A Homochiral Porous Organic Cage-Polymer Membrane for Enantioselective Resolution.

Membrane-based enantioselective separation is a promising method for chiral resolution due to its low cost and high efficiency. However, scalable fabrication of chiral separation membranes displaying both high enantioselectivity and high flux of enantiomers is still a challenge. Here, we report the preparation of homochiral porous organic cage (CC3-R)-based enantioselective thin-film-composite membranes using polyamide (PA) as the matrix, where fully organic and solvent-processable cage crystals have good compatibility with the polymer scaffold. The hierarchical CC3-R channels consist of chiral selective windows and inner cavities, leading to favorable chiral resolution and permeation of enantiomers; the CC3-R/PA composite membranes display an enantiomeric excess (ee) of 95.2% for R-(+)-limonene over S-(-)-limonene and a high flux of 99.9 mg h-1 m-2. This work sheds light on the use of homochiral porous organic cages for preparing enantioselective membranes and demonstrates a new route for the development of next-generation chiral separation membranes. This article is protected by copyright. All rights reserved.

Nanoconfinement enabled non-covalently decorated MXene membranes for ion-sieving.

Covalent modification is commonly used to tune the channel size and functionality of 2D membranes. However, common synthesis strategies used to produce such modifications are known to disrupt the structure of the membranes. Herein, we report less intrusive yet equally effective non-covalent modifications on Ti3C2Tx MXene membranes by a solvent treatment, where the channels are robustly decorated by protic solvents via hydrogen bond network. The densely functionalized (-O, -F, -OH) Ti3C2Tx channel allows multiple hydrogen bond establishment and its sub-1-nm size induces a nanoconfinement effect to greatly strengthen these interactions by maintaining solvent-MXene distance and solvent orientation. In sub-1-nm ion sieving and separation, as-decorated membranes exhibit stable ion rejection, and proton-cation (H+/Mn+) selectivity that is up to 50 times and 30 times, respectively, higher than that of pristine membranes. It demonstrates the feasibility of non-covalent methods as a broad modification alternative for nanochannels integrated in energy-, resource- and environment-related applications.

A Homochiral Poly(2-oxazoline)-based Membrane for Efficient Enantioselective Separation.

Chiral separation membranes have shown great potential for the efficient separation of racemic mixtures into enantiopure components for many applications, such as in the food and pharmaceutical industries; however, scalable fabrication of membranes with both high enantioselectivity and flux remains a challenge. Herein, enantiopure S-poly(2,4-dimethyl-2-oxazoline) (S-PdMeOx) macromonomers were synthesized and used to prepare a new type of enantioselective membrane consisting of a chiral S-PdMeOx network scaffolded by graphene oxide (GO) nanosheets. The S-PdMeOx-based membrane showed a near-quantitative enantiomeric excess (ee) (98.3±1.7 %) of S-(-)-limonene over R-(+)-limonene and a flux of 0.32 mmol m-2 h-1 . This work demonstrates the potential of homochiral poly(2,4-disubstituted-2-oxazoline)s in chiral discrimination and provides a new route to the development of highly efficient enantioselective membranes using synthetic homochiral polymer networks.

Identification of mercury species in coal combustion by-products from power plants using thermal desorption-atomic fluorescence spectrometry on-line coupling system.

Along with the environmental protection policies becoming strict in China, the air pollution control devices (especially selective catalytic reduction (SCR)) are widely equipped in coal-fired power plants. The installation and run of these devices will inevitably affect mercury (Hg) species distribution in coal fired by-products such like fly ash (FA) and gypsum. In this work, a new on-line coupling system based on atomic fluorescence spectrometry (AFS) with a home-made chromatographic workstation was successfully developed to identify Hg species through thermal programmed desorption (TPD). The influences of matrix, furnace temperature, and carrier gas flow on analytical performance were investigated and the parameters were optimized. The FA and gypsum samples from coal-fired power plants equipped with SCR were collected and the mercury species were analyzed by the developed coupling system. HgCl2 and HgO were the main species in FA, while Hg2Cl2 and HgO were the main species in gypsum. All of Hg species in the studied FA and gypsum samples were released below 400 °C. A sequential extraction procedure was applied to further verify the operational Hg species including mobile and non-mobile fractions in FA and gypsum samples. This study demonstrated that AFS coupled with TPD procedure was an effective method to analyze Hg species in coal combustion by-products from power plants.

