UV-Vis spectroscopy, and by specific surface area (SBET) measurements. The composites’ photocatalytic activity under solar irradiation was validated by monitoring degradation of the AB25 dye. This study presented that it was possible both to prepare PANI and to prevent ZnO dissolution if in situ polymerization starts from neutral media with the addition of DEG. Additionally, efficient removal of AB25 dye, about 90% in 60 min, was achieved. The first-order rate constants of the photodegradation of AB25 by PANI/ZnO 0.02/0.024/0.04 DEG (and pure ZnO)) were computed to be 0.0272/0.0281/0.0325 (and 0.0062) min−1, indicating that the morphology and surface of the photocatalysts have significantly influenced the catalytic activity.
The use of zinc oxide nanoparticles (nano-ZnO) has rapidly increased in recent years, and this has triggered the need for versatile toxicity tests that can be used to test a range of different exposure scenarios. Acute exposure studies, using a variety of plant species, have overwhelmingly demonstrated nano-ZnO-induced toxicity, but substantial differences in the degree of phytotoxicity are reported in different studies. Here, we analysed the role of exposure time in determining the variation in phytotoxic effects. Using the model species Lemna minor, the effects of short-term (24 h), standardised (1 week) and chronic (up to 6 weeks) nano-ZnO exposure were compared. Nano-ZnO effects on Lemna minor growth indicators (biomass growth rate, root length), chlorophyll content and photosynthetic efficiency were measured. Rapid inhibitory effects of nano-ZnO on the maximal quantum yield of photosystem II could be measured after just 24-h exposure. Standardised (1 week) experiments revealed phytotoxic effects on Lemna minor biomass growth. More severe inhibitory effects on growth developed gradually over 4 to 6 weeks exposure to nano-ZnO, and these were qualitatively associated with increased zinc content in the plant. Such dynamics of nano-ZnO toxicity have not been elucidated before, and this study emphasises the importance of exposure time in studies of nanoparticle toxicity. We conclude that short-term, standardised experiments can potentially underestimate the environmental phytotoxicity, which may result from chronic exposure to nano-ZnO.
There has been rapid growth in nanotechnology in both the public and private sectors worldwide, but concern about nanosafety exists. To assess size-dependent cytotoxicity on human cancer cells, we studied the cytotoxic effect of three kinds of zinc oxide nanoparticles (ZnO NPs) on human epithelial colorectal adenocarcinoma (Caco-2) cells. Nanoparticles were first characterized by size, distribution, and intensity. Multiple assays have been adopted to measure the cell activity and oxidative stress. The cytotoxicity of ZnO NPs was time dependent and dose dependent. The 24-h exposure was chosen to confirm the viability and accessibility of the cells and taken as the appropriate time for the following test system. The IC50 value was found at a low concentration. The oxidative stress elicited a significant reduction in glutathione with increase in reactive oxygen species and lactate dehydrogenase. The toxicity resulted in a deletion of cells in the G1 phase and an accumulation of cells in the S and G2/M phases. One type of metallic oxide (ZnO) exerted different cytotoxic effects according to different particle sizes. Data from the previous experiments showed that 26-nm ZnO NPs appeared to have the highest toxicity to Caco-2 cells. The study demonstrated the toxicity of ZnO NPs to Caco-2 cells and the impact of particle size, which could be useful in the medical applications.
Brine shrimp (Artemia salina) larvae were exposed to different sizes of zinc (Zn) and zinc oxide (ZnO) nanoparticles (NPs) to evaluate their toxicity in marine aquatic ecosystems. Acute exposure was conducted in seawater with 10, 50 and 100 mg/L concentrations of the NPs for 24 h and 96 h. Phase contrast microscope images confirmed the accumulation of the NPs inside the guts. Artemia were unable to eliminate the ingested particles, which was thought to occur due the formation of massive particles in the guts. Although the suspensions of the NPs did not exhibit any significant acute toxicity within 24 h, mortalities increased remarkably in 96 h and escalated with increasing concentration of NP suspension to 42% for Zn NPs (40-60 nm) (LC50 ~100 mg/L) and to about 34% for ZnO NPs (10-30 nm) (LC50 >100 mg/L). The suspensions of Zn NPs were more toxic to Artemia than those of ZnO NPs under comparable regimes. This effect was attributed to higher Zn(2+) levels (ca. up to 8.9 mg L(-1)) released to the medium from Zn NPs in comparison to that measured in the suspensions of ZnO NPs (ca. 5.5 mg L(-1)). In addition, the size of the nanopowders appeared to contribute to the observed toxicities. Although the suspensions possessed aggregates of comparable sizes, smaller Zn NPs (40-60 nm) were relatively more toxic than larger Zn NPs (80-100 nm). Likewise, the suspensions of 10-30 nm ZnO NPs caused higher than those of 200 nm ZnO NPs. Lipid peroxidation levels were substantially higher in 96 h (p<0.05) indicating that the toxic effects were due to the oxidative stress.
The present study focuses on the biochemical responses of the aquatic plant duckweed (Spirodela polyrhiza L.) to zinc oxide nanoparticles (ZnO NPs). Laboratory experiments were performed using a 96-h exposure to 25-nm NPs at different concentrations (0, 1, 10, and 50 mg/L). Growth, chlorophyll-to-pheophytin ratio (D665/D665a) and activities of superoxide dismutase, catalase, peroxidase (POD), and Na(+), K(+)-ATPase were determined as indices to evaluate the toxicity of NPs in the culture medium. To understand better whether the Zn(2+) released from the ZnO NP suspensions plays a key role in toxicity of the NPs, we investigated particle aggregation and dissolution in the medium. Furthermore, two exposure treatments for the group with the highest concentration (50 mg/L) were performed: (1) exposure for the full 96 h (50a treatment) and (2) the medium being replaced with culture medium without NPs after 12 h (50b treatment). Our results indicate that ZnO NPs induced adverse effects in S. polyrhiza at the concentration of 50 mg/L in the culture medium. Zn(2+) released from the NPs might be the main source of its toxicity to this species.
