Quantification of carbon nanotubes in different environmental matrices by a microwave induced heating method

Analysis of carbon nanotube levels in organic matter: an inter-laboratory comparison to determine best practice

Carbon nanotubes (CNTs) are increasingly being used in industrial applications, but their toxicological data in animals and humans are still sparse. To assess the toxicological dose-response of CNTs and to evaluate their pulmonary biopersistence, their quantification in tissues, especially lungs, is crucial. There are currently no reference methods or reference materials for low levels of CNTs in organic matter. Among existing analytical methods, few have been fully and properly validated. To remedy this, we undertook an inter-laboratory comparison on samples of freeze-dried pig lung, ground and doped with CNTs. Eight laboratories were enrolled to analyze 3 types of CNTs at 2 concentration levels each in this organic matrix. Associated with the different analysis techniques used (specific to each laboratory), sample preparation may or may not have involved prior digestion of the matrix, depending on the analysis technique and the material being analyzed. Overall, even challenging, laboratories' ability to quantify CNT levels in organic matter is demonstrated. However, CNT quantification is often overestimated. Trueness analysis identified effective methods, but systematic errors persisted for some. Choosing the assigned value proved complex. Indirect analysis methods, despite added steps, outperform direct methods. The study emphasizes the need for reference materials, enhanced precision, and organized comparisons.

Evaluation of bioaccumulation of nanoplastics, carbon nanotubes, fullerenes, and graphene family materials

Bioaccumulation is a key factor in understanding the potential ecotoxicity of substances. While there are well-developed models and methods to evaluate bioaccumulation of dissolved organic and inorganic substances, it is substantially more challenging to assess bioaccumulation of particulate contaminants such as engineered carbon nanomaterials (CNMs; carbon nanotubes (CNTs), graphene family nanomaterials (GFNs), and fullerenes) and nanoplastics. In this study, the methods used to evaluate bioaccumulation of different CNMs and nanoplastics are critically reviewed. In plant studies, uptake of CNMs and nanoplastics into the roots and stems was observed. For multicellular organisms other than plants, absorbance across epithelial surfaces was typically limited. Biomagnification was not observed for CNTs and GFNs but were observed for nanoplastics in some studies. However, the reported absorption in many nanoplastic studies may be a consequence of an experimental artifact, namely release of the fluorescent probe from the plastic particles and subsequent uptake. We identify that additional work is needed to develop analytical methods to provide robust, orthogonal methods that can measure unlabeled (e.g., without isotopic or fluorescent labels) CNMs and nanoplastics.

Effects of multi-walled carbon nanotubes in soil on earthworm growth and reproduction, enzymatic activities, and metabolomics

Increased production and environmental release of multi-walled carbon nanotubes (MWCNTs) increase soil exposure and potential risk to earthworms. However, MWCNT toxicity to earthworms remains unclear, with some studies identifying negative effects and others negligible effects. In this study, to determine whether exposure to MWCNTs negatively affects earthworms and to elucidate possible mechanisms of toxicity, earthworms were exposed to sublethal soil concentrations of MWCNTs (10, 50, and 100 mg/kg) for 28 days. Earthworm growth and reproduction, activities of cytochrome P450 (CYP) isoforms (1A2, 2C9, and 3A4) and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione-s-transferase (GST)), and metabolomics were determined. Effects of MWCNTs on earthworms depended on exposure concentration. Exposure to MWCNTs did not significantly affect growth and reproduction of individual earthworms. Exposure to 50 mg/kg MWCNTs significantly increased activities of CYP2C9, CYP3A4, SOD, CAT, and GST but clearly reduced levels of L-aspartate, L-asparagine, and glutamine. With exposure to 100 mg/kg MWCNTs, toxic effects on earthworms were observed, with significant inhibition in activities of CYP isoenzymes and SOD, significant reductions in L-aspartate, L-asparagine, glutamine, and tryptophan, and simultaneous accumulations of citrate, isocitrate, fumarate, 2-oxoglutarate, pyruvate, D-galactose, carbamoyl phosphate, formyl anthranilate, hypoxanthine, and xanthine. Results suggest that toxicity of MWCNTs to earthworms is associated with reduced detoxification capacity, excessive oxidative stress, and disturbance of multiple metabolic pathways, including amino acids metabolism, the tricarboxylic acid cycle, pyruvate metabolism, D-galactose metabolism, and purine metabolism. The study provides new insights to better understand and predict the toxicity of MWCNTs in soil.