Gaseous Arsenic Capture in Flue Gas by CuCl2-Modified Halloysite Nanotube Composites with High-Temperature NOx and SOx Resistance.

Gaseous arsenic emitted from coal combustion flue gas (CCFG) causes not only severe contamination of the environment but also the failure of selective catalytic reduction (SCR) catalysts in power plants. Development of inexpensive and effective adsorbents or techniques for the removal of arsenic from high-temperature CCFG is crucial. In this study, halloysite nanotubes (HNTs) at low price were modified with CuCl2 (CuCl2-HNTs) through ultrasound assistance and applied for capturing As2O3(g) in simulated flue gas (SFG). Experiments on arsenic adsorption performance, adsorption mechanism, and adsorption energy based on density functional theory were performed. Modification with CuCl2 clearly enhanced the arsenic uptake capacity (approximately 12.3 mg/g) at 600 °C for SFG. The adsorbent exhibited favorable tolerance to high concentrations of NOx and SOx. The As2O3(III) was oxidized and transformed into As2O5(V) on the CuCl2-HNTs. The Al-O bridge had the highest adsorption energy for the O end of the As-O group (-2.986 eV), and the combination formed between arsenic-containing groups and aluminum was stable. In addition, the captured arsenic could be stabilized in the sorbent at high temperature, making it possible to use the sorbent before the SCR system. This demonstrates that CuCl2-HNTs is a promising sorbent for arsenic oxidation and removal from CCFG.

Distribution and chemical speciation of arsenic in different sized atmospheric particulate matters.

The distribution and chemical speciation of arsenic (As) in different sized atmospheric particulate matters (PMs), including total suspended particles (TSP), PM10, and PM2.5, collected from Baoding, China were analyzed. The average total mass concentrations of As in TSP, PM10, and PM2.5 were 31.5, 35.3, and 54.1 µg/g, respectively, with an order of PM2.5 >PM 10 > TSP, revealing that As is prone to accumulate on fine particles. Due to the divergent toxicities of different As species, speciation analysis of As in PMs is further conducted. Most of previous studies mainly focused on inorganic arsenite (iAsIII), inorganic arsenate (iAsV), monomethylarsonate (MMA), and dimethylarsinate (DMA) in PMs, while the identification and sensitive quantification of trimethylarsine oxide (TMAO) were rarely reported. In this study, a high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry system was optimized for As speciation including TMAO in PMs. An anion exchange column was used to separate MMA, DMA and iAsV, while a cation exchange column to separate TMAO and iAsIII. Results showed that iAsV was the dominate component in all the samples, corresponding to a portion of 79.2% ± 9.3% of the total extractable species, while iAsIII, TMAO and DMA made up the remaining 21%. Our study demonstrated that iAsIII accounted for about 14.4% ± 11.4% of the total extracted species, with an average concentration of 1.7 ± 1.6 ng/m3. It is worth noting that TMAO was widely present in the samples (84 out of 97 samples), which supported the assumption that TMAO was ubiquitous in atmospheric particles.

Synergistic effects of Fe-Mn binary oxide for gaseous arsenic removal in flue gas.

High-efficient and economic sorbents are highly desired for arsenic (As) emission control in flue gas from coal-fired power plant. A series of Fe-Mn binary oxides were prepared by a facile method, and their behaviors for gaseous arsenic removal in flue gas were investigated. The binary oxide exhibited a remarkable synergistic effect for arsenic removal compared with Mn or Fe monometallic oxide. The possible effects of CO2, NO, SO2, and O2 on the removal performance were also studied. The adsorption ability was excellent and stable in simulated flue gas conditions. X-ray photoelectron spectroscopy (XPS) and high-performance liquid chromatography atomic fluorescence spectroscopy (HPLC-AFS) coupling system were applied to analyze the species of surface-adsorbed arsenicals and soluble arsenicals. It was confirmed that the good sorption performance resulted from oxidation of As2O3 (As(III)) to As2O5 (As(V)) by Mn oxide and followed by efficient adsorption of As(V) on Fe oxide. Considering the toxicity of pentavalent arsenicals is lower than trivalent arsenicals, the oxidation of arsenic compounds can not only enhance its removal capacity but also decrease the toxicity of arsenicals after capture.