Nano zinc oxide (nZnO) is increasingly used in sunscreen products, with high potential of being released directly into marine environments. This study primarily aimed to characterize the aggregate size and solubility of nZnO and bulk ZnO, and to assess their toxicities towards five selected marine organisms. Chemical characterization showed that nZnO formed larger aggregates in seawater than ZnO, while nZnO had a higher solubility in seawater (3.7 mg L(-1)) than that of ZnO (1.6 mg L(-1)). Acute tests were conducted using the marine diatoms Skeletonema costatum and Thalassiosia pseudonana, the crustaceans Tigriopus japonicus and Elasmopus rapax, and the medaka fish Oryzias melastigma. In general, nZnO was more toxic towards algae than ZnO, but relatively less toxic towards crustaceans and fish. The toxicity of nZnO could be mainly attributed to dissolved Zn(2+) ions. Furthermore, molecular biomarkers including superoxide dismutase (SOD), metallothionein (MT) and heat shock protein 70 (HSP70) were employed to assess the sublethal toxicities of the test chemicals to O. melastigma. Although SOD and MT expressions were not significantly increased in nZnO-treated medaka compared to the controls, exposure to ZnO caused a significant up-regulation of SOD and MT. HSP70 was increased two to fourfold in all treatments indicating that there were probably other forms of stress in additional to oxidative stress such as cellular injury.
Size is a key factor controlling the rate of dissolution of nanoparticles, such property can be explored for producing controlled release fertilizers. Hence, one can expect the increasing discharge of nanoparticles closer to water streams in the near future. In this study, we employed the model fresh water organism Daphnia magna to investigate the uptake, acute toxicity and depuration of ZnO nanoparticles. The present study shows that the median lethal concentration (LC50) depended on particle size and the presence of surfactant. The LC50 for positive control ZnSO4 (2.15 mg L⁻¹), 20 nm ZnO (1.68 mg L⁻¹), and 40 nm ZnO (1.71 mg L⁻¹) were statistically the same. However, the addition of surfactant increased the LC50 of 40 nm and 60 nm to 2.93 and 3.24 mg L⁻¹, respectively. The 300 nm ZnO was the least toxic nanoparticle presenting LC50 of 6.35 mg L⁻¹. X-ray fluorescence chemical imaging revealed that Zn accumulated along the digestive system regardless the particle size. Finally, contrary to what have been reported by several papers, the present study did not detect any depuration of ZnO nanoparticles in the next 24 h past the exposure assays. Thus, the ability of organisms to expel ingested nanomaterials might be dependent on specific physical-chemical features of such nanomaterials.
UV-C and UV-C/peroxydisulfate (PS) treatments of 3,5-dichlorophenol (3,5-DCP), a model industrial pollutant, were comparatively investigated in two different water matrices namely distilled water (DW) and simulated treated urban wastewater (SWW). The treatment performance of the selected treatment processes was comprehensively examined by following changes in 3,5-DCP, dissolved organic carbon (DOC), PS consumption, Cl- release, aromatic/aliphatic degradation products and acute toxicities towards the marine photobacterium Vibrio fischeri and freshwater microalga Pseudokirchneriella subcapitata. The treatability of 2 mg/L (12.3 µM) 3,5-DCP in DW was investigated under different operating conditions such as initial PS concentrations (0.00-1.00 mM) and pH values (3-11) at a fixed light intensity (0.5 W/L). Increasing the pH and PS concentration exhibited positive effects on 3,5-DCP degradation. Even 10 mg/L 3,5-DCP was completely degraded with UV-C/PS treatment in 40 min in the presence of 0.03 mM PS at pH 6.3 accompanied with 95% DOC removal that was achieved after 120 min treatment. The second-order rate constant of 3,5-DCP (10 mg/L) with SO4●- was determined as 1.77×109 M-1s-1 using competition kinetics. Cl- release and formation of hydroquinone were evidences of 3,5-DCP degradation involving SO4●-. 3,5-DCP (2 mg/L) was also subjected to UV-C and UV-C/PS treatments in SWW. 3,5-DCP (100% after 60 min) and in particular DOC (26% after 120 min treatment) removal efficiencies observed in DW decreased dramatically in SWW. The original and UV-C/PS-treated samples were non-toxic towards Vibrio fischeri; however, Pseudokirchneriella subcapitata toxicity increased from 20% to 47% through 80 min UV-C/PS treatment of 3,5-DCP.