Advances of nanomaterials for air pollution remediation and their impacts on the environment

One of the most favorable environmental applications of nanotechnology has been in air pollution remediation in which different nanomaterials are used as nanoadsorbents, nanocatalysts, nanofilters, and nanosensors. The nanomaterials have the ability to adsorb several contaminants existing in the air. Also, certain semiconducting nanomaterials materials can be used for photocatalytic remediation. Air contamination control can also be achieved by nanostructured membranes with pores sufficiently small to separate various pollutants from the exhaust. Nanomaterial enabled sensors are also used for the detection of harmful gases such as hydrogen sulfide, sulphur dioxide, and nitrogen dioxide. Conversely, because of the uncertainties in addition to irregularities in size, shape as well as chemical compositions, the existence of some nanomaterials might cause harmful effects on the environment along with the health of people. Thus, concerns were expressed about the transport and conversion of nanoparticles discharged into the surroundings. This review critically examined and assessed the present literature on the application of nanomaterials in the air, together with its negative impacts. The main focus is placed on the application of carbon-based and metal-based nanomaterials for air pollution remediation. It is noted that these nanomaterials demonstrating fascinating properties for improving the environmental pollution remediation system.

Analysis of Single-Walled Carbon Nanotubes in Estuarine Sediments by Density Gradient Ultracentrifugation Coupled to Near-Infrared Fluorescence Spectroscopy Reveals Disassociation of Residual Metal Catalyst Nanoparticles

The continued growth of the nanotechnology industry and the incorporation of nanomaterials into consumer applications will inevitably lead to their release into environmental systems. Single-walled carbon nanotubes (SWCNTs) in particular have exhibited many attractive optical, mechanical, and electrical properties that lend themselves to new and exciting applications. Assessing their environmental impact upon release into the environment is contingent upon quantifying and characterizing SWCNTs in environmental matrixes. In this study, SWCNTs were isolated from estuarine sediments using density gradient ultracentrifugation (DGU), followed by online flow-through analysis of the density fractions via near-infrared spectroscopy. This approach yielded significant improvements in the quantitative detection limit, from 62 to 1.5 μg g^-1. In addition, fractions of the density gradient were also obtained for further analysis by bulk inductively coupled plasma mass spectrometry (ICP-MS) and single-particle ICP-MS. Using fluorescent, semiconductive SWCNTs, the primary fluorescent nanotube fraction was found to be separated from the sediment matrix during DGU; however, the residual metal catalyst particles that had been assumed to be physically bound to the SWCNTs were found to form a separate band in the density gradient apart from the fluorescent SWCNTs. This result was repeated for a number of SWCNT types regardless of the metal catalyst and synthesis method, with a 0.1 g cm^-3 density difference between most fractions. The apparent disconnect between the fluorescent fraction of SWCNTs and their metal-containing constituents potentially complicates CNT risk assessment as analysis techniques focusing solely on either CNT fluorescence or metal fingerprints may misrepresent exposure concentrations and their toxicological implications.

High adsorptivity and recycling performance activated carbon fibers for Cu(II) adsorption

In order to develop adsorbent materials with high Cu(II) adsorptivity and renewable recycling for Cu(II), nitric acid oxidation process is optimized and ameliorated by microwave and sonication to obtain an efficient modification and regeneration processes. Microwave-assisted nitric acid oxidation process has the most significant enhancement effect to the Cu(II) adsorptivity of activated carbon fiber felts (ACFFs), which can reach 23.13 mg/g and 4.55 times of pristine felts. It is due to this process can greatly increase the ultramicropore volume and polar oxygen-containing groups. In addition, sonication-assisted-pickling regeneration process achieves efficient regenerations and enhancements of Cu(II) adsorptivity for ACFFs. The Cu(II) adsorptivity and regeneration rate of ACFFs are still up at 25.51 mg/g and 379.59% after five times recycling by the process of sonication-assisted pickling regeneration process.

Multivariate Calibration for Carbon Nanotubes in the Environment Using the Microwave Induced Heating Method

