Letters to the Editor

Particle exposure levels during CVD growth and subsequent handling of vertically-aligned carbon nanotube films

Supercapacitors have emerged as potential candidates for energy storage devices. Engineered nanomaterials (ENMs) have been explored for the fabrication of high-performance supercapacitor applications. The expanding number of distinctive sorts and amounts of commercial items containing fabricated nanomaterials may produce unused sort of nanowastes that can be discharged into the environment amid the generation of the commercial nanoproducts. Life cycle contemplations are an imperative perspective of the secure utilize of new materials and chemical risk assessment (CRA) emerged as a foremost significant perspective in assessing and evaluating the safety of ENMs. There are parcels of challenges confronted with the case of nanomaterials evaluation depending on the association of ENMs with the encompassing compartments. The improvement of approved test guidelines and conventions would greatly aid the univocal hazard identification of ENMs. Ultimately, the introduced nanosafety approach will grow socioeconomic benefits, superior environment, and livelihood, which advances more speculation in vitality ventures toward economic improvement.

The progress of flexible/wearable electronic devices with multi-functionality has stimulated the rapid development of the matching power supply devices. Flexible supercapacitors with high electrochemical performance and mechanical flexibility are considered as attractive technologies to power flexible electronics and have been studied intensively. Carbon nanomaterials, such as carbon nanotube, graphene, and their composites, possess unprecedented physical/chemical properties and exhibit great potential for use in flexible supercapacitors. In this review, the recent progress of state-of-the-art flexible supercapacitors using advanced carbon nanomaterials is expounded comprehensively and systematically, the topic covered the micro/nano-structure control, macroscopic morphologies design, property optimization and application of carbon nanomaterials. Based on the current advances, the challenges and prospects of carbon nanomaterials applied in flexible supercapacitors are outlined and highlighted. As last, the matching between the characters of carbon nanomaterials, construction of flexible supercapacitors and fabrication technologies are put forward.

Characterization of the exposition to nanoparticles and nano-objects at workplaces is a huge technical challenge. Workplace exposure during short durations is particularly difficult to detect due to the low performances of the samplers. This article proposes a solution allowing for characterizing emissions at workplaces and presents the results obtained from a nanomaterials exposure measurement campaign performed on six different process lines (PLs) distributed all over Europe. By using our Short Time Sampling (STS) approach, the emitted nanomaterials are characterized in terms of their number concentration, size, shape and chemical composition. The background noise without any production activity is first measured for each PL and then it is distinguished from the emitted nanomaterials during production. The PLs yield different nanomaterial emission levels: the PL using the extrusion of polymer composites shows high emission whereas the PL dealing with the electrospinning of polyamide nanofibers shows the least i.e. no significant change in the background noise during the process and no detectable nanofiber emission either. The nanomaterials get emitted in the form of nanoparticles or submicronic fibers, or their agglomerates and aggregates i.e. Nano Objects, Agglomerates and Aggregates (NOAA). By the developed technique, 9 out of 37 of the studied steps have been shown to exhibit exposures to nanoparticles and nano-objects. For nanosafety measures, the energetic processes like spraying, extrusion, transport and cleaning activities of the nanomaterials in the powder form require most attention.

Elemental carbon (EC) can cause lung cancer or inflammation. Therefore, the objective of this study is to identify the possibility of real-time estimation of the EC concentration of multi-walled carbon nanotubes (MWCNTs) for workplace emission assessment. MWCNT aerosol particles were generated at a relatively constant rate over a period of 24 h, and the aerosolized MWCNTs were generally smaller than 1 μm. On-line measurement was performed by using an aethalometer and a scanning mobility particle sizer (SMPS) to determine black carbon (BC) concentration and particle mass concentration of the MWCNTs, respectively. Off-line analysis was conducted according to the National Institute for Occupational Safety and Health (NIOSH) method 5040 to obtain EC concentration of the MWCNTs. Then, correlations among the BC concentration, particle mass concentration, and EC concentration were investigated for the MWCNT particles. The particle number concentration converted from the SMPS measurement data and the BC concentration measured by the aethalometer were found to be in linear relation with the filter-sampling-based EC concentration, when the EC concentration of the MWCNTs was determined by the NIOSH method 5040. It is therefore anticipated that the use of the aethalometer and the SMPS can be of great help to the MWCNT emission assessment.

Highly surface active nano-scale materials, when released into the natural environment, tend to adsorb geo- and bio-macromolecules and end up presenting a modified interface to biological species. Capped nanocrystals and polymer/surfactant modified nanomaterials also are known to undergo ligand exchange when exposed to natural systems. Thus, nano-bio interactions will primarily be governed by the adsorbed or exchanged natural macromolecules. To-date there has been no established technique determining the kinetics of ligand exchange or characterizing the bound geo-biomacromolecular corona in an environmental setting. Single-molecule imaging utilizing near-infra red spectrometry, and single-molecule imaging of fluorophore-tagged polymeric ligands can enable detailed characterization of biopolymeric corona. This perspective aims to highlight the importance of ligand exchange, identify roles of surface ligands on nano-bio interaction, and present initial evidence of macromolecular characterization on nanotube surfaces using single-molecule techniques. This commentary also aims to outline the challenges facing nano-environmental health and safety community on assessing biological interaction with complex nano-scale heterostructures in a realistic environmental matrix.

For exposure and risk assessment in occupational settings involving engineered nanomaterials (ENMs), it is important to understand the mechanisms of release and how they are influenced by the ENM, the matrix material, and process characteristics. This review summarizes studies providing ENM release information in occupational settings, during different industrial activities and using various nanomaterials. It also assesses the contextual information — such as the amounts of materials handled, protective measures, and measurement strategies — to understand which release scenarios can result in exposure. High-energy processes such as synthesis, spraying, and machining were associated with the release of large numbers of predominantly small-sized particles. Low-energy processes, including laboratory handling, cleaning, and industrial bagging activities, usually resulted in slight or moderate releases of relatively large agglomerates. The present analysis suggests that process-based release potential can be ranked, thus helping to prioritize release assessments, which is useful for tiered exposure assessment approaches and for guiding the implementation of workplace safety strategies. The contextual information provided in the literature was often insufficient to directly link release to exposure. The studies that did allow an analysis suggested that significant worker exposure might mainly occur when engineering safeguards and personal protection strategies were not carried out as recommended.