Developing efficient sunlight photocatalysts with enhanced photocorrosion resistance and minimal ecotoxicological effects on aquatic biota is critical to combat water contamination. Here, the role of chemical composition, architecture, and fixation on the ecotoxicological effects on microalgae of different ZnO and ZnO@ZnS based water decontamination photocatalysts was analyzed in depth. In particular, the ecotoxicological effects of films, nanoparticles and biomimetic micro/nano-ferns were carefully assessed by correlating the algae’s viability to the Zn(II) release, the photocatalyst–microalgae interaction, and the production of reactive oxygen species (ROS). The results showed a drastic improvement in algal viability for supported ZnO@ZnS core@shell micro/nanoferns, as their ecotoxicity after 96 h light exposure was significantly lower (3.7–10.0% viability loss) compared to the ZnO films (18.4–35.5% loss), ZnO micro/nanoferns (28.5–53.5% loss), ZnO nanoparticles (48.3–91.7% loss) or ZnO@ZnS nanoparticles (8.6–19.2% loss) for catalysts concentrations ranging from 25 mg L−1 to 400 mg L−1. In particular, the ZnO@ZnS micro/nanoferns with a concentration of 400 mg L−1 exhibited excellent photocatalytic efficiency to mineralize a multi-pollutant solution (81.4 ± 0.3% mineralization efficiency after 210 min under UV-filtered visible light irradiation) and minimal photocorrosion (<5% of photocatalyst dissolution after 96 h of UV-filtered visible light irradiation). Remarkably, the ZnO@ZnS micro/nanoferns showed lower loss of algal viability (9.8 ± 1.1%) after 96 h of light exposure, with minimal reduction in microalgal biomass (9.1 ± 1.0%), as well as in the quantity of chlorophyll-a (9.5 ± 1.0%), carotenoids (8.6 ± 0.9%) and phycocyanin (5.6 ± 0.6%). Altogether, the optimized ZnO@ZnS core@shell micro/nanoferns represent excellent ecofriendly photocatalysts for water remediation in complex media, as they combine enhanced sunlight remediation efficiency, minimal adverse effects on biological microorganisms, high reusability and easy recyclability.
In this study the effect of copper oxide nanomaterials (CuO NMs), uncoated and with three different surface coatings (i.e. carboxylated, pegylated and ammonia groups), was evaluated on acute toxicity and accumulation dynamics in Daphnia magna. Biosorption and elimination rate constants were determined for D. magna following waterborne exposure to dissolved copper and copper oxide NMs using biodynamic modeling. The relationship between modeled parameters and acute toxicity endpoints was evaluated to investigate if accumulation dynamics parameters could be used as a predictor of acute toxicity. The Langmuir equation was used to characterize the biosorption dynamics of copper NMs and copper chloride, used as dissolved copper control. Uptake rates showed the following ranking: pristine‐CuO NMs > NH3‐CuO NMs > aqueous Cu > PEG‐CuO NMs > COOH‐CuO NMs. To determine copper elimination by D. magna a one compartment model was used. Different elimination rate constants were estimated for each chemical substance tested. Those which were easily biosorbed were also easily removed from organisms. Biosorption and depuration properties of NMs were correlated with zeta potential values and diameter of NMs agglomerates in the suspensions. There is no link between biosorption and toxicity. Waterborne exposures to more difficult to biosorb CuO NMs are likely to induce adverse effects more than those which are easily to biosorb. It is proposed that some physicochemical properties of NMs in media, including zeta potential and agglomerate diameter, can lead to higher biosorption but do not necessarily affect toxicity. The mode of interaction of the NMs with the organism, seems to be complex and depends on chemical speciation and physicochemical properties of NMs inside an organism. Moreover our findings highlight that coating type affects the biosorption dynamics, depuration kinetics and dissolution rate of NMs in media. This article is protected by copyright. All rights reserved.
Inherently conducting polymers (ICPs) are a specific category of synthetic polymers with distinctive electro-optic properties, which involve conjugated chains with alternating single and double bonds. Polyaniline (PANI), as one of the most well-known ICPs, has outstanding potential applications in biomedicine because of its high electrical conductivity and biocompatibility caused by its hydrophilic nature, low-toxicity, good environmental stability and nanostructured morphology. Some of the limitations in the use of PANI, such as its low processability and degradability, can be overcome by the preparation of its blends and nanocomposites with various (bio)polymers and nanomaterials, respectively. This review describes the state-of-the-art of biological activities and applications of conductive PANI-based nanocomposites in the biomedical fields, such as antimicrobial therapy, drug delivery, biosensors, nerve regeneration and tissue engineering. The latest progresses in the biomedical applications of PANI-based nanocomposites are reviewed to provide a background for future research.
ZnO/PANI nanocomposite was produced through performing an aniline in-situ chemical polymerization method on ZnO nanostructure. Different techniques including FT-IR, FE-SEM, EDX, DRS, and TGA were employed to identify the composition and the structure on used nanocomposites. The results of all methods confirmed the quality of produced ZnO/PANI nanocomposite so that it could be activated under UV and visible light radiation. Photocatalytic activity of synthesized nanocomposites in the degradation of metronidazole molecules (MNZ) in aqueous solutions under UV and visible light radiation as a function of time, MNZ concentration, catalyst dose, pH of the solution, and catalyst stability were evaluated for several stages of the degradation process. Desired conditions for maximum efficiency of MNZ degradation under UV and visible light radiation for 120 and 150 min, 1.0 mg L-1 ZnO/PANI nanocomposite, 10 mg L-1 MNZ concentration, and pH 7.0 were 97% for both types of light. In the optimal performance condition, kinetic studies, COD, TOC, AOS, reusability test, and predicted degradation mechanism were considered in the present study. The photocatalytic activity of ZnO/PANI nanocomposite is higher than ZnO under UV and visible light radiation. The constant degradation rate of MNZ by ZnO/PANI nanocomposite was 253×10-4 min-1, which was almost 63 times higher than ZnO photocatalysts. Besides, it was confirmed the important role of hydroxyl radicals (•OH) and superoxide anion radical (•O2−) in MNZ degradation. Finally, a mechanism for enhancing photocatalytic activity was discussed. The improved photocatalytic performance under UV and visible light radiation are associated with the significant absorption of UV and visible light and reduction of charge carrier recombination.