Preparation of halloysite nanotubes-encapsulated magnetic microspheres for elemental mercury removal from coal-fired flue gas.

Halloysite nanotubes (HNTs) as a natural and inexpensive clay mineral with hollow nanotubular structures, good biocompatibility and active surfaces have been ubiquitously applied in many fields. In this work, a novel multifunctional core-shell sorbent based on HNTs, CuCl2-HNTs encapsulated magnetic microspheres (SiO2@Fe3O4), was successfully fabricated and applied for Hg0 removal from flue gas with good performance for the first time. The core-shell structure prevented the composites from aggregating but kept their magnetism, which enabled the adsorbents being easily separated for reuse by an external magnetic field. In addition, the special structure also significantly enhanced the adsorption capacity of the composites by dispersing the CuCl2 modified HNTs on the prepared magnetic microspheres. The adsorption performance was comprehensively investigated and fitted by dynamic models. The adsorption followed surface adsorption, particle diffusion and chemisorption with very good SO2 tolerance. The Cu+, Cl- and lattice oxygen were the crucial components for Hg0 removal. In order to further understand the possible mechanism, an online home-made coupling system of temperature-programmed decomposition (TPD) was used to investigate the mercury species on the spent adsorbent in addition to X-ray photoelectron spectroscopy analysis. The results confirmed the mercury species adsorbed were primarily Hg0, HgO and HgCl2.

Fractions of arsenic and selenium in fly ash by ultrasound-assisted sequential extraction.

Sequential extraction has been validated as an effective method to assess the fractions of elements in fly ash. However, the time consumption and high labor costs limit the application of the conventional sequential extraction (CSE) for fast screening of elemental fractions in fly ash. In this study, two ultrasound-assisted sequential extraction (UASE) methods were developed for fast analysis of arsenic (As) and selenium (Se) fractions in fly ash (FA). The parameters of UASE were optimized by comparing the results of As and Se obtained from UASE with those values observed via CSE. The operation time of sequential extraction procedures for As and Se were shortened from 24.5 h to less than 90 min. A certified reference material (CRM, GBW08401) and real fly ash samples were applied to validate the developed UASE. The recoveries of As and Se were found in the range of 82.3% to 114%. For all fractions, the performance of UASE was faster than CSE with the acceptable uncertainties. The analytical results demonstrated that the concentration of As in F3 was found to be higher than other fractions, while the main forms of Se were found to be in F1 and F3 in the fly ash samples. Based on the advantages of high efficiency and easy operation, the developed UASE procedures can be applied for fast screening of the mobility and bioavailability of As and Se in FA from coal fired power plants.

Accelerated screening of arsenic and selenium fractions and bioavailability in fly ash by microwave assistance.

Huge amounts of fly ash (FA) can be annually produced in power plants. Fly ash always contains high levels of arsenic (As) and selenium (Se) due to the preconcentration of these two elements during coal combustion process. It would be much concerned to screen their fractions and potential environmental behaviors in fly ash for beneficial use and treatment. Fast and practical methods for this purpose are urgently needed. Two fast and effective microwave-assisted sequential extraction schemes (MASE) were developed for fast screening As and Se fractions in fly ash for the first time. The extraction parameters including microwave irradiation time, temperature and power energy were optimized by comparing the results from MASE and the conventional scheme (Wenzel method). The results indicate that the extraction efficiency of As and Se in various fractions can be significantly accelerated by microwave irradiation. The whole procedure operation time can be significantly reduced from 24.5 h to 44 min by microwave assistance compared with the conventional shaking schemes. The recoveries of As and Se in the various extracted fractions were all above 80% with relative standard deviations (RSDs) below 8%. The developed methods were further confirmed by the validation of the certified reference material GBW08401 and fly ash samples from six power plants. The developed MASE methods are practical and effective for fast screening arsenic and selenium fractions in fly ash samples.

A comparative study on arsenic fractions in indoor/outdoor particulate matters: a case in Baoding, China.

