Mixed Cellulose Ester Filters Research Articles

Wax screen-based fabrication of paper devices for the determination of iron in particulates of selected welding fumes in Addis Ababa, Ethiopia

In this study a paper-based analytical device was developed using screen printing technique for the determination of particulate iron from welding fumes. The operational parameters such as volume and concentration of 1,10-phenanthroline, volume and concentration of hydroxylamine were optimized by the Box Behnken Design (BBD) using Minitab. Additionally, the µ-PAD's sample solution holding capacity and reaction time were also optimized. Under the optimized condition, particulate metal concentrations were colorimetrically quantified usinga handheld mobile phone and image processing software, ImageJ. Very good analytical performance such as good linearity of the calibration curve and better selectivity was observed by the developed method. The limit of detection for Fe3+ assay was 4.6 mg/L; which is adequate to determine the threshold concentration limit of particulate iron set by the regulatory bodies (6 mg/L). The µ-PAD revealed 95-99% recovery compared with the UV-Vis spectrophotometry (98-100%). Furthermore, welding fume samples were collected in Addis Ababa over five days, using mixed cellulose ester filters and the findings show a high concentration that exceeds the standard levels. Analyzing particulate iron with µ-PADs yielded results consistent with UV-Vis spectrophotometry, suggesting µ-PADs' potential application for occupational particulate iron exposure measurement, eliminating the need for expensive analytical devices.
 KEY WORDS: µ-PADs, Particulate iron, Response surface methodology, Wax screen-printing, Welding fume, Colorimetric detection
 Bull. Chem. Soc. Ethiop. 2024, 38(3), 563-576. 
 DOI: https://dx.doi.org/10.4314/bcse.v38i3.2 

Deep learning for asbestos counting

The PCM (phase contrast microscopy) method for asbestos counting needs special sample treatments, hence it is time consuming and rather expensive. As an alternative, we implemented a deep learning procedure on images directly acquired from the untreated airborne samples using standard Mixed Cellulose Ester (MCE) filters. Several samples with a mix of chrysotile and crocidolite with different concentration loads have been prepared. Using a 20x objective lens coupled with a backlight illumination system a number of 140 images were collected from these samples, which along with additional 13 highly fibre loaded artificial images constituted the database. About 7500 fibres were manually recognised and annotated following the National Institute for Occupational Safety and Health (NIOSH) fibre counting Method 7400 as input for the training and validation of the model. The best trained model provides a total precision of 0.84 with F1-Score of 0.77 at a confidence of 0.64. A further post-detection refinement to ignore detected fibres < 5 µm in length improves the final precision. This method can be considered as a reliable and competent alternative to conventional PCM.

Silane-Grafted MXene (Ti3C2T X ) Membranes for Enhanced Water Purification Performance.

The current communication describes the modifications of MXene (Ti3C2Tx) with silane grafting reaction for membrane preparation for enhanced water purification. The MXene was successfully grafted with n-octadecyltrichlorosilane (MODCS), n-octyltrichlorosilane (MNOCS), and triphenylchlorosilane (MTPCS) in order to make a hydrophobic MXene that could be able to bind with the organic matrix/polymers. The modified MXenes were transformed into thin membranes by forming an MXene/polyvinyl alcohol (PVA) composite over a filter paper support, that is, MCE (mixed cellulose ester filter paper). MXene membranes were also formed without the MCE support by using PVA and glutaraldehyde (PVA/GA) where GA was used as a cross-linker to stabilize PVA and make it water-resistant. The conditions of membrane formation were optimized to investigate optimum compatible conditions with the modified materials. The resulting membranes were tested for the removal of various organic pollutants that included mesitylene (or trimethylbenzene); polyaromatic hydrocarbons (chrysene, as a model); biphenyl; bisphenol A; benzene, toluene, ethylbenzene, and styrene; methylene blue; and Sudan II dyes. The MTPCS PVA/GA cross-linked membrane showed the best results for a pollutant removal efficiency up to 98%. Overall, all six types of membranes showed the removal efficiency in the range of 52–98%. It was observed that the membrane exhibits reusability up to five cycles.