Among nanomaterials, zinc oxide (ZnO) is notable for its excellent biocidal properties. In particular, it can be incorporated in mortars to prevent biofouling. However, the morphology of these nanomaterials (NMs) and their impact on the action against biofouling are still unknown. This study aimed to assess how the morphology and surface modification can affect the ecotoxicology of ZnO NMs. The morphologies evaluated were nanoparticles (NPs) and nanorods (NRs), and the ZnO NMs were tested pure and with surface modification through amine functionalization (@AF). The toxic effects of these NMs were evaluated by acute and chronic ecotoxicity tests with the well-established model microcrustacean Daphnia magna. The ZnO NMs were characterized by transmission electron microscopy, X-ray diffraction and infrared spectroscopy. The EC50 48h to D. magna indicated higher acute toxicity of [email protected] NRs compared to all tested NMs. Regarding the chronic test with D. magna, high toxic effects on reproduction and longevity were observed with [email protected] NRs and effects on growth were observed with ZnO NRs. In general, all tested ZnO NMs presented high toxicity when compared to the positive control, and the NRs presented higher toxicity than NPs in all tested parameters, regardless of the form tested (pure or with surface modification). Additionally, the pathways of ecotoxicity of the tested ZnO NMs was found to be related to combined factors of Zn ion release, effective diameter of particles and NM internalization in the organism.
The toxic effects of zinc oxide (ZnO) nano- and non-nanoparticles on two species of soil organisms, the free-living nematode Panagrellus redivivus and the springtail Folsomia candida, were investigated. The toxicity of ZnO particles (with 15 and 140 nm average particle size) and ZnCl2 (used as a positive control for zinc ion dissolution) was tested in two different kinds of test media. Milli-Q water vs. soil solution was used for the tests involving P. redivivus, and plaster of paris vs. artificial soil for F. candida. For P. redivivus, application of the soil solution decreased the toxic effect. It is considered that this may be due to the less dissolved zinc ions, the organic matter content and ZnO aggregation. Furthermore, all of the compounds caused concentration-dependent mortality to the tested nematode species. In the tests with F. candida, the toxic effects of both ZnO and ZnCl2 were significantly lower in the tests involving plaster of paris. This could have resulted from the avoidance of the contaminated foods by the springtails. A decreasing effect on reproduction was observed only in the tests using artificial soil. Additionally, the ZnO particles of 140 nm significantly increased mortality in the soil solution test with P. redivivus and in the artificial soil in the tests with F. candida. Possibly, this is a consequence of a greater aggregation of the nanoparticle-sized ZnO at the end of the experiment, which resulted in a lower level of toxicity.
This study aims to evaluate the potential toxic effects of ZnO nanoparticles on Artemia franciscana nauplii. The ZnO NPs suspension was characterized by TEM, EDS and DLS techniques. Acute toxicity was investigated by exposure of nauplii to concentrations of 1, 5, 7.5, 10, 15, 20, 25 and 30 mg/L of ZnO NPs for 48 h and 96 h. The 96-h EC10 and EC50 values of ZnO NPs were found to be 1.39 mg/L and 4.86 mg/L respectively. The ZnO NPs suspensions did not cause any significant acute toxicity after 48 h of exposure, but the immobilization rate increase significantly compare to control group after 96 h (P < 0.05). The results showed that the uptake, accumulation, and elimination of NPs in nauplii depends on the concentration of NPs and time. The elimination rates of 46.66% and 83.85% were recorded at 1 and 10 mg/L of NPs after 24 h of depuration period, respectively.
Rapid industrialization and extensive use of pesticides in agriculture practices have contributed to the leaking of pesticide residues into water. Among them, organochlorines are highly toxic with half-lives of many years followed by organophosphates (OPs). Being banned in many countries, most of the pesticides are still persisting in the environment. Due to high perseverance, toxicity and potential to bioaccumulation, their removal is imperative. In this direction, conventional adsorbents such as commercial activated carbon, agricultural and natural waste were highly employed. In modern era, nanomaterials (including nanocomposites and nanobiocomposite) with high surface area come out as most economic, rapid and effective catalyst. TiO2 (photocatalyst) and Fe⁰ by itself or with oxidizing agents are playing a promising role in elimination of pesticide pollution and open the opportunities for exploring other nanoparticles as well. Further, their modified, doped or composites form showed enhanced characteristics due to introduction of new energy levels or increase in surface area. In contrast to TiO2 and Fe⁰, various nanostructured metal oxides found to degrade OP pesticides by rapid reactive adsorption followed by cleavage of P–O bond via SN² mechanism. The present review focuses on the present status of pesticide removal using nanoparticles through adsorption together with photocatalytic or redox or reactive degradation. Herein, detailed information on several pesticides, problems related to pesticide, their metabolites, environmental concentration and need for degradation has been presented. In addition, importance of green synthesized nanoparticles along with limitation and potential health risk of nanomaterials in degradation of various organic pollutants has been highlighted.
Until now, the treatment of multiple water pollutants by using one simple material has still been a challenge. Pompon-like ZnO-Polyaniline heterostructures with different content of Polyaniline as out-layer were synthesized by hydrothermal method and hybridization. Their several applications were subsequently investigated for water pollutants treatment including photo-degradation of organic pollutants, photo-induced adsorption of heavy metal ions (Hg(II), Cr(VI)) and inactivation of Pathogenic bacteria (E. coli bacteria and staphylococcus aureus) under visible light. The results indicate that the aforementioned pollutants can be effectively removed by Pompon-like ZnO-Polyaniline heterostructure. The enhanced photochemical performance is attributed to: (1) the improved monodispersity and relative large specific surface area of pompon-like ZnO-PANI enhance the production of photo-induced OH and O2⁻•; (2) the high separation efficiency of photo-generated electron-hole pairs, which comes from the synergistic effect of P-N type heterojunction.