The distribution and bioavailability of arsenic (As) in indoor/outdoor total suspended particulates (TSP), inhalable particulate matters (PM10), and fine particulate matters (PM2.5) in Baoding, China were investigated. The average I/O ratios for TSP, PM10, and PM2.5 were 0.52, 0.66, and 0.96, respectively. There was no significant correlation between indoor/outdoor TSP, PM10, and PM2.5. The indoor/outdoor concentrations of As surpassed the limited value of As. I/O ratios of arsenic in TSP, PM10, and PM2.5 were 0.52, 0.58, and 0.55, respectively. The contents of arsenic in different fractions were mainly affected by the total concentrations of arsenic in particulate matters (PM) rather than the particle sizes for TSP and PM10. Arsenic was mainly in non-specifically sorbed fraction (F1) in both indoor and outdoor PM2.5. The evaluated carcinogenic risk (CR) was within the safe level. The bioavailability of As increased with particle size decreasing for both indoor and outdoor PM. The potential bioavailability of As in outdoor particles was higher than that of indoor particles with the same size, especially PM2.5.

Speciation and bioaccessibility of heavy metals in PM2.5 in Baoding city, China.

The health risks and toxicity of heavy metals (HMs) in PM2.5 are not only associated with their total amounts, but also with their species and bioaccessibility. In this study, the speciation (fractions) and bioaccessibility of HMs (Pb, Cd, Cr, Cu and Zn) as well as their correlations in fine particulate matter (PM2.5) samples from four seasons were studied. A sequential extraction procedure was applied to divide the studied HMs into four fractions: acid-soluble fraction (F1), reducible fraction (F2), oxidative fraction (F3) and residual fraction (F4). The simulated body fluids (gastrointestinal and lung phases) were used for in vitro tests in order to evaluate the bioaccessibility of HMs. The distribution of HMs in PM2.5 was season and element dependent. It was found that Zn was the most abundant element among the five measured metals and followed by Pb, Cu, Cr and Cd. The total contents of each HM in different seasons were in the following order: winter > autumn > spring > summer. The studied HMs were mainly concentrated in acid-soluble fraction (F1) with high bioaccessibility (p < 0.05) except for Cr. Zn, Pb and Cu possessed the highest bioaccessibility in summer while Cd and Cr were the highest in winter. In vitro tests indicated that HMs in PM2.5 were much more accessible to gastrointestinal fluids rather than lung phase (Gamble's solution). A significant correlation was found between the results from the optimized BCR sequential extraction and solubility bioaccessibility research consortium (SBRC). The fractions extracted by SBRC were consistent with the first two fractions extracted by the sequential extraction method.

Bioavailability/speciation of arsenic in atmospheric PM2.5 and their seasonal variation: A case study in Baoding city, China.

Arsenic (As) can be easily enriched in atmospheric particulate matters (PMs), especially in fine particulate matters (PM2.5). In this study, thirty two PM2.5 samples were collected in four seasons in Baoding, China, where the haze pollution was very serious in recent years. The total contents, species and bioavailability of arsenic in PM2.5 samples were investigated. Species of arsenic in the PM2.5 samples were discriminated as five fractions using a sequential extraction method: non-specifically sorbed fraction (F1), specifically-sorbed fraction (F2), amorphous and poorly-crystalline hydrous oxides of Fe and Al fraction (F3), well-crystallized hydrous oxides of Fe and Al fraction (F4) and residual fraction (F5). Bioavailabilities of arsenic in the PM2.5 samples were evaluated by in vitro tests using both solubility bioavailability research consortium (SBRC) and Gamble's solution extraction methods. The total volume concentrations of As in PM2.5 were significantly higher in winter than the other seasons. However, the highest mass concentration of As was found in spring. Scanning electron microscopy (SEM) characterization indicated that the physical morphology of the particles varied in different seasons. Significant differences of fraction distribution and BFs were found between different seasons. Arsenic in PM2.5 samples mainly presented in F1 with high bioavailability factor (BF), especially for the samples in summer. In vitro tests indicated that arsenic in PM2.5 could be dissolved more easily in gastric phase rather than intestinal and lung phases. There was a significant correlation between species and in vitro tests. Interestingly, a synergy effect was found between F2 and F3. Health risk assessment indicated that arsenic in PM2.5via inhalation exposure for both children and adults could cause adverse effects. Principal component analysis suggested that the arsenic in PM2.5 was from the similar sources between summer and autumn, winter and spring, respectively.