Development of Culture-Independent Detection Method for Beer Spoilage Lactic Acid Bacteria

In microbiological quality control of final beer products, 100–400 ml beer samples are traditionally filtered on a membrane filter, followed by a lengthy culturing process in/on a laboratory medium that usually requires 3–14 days. This study aims to detect beer spoilage lactic acid bacteria (LAB) in a culture-independent fashion, using a direct polymerase chain reaction (PCR) approach. In order to detect a trace level of spoilage LAB in beer products, pressure cycling technology was evaluated to determine if this technology could improve the direct recovery of DNA from membrane filters for PCR detection. In this study, a mixed cellulose ester filter was adopted to allow a larger volume of beer to be filtrated. As a result of the optimization of the DNA extraction process that minimizes the loss of DNA and the effect of PCR inhibitors, 100 (1–10) cells/300 ml beer were successfully detected for beer spoilage LAB. Furthermore, a challenge test using 3,000 ml beer showed that 100 cells of Levilactobacillus (Lactobacillus) brevis were detectable without the negative effects of beer-originated PCR inhibitors, indicating that a trace level of contamination, corresponding to 1 cell in 300 ml of beer products, is detectable. It was also shown that the test was completed in approximately 8 hours. Therefore, this newly developed method is considered to be useful for the culture-independent direct detection of an extremely low level of beer spoilage LAB without a traditional culturing process. Supplemental data for this article is available online at at.

Imbibition of Newtonian Fluids in Paper-like Materials with the Infinitesimal Control Volume Method

Paper-based microfluidic devices are widely used in point-of-care testing applications. Imbibition study of paper porous media is important for fluid controlling, and then significant to the applications of paper-based microfluidic devices. Here we propose an analytical approach based on the infinitesimal control volume method to study the imbibition of Newtonian fluids in commonly used paper-like materials. Three common paper shapes (rectangular paper strips, fan-shaped and circular paper sheets) are investigated with three modeling methods (corresponding to equivalent tiny pores with circle, square and regular triangle cross section respectively). A model is derived for liquid imbibition in rectangular paper strips, and the control equations for liquid imbibition in fan-shaped and circular paper sheets are also derived. The model is verified by imbibition experiments done using the mixed cellulose ester filter paper and pure water. The relation of imbibition distance and time is similar to that of the Lucas−Washburn (L−W) model. In addition, a new porosity measurement method based on the imbibition in circular paper sheets is proposed and verified. Finally, the flow rates are investigated. This study can provide guidance for the design of different shapes of paper, and for better applications of paper-based microfluidic devices.

Evaluation of enhanced darkfield microscopy and hyperspectral imaging for rapid screening of TiO2 and SiO2 nanoscale particles captured on filter media.

Here we report on initial efforts to evaluate enhanced darkfield microscopy (EDFM) and light scattering Vis-NIR hyperspectral imaging (HSI) as a rapid screening tool for the offline analysis of mixed cellulose ester (MCE) filter media used to collect airborne nanoparticulate from work environments. For this study, the materials of interest were nanoscale titanium dioxide (TiO2 ) and silicon dioxide (SiO2 ; silica), chosen for their frequent use in consumer products. TiO2 and SiO2 nanoscale particles (NPs) were collected on MCE filter media and were imaged and analyzed via EDFM-HSI. When visualized by EDFM, TiO2 and SiO2 NPs were readily apparent as bright spherical structures against a dark background. Moreover, TiO2 and SiO2 NPs were identified in hyperspectral images. EDFM-HSI images and data were compared to scanning transmission electron microscopy (STEM), a NIST-traceable technique for particle size analysis, and the current gold standard for offline analysis of filter media. As expected, STEM provided more accurate sizing and morphology data when compared to EDFM-HSI, but is not ideal for rapid screening of the presence of NPs of interest since it is a costly, low-throughput technique. In this study, we demonstrate the utility of EDFM-HSI in rapidly visualizing and identifying TiO2 and SiO2 NPs on MCE filters. This screening method may prove useful in expediting time-to-knowledge compared to electron microscopy. Future work will expand this evaluation to other industrially relevant NPs, other filter media types, and real-world filter samples from occupational exposure assessments.