Aniline was oxidized with three strong inorganic oxidants (ammonium peroxydisulfate, cerium(IV) sulfate, potassium dichromate), two weak inorganic oxidants (iron(III) chloride, silver nitrate), and one organic oxidant (p-benzoquinone) in aqueous solutions of methanesulfonic acid (MSA) of various concentration. Whereas oxidation of aniline with ammonium peroxydisulfate yielded high-molecular-weight conducting polyaniline (PANI) in the whole acidity range, the oxidation with cerium(IV) sulfate led also to a single product close to PANI with considerably lower molecular weight and lower conductivity. Potassium dichromate gave PANI only at high concentration of MSA. The use of iron(III) chloride yielded composite mixtures of PANI and low-molecular-weight aniline oligomers. The oxidation of aniline with silver nitrate led to composites of silver and an organic part, which was constituted either by aniline oligomers or conducting polyaniline or both. p-Benzoquinone as oxidant produced mainly aniline oligomers with poor conductivity and 2,5-dianilino-p-benzoquinone-like structure detected in FTIR and Raman spectra when oxidation proceeded with weak oxidants. A general model of oxidation with strong and weak oxidants was formulated.
The role of soluble zinc has been determined in Daphnia magna by a morphological approach, integrating a previous paper in which the ultrastructural damages to gut epithelial cells have been studied after ZnO nanoparticles exposure. In the present paper, the toxicity and morphological effects of soluble zinc from ZnSO4 have been determined in a 48-h acute exposure test. Daphnids have been exposed to six nominal zinc concentrations (0.075, 0.15, 0.3, 0.6, 1.2, and 2.4mg Zn/L) and then fixed for microscopic analyses. Data from the acute toxicity tests gave an EC50 value of 0.99mg/L and showed that no immobilization appeared up to 0.3mg Zn/L. Ultrastructural analyses of samples from the two highest concentrations showed large vacuolar structures, swelling of mitochondria, multilamellar bodies, and a great number of autophagy vacuoles. These findings have been compared to those from our previous study, and similarities and/or differences discussed. Based on the overall results it can be concluded that dissolved zinc ions played a key role in ZnO nanoparticle toxicity and that the morphological approach is an extremely useful tool for comparing toxicological effects as well. A possible common toxic mechanism of soluble zinc and ZnO nanoparticles was also proposed.
Nano-ZnO particles have been reported to be toxic to many aquatic organisms, although it is debated whether this is caused by nanoparticles per sé, or rather dissolved Zn. This study investigated the role of dissolved Zn in nano-ZnO toxicity to Lemna minor. The technical approach was based on modulating nano-ZnO dissolution by either modifying the pH of the growth medium and/or surface coating of nano-ZnO, and measuring resulting impacts on L. minor growth and physiology. Results show rapid and total dissolution of nano-ZnO in the medium (pH 4.5). Quantitatively similar toxic effects were found when L. minor was exposed to nano-ZnO or the “dissolved Zn equivalent of dissolved nano-ZnO”. The conclusion that nano-ZnO toxicity is primarily caused by dissolved Zn was further supported by the observation that phytotoxicity was absent on medium with higher pH-values (>7), where dissolution of nano-ZnO almost ceased. Similarly, the reduced toxicity of coated nano-ZnO, which displays a slower Zn dissolution, is also consistent with a major role for dissolved Zn in nano-ZnO toxicity.
We demonstrate a simple and cost-effective synthesis of an organic (polyaniline, PANI)/inorganic (zinc oxide, ZnO) one-dimensional coaxial nanowire (1D-CNW) array directly on a conducting substrate by (1) electrochemical deposition of aniline and its polymerization to PANI on the pore walls of a track-etched polycarbonate membrane and (2) subsequent electrodeposition of ZnO in the core of hollow PANI nanowires (NWs). The surface morphology and heterojunction formation in 1D-CNWs at the interface of PANI (shell)/ZnO (core) are analyzed by field-emission scanning electron microscopy and transmission electron microscopy (TEM). The diameter and length of 1D-CNWs are in the ranges of 50−200 nm and 3−5 μm, respectively. In addition, the single-crystalline nature of ZnO (inorganic core)/polycrystalline PANI (organic shell) and atomic composition of the inorganic/organic heterojunction are determined by selected-area electron diffraction and TEM−energy-dispersive X-ray spectroscopy, respectively. Amperometric analysis is used to explain the growth mechanism for formation of the core and shell in 1D-CNWs. Photoluminescence (PL) is found to be significantly larger by a factor ∼3 in the case of PANI/ZnO 1D-CNWs compared to that of ZnO NWs. A model for PANI (shell)/ZnO (core) coaxial 1D-CNWs is also proposed based on heterojunction arrangement to explain the PL enhancement by generation of hole and electron pairs together with minimization of recombination losses upon UV illumination. Subsequently, it also explains the progression of conduction of a free electron all the way through to the polymeric sequence of PANI to get an amplified photocurrent to engender PL enhancement in the visible region.
Metal oxide nanomaterials are widely used in practical applications and represent a class of nanomaterials with the highest global annual production. Many of those, such as TiO2 and ZnO, are generally considered non-toxic due to the lack of toxicity of the bulk material. However, these materials typically exhibit toxicity to bacteria and fungi, and there have been emerging concerns about their ecotoxicity effects. The understanding of the toxicity mechanisms is incomplete, with different studies often reporting contradictory results. The relationship between the material properties and toxicity appears to be complex and diifficult to understand, which is partly due to incomplete characterization of the nanomaterial, and possibly due to experimental artefacts in the characterization of the nanomaterial and/or its interactions with living organisms. This review discusses the comprehensive characterization of metal oxide nanomaterials and the mechanisms of their toxicity.