The goal of the present paper is to develop chemometrics-based multivariate calibration approaches for simultaneously determining quantity of individual carbon nanotubes (CNTs) in a multicomponent environmental matrix using a microwave induced heating method. A multifactor and multilevel experiment design was used to create 4 separate calibration datasets. Each calibration dataset contained 25 orthogonal CNTs with 2 or 3 factors (CNTs: single-walled CNTs (SWCNTs)/multi-walled CNTs (MWCNTs)/carboxylated MWCNTs (MWCNT-COOH)) and 5 levels (CNTs mass). The temperature rise (ΔT) spectral information was obtained for each sample by exposing to varying microwave conditions. This study showed the potential and applicability of partial least square regression (PLS), least square-support vector machine (LS-SVM) and artificial neural networks (ANN) in predicting quantities of SWCNTs, MWCNTs and MWCNT-COOH in environmental matrices with microwave induced temperature rises data. Our results revealed that the developed LS-SVM model presented higher R² and lower root mean square error of prediction (RMSEP) (R² = 0.74-0.93, RMSEP =0.0251 mg to 0.0328 mg in 2-component systems and R² = 0.64-0.95, RMSEP = 0.0243 mg to 0.0410 mg in 3-component systems), while the ANN model was only accurate in estimating mass of SWCNT and MWCNT in a 2-component mixture (R² = 0.77-0.89, RMSEP = 0.0322 mg to 0.0503 mg). The PLS model was found not effectively interpret relationship between microwave induced temperature rises data and mass of CNTs, indicated by small R² (0.20-0.87) and large RMSEP (0.0209 mg -0.1021 mg).

Rapid and versatile pre-treatment for quantification of multi-walled carbon nanotubes in the environment using microwave-induced heating

The concerns regarding potential environmental release and ecological risks of multi-walled carbon nanotubes (MWCNTs) rise with their increased production and use. As a result, there is the need for an analytical method to determine the environmental concentration of MWCNTs. Although several methods have been demonstrated for the quantification of well-characterized MWCNTs, applying these methods to field samples is still a challenge due to interferences from unknown characteristics of MWCNTs and environmental media. To bridge this gap, a recently developed microwave-induced heating method was investigated for the quantification of MWCNTs in field samples. Our results indicated that the microwave response of MWCNTs was independent of the sources, length, and diameter of MWCNTs; however, the aggregated MWCNTs were not able to convert the microwave energy to heat, making the method inapplicable. Thus, a pre-treatment process for dispersing bundled MWCNTs in field samples was crucial for the use of the microwave method. In the present paper, a two-step pre-treatment procedure was proposed: the aggregated MWCNTs loaded environmental samples were first exposed to high temperature (500 °C) and then dispersed by using an acetone-surfactant solution. A validation study was performed to evaluate the effectiveness of the pre-treatment process, showing that an 80-120% recovery range of true MWCNT loading successfully covered the microwave-measured MWCNT mass.

Detection and Quantification of Graphene-Family Nanomaterials in the Environment

An increase in production of commercial products containing graphene-family nanomaterials (GFNs) has led to concern over their release into the environment. The fate and potential ecotoxicological effects of GFNs in the environment are currently unclear, partially due to the limited analytical methods for GFN measurements. In this review, the unique properties of GFNs that are useful for their detection and quantification are discussed. The capacity of several classes of techniques to identify and/or quantify GFNs in different environmental matrices (water, soil, sediment, and organisms), after environmental transformations, and after release from a polymer matrix of a product is evaluated. Extraction and strategies to combine methods for more accurate discrimination of GFNs from environmental interferences as well as from other carbonaceous nanomaterials are recommended. Overall, a comprehensive review of the techniques available to detect and quantify GFNs are systematically presented to inform the state of the science, guide researchers in their selection of the best technique for the system under investigation, and enable further development of GFN metrology in environmental matrices. Two case studies are described to provide practical examples of choosing which techniques to utilize for detection or quantification of GFNs in specific scenarios. Because the available quantitative techniques are somewhat limited, more research is required to distinguish GFNs from other carbonaceous materials and improve the accuracy and detection limits of GFNs at more environmentally relevant concentrations.

Analytical Nanoscience and Nanotechnology: Where we are and where we are heading

The main aim of this paper is to offer an objective and critical overview of the situation and trends in Analytical Nanoscience and Nanotechnology (AN&N), which is an important break point in the evolution of Analytical Chemistry in the XXI century as they were computers and instruments in the second half of XX century. The first part of this overview is devoted to provide a general approach to AN&N by describing the state of the art of this recent topic, being the importance of it also emphasized. Secondly, particular but very relevant trends in this topic are outlined: the analysis of the nanoworld, the so "third way" in AN&N, the growing importance of bioanalysis, the evaluation of both nanosensors and nanosorbents, the impact of AN&N in bioimaging and in nanotoxicological studies, as well as the crucial importance of reliability of the nanotechnological processes and results for solving real analytical problems in the frame of Social Responsibility (SR) of science and technology. Several reflections are included at the end of this overview written as a bird's eye view, which is not an easy task for experts in AN&N.