Evaluation of classification methods for identifying multiwalled carbon nanotubes collected on mixed cellulose ester filter media

Enhanced darkfield microscopy (EDFM) and hyperspectral imaging (HSI) are being evaluated as a potential rapid screening modality to reduce the time-to-knowledge for direct visualisation and analysis of filter media used to sample nanoparticulate from work environments, as compared to the current analytical gold standard of transmission electron microscopy (TEM). Here, we compare accuracy, specificity, and sensitivity of several hyperspectral classification models and data preprocessing techniques to determine how to most effectively identify multiwalled carbon nanotubes (MWCNTs) in hyperspectral images. Several classification schemes were identified that are capable of classifying pixels as MWCNT(+) or MWCNT(-) in hyperspectral images with specificity and sensitivity over 99% on the test dataset. Functional principal component analysis (FPCA) was identified as an appropriate data preprocessing technique, testing optimally when coupled with a quadratic discriminant analysis (QDA) model with forward stepwise variable selection and with a support vector machines (SVM) model. The success of these methods suggests that EDFM-HSI may be reliably employed to assess filter media exposed to MWCNTs. Future work will evaluate the ability of EDFM-HSI to quantify MWCNTs collected on filter media using this classification algorithm framework using the best-performing model identified here - quadratic discriminant analysis with forward stepwise selection on functional principal component data - on an expanded sample set.

A dual-readout paper-based sensor for on-site detection of penicillinase with a smartphone

• Dual-readout paper-based sensor via enzyme-mediated alginate hydrogelation. • Converting solution viscosity and pH to diameter and color readout. • Smartphone-based device to record and analyze both signals for quantitative detection. • Excellent reproducibility and selectivity for on-site detection of penicillinase. A dual-readout paper-based sensor with smartphone detection is developed for quantitative determination of penicillinase. The sensor is accomplished with the aid of penicillinase-mediated alginate hydrogelation, which changes both the viscosity and pH of the reaction solution. The solution is dropped on a mixed cellulose ester filter paper for sensing, which is coated with a color indicator, bromothymol blue-cetyltrimethylammonium bromide-alginate complex. Dual signals of the targets are easily achieved from the sensing spot on the paper since the modulations of viscosity and pH of the reaction solution would result in changes of diffusion diameter and color of the spot, respectively. A smartphone-based readout device is developed to record and analyze both the diffusion diameter and color signal for quantitative detection of penicillinase. The wide linear range (8.00 × 10 −3 - 2.67 mU/μL for distance-readout and 8.00 × 10 -2 to 2.67 mU/μL for color-readout) with low limit-of-detection (2.67 × 10 -3 mU/μL for distance-readout and 2.67 × 10 -2 mU/μL for color-readout) have been achieved using the dual-readout paper-based sensors. The proposed method is successfully applied for the detection of penicillinase in milk samples with excellent sensitivity and reproducibility, showing its potential value for analysis of complex real samples.