Polyaniline (PANI) hybrid defective ZnO nanoparticles were synthesized by a facile chemisorption method together with a cold plasma treatment (CPT) technique. The PANI was dispersed uniformly onto the defective ZnO surface, and an intimate contact on the interface was observed. The coated PANI could act cooperatively with deliberately introduced defects (oxygen vacancy and interstitial zinc) to achieve remarkably enhanced photocatalytic activity. Moreover, the monomolecular-layered PANI could effectively stabilize defects on the surface of ZnO, which is of significance for practical application. It is hoped that the present work may provide an efficient and applicable method to develop photocatalysts with excellent performance.
The present study investigated the impact of solar UV radiation on ZnO nanoparticle toxicity through photocatalytic ROS generation and photo-induced dissolution. Toxicity of ZnO nanoparticles to Daphnia magna was examined under laboratory light versus simulated solar UV radiation (SSR). Photocatalytic ROS generation and particle dissolution were measured on a time-course basis. Two toxicity mitigation assays using CaCl2 and N-acetylcysteine were performed to differentiate the relative importance of these two modes of action. Enhanced ZnO nanoparticle toxicity under SSR was in parallel with photocatalytic ROS generation and enhanced particle dissolution. Toxicity mitigation by CaCl2 to a less extent under SSR than under lab light demonstrates the role of ROS generation in ZnO toxicity. Toxicity mitigation by N-acetylcysteine under both irradiation conditions confirms the role of particle dissolution and ROS generation. These findings demonstrate the importance of considering environmental solar UV radiation when assessing ZnO nanoparticle toxicity and risk in aquatic systems.
The toxic effects of two differently sized ZnO nanopowders have been studied in Daphnia magna using advanced microscopy techniques. Five nanoZnO suspensions (0.1, 0.33, 1, 3.3 and 10 mg/L) were tested. The results of the 48-h acute toxicity tests performed with ZnO < 100 nm (bZnO) and ZnO < 50 nm (sZnO) showed slight effects, with EC50 values of 3.1 and 1.9 mg/L for bZnO and sZnO, respectively. Specimens exposed to 1 and 3.3 mg/L have been microscopically analysed and nanoparticles (NPs) from both concentrations have been found into midgut cells: i) in the microvilli; ii) in endocytic vesicles near the upper cell surface; iii) in some endosomes, as well as in mitochondria, in multivesicular and multilamellar bodies; iv) into the enterocytes' nuclei; v) free in the cytoplasm; vi) in the paracellular space between adjacent cells; vii) into the folded basal plasma membrane, and viii) in the gut muscolaris, suggesting that not only both nanoZnOs are able to interact with the plasmatic membrane of D. magna enterocytes, but also that they are capable to cross epithelial barriers. The ultrastructural changes increased with increasing concentrations and the worst morphological fields came from samples exposed to 3.3 mg/L of both nanoZnOs. Morphological effects were qualitatively similar between the two nanomaterials, but they appear to be much more frequent for sZnO NPs. Data from ICP-OES analyses demonstrated that the maximum Zn(++) concentration in our tested suspensions was 0.137 mg/L, which is well below the reported NOEC for the soluble Zinc. The corresponding Zn-salt exposures (0.1 mg/L Zn(++)) gave 0% of immobilized daphnids for both NPs suggesting that in our test medium nanoZnO toxicity is not driven by their solubilized ions. The large presence of NPs inside midgut cells after only 48-h exposure to nanoZnOs and their effects on the intestinal cells highlighted the toxic potential of these nanomaterials, also suggesting that studies on chronic effects are needed.
Nano-sized polyaniline (PANI) particles dispersed in aqueous solution were prepared using both poly(vinyl alcohol) (PVA) and poly(styrene sulfonic acid) (PSSA) as polymeric stabilizers. Size of the spherical PANI particle synthesized using PVA with a HCl dopant (PANI-HCl/PVA) was about 150 nm in diameter, and that with PSSA (PANI-PSSA) was about 50 nm, with a uniform size distribution. Doping level of the PANI-PSSA measured by UV–visible spectrometer was higher than that of PANI-HCl/PVA. The PVA based composite films using both PANI-HCl (PANI-HCl/PVA) and PANI-PSSA (PANI-PSSA/PVA) were prepared by a casting method for different PANI content and their electrical conductivities were measured. A percolation threshold of PANI concentration for conductivity of composite was found only around 10 wt.% of PANI for the PANI-PSSA/PVA, and furthermore, the PANI-PSSA/PVA became more conductive above the threshold point than PANI-HCl/PVA.
Polyaniline (PANI) is prepared by the oxidation of aniline. Depending on the acidity conditions during the chemical oxidation, different types of products can be identified. The aniline dimers, semidines, are the first oxidation products. In the next step, aniline trimers containing a phenazine moiety, the nucleates, are produced. At moderate acidity, pH>3.5, the reaction pathway further leads to higher brown non-conducting aniline oligomers. Alternatively, when the acidity is sufficiently high, pH
The purpose of this study was to investigate the 48 h acute toxicity of capped silver nanoparticles (AgNPs), and capped and uncapped titanium dioxide (nTiO2) to Daphnia magna neonates. In addition, a 24 days chronic toxicity study was performed for D. magna exposed to uncapped nTiO2 to evaluate effects on growth, reproduction and survival. The 48 h median lethal concentrations (LC50) for carboxy-functionalized capped AgNPs and uncapped nTiO2 were 2.75 μg/L and 7.75 mg/L, respectively. In contrast, no mortalities were observed for Daphnia exposed to carboxy-functionalized capped nTiO2 at concentrations up to 30 mg/L. In the chronic toxicity experiment with uncapped nTiO2, the growth, reproduction and survival of D. magna were significantly (p < 0.05) reduced at concentrations ranging from 4.5 to 7.5 mg/L. Growth and reproduction were reduced by 35 % and 93 %, respectively in the treatments at the highest uncapped nTiO2 concentration (7.5 mg/L). Time to first reproduction was delayed by 2-3 days in D. magna and the test organisms produced only 1-2 broods over 24 days exposure to the highest concentration of uncapped nTiO2. Overall, the results from the present study indicate that exposures of aquatic invertebrates to nanoparticles could have important ecological effects on lower trophic levels in aquatic ecosystems.