Assessment of the potential release of nanomaterials from electrospun nanofiber filter media

Due to the special properties of electrospun nanofibers such as high surface area and porosity, ease of surface functionalization, low pressure drop, suitable mechanical strength, their application in the fabrication of air purifying filtration media has increased dramatically in the recent years. The release of nanomaterials from electrospun nanofibers and human exposure to these substances is one of the concerns regarding to application of nanofiber media in air purifying applications.The aims of present study were to fabricate and characterize the nanofiber filter media, and to determine the release of nanomaterials from them during their application in a filter test rig for removing potassium chloride (KCl) nanoparticles. Polyacrylonitrile, one of the most commonly used polymers in electrospun nanofiber filter media, was embedded with various nanomaterials including magnesium oxide nanoparticles and single wall carbon nanotube and was converted to nanofiber filter mats via electrospinning process. The air samples were collected at the downstream of prepared nanofiber filter mats using polycarbonate (PC) and mixed cellulose ester (MCE) filters according to NIOSH methods 7404 and 7402. The PC filters were analyzed by FE-SEM microscopy for assessing potential release of nanofibers and MCE filters were analyzed by CytoViva's Hyper Spectral Imaging System coupled with Enhanced Dark Field Microscopy (HIS-EDFM) for assessing the potential release of nanomaterials (SWNTs and MgO NPs) from the electrospun nanofiber filter mats. The findings indicated that electrospun nanofibers and their embedded nanoparticles were rarely detached and released from the filter media during normal filtration process. Therefore, it is possible to obtain a very low release by improving quality of the nanofiber filter media and applying a safe design approach.

Droplet digital PCR assays for the quantification of brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus)from environmental DNA collected in the water of mountain lakes.

Classical methods for estimating the abundance of fish populations are often both expensive, time-consuming and destructive. Analyses of the environmental DNA (eDNA) present in water samples could alleviate such constraints. Here, we developed protocols to detect and quantify brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) populations by applying the droplet digital PCR (ddPCR) method to eDNA molecules extracted from water samples collected in 28 Swedish mountain lakes. Overall, contemporary fish CPUE (catch per unit effort) estimates from standardized survey gill nettings were not correlated to eDNA concentrations for either of the species. In addition, the measured environmental variables (e.g. dissolved organic carbon concentrations, temperature, and pH) appear to not influence water eDNA concentrations of the studied fish species. Detection probabilities via eDNA analysis showed moderate success (less than 70% for both species) while the presence of eDNA from Arctic char (in six lakes) and brown trout (in one lake) was also indicated in lakes where the species were not detected with the gillnetting method. Such findings highlight the limits of one or both methods to reliably detect fish species presence in natural systems. Additional analysis showed that the filtration of water samples through 1.2 μm glass fiber filters and 0.45 μm mixed cellulose ester filters was more efficient in recovering DNA than using 0.22 μm enclosed polyethersulfone filters, probably due to differential efficiencies of DNA extraction. Altogether, this work showed the potentials and limits of the approach for the detection and the quantification of fish abundance in natural systems while providing new insights in the application of the ddPCR method applied to environmental DNA.

Direct deposition of two-dimensional MXene nanosheets on commercially available filter for fast and efficient dye removal

Generally, the efficiency of water purification can be greatly increased by a high-flux membrane separation technology. One major challenge in the application of this technology is to achieve high removal efficacy of target pollutants with elevated water flux. Here we report a novel self-assembled composite by depositing two-dimensional MXene nanosheets on a commercialized mixed cellulose ester filter (as designated as MCM). Morphology study reveals that MCM exhibits an ultrathin flaked structure with uniform nanochannels which is stapled on a porous support. The tailored membrane has been successfully applied in the methylene blue solution treatment and 100% ± 0.1% removal rate is achieved while the feed concentration of dye solution is up to 90 mg·L−1. Concurrently, stable and comparatively elevated water flux was achieved, i.e., 28.94 ± 0.74 L·m-2·h−1, which is 1.88-fold of that of the commercialized UTC60 membrane. Further investigations on the separation mechanism are performed to get more insights into separation performance exhibited by MCM. It is found that the size-selective sieving, electrostatic repulsion of MXene and the high porosity of substrate play the synergistic effect on the fast and efficient dye removal behavior. Taken together, the composite membrane fabricated in present work provides an alternatively high-efficiency approach for dye treatment, and unflagging efforts will be further invested on the development and large-scale application of MXene-based membrane.

Converting solution viscosity to distance-readout on paper substrates based on enzyme-mediated alginate hydrogelation: Quantitative determination of organophosphorus pesticides

Quantitatively paper-based senor is performed with simple distance-readout on mixed cellulose ester (MCE) filter paper based on acetylcholinesterase (AChE)-mediated alginate hydrogel. The method is accomplished with the aid of the inhibition effect of target samples on the AChE enzyme-catalyzed hydrolysis of acetylcholine, which changes the pH value of the solution to release Ca2+ and trigger alginate hydrogelation. The viscosity of the solution is thus regulated with the presence of target samples in the reaction mixture, leading to a significant change in the diffusion diameter of the solution spotted on the filter paper. The concentration in the sample is quantitatively determined by ruler-measureable diffusion diameter of the spot on the paper. With successfully application for quantitatively sensing of organophosphorus pesticides (OPs), we show that the method exhibits excellent reproducibility with RSD (n = 5) as low as 0.09% and good selectivity for detection of OPs. The dynamic range of the method is up to 66.7 ng/mL with the limit-of-detection (LOD) of 3.3 ng/mL. The present study provides a new approach for developing paper-based sensors with quantitative distance-readout, by utilizing enzymatic inhibition to modulate liquid viscosity, which would be of value for target detection in complex samples.

Inactivation of bacterial and fungal spores by UV irradiation and gaseous iodine treatment applied to air handling filters

Exposure to viable bacterial and fungal spores re-aerosolized from air handling filters may create a major health risk. Assessing and controlling this exposure have been of interest to the bio-defense and indoor air quality communities. Methods are being developed for inactivating stress-resistant viable microorganisms collected on ventilation filters. Here we investigated the inactivation of spores of Bacillus thuringiensis var. kurstaki (Btk), a recognized simulant for B. antracis, and Aspergillus fumigatus, a common opportunistic pathogen used as an indicator for indoor air quality. The viability change was measured on filters treated with ultraviolet (UV) irradiation and gaseous iodine. The spores were collected on high-efficiency particulate air (HEPA) and non-HEPA filters, both flattened for testing purposes to represent “surface” filters. A mixed cellulose ester (MCE) membrane filter was also tested as a reference. Additionally, a commercial HEPA unit with a deep-bed (non-flattened) filter was tested. Combined treatments of Btk spores with UV and iodine on MCE filter produced a synergistic inactivation effect. No similar synergy was observed for A. fumigatus. For spores collected on an MCE filter, the inactivation effect was about an order of magnitude greater for Btk compared to A. fumigatus. The filter type was found to be an important factor affecting the inactivation of Btk spores while it was not as influential for A. fumigatus. Overall, the combined effect of UV irradiation and gaseous iodine on viable bacterial and fungal spores collected on flat filters was found to be potent. The benefit of either simultaneous or sequential treatment was much lower for Btk spores embedded inside the deep-bed (non-flattened) HEPA filter, but for A. fumigatus the inactivation on flattened and non-flattened HEPA filters was comparable. For both species, applying UV first and gaseous iodine second produced significantly higher inactivation than when applying them simultaneously or in an opposite sequence.

Sample preparation method for visualization of nanoparticulate captured on mixed cellulose ester filter media by enhanced darkfield microscopy and hyperspectral imaging