Both the non-conducting polyaniline, emeraldine base, and its conducting form, polyaniline hydrochloride, were tested for their biocompatibility in terms of skin irritation, sensitization and cytotoxicity performed on human immortalized non-tumorigenic keratinocyte and human hepatocellular carcinoma cell lines. The testing was carried out on extracts of polyaniline powders in agreement with requirements of international standards applicable for testing of medical devices. The results can be hence generally employed in all types of materials and devices containing polyaniline in various concentrations. The study confirmed that polyaniline has not induced any sensitization and skin irritation either. In contrast, both polyaniline forms showed considerable cytotoxicity, which was higher for polyaniline hydrochloride compared to polyaniline base and was observed on both cell lines. Differences between cytotoxicity found on human immortalized non-tumorigenic keratinocyte cell line and human hepatocellular carcinoma cell line were attributed to variability in specific metabolic capabilities of the respective cell lines. Significant reduction of cytotoxicity was achieved through deprotonation and reprotonation procedure, used as an additional purification step after polymer synthesis. Accordingly, the cytotoxicity is thus caused rather by the reaction by-products and residues than by polyaniline itself.
The dissolution of ZnO nanoparticles (nano-ZnO) plays an important role in the toxicity of nano-ZnO to the aquatic organisms. The effects of water chemistry such as pH, ionic components, and dissolved organic matter (DOM) on the dissolution of nano-ZnO and its toxicity to Escherichia coli (E. coli) were investigated in synthetic and natural water samples. The results showed that the toxicity of nano-ZnO to E. coli depended on not only free Zn(2+) but also the coexisting cations which could reduce the toxicity of Zn(2+). Increasing solution pH, [Formula: see text] , and DOM reduced the concentration of free Zn(2+) released from nano-ZnO, and thus lowered the toxicity of nano-ZnO. In addition, both Ca(2+) and Mg(2+) dramatically reduced the toxicity of Zn(2+) to E. coli. These results highlight the importance of water chemistry on the toxicity evaluation of nano-ZnO in natural waters.
BACKGROUND: Nanoparticulate titanium dioxide (TiO 2 ) has the advantages of high chemical stability, high photocatalytic activity to oxidise pollutants in air and water, relatively low price and non‐toxicity. However, its high surface energy leads to the aggregation of nanoparticles. In addition, the wide band gap of TiO 2 (3.2 eV) only allows it to absorb ultraviolet (UV) light (<387 nm), which represents just a small fraction (3–5%) of the solar photons. These factors have limited its use in many fields. In this study, nanoparticulate TiO 2 was modified by polyaniline (PANI) in order to enhance its photoactivity under UV light and sunlight illumination.
RESULTS: TiO 2 nanoparticles were modified by PANI via a chemical oxidative method. The introduction of small amounts of PANI enhanced the dispersion of TiO 2 nanoparticles and improved the photocatalytic activity under UV light. In addition, the band gap energies of all PANI/TiO 2 nanocomposites were lower than that of neat TiO 2 nanoparticles, so the PANI/TiO 2 nanocomposites can be excited to produce more electron–hole pairs under sunlight, which could result in higher photocatalytic activities.
CONCLUSION: The modification of nanoparticulate TiO 2 by PANI can increase its photoactivity in the process of phenol degradation under UV light and sunlight illumination. Copyright © 2008 Society of Chemical Industry
This paper reports on the effect of aqueous and nano-particulated Pb on oxidative stress (lipid peroxidation), cytoxicity, and cell mortality. As determined by the Thiobarbituric Acid Reactive Substances (TBARS) method, only 6h after incubation aqueous suspensions bearing nano-sized PbO(2), soluble Pb(II), and brain-homogenate only suspensions, were determined to contain as much as ca. 7, 5, and 1 nmol TBARS mg protein(-1), respectively. Exposure of human cells (central nervous system, prostate, leukemia, colon, breast, lung cells) to nano-PbO(2) led to cell-growth inhibition values (%) ca. ≤18.7%. Finally, as estimated by the Artemia salina test, cell mortality values were found to show high-survival larvae rates. Microscopic observations revealed that Pb particles were swallowed, but caused no mortality, however.
The present study evaluated phototoxicity of nanoparticulate ZnO and bulk-ZnO under natural sunlight (NSL) versus ambient artificial laboratory light (AALL) illumination to a free-living nematode Caenorhabditis elegans. Phototoxicity of nano-ZnO and bulk-ZnO was largely dependent on illumination method as 2-h exposure under NSL caused significantly greater mortality in C. elegans than under AALL. This phototoxicity was closely related to photocatalytic reactive oxygen species (ROS) generation by the ZnO particles as indicated by concomitant methylene blue photodegradation. Both materials caused mortality in C. elegans under AALL during 24-h exposure although neither degraded methylene blue, suggesting mechanisms of toxicity other than photocatalytic ROS generation were involved. Particle dissolution of ZnO did not appear to play an important role in the toxicity observed in this study. Nano-ZnO showed greater phototoxicity than bulk-ZnO despite their similar size of aggregates, suggesting primary particle size is more important than aggregate size in determining phototoxicity.