A significant hurdle in conducting effective health and safety hazard analysis and risk assessment for the nanotechnology workforce is the lack of a rapid method for the direct visualization and analysis of filter media used to sample nanomaterials from work environments that represent potential worker exposure. Current best-known methods include transmission electron microscopy (TEM) coupled with energy dispersive x-ray spectroscopy (EDS) for elemental identification. TEM-EDS is considerably time-, cost-, and resource-intensive, which may prevent timely health and safety recommendations and corrective actions. A rapid screening method is currently being explored using enhanced darkfield microscopy with hyperspectral imaging (EDFM-HSI). For this approach to be effective, rapid, and easy, sample preparation that is amenable to the analytical technique is needed. Here, we compare the sample preparation steps for mixed cellulose ester (MCE) filter media specified in NIOSH Method 7400-Asbestos and Other Fibers by Phase Contrast Microscopy (PCM)-against a new method, which involves saturation of the filter media with acetone. NIOSH Method 7400 was chosen as a starting point since it is an established technique for preparing transparent MCE filters for optical microscopy. Limitations in this method led to the development and comparison of a new method. The new method was faster, easier, and rendered filters more transparent, resulting in improved visualization and analysis of nanomaterials via EDFM-HSI. This new method is suitable for a rapid screening protocol due to its speed, ease of use, and the improvement in image acquisition and analysis.

A comparison of air sampling methods for Clostridium difficile endospore aerosol

The airborne dissemination of Clostridium difficile (C. difficile) endospores (spores) in healthcare environments is documented in multiple studies. Once airborne, spores have the potential for transport on air currents to other areas. This study compared the methods in the collection of C. difficile spore aerosol. This study determined the relative efficiency of commonly used bioaerosol air sampling methods when characterizing airborne C. difficile spore concentrations. Air samplers evaluated in this study were the AirTrace slit-to-agar impactor, AGI-30 impinger, SKC BioSampler impinger, and a 47-mm mixed cellulose ester (MCE) filter cassette. Non-toxigenic C. difficile spores were nebulized into an enclosure contained in a biological safety cabinet. Side-by-side air samples were drawn from the enclosure. The slit-to-agar impactor, successfully used in previous studies to collect airborne spores, served as the reference method. Relative efficiency for the 47-mm MCE filter cartridge was higher than the slit-to-agar impactor (mean 136.6%, 95% CI 124.7–148.5%). Efficiencies of the impingers were similar and were low (mean 4.13%, 95% CI 2.27–5.99%). Impingers failed to maintain culturability of C. difficile spores during sampling. This study is the first to compare the efficiencies of commonly used bioaerosol sampling methods to collect airborne C. difficile spores. Filter air sampling provided the greatest collection of airborne spores. Slit-to-agar air sampling may underestimate the number of airborne spores present. Impinger air sampling could significantly underestimate the actual number of airborne C. difficile spores present or fail to detect airborne spores.

Influence of filtration during sample pretreatment on the detection of antibiotics and non-steroidal anti-inflammatory drugs in natural surface waters

Owing to the ease and effectiveness of removing suspended substances (SSs), filtration has become a universal pretreatment step during water sample preparation. However, it can lead to the underestimation of contaminants if the targets easily associate with the SSs or filters. For the first time, this study comprehensively assessed issues related to filtration for the accurate quantification of 35 typical pharmaceuticals, including 28 antibiotics and seven non-steroidal anti-inflammatory drugs (NSAIDs), in water samples by comparing the effects of different filter materials, preservatives, and water matrices on the recoveries. The results showed that some sulfonamides and NSAIDs had an affinity for nylon filters, whereas trimethoprim and macrolides were easily retained on mixed cellulose ester filters. The use of glass fiber filter (0.7 μm) resulted in improved recovery of all the targets. Acidification promoted the adsorption of fluoroquinolones, tylosin, and roxithromycin on SSs, whereas 5% methanol resulted in desorption of macrolides from the SSs and other pharmaceuticals (sulfadiazine, trimethoprim, etc.) from the solid-phase extraction cartridges. Without additional detection of targets adsorbed on the SSs and filters, the addition of appropriate surrogates prior to filtration can help correct the loss.