The acute toxicity and oxidative effects of nano-scale titanium dioxide, zinc oxide and their bulk counterparts in zebrafish were studied. It was found that although the size distribution of nanoparticles (NPs) was similar to that of the bulk particles in suspension, the acute toxicity of the TiO(2) NPs (96-h LC(50) of 124.5mg/L) to zebrafish was greater than that of the bulk TiO(2), which was essentially non-toxic. The acute toxicities observed for ZnO NPs, a bulk ZnO suspension, and a Zn(2+) solution were quite similar to each other (96-h LC(50) of 4.92, 3.31 and 8.06 mg/L, respectively). In order to explore the underlying toxicity mechanisms of NPs, ·OH radicals generated by NPs in suspensions and five biomarkers of oxidative effects, i.e. superoxide dismutase, catalase activities, malondialdehyde, reduced glutathione and protein carbonyl were investigated. Results showed that after the illumination for 96 h, the quantities of ·OH in the NP suspensions were much higher than ones in the bulk particles suspensions. The malondialdehyde content of zebrafish gills exposed to either illumination or dark were 217.2% and 174.3% of controls, respectively. This discrepancy indicates the occurrence of lipid peroxidation which is partly due to the generation of ·OH. In contrast, exposure to 5mg/L ZnO NPs and bulk ZnO suspension induced oxidative stress in the gills without oxidative damage. Oxidative effects were more severe in the livers, where the protein carbonyl content, in the light and dark groups exposed to 50mg/L TiO(2) NPs, was 178.1% and 139.7% of controls, respectively. The malondialdehyde levels in the liver of fish exposed to 5mg/L ZnO NPs and bulk ZnO were elevated (204.2% and 286.9% of controls, respectively). Additionally, gut tissues exhibited oxidative effects after exposure to NP suspensions. These results highlight the importance of a systematic assessment of metal oxide NP toxicity mechanisms.
Although novel nanomaterials are being produced and applied in our daily lives at a rapid pace, related health and environmental toxicity assessments are lagging behind. Recent reports have concluded that the physicochemical properties of nanoparticles (NPs) have a crucial influence on their toxicities and should be evaluated during risk assessments. Nevertheless, several controversies exist regarding the biological effects of NP size and surface area. In addition, relatively few reports describe the extents to which the physicochemical properties of NPs influence their toxicity. In this study, we used six self-synthesized and two commercial ZnO and TiO₂ nanomaterials to evaluate the effects of the major physicochemical properties of NPs (size, shape, surface area, phase, and composition) on human lung epithelium cells (A549). We characterized these NPs using transmission electron microscopy, X-ray diffraction, the Brunauer-Emmett-Teller method, and dynamic laser scattering. From methyl thiazolyl tetrazolium (MTT) and Interleukin 8 (IL-8) assays of both rod- and sphere-like ZnO NPs, we found that smaller NPs had greater toxicity than larger ones--a finding that differs from those of previous studies. Furthermore, at a fixed NP size and surface area, we found that the nanorod ZnO particles were more toxic than the corresponding spherical ones, suggesting that both the size and shape of ZnO NPs influence their cytotoxicity. In terms of the effect of the surface area, we found that the contact area between a single NP and a single cell was more important than the total specific surface area of the NP. All of the TiO₂ NP samples exhibited cytotoxicities lower than those of the ZnO NP samples; among the TiO₂ NPs, the cytotoxicity increased in the following order: amorphous>anatase>anatase/rutile; thus, the phase of the NPs can also play an important role under size-, surface area-, and shape-controlled conditions.
The stability and bioavailability of nanoparticles is governed by the interfacial properties that nanoparticles acquire when immersed in a particular aquatic media as well as the type of organism or cell under consideration. Herein, high-throughput screening (HTS) was used to elucidate ZnO nanoparticle stability, bioavailability, and antibacterial mechanisms as a function of iron doping level (in the ZnO nanoparticles), aquatic chemistry, and bacterial cell type. ζ-Potential and aggregation state of dispersed ZnO nanoparticles was strongly influenced by iron doping in addition to electrolyte composition and dissolved organic matter; however, bacterial inactivation by ZnO nanoparticles was most significantly influenced by Zn(2+) ions dissolution, cell type, and organic matter. Nanoparticle IC(50) values determined for Bacillus subtilis and Escherichia coli were on the order of 0.3-0.5 and 15-43 mg/L (as Zn(2+)), while the IC(50) for Zn(2+) tolerant Pseudomonas putida was always >500 mg/L. Tannic acid decreased toxicity of ZnO nanoparticles more than humic, fulvic, and alginic acid, because it complexed the most free Zn(2+) ions, thereby reducing their bioavailability. These results underscore the complexities and challenges regulators face in assessing potential environmental impacts of nanotechnology; however, the high-throughput and combinatorial methods employed promise to rapidly expand the knowledge base needed to develop an appropriate risk assessment framework.
It is now widely recognized that dissolution plays an important role in metallic nanoparticle toxicity, but to what extent remains unclear. In the present study, it was found that ZnO-engineered nanoparticle (ZnO-EN) toxicity to the marine diatom Thalassiosira pseudonana could be solely explained by zinc ion (Zn(2+) ) release. This is based on comparable inhibitive effects from ZnO-EN addition media, with or without the ultrafiltration through a 3-kD membrane, and from the media in which only Zn(2+) was added. Considering the importance of dissolution in ZnO-EN toxicity, Zn(2+) release kinetics was systematically examined under different conditions for the first time. It was found to be mainly influenced by pH as well as the specific surface area of the nanoparticles. In contrast, natural organic compounds either enhance or reduce Zn(2+) release, depending on their chemical composition and concentration. Compared with deionized water, ZnO-EN dissolution rates were accelerated in seawater, whereas ZnO-EN concentration itself only had a very small effect on Zn(2+) release. Therefore, dissolution as affected by several physicochemical factors should not be neglected in the effects, behavior, and fate of ENs in the environment.