Environmental DNA filtration techniques affect recovered biodiversity

Freshwater metazoan biodiversity assessment using environmental DNA (eDNA) captured on filters offers new opportunities for water quality management. Filtering of water in the field is a logistical advantage compared to transport of water to the nearest lab, and thus, appropriate filter preservation becomes crucial for maximum DNA recovery. Here, the effect of four different filter preservation strategies, two filter types, and pre-filtration were evaluated by measuring metazoan diversity and community composition, using eDNA collected from a river and a lake ecosystem. The filters were preserved cold on ice, in ethanol, in lysis buffer and dry in silica gel. Our results show that filters preserved either dry or in lysis buffer give the most consistent community composition. In addition, mixed cellulose ester filters yield more consistent community composition than polyethersulfone filters, while the effect of pre-filtration remained ambiguous. Our study facilitates development of guidelines for aquatic community-level eDNA biomonitoring, and we advocate filtering in the field, using mixed cellulose ester filters and preserving the filters either dry or in lysis buffer.

An examination of MCE filter morphology and implications on preparation and analysis of air samples for asbestos

ABSTRACTMorphological imperfections of mixed-cellulose ester filters and their possible influence on sample preparation and analysis of asbestos were examined. Filters were identified with large regions of non-porous “dead zones” which could negatively affect fiber deposition and, therefore, fiber recovery and analysis by Transmission Electron Microscopy (TEM). As these imperfections are effectively erased during the preparation of the sample, they may not be readily observed by TEM. Un-collapsed filters as well as those collapsed using dimethylformamide (DMF) and two acetone techniques were examined. In order to minimize negative sampling and analytical bias, it is suggested that MCE samples be collapsed utilizing a 35% DMF solution, etched with a correctly calibrated low-temperature etcher, carbon coated using a rotating and tilted stage, and analyzed with a strong analyst-independent grid square opening randomization scheme.

Spatio-seasonal variation of airborne asbestos concentration in urban areas of Shiraz, Iran.

Background Asbestos fiber is mainly released from friction product in brakes and clutch linings and from reinforcing agent in the asbestos-cement industry. It leads to serious health problem such as mesothelioma and lung cancer. The objectives of this study were to monitor the levels of asbestos fibers in ambient air of Shiraz, Iran during 2014, and to draw its GIS distribution map for the city. Methods Samples were collected by mixed cellulose ester filters mounted on an open-faced filter holder using a SKC sampling pump. Fiber counting was conducted using both phase contrast microscopy (PCM) method to determine total fibers, and scanning electron microscopy (SEM) method to identify non-asbestos from asbestos fibers. Results The average concentrations of asbestos fibers in ambient air of the city were 1.11±0.25 PCM f/l and 12.21±2.52 SEM f/l. The highest concentration of asbestos fibers was measured in Valiasr square amounting 1.96±0.34 PCM f/l and 16.87 ±2.14 SEM f/l. Conclusions The average of asbestos fibers in all sampling points was higher than the WHO guideline (0.05 PCM f/l, 2.2 SEM f/l). This may be attributed to the frequently occurrence of heavy traffic, the existence of relevant industries in and around the city, and the topographic characteristics of the city. Thus, product substitution, traffic smoothing and industrial sites relocating are suggested to eliminate the asbestos fibers emission.

Hybrid MWCNTs membrane with well-tunable wettability

With the development of surface science, surface with special wettability, such as reversible or gradient, gradually becomes the focus of the field of science now. Here, via a facile, green organic solvent-free route, we have fabricated superhydrophobic hybrid MWCNTs membrane on mixed cellulose ester filter with great flexibility and tailorability. Importantly, induced by acetic acid vapour and NH3 vapour without external energy, wettability of it can be reversibly switched between superhydrophobic (low adhesion) to hydrophobic (high adhesion). Furthermore, hybrid MWCNTs membrane can achieve diverse range of gradient wettability. The principle of theory behind phenomenon also has been explained through surface chemical composition and microscopic surface topography by means of Field-emission scanning electron microscope (FESEM) images, X-ray photoelectron spectroscopy (XPS) and Fourier transformer infrared spectra (FTIR) spectroscopy. This work has solved some critical problems in this field. The limitations and potential application of our work also be